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LANs to WANs Management guide
wlilakiatsakunText book
LANs to WANs The complete management guide
Topics
Local Area Networks (Revisited) LAN administration LAN restoration Planning Storage Network Management Managing Bridges Routers Gateways Managing the Wireless Infrastructure Managing Network Security WAN Restoration Planning
LAN (revisited)
Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station
compete with each other Addressing scheme
Devices HubSwitchRouter
Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernetsketch
CSMA (Carrier Sense Multiple Access)
CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission
Human analogy donrsquot interrupt others
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Topics
Local Area Networks (Revisited) LAN administration LAN restoration Planning Storage Network Management Managing Bridges Routers Gateways Managing the Wireless Infrastructure Managing Network Security WAN Restoration Planning
LAN (revisited)
Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station
compete with each other Addressing scheme
Devices HubSwitchRouter
Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernetsketch
CSMA (Carrier Sense Multiple Access)
CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission
Human analogy donrsquot interrupt others
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
LAN (revisited)
Protocol ndashEthernetIEEE 8023 Define physical layer and MAC layer Media Access Control ndash CSMACD Contention-based meaning that station
compete with each other Addressing scheme
Devices HubSwitchRouter
Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernetsketch
CSMA (Carrier Sense Multiple Access)
CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission
Human analogy donrsquot interrupt others
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernetldquodominantrdquo wired LAN technology cheap $20 for 100Mbs first widely used LAN technology Simpler cheaper than token LANs and ATM Kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernetsketch
CSMA (Carrier Sense Multiple Access)
CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission
Human analogy donrsquot interrupt others
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
CSMA (Carrier Sense Multiple Access)
CSMA listen before transmitIf channel sensed idle transmit entire frame If channel sensed busy defer transmission
Human analogy donrsquot interrupt others
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
CSMA collisions
collisions can still occurpropagation delay means two nodes may not heareach otherrsquos transmissioncollisionentire packet transmission time wasted
spatial layout of nodes
noterole of distance amp propagation delay in determining collision probability
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
CSMACD (Collision Detection)
CSMACD carrier sensing deferral as in CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs receiver shut off while transmitting
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
CSMACD collision detection
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Addressing Scheme 32-bit IP address
network-layer address used to get datagram to destination IP subnet
MAC (or LAN or physical or Ethernet) address used to get datagram from one interface to
another physically-connected interface (same network)
48 bit MAC address (for most LANs) burned in the adapter ROM
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
LAN Addresses
Each adapter on LAN has unique LAN address
Broadcast address =FF-FF-FF-FF-FF-FF
= adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
LAN Address (more)
MAC address allocation administered by IEEE MAC address is divided as following
First 24 bit is defined as Vendor number Last 24 bit is defined as serial number of devices
manufacturer buys portion of MAC address space (to assure uniqueness) Cisco ndash 00000C Fujisu ndash 00000E
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
MAC flat address portability can move LAN card from one LAN to another
IP hierarchical address NOT portable Sometimes it is called Physical address
Question how to determineMAC address of a hostknowing hostrsquos IP address
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
ARP Address Resolution Protocol
Each IP node (Host Router) on LAN has ARP table
ARP Table IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt
TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
237196723
237196778
237196714
237196788
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
ARP protocol Same LAN (network)
A wants to send datagram to B and Brsquos MAC address not in Arsquos ARP table
A broadcasts ARP query packet containing Bs IP address Dest MAC address = FF-FF-FF-FF-FF-FF all machines on LAN receive ARP query
B receives ARP packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information that times out (goes
away) unless refreshed ARP is ldquoplug-and-playrdquo
nodes create their ARP tables without intervention from net administrator
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Routing to another LAN
walkthrough send datagram from A to B via R assume A knowrsquos B IP address
A
RB
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
A creates datagram with source A destination B
A uses ARP to get Rrsquos MAC address for 111111111110
A creates link-layer frame with Rs MAC address as dest frame contains A-to-B IP datagram
Arsquos adapter sends frame Rrsquos adapter receives frame
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
R removes IP datagram from Ethernet frame sees its destined to B
R uses ARP to get Brsquos MAC address R creates frame containing A-to-B IP datagram
sends to B
A
RB
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
LAN topology Bus topology popular through mid 90s Now star topology prevails Connection choices hub or switch (more
later)
hub orswitch
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernet Frame Structure
Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame
Preamble 7 bytes with pattern 10101010 followed by one
byte with pattern 10101011 used to synchronize receiver sender clock rates
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernet Frame Structure (more)
Addresses 6 bytes if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to net-layer protocol
otherwise adapter discards frame
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Type indicates the higher layer protocol (mostly IP but others may be supported such as Novell IPX and AppleTalk)
CRC checked at receiver if error is detected the frame is simply dropped
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Unreliable connectionless service
Connectionless No handshaking between sending and receiving adapter
Unreliable receiving adapter doesnrsquot send acks or nacks to sending adapter stream of datagrams passed to network layer can
have gaps gaps will be filled if app is using TCP otherwise app will see the gaps
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernet uses CSMACD No slots adapter doesnrsquot transmit if
it senses that some other adapter is transmitting that is carrier sense
transmitting adapter aborts when it senses that another adapter is transmitting that is collision detection
Before attempting a retransmission adapter waits a random time that is random access
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernet CSMACD algorithm
1 Adaptor receives datagram from net layer amp creates frame
2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits
3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
4 If adapter detects another transmission while transmitting aborts and sends jam signal
5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Ethernetrsquos CSMACD (more)
Jam Signal make sure all other transmitters are aware of collision 48 bits
Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec
Exponential Backoff Goal adapt retransmission
attempts to estimated current load
heavy load random wait will be longer
first collision choose K from 01 delay is K 512 bit transmission times
after second collision choose K from 0123hellip
after ten collisions choose K from 01234hellip1023
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
CSMACD efficiency Tprop = max prop between 2 nodes in LAN ttrans = time to transmit max-size frame
Efficiency goes to 1 as tprop goes to 0 Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and
cheap
transprop tt 51
1efficiency
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
10BaseT and 100BaseT 10100 Mbps rate latter
called ldquofast ethernetrdquo T stands for Twisted Pair Nodes connect to a hub
ldquostar topologyrdquo 100 m max distance between nodes and hub
twisted pair
hub
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
HubsHubs are essentially physical-layer
repeaters bits coming from one link go out all
other links at the same rate no frame buffering no CSMACD at hub adapters detect
collisions provides net management functionality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Gbit Ethernet uses standard Ethernet frame format allows for point-to-point links and shared
broadcast channels in shared mode CSMACD is used short
distances between nodes required for efficiency
uses hubs called here ldquoBuffered Distributorsrdquo Full-Duplex at 1 Gbps for point-to-point links 10 Gbps now
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Interconnecting with hubs
hub
hubhub
hub
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Backbone hub interconnects LAN segments
Extends max distance between nodes But individual segment collision domains
become one large collision domain If a link capacity is 10Mbps the overall
capacity is 10 Mbps too Canrsquot interconnect 10BaseT amp 100BaseT
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switch Link layer device
stores and forwards Ethernet frames examines frame header and selectively
forwards frame based on MAC dest address when frame is to be forwarded on segment
uses CSMACD to access segment transparent
hosts are unaware of presence of switches plug-and-play self-learning
switches do not need to be configured
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Forwarding
bull How do determine onto which LAN segment to forward framebull Looks like a routing problem
hub
hubhub
switch1
2 3
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Self learning
A switch has a switch table entry in switch table
(MAC Address Interface Time Stamp) stale entries in table dropped (TTL can be
60 min) switch learns which hosts can be reached
through which interfaces when frame received switch ldquolearnsrdquo
location of sender incoming LAN segment records senderlocation pair in switch table
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
FilteringForwarding
When switch receives a frameindex switch table using MAC dest addressif entry found for destination
then if dest on segment from which frame arrived
then drop the frame else forward the frame on interface indicated else flood
forward on all except the interface on which the frame arrived
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switch exampleSuppose C sends frame to D
Switch receives frame from from C notes in bridge table that C is on interface 1 because D is not in table switch forwards frame into
interfaces 2 and 3 frame received by D
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEG
1123
12 3
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switch exampleSuppose D replies back with frame to C
Switch receives frame from from D notes in bridge table that D is on interface 2 because C is in table switch forwards frame only to
interface 1 frame received by C
hub
hub hub
switch
A
B CD
EF
G H
I
address interface
ABEGC
11231
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switch traffic isolation switch installation breaks subnet into
LAN segments
hub hub hub
switch
collision domain collision domain
collision domain
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
switch filters packets same-LAN-segment frames not
usually forwarded onto other LAN segments
segments become separate collision domains
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switches dedicated access
Switch with many interfaces
Hosts have direct connection to switch
No collisions full duplex
Switching A-to-Arsquo and B-to-Brsquo simultaneously no collisions
switch
A
Arsquo
B
Brsquo
C
Crsquo
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
More on Switches
cut-through switching frame forwarded from input to output port without first collecting entire frame slight reduction in latency
combinations of shareddedicated 101001000 Mbps interfaces
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Institutional network
hub
hubhub
switch
to externalnetwork
router
IP subnet
mail server
web server
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Switches vs Routers
both store-and-forward devices routers network layer devices (examine
network layer headers) switches are link layer devices
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
routers maintain routing tables implement routing algorithms
switches maintain switch tables implement filtering learning algorithms
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Summary comparison hubs routers switches
traffi c isolation
no yes yes
plug amp play yes no yes
optimal routing
no yes no
cut through
yes no yes
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Redundant topology
Networks with redundant paths and devices allow for more network uptime
Redundant topologies eliminate single points of failure
If a path or device fails the redundant path or device can take over the tasks of the failed path or device
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
If Switch A fails traffic can still flow from Segme nt2 to Segment1 and to the router through Swi
tch B Switches learn the MAC addresses of devices on
their ports so that data can be properly forward ed to the destination
Switches flood frames for unknown destinations until they learn the MAC addresses of the device
s Broadcasts and multicasts are also flooded A redundant switched topology may cause broa
dcast storms multiple frame copies and MAC a ddress table instability problems
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Broadcast strom
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Spanning Tree Protocol
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Finally - there is one spanning tree per network On e very switched network
One root bridge per network - One root port per non root bridge One designated port per segment - non designated ports
Root ports and designated ports are used for fo rwarding (F) data traffic
- Non designated ports discard data traffic Thes e ports are called blocking (B) or discarding por
ts
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLAN (Virtual LAN) overview
VLANs allow almost complete independ ence of the physical and logical topologi
es Administrators can use VLANs to define
groupings of workstations even if they are separated by switches and on differ ent LAN segments
O ne VLAN means one collision domain a nd one broadcast domain
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLAN A VLAN is a logical group of network stati
ons services and devices that is not rest ricted to a physical LAN segment
VLANs facilitate easy administration of lo gical groups of stations and servers that c
an communicate as if they were on the sa me physical LAN segment
They also facilitate easier administration of moves adds and changes in members of these groups
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLAN services VLANs are created to provide segmentation servi
ces traditionally provided by physical routers in L AN configurations
VLANs address scalability security and network management
Routers in VLAN topologies provide broadcast filt ering security and traffic flow management
Switches do not bridge traffic between VLANs as this violates the integrity of the VLAN broadcast
domain Traffic should only be routed between VLANs
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Static VLAN
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Dynamic VLAN
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
Port-centric VLAN
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLAN Transmission
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLANrsquos benefit
VLANs allow network administrators to or ganize LANs logically instead of physically
This allows network administrators to perf orm several tasks
Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality
VLAN Type - Port based VLANs MAC address based VLANs - Protocol based VLANs The number of VLANs in a switch vary bas
ed on several factors Traffic patterns Types of applications Network management needs Group commonality