[email protected]@gmail.com Network Layer Network Layer 4-4-11
Network Layer
Computer NetworksComputer Networks
Shahrood University of TechnologyShahrood University of TechnologyDepartment of Computer Engineering & ITDepartment of Computer Engineering & IT
[email protected]@gmail.com Network Layer Network Layer 4-4-33
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-44
Network Layer FunctionsNetwork Layer Functions
transport packet from sending to receiving hosts
network layer protocols in every host, router
three important functions: path determination: route
taken by packets from source to dest. (Routing Algorithms)
forwarding: move packets from router’s input to appropriate router output
call setup: some network architectures require router call setup along path before data flows
application
transportnetworkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
networkdata linkphysical
application
transportnetworkdata linkphysical
[email protected]@gmail.com Network Layer Network Layer 4-4-55
Network Service ModelNetwork Service Model
Q: What service model for “channel” transporting packets from sender to receiver?
Services guaranteed bandwidth? preservation of inter-
packet timing (no jitter)? loss-free delivery? in-order delivery? congestion feedback to
sender?
virtual circuitor
datagram?
The most important abstraction provided
by network layer:
[email protected]@gmail.com Network Layer Network Layer 4-4-66
Virtual circuitsVirtual circuits
call setup, teardown for each call before data can flow each packet carries VC identifier (not destination host ID) every router on source-destination path maintains “state”
for each passing connection transport-layer connection only involved two end systems
Link and router resources (bandwidth, buffers) may be allocated to VC
to get circuit-like performance.
“source-to-destination path behaves much like telephone circuit”
performance-wise network actions along source-to-destination path
[email protected]@gmail.com Network Layer Network Layer 4-4-77
Virtual Circuits: Signaling ProtocolsVirtual Circuits: Signaling Protocols
used to setup, maintain teardown VC used in ATM, frame-relay, X.25 not used in today’s Internet
1. Initiate call
2. Incoming call3. Accept call
4. Call connected5. Data flow begins
6. Receive data
application
transportnetworkdata linkphysical
application
transportnetworkdata linkphysical
[email protected]@gmail.com Network Layer Network Layer 4-4-88
Datagram networks: Datagram networks: the Internet modelthe Internet model
1. Send Data
2. Receive Data
application
transportnetworkdata linkphysical
application
transportnetworkdata linkphysical
no call setup at network layer routers: no state about end-to-end connections
no network-level concept of “connection” packets forwarded using destination host address
packets between same source-destination pair may take different paths
[email protected]@gmail.com Network Layer Network Layer 4-4-99
Network Layer Service Models:Network Layer Service Models:
Internet model being extended: Integrated services, Differentiated Services Chapter 6
NetworkArchitecture
Internet
ATM
ATM
ATM
ATM
ServiceModel
best effort
CBR
VBR
ABR
UBR
Bandwidth
none
constantrateguaranteedrateguaranteed minimumnone
Loss
no
yes
yes
no
no
Order
no
yes
yes
yes
yes
Timing
no
yes
yes
no
no
Congestionfeedback
no (inferredvia loss)nocongestionnocongestionyes
no
Guarantees ?
CB
R:
Const
ant
bit
rate
VB
R:
Vari
able
bit
rate
AB
R:
Availa
ble
bit
rate
UB
R:
Unsp
eci
fied b
it r
ate
[email protected]@gmail.com Network Layer Network Layer 4-4-1010
QoS FactorsQoS Factors
Timing Connection Establishment Delay End-To-End Delay
Connection Establishment Failure Probability Throughput or Bandwidth Guarantee Ordering Preservation Congestion Indication (Control) Bit-Error rate or Packet-Loss Rate Control Protection Priority Resilience (Return Back to Normal Operation).
[email protected]@gmail.com Network Layer Network Layer 4-4-1111
Service ClasesService Clases
Guaranteed Quality of Service Predictive Quality of Service Best Effort Quality of Service
Guaranteed Quality of Service Predictive Quality of Service Best Effort Quality of Service
[email protected]@gmail.com Network Layer Network Layer 4-4-1212
Guaranteed QoSGuaranteed QoS
Specified through QoS parameter values deterministic statistical
Single value - average (threshold, target) Pair of values - interval Triple of values – max., mean, min.
Specified through QoS parameter values deterministic statistical
Single value - average (threshold, target) Pair of values - interval Triple of values – max., mean, min.
[email protected]@gmail.com Network Layer Network Layer 4-4-1313
Predictable ServicePredictable Service
Parameter bounds based on history, that is, past network behavior.
Parameter values are measured, and certain statistical analyses may be carried out
Parameter bounds based on history, that is, past network behavior.
Parameter values are measured, and certain statistical analyses may be carried out
[email protected]@gmail.com Network Layer Network Layer 4-4-1414
Best Effort ServicesBest Effort Services
No guarantees of quality, no QoS parameter values UDP/IP
Partial guarantees, some QoS parameter values are given. TCP/IP
No guarantees of quality, no QoS parameter values UDP/IP
Partial guarantees, some QoS parameter values are given. TCP/IP
[email protected]@gmail.com Network Layer Network Layer 4-4-1515
Datagram or VC Network: why?Datagram or VC Network: why?
Internet data exchange among
computers “elastic” service, no
strict timing req. “smart” end systems
(computers) can adapt, perform
control, error recovery simple inside
“network”, complexity at “edge”
many link types different characteristics uniform service is
difficult
ATM evolved from telephony human conversation:
strict timing, reliability requirements
need for guaranteed service
“dumb” end systems telephones complexity inside
network
[email protected]@gmail.com Network Layer Network Layer 4-4-1616
Active Queue Management (AQM)Active Queue Management (AQM)
Performance Degradation in current TCP Congestion Control Multiple packet loss Low link utilization Congestion collapse
The role of the router (i.e., network) Control congestion effectively with a network Allocate bandwidth fairly
[email protected]@gmail.com Network Layer Network Layer 4-4-1717
Buffering in IP routersBuffering in IP routers
Buffer size Space for bursts of
packets Latency
Router
Internet Router
NetworkInterface
NetworkInterface
Dropping packets When? What?
[email protected]@gmail.com Network Layer Network Layer 4-4-1818
FIFO Queueing in the RouterFIFO Queueing in the Router(Drop Tail)(Drop Tail)
Single queue maintained
NetworkInterface
NetworkInterface
[email protected]@gmail.com Network Layer Network Layer 4-4-1919
FIFO Queueing in the Router FIFO Queueing in the Router (Drop Tail)(Drop Tail)
Single queue maintained Dequeue from head
NetworkInterface
NetworkInterface
[email protected]@gmail.com Network Layer Network Layer 4-4-2020
FIFO Queueing in the Router FIFO Queueing in the Router (Drop Tail)(Drop Tail)
Single queue maintained Dequeue from head Enqueue at tail
NetworkInterface
NetworkInterface
[email protected]@gmail.com Network Layer Network Layer 4-4-2121
FIFO Queueing in the Router FIFO Queueing in the Router (Drop Tail)(Drop Tail)
Single queue maintained Dequeue from head Enqueue at tail When full
NetworkInterface
NetworkInterface
[email protected]@gmail.com Network Layer Network Layer 4-4-2222
FIFO Queueing in the Router FIFO Queueing in the Router (Drop Tail)(Drop Tail)
Single queue maintained Dequeue from head Enqueue at tail When full drop arriving packet (drop-tail)
NetworkInterface
NetworkInterface
[email protected]@gmail.com Network Layer Network Layer 4-4-2323
Active Queue ManagementActive Queue Management
Goals:
Better congestion notification for responsive flows (i.e. TCP)
Maintain shorter queues
Fairness in drops (proportional)
[email protected]@gmail.com Network Layer Network Layer 4-4-2424
RED OperationRED Operation
[email protected]@gmail.com Network Layer Network Layer 4-4-2525
Time
Max Queue Size
Active Queue ManagementActive Queue ManagementRandom Early Detection (RED)Random Early Detection (RED)
Max Threshold
Min Threshold
Forced drop
Probabilistic drops
No drops
Drop probability
Average queue length
[email protected]@gmail.com Network Layer Network Layer 4-4-2626
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models4.2 Routing Principles
Link state routing Distance vector routing
4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-2727
RoutingRouting
Graph abstraction for routing algorithms:
graph nodes are routers
graph edges are physical links link cost: delay, $
cost, or congestion level
Goal: determine “good” path
(sequence of routers) thru network from source to
dest.
“good” path: typically means minimum
cost path other definitions possible
A F
D
C
E
B
1
1
1
2
2
2
53
53
Routing protocol
Abstract model of a network
[email protected]@gmail.com Network Layer Network Layer 4-4-2828
Routing Algorithm ClassificationsRouting Algorithm Classifications
1. Global: all routers have complete
topology, link cost info “link state” algorithms
2. Decentralized: router knows physically-
connected neighbors, link costs to neighbors
iterative process of computation, exchange of info with neighbors
“distance vector” algorithms
1. Static: routes update slowly
over time
2. Dynamic: routes update more
quickly periodic update in response to link
cost changes
[email protected]@gmail.com Network Layer Network Layer 4-4-2929
A Link-State Routing AlgorithmA Link-State Routing Algorithm
Dijkstra’s algorithm (global) net topology, link costs known to all
nodes accomplished via “link state
broadcast” all nodes have same information
computes least cost paths from one node (‘source”) to all other nodes gives routing table for that node
iterative: after k iterations, know least cost path to k destinations.
[email protected]@gmail.com Network Layer Network Layer 4-4-3030
Notation:Notation:
N: set of nodes whose least cost path definitively known
c(i,j): link cost from node i to j. cost infinite if not direct neighbors
p(v): nodes along path from source to v
D(v): current value of cost of path from source to destination v.
N: A, B, C, D, E, F
C(A,C)=5; C(C,A)=5C(B,D)=2; C(D,B)=3…
Source=Ap(F): A-D-E-FD(F)=4
A F
D
C
E
B
1
1
1
2
2
2
53
53
5
3
Example:
[email protected]@gmail.com Network Layer Network Layer 4-4-3131
1 Initialization: 2 N = {A} 3 for all nodes v 4 if v adjacent to A 5 then D(v) = c(A,v) 6 else D(v) = infinity 7 8 Loop 9 find w not in N such that D(w) is a minimum 10 add w to N 11 update D(v) for all v adjacent to w and not in N: 12 D(v) = min( D(v), D(w) + c(w,v) ) 13 /* new cost to v is either old cost to v or known 14 shortest path cost to w plus cost from w to v */ 15 until all nodes in N
Dijsktra’s AlgorithmDijsktra’s Algorithm
v
w
D(v) c(w,v)
D(w)
A
n(n+1)/2)times
n =
num
ber
of
nodes
(exce
pt
the s
ourc
e)
[email protected]@gmail.com Network Layer Network Layer 4-4-3232
Dijkstra’s Algorithm: exampleDijkstra’s Algorithm: example
computes least cost paths from node A to all other nodes
Step012345
start NA
ADADE
ADEBADEBC
ADEBCFADEBCF
D(B),p(B)2,A-B2,A-B2,A-B2,A-B2,A-B2,A-B
D(C),p(C)5,A-C
4,A-D-C3,A-D-E-C3,A-D-E-C3,A-D-E-C3,A-D-E-C
D(D),p(D)1,A-D1,A-D1,A-D1,A-D1,A-D1,A-D
D(E),p(E)infinity
2,A-D-E2,A-D-E2,A-D-E2,A-D-E2,A-D-E
D(F),p(F)infinityinfinity
4,A-D-E-F4,A-D-E-F4,A-D-E-F4,A-D-E-F
A F
D
C
E
B
1
1
1
2
2
2
53
53
D(v): Distance (cost) of A to v.P(v): nodes along path fromA to v.
[email protected]@gmail.com Network Layer Network Layer 4-4-3434
D
C
B
A
0
1
1
1+e
e
e
1
0 0
Fig. a- Initial routing
Dijkstra’s Algorithm: discussion2Dijkstra’s Algorithm: discussion2
Oscillations possibility: Suppose link costs are equal to
the load carried on the link, or the delay that experienced.
Link costs are not symmetric, c(A,B) equals c(B,A) only if the load on both directions on the AB link is the same.
Nodes B and D originates a unit of traffic destined for A.
Node C originates e unit for A.
[email protected]@gmail.com Network Layer Network Layer 4-4-3535
… oscillations possible: Algorithm is run: C
determines (Fig. a) the clockwise path to A has a cost of 1, while the counterclockwise path to A has a cost of 1 + e. Hence C ’s least-cost path to A is now clockwise.
Similarly, B determines that its new least-cost path to A is also clockwise, resulting in costs shown in Fig. b.
Discussion2 (cont.)Discussion2 (cont.)
D
C
B
A
1+e00
0
1
2+e
Fig. b- B, C find better path to A is clockwise
1
e
1
D
C
B
A
0
1
1
1+e
e
e
1
0 0
Fig. a- Initial routing
[email protected]@gmail.com Network Layer Network Layer 4-4-3636
… oscillations possible:
When algorithm is run next, nodes B, C, and D all detect a zero-cost path to A in the counterclockwise direction, and all route their traffic to the counterclockwise routes.
The next time the LS algorithm is run, B, C, and D all then route their traffic to the clockwise routes.
Discussion2 (cont.)Discussion2 (cont.)
D
C
B
A
1+e00
0
1
2+e
11
e
Fig. c- B, C, D find better path to A is counterclockwise
D
C
B
A
01+e1
2+e
0
0
11
e
Fig. d- B, C, D find better path to A is clockwise
[email protected]@gmail.com Network Layer Network Layer 4-4-3737
To prevent such oscillations: Solution1 :link costs not depend on the amount of traffic carried ,an
unacceptable solution since one goal of routing is to avoid highly congested (for example, high-delay) links.
Solution2 :all routers do not run the LS algorithm at the same time (a reasonable solution). Routers run the LS algorithm with the same periodicity, the
execution instance of the algorithm would not be the same at each node.
Researchers have noted: Routers in the Internet can self-synchronize among themselves. That is, even though they initially execute the algorithm with the same period but at different instants of time, the algorithm execution instance can eventually become, and remain, synchronized at the routers.
Avoid such self-synchronization: Introduce randomization into the period between execution instants of the algorithm at each node.
Dijkstra’s Algorithm: discussion2Dijkstra’s Algorithm: discussion2
[email protected]@gmail.com Network Layer Network Layer 4-4-3838
Distance Vector Routing Algorithm Distance Vector Routing Algorithm (Decentralized)(Decentralized)
Iterative: continues until no
nodes exchange info. self-terminating: no
“signal” to stop
Asynchronous: nodes need not
exchange info/iterate in lock step!
distributed: each node
communicates only with directly-attached neighbors
Distance Table data structure each node has its own:
row for each possible destinationcolumn for each directly-attached neighbor to node
example: in node X, for dest. Y via neighbor Z: DX(Y,Z)
distance from X to Y, via Z as next hop
D (Y,Z)X
c(X,Z) + min {D (Y,w)}Z
w=
[email protected]@gmail.com Network Layer Network Layer 4-4-3939
Distance Table: exampleDistance Table: example
Bw
=
2
D
CB
A
E1
7
1
8
2source
ABCD
A
1764
B
1489
11
D
5542
c(E,B) + min {D (A,w)}=8 + 6 = 14
ED (A,B)=
A
E B
D (A,C)B
D
C
…c(E,B)
E’s neighborB’s neighbor
neighbor: j
dest
inat
ion:
i
D(i, j)E
Distance table:
[email protected]@gmail.com Network Layer Network Layer 4-4-4040
Distance table gives routing tableDistance table gives routing table
D ()
A
B
C
D
A
1
7
6
4
B
14
8
9
11
D
5
5
4
2
E
cost to destination via
des
tina
tion
A
B
C
D
A,1
D,5
D,4
D,4
Outgoing link to use, cost
des
tina
tion
Distance table Routing tableof node E
D ()E
[email protected]@gmail.com Network Layer Network Layer 4-4-4141
Distance Vector Routing: overviewDistance Vector Routing: overview
Iterative, asynchronous: each local iteration caused by:
local link cost change message from neighbor:
its least cost path change from neighbor
Distributed: each node notifies
neighbors only when its least cost path to any destination changes
neighbors then notify their neighbors if necessary
wait for (change in local link cost or message from neighbor)
recompute distance table
if least cost path to any destination has changed,
notify neighbors
Each node:
[email protected]@gmail.com Network Layer Network Layer 4-4-5050
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-5151
Hierarchical RoutingHierarchical Routing
scale: with 200 million destinations (hosts):
can’t store all dest’s in routing tables (memory limitation)!
routing table exchange would leave no bandwidth left for sending data packets!
DV algorithm that iterated among large number of routers never converge!
administrative autonomy:
internet = network of networks
each network admin may want to control routing in its own network
The routing study thus far was idealized all routers identical network “flat”… not true in practice
[email protected]@gmail.com Network Layer Network Layer 4-4-5252
Hierarchical RoutingHierarchical Routing
aggregate routers into regions, “autonomous systems” (AS)
routers in same AS run same routing protocol “intra-AS” routing
protocol routers in different AS
can run different intra-AS routing protocol
special routers in AS run intra-AS routing
protocol with all other routers in AS
also responsible for routing to destinations outside AS run inter-AS routing
protocol with other gateway routers
gateway routers
[email protected]@gmail.com Network Layer Network Layer 4-4-5353
Intra-AS and Inter-AS routingIntra-AS and Inter-AS routingGateways:
•perform inter-AS routing amongst themselves•perform intra-AS routers with other routers in their AS
Inter/intra-AS routing in
gateway A.c
C
A
B
C.b
A.aA.c
B.a
a b
ad
bc
ac
b
▪Routers in an AS have information about routing paths within that AS.
Intra-ASIntra-ASRouting Routing
AlgorithmAlgorithm
Inter-ASInter-ASRouting Routing
AlgorithmAlgorithm
Routing TableRouting Table
DLDL DLDL DLDL
PHLPHLPHLPHL PHL To/from B.a and A.aTo/from A.b
To/from A.d
[email protected]@gmail.com Network Layer Network Layer 4-4-5454
Intra-AS and Inter-AS routingIntra-AS and Inter-AS routing
Host2
C
A
B
Intra-AS routingwithin AS A
Intra-AS routingwithin AS B
Host1
ab
ad
bc
ac
b
C.b
A.a
B.aInter-A
S routin
g
between A and
BA.c
[email protected]@gmail.com Network Layer Network Layer 4-4-5555
Chapter 4 outlineChapter 4 outline
4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol
4.4.1 IPv4 addressing 4.4.2 Moving a datagram from source to destination 4.4.3 Datagram format 4.4.4 IP fragmentation 4.4.5 ICMP: Internet Control Message Protocol 4.4.6 DHCP: Dynamic Host Configuration Protocol 4.4.7 NAT: Network Address Translation
4.5 Routing in the Internet4.6 What’s Inside a Router4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-5656
The Internet Network layerThe Internet Network layer
Host, Router network-layer-functions:
forwardingtable
Routing protocols•path selection•RIP, OSPF, BGP
IP protocol•addressing conventions•datagram format•packet handling conventions
ICMP protocol•error reporting•router “signaling”
Transport layer: TCP, UDP
Link layer
physical layer
Netw
ork
layer
ICMP: Internet Control Message Protocol, RFC792
[email protected]@gmail.com Network Layer Network Layer 4-4-5757
Internet Routing ProtocolInternet Routing Protocol Intra-AS: administrator responsible for choice of
routing algorithm within network Also known as Interior Gateway Protocols (IGP) Most common Intra-AS routing protocols:
RIP: Routing Information Protocol (RFCs1058,2453)– It is a distance vector protocol.– Routing updates are exchanged between neighbors app. Every 30sec.
OSPF: Open Shortest Path First (RFC2328) (Open Spec.) IGRP: Interior Gateway Routing Protocol (Cisco
proprietary)– These are link-state protocol that uses flooding of link information and a
Dijkstra least-cost path algorithm.
Intra-AS: administrator responsible for choice of routing algorithm within network Also known as Interior Gateway Protocols (IGP) Most common Intra-AS routing protocols:
RIP: Routing Information Protocol (RFCs1058,2453)– It is a distance vector protocol.– Routing updates are exchanged between neighbors app. Every 30sec.
OSPF: Open Shortest Path First (RFC2328) (Open Spec.) IGRP: Interior Gateway Routing Protocol (Cisco
proprietary)– These are link-state protocol that uses flooding of link information and a
Dijkstra least-cost path algorithm.
Inter-AS: unique standard for inter-AS routing: BGP (RFC1771) Inter-AS: unique standard for inter-AS routing: BGP (RFC1771)
[email protected]@gmail.com Network Layer Network Layer 4-4-5858
IP Addressing: IntroductionIP Addressing: Introduction
IP address: 32-bit identifier for host, router interface
interface: connection between host/router and physical link router’s typically have
multiple interfaces host may have multiple
interfaces IP addresses associated
with each interface
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
223.1.1.1 = 11011111 00000001 00000001 00000001
223 1 11
[email protected]@gmail.com Network Layer Network Layer 4-4-5959
IP AddressingIP Addressing
IP address: network part (high
order bits) host part (low order
bits) What’s a network ?
(from IP address perspective) device interfaces with
same network part of IP address
can physically reach each other without intervening router
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
network consisting of 3 IP networks
LAN
[email protected]@gmail.com Network Layer Network Layer 4-4-6060
IP AddressingIP Addressing
How to find the networks?
Detach each interface from router, host
create “islands of isolated networks
223.1.1.1
223.1.1.3
223.1.1.4
223.1.2.2223.1.2.1
223.1.2.6
223.1.3.2223.1.3.1
223.1.3.27
223.1.1.2
223.1.7.0
223.1.7.1223.1.8.0223.1.8.1
223.1.9.1
223.1.9.2
Interconnected system consistingof six networks.
[email protected]@gmail.com Network Layer Network Layer 4-4-6161
Getting a datagram from source to dest.Getting a datagram from source to dest.
IP datagram:
miscfields
sourceIP addr
destIP addr data
datagram remains unchanged, as it travels source to destination
addr fields of interest here
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
A
EB
Dest. Net. Next Router Nhops
223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2
forwarding table in A
[email protected]@gmail.com Network Layer Network Layer 4-4-6262
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27 EB
Getting a datagram from source to Getting a datagram from source to dest.dest.
Starting at A, send IP datagram addressed to B:
look up net. address of B in forwarding table
find B is on same net. as A link layer will send datagram
directly to B inside link-layer frame B and A are directly
connected
Dest. Net. Next Router Nhops
223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2
miscfields223.1.1.1223.1.1.3data
forwarding table in A
A
[email protected]@gmail.com Network Layer Network Layer 4-4-6363
Getting a datagram from source to Getting a datagram from source to dest.dest.
Dest. Net. Next Router Nhops
223.1.1 1223.1.2 223.1.1.4 2223.1.3 223.1.1.4 2
Starting at A, dest. E: look up network address of
E in forwarding table E on different network
A, E not directly attached
routing table: next hop router to E is 223.1.1.4
link layer sends datagram to router 223.1.1.4 inside link-layer frame
datagram arrives at 223.1.1.4
continued…..
miscfields223.1.1.1223.1.2.3 data
forwarding table in A
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27 E
A
B
[email protected]@gmail.com Network Layer Network Layer 4-4-6464
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
A
EB
Getting a datagram from source to dest.Getting a datagram from source to dest.
Arriving at 223.1.4, destined for 223.1.2.2
look up network address of E in router’s forwarding table
E on same network as router’s interface 223.1.2.9 router, E directly
attached link layer sends datagram
to 223.1.2.2 inside link-layer frame via interface 223.1.2.9
datagram arrives at 223.1.2.2
miscfields223.1.1.1223.1.2.3 data Dest. Net Router Nhops Interface
223.1.1 - 1 223.1.1.4 223.1.2 - 1 223.1.2.9
223.1.3 - 1 223.1.3.27
forwarding table in router
[email protected]@gmail.com Network Layer Network Layer 4-4-6565
Private or Non-Routable addressesPrivate or Non-Routable addresses
Some addresses are reserved for use on local networks that are not connected to the Internet
Routers do not consider these addresses to be valid Internet addresses, and will not route a packet to any of them
These addresses may be used on private internets not directly connected to the Internet.
10.0.0.0/8 10.0.0.0 to 10.255.255.255 172.16.0.0/12 172.16.0.0 to 172.31.255.255 192.168.0.0/16 192.168.0.0 to
192.168.255.255
[email protected]@gmail.com Network Layer Network Layer 4-4-6666
IP Addresses: Class-fullIP Addresses: Class-full
given notion of “network”, let’s re-examine IP addresses:
“class-full” addressing:
0 network host
110 network host
A
10 network hostB
C
D
class1.0.0.0 to127.255.255.255
128.0.0.0 to191.255.255.255
192.0.0.0 to223.255.255.255
224.0.0.0 to239.255.255.255
32 bits
1110 multicast address
E 240.0.0.0 to255.255.255.2551111 reserved
format range
[email protected]@gmail.com Network Layer Network Layer 4-4-6767
Class-full SummaryClass-full Summary
Address Class
ApplicationNumber of Network
Bits
Number of Host Bits
Decimal Address Range
Number of Networks
Number of Possible
Host
Class ALarge
Networks8 bits 24 bits 1 - 126 126 16,777,214
Class BMedium-
sized 16 bits 16 bits 128 - 191 65,534 65,534
Class CSmall
Networks24 bits 8 bits 192 - 223 2,097,152 254
The Class System
[email protected]@gmail.com Network Layer Network Layer 4-4-6868
Address depletionAddress depletion
In 1991 IAB identified 3 dangers Running out of class B addresses Increase in nets has resulted in routing table
explosion Increase in net/hosts exhausting 32 bit address
space Four strategies to address
Creative address space allocation {RFC 2050} Private addresses {RFC 1918}, Network Address
Translation (NAT) {RFC 1631} Classless InterDomain Routing (CIDR) {RFC 1519} IP version 6 (IPv6) {RFC 1883}
[email protected]@gmail.com Network Layer Network Layer 4-4-6969
Creative IP address allocationCreative IP address allocation
Class A addresses 64 – 127 reserved Handle on individual basis
Class B only assigned given a demonstrated need
Class C divided up into 8 blocks allocated to regional
authorities 208-223 remains unassigned and unallocated
Three main registries handle assignments APNIC – Asia & Pacific www.apnic.net ARIN – N. & S. America, Caribbean & sub-Saharan
Africa www.arin.net RIPE – Europe and surrounding areas www.ripe.net
[email protected]@gmail.com Network Layer Network Layer 4-4-7070
Private IP AddressesPrivate IP Addresses
IP addresses that are not globally unique, but used exclusively in an organization
Three ranges: 10.0.0.0 - 10.255.255.255 a single class A net 172.16.0.0 - 172.31.255.255 16 contiguous class Bs 192.168.0.0 – 192.168.255.255 256 contiguous class
Cs Connectivity provided by Network Address
Translator (NAT) translates outgoing private IP address to Internet IP
address, and a return Internet IP address to a private address
Only for TCP/UDP packets
[email protected]@gmail.com Network Layer Network Layer 4-4-7171
Several Addresses within the classes are reserved for special use. 0.0.0.0 :Source IP Addr. Just after Boot network part of dest. Addr.= 0 :Source and
Destination are in same network. Dest. Addr.=255.255.255.255 :Broadcast
in Sender’s network. host part of Dest.=111… : Broadcast in
destination network. Dest. Addr. = 127.anything : Loop Back
Special Purpose IP AddressesSpecial Purpose IP Addresses
[email protected]@gmail.com Network Layer Network Layer 4-4-7272
Address Block Present Use Reference0.0.0.0/8 "This" Network [RFC1700, page 4] 10.0.0.0/8 Private-Use Networks [RFC1918] 14.0.0.0/8 Public-Data Networks [RFC1700, page 181] 24.0.0.0/8 Cable Television Networks 39.0.0.0/8 Reserved, subject to allocation [RFC1797] 127.0.0.0/8 Loop back [RFC1700, page 5] 128.0.0.0/16 Reserved but subject to allocation 169.254.0.0/16 Link Local – 172.16.0.0/12 Private-Use Networks [RFC1918] 191.255.0.0/16 Reserved but subject to allocation – 192.0.0.0/24 Reserved but subject to allocation – 192.0.2.0/24 Test-Net 192.88.99.0/24 6to4 Relay Anycast [RFC3068] 192.168.0.0/16 Private-Use Networks [RFC1918]198.18.0.0/15 Network Interconnect Device Benchmark Testing [RFC2544] 223.255.255.0/24 Reserved but subject to allocation – 224.0.0.0/4 Multicast [RFC3171] 240.0.0.0/4 Reserved for Future Use [RFC1700]
Special Purpose Addresses-ListSpecial Purpose Addresses-List
[email protected]@gmail.com Network Layer Network Layer 4-4-7373
Class Inter Domain Routing Class Inter Domain Routing (CIDR)(CIDR)
Many organization have > 256 computers but few have more than several thousand
Instead of giving class B (16384 nets) give sufficient contiguous class C addresses to satisfy needs < 256 addresses assign 1 class C … < 8192 addresses assign 32 contiguous
Class C nets
[email protected]@gmail.com Network Layer Network Layer 4-4-7474
IP addressing: CIDRIP addressing: CIDR
Classful addressing: inefficient use of address space, address space exhaustion e.g., class B net allocated enough addresses for 65K hosts,
even if only 2K hosts in that network
CIDR: Classless Inter Domain Routing (RFC1519) network portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in network
portion of address
11001000 00010111 00010000 00000000
networkpart
hostpart
200.23.16.0/23
[email protected]@gmail.com Network Layer Network Layer 4-4-7575
Bit Masks and Subnet MasksBit Masks and Subnet Masks
In a production environment this prefix typically varies in length from 8 to 30 bits
/30 yields two usable hosts and is used for WAN connections
/16 = 255.255.0.0/17 = 255.255.128.0/18 = 255.255.192.0/19 = 255.255.224.0/20 = 255.255.240.0/21 = 255.255.248.0/22 = 255.255.252.0/23 = 255.255.254.0
/16 = 255.255.0.0/17 = 255.255.128.0/18 = 255.255.192.0/19 = 255.255.224.0/20 = 255.255.240.0/21 = 255.255.248.0/22 = 255.255.252.0/23 = 255.255.254.0
/24 = 255.255.255.0 /25 = 255.255.255.128 /26 = 255.255.255.192/27 = 255.255.255.224/28 = 255.255.255.240/29 = 255.255.255.248/30 = 255.255.255.252/31 = not usable/32 = not usable
/24 = 255.255.255.0 /25 = 255.255.255.128 /26 = 255.255.255.192/27 = 255.255.255.224/28 = 255.255.255.240/29 = 255.255.255.248/30 = 255.255.255.252/31 = not usable/32 = not usable
/8 = 255.0.0.0/9 = 255.128.0.0/10 = 255.192.0.0/11 = 255.224.0.0/12 = 255.240.0.0/13 = 255.248.0.0/14 = 255.252.0.0/15 = 255.254.0.0
/8 = 255.0.0.0/9 = 255.128.0.0/10 = 255.192.0.0/11 = 255.224.0.0/12 = 255.240.0.0/13 = 255.248.0.0/14 = 255.252.0.0/15 = 255.254.0.0
[email protected]@gmail.com Network Layer Network Layer 4-4-7676
Network Prefix Equivalent Number of Class Addresses Number of Hosts
/27 1/8th of a Class C 32
/26 1/4th of a Class C 64
/25 1/2 of a Class C 128
/24 1 Class C 256
/23 2 Class C 512
/22 4 Class C 1,024
/21 8 Class C 2,048
/20 16 Class C 4,096
/19 32 Class C 8,192
/18 64 Class C 16,384
/17 128 Class C 32,768
/16 256 Class C or 1 Class B 65,536
/15 512 Class C or 2 Class B 131,072
/14 1,024 Class C or 4 Class B 262,144
/13 2048 Class C or 8 Class B 524,288
/12 4096 Class C or 16 Class B 1,048,576
/11 8192 Class C or 32 Class B 2,097,152
/10 16384 Class C or 64 Class B 4,194,304
/9 32768 Class C or 128 Class B 8,388,608
/8 65,536 Class C or 256 Class B or 1 Class A 16,777,216
Prefix Equivalents
[email protected]@gmail.com Network Layer Network Layer 4-4-7777
ProtocolsProtocols
Class-full Routing Protocols
Classless Routing Protocol
RIP version1 RIP version2
IGPR EIGPR
EGP OSPF
BGP3 BGP4
IS-IS
[email protected]@gmail.com Network Layer Network Layer 4-4-7878
ExamplesExamples
[email protected]@gmail.com Network Layer Network Layer 4-4-7979
IP addresses: how to get one?IP addresses: how to get one?
Q: How does host get IP address?
IP addr. is configures into host by admin. in a file Wintel: control-panel->network-
>configuration->tcp/ip->properties UNIX: /etc/rc.config
DHCP: Dynamic Host Configuration Protocol (RFC2131): dynamically get address from as server “plug-and-play”
[email protected]@gmail.com Network Layer Network Layer 4-4-8080
Subnetting (Extended Network Subnetting (Extended Network Prefix)Prefix)
Q: How an organization gets network part of IP addr?A: It gets allocated portion of its ISP’s address
space.
ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20
Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23 Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. ….
Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23
The ISP divides the block into 8 smaller addr. blocks (subnets) and gives them to 8
organization.
The ISP have been allocated the address block
[email protected]@gmail.com Network Layer Network Layer 4-4-8181
Hierarchical addressing: route aggregationHierarchical addressing: route aggregation
Hierarchical addressing allows efficient advertisement of routing information:
“Send me anythingwith addresses beginning 200.23.16.0/20”
200.23.16.0/23200.23.16.0/23
200.23.18.0/23200.23.18.0/23
200.23.30.0/23200.23.30.0/23
Organization 0
Organization 7Internet
Organization 1
ISP2 “Send me anythingwith addresses beginning 199.31.0.0/16”
200.23.20.0/23200.23.20.0/23Organization 2
...
...
199.31.0.0/16
route aggregation or route summarization.
ISP1
200.23.16.0/20
[email protected]@gmail.com Network Layer Network Layer 4-4-8282
Hierarchical addressing: more specific routesHierarchical addressing: more specific routes
“Send me anythingwith addresses beginning 200.23.16.0 /20”
200.23.16.0/23200.23.16.0/23
200.23.18.0/23200.23.18.0/23
200.23.30.0/23200.23.30.0/23
ISP1
Organization 0
Organization 7 Internet
Organization 1 ISP2“Send me anythingwith addresses beginning 199.31.0.0/16or 200.23.18.0 /23”
200.23.20.0/23Organization 2
...
...
23 bits
20 bits
ISP2 has a more specific route to Organization 1The routers in Internet use a longest prefix matching rule, and route toward ISP2, as it advertises the longest (more specific) address prefix that matches the destination address.
[email protected]@gmail.com Network Layer Network Layer 4-4-8383
Subnet Mask-1Subnet Mask-1
A subnet mask is applied to the host bits to determine how the network is subnetted, e.g. if the host is: 137.138.28.228, and the subnet
mask is 255.255.255.0 then the right hand 8 bits are for the host (255 is decimal for all bits set in an octet)
Host addresses of all bits set or no bits set, indicate a broadcast, i.e. the packet is sent to all hosts.
[email protected]@gmail.com Network Layer Network Layer 4-4-8484
Subnet Mask-2Subnet Mask-2
ISP's block 11001000 00010111 00010000 00000000 200.23.16.0/20ISP’s subnet mask 11111111 11111111 11110000 00000000 255.255.240.0
Organization 0 11001000 00010111 00010000 00000000 200.23.16.0/23Organization 1 11001000 00010111 00010010 00000000 200.23.18.0/23 Organization 2 11001000 00010111 00010100 00000000 200.23.20.0/23 ... ….. …. ….
Organization 7 11001000 00010111 00011110 00000000 200.23.30.0/23 Or’s subnet mask 11111111 11111111 11111110 00000000 255.255.254.0
Network part of an IP address= subnet mask & IP addressNetwork part of an IP address= subnet mask & IP address
[email protected]@gmail.com Network Layer Network Layer 4-4-8585
IP addressing: ICANNIP addressing: ICANN
Q: How does an ISP get block of addresses?
A: ICANN: Internet Corporation for Assigned
Names and Numbers allocates addresses manages DNS assigns domain names, resolves disputes
[email protected]@gmail.com Network Layer Network Layer 4-4-8686
CIDR: Subneting Example CIDR: Subneting Example
You are assigned the CIDR address 200.32.108.0 /22 and you must support the network shown in the diagram. Create an addressing scheme that will meet the diagram
requirements.
100 computers
100 computers
100 computers
300 computers
[email protected]@gmail.com Network Layer Network Layer 4-4-8787
Given the CIDR address 200.32.108.0 /22 How many Class C networks do we have? 3 classes How many host addresses do we have? 4x254
addresses What is the largest LAN requirement? 300 addresses
Host required - 300, 100, 100, 100, and 3 WAN links
CIDR: Subneting Example CIDR: Subneting Example (Questions)(Questions)
[email protected]@gmail.com Network Layer Network Layer 4-4-8888
200.32.108.0 200.32. 110.0
0 0
0 0255 255
255 255
200.32. 109.0 200.32. 111.0
[email protected]@gmail.com Network Layer Network Layer 4-4-8989
200.32. 110.0
0 0
0 0255 255
255 255
300
hos
ts
200
.32.
108
.0 /2
3
200.32.108.0
200.32. 109.0
200.32. 111.0
[email protected]@gmail.com Network Layer Network Layer 4-4-9090
0 0
0 0255 255
255 255
300
hos
ts
200
.32.
108
.0 /2
3127
128
100
hos
ts
200
.32.
110
.0 /2
5
100
hos
ts
200
.32.
110
.128
/25
200.32.108.0 200.32. 110.0
200.32. 109.0
200.32. 111.0
[email protected]@gmail.com Network Layer Network Layer 4-4-9191
0 0
0 0255 255
255 255
300
hos
ts
200
.32.
108
.0 /2
3127
128
100
hos
ts
200
.32.
110
.0 /2
5
100
hos
ts
200
.32.
110
.128
/25
127
128
100
hos
ts
200
.32.
111
.0 /2
5
200.32.108.0 200.32. 110.0
200.32. 109.0 200.32. 111.0
[email protected]@gmail.com Network Layer Network Layer 4-4-9292
0 0
0 0255 255
255 255
300
hos
ts
200
.32.
108
.0 /2
3127
128
100
hos
ts
200
.32.
110
.0 /2
5
100
hos
ts
200
.32.
110
.128
/25
127
128
100
hos
ts
200
.32.
111
.0 /2
5
191192
223
224
248
247
243252
251244
WAN links /30
240239
200.32.108.0 200.32. 110.0
200.32. 109.0 200.32. 111.0
[email protected]@gmail.com Network Layer Network Layer 4-4-9393
CIDR: Subneting Example CIDR: Subneting Example (Results)(Results)
Given the CIDR address 200.32.108.0 /22
200.32.108.0 /23
200.32.110.0 /25200.32.110.128 /25
200.32.111.0 /25
200.32.111.240 /30
200.32.111.244 /30
2 Class C’s
1/2 Class C1/2 Class C
1/2 Class C
100 computers
100 computers
300 computers
100 computers
200.32.111.248 /30
[email protected]@gmail.com Network Layer Network Layer 4-4-9494
Company XYZ needs to address 400 hosts. Its ISP gives them two contiguous Class C addresses:
207.21.54.0/24 207.21.55.0/24
Company XYZ can use a prefix of 207.21.54.0 /23 to supernet these two contiguous networks. (Yielding 510 hosts)
207.21.54.0 /23 207.21.54.0/24 207.21.55.0/24
23 bits in common
Supernetting Example-1Supernetting Example-1
[email protected]@gmail.com Network Layer Network Layer 4-4-9595
Supernetting Example-2Supernetting Example-2
addressing authority of ISP,include XYZ, be advertized to Internet as a single supernt
[email protected]@gmail.com Network Layer Network Layer 4-4-9696
CIDR and the ProviderCIDR and the Providerexample of route aggregation
advertising address: a.b.c.d/x
[email protected]@gmail.com Network Layer Network Layer 4-4-9797
IP datagram format datagram format
ver length
32 bits
data (variable length,typically a TCP
or UDP segment)
16-bit identifier
Checksum: 1’s add of 16bits words in header
time tolive
32 bit source IP address
IP protocol versionNumber[4bits]
header length (bytes)[4bits]
max numberremaining hops
(decremented at each router)
fragmentation/Reassembly/DF, MF Flags
total datagramlength (bytes)
upper layer protocolto deliver payload to(rfc 1700)
head.len
“type” ofservice
“type” of data: Priority [3bits]Delay[1bit]
Throughput[1bit]Reliability[1bit]
flags fragment offset
upper layer
32 bit destination IP address
Options (if any)
e.g. timestamp,record routetaken, specifylist of routers to visit.
how much overhead with TCP?
20 bytes of TCP 20 bytes of IP = 40 bytes +
app layer overhead
A packet is unique in Internet by:Id + S. IP Add + D. IP Add + Upper L.
1 :ICMP6 :TCP17 :UDP
[email protected]@gmail.com Network Layer Network Layer 4-4-9898
IP Fragmentation & ReassemblyIP Fragmentation & Reassembly
network links have MTU (max.transfer size) - largest possible link-level frame.
different link types, different MTUs
large IP datagram divided (“fragmented”) within net
one datagram becomes several datagrams
“reassembled” only at final destination
IP header bits used to identify, order related fragments
reassembly
fragmentation: in: one large datagramout: 3 smaller datagrams
[email protected]@gmail.com Network Layer Network Layer 4-4-9999
IP Fragmentation and ReassemblyIP Fragmentation and Reassembly
ID=x
offset=0
fragflag=0
length=4000
ID=x
offset=0
fragflag=1
length=1500
ID=x
offset=1480
fragflag=1
length=1500
ID=x
offset=2960
fragflag=0
length=1040
One large datagram becomes3 smaller datagrams.
Example 4000 byte
datagram MTU = 1500
bytes
0……….3979data
20 Byte
4000 Bytes
0……….1479
1480…2959
[email protected]@gmail.com Network Layer Network Layer 4-4-105105
DHCP: Dynamic Host Configuration Protocol: Dynamic Host Configuration Protocol
Goal: allow host to dynamically obtain its IP address from network server when it joins networkCan renew its lease on address in useAllows reuse of addresses (only hold address while connected an “on”Support for mobile users who want to join network (more shortly)
DHCP overview: host broadcasts “DHCP discover” msg DHCP server responds with “DHCP offer” msg host requests IP address: “DHCP request” msg DHCP server sends address: “DHCP ack” msg
[email protected]@gmail.com Network Layer Network Layer 4-4-106106
DHCP client-server scenarioDHCP client-server scenario
223.1.1.1
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
DHCP server
arriving DHCP client needsaddress in thisnetwork
A
BE
[email protected]@gmail.com Network Layer Network Layer 4-4-107107
DHCP client-server scenarioDHCP client-server scenario
DHCP server: 223.1.2.5arriving client
time
DHCP discover
src : 0.0.0.0, 68 dest.: 255.255.255.255,67yiaddr: 0.0.0.0transaction ID: 654
DHCP offer
src: 223.1.2.5, 67 dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 654Lifetime: 3600 secs
DHCP request
src: 0.0.0.0, 68 dest:: 255.255.255.255, 67yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs
DHCP ACK
src: 223.1.2.5, 67 dest: 255.255.255.255, 68yiaddrr: 223.1.2.4transaction ID: 655Lifetime: 3600 secs
[email protected]@gmail.com Network Layer Network Layer 4-4-108108
NAT: Network Address TranslationNAT: Network Address Translation
10.0.0.1
10.0.0.2
10.0.0.3
10.0.0.4
138.76.29.7
local network(e.g., home network)
10.0.0/24
rest ofInternet
Datagrams with source or destination in this networkhave 10.0.0/24 address for
source, destination (as usual)
All datagrams leaving localnetwork have same single source
NAT IP address: 138.76.29.7,different source port numbers
[email protected]@gmail.com Network Layer Network Layer 4-4-109109
NAT: Network Address TranslationNAT: Network Address Translation
Motivation: local network uses just one IP address as far as outside word is concerned: no need to be allocated range of addresses from
ISP: - just one IP address is used for all devices can change addresses of devices in local network
without notifying outside world can change ISP without changing addresses of
devices in local network devices inside local net not explicitly
addressable, visible by outside world (a security plus).
[email protected]@gmail.com Network Layer Network Layer 4-4-110110
NAT: Network Address TranslationNAT: Network Address Translation
Implementation: NAT router must:
outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #). . . remote clients/servers will respond using (NAT IP
address, new port #) as destination addr.
remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) translation pair
incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table
[email protected]@gmail.com Network Layer Network Layer 4-4-111111
NAT: Network Address TranslationNAT: Network Address Translation
10.0.0.1
10.0.0.2
10.0.0.3
S: 10.0.0.1, 3345D: 128.119.40.186, 80
1
10.0.0.4
138.76.29.7
1: host 10.0.0.1 sends datagram to 128.119.40, 80
NAT translation tableWAN side addr LAN side addr
138.76.29.7, 5001 10.0.0.1, 3345…… ……
S: 128.119.40.186, 80 D: 10.0.0.1, 3345
4
S: 138.76.29.7, 5001D: 128.119.40.186, 80
2
2: NAT routerchanges datagramsource addr from10.0.0.1, 3345 to138.76.29.7, 5001,updates table
S: 128.119.40.186, 80 D: 138.76.29.7, 5001
3
3: Reply arrives dest. address: 138.76.29.7, 5001
4: NAT routerchanges datagramdest addr from138.76.29.7, 5001 to 10.0.0.1, 3345
[email protected]@gmail.com Network Layer Network Layer 4-4-112112
NAT: Network Address TranslationNAT: Network Address Translation
16-bit port-number field: 60,000 simultaneous connections with a
single LAN-side address! NAT is controversial:
routers should only process up to layer 3 violates end-to-end argument
NAT possibility must be taken into account by app designers, eg, P2P applications
address shortage should instead be solved by IPv6
[email protected]@gmail.com Network Layer Network Layer 4-4-113113
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet
4.5.1 Intra-AS routing: RIP and OSPF 4.5.2 Inter-AS routing: BGP
4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-114114
Routing in the Internet Routing in the Internet (RC1812) Requirements for IP Version 4 RoutersRequirements for IP Version 4 Routers
The Global Internet consists of Autonomous Systems (AS) interconnected with each other: Stub AS: small corporation: one connection to other
AS’s Multihomed AS: large corporation (no transit): multiple
connections to other AS’s Transit AS: provider, hooking many AS’s together
Two-level routing: Intra-AS: administrator responsible for choice of routing
algorithm within network Inter-AS: unique standard for inter-AS routing: BGP
(RFC1771)
[email protected]@gmail.com Network Layer Network Layer 4-4-115115
Internet AS HierarchyInternet AS Hierarchy
Intra-AS border (exterior gateway) routers
Inter-AS (interior gateway) routers
C
A B
C.b
A.aA.c
B.a
a b
ad
bc
ac
b
[email protected]@gmail.com Network Layer Network Layer 4-4-116116
Intra-AS RoutingIntra-AS Routing
Also known as Interior Gateway Protocols (IGP) Most common Intra-AS routing protocols:
RIP: Routing Information Protocol
OSPF: Open Shortest Path First
IGRP: Interior Gateway Routing Protocol (Cisco proprietary)
[email protected]@gmail.com Network Layer Network Layer 4-4-117117
RIP ( Routing Information Protocol) ( Routing Information Protocol)
Distance vector algorithm Included in BSD-UNIX Distribution in 1982 Distance metric: # of hops (max = 15 hops)
Can you guess why?
Distance vectors: exchanged among neighbors every 30 sec via Response Message (also called advertisement)
Each advertisement: list of up to 25 destination nets within AS
[email protected]@gmail.com Network Layer Network Layer 4-4-118118
RIP: ExampleRIP: Example
Destination Network Next Router Num. of hops to dest. w A 2
y B 2 z B 7
x -- 1…. …. ....
C
Routing table in D
w x yzz
A D B
[email protected]@gmail.com Network Layer Network Layer 4-4-119119
RIP: ExampleRIP: Example
Destination Network Next Router Num. of hops to dest. w A 2
y B 2 z B A 7 5
x -- 1…. …. ....Routing table in D
Dest Next hops w - - x - - z C 4 …. … ...
Advertisementfrom A to D
w x yzz
A D B
[email protected]@gmail.com Network Layer Network Layer 4-4-120120
RIP: Link Failure and RecoveryRIP: Link Failure and Recovery
If no advertisement heard after 180 sec --> neighbor/link declared dead routes via neighbor invalidated new advertisements sent to neighbors neighbors in turn send out new advertisements
(if tables changed) link failure info quickly propagates to entire net poison reverse used to prevent ping-pong loops
(infinite distance = 16 hops)
[email protected]@gmail.com Network Layer Network Layer 4-4-121121
RIP Table processingRIP Table processing
RIP routing tables managed by application-level process called route-d (daemon)
advertisements sent in UDP packets, periodically repeated
physical
link
network forwarding (IP) table
Transprt (UDP)
routed
physical
link
network (IP)
Transprt (UDP)
routed
forwardingtable
[email protected]@gmail.com Network Layer Network Layer 4-4-122122
RIP Table example (continued)RIP Table example (continued)
Router: giroflee.eurocom.fr
Three attached class C networks (LANs) Router only knows routes to attached LANs Default router used to “go up” Route multicast address: 224.0.0.0 Loopback interface (for debugging)
Destination Gateway Flags Ref Use Interface -------------------- -------------------- ----- ----- ------ --------- 127.0.0.1 127.0.0.1 UH 0 26492 lo0 192.168.2. 192.168.2.5 U 2 13 fa0 193.55.114. 193.55.114.6 U 3 58503 le0 192.168.3. 192.168.3.5 U 2 25 qaa0 224.0.0.0 193.55.114.6 U 3 0 le0 default 193.55.114.129 UG 0 143454
[email protected]@gmail.com Network Layer Network Layer 4-4-123123
OSPF (Open Shortest Path First) (Open Shortest Path First)
“open”: publicly available Uses Link State algorithm
LS packet dissemination Topology map at each node Route computation using Dijkstra’s algorithm
OSPF advertisement carries one entry per neighbor router
Advertisements disseminated to entire AS (via flooding) Carried in OSPF messages directly over IP (rather than
TCP or UDP
[email protected]@gmail.com Network Layer Network Layer 4-4-124124
OSPF “advanced” features (not in RIP)OSPF “advanced” features (not in RIP)
Security: all OSPF messages authenticated (to prevent malicious intrusion)
Multiple same-cost paths allowed (only one path in RIP)
For each link, multiple cost metrics for different TOS (e.g., satellite link cost set “low” for best effort; high for real time)
Integrated uni- and multicast support: Multicast OSPF (MOSPF) uses same topology
data base as OSPF Hierarchical OSPF in large domains.
[email protected]@gmail.com Network Layer Network Layer 4-4-125125
Hierarchical OSPFHierarchical OSPF
[email protected]@gmail.com Network Layer Network Layer 4-4-126126
Hierarchical OSPFHierarchical OSPF
Two-level hierarchy: local area, backbone. Link-state advertisements only in area each nodes has detailed area topology; only know
direction (shortest path) to nets in other areas. Area border routers: “summarize” distances to
nets in own area, advertise to other Area Border routers.
Backbone routers: run OSPF routing limited to backbone.
Boundary routers: connect to other AS’s.
[email protected]@gmail.com Network Layer Network Layer 4-4-127127
Inter-AS routing in the Internet: Inter-AS routing in the Internet: BGP
Figure 4.5.2-new2: BGP use for inter-domain routing
AS2 (OSPF
intra-AS routing)
AS1
(RIP intra-AS routing) BGP
AS3 (OSPF intra-AS
routing)
BGP
R1 R2
R3
R4
R5
[email protected]@gmail.com Network Layer Network Layer 4-4-128128
Internet inter-AS routing: BGPInternet inter-AS routing: BGP
BGP (Border Gateway Protocol): the de facto standard
Path Vector protocol: similar to Distance Vector protocol each Border Gateway broadcast to
neighbors (peers) entire path (i.e., sequence of AS’s) to destination
BGP routes to networks (ASs), not individual hosts
E.g., Gateway X may send its path to dest. Z:
Path (X,Z) = X,Y1,Y2,Y3,…,Z
[email protected]@gmail.com Network Layer Network Layer 4-4-129129
Internet inter-AS routing: BGPInternet inter-AS routing: BGP
Suppose: gateway X send its path to peer gateway W W may or may not select path offered by X
cost, policy (don’t route via competitors AS), loop prevention reasons.
If W selects path advertised by X, then:Path (W,Z) = w, Path (X,Z)
Note: X can control incoming traffic by controlling it route advertisements to peers: e.g., don’t want to route traffic to Z -> don’t advertise any routes to Z
[email protected]@gmail.com Network Layer Network Layer 4-4-130130
BGP: controlling who routes to youBGP: controlling who routes to you
A,B,C are provider networks X,W,Y are customer (of provider networks) X is dual-homed: attached to two networks
X does not want to route from B via X to C .. so X will not advertise to B a route to C
Figure 4.5- BGPnew : a simple BGP scenario
A
B
C
W X
Y
legend: provider network
customer network
[email protected]@gmail.com Network Layer Network Layer 4-4-131131
BGP: controlling who routes to youBGP: controlling who routes to you
A advertises to B the path AW B advertises to W the path BAW Should B advertise to C the path BAW?
No way! B gets no “revenue” for routing CBAW since neither W nor C are B’s customers
B wants to force C to route to w via A B wants to route only to/from its customers!
A
B
C
W X
Y
legend: provider network
customer network
[email protected]@gmail.com Network Layer Network Layer 4-4-132132
BGP operationBGP operation
Q: What does a BGP router do? Receiving and filtering route advertisements
from directly attached neighbor(s). Route selection.
To route to destination X, which path )of several advertised) will be taken?
Sending route advertisements to neighbors.
[email protected]@gmail.com Network Layer Network Layer 4-4-133133
BGP messagesBGP messages
BGP messages exchanged using TCP. BGP messages:
OPEN: opens TCP connection to peer and authenticates sender
UPDATE: advertises new path (or withdraws old)
KEEPALIVE keeps connection alive in absence of UPDATES; also ACKs OPEN request
NOTIFICATION: reports errors in previous msg; also used to close connection
[email protected]@gmail.com Network Layer Network Layer 4-4-134134
Why different Intra- and Inter-AS routing ?Why different Intra- and Inter-AS routing ?
Policy: Inter-AS: admin wants control over how its traffic
routed, who routes through its net. Intra-AS: single admin, so no policy decisions
needed
Scale: hierarchical routing saves table size, reduced
update trafficPerformance: Intra-AS: can focus on performance Inter-AS: policy may dominate over performance
[email protected]@gmail.com Network Layer Network Layer 4-4-135135
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models
4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-136136
Router Architecture OverviewRouter Architecture Overview
Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) switching datagrams from incoming to outgoing link
[email protected]@gmail.com Network Layer Network Layer 4-4-137137
Input Port FunctionsInput Port Functions
Decentralized switching: given datagram dest., lookup output
port using routing table in input port memory
goal: complete input port processing at ‘line speed’
queuing: if datagrams arrive faster than forwarding rate into switch fabric
Physical layer:bit-level reception
Data link layer:e.g., Ethernetsee chapter 5
[email protected]@gmail.com Network Layer Network Layer 4-4-138138
Input Port QueuingInput Port Queuing
Fabric slower that input ports combined -> queueing may occur at input queues
Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward
queueing delay and loss due to input buffer overflow!
[email protected]@gmail.com Network Layer Network Layer 4-4-139139
Three Types of Switching FabricsThree Types of Switching Fabrics
[email protected]@gmail.com Network Layer Network Layer 4-4-140140
Switching Via MemorySwitching Via Memory
First generation routers: packet copied by system’s (single) CPU speed limited by memory bandwidth (2 bus crossings per datagram)
InputPort
OutputPort
Memory
System Bus
Modern routers: input port processor performs lookup, copy into memory
Cisco Catalyst 8500
[email protected]@gmail.com Network Layer Network Layer 4-4-141141
Switching Via a BusSwitching Via a Bus
datagram from input port memory to output port memory via a
shared bus bus contention: switching speed
limited by bus bandwidth 1 Gbps bus, Cisco 1900: sufficient
speed for access and enterprise routers (not regional or backbone)
[email protected]@gmail.com Network Layer Network Layer 4-4-142142
Switching Via An Interconnection NetworkSwitching Via An Interconnection Network
overcome bus bandwidth limitations Banyan networks, other interconnection nets
initially developed to connect processors in multiprocessor
Advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric.
Cisco 12000: switches Gbps through the interconnection network
[email protected]@gmail.com Network Layer Network Layer 4-4-143143
Output PortsOutput Ports
Buffering required when datagrams arrive from fabric faster than the transmission rate
Scheduling discipline chooses among queued datagrams for transmission
[email protected]@gmail.com Network Layer Network Layer 4-4-144144
Output port queuingOutput port queuing
buffering when arrival rate via switch exceeds output line speed
queueing (delay) and loss due to output port buffer overflow!
[email protected]@gmail.com Network Layer Network Layer 4-4-145145
Chapter 4 OutlineChapter 4 Outline
4.1 Introduction and Network Service Models
4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-146146
IPv6
Initial motivation: 32-bit address space completely allocated by 2008.
Additional motivation: header format helps speed
processing/forwarding header changes to facilitate QoS new “anycast” address: route to “best” of
several replicated servers IPv6 datagram format:
fixed-length 40 byte header no fragmentation allowed
[email protected]@gmail.com Network Layer Network Layer 4-4-147147
IPv6 Header (Cont)IPv6 Header (Cont)
Priority: identify priority among datagrams in flowFlow Label: identify datagrams in same “flow.” (concept of“flow” not well defined).Next header: identify upper layer protocol for data
[email protected]@gmail.com Network Layer Network Layer 4-4-148148
Other Changes from IPv4Other Changes from IPv4
Checksum: removed entirely to reduce processing time at each hop
Options: allowed, but outside of header, indicated by “Next Header” field
ICMPv6: new version of ICMP additional message types, e.g. “Packet Too
Big” multicast group management functions
[email protected]@gmail.com Network Layer Network Layer 4-4-149149
Transition From IPv4 To IPv6Transition From IPv4 To IPv6
Not all routers can be upgraded simultaneous no “flag days” How will the network operate with mixed IPv4
and IPv6 routers? Two proposed approaches:
Dual Stack: some routers with dual stack (v6, v4) can “translate” between formats
Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers
[email protected]@gmail.com Network Layer Network Layer 4-4-150150
Dual Stack ApproachDual Stack Approach
IPv6 IPv6 IPv6 IPv6IPv4 IPv4
Flow: XSrc: ADest: F
data
Flow: ??Src: ADest: F
data
Src:ADest: F
data
A-to-B:IPv6
Src:ADest: F
data
B-to-C:IPv4
B-to-C:IPv4
B-to-C:IPv6
A B C D E F
[email protected]@gmail.com Network Layer Network Layer 4-4-151151
Tunneling-AnalogyTunneling-Analogy
IPv6 IPv6 IPv6 IPv6
tunnelLogical view:A B E F
Analogy:
[email protected]@gmail.com Network Layer Network Layer 4-4-152152
Tunneling-Physical ViewTunneling-Physical View
Physical view:
IPv6 IPv6 IPv6 IPv6IPv4 IPv4
Flow: XSrc: ADest: F
data
Flow: XSrc: ADest: F
data
Flow: XSrc: ADest: F
data
Src:BDest: E
Flow: XSrc: ADest: F
data
Src:BDest: E
A-to-B:IPv6
E-to-F:IPv6
B-to-C:IPv6 inside
IPv4
B-to-C:IPv6 inside
IPv4
A B C D E F
IPv6 IPv6 IPv6 IPv6
tunnelLogical view:A B E F
[email protected]@gmail.com Network Layer Network Layer 4-4-153153
Differentiated services are intended to enable deployment of scalable service discrimination in the Internet.
Architecture is separated into two major components, one of which is fairly well-understood and the other of which is just beginning to be understood.
Decision is made to separate the forwarding and routing components (as in original design of Internet).
Packet forwarding is the relatively simple task that needs to be performed on a per-packet basis as quickly as possible.
Forwarding uses the packet header to find an entry in a routing table that determines the packet's output interface.
Routing sets the entries in that table and may need to reflect a range of transit and other policies as well as to keep track of route failures.
RFC2474: Differentiated Services Field (DS : Differentiated Services Field (DS Field) in the IPv4 and IPv6 HeadersField) in the IPv4 and IPv6 Headers
[email protected]@gmail.com Network Layer Network Layer 4-4-154154
Routing tables are maintained as a background process to the forwarding task. Further, routing is the more complex task and it has continued to evolve over the past 20 years.
Analogously, the differentiated services architecture contains two main components.
One is the fairly well-understood behavior in the forwarding path and the other is the more complex and still emerging background policy and allocation component that configures parameters used in the forwarding path.
The forwarding path behaviors include the differential treatment an individual packet receives, as implemented by queue service disciplines and/or queue management disciplines.
These per-hop behaviors are useful and required in network nodes to deliver differentiated treatment of packets no matter how we construct end-to-end or intra-domain services.
Focus is on the general semantics of the behaviors rather than the specific mechanisms used to implement them since these behaviors will evolve less rapidly than the mechanisms.
RFC2474 (cont)RFC2474 (cont)
[email protected]@gmail.com Network Layer Network Layer 4-4-155155
Chapter 4 roadmapChapter 4 roadmap
4.1 Introduction and Network Service Models
4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-156156
Multicast: one sender to many receiversMulticast: one sender to many receivers
Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students
Question: how to achieve multicast
Multicast via unicast
source sends N unicast datagrams, one addressed to each of N receivers
multicast receiver (red)
not a multicast receiver (red)
routersforward unicastdatagrams
[email protected]@gmail.com Network Layer Network Layer 4-4-157157
Multicast: one sender to many receiversMulticast: one sender to many receivers
Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students
Question: how to achieve multicast
Network multicast Router actively
participate in multicast, making copies of packets as needed and forwarding towards multicast receivers
Multicastrouters (red) duplicate and forward multicast datagrams
[email protected]@gmail.com Network Layer Network Layer 4-4-158158
Multicast: one sender to many receiversMulticast: one sender to many receivers
Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students
Question: how to achieve multicast
Application-layer multicast
end systems involved in multicast copy and forward unicast datagrams among themselves
[email protected]@gmail.com Network Layer Network Layer 4-4-159159
Internet Multicast Service ModelInternet Multicast Service Model
multicast group concept: use of indirection hosts addresses IP datagram to multicast group routers forward multicast datagrams to hosts
that have “joined” that multicast group
128.119.40.186
128.59.16.12
128.34.108.63
128.34.108.60
multicast group
226.17.30.197
[email protected]@gmail.com Network Layer Network Layer 4-4-160160
Multicast groupsMulticast groups
class D Internet addresses reserved for multicast:
host group semantics:o anyone can “join” (receive) multicast groupo anyone can send to multicast groupo no network-layer identification to hosts of
members needed: infrastructure to deliver mcast-addressed
datagrams to all hosts that have joined that multicast group
[email protected]@gmail.com Network Layer Network Layer 4-4-161161
Joining a multicast group: two-step processJoining a multicast group: two-step process
local: host informs local mcast router of desire to join group: IGMP (Internet Group Management Protocol)
wide area: local router interacts with other routers to receive mcast datagram flow many protocols (e.g., DVMRP, MOSPF, PIM)
IGMPIGMP
IGMP
wide-areamulticast
routing
[email protected]@gmail.com Network Layer Network Layer 4-4-162162
IGMP: Internet Group Management ProtocolIGMP: Internet Group Management Protocol
host: sends IGMP report when application joins mcast group IP_ADD_MEMBERSHIP socket option host need not explicitly “unjoin” group when
leaving router: sends IGMP query at regular intervals
host belonging to a mcast group must reply to query
query report
[email protected]@gmail.com Network Layer Network Layer 4-4-163163
IGMPIGMP
IGMP version 1 router: Host
Membership Query msg broadcast on LAN to all hosts
host: Host Membership Report msg to indicate group membership randomized delay
before responding implicit leave via no
reply to Query RFC 1112
IGMP v2: additions include
group-specific Query Leave Group msg
last host replying to Query can send explicit Leave Group msg
router performs group-specific query to see if any hosts left in group
RFC 2236
IGMP v3: under development as Internet draft
[email protected]@gmail.com Network Layer Network Layer 4-4-164164
Multicast Routing: Problem StatementMulticast Routing: Problem Statement
Goal: find a tree (or trees) connecting routers having local mcast group members tree: not all paths between routers used source-based: different tree from each sender to rcvrs shared-tree: same tree used by all group members
Shared tree Source-based trees
[email protected]@gmail.com Network Layer Network Layer 4-4-165165
Approaches for building multicast treesApproaches for building multicast trees
Approaches: source-based tree: one tree per source
shortest path trees reverse path forwarding
group-shared tree: group uses one tree minimal spanning (Steiner) center-based trees
…we first look at basic approaches, then specific protocols adopting these approaches
[email protected]@gmail.com Network Layer Network Layer 4-4-166166
Shortest Path TreeShortest Path Tree
mcast forwarding tree: tree of shortest path routes from source to all receivers Dijkstra’s algorithm
R1
R2
R3
R4
R5
R6 R7
21
6
3 4
5
i
router with attachedgroup member
router with no attachedgroup member
link used for forwarding,i indicates order linkadded by algorithm
LEGENDS: source
[email protected]@gmail.com Network Layer Network Layer 4-4-167167
Reverse Path ForwardingReverse Path Forwarding
if (mcast datagram received on incoming link on shortest path back to center)
then flood datagram onto all outgoing links else ignore datagram
rely on router’s knowledge of unicast shortest path from it to sender
each router has simple forwarding behavior:
[email protected]@gmail.com Network Layer Network Layer 4-4-168168
Reverse Path Forwarding: exampleReverse Path Forwarding: example
• result is a source-specific reverse SPT– may be a bad choice with asymmetric links
R1
R2
R3
R4
R5
R6 R7
router with attachedgroup member
router with no attachedgroup member
datagram will be forwarded
LEGENDS: source
datagram will not be forwarded
[email protected]@gmail.com Network Layer Network Layer 4-4-169169
Reverse Path Forwarding: pruningReverse Path Forwarding: pruning
forwarding tree contains subtrees with no mcast group members no need to forward datagrams down subtree “prune” msgs sent upstream by router with no
downstream group members
R1
R2
R3
R4
R5
R6 R7
router with attachedgroup member
router with no attachedgroup member
prune message
LEGENDS: source
links with multicastforwarding
P
P
P
[email protected]@gmail.com Network Layer Network Layer 4-4-170170
Shared-Tree: Steiner TreeShared-Tree: Steiner Tree
Steiner Tree: minimum cost tree connecting all routers with attached group members
problem is NP-complete excellent heuristics exists not used in practice:
computational complexity information about entire network needed monolithic: rerun whenever a router needs
to join/leave
[email protected]@gmail.com Network Layer Network Layer 4-4-171171
Center-based treesCenter-based trees
single delivery tree shared by all one router identified as “center” of tree to join:
edge router sends unicast join-msg addressed to center router
join-msg “processed” by intermediate routers and forwarded towards center
join-msg either hits existing tree branch for this center, or arrives at center
path taken by join-msg becomes new branch of tree for this router
[email protected]@gmail.com Network Layer Network Layer 4-4-172172
Center-based trees: an exampleCenter-based trees: an example
Suppose R6 chosen as center:
R1
R2
R3
R4
R5
R6 R7
router with attachedgroup member
router with no attachedgroup member
path order in which join messages generated
LEGEND
21
3
1
[email protected]@gmail.com Network Layer Network Layer 4-4-173173
Internet Multicasting Routing: DVMRPInternet Multicasting Routing: DVMRP
DVMRP: distance vector multicast routing protocol, RFC1075
flood and prune: reverse path forwarding, source-based tree RPF tree based on DVMRP’s own routing tables
constructed by communicating DVMRP routers no assumptions about underlying unicast initial datagram to mcast group flooded
everywhere via RPF routers not wanting group: send upstream
prune msgs
[email protected]@gmail.com Network Layer Network Layer 4-4-174174
DVMRP: continued…DVMRP: continued…
soft state: DVMRP router periodically (1 min.) “forgets” branches are pruned: mcast data again flows down unpruned branch downstream router: reprune or else continue to
receive data routers can quickly regraft to tree
following IGMP join at leaf odds and ends
commonly implemented in commercial routers Mbone routing done using DVMRP
[email protected]@gmail.com Network Layer Network Layer 4-4-175175
TunnelingTunneling
Q: How to connect “islands” of multicast routers in a “sea” of unicast routers?
mcast datagram encapsulated inside “normal” (non-multicast-addressed) datagram
normal IP datagram sent thru “tunnel” via regular IP unicast to receiving mcast router
receiving mcast router unencapsulates to get mcast datagram
physical topology logical topology
[email protected]@gmail.com Network Layer Network Layer 4-4-176176
PIM: Protocol Independent MulticastPIM: Protocol Independent Multicast
not dependent on any specific underlying unicast routing algorithm (works with all)
two different multicast distribution scenarios :
Dense: group members
densely packed, in “close” proximity.
bandwidth more plentiful
Sparse: # networks with group
members small wrt # interconnected networks
group members “widely dispersed”
bandwidth not plentiful
[email protected]@gmail.com Network Layer Network Layer 4-4-177177
Consequences of Sparse-Dense Dichotomy:Consequences of Sparse-Dense Dichotomy:
Dense group membership by
routers assumed until routers explicitly prune
data-driven construction on mcast tree (e.g., RPF)
bandwidth and non-group-router processing profligate
Sparse: no membership until
routers explicitly join receiver- driven
construction of mcast tree (e.g., center-based)
bandwidth and non-group-router processing conservative
[email protected]@gmail.com Network Layer Network Layer 4-4-178178
PIM- Dense ModePIM- Dense Mode
flood-and-prune RPF, similar to DVMRP but
underlying unicast protocol provides RPF info for incoming datagram
less complicated (less efficient) downstream flood than DVMRP reduces reliance on underlying routing algorithm
has protocol mechanism for router to detect it is a leaf-node router
[email protected]@gmail.com Network Layer Network Layer 4-4-179179
PIM - Sparse ModePIM - Sparse Mode
center-based approach router sends join msg
to rendezvous point (RP) intermediate routers
update state and forward join
after joining via RP, router can switch to source-specific tree increased performance:
less concentration, shorter paths
R1
R2
R3
R4
R5
R6R7
join
join
join
all data multicastfrom rendezvouspoint
rendezvouspoint
[email protected]@gmail.com Network Layer Network Layer 4-4-180180
PIM - Sparse ModePIM - Sparse Mode
sender(s): unicast data to RP,
which distributes down RP-rooted tree
RP can extend mcast tree upstream to source
RP can send stop msg if no attached receivers “no one is listening!”
R1
R2
R3
R4
R5
R6R7
join
join
join
all data multicastfrom rendezvouspoint
rendezvouspoint
[email protected]@gmail.com Network Layer Network Layer 4-4-181181
Chapter 4 roadmapChapter 4 roadmap
4.1 Introduction and Network Service Models
4.2 Routing Principles4.3 Hierarchical Routing4.4 The Internet (IP) Protocol4.5 Routing in the Internet4.6 What’s Inside a Router?4.7 IPv64.8 Multicast Routing4.9 Mobility
[email protected]@gmail.com Network Layer Network Layer 4-4-182182
What is mobility?What is mobility?
spectrum of mobility, from the network perspective:
no mobility high mobility
mobile user, usingsame access point
mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)
mobile user, connecting/ disconnecting from network using DHCP.
[email protected]@gmail.com Network Layer Network Layer 4-4-183183
Mobility: VocabularyMobility: Vocabulary
home network: permanent “home” of mobile(e.g., 128.119.40/24)
Permanent address: address in home network, can always be used to reach mobilee.g., 128.119.40.186
home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote
wide area network
correspondent
[email protected]@gmail.com Network Layer Network Layer 4-4-184184
Mobility: more vocabularyMobility: more vocabulary
Care-of-address: address in visited network.(e.g., 79,129.13.2)
wide area network
visited network: network in which mobile currently resides (e.g., 79.129.13/24)
Permanent address: remains constant (e.g., 128.119.40.186)
home agent: entity in visited network that performs mobility functions on behalf of mobile.
correspondent: wants to communicate with mobile
[email protected]@gmail.com Network Layer Network Layer 4-4-185185
How do How do youyou contact a mobile friend: contact a mobile friend:
search all phone books?
call her parents? expect her to let you
know where he/she is?
I wonder where Ali moved to?
Consider friend frequently changing addresses, how do you find her?
[email protected]@gmail.com Network Layer Network Layer 4-4-186186
Mobility: approachesMobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
Let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
[email protected]@gmail.com Network Layer Network Layer 4-4-187187
Mobility: approachesMobility: approaches
Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile
located no changes to end-systems
let end-systems handle it: indirect routing: communication from
correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
not scalable
to millions of mobiles
[email protected]@gmail.com Network Layer Network Layer 4-4-188188
Mobility: registrationMobility: registration
End result: Foreign agent knows about mobile Home agent knows location of mobile
wide area network
home network
visited network
1
mobile contacts foreign agent on entering visited network
2
foreign agent contacts home agent home: “this mobile is resident in my network”
[email protected]@gmail.com Network Layer Network Layer 4-4-189189
Mobility via Indirect RoutingMobility via Indirect Routing
wide area network
homenetwork
visitednetwork
3
2
41
correspondent addresses packets using home address of mobile
home agent intercepts packets, forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
[email protected]@gmail.com Network Layer Network Layer 4-4-190190
Indirect Routing: commentsIndirect Routing: comments
Mobile uses two addresses: permanent address: used by correspondent
(hence mobile location is transparent to correspondent)
care-of-address: used by home agent to forward datagrams to mobile
foreign agent functions may be done by mobile itself triangle routing: correspondent-home-network-
mobile inefficient when correspondent, mobile are in same network
[email protected]@gmail.com Network Layer Network Layer 4-4-191191
Forwarding datagrams to remote mobileForwarding datagrams to remote mobile
Permanent address: 128.119.40.186
Care-of address: 79.129.13.2
dest: 128.119.40.186
packet sent by correspondent
dest: 79.129.13.2 dest: 128.119.40.186
packet sent by home agent to foreign agent: a packet within a packet
dest: 128.119.40.186
foreign-agent-to-mobile packet
[email protected]@gmail.com Network Layer Network Layer 4-4-192192
Indirect Routing: moving between networksIndirect Routing: moving between networks
suppose mobile user moves to another network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile
(but with new care-of-address) Mobility, changing foreign networks
transparent: on going connections can be maintained!
[email protected]@gmail.com Network Layer Network Layer 4-4-193193
Mobility via Direct RoutingMobility via Direct Routing
wide area network
homenetwork
visitednetwork
4
2
41correspondent requests, receives foreign address of mobile
correspondent forwards to foreign agent
foreign agent receives packets, forwards to mobile
mobile replies directly to correspondent
3
[email protected]@gmail.com Network Layer Network Layer 4-4-194194
Mobility via Direct Routing: commentsMobility via Direct Routing: comments
overcome triangle routing problem non-transparent to correspondent:
correspondent must get care-of-address from home agent What happens if mobile changes networks?
[email protected]@gmail.com Network Layer Network Layer 4-4-195195
Mobile IPMobile IP
RFC 3220 has many features we’ve seen:
home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)
three components to standard: agent discovery registration with home agent indirect routing of datagrams
[email protected]@gmail.com Network Layer Network Layer 4-4-196196
Mobile IP: agent discoveryMobile IP: agent discovery
agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9)
RBHFMGV bits reserved
type = 16
type = 9 code = 0 = 9
checksum = 9
router address
standard ICMP fields
mobility agent advertisement
extension
length sequence #
registration lifetime
0 or more care-of-addresses
0 8 16 24
R bit: registration required
H,F bits: home and/or foreign agent
[email protected]@gmail.com Network Layer Network Layer 4-4-197197
Mobile IP: registration exampleMobile IP: registration example
visited network: 79.129.13/24 home agent
HA: 128.119.40.7foreign agent
COA: 79.129.13.2 COA: 79.129.13.2
….
ICMP agent adv. Mobile agent MA: 128.119.40.186
registration req.
COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 ….
registration req.
COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format ….
registration reply
HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format ….
registration reply
HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 ….
time
[email protected]@gmail.com Network Layer Network Layer 4-4-198198
Network Layer: summaryNetwork Layer: summary
What we’ve covered: network layer services routing principles: link state
and distance vector hierarchical routing IP Internet routing protocols RIP,
OSPF, BGP what’s inside a router? IPv6 mobility