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CSE452:Computer Networks
The Internet Protocol(IP)IPv4 & IPv6
CIDR, Subnet
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The Internet Network layer
routingtable
Host, router network layer functions:
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
Networklayer
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IP 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 interface, not host, 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
223.1.1.1 = 11011111 00000001 00000001 00000001
223 1 11
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IP 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(for IP addresses starting with 223, first 24 bits are network address)
LAN
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IP AddressingHow 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 consisting
of six networks
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IP Addresses
0network host
10 network host
110 network host
1110 multicast address
A
B
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
given notion of “network”, let’s re-examine IP addresses:
“class-full” addressing:
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IP Addressing An IP address is a 32-bit sequence of 1s and 0s.
To make the IP address easier to use, the address is usually written as four decimal numbers separated by periods.
This way of writing the address is called the dotted decimal format.
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Decimal and Binary Conversion
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IPv4 Addressing
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Class A, B, C, D, and E IP Addresses
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Reserved IP Addresses 1. Certain host addresses are reserved and cannot be assigned
to devices on a network. 2. An IP address that has binary 0s in all host bit positions
is reserved for the network address. 3. An IP address that has binary 1s in all host bit positions
is reserved for the broadcast address.
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Network Address
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Broadcast Address
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Public and Private IP Addresses 1. No two machines that connect to a public network can have the same IP
address because public IP addresses are global and standardized.
2. Procedure was needed to make sure that addresses were in fact unique.
3. Originally, an organization known as the Internet Network Information Center (InterNIC) handled this procedure. InterNIC no longer exists and has been succeeded by the Internet Assigned Numbers Authority (IANA).
4. IANA carefully manages the remaining supply of IP addresses to ensure that duplication of publicly used addresses does not occur.
5. However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique.
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Public and Private IP Addresses 1. RFC 1918 sets aside three blocks of IP addresses for private,
internal use.
2. Addresses that fall in these ranges are not routed on the Internet backbone. Internet router immediately discard private addresses.
3. Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses using Network Address Translation (NAT).
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IP 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 InterDomain Routing 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
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Millions of Addresses Available Over 16,000,000
Efficiency Non-subnetted networks are wasteful Division of networks not optimal
Smaller Network Easier to manage Smaller broadcast domains
So Make the network as small as possible Divide the network into subnetworks Borrow some bits from the host add.
Why Subnet?
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What You Need Understand Address System Understand Classes of Networks “Two-Tums” Table
Formulas Magic Numbers Subnet Mask
“ANDing” Process
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Dissecting the Address> Classes <
CLASS RANGES: A: 0 – 127 N . H . H . H
B: 128 – 191 N . N . H . H
C: 192 – 223 N . N . N . H
_ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ 1 0 0 0 0 0 0 0 .0 0 0 1 0 0 0 0 .0 0 1 0 0 0 0 0. 0 0 0 0 1 1 0 1 (Digital)
128 . 16 . 32 . 13 (Decimal)
CLASSB
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TWO-TUMS
27 26 25 24 23 22 21 20
128 192 224 240 248 252 254 255
128 64 32 16 8 4 2 1
MAGIC NUMBERS:
SUBNET MASK:
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Magic Formulas
Number of Usable Subnets
2n – 220 - 2 = 1 - 2 = -121 - 2 = 2 - 2 = 022 - 2 = 4 - 2 = 223 - 2 = 8 - 2 = 6
Number of Usable Hosts/Subnet
2h-n – 228-0- 2 = 256 - 2 = 254
28-1- 2 =? 28-2- 2 = ?28-3- 2 =?
n = # borrowed bitsh = # bits available in host address
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Subnet Mask
What is a Subnet Mask?“Extended Network Prefix”Indicates extent of the Network numbers1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . _ _ _ _ _ _ _ _
Why is it needed?Used by router to determine Network
AddressHow?
Uses “ANDing” to compare Mask to IP Address
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ANDing Process
MASK: 11111111.11111111.11111111.00000000
255 . 255 . 255 . 0
IP: 11001000.11001000.11001000.00001010
200 . 200 . 200 . 10
Network Address: 11001000.11001000.11001000.00000000
200 . 200 . 200 . 0
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How to Subnet?* Subnet: Borrow
_ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ ._ _ _ _ _ _ _ _ 1 0 0 0 0 0 0 0 .0 0 0 1 0 0 0 0 .0 0 1 0 0 0 0 0. 0 0 0 0 1 1 0 1 (Digital)
128 . 16 . 32 . 13 (Decimal)
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Easy Example
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Set Up Subnets
200.200.200.10
5 Subnets
•What is the Subnet Mask?•What are the Network Addresses?•What is the Broadcast Domain•What IP Addresses are available?
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Steps….
1. What is the CLASS?2. How many BITS do we
need to borrow?3. Determine Subnet Mask
4. Determine “Magic Number”
5. Set up Table for IP Address (“Wire”), Range & Broadcast Domain
6. Fill in Table
1. C [Range: 192 – 223]]2. 5 Subnets 3 [23-2 =
6]
3. 255.255.255.224• Use Subnet Mask #• Borrow 3 Bits
4. 32
5. Wire Range BC
6.
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Table200.200.200.10
WIRE RANGE BC
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Table200.200.200.10
WIRE RANGE BC200.200.200.0
Class C
Borrow 5 Bits
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Table200.200.200.10
WIRE RANGE BC200.200.200.0
200.200.200.32
200.200.200.64
200.200.200.96
+.32
+.32
Magic Number
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Table200.200.200.10
WIRE RANGE BC200.200.200.0
200.200.200.32
200.200.200.64
200.200.200.96
200.200.200.128
200.200.200.160
200.200.200.192
200.200.200.224
Subnet Mask
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Table200.200.200.10
WIRE RANGE BC200.200.200.0 200.200.200.31
200.200.200.32 200.200.200.63
200.200.200.64
200.200.200.96
200.200.200.128
200.200.200.160
200.200.200.192
200.200.200.224
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Table200.200.200.10
WIRE RANGE BC200.200.200.0 200.200.200.31
200.200.200.32 200.200.200.63
200.200.200.64 200.200.200.95
200.200.200.96 200.200.200.127
200.200.200.128 200.200.200.159
200.200.200.160 200.200.200.191
200.200.200.192 200.200.200.223
200.200.200.224 200.200.200.255
Broadcast Domain
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Table200.200.200.10
WIRE RANGE BC200.200.200.0 200.200.200.31
200.200.200.32 200.200.200.63
200.200.200.64 200.200.200.95
200.200.200.96 200.200.200.127
200.200.200.128 200.200.200.159
200.200.200.160 200.200.200.191
200.200.200.192 200.200.200.223
200.200.200.224 200.200.200.225
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Table200.200.200.10
WIRE RANGE BC200.200.200.0 200.200.200.1 –
200.200.200.30200.200.200.31
200.200.200.32 200.200.200.33 – 200.200.200.62
200.200.200.63
200.200.200.64 200.200.200.65 – 200.200.200.94
200.200.200.95
200.200.200.96 200.200.200.97 - 200.200.200.126
200.200.200.127
200.200.200.128 200.200.200.129 – 200.200.200.158
200.200.200.159
200.200.200.160 200.200.200.161 – 200.200.200.190
200.200.200.191
200.200.200.192 200.200.200.193 – 200.200.200.222
200.200.200.223
200.200.200.224 200.200.200.225 – 200.200.200.254
200.200.200.255
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Table200.200.200.10
WIRE RANGE BC200.200.200.0 200.200.200.1 –
200.200.200.30200.200.200.31
200.200.200.32 200.200.200.33 – 200.200.200.62
200.200.200.63
200.200.200.64 200.200.200.65 – 200.200.200.94
200.200.200.95
200.200.200.96 200.200.200.97 - 200.200.200.126
200.200.200.127
200.200.200.128 200.200.200.129 – 200.200.200.158
200.200.200.159
200.200.200.160 200.200.200.161 – 200.200.200.190
200.200.200.191
200.200.200.192 200.200.200.193 – 200.200.200.222
200.200.200.223
200.200.200.224 200.200.200.225 – 200.200.200.254
200.200.200.255
Reserved forNetwork Addresses
Reserved forBroadcastAddresses
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Table200.200.200.10
WIRE RANGE BC
200.200.200.33 – 200.200.200.62
200.200.200.65 – 200.200.200.94
200.200.200.97 - 200.200.200.126
200.200.200.129 – 200.200.200.158
200.200.200.161 – 200.200.200.190
200.200.200.193 – 200.200.200.222
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Set Up Subnets
200.200.200.0
200.200.200.33 - .62
200.200.200.161 - .190
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Obtaining an Internet Address
1.Static addressing Each individual device must be configured
with an IP address.
2.Dynamic addressing Reverse Address Resolution Protocol (RARP) Bootstrap Protocol (BOOTP) Dynamic Host Configuration Protocol (DHCP) DHCP initialization sequence Function of the Address Resolution Protocol ARP operation within a subnet
Obtaining an IP Address1. A network host needs to obtain a globally unique address in
order to function on the Internet.
2. MAC has only significance only in LAN to identify host.
3. Router does not use MAC address(?) to forward packets outside LAN.
4. IP addresses are used for Internet communication.
5. IP is hierarchical addressing Scheme that allows individual addresses to be associated together and treated together.
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Obtaining an IP AddressRegardless of the method chosen no two interfaces can have the same IP
address.
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Static Assignment of an IP Address 1. Static assignment works best on small, infrequently changing
networks. 2. The system administrator manually assigns and tracks IP addresses
for each computer, printer, or server on the intranet. 3. Servers should be assigned a static IP address so workstations and
other devices will always know how to access needed services. 4. Other devices that should be assigned static IP addresses are network
printers, application servers, and routers.
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IP addresses: how to get one?
hard-coded by system admin in a file Wintel: control-panel->network->configuration->tcp/ip->properties
UNIX: /etc/rc.config
DHCP: Dynamic Host Configuration Protocol: dynamically get address: “plug-and-play” 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
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DHCP client-server scenario
DHCP server
arriving DHCP client
223.1.2.5
Figure 4.4.2-N1: DHCP client-server scenario
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DHCP client-server scenario
DHCP server: 223.1.2.5 arriving client
time
DHCP discoversrc : 0.0.0.0, 68 dest.: 255.255.255.255,67DHCPDISCOVERyiaddr: 0.0.0.0transaction ID: 654
DHCP offersrc: 223.1.2.5, 67 dest: 223.1.2.4, 68DHCPOFFERyiaddrr: 223.1.2.4transaction ID: 654DHCP server ID: 223.1.2.5Lifetime: 3600 secs
DHCP requestsrc: 0.0.0.0, 68 dest:: 255.255.255.255, 67DHCPREQUESTyiaddrr: 223.1.2.4transaction ID: 655DHCP server ID: 223.1.2.5Lifetime: 3600 secs
DHCP ACKsrc: 223.1.2.5, 67 dest: 223.1.2.4, 68DHCPACKyiaddrr: 223.1.2.4transaction ID: 655DHCP server ID: 223.1.2.5Lifetime: 3600 secs
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DHCP IP Address Management • DHCP allows a host to obtain an IP address dynamically without the
network administrator having to set up an individual profile for each device.
• All that is required when using DHCP is a defined range of IP addresses on a DHCP server.
• As hosts come online, they contact the DHCP server and request an address.
• The DHCP server chooses an address and leases it to that host. • With DHCP, the entire network configuration of a computer can be
obtained in one message. • The major advantage that DHCP has over BOOTP is that it allows users to
be mobile. • This mobility allows the users to freely change network connections from
location to location. • The importance to this DHCP advancement is its ability to lease an IP
address to a device and then reclaim that IP address for another user after the first user releases it.
• This means that DHCP offers a one to many ratio of IP addresses and that an address is available to anyone who connects to the network.
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IP addresses: how to get one?
Network (network portion): get allocated portion of 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
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Hierarchical addressing: route aggregation
“Send me anythingwith addresses beginning 200.23.16.0/20”
200.23.16.0/23
200.23.18.0/23
200.23.30.0/23
Fly-By-Night-ISP
Organization 0
Organization 7Internet
Organization 1
ISPs-R-Us“Send me anythingwith addresses beginning 199.31.0.0/16”
200.23.20.0/23Organization 2
...
...
Hierarchical addressing allows efficient advertisement of routing information:
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Hierarchical addressing: more specific routes
ISPs-R-Us has a more specific route to Organization 1
“Send me anythingwith addresses beginning 200.23.16.0/20”
200.23.16.0/23
200.23.18.0/23
200.23.30.0/23
Fly-By-Night-ISP
Organization 0
Organization 7Internet
Organization 1
ISPs-R-Us“Send me anythingwith addresses beginning 199.31.0.0/16or 200.23.18.0/23”
200.23.20.0/23Organization 2
...
...
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IP addressing: the last word...
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
