Lecture, November 20, 2002

1

Lecture, November 20, 2002

Message Delivery to Processes

Internet AddressingAddress resolution protocol (ARP)Dynamic host reconfiguration protocol (DHCP)TunnelingMobile IP

Routing in Virtual Circuit Networks

2

Message delivery to processes

Host

Process

Network Network

RouterNetworkinterface

Port

IP address = (NetworkId, HostId)

3

Addressing

Address spacesFlatHierarchical

Addressing ModesUnicastMulticastBroadcastAnycast

4

Internet addressing

IPv4 address encoding – classes

Problems and solutionsSubnettingClassless address encoding

Address resolution protocol (ARP)

Dynamic host reconfiguration protocol (DHCP)

Tunneling

Mobile IP

5

IPv4 packet format

32-bit destination IP address

options (if any)

32-bit source IP address

header checksum

packet length (bytes)

fragment identifier

Payload

12-bit fragment offset

ToS

upper layer prottime to live

flags

hlenversion

0 16 318

6

IPv4 address encoding

A

B

C

D

0 NetworkId

110 NetworkId

HostId

HostId

HostId

1110 Multicast address

10 NetworkId

0 8 16 31

E 1111 Reserved

24

7

Problems with IPv4 address encoding

The size of the IP address space is: 232

Class C addresses not very useful…

Class B addresses wasteful…

We would like to group network addresses to reduce the size of forwarding tables.

8

Subnetting

Define a subnet mask and a subnet number.Obtain the subnet number:

(IP address) AND (subnet mask)The whole idea is to allocate a single network number to a collection of networks.All hosts in a subnet have the same subnet number.Routing: given a destination IP address the router ANDs this address with the masks of all entries to determine the subnet number of the destination. Example.

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Subnetting

1111 1111 1111 1111 1111 1111 1000 0000

0 8 16 31

(a)

(b)

HostId0001 0111 0000 1110

NetworkId 1011 1000 0010 1100

HostId0000 1110

SubnetId0001 0111

(c)

NetworkId 1011 1000 0010 1100

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Subnet mask: 255.255.255.128Subnet Number: 184.44.23.128

SubnetNumber SubnetMask NextHop184.44.23.0 255.255.255.128 R1184.44.23.128 255.255.255.128 I0184.44.13.0 255.255.255.0 I1184.44.51.128 255.255.255.128 R3

Forwarding table of router R2

R1

0

1

R2

0

1

R3

0

1

H1

0

H2

0

H5

0

H4

0

Subnet mask: 255.255.255.128Subnet Number: 184.44.23.0

184.44.23.14

Subnet mask: 255.255.255.0Subnet Number: 184.44.13.0

Subnet mask: 255.255.255.128Subnet Number: 184.44.51.128

184.44.23.35

184.44.23.145

184.44.23.129

184.44.13.20

184.44.13.15184.44.13.19

184.44.51.136 184.44.51.129

184.44.23.133

184.44.23.137

H3

0

2

Internet

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Classless interdomain routing - CIDR

A block of class C addresses are aggregated to have a common prefix.

Example:

195.2.32.xx 11000101 00000010 00100000 xxxxxxxx

195.2.63.yy 11000101 00000010 00111111 yyyyyyyy

Have a common 18 bit prefix

11000101 00000010 001

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Classless interdomain routing - CIDR

In this bloc we have 214 addresses

(32-18=14).

If all potential 16,384 hosts in this block are

connected to LANs connected to the same router and

All routers know to use an 18 bit prefix for the lookup phase of forwarding

we are in business.

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Address Resolution Protocol

ARP response

Local Area Network

Source Hardware Address (bytes 0-3)

Source HardwareAddress (bytes 4-5)

Source IP Address(bytes (0-1)

Source IP Address(bytes 2-3)

Target HardwareAdress (bytes 0-1)

Target Hardware Address (bytes 2-5)

Target IP Address (bytes 0-3)

LAN type(e.g. Ethernet, FDDI)

Protocol Type(e.g. IP)

Hlen =48

Plen=32Operation

(request/response)

0 8 16 31

ARP query

host B

host A

(a) (b)

Switch

Internet

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TunnelingInternetwork

IPheadersrc = 129.5.17.10dst =135.12.7.1

135.12.7.1

Destination NextHop 192.10.5 Inteface 0 195.4.50 Virtual Inteface default Interface 1

Tunnel

0

1

VI

Network 1192.10.5

192.10.5.14

192.10.5.2

R1

195.4.50.3

7

129.5.17.10

Network 2195.4.50

2195.4.50.7

R2

IP payload

IPheadersrc = 192.10.5.14dst =195.4.50.3

IP payload

IPheadersrc = 192.10.5.14dst =195.4.50.3

IP payload

IPheadersrc = 192.10.5.14dst =195.4.50.3

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Dynamic host reconfiguration protocol - DHCP

DHCP responseunicast frame

Destination address:the physical address

of host interface

DHCP requestbroadcast frame

Local Area Network

DHCPserver

Laptop

DHCP relay DHCP responseUDP datagram for the

DHCP relay

DHCP requestUDP datagram for the

DHCP server

Internet

16

Mobile IP

Internet

Home network 117.17

Tunnel

(1)

(2)

(3)

Sending Host

Router

Home Agent117.17.10.5

Router

Sender's networkRouter

Foreign network 192.6

Foreign Agent192.6.1.8

Mobile Host117.17.1..33

Tunnel

17

IPv6flow label

payload length (bytes)

0 16 318

version priority

next header hop limit

128-bit source IP address

128-bit destination IP address

Payload

18

UDP

payload

0 16 318

source port

checksum length

destination port