1

Topic : Basics of WAN &WAN Protocols

Sub-Topic : Packet Transfer Mechanism using Router and IP address

In the previous classes, you have learnt about

• IP Address

• Network prefix and host number

• Internet address

• Sub-netting and no sub-netting

• Default gateways

3

Objectives

On completion of this period ,you would be able to know about

• Packet transfer mechanism using routers and IP addresses

4

Computer Network

SynApp: equipped routers or hosts. Primary function is to create synopses of network traffic. May have limited query processing and storage component as well.

Forensic Server: Responsible for archiving synopses, query processing & routing, enforcing monitoring, security policies, for the domain.

ForNet Domain: A domain covered by single monitoring and privacy policies.

Fig .1

5

Recap

• Let us remember the functions of a router and also IP address details in the following slides

6

Routers

• A router is a hardware component used to interconnect networks

Router

LAN WAN

Fig .2

7

• A router has a network interface card for each network that it is connected to

• Networks can use different technologies

• Router forwards packets between networks

• Router’s job is to transform packets from one network to meet the standards of the second network

Routers

8

Routers with More Than Two Interfaces

Fig .3

9EC606A .64 9

Internetwork

• An internetwork is composed of arbitrarily many networks interconnected by routers

Router

Fig .4

9EC606A .64 10

WAN78.0.0.0

Token Ring227.240.129.0

78.0.0.17

227.240.129.17

227.240.129.2

131.108.99.5

Ethernet 131.108.0.0

Router

Fig .5

Internetwork

11

Routers and IP Addressing

• What about routers - connected to two networks ?

• Router has multiple IP addresses - one for each interface as shown in the previous slide

• IP address depends on network address

• IP address specifies an interface, or network attachment point, not a computer

12

TCP/IP Addresses

• Addressing in TCP/IP is specified by the Internet Protocol (IP)

• Each host is assigned a 32-bit number

• This 32-bit number is called the IP address or Internet address

13

TCP/IP Addresses

• Each IP address is unique across entire Internet

• The format of IP addresses makes routing efficient

• Each IP address is divided into a prefix and a suffix

• Prefix identifies network to which computer is attached

• Suffix identifies computer within that network

9EC606A .64 14

Packet Transfer Mechanism Using Routers And IP Address

• The network layer monitors the delivery of the packet

using physical networks

• In direct delivery source and destination of packet are

located on same physical network

• In an indirect delivery, packet moves from router to router

until it reaches its final destination

9EC606A .64 15

Packet Transfer Mechanism Using Routers and IP Address

• When a packet is placed in its route to its destination it is

known as forwarding

• It requires a router or a host to have a routing table

• There are many forwarding techniques

9EC606A .64 16

Forwarding Techniques

• Next hop method

• Network / host – specific method

• Default method

• The path from source to destination is a function of

routing protocols

9EC606A .64 17

Examples of Routing Protocols

• Routing Information Protocol

• Open shortest path first

• Intermediate system to Intermediate system

9EC606A .64 18

• Packets from one network protocol are wrapped in a

packet for another protocol

• It is called tunneling done by wrapper network protocol

• The routing protocols determine best path for the packet

to travel

• They maintain routing tables that contain information

about networks topology

Examples of Routing Protocols

9EC606A .64 19

• In the internet world, IP is used to transport packets

through the internet

• It uses the information contained in the routing tables

with routers

• The routing tables may contain several possible routes

• The routing algorithm calculates the least-cost path from

source to destination

Examples of Routing Protocols

9EC606A .64 20

• Routers also maintain routing tables that contain

destination address of a node or network

• It also has network interface associated with a particular

router address

• A special type of route is called static route (fixed) that

can be entered manually or through software in routing

table

• The static route cannot be changed dynamically

Examples of Routing Protocols

9EC606A .64 21

• Two general routing algorithms are used for computing

metric information. i.e. hops, propagation delay,

bandwidth, time, channel utilization error rates etc

Examples of Routing Protocols

9EC606A .64 22

Example of Routing Table

• Routing Table generated on a Unix system with IP address 187.96.25.2 [Local-Host Routing]

Destination Gateway Flags Interface

Local host Local host UH le O

215.103.16.227

187.96.25.13 UGHD le O

215.103.16.141

187.96.25.35 UGHD le 1

Default 187.96.25.1 UG

187.96.25.0 187.96.25.2 U leO

9EC606A .64 23

where

• U = route is up & operational

• G = packet must pass through at least one router

• H = route to a specific host and not a network

• D = route was created dynamically

Example Routing Table Contd…

9EC606A .64 24

• The table’s first entry illustrated local host-routing

• It indicates that any packets meant for local network

87.96.25.0

• It will be forwarded through gateway 187.96.25.2 (IP

address of the host). Local host acts as router

Example Routing Table Contd….

9EC606A .64 25

• The second entry in the table indicates that the packets are

forwarded to another router

• The Packets whose destination address is 215.103.16.227 are

forwarded to the router (187.96.25.13) through interface leO

• This router will have the information to where this packet is to

be delivered

Example Routing Table Contd….

9EC606A .64 26

• The third entry indicates the packets with destination

address 215.103.16.141 are to forwarded to gateway

• The gateway whose address 187.96.25.35 accessible

through le 1 interface

Example Routing Table Contd….

9EC606A .64 27

• The Fourth entry entry of table is a default route

• When router receives a packet with unknown destination

address

• The router forwards packet to default router

Example Routing Table Contd….

28

• If host system receives a packet with destination address

212.133.65.3

• It forwards to router with destination address 187.96.25.1

(since there is no entry in host’s routing table for

212.133.65.3

Example Routing Table Contd….

29

• Routers exchange routing table information with

neighbor routers periodically depending upon routing

protocol used

• They do so in order to update the routing tables as one

router may be connected to more than one router

Example Routing Table Contd….

30

Summary

In this class, you have learnt about

• Packet transfer mechanism using routers

• And IP addresses with routing options used

31

Quiz

1) What is the length of the IP address

a) 16-bit

b) 32-bit

c) 8-bit

d) 64-bit

32

Quiz

2) A routing table specifies about

a) various routes that can be used

b) identifies the address

c) it’s a table of IP addresses

d) none of the above`

33

Frequently Asked Questions

1) Explain how packet transfer mechanism is done using

routers & IP addresses

2) What are the various forwarding techniques used ?

3) Discuss with an example importance of a routing table

along with its options