packet transfer mechanism using routers and ip addresses

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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

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Objectives

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

• Packet transfer mechanism using routers and IP addresses

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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

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Recap

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

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Routers

• A router is a hardware component used to interconnect networks

Router

LAN WAN

Fig .2

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• 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

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Routers with More Than Two Interfaces

Fig .3

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Internetwork

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

Router

Fig .4

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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

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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

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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

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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

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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

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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

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Forwarding Techniques

• Next hop method

• Network / host – specific method

• Default method

• The path from source to destination is a function of

routing protocols

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Examples of Routing Protocols

• Routing Information Protocol

• Open shortest path first

• Intermediate system to Intermediate system

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• 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

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• 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

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• 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

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• 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

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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

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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…

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• 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….

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• 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….

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• 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….

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• 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….

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• 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….

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• 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….

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Summary

In this class, you have learnt about

• Packet transfer mechanism using routers

• And IP addresses with routing options used

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Quiz

1) What is the length of the IP address

a) 16-bit

b) 32-bit

c) 8-bit

d) 64-bit

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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`

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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