Router&routing

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Concepts of Router and Routing

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Router

• A device that connects two or more computer networks

together is called as a Router

• It allows two or more different computer networks to

send data to each other

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Router Contd….

Fig.1

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Fig.2

Router Contd….

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Fig.3

Router Contd….

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• A router is a computer whose software and hardware

are designed to perform the tasks of routing and

forwarding information (sending the information

to the destination).

Router Contd….

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Routers generally contain

• A specialized operating system

• RAM

• NVRAM

• Flash memory and

• one or more processors

Router Contd….

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• Routers operate in two different planes

• Control Plane: The router learns the outgoing interface

that is most appropriate for forwarding specific packets to

specific destinations

• Forwarding Plane: The router is responsible for the actual

process of sending a packet received on a logical interface

to an outbound logical interface

Router Contd….

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• Routers periodically disseminate topology information to all the other routers with the help of control packets (e.g. :HELLO, TC packets)

• Topology information contains the information about the one hop and two hop neighbors to each of the router, link cost etc

• Link cost can be defined in several terms: a time estimate, a distance estimate, congestion estimate, bandwidth estimate etc. for the communication link between router and its one hop neighbor

• After learning the topology information, every router computes shortest route from itself to every other router in the Internet

• The computed shortest routes are stored in a route cache in the form of routing table

• Routing table gives the nest hop router to which packet has to be forwarded to send it in the shortest path for each destination IP address ( network part of IP address)

Control Plane Activities

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• The Packet which arrive at Router’s interface is first buffered (stored)

• The Router examines the packet’s header and the picks the destination IP address to where the packet has to reach

• It looks into the routing table to know the next hop router to which the packet has to be forwarded in order to send it in the shortest path

• Then Router forwards the packet to the corresponding next Router address via one of its ports

• The same process is carried out at each Router along the shortest path till the destination router is reached

Forward Plane Activities

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Types of Routers

Various types of routers

• Edge Router

• Border Router

• Core router

• Enterprise Router

• Access Router

• Distribution Router

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Symbol for Router

Fig.4

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Router Connecting Various Subnets

TOKEN RING

NETWORK

A

BUS NETWORK

B

ROUTER

ETHERNET

NETWORK

C

Fig.5

X Y

Z

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• Router must have three interfaces and three Network

Interface Cards (NICs) to interact with the networks A, B and

C at the junctions X and Y and Z as shown in figure 5

• In Internet, there are number of networks that communicate

with each other. Therefore, there would be as many routers

as networks

Router Concepts

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Routing

• Routing is the process of selecting paths in a network to

send data or physical traffic

• Routing is performed for many kinds of networks,

including the telephone network , the Internet, and

transport networks

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• Routing directs forwarding, the passing of logically

addressed packets from their source towards their

ultimate destination through intermediary nodes

• Nodes are hardware devices called routers, bridges,

gateways, firewalls, or switches

Router Contd….

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• Ordinary computers with multiple network cards can also

forward packets and perform routing, though they are not

specialized hardware and may suffer from limited

performance

• The routing process usually directs forwarding on the

basis of routing tables which maintain a record of the

routes to various network destinations

• Thus constructing routing tables, which are held in the

routers' memory, becomes very important for efficient

routing

Router Contd….

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• Therefore, Routing is the process of sending the data in

the form of packets called datagrams from the source to

the destination computers through many networks

• Routing algorithms take the decisions about routing

process and factors affecting them are as follows

• Least cost routing

• Distributed routing

• Packet life time

Router Contd….

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ROUTING AND ROUTERS

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Summary

In this class, you have learnt about

• Router and routing concepts

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Quiz

1. A Router is connected to five networks.

Then number of NICs required by the

router is

a) 2

b) 3

c) 5d) 7

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Frequently Asked Questions

1. Differentiate between Router and Routing?

2. List the various types of routers

3. Write short notes on routing