Lecture 04 networking

Information Technology III - 3104

Lecture 04 -Routing and Routing Protocols

Direct Delivery

Send a message to a machine in the LAN

Indirect Delivery

Indirect Delivery

To send a packet from source to destinationpacket should go from router to router

All routers should maintain a routing table

IP packet is analyzed at the router and correct path is selected form the routing table

The packet is sent though that path

Indirect delivery is done using the routing strategies

Routing Strategies

There are four routing strategies- Fixed Routing- Flooding- Random Routing- Adaptive Routing

Fixed RoutingRouting information is centrally maintained

This is called a Directory (A central database)

Advantage - Updating new information is easy as need to change at one location (central Database)

Disadvantages - Each and every IP packet should be analyzed- Network traffic may increase at the central database because it has to serve lots of requests from routers- Dynamic changes are not possible

FloodingWhen an IP packet comes, the router will send it on all paths.

- retransmitted to neighbors Advantages

- Simple mechanism (IP packets are not analyzed at router) - Most likely it will reach the destination (Highly reliable)

Disadvantages - Causes high network traffic- Duplicate packets might reach the destination- Wastes Network bandwidth

Random RoutingWhen an IP packet comes to the router, it decides the

path randomly and sends the IP packet in that path

Advantages- Will not cause unnecessary network traffic- Simple

Disadvantage - No guarantee that the IP packet will reach to the destination

Adaptive RoutingEach router maintains a routing table

Also it can be changed according to the network changes (Adaptive)

Advantages - Network traffic is minimized- The best route will be selected most of the time

Disadvantages - Routers need to keep a routing table - Process each IP packet- Need to update routing tables automatically with the changes in the network

Routing Methods used in Adaptive Routing

Next hop routing Host specificNetwork specific

Default routing

Host Specific RoutingEach router keeps a table entry for each host (one record for

one host)Table entry has Host IP and the Interface

Host Address InterfaceA E0B S0C S1

Disadvantages• Large number of records (if multiple paths are available number

of records increases)• Table updating is difficult and complex as it should be done for

each and every host (if the host IP changes)

Network Specific RoutingEach router keeps a table entry for each network (one record

for one network)Table entry has Network address and Interface

Advantages• Number of records are limited (Table updates are not for each

host but for a network)

• Update is easy

Network Address InterfaceA E0B S0C S1

Default Routing Another record in the routing table

Indicates the route/path to be taken, if any of the records does not match with the IP packet destination IP address

Stub networks only use default routing , which means that they have only one exit port out of the network

Routing Table update Methods

Basically there are three methods to update routing tables- Connected- Static- Dynamic

ConnectedOnce the router is connected to the network its interfaces are

given IP addresses

With that router automatically identifies the network addresses to which it connected

StaticAdministrator can manually give routing table

records

Dynamic

Routing tables are updated automatically by using routing rules ( protocols )

Routing tables haveInitially only ‘connected’ records Then add few ‘static’ records Then add dynamic updates

Routing Protocols

Features of routing protocolsNetwork changes (addition or removal or fault) are

automatically updated in routing tables of all routers

When there are many routes to a destination, the best route should be selected

Share the traffic through different routes

What Is a Routing Protocol?Routing Protocols

allow routers to dynamically advertise and learn routes, determine which routes are available and which are the most efficient routes to a destination

20

NetworkProtocol

DestinationNetwork

ConnectedRIP

IGRP

10.120.2.0172.16.2.0172.17.3.0

Exit Interface

E0S0S1

Routing Protocol: RIP, IGRP,OSPF

172.17.3.0

172.16.1.010.120.2.0

E0S0

Routing Protocols

Routing Protocols cont.An autonomous system (AS) is a collection of routers

under a common administrationex : a company's internal network

Interior Gateway Protocols (IGP) are used for intra-autonomous system routing

(routing inside an autonomous system)

Exterior Gateway Protocols (EGP) are used for inter-autonomous system routing

(routing between autonomous systems)

Routing Protocols cont.

Distance Vector Routing Protocols

Routes are advertised as vectors of distance and direction

Distance is defined in terms of a metric such as hop count and direction is simply the next-hop router or exit interface

Send periodic updates of their routing information

Use the Bellman-Ford algorithm for best path selection

Work best in situations where:- Network is simple- Administrators do not have enough knowledge to configure

Ex : RIP, IGRP, EIGRP

Link State Routing Protocols link-state routing protocol send information about the state of

its links to other routers in the routing domain

The state of those links includes information about the type of network and any neighboring routers on those networks

A link-state update only sent when there is a change in the topology

Use the Dijkstra algorithm for best path/ route selection

Work best in situations where:- Network design is complex (large networks)- Administrators have a good knowledge of network

Ex : OSPF, IS-IS

Routing Algorithms

Bellman-Ford AlgorithmUsed by distance vector routing protocols

Dijkstras AlgorithmUsed by link state routing protocols