Chirag's Blog: Classification of Unicast Routing Protocol | What is routing | How route will be selected in network | Interdomain routing protocol

Introduction of Routing

It is a process of moving a data packet from source to destination across one or more network. In routing, the data packet choosing optimal path from one network to another. The main function of the network layer is to route packets from source to destination. Routing is performed on network layer device called as a router.

A host or router has a routing table with an entry for each destination, or a combination of destinations, to route IP packets. Routing table can be either static or dynamic. A static routing table contains information entered manually. The administrator enters the route for each destination into the table. Dynamic routing table is updated periodically by using one of the dynamic routing protocols such as RIP, OSPF or BGP.

If there will be any changes in internet or in topologies, manual entries can be done in static table by administrator. Dynamic table is updated automatically when there is a change somewhere in the internet or changes in any topologies. Now a day, dynamic table is used because of sudden changes in the internet. For example, one of the routers in the internet may fail or link between any two routers is down. So, because of these reasons dynamic table is required.

How route will be selected in network from source to destination?

To accomplish a route through the network must be selected generally more than one route is possible. The selection of route is generally based on some performance criteria. The simplest criteria are to choose shortest route through the network. The shortest route means that passes through the least number of nodes. This shortest route selection results in least number of hops per packet. A routing algorithm is designed to perform this task. The routing algorithm is a part of network layer software.

Classification of Routing Protocol

An internet is divided into autonomous systems. An autonomous system is a group of networks and routers under the authority of a single administration. Below figure shows the autonomous system. Routing inside an autonomous system is referred to as intra-domain routing. Routing between autonomous system is referred to as inter-domain routing.

There may be different intra-domain routing protocols working in different autonomous system. Only one inter-domain routing protocol handles routing between autonomous systems. Classification of unicast routing protocols are based on intra domain and inter domain.