What is Routing Protocol

In this section, we will discuss what is Routing Protocol, its function, types, and application.

What is Routing Protocol

The routing protocol is a type of network protocol that is responsible for sharing routing information among the neighbor routers and finds the best possible and reliable path to forward the packet from source to destination network.

Dynamic routing uses different routing protocols based on different metric values such as hop count, cost, bandwidth, etc. to provide the best path for packet delivery from one network to another network.

Routing protocols work on the basis of a complex set of algorithms. Each routing protocols use a different algorithm to calculate the best path from source to destination.

For example, RIP uses the Bellman-Ford algorithm, wheres OSPF uses the open shortest path algorithm.

Classification of Routing Protocols

Routing protocols are classified on the basis of their Purpose, Operation, and Behaviour.

Based on Operation

Routing protocols are classified into three categories based on their operational characteristics:

  • Distance Vector
  • Link State
  • Hybrid

It has been discussed in earlier section Click on the link —> to go to distance vector and link-state routing protocols.

Base on purpose

Dynamic routing protocols are classified into the following categories based on their purposes

  • Interior Gateway Protocol
  • Exterior Gateway Protocol

Interior Gateway Protocol(IGP)

IGPs are used within a group of routers that falls under a single Autonomous System. All the router with the AS shares common routing information and routing advertisement are shared within the AS.

It is also called intra- AS routing.

Examples of IGPs are RIP v1, RIP v2, EIGRP, IGRP, OSPF, and IS-IS.

Exterior Gateway Protocol(EGP)

EGP is used for routing between  autonomous system. It shares routing updates between different AS.  Service providers and large companies comprise of different AS.

EGP is also known as Inter-AS routing.

Examples of EGP is  Border Gateway Protocol (BGP).

Autonomous System

An autonomous system is a group of routers that shares identical routing information and is controlled by the common administration such as a company or a group of companies, or an organization, ISP, etc.

The autonomous system acts as a boundary line for the routing protocol. A single AS is configured with the same routing protocols within a company or a group of companies.

AS is denoted by a global unique numeric value that ranges from 1 to 65535. It is also called ASN ( Autonomous System Number). ASN is governed by the IANA ( Internet Assigned Numbers Authority).

There are two types of AS: Public and private.

Public AS is used for Internet Backbone, wheres private AS is used in the internal network of any organization.

Based on Behaviour:

A routing protocol is categorized into Classful and Classless Routing protocols on the basis of its behavior.

Classful Routing Protocol

Classful Routing Protocols are legacy protocols that support classful IP v4 addressing scheme. They are used in older networks.

The classful routing is easy to implement and it does not send network mask information in the routing update.  The network addresses are distinguished by their different classes ( A, B, or C).

The examples of classful routing protocols are RIPv1 and IGRP.

Classless Routing Protocol

The classful addressing is no more used by modern IP networks. Hence, the classful routing protocols have become obsolete. The introduction of a classless addressing scheme led to the use of classless routing protocols.

Thus, the classless routing protocol supports the features of VLSM and CIDR. The routing update includes all the subnet mask information of the network addresses of different networks.

The examples of classless IPv4 routing protocols are EIGRP, OSPF, and IS-IS.

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