An Interior Gateway Protocol is a routing protocol that is used to exchange routing information between routers within an autonomous system. An autonomous system contains a set of routers that share common traffic policies and administration and is managed by a single organization. Thus routing protocols running within an autonomous system are Interior Gateway Protocols.

Interior Gateway Protocols can be divided into two categories shown below

· Distance Vector: They use the Bellman-Ford algorithm for exchanging routing information. Routers using Distance Vector routing protocols do not posses the topological information about the network but instead rely on the neighbor’s information, which is the reason this method is known as routing by rumor. We will cover in Distance Vector routing protocols in detail in the upcoming lessons. Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are examples of Distance Vector routing protocols. RIP is an open standard protocol while IGRP is a Cisco proprietary protocol. Enhanced Interior Gateway Routing Protocol (EIGRP) is also a Cisco Proprietary protocol is that is categorized as an advanced Distance Vector protocol or as a hybrid protocol.

· Link State: They possess complete topological information about the network and based on this information each router independently calculates and builds the routing table. Link State routing protocols will also be covered in detail in the upcoming lessons. Open Shortest Path First (OSPF) and Intermediate Systems-to-Intermediate Systems (IS-IS) are examples of Link State routing protocols.


Configuring of Interior Gateway Routing Protocols is fairly simple, what is most important is that the student must learn the working of each protocol and troubleshoot if any problem arises.

Shown below is our network topology, and we will configure a routing protocol so that subnets and can communicate with each other. First, we learn to configure RIP to fulfill our requirement and then we will use OSPF for the same task so that we may have an idea of configuring both protocols.

RIP Version 2 Configuration

RouterA(config)# router rip

RouterA(config-router)# version 2

RouterA(config-router)# no auto-summary

RouterA(config-router)# network

RouterA(config-router)# network

RouterB(config)# router rip

RouterB(config-router)# version 2

RouterB(config-router)# no auto-summary

RouterB(config-router)# network

RouterB(config-router)# network

RIP version 2 configuration is fairly simple, we specify the command ‘router rip’ to enter routing protocol configuration mode and then specify the version which is ‘version 2’ the latest version and then specify to disable automatic summarization of networks using the ‘no auto-summary’ command, then we will specify the network on which RIP must be enabled and which should be advertised to other routers.

OSPF Configuration

RouterA(config)# router ospf 100

RouterA(config-router)# network area 0

RouterA(config-router)# network area 0

RouterB(config)# router ospf 100

RouterB(config-router)# network area 0

RouterB(config-router)# network area 0

OSPF configuration is also very simple, we enter the routing protocol configuration mode by entering the command ‘router ospf 100’, 100 is the OSPF process number, and then we enable the ospf process on our links using the network command. OSPF uses the concept of areas to logically divide the network for scalability.

In today’s lesson, we covered IGPs, their types, and configuration and we will continue our study of routing for a while with more topics covering the routing and IGPs in detail in the upcoming lessons.