IGP(Interior Gateway Protocols) :

IGP(Interior Gateway Protocols) are commonly made up of routing protocols. It can be used within ina an autonomous system. It is used inside – interior to – an independent network system. We can run  Interior GAteways Protocols within the LAN(Local Area Network). It is developed by Cisco Systems, Inc(mid-1980s). While creating IGP, there is a cisco goal, within an autonomous system it provides a protocol that is robust.

Commonly used Interior Gateway Protocols are the following:

  • First, Routing Information Protocol(shortly RIP).
  • Second, Open Shortest Path First(shortly OSPF).
  • An another type protocol named, Intermediate System To Intermediate System(shortly, IS-IS)
  • The next and the final one is Enhanced Interior Gateway Routing Protocol(Shortly, EIGRP).

The network path information within an autonomous system can find out by using the Interior Gateway Protocol.


  1. It is a distant vector IGP.
  2. The routes can be compared mathematically with the help of a distance vector routing protocol. This protocol uses some measurement of distance for this purpose.
  3. supports hold-downs.
  4. Uses composite matrices.
  5. Uses multipath routing.
  6. supports split horizons.
  7. supports unequal-cost load balancing.

Configuring IGP:


-Router IGRP AS_number(1 to 65535)

-Network IP_networks.

Configure IGRP,


Router#configure terminal

Router#(config)#router igrp 100 (AS Number)

Router#(config-router)# network_network address of own router

Router#(config-router)# exit


Verifying IGRP configuration:-

  1. show the IP route. (It shows that the routing protocol added was IGRP)
  2. show IP protocols.
  3. show IP igrp events.

EGP(Exterior Gateway Protocol):

Unlike IGP EGP’s are used in different autonomous systems. Here in the case of EGP, were widely used in WAN(Wide Area Network). To exchange network reachability information between BGP routers, it uses an InterAS(or Interdomain) routing protocol. To transfer the routing messages it uses the protocol, TCP, on port 179. It is a distance-vector protocol. In the case of BGP, the main difference with the IGP is that the routing messages hold the complete routes, unlike IGP. The routing policies are specified by the network administrators.

The protocol used by the internet and the customer’s edge devices are connected by this protocol, run by ISPs

Also, read…

BGP operation:

  • To exchange a piece of information, there include two BGP routers. And these routers are called peers.
  1. In the starting, the BGP routers send the complete routing table.
  2. Until the connection ends the BGP router maintains the current version of the entire BGP routing tables of all of its peers.
  3. Then the updations are sent as the messages to the routing table to modify the routing table.
  4. If there is any special conditions or error occurred, it sends the notification message.
  • Route: It can be simply defined as a unit of information. The purpose of using this is to connect a destination and the attributes of a path to that destination.
  1. The Routing Information Bases (RIBs) can be used to stores information about the routes.

A RIB within a BGP router mainly contains three different parts:

  1. Adj-RIBs-In: It stores the routing information that is unprocessed. This information is sent by the peers to the local BGP router.
  2. Loc-RIB: The routes selected by the Decision Process of the local BGP router are stored here.
  3. Adj-RIBs-Out: It organizes the routes to send to particular peers. This is done with the help of the UPDATE messages of the local speaker.

Commonly used Exterior Gateway Protocols:

1)   One of the major type is, Distance-vector routing protocol(Eg: RIP, RIPv2RIPng, IGRP.)

  • It works based on the Bellman-Ford algorithm.

2)   The second one is Advanced distance vector routing protocol(examples include EIGRP.)

3)  The last type is, Link-state routing protocol(examples include OSPF, IS-IS.)


  • Used within a different autonomous system.
  • It uses cost matric to identify the best route.
  • The response contains the complete routing table.
  • Mostly used by larger organizations.
  • It uses a database that contains the neighboring network and the paths.

Download Difference between IGP(Interior Gateway Protocols) and EGP(Exterior Gateway Protocol) Protocols in pdf – Click here