IGP & EGP

Interior Gateway Protocol (IGP)

An Interior Gateway Protocol (IGP) is a routing protocol which is use to exchange routing information within an autonomous system (AS). We can understand it as exchanging routing information between gateways (hosts or routers) within an autonomous network (The Corporate LAN network is an example, where as we can implement IGP). The routing information can be used by the Internet Protocol (IP) or other network protocols to specify how to route packets.

The interior gateway protocols can be divided into two categories:

1-      Distance-vector Routing Protocol 

2-      Link-state Routing Protocol

  

Exterior Gateway Protocol (EGP)

While an Exterior Gateway Protocol (EGP) is a routing protocol which is use to determining the network reach-ability between autonomous systems and makes use of Interior Gateway Protocol to resolve routes within an AS. EGP is commonly used between hosts on the Internet to exchange routing information. EGP is based on periodic polling using Hello/I-Heard-You (I-H-U) message exchanges to monitor neighbor reach-ability and Poll commands to solicit Update responses. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen. 

BGP (Border Gateway protocol) is an example of EGP, which is used on the edge of network (Huge Network) and mostly used by ISP's Networks.