What is IGP and EGP? Difference between Interior Gateway Protocols and Exterior Gateway Protocol

In this article you will learn about definitions of IGP and EGP, also you will get to know about difference between Interior Gateway Protocols and Exterior Gateway Protocol (IGRP vs. EGP).

Interior Gateway Protocol (IGP):

When the data packets are to be transferred within the same autonomous systems, Interior Gateway Protocols are used (IGP). For the communication to happen between the networks using Interior Gateway Protocol, both the networks must belong to same autonomous system.

The router identifies the autonomous system of a network using autonomous system number. If the autonomous system number of two networks is different, we cannot use Interior Gateway Protocol to establish a communication link between those two networks.

Generally, there are three categories of Interior Gateway protocols

  1. Distance Vector Protocols
  2. Link State Protocols
  3. Hybrid Protocols

Distance Vector Protocols:

Bellman Ford algorithm is used in distance vector protocols and the routers that uses distance vector protocol does not have information about entire network. The routers advertise the distance value calculated. The distance value information is tabulated as routing table. Some of the examples of protocols that use distance vector protocol are RIP, RIP version2, RIPng, and IGRP etc

Link State Protocols:

The routers using link state protocol has the information about the entire topology. Based on the information about the topology, routers are capable of selecting best next hop independently. The best next hops are tabulated as routing table. OSPF, IS-IS (Intermediate System to Intermediate System) are some of the example of protocols that uses link state routing protocol.

Hybrid Protocol:

The hybrid protocols are the combination of distance vector and link state routing protocols. They have the features of both the categories. EIGRP is the best example of Hybrid Protocol.

Exterior Gateway Protocol (EGP): 

Exterior Gateway Protocol is used to transfer the data packets between two different autonomous systems. The router identifies the device autonomous system based on autonomous system number assigned to that network.  Exterior Gateway protocol (EGP) and Border Gateway Protocols (BGP) are the examples of Exterior Gateway Protocols.

Routers that uses Exterior Gateway Protocol (EGP) maintains the information about all the IP addresses assigned to the devices, best path to a particular network and cost metrics etc.

Differences between EGP and IGP

Though the Exterior Gateway Protocol and Interior Gateway protocols are used to transmit the data packets between different networks using routable protocols like Internet Protocol; they are different from each other.

Interior Gateway Protocol is used to forward the packets among different networks that use the same autonomous system number. Whereas the exterior Gateway Protocol have the capability of forwarding data packets to different networks with different autonomous system numbers.

Note: Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS) are IGP Protocols.

However BGP (Border Gateway Protocol) is EGP Protocol.

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