Interior Gateway Protocol

When it comes to the protocol classifications, routing protocols can be classified according to their various characteristics. They can be classified by their purpose, operation, and behavior.

The routing protocols are divided into the Interior Gateway Protocol IGP’s and Exterior Gateway Protocol EGP’s according to their purpose.

As it is very clearly stated in the following figure, the routing protocols are divided into three types, which are static, default, and Dynamic Routing Protocols. However, that’s the dynamic routing protocol which is furthermore classified into Interior Gateway Protocol IGP’s and ExteriorGateway Protocol EGP’s, according to their purpose.

In this post, we will be discussing the Interior Gateway protocol.

Interior Gateway Protocol

But even before getting into our main topic which is Interior Gateway protocol, we need to describe the Autonomous System (AS). Because the Internet is based on the AS concept and that’s why we need to have IGP’s and EGP’s, it is very much important to have an understanding of the Autonomous System.

What is the Autonomous System?

So, a group of connected routers managed and administered by a single entity or domain, for example, a company or an organization, is known as an autonomous system. Now there might be one or more than one network operator involved in administering these routers, but they need to be doing this on behalf of a single entity which for example could be an ISP network or a company’s internal network.

Ok, so now that we have understood what an autonomous system is, it is easy to understand what is Interior Gateway protocol.

what is Interior Gateway protocol?

IGP or Interior Gateway Protocol is a type of dynamic routing protocol which is used to share the routing information inside/within the same autonomous system. IGP’s are furthermore divided into Distance vector protocol and link-state protocol.

If an Interior Gateway Protocol would need to communicate with a network outside of its autonomous system, then they need to get help from EGP or exterior gateway protocol which are always installed at the edge routers and have a foot in two worlds, one on the Internet and another one in the organizations inside network.

Following protocols are examples of interior gateway protocols.

  • Routing Information Protocol version one (RIPv1) and Routing Information Protocol version two (RIPv2), which are popular for being used in small to medium-sized networks, and are based on the distance-vector algorithm.
  • Open Shortest Path First (OSPF), which is famous for being used in medium to large-sized networks, is based on the link-state algorithm.
  • Interior Gateway Routing Protocol (IGRP), which is Cisco developed proprietary protocol, is based on the distance-vector protocol algorithm.
  • Enhanced Interior Gateway Routing Protocol (EIGRP), which is also based on the Distance-vector algorithm.
  • Intermediate System-to-Intermediate System (IS-IS), which is a link-state routing protocol.

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