Interior Gateway Protocol Definition

An interior gateway protocol (IGP) is a routing protocol that is used to exchange routing information among routers within an autonomous system, such as a enterprise's LAN (local area network). IGPs typically support limited geographical areas.

A router is an electronic device and/or software that connects at least two networks and forwards packets among them according to the information in the packet headers and routing tables. A routing protocol is a set of rules used by routers to determine the most appropriate paths into which they should forward packets towards their intended destinations.

An autonomous system, also sometimes called a routing domain, is a network, or group of networks, that is controlled by a common administrator (or group of administrators) on behalf of a business, university, ISP (Internet service provider) or other organization and that presents a common routing policy to the Internet.

This contrasts with an exterior gateway protocol (EGP), which is a routing protocol that is used to exchange routing information between two hosts in a network of autonomous systems. An EGP is typically used between hosts on the Internet to share routing table information.

The most commonly used IGPs are RIP (routing information protocol), OSPF (open shortest path first) and IS-IS (intermediate system to intermediate system). An example of an EGP is BGP (border gateway protocol).

Created November 19, 2005.
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