Exterior Gateway Protocol Definition

An exterior gateway protocol (EGP) is a routing protocol that is used to exchange routing information between routers on a network of autonomous systems.

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 table is a database in a router that stores and updates the locations (addresses) of other routers and the most efficient routes to them in order to direct routing. Routing is the process of moving packets across a network from one router to a another. 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.

The first EGP, which was also called EGP (and which should not be confused with the generic term EGP), was originally developed in 1982 by Eric C. Rosen and became the primary routing protocol for the Internet. It was a relatively simple protocol that did not use metrics and could not make intelligent routing decisions. The method for updating the routing tables was cumbersome, and it could not detect routing loops in complex environments.

Thus, it was gradually phased out in favor of BGP (border gateway protocol), which makes intelligent decisions and has proved to be highly scalable. Defined in 1989, BGP is now the dominant EGP for the Internet.

Created November 20, 2005.
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