The Exterior Gateway Protocol (EGP) is a routing protocol for the Internet originally specified in 1982 by Eric C. Rosen of Bolt, Beranek and Newman, and David L. Mills.
Exterior Gateway Protocol (EGP) is a protocol for exchanging routing information between two neighbor gateway hosts (each with its own router) in a network of autonomous systems. EGP is commonly used between hosts on the Internet to exchange routing table information. 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. Each router polls its neighbor at intervals between 120 and 480 seconds and the neighbor responds by sending its complete routing table. EGP-2 is the latest version of EGP.
EGP was developed by Bolt, Beranek and Newman in the early 1980s. It was first described in RFC 827 and formally specified in RFC 904 (1984). EGP is a simple reachability protocol, and, unlike modern distance-vector and path-vector protocols, it is limited to tree-like topologies.
During the early days of the Internet, EGP version 3 (EGP3) was used to interconnect autonomous systems. Currently, BGP version 4 is the accepted standard for Internet routing and has essentially replaced the more limited EGP3.