Exterior Gateway Protocol

Exterior gateway protocol (EGP) supports redundancies in the network paths by implementing routing policies supporting transfer of data through different Internet service providers (ISPs) simultaneously. The EGP class of protocols with modifications and newer versions continued to be used for the communication among autonomous systems (ASs). It was sheer chance that the first protocol developed for the EGP class of routing was also named the EGP, which became obsolete with time and was replaced with another protocol named the Border Gateway Protocol (BGP). BGP was designed for decentralized routing and came as a replacement for EGP to support transition from Advanced Research Projects Agency Network (ARPANET) to National Science Foundation Network (NSFNet). To participate in BGP routing, each AS should have at least one router running BGP. An AS may also have more than one router running BGP, and these routers may even communicate within the AS using BGP.