What is Exterior Gateway Protocol (EGP)?

Exterior Gateway Protocol (EGP) is a defunct routing protocol used in autonomous systems to exchange data between surrounding gateway sites. Border Gateway Protocol supplanted EGP, widely utilized by research institutes, universities, government agencies, and commercial companies (BGP).

EGP is built on poll instructions to request update answers and periodic message exchange polling for neighbor reachability. RFC 904, which was issued in April of 1984, details EGP.

External Gateway Protocol is another name for the Exterior Gateway Protocol.

Research institutes widely used EGP, universities, government agencies, and business enterprises to interconnect autonomous computers in the early days of the Internet. Still, it was eventually supplanted by Border Gateway Protocol (BGP).

Working of EGP

Internet hosts used EGP for data table routing exchanges before BGP was introduced. Available routers, addresses, cost metrics, and each optimal route selection path are all listed in the EGP routing table. The EGP model is designed to automate limited events, actions, and transitions.

The EGP mechanisms are as follows −

  • Obtain neighbors

  • Keep an eye on your neighbors.

  • Data is exchanged via update messages.

EGP allows neighboring routers in different domains to share information, whereas Interior Gateway Protocols are utilized within a domain.

The Advanced Research Projects Agency Network's main routers use EGP to convey reachability to and from them (ARPANET). Individual source nodes in separate Internet administrative domains known as autonomous systems (ASs) sent information to the core routers, then relayed down via the backbone until it reached the destination network within another AS.

Unlike most other protocols, EGP is solely concerned with network reachability and uses no metrics to choose the optimum way.

Pros and Cons of EGP

EGP was the first exterior gateway protocol to gain general popularity on the Internet, and it has several pros and disadvantages. The routing table remains stable with minimum changes because the protocol does not react to faults within the Autonomous system.

EGP is a simple reachability protocol limited to tree-like topologies and does not support multipath networking settings, making it less efficient than newer distance-vector and path-vector protocols.

As this routing system is designed to be centrally managed, it has limited scalability, a significant disadvantage in today's rapidly increasing Internet. The commercialized Internet is not under the supervision of any central authority. The Internet is made up of several interconnected networks. In a distributed architecture, autonomous systems require internal and external routing protocols to make intelligent routing decisions. As a result, EGP has fallen out of favor.