EGP

networkingISP & telecom

Stands for: Exterior Gateway Protocol (the class, and the historical protocol)

Exterior Gateway Protocol - the class of protocols that route BETWEEN autonomous systems, and also the name of the specific 1980s protocol BGP replaced.

The term does double duty. As a class, EGP means inter-domain routing - today effectively synonymous with BGP, where policy, business relationships, and reachability matter more than shortest paths. As a proper noun, EGP (RFC 904, 1984) was the actual protocol of the early internet's tree-shaped topology; its inability to handle arbitrary meshes is precisely what BGP was invented to fix in 1989. Exam answers and old documents use both senses, so the disambiguation is worth carrying.

EGP names both a specific obsolete protocol and the class of protocols that route between autonomous systems, in contrast to interior protocols that route within one. Only the class sense is current, and BGP is its sole surviving member.

The distinction the class captures is about trust and policy rather than about algorithms. An interior protocol optimizes a path within one administration where everyone shares an objective; an exterior protocol carries routes between organizations with different commercial interests, so it must express policy and cannot simply prefer the shortest path. That is why BGP's decision process is a list of policy tie-breakers rather than a metric, and why understanding it means understanding business relationships.

Also known as: egp, exterior gateway protocol, inter-domain routing

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