Exterior Gateway Protocol

Key Points

• Operates between routing domains
• Supports inter-domain route exchange
• Historically associated with internet routing evolution
• In modern practice BGP is the dominant EGP
• Governs inter-domain routing behavior

Definition

Exterior Gateway Protocol is a routing protocol class used to exchange reachability information between separate autonomous systems. It governs inter-domain routing behavior.

Concept

Exterior Gateway Protocol is a networking term used for protocols that exchange routes across administrative domain boundaries. It exists to support inter-domain connectivity and policy handling. It is used in internet routing history and in the conceptual classification of external routing. In modern networks, BGP is the primary protocol associated with this class.

Explainer

Exterior Gateway Protocol is a class of routing protocols used to exchange reachability information between separate autonomous systems or routing domains. It works by moving routing data across administrative boundaries so external networks can learn how to reach prefixes beyond their own domain. It is used primarily as a conceptual class in internet routing, where BGP is the dominant operational implementation. Constraints include policy complexity, trust boundaries, filtering requirements, and the need to manage inter-domain reachability carefully. Failure modes include route leaks, hijacks, incorrect policy propagation, and misclassification of external reachability. Tradeoffs involve broad interconnection versus greater policy and security complexity, and flexible external routing versus reduced simplicity. Exterior Gateway Protocol matters because it defines the routing class used at the edges of autonomous systems. Cross-industry relevance is strongest in internet routing, telecom, cloud interconnects, and large network design.