The Exterior Gateway Protocol (EGP) is a protocol used for distributing routing information to routers that connect different autonomous systems (AS). An autonomous system is a network or group of networks under the control of a single administrative entity that presents a common routing policy to the outside world.
Main features of EGP
- Routing Information Distribution: EGP is designed to allow the exchange of routing information between routers located at the boundaries of different autonomous systems. This exchange is crucial to ensure that data can find the optimal path when it needs to be transmitted from one network to another across various AS.
- Connectivity between Autonomous Systems: One of the main functions of EGP is to establish and maintain connectivity between various autonomous systems. This is done by announcing the routes that an AS can reach to other AS, thus allowing the construction of global routing tables.
- Routing Hierarchy: EGP operates on a hierarchical basis, where the main routers (often called “gateways”) of each AS exchange information with their peers in other AS. This helps maintain a scalable and organized view of the global network topology.
- Reliability and Scalability: Although EGP is no longer the most widely used exterior routing protocol (largely replaced by the Border Gateway Protocol, BGP), it was fundamental in the development of early large-scale networks. Its design helped establish key principles for the scalability and reliability of routing between autonomous systems.
Limitations of EGP
Despite the historical importance of EGP, it has some significant limitations:
- Does not support dynamic routing: EGP was designed in an era when networks were relatively static. It is not suitable for handling the dynamism of modern networks where routes can change frequently.
- Limited scale: With the expansion of the Internet, EGP showed limitations in terms of scalability. It was not designed to handle the vast amount of routes present in the current global Internet.
- Replaced by BGP: Due to its limitations, EGP has been largely replaced by the Border Gateway Protocol (BGP), which offers better dynamic routing capabilities and scalability.
Conclusion
The Exterior Gateway Protocol (EGP) played a crucial role in the early years of computer network development, enabling communication between different autonomous systems and contributing to the formation of the foundations for global-scale routing. Although superseded by BGP, EGP remains an important historical reference point in the development of routing protocols.