The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Exterior Gateway/Routing Protocols (BGP and EGP)                      9  TCP/IP Border Gateway Protocol (BGP/BGP-4)                           9  BGP Fundamentals and General Operation

BGP Fundamentals and General Operation 1 2 3 4 BGP Topology, Speakers, Border Routers and Neighbor Relationships (Internal and External Peers)

As I describe briefly in the overview of routing protocol concepts, the way that routers were connected in the early Internet was quite different than it is today. The early Internet had a set of centralized routers functioning like a “core” autonomous system. These routers used the Gateway-to-Gateway Protocol for communication between them within the AS, and the aptly-named Exterior Gateway Protocol (EGP) to talk to routers outside the core.

When the Internet grew and moved to autonomous system (AS) architecture, EGP was still able to function as the exterior routing protocol for the Internet. However, as the number of autonomous systems in an internetwork grows, the importance of communication between them grows as well. EGP was functional but had several weaknesses that became more problematic as the Internet grew in size. It was necessary to define a new exterior routing protocol that would provide enhanced capabilities for use on the growing Internet.

In June 1989, the first version of this new routing protocol was formalized, with the publishing of RFC 1105, A Border Gateway Protocol (BGP). This initial version of the BGP standard defined most of the concepts behind the protocol, as well as key fundamentals such as messaging, message formats and how devices operate in general terms. It established BGP as the Internet's exterior routing protocol of the future.

BGP Fundamentals and General Operation 1 2 3 4 BGP Topology, Speakers, Border Routers and Neighbor Relationships (Internal and External Peers)