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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)

BGP General Operation and Messaging 1 BGP Message Generation and Transport, and General Message Format

The previous section described the concepts and general operation of the Border Gateway Protocol (BGP). To get a better understanding of exactly how BGP works, it is helpful to take a deeper look at its four different message types and how they are used. As we do this, we can examine the fields in each message type, to help us comprehend not just the way that messaging is accomplished, but the way that routing data is actually communicated.

In this section I provide a comprehensive description of the communication that takes place between BGP speakers by providing details on BGP message types, how they are used, and the data elements they contain. I begin with a description of common attributes of BGP message generation and transport, and the general format used for all BGP messages. I then provide a detailed description of each of the four BGP message types: Open, Update, Keepalive and Notification messages.

BGP General Operation and Messaging 1 BGP Message Generation and Transport, and General Message Format