3.2 Considerations for BGP Migrations

BGP is a database exchange protocol, featuring peer flow control and information flooding with loop avoidance. As a lesson learned from the past, the structure of the information that is distributed follows a variable encoding paradigm using TLV elements, which allows for extensibility. The information is qualified with an Address Family Identifier (AFI) and a Subsequent Address Family Identifier (SAFI) to identify the payload (for example, IPv4, IPv6, and NSAP), which makes BGP suitable as the transport protocol for a wide variety of applications.

For vanilla BGP, the data exchanged in this database is reachabilityinformation, tagged with a flexible list of attributes. New applications, such as VPLS and Route Target (RT) constraints, give different semantics to the exchanged data. Instead of reachability, VPLS exchanges membership information for autodiscovery and signaling. RT constraints exchange RT membership information. Hence, the data exchanged for these new applications is not reachability, but rather membership.