BGP4
Border Gateway Protocol version 4
BGP-4 is an example of a Path Vector routing protocol and is described as the needle and thread which binds the Internet together. BGP-4 allows Policy and Reachability information to be passed between Border Routers of adjacent AS (Autonomous Systems) and also between Border Routers of the same AS, thus supporting global routing of IP datagrams. BGP-4 Update messages are passed between routers. These messages contain lists of destination prefixes (routes) in the NLRI (network Layer Reachability Information) field, as well as Path Attributes associated with those routes.