BGP Overview
�¡ BGP stands for Border Gateway Protocol.
�¡ BGP uses the concept of autonomous systems. An autonomous system
is a group of networks under a common administration.
�¡ Autonomous systems run Interior Gateway Protocols (IGP) within the
system. They run an Exterior Gateway Protocol (EGP) between them.
�¡ BGP version 4 is the only EGP currently in use.
�¡ BGP neighbors are called peers and must be statically configured.
�¡ BGP uses TCP port 179.
�¡ BGP is a path-vector protocol. Its route to a network consists of a list
of autonomous systems on the path to that network.
�¡ BGP�fs loop prevention mechanism is autonomous system number.
When an update about a network leaves an autonomous system, that
autonomous system�fs number is prepended to the list of autonomous
systems that have handled that update. When an autonomous system
receives an update, it examines the autonomous system list. If it finds
its own autonomous system number in that list, the update is
discarded.
In Figure 6-1, BGP routers in AS 65100 see network 10.1.1.0 as having an
autonomous system path of 65200 65300 65400.