The Border Gateway Protocol (BGP) is a path vector routing protocol that is based on a method of network prefixes that traverse through a series of dedicated BGP router groups that effectively hide data, table lookup, and other memory-intensive processing from other routers on the networks. This special BGP router group is known simply as an autonomous system (AS). It is important to understand the concept of an AS and all the attributes associated with this powerful group so you can understand the special properties that BGP offers.

BGP is an inter-AS routing protocol, meaning that it is predicated on information learned by prefix traversal through multiple ASs, using the External Gateway Protocol (EGP) interdomain routing method.

The primary role of BGP is to make available to a given AS and all the devices on it information about all other ASs and devices to which the AS can successfully send data.