Overview

Border Gateway Protocol (BGP) is an exterior gateway protocol (EGP). It is called internal BGP (IBGP) when it runs within an AS and called external BGP (EBGP) when it runs between ASs.

The current version in use is BGP-4 (RFC 4271).

BGP has the following characteristics:

• Focuses on route control and selection rather than route discovery and calculation.

• Uses TCP to enhance reliability.

• Measures the distance of a route by using a list of ASs that the route must travel through to reach the destination. BGP is also called a path-vector protocol.

• Supports CIDR.

• Reduces bandwidth consumption by advertising only incremental updates. BGP is very suitable to advertise large numbers of routes on the Internet.

• Eliminates routing loops by adding AS path information to BGP route updates.

• Uses policies to implement flexible route filtering and selection.

• Has good scalability.