Border Gateway Protocol (BGP)

Border Gateway Protocol (BGP) version 4 is the latest version of BGP and is defined in RFC 1771. BGP is an exterior routing protocol used to connect between autonomous systems.

Exterior Routing Protocols

The best way to categorize routing protocols is to decide if they are interior or exterior. An interior routing protocol, such as RIP or IGRP, is used to exchange routing information within an autonomous system. An exterior routing protocol, such as BGP, is used to connect between autonomous systems. BGP is the most widely used exterior routing protocol; it is used by almost anyone who wants to communicate on the Internet.

The main goal of BGP is to provide an interdomain routing system that will guarantee a loop-free exchange or routing information between autonomous systems. BGP was designed to allow ISPs to communicate and exchange packets.

BGP is not always the best protocol to use in all networks. If any of the following describes your network, you might want to use another protocol:

• If your network only has a single connection to the internet or another AS

• Limited memory or processor power on BGP routers to handle constant updates

• Very limited understanding of route filtering and BGP path selection process

• Very little bandwidth between autonomous systems

If your network is limited to the above list, you may want to use static routes to connect to another autonomous system.