Cabletron Systems 9032578-05 manual Chapter BGP Configuration Guide, BGP Overview

Chapter 12

BGP Configuration

Guide

BGP Overview

The Border Gateway Protocol (BGP) is an exterior gateway protocol that allows IP routers to exchange network reachability information. BGP became an internet standard in 1989 (RFC 1105) and the current version, BGP-4, was published in 1994 (RFC 1771). BGP is typically run between Internet Service Providers. It is also frequently used by multi- homed ISP customers, as well as in large commercial networks.

Autonomous systems that wish to connect their networks together must agree on a method of exchanging routing information. Interior gateway protocols such as RIP and OSPF may be inadequate for this task since they were not designed to handle multi-AS, policy, and security issues. Similarly, using static routes may not be the best choice for exchanging AS-AS routing information because there may be a large number of routes, or the routes may change often.

Note: This chapter uses the term Autonomous System (AS) throughout. An AS is defined as a set of routers under a central technical administration that has a coherent interior routing plan and accurately portrays to other ASs what routing destinations are reachable by way of it.

In an environment where using static routes is not feasible, BGP is often the best choice for an AS-AS routing protocol. BGP prevents the introduction of routing loops created by multi-homed and meshed AS topologies. BGP also provides the ability to create and enforce policies at the AS level, such as selectively determining which AS routes are to be accepted or what routes are to be advertised to BGP peers.

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