Cabletron Systems CoreWatch, User Manual

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CoreWatch User’s Manual 269
Chapter 15
Configuring BGP
on the SSR
BGP Overview
The Border Gateway Protocol (BGP) is an exterior gateway protocol that allows IP routers
to exchange network connectivity 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 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 are not designed to handle multi-AS 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:
An Autonomous System (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 security is a concern and 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.