Riverstone Networks WICT1-12 - Manual (Page 259)

Riverstone Networks RS Switch Router User Guide Release 8.0 16-1
16 BGP CONFIGURATION GUIDE
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.
16.1 THE RS BGP IMPLEMENTATION
The RS routing protocol implementation, ROSRD, is a modular software program that consists of core services,
a routing database, and protocol modules that support multiple routing protocols (RIP versions 1 and 2, OSPF
version 2, BGP version 4, and integrated IS-IS).
BGP can be configured with the RS command line interface (CLI). Since the RS IP routing code is compatible
with GateD 4.0.3 code, BGP can also be configured using a GateD configuration file (
gated.conf
).
Additionally, even if the RS is configured using the CLI, the
gated.conf
equivalent can be displayed by entering
the
ip-router show configuration-file
command at the RS Enable prompt. VLANs, interfaces, ACLs,
and many other RS configurable entities and functionality can only be configured using the RS CLI. Therefore, a
gated.conf
file is dependent upon some RS CLI configuration.