CANOGA PERKINS 9171 Configuration Guide - Manual (Page 112)

CanogaOS Configuration Guide
18-1
18 Configuring BGP
18.1 Overview
The Border Gateway Protocol (BGP) is an inter-Autonomous System routing protocol.
The primary function of a BGP speaking system is to exchange network reachability
information with other BGP systems. This network reachability information includes
information on the list of Autonomous Systems (ASes) that reachability information
traverses. This information is sufficient for constructing a graph of AS connectivity for this
reachability, from which routing loops may be pruned and, at the AS level, some policy
decisions may be enforced.
BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing
(CIDR) [RFC1518, RFC1519]. These mechanisms include support for advertising a set
of destinations as an IP prefix and eliminating the concept of network "class" within BGP.
BGP-4 also introduces mechanisms that allow aggregation of routes, including
aggregation of AS paths.
Routing information exchanged via BGP supports only the destination-based forwarding
paradigm, which assumes that a router forwards a packet based solely on the
destination address carried in the IP header of the packet. This, in turn, reflects the set
of policy decisions that can (and cannot) be enforced using BGP. BGP can support
only those policies conforming to the destination-based forwarding paradigm.
For more BGP information please reference [RFC 1771, RFC 4271].
18.2 Basic Topology (EBGP)
Figure 18-1: EBGP
AS200 AS100
BGP
Router A Router B
Eth-0-13 Eth-0-1 Eth-0-1
1.1.1.0/24 2.2.2.0/24
AS200
AS100
RIP
OSPF
Router A Router B
EBGP