
Configuring IP Services
6-2 114065 Rev. A
BGP Concepts and Terminology
BGP is an exterior gateway protocol designed to exchange network reachability
information with other BGP systems in other autonomous systems.
BGP exchanges routing information in the form of routing updates. An update
includes a network number, a list of autonomous systems that the routing
information has passed through (the AS path), and a list of other path attributes.
Figure 6-1 shows two autonomous systems: AS1 and AS2. Networks within AS1
and AS2 are connected by routers running an interior gateway protocol -- in this
case, OSPF. AS1 and AS2 are connected by routers that run an exterior gateway
protocol -- BGP -- in addition to OSPF.
Figure 6-1. BGP Connecting Autonomous Systems Running OSPF
A BGP router employs a BGP speaker, which is an entity within the router that
transmits and receives BGP messages and acts upon them. A BGP speaker forms
a neighbor relationship with another BGP speaker by establishing a peer-to-peer
session over a common inter-AS network.
OSPF/
BGP
OSPF/
BGP
OSPF
OSPF
OSPF
BGP
Connection
AS1
AS2
OSPF
OSPF
IP00025A
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