
Configuring BGP Services
117356-B Rev. 00
8-5
In Figure 8-2, AS 20 is the transit AS. It provides information about its internal
networks, as well as transit networks, to the remaining ASs. The IBGP
connections between BGP routers A, B, and C are necessary to provide consistent
information to the ASs.
IBGP Route Server
A BGP router configured for internal BGP (IBGP) must establish a peer-to-peer
session with every other IBGP speaker in the AS. In an AS with a large number of
IBGP speakers, this
full-mesh topology
can result in high bandwidth and
maintenance costs. For example, a full-mesh topology for an AS with 50 IBGP
speakers requires 1,225 internal peer-to-peer connections.
To avoid the high costs of a full-mesh topology to support IBGP speakers within
an AS, you can configure a router to function as an
IBGP route server
. IBGP
speakers that need to communicate with other BGP speakers in the AS establish a
single peer-to-peer session with the IBGP route server.
Figure 8-3
, for example, shows an AS with five IBGP speakers connected as
clients to an IBGP route server
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