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Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RC-25
Cisco IOS XR Routing Configuration Guide
Figure 3 Three Fully Meshed iBGP Speakers
With route reflectors, all iBGP speakers need not be fully meshed because there is a method to pass
learned routes to neighbors. In this model, an iBGP peer is configured to be a route reflector responsible
for passing iBGP learned routes to a set of iBGP neighbors. In Figure 4, Router B is configured as a route
reflector. When the route reflector receives routes advertised from Router A, it advertises them to Router
C, and vice versa. This scheme eliminates the need for the iBGP session between routers A and C.
Figure 4 Simple BGP Model with a Route Reflector
The internal peers of the route reflector are divided into two groups: client peers and all other routers in
the autonomous system (nonclient peers). A route reflector reflects routes between these two groups.
The route reflector and its client peers form a cluster. The nonclient peers must be fully meshed with
each other, but the client peers need not be fully meshed. The clients in the cluster do not communicate
with iBGP speakers outside their cluster.
S4217
External
BGP
speaker
Routes
advertised
Fully meshed
autonomous
system
Routes
Routes
Routes not
advertised
Router A Router A
Router B
Router C
S4219
External
BGP
speaker
Partially meshed autonomous system
Route
reflector
Reflected
routes
Routes
Routes
Router A
Router B
Router A Router C