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You can apply a community list or an extended community list to a routing policy for route
control. For more information, see "BGP path attributes."
• Route reflect
or
IBGP peers must be fully meshed to maintain connectivity. If n routers exist in an AS, the
number of IBGP connections is n(n-1)/2. If a large number of IBGP peers exist, large amounts
of network and CPU resources are consumed to maintain sessions.
Using route reflectors can solve this issue. In an AS, a router acts as a route reflector, and other
routers act as clients connecting to the route reflector. The route reflector forwards routing
information received from a client to other clients. In this way, all clients can receive routing
information from one another without establishing BGP sessions.
A router that is neither a route reflector nor a client is a non-client, which, as shown in Figure 54,
must e
stablish BGP sessions to the route reflector and other non-clients.
Figure 54 Network diagram for a route reflector
The route reflector and clients form a cluster. Typically a cluster has one route reflector. The ID
of the route reflector is the Cluster_ID. You can configure more than one route reflector in a
cluster to improve availability, as shown in Figure 55. T
he configured route reflectors must have
the same Cluster_ID to avoid routing loops.
Figure 55 Network diagram for route reflectors
When the BGP routers in an AS are fully meshed, route reflection is unnecessary because it
consumes more bandwidth resources. You can use commands to disable route reflection
instead of modifying network configuration or changing network topology.
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