3Com MSR 50 Series Configuration Manual page 837

Besides using the well-known community attribute, you can define the extended
community attribute using a community list to help define a routing policy.
Route reflector
IBGP peers should be fully meshed to maintain connectivity. Suppose there are n
routers in an AS, the number of IBGP connections is n(n-1)/2. If there are many
IBGP peers, most network and CPU resources will be consumed.
Using route reflectors can solve the 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 (reflects) routing information between clients. BGP
connections between clients need not be established.
The router neither a route reflector nor a client is a non-client, which has to
establish connections to the route reflector and all non-clients, as shown below.
Figure 243 Network diagram for route reflector
IBGP
Client
Cluster
Client
The route reflector and clients form a cluster. In some cases, you can configure
more than one route reflector in a cluster to improve network reliability and
prevent single point failure, as shown in the following figure. The configured route
reflectors must have the same Cluster_ID to avoid routing loops.
Figure 244 Network diagram for route reflectors
Route
Reflector1
Cluster
IBGP
Client
Route
Reflector
IBGP
IBGP
IBGP
Client
Route
Reflector2
IBGP
IBGP
IBGP
Client
Client
BGP Overview
Non-Client
IBGP
IBGP
Non-Client
AS 65000
AS 65000
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