3com S7906E Manuel De Montage

1-13

Besides using well-known community attributes, you can define extended community attributes by

using a community list to define a routing policy.

Route reflector

iBGP peers should be fully meshed to maintain connectivity. If there are n routers in an AS, the number

of iBGP connections is n (n-1)/2, and therefore large amounts of network and CPU resources will be

consumed.

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 between

clients, and thus BGP sessions between clients need not be established.

A router that is neither a route reflector nor a client is a non-client, which has to establish BGP sessions

to the route reflector and other non-clients, as shown below.

Figure 1-13 Network diagram for route reflector

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 1-14 Network diagram for route reflectors

Route reflector1

Route reflector2

Client

IBGP

Cluster

IBGP

AS 65000

When the BGP routers in an AS are fully meshed, route reflection is unnecessary because it consumes

more bandwidth resources. You can use related commands to disable route reflection in this case.