187
•
Peer group
You can organize BGP peers with the same attributes into a group to simplify their configurations.
When a peer joins the peer group, the peer obtains the same configuration as the peer group. If
the configuration of the peer group is changed, the configuration of group members is changed.
•
Community
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 reflector
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 53
,
must establish BGP sessions to the route reflector and other non-clients.
Figure 53
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 54
. The configured route reflectors must have the same
Cluster_ID to avoid routing loops.
