client peers need not be fully meshed. The clients in the cluster do not communicate with iBGP speakers
outside their cluster.
Figure 8: More Complex BGP Route Reflector Model
Figure 8: More Complex BGP Route Reflector Model, on page 49 illustrates a more complex route reflector
scheme. Router A is the route reflector in a cluster with routers B, C, and D. Routers E, F, and G are fully
meshed, nonclient routers.
When the route reflector receives an advertised route, depending on the neighbor, it takes the following actions:
•
A route from an external BGP speaker is advertised to all clients and nonclient peers.
•
A route from a nonclient peer is advertised to all clients.
•
A route from a client is advertised to all clients and nonclient peers. Hence, the clients need not be fully
meshed.
Along with route reflector-aware BGP speakers, it is possible to have BGP speakers that do not understand
the concept of route reflectors. They can be members of either client or nonclient groups, allowing an easy
and gradual migration from the old BGP model to the route reflector model. Initially, you could create a single
cluster with a route reflector and a few clients. All other iBGP speakers could be nonclient peers to the route
reflector and then more clusters could be created gradually.
An autonomous system can have multiple route reflectors. A route reflector treats other route reflectors just
like other iBGP speakers. A route reflector can be configured to have other route reflectors in a client group
or nonclient group. In a simple configuration, the backbone could be divided into many clusters. Each route
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
OL-30423-03 49
Implementing BGP
BGP Route Reflectors
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