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Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RC-36
Cisco IOS XR Routing Configuration Guide
OL-14356-01
The internal peers of the route reflector are divided into two groups: client peers and all other routers in
the autonomous system (nonclient peers). A route reflector reflects routes between these two groups.
The route reflector and its client peers form a cluster. The nonclient peers must be fully meshed with
each other, but the 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 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.
S4218
External
BGP
speaker
Routes
advertised
Route reflector
Cluster
Client Client Client
Nonclient
Nonclient
Nonclient
Partially meshed
autonomous system
Router A
Router B
Router G
Router F
Router E
Router C Router D
Router A