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Implementing BGP on Cisco IOS XR Software
Information About Implementing BGP on Cisco IOS XR Software
RC-26
Cisco IOS XR Routing Configuration Guide
Figure 5 More Complex BGP Route Reflector Model
Figure 5 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 reflector would be configured with other route reflectors as nonclient peers (thus, all route
reflectors are fully meshed). The clients are configured to maintain iBGP sessions with only the route
reflector in their cluster.
Usually, a cluster of clients has a single route reflector. In that case, the cluster is identified by the router
ID of the route reflector. To increase redundancy and avoid a single point of failure, a cluster might have
more than one route reflector. In this case, all route reflectors in the cluster must be configured with the
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