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The route reflector(RR), a new addition to BGP, offers an alternative to the logical full-mesh requirement of IBGP. A RR acts as a focal point for IBGP sessions. The Purpose of the RR is concentration. Multiple BGP routers can peer with a central point, the RR - acting as a route reflector server - rather than peer with every other router in a full mesh. All the other IBGP routers become route reflector clients.
This approach, similar to OSPF's DR/BDR feature, provides large ISPs with added IBGP scalability. A network requiring more than 100 statements just to define the remote-as of each peer quickly becomes a headache to administer. The RR can offer a viable solution for the larger networks administered by ISPs.
Router Reflector Clients vs Route Reflector Speakers
IBGP peers of a route reflector fall under two categories: clients and nonclients. A route reflector and its clients form a cluster.
All IBGP peers of the route reflector that are not part of the cluster are nonclients and must be fully meshed to all other IBGP routers.
Configuring route reflector clients to peer with IBGP speakers outside their cluster can cause routing loops.
Rules
RR servers propagate routes inside the AS based on the following rules:
If a route is received from nonclient peer, reflect to clients only.
If a route is received from a client peer, reflect to all nonclient peers and also to client peers, except the originator of the route.
If a route is received from an EBGP peer, reflect to all client and nonclient peers.
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