9.1 Route Reflectors
9.1.1 Route reflector basics
Autonomous systems consisting of hundreds of BGP routers can pose a serious management problem. If Internal BGP (IBGP) speakers are configured as a logical full mesh, BGP operation becomes extremely complex, as shown in the figure. Imagine a network in which more than 100 neighbor statements are required just to define the remote-as of each peer!

The route reflector (RR) is a recent addition to BGP (IOS 11.1) that offers an alternative to the logical full-mesh requirement of IBGP. An RR acts as a focal point for IBGP sessions. Multiple BGP routers can peer with a central point (the RR) rather than peer with every other router in a full mesh. This approach, similar to OSPF's DR/BDR feature, provides large ISPs with added IBGP scalability.

The use of route reflectors is recommended only for autonomous systems that support a large internal BGP mesh, approximately more than 100 sessions per router. This feature introduces processing overhead on the routers that act as route reflectors and, if configured incorrectly, can cause routing loops and instability. Therefore, if your network can tolerate it, a logical full mesh is usually the best solution.