9.1 Route Reflectors
9.1.1 Route reflector basics
Autonomous systems (ASs) consisting of hundreds of routing nodes can pose a serious routing management problem. Since IBGP speakers must be configured as a full mesh, it's easy for the mesh of routers to grow beyond the provider's control.

To relax the full mesh requirement of IBGP, and provide easier scaling in large-scale IBGP environments, Router Reflectors were introduced into BGP. Route reflectors (RRs) are essentially concentration routers, which act as a focal point for internal BGP sessions. Multiple BGP routers can peer with a central point (the RR), rather peering in a full mesh.

Route reflectors are recommended only for ASs with a large internal BGP mesh, on the order of more than 100 sessions per router. The RR concept introduces processing overhead on the concentration router and, if configured incorrectly, can cause routing loops and routing instability. As a result, RRs are not recommended for every topology. If it can be tolerated, a full mesh is the better solution.