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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.
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