Date Added: Apr 2010
The role of BGP inside an AS is to disseminate the routes learned from external peers to all routers of the AS. A straightforward, but not scalable, solution, is to resort to a full-mesh of iBGP sessions between the routers of the domain. Achieving scalability in the number of iBGP sessions is possible by using Route Reflectors (RR). Relying on a sparse iBGP graph using RRs, however, has a negative impact on routers' ability to quickly switch to an alternate route in case of a failure. This stems from the fact that routers do not often know routes towards distinct next-hops, for any given prefix.