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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.
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