Need for Route reflectors

Posted: February 12, 2016 in BGP

Simple reason is AS number is used for loop avoidance.

When routes are exchanged between the routers which belongs to the same As , AS_PATH list is not modified (routing update within AS).
So this situation can create routing loop and to avoid this there is BGP split horizon rule

Due to split horizon rule we need to create full mesh of IBGP sessions between the routers within same AS to avoid routing black hole. This full mesh condition is really bad consider example if there is a stub router with single neighbor with single uplink
(If there are N router in the As then we need to create (N*(N-1))/2 sessions)

To avoid such large number of BGP session and conserve useful resources we are using Route reflectors which bypasses Split horizon rule


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