In a simple arrangement, all routers participating in BGP routing, within a single AS must be configured in a full mesh: each router must be configured as peer to every other router. This causes scaling problems since the number of required connections develops quadratically with the number of routers involved. To alleviate the problem, BGP implements two options: route reflectors.
Route reflectors (RR) are one method to get rid of the full-mesh of IBGP peers in your network.
BGP route reflector rules-
- An IBGP prefix received from an RR-client is advertised to all peers including the RR-client that advertised the prefix.
- Routes originated by the router and routes received from EBGP neighbors and selected as "best" routes are advertised to all internal and external BGP peers.
- A RR non-client advertising a prefix is advertised to all EBGP peers and IBGP RR-clients.
- Routes received from RR-clients and selected as "best" routes are advertised to all internal and external BGP peers.
- The RR adds the Originator ID to the routes received from its RR-clients.
- The RR appends its own Router ID to the Cluster List attribute.