BGP: Difference between revisions

*Any route received from an iBGP neighbor must not be advertised to any other iBGP neighbor.

*This requires all iBGP routers be connected in logical full mesh topology, which is not scalable.

Two solution possible:

BGP confederations

Route reflectors

*A route reflector is BGP router that is allowed to break the iBGP loop avoidance rule.

*Route reflectors can advertise updates received from an iBGP peer to another iBGP peer.

*This allow for building iBGP networks that scale easily.

*IBGP routers are divided into:

Route Reflectors

Route Reflector Clients

Non-Client Peers

*Routes received from:

Route-Reflector-client is reflected to other clients and non-client neighbors

Non-client neighbors are reflected to Route-Reflector-client neighbors only

*Sets the '''Originator-ID''' attribute in the reflected update if it is not already set.

*Adds the Cluster-ID to the Cluster-list attribute in the reflected update.

*RR reflects routes considered as best routes only.

*If more than one update is received for the same destination only the BGP best route is reflected.

*RR is not allowed to change any attributes of the reflected routes including the next-hop attribute.

*Loop Prevention:

If a router received an iBGP route with the Originator-ID attribute set to its own router-id, the route is discarded.

If a route reflector receives a route with a cluster-list attribute containing its cluster-id, the route is discarded.

*Config:

;RR1 router:

router bgp 100

neighbor 172.16.1.2 remote-as 100

neighbor 172.16.1.2 route-reflector-client

neighbor 172.16.1.2 description Client1

;Client1 router:

router bgp 100

neighbor 172.16.1.1 remote-as 100

neighbor 172.16.1.1 description RR1

network 11.1.1.1 mask 255.255.255.255 --> Route to be reflected