BGP Route Reflectors

RR — Route Reflector

Cluster

A route reflector and its clients.

Cluster List

The sequence of Cluster_IDs through which the route has passed. If a router sees its own Router_ID a loop has occurred.

Originator_ID

• The router that introduced the route into the AS.
• Used to prevent loops between clients.

Route Reflection Rules

A RR will not change any attributes of a route.

1. If a route is learned from a non-client iBGP peer, reflect to clients
2. If a route is learned from a client, reflect to everyone
3. If a route is learned from a eBGP peer, reflect to everyone

Notes

• Route reflectors can be clients of each other. This causes extra overhead.
• If multiple route reflectors server the same cluster they should have the same Cluster_ID.

BGP Route Reflectors Loop Prevention

• If a BGP router that receives a route from an iBGP neighbor in the incoming update detects the presence of its own Router-ID in the Originator-ID attribute it will reject the update.
• If a BGP router that receives a route from an iBGP neighbor is configured to operate as a route reflector and in the incoming update detects the presence of its own Cluster-ID in the Cluster-list attribute it will reject the update.

Only the route reflector is aware of the reflecting. The clients are dumb

If you configure route reflectors as a cluster you must manually configure the cluster_ID