Route reflection

By design, IBGP peers do not advertise iBGP routes to other iBGP peers. In order for iBGP peers to learn all the routes within the autonomous system as well as all the external routes, the iBGP peers would have to be fully meshed. This means for n iBGP peers there would have to be n*(n-1)/2 iBGP sessions. In a large autonomous system network configuration would become an issue.

Route Reflection is one of the alternate solutions to alleviate this problem. In the BGP network, one of the iBGP speakers is designated as the route reflector. The route reflector advertises the routes it learns to other iBGP peers.

In a route reflector configuration the other iBGP peers are classified as clientpeers and non-client peers.

The action taken by the route reflector (after determining the best route) depends on whether the best route was received from a client peer or a non-client peer. If the route was received from a client peer, the route reflector will reflect that route to all the client peers and non-client peers.

If the route was received from a non-client peer, then the route is advertised to all its configured clients.

Route reflection introduces two new discretionary attributes: Originator ID and Cluster List, which are used in determining the best path as defined in BGP route selection.

In an Autonomous System more than one route reflector can be configured.