Tag :: BGP-LS

The BGP-LS extension allows IGPs (OSPF/IS-IS) link state database information to be injected into BGP. This is typically used in deployments where some external component, (like a controller or Path Computation Engine) can do centralized path computations by learning the entire IGP topology through BGP-LS. The controller can then communicate the computed paths based on the BGP-LS updates to the head end device in the network. The mechanism used by the controller to communicate the computed TE paths is outside the scope of this document. Using BGP-LS instead of an IGP peering with the controller to distribute IGP link state information has the following advantages.

Normally, an ingress router has no control over an autonomous system border router’s (ASBR) selection of inter-AS links. In the example below, Peer 2 and Peer 3 both advertise reachability to some remote network to ASBR 1 (e.g. service route 172.16.1.0/24). ASBR 1 would then use normal bestpath selection rules to select a preferred egress path (for traffic flowing to that service route). However, this means that the ingress router has no control over which egress path is chosen.