TOI Author :: Denis Evoy

The FIB contains mappings between a prefix (identifying a destination network) and its associated Forwarding Equivalence Class (FEC), with the FEC containing one or more resolved Vias defining how traffic should be forwarded towards that destination network.

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.

In a Service Provider network, a Provider Edge (PE) device learns VPN paths from remote PEs and uses the Route Target