Optimized Option C and Basic FEC Generation for Inter-AS

Not all leaf nodes can support label route or recursive opaque, so recursive opaque functionality can be transferred from the leaf to the ASBR, as shown in Figure 1.

Figure 1. Optimized Option C — Leaf Router Not Responsible for Recursive FEC

In Figure 1, the root advertises its unicast routes to ASBR-3 using IGP, and the ASBR-3 advertises these routes to ASBR-1 using label-BGP. ASBR-1 can redistribute these routes to IGP with next-hop ASBR-1. The leaf resolves the actual root 10.0.0.14 using IGP and creates a type 1 opaque value <Root 10.0.0.14, Opaque <8193>> to ASBR-1. In addition, all P routers in AS 2 know how to resolve the actual root because of BGP-to-IGP redistribution within AS 2.

ASBR-1 attempts to resolve the 10.0.0.14 actual route via BGP, and creates a recursive type 7 opaque value <Root 10.0.0.2, Opaque <10.0.0.14, 8193>>.