MPLS L3VPN Inter-AS Options

When implementing MPLS L3VPNs, there are cases where you may have some remote customer sites in locations where the same service provider cannot serve both sites. The result is that the backbone network that interconnects the sites, has more than one BGP AS, thus some sort of mechanism must be established to allow inter-AS communication to take place without disrupting the VPN.

There are three ways to do this, and they are called Options A, B and C:

  • Option A: Back-to-Back VRF
  • Option B: MP-eBGP for VPNv4
  • Option C: Multihop MP-eBGP between RR + Labels