Inter-AS VLL

The MPLS VPN solution is widely used. However, single networks are often spread over different geological locations and are connected to different ISP networks. Operators who manage different metropolitan area networks (MANs) or backbone networks often encounter inter-AS issues and a different interworking model than the MPLS VPN architecture is required.

The inter-AS VLL is an interworking model that features a VPN that spans multiple ASs. In inter-AS networking, the devices located at the edge of ASs are AS boundary routers (ASBRs).

Inter-AS VLL implementation depends on the VLL mode being used:

The CCC mode uses a single label, so an inter-AS VLL can be set up using static LSPs between ASBRs.
The SVC, Martini, and Kompella modes can implement inter-AS VLL Option A, virtual routing and forwarding (VRF)-to-VRF.

In inter-AS Option A, a sub-interface must be reserved for each inter-AS VC on an ASBR. The ASBRs do not require MPLS or other additional inter-AS configurations. With Option A, the ASBRs of the two ASs are directly connected and function as PE devices in their respective ASs. The two ASBRs regard each other as CE devices. Figure 1 shows an inter-AS option A network.

Figure 1 Inter-AS Option A

For details about the inter-AS VPN, see Inter-AS VPN in the BGP/MPLS IP VPN Configuration.