L3VPN: Inter-AS: ASBR Option B

For the ASBR Option-B interprovider VPN solution, the customer requires VPN services for different sites, yet the same service provider is not available for all of those sites. With option B, the ASBRs keep all VPN-IPv4 routes in the routing information base (RIB), and the labels associated with the prefixes are kept in the forwarding information base (FIB). Because the RIB and FIB tables can take too much of the respective allocated memory, this solution is not very scalable for an interprovider VPN. If a transit service provider is used between service provider 1 and service provider 2, the transit service provider also has to keep all VPN-IPv4 routes in the RIB and the corresponding labels in the FIB. The ASBRs at the transit service provider have the same functionality as ASBRs at service provider 1 or service provider 2 in this solution. The PE routers within each AS use multiprotocol internal BGP (MP-IBGP) to distribute labeled VPN-IPv4 routes to an ASBR or to a route reflector of which the ASBR is a client. The ASBR uses MP-EBGP to distribute the labeled VPN-IPv4 routes to its peer ASBR router in the neighboring AS. The peer ASBR then uses MP-IBGP to distribute labeled VPN-IPv4 routes to PE routers, or to a route reflector of which the PE routers are a client.