MPLS Configuration on Cisco IOS Software

Option 2: Inter-Provider VPNs Using ASBR-to-ASBR Approach

In the back-to-back VRF method, ASBRs use traditional IPv4 routing to integrate VPNs across two adjacent service provider networks. In the second method, the ASBRs use MP-eBGP to peer with each other to transport VPNv4 routes between autonomous systems. This is called the ASBR-to-ASBR approach, also known as MP-eBGP for VPNv4 exchange. This approach, therefore, alleviates the need to have per-VPN configuration on the ASBRs as seen in the back-to-back VRF method, and, thus, allows VPNv4 prefixes to be transported across multiple providers. However, to allow the transportation of VPNv4 prefixes, the link between the autonomous systems must support the exchange of MPLS packets because the ...