On an IP/MPLS network transmitting VPN services, PEs establish a multi-segment MPLS tunnel between each other. Therefore VPN services are sent to multiple PEs. In this case, VPN service provision on PEs becomes complex, and the VPN service scalability decreases. As PEs establish BGP peer relationships, a routing policy can be used to assign MPLS labels for BGP routes so that an E2E BGP tunnel can be established. The BGP tunnel consists of a primary BGP LSP and a backup BGP LSP. VPN services can travel along the E2E BGP tunnel, which simplifies service provision and improves VPN service scalability.
To rapidly detect faults in an E2E BGP tunnel, BFD for BGP tunnel is used. BFD for BGP tunnel establishes a dynamic BFD session, also called a BGP BFD session, which is bound to both the primary and backup BGP LSPs. If both BGP LSPs fail, the BGP BFD session detects the faults and triggers VPN FRR switching.