How is an MPLS VPN established between the ME60 and the C3xxx in the Option-B solution?
The version of the ME60 is V100R005C02B01B; the version of the VRP is 5.30.
1. Usually, the IP addresses of interconnecting interfaces are used to establish VNPv4 EBGP neighbors. After that, a VPN is established, and the CE devices can communicate with each other.
In C3xxx implementations, when an ASBR device is to forward the VPN routing information learned from the peer ASBR device, the device can change or keep the next hop. If the next hop is not changed, the VPN route uses the peer device address as the next hop, and a /32 host routing entry is automatically added to the local routing table. This address can be broadcast over the IGP. After that, the LSP related with the address is generated through LDP. The ME60 replaces the next hop with the address of the peer ASBR device.
2. When multiple load balancing links between the ASBR devices exist, can the VPNv4 EBGP neighbors be established by using loopback addresses of the devices? Configure a static route with the peer device address as the destination address on each ASBR device and then establish VPNv4 EBGP neighbors. Note that MPLS LDP is disabled on the interconnecting interfaces. After the preceding configurations, the C3xxx can learn the VPN route, but the ME60 cannot learn it. With MPLS LDP enabled on the interconnecting interfaces, VPN clients can communicate with each other normally.
In normal cases, the IP addresses of interconnecting interfaces are used to establish VPNv4 EBGP neighbors, and MPLS forwarding is automatically enabled on the interconnecting relay. But for VPNv4 EBGP neighbors established by using the loopback addresses, the interface specified as the next hop in the loopback routing table cannot be used for MPLS forwarding. Instead, only ordinary IP forwarding is used. Though the C3xxx can normally learn the VPN route, it cannot forward data according to the route. A rewrite null message is displayed on the ASBR device, and MPLS packets are discarded. In the Option-C solution, if multiple-hop EBGP neighbors are established by using loopback addresses but MPLS LDP is disabled on the interconnecting interfaces, the symptom that the communication fails though routes can be created and labels can be learnt also appears. The reason is similar to that of the symptom appears in the Option-B solution, except that VPN private routes are used by the ASBR devices in the Option-B solution, while public routes are used by the ASBR devices in the Option-C solution.