MPLS L3VPN FRR

MPLS L3VPN Fast Reroute (FRR) is applicable to a dual-homed scenario, as shown in Figure 62. By using BFD to detect the primary link, FRR enables a PE to use the backup link when the primary link fails. The PE then selects a new optimal route, and uses the new optimal route to forward traffic.

Figure 62: Network diagram

As shown in Figure 62, configure FRR on PE 2, and specify the backup next hop for VPN 1 as PE 3. When PE 2 receives an IPv4 route from CE 2 and a VPNv4 route from PE 3 (both routes are destined for VPN 1 connected to CE 2), PE 2 uses the IPv4 route as the primary link, and the VPNv4 route as the backup link.

PE 2 uses ARP or echo-mode BFD to detect the connectivity of the link from PE 2 to CE 2. When the link operates correctly, traffic from CE 1 to CE 2 goes through the path CE 1—PE 1—PE 2—CE 2. When the link fails, PE 2 switches traffic to the link PE 2—PE 3—CE 2, and traffic from CE 1 to CE 2 goes through the path CE 1—PE 1—PE 2—PE 3—CE 2. This avoids traffic interruption before route convergence completes (switching to the link CE 1—PE 1—PE 3—CE 2).

In this scenario, PE 2 is responsible for primary link detection and traffic switchover.