MPLS L3VPN FRR
MPLS L3VPN Fast Reroute (FRR) is applicable to a dual-homed scenario, as shown in Figure 68. 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.
MPLS L3VPN FRR supports the following types of backup:
VPNv4 route backup for a VPNv4 route.
VPNv4 route backup for an IPv4 route.
IPv4 route backup for a VPNv4 route.
VPNv4 route backup for a VPNv4 route
As shown in Figure 68, configure FRR on the ingress node PE 1, and specify the backup next hop for VPN 1 as PE 3. When PE 1 receives a VPNv4 route to CE 2 from both PE 2 and PE 3, it uses the route from PE 2 as the primary link, and the route from PE 3 as the backup link.
Figure 68: Network diagram
Configure BFD for LSPs or MPLS TE tunnels on PE 1 to detect the connectivity of the public tunnel from PE 1 to PE 2. When the tunnel PE 1—PE 2 operates correctly, traffic from CE 1 to CE 2 goes through the path CE 1—PE 1—PE 2—CE 2. When the tunnel fails, the traffic goes through the path CE 1—PE 1—PE 3—CE 2.
In this scenario, PE 1 is responsible for primary link detection and traffic switchover.
For more information about BFD for LSPs or MPLS TE tunnels, see "Configuring MPLS OAM."
VPNv4 route backup for an IPv4 route
As shown in Figure 69, configure FRR on the egress node 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.
Figure 69: Network diagram
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.
IPv4 route backup for a VPNv4 route
As shown in Figure 70, configure FRR on PE 1, and specify the backup next hop for VPN 1 as CE 2. When PE 1 receives an IPv4 route from CE 2 and a VPNv4 route from PE 2 (both routes are destined for VPN 1 connected to CE 2), PE 1 uses the VPNv4 route as the primary link, and the IPv4 route as the backup link.
Figure 70: Network diagram
Configure BFD for LSPs or MPLS TE tunnels on PE 1 to detect the connectivity of the public tunnel from PE 1 to PE 2. When the tunnel operates correctly, traffic from CE 1 to CE 2 goes through the path CE 1—PE 1—PE 2—CE 2. When the tunnel fails, the traffic goes through the path CE 1—PE 1—CE 2.
In this scenario, PE 1 is responsible for primary link detection and traffic switchover.