BFD for TE CR-LSP
BFD for TE is an end-to-end rapid detection mechanism supported by MPLS TE. BFD for TE rapidly detects faults in links on an MPLS TE tunnel. BFD for TE supports BFD for TE tunnel and BFD for TE CR-LSP. This section describes BFD for TE CR-LSP only.
Traditional detection mechanisms, such as RSVP Hello and Srefresh, detect faults slowly. BFD rapidly sends and receives packets to detect faults in a tunnel. If a fault occurs, BFD triggers a traffic switchover to protect traffic.
On the network shown in Figure 4-32, BFD is disabled. If LSRE fails, LSRA or LSRF cannot promptly detect the fault because a Layer 2 switch exists between them. Although the Hello mechanism detects the fault, detection lasts for a long time.
If LSRE fails, LSRA and LSRF detect the fault rapidly, and traffic switches to the path LSRA -> LSRB -> LSRD -> LSRF.
BFD for TE detects faults in a CR-LSP. After detecting a fault in a CR-LSP, BFD for TE immediately notifies the forwarding plane of the fault to rapidly trigger a traffic switchover. BFD for TE is usually used together with a hot-standby CR-LSP.
A BFD session is bound to a CR-LSP. A BFD session is set up between the ingress and egress. A BFD packet is sent by the ingress to the egress along a CR-LSP. Upon receipt, the egress responds to the BFD packet. The ingress can rapidly monitor the status of links through which the CR-LSP passes based on whether a reply packet is received.
If a link fault is detected, BFD notifies the forwarding module of the fault. The forwarding module searches for a backup CR-LSP and switches traffic to the backup CR-LSP. In addition, the forwarding module reports the fault to the control plane.
On the network shown in Figure 4-33, a BFD session is set up to detect faults in the link through which the primary CR-LSP passes. If a link fault occurs, the BFD session on the ingress immediately notifies the forwarding plane of the fault. The ingress switches traffic to the bypass CR-LSP and sets up a new BFD session to detect faults in the bypass CR-LSP.
BFD for TE Deployment
The networking shown in Figure 4-34 applies to BFD for TE CR-LSP and BFD for hot-standby CR-LSP.
On the network shown in Figure 4-34, a primary CR-LSP is established along the path LSRA -> LSRB, and a hot-standby CR-LSP is configured. A BFD session is set up between LSRA and LSRB to detect faults in the primary CR-LSP. If a fault occurs on the primary CR-LSP, the BFD session rapidly notifies LSRA of the fault. After receiving the fault information, LSRA rapidly switches traffic to the hot-standby CR-LSP to ensure traffic continuity.
