MPLS BFD
MPLS BFD uses a BFD session to proactively verify the connectivity of an LSP tunnel, an MPLS TE tunnel, or a PW tunnel.
MPLS BFD establishes a BFD session between the ingress and egress of the tunnel to be inspected, adds the label associated with the tunnel into a BFD control packet at the ingress, sends the packet to the egress node over the tunnel, and determines the tunnel status according to the BFD control packet returned by the egress. When BFD detects a connectivity failure, it triggers the pre-configured action, such as FRR or path protection switching, to ensure uninterrupted traffic forwarding.
A BFD session for LSP, MPLS TE tunnel, or PW connectivity verification can be established in one of the following modes:
Static mode—You manually specify the local and remote discriminators through command lines to establish the BFD session.
Dynamic mode—The system automatically runs MPLS ping to negotiate the discriminators to establish the BFD session.
In static mode, the egress node returns a BFD control packet to the ingress node through the reverse tunnel. If no reverse tunnel exists, the ingress node cannot receive the BFD control packet, resulting in a verification failure.
In dynamic mode, the egress node returns a BFD control packet to the ingress node through the reverse tunnel. If no reverse tunnel exists, the egress mode returns a BFD packet through IP routing.
Use the static mode to test the connectivity of a pair of LSPs or MPLS TE tunnels in opposite directions (one from local to remote, and the other from remote to local) between two devices. Use the dynamic mode to test the connectivity of one LSP or MPLS TE tunnel from the local device to the remote device.
A PW is bidirectional. You will get the correct result using either the static or dynamic mode.