H3C Technologies H3C S6800 Series Switches - Manual (Page 426)

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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.
Periodic MPLS tracert
The periodic MPLS tracert function automatically traces an LSP tunnel at a specific interval. It locates
errors on the LSP tunnel, verifies the consistency of the data plane and control plane, and records the
detected errors in system logs. You can check the logs to monitor LSP connectivity.
If both BFD and periodic MPLS tracert are configured for an LSP, and the periodic tracert function detects
a data plane and control plane inconsistency, the device does the following tasks:
1. Deletes the BFD session for the LSP.
2. Re-establishes the BFD session based on the control plane.
Protocols and standards
• RFC 4379, Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures
• RFC 5085, Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for
Pseudowires
• RFC 5885, Bidirectional Forwarding Detection (BFD) for the Pseudowire Virtual Circuit Connectivity
Verification (VCCV)
Configuring MPLS OAM for LSP tunnels
To verify LSP connectivity, you can use one of the following:
• Use the ping mpls ipv4 command or the tracert mpls ipv4 command to trigger LSP connectivity
verification as needed.
• Configure BFD for MPLS or periodic MPLS tracert for the system to automatically verify LSP
connectivity.