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Configuration Guide - MPLS

S7700 and S9700 V200R011C10

This document describes MPLS configurations supported by the switch, including the principle and configuration procedures of static LSPs, MPLS LDP, MPLS TE, MPLS QoS, MPLS OAM, Seamless MPLS, and MPLS common features, and provides configuration examples.
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MPLS OAM Detection

MPLS OAM Detection

MPLS OAM packets are classified into the following types:

  • Connectivity detection packets

    • Fast Failure Detection (FFD) packets

    • Connectivity Verification (CV) packets

  • Forward Defect Indication (FDI) packets

  • Backward Defect Indication (BDI) packets

MPLS OAM monitors:


MPLS OAM monitors traffic engineering (TE) LSP connectivity by periodically sending CV or FFD packets along the TE LSP. Figure 6-1 shows how MPLS OAM works on a TE LSP.

Figure 6-1  MPLS OAM for a TE LSP

The process is as follows:

  1. The ingress sends a CV or FFD packet along an LSP to be detected. The packet passes through the LSP and arrives at the egress.

  2. The egress compares the packet type, interval, and Trail Termination Source Identifier (TTSI) in the received packet with the local values to check whether the packet is valid. In addition, the egress counts the number of valid and invalid packets it receives within a detection cycle to detect LSP connectivity.

    The detection interval for CV packets is a fixed value. The detection cycle for FFD packets is three times the detection interval.

  3. When the egress detects an LSP fault, the egress analyzes the fault type and encapsulates information about the fault in a BDI packet. It then sends this packet to the ingress through a reverse tunnel. If the protection group is configured correctly, protection switching is triggered.

    This process ensures that the ingress is notified of specific faults in a timely manner.

    The following types of faults are detected:

    • Non-MPLS layer faults

      • dServer: a fault occurring on the server layer below the MPLS network.

        Faults of this type are reported to MPLS OAM by the server layer. MPLS OAM handles these faults.

        The lower layer network that bears MPLS services may have its own protection and fault detection mechanisms. When a lower layer fault occurs on an LSP, the downstream label switching router (LSR) that is closest to the fault notifies the egress of the fault. Faults occurring on the lower layer do not trigger switchover, but the network management device must be notified of them. In addition, the ingress can be notified of lower layer faults by sending BDI packets.

      • dPeerME: a server layer fault occurring on a peer maintenance entity outside the MPLS subnet.

        Faults of this type are reported to MPLS OAM by the other network layers connected to the MPLS subnet. MPLS OAM handles these faults.

    • MPLS layer faults

      • dLOCV: loss of connectivity verification.

        A dLOCV fault occurs when no CV or FFD packet is received within three consecutive detection cycles.

      • dTTSI_Mismatch: a TTSI mismatch.

        A dTTSI_Mismatch fault occurs when no CV or FFD packet with a valid TTSI is received within three consecutive detection cycles.

      • dTTSI_Mismerge: a TTSI mismerge.

        A dTTSI_Mismerge fault occurs when CV or FFD packets with both valid and invalid TTSIs are received within three consecutive detection cycles.

      • dExcess: excessive rate for receiving connectivity detection packets.

        A dExcess fault occurs when five or more valid CV or FFD packets are received within three consecutive detection cycles.

    • Other faults

      dUnknown: an unknown fault on an MPLS network.

      Faults that are not defined in the protocol are classified as dUnknown. For example, if the egress detects that both CV packets and FFD packets are sent along the same LSP, an undefined fault occurs and is classified as dUnknown.

Updated: 2019-10-18

Document ID: EDOC1000178315

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