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NE40E V800R010C00 Configuration Guide - MPLS 01

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(Optional) Setting the Hold-max-cost Timer Value

(Optional) Setting the Hold-max-cost Timer Value

When an LDP session on a primary LSP fails, traffic is transmitted along a backup LSP within the timeout period of the hold-max-cost timer before the LDP session on the primary LSP recovers.

Context

Select parameters based on networking requirements:
  • If an IGP carries only LDP services, configure infinite to ensure that a selected IGP route is kept consistent with the LDP LSP.
  • If an IGP carries multiple types of services including LDP services, set the value to ensure that an LDP session teardown does not affect IGP route selection or other services.

Procedure

  • If OSPF is used, perform the following steps on the interfaces on both ends of the link between the node where the primary LSP and the backup LSP diverge from each other and its LDP peer on the primary LSP:
    1. Run:

      system-view

      The system view is displayed.

    2. Run:

      interface interface-type interface-number

      The interface view is displayed.

    3. Run:

      ospf timer ldp-sync hold-max-cost { value | infinite }

      The hold-max-cost timer value is set.

      The hold-max-cost timer value is equal to the interval at which the local node sends an LSA to advertise the maximum cost.

      NOTE:
      To set a value for the hold-max-cost timer on an OSPF multi-area adjacency interface, run the ospf timer ldp-sync hold-max-cost { value | infinite } multi-area area-id command.

    4. (Optional) Set the maximum cost for OSPF links.

      In an IGP-LDP synchronization scenario, when an LDP tunnel's next hop changes, a large number of entries need to be updated. If upstream and downstream forwarding entries reside on different boards, they may not be updated synchronously during traffic switchback. As a result, packet loss occurs if upstream forwarding entries are updated but downstream forwarding entries are not. To prevent packet loss, FRR forwarding entries can be created for the switchback path, and the link's primary/secondary status can be updated during traffic switchback. As defined in standard protocols, in an IGP-LDP synchronization scenario, if LDP is not in the fully operational state, OSPF needs to set the link cost to LSInfinity (65535). However, as defined in standard protocols, a link cannot participate in FRR route computation if its cost is 65535. To resolve this conflict in an IGP-LDP synchronization scenario, run the maximum-link-cost cost command to change the maximum cost for OSPF links.

      1. Run the system-view command to enter the system view.
      2. Run the ospf [ process-id ] command to enter the OSPF view.
      3. Run the maximum-link-cost cost command to set the maximum cost for OSPF links.

    5. Run:

      commit

      The configurations are committed.

  • If IS-IS is used, perform the following steps on the interfaces on both ends of the link between the node where the primary LSP and the backup LSP diverge from each other and its LDP peer on the primary LSP.
    1. Run:

      system-view

      The system view is displayed.

    2. Run:

      isis [ process-id ]

      A specified IS-IS process is started, and the IS-IS view is displayed.

    3. Run:

      timer ldp-sync hold-max-cost { infinite | interval }

      The time is set for all interfaces in the IS-IS process to take to wait for leaving the LDP-IGP synchronization state.

    Perform the following steps on the interfaces on both ends of the link between the node where the primary LSP and the backup LSP diverge from each other and the LDP peer on the primary LSP.

    1. Run:

      system-view

      The system view is displayed.

    2. Run:

      interface interface-type interface-number

      The interface view is displayed.

    3. Run:

      isis timer ldp-sync hold-max-cost { value | infinite }

      The hold-max-cost timer value is set.

      The hold-max-cost timer value is equal to the interval at which the local node advertises the maximum cost in LSPs.

    4. Run:

      commit

      The configurations are committed.

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Updated: 2018-07-12

Document ID: EDOC1100028530

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