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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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LDP Session Flapping

LDP Session Flapping

Common Causes

This fault is commonly caused by one of the following:

  • The configuration of the LDP GR timer, the LDP MTU, LDP authentication, the LDP Keepalive timer, or the LDP transport address is set, changed, or deleted.

  • An interface flaps.

  • Routes flap.

Troubleshooting Flowchart

After an LDP session is configured, the LDP session flaps.

The troubleshooting roadmap is as follows:
  • Check that LDP GR, a Keepalive timer, LDP authentication, MTU signaling, or a transport address is configured.

  • Check that the interface does not alternate between Down and Up.

  • Check that the routes do not alternate between unreachable and reachable.

Figure 24-1 shows the troubleshooting flowchart.

Figure 24-1 Troubleshooting flowchart for LDP session flapping

Troubleshooting Procedure

Context

NOTE:

Saving the results of each troubleshooting step is recommended. If your troubleshooting fails to correct the fault, you will have a record of your actions to provide Huawei technical support personnel.

Procedure

  1. Check that LDP GR, a Keepalive timer, LDP authentication, an LDP MTU, or a transport address is configured.
    1. Run the display this command in the LDP view to view the configuration of LDP GR, an LDP MTU, or LDP authentication.

      • If the following information is displayed, LDP GR is configured.
        mpls ldp
         graceful-restart
        
      • If the command output displays the following information, the LDP MTU value is set.
        mpls ldp
         mtu-signalling
        
      • If the command output displays the following information, LDP authentication is configured.
        mpls ldp
         md5-password cipher 2.2.2.2 %$%$f
        
        or
        mpls ldp
         authentication key-chain peer 2.2.2.2 name kc1
        

    2. Run the display this command in the interface view to view an LDP Keepalive timer or an LDP transport address.

      • If the command output displays the following information, the LDP Keepalive timer is set. The timer value (30 seconds in the following example) depends on the real-world situation.
        mpls ldp
        mpls ldp timer keepalive-hold 30
        
      • If the command output displays the following information, the LDP transport address is set. The transport address and interface type and number can be set as needed.
        mpls ldp
        mpls ldp transport-address interface 
        

    • If any of the configurations you checked in sub-steps 1 and 2, wait 10 seconds and check whether the LDP session flaps.

    • If no configuration has been performed, go to Step 2.

  2. Check that the interface does not alternate between Down and Up.

    Run the display ip interface brief command and view the Physical and Protocol fields in the command output. If both fields display Up, the interface is Up; if one field displays Down, the interface is Down. If the interface always alternates between Down and Up, the interface flaps.

    • If the interface alternates between Down and Up, see the section "Interface Flapping".

    • If the interface does not flap, go to Step 3.

  3. Check that the routes do not alternate between unreachable and reachable.

    Run the display fib command quickly to check routing information. If routes are reachable, routing information is displayed. If no route is reachable, no routing information is displayed. If sometimes routing information is displayed, but sometimes not, the routes alternate between unreachable and reachable.

    • If routes alternate between unreachable and reachable or no route exists, see The Ping Operation Fails.

    • If the routes do not flap, go to Step 4.

  4. Collect the following information, and contact technical support personnel.

    • Results of the preceding troubleshooting procedure
    • Configuration files, logs, and alarms

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Updated: 2019-08-09

Document ID: EDOC1000079719

Views: 493688

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