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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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Congestion Avoidance Fails to Take Effect

Congestion Avoidance Fails to Take Effect

This section describes the troubleshooting flowchart and provides a step-by-step troubleshooting procedure to use when congestion avoidance fails to take effect.

Common Causes

This fault is commonly caused by one of the following:
  • Congestion avoidance is not configured on the outbound interface.
  • WRED parameters are set incorrectly.
  • Packets enter incorrect queues.

Troubleshooting Flowchart

Figure 21-7 shows the troubleshooting flowchart.
Figure 21-7  Troubleshooting flowchart for ineffective congestion avoidance

Troubleshooting Procedure

NOTE:

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

The congestion avoidance mechanism discards packets based on the maximum number of packets buffered in a queue and the actual length of packets. If the upper and lower drop thresholds and the queue length are not set properly, for example, the queue length is too long or the upper or lower drop threshold is too high, congestion may occur.

Procedure

  1. Check whether congestion avoidance is configured on the outbound interface.

    Check Item

    Method

    Queue-based congestion avoidance

    Run the display this command in the view of the outbound interface to check whether the qos queue-profile command is used. If the qos queue-profile command is used, run the display this command in the queue profile view to check whether the queue drop-profile command is used. If the queue drop-profile command is used, queue-based congestion avoidance is configured on the interface.

    Flow-based congestion avoidance

    Run the display this command in the view of the outbound interface to check whether the traffic-policy command is used. If the traffic-policy command is used, run the display traffic policy user-defined command to check whether the drop-profile command is used. If the drop-profile command is used, flow-based congestion avoidance is configured.

    NOTE:

    Flow-based congestion avoidance can be configured only for CBWFQ queues on WAN-side interfaces.

    • If queue-based congestion avoidance or flow-based congestion avoidance is not configured, configure it on the outbound interface.
    • If queue-based congestion avoidance or flow-based congestion avoidance is configured, go to step 2.

  2. Check whether WRED parameters are set correctly.

    Run the display drop-profile command to check whether WRED parameters in the drop profile are correct.
    • If not (for example, when the upper and lower drop thresholds are 100, congestion avoidance does not take effect if tail drop is used), run the dscp discard-percentage or ip-precedence discard-percentage command to change the upper and lower drop thresholds.
    • If yes, go to step 3.

  3. Check whether packets enter specified queues.

    Run the display qos queue statistics interface command to view queue-based traffic statistics on the outbound interface. Check whether packets enter specified queues.

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

    • Results of the preceding troubleshooting procedure
    • Configuration file, log file, and alarm file of the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600

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Updated: 2019-05-10

Document ID: EDOC1000079719

Views: 449245

Downloads: 4305

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