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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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ARP Learning Fails

ARP Learning Fails

Common Causes

The following table describes the possible causes of an ARP learning failure (assuming that the device sends an ARP request to trigger ARP learning).

Condition

Possible Cause

The ARP request is not sent out.

A large number of ARP requests are triggered by ARP Miss messages, and the device has not processed this ARP request.

The remote device does not receive the ARP request.

The link between the device and the remote device is faulty, so the ARP request is discarded on the network.

The remote device receives the ARP request but discards it.

The remote device receives a large number of ARP packets. The rate of ARP packets exceeds the CAR, so the device discards the ARP request sent by the device.

The device does not receive the ARP reply sent by the remote device.

The link between the device and the remote device is faulty, so the ARP request is discarded on the network.

The device receives the ARP reply but does not send it to the CPU.

The rate of ARP packets received by the device exceeds the CPCAR or ARP packet rate limit, so the ARP reply is discarded.

The ARP reply is sent to the CPU but is discarded.

The ARP module of the device is faulty.

Troubleshooting Flowchart

Figure 22-12 shows the troubleshooting flowchart.

Figure 22-12  Troubleshooting flowchart for ARP learning failure

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.

Procedure

  1. Check that the link between the device and the remote device works properly.

    • Perform ping operations between the device and the remote device. If the ping operations fail, check the routing configuration on the two devices.
    • View traffic statistics on the two devices to check whether packets are discarded on the link. If any device on the link does not support the traffic statistics function, perform a ping test to check whether packets are discarded on the device. If packets are discarded on the link, rectify the link fault.

  2. Check that the device processes ARP packets properly.

    Run the debugging arp packet interface interface-type interface-number command in the user view to enable ARP debugging. Check whether information about ARP request and ARP reply packets is displayed.

    NOTE:

    In the debugging information, the operation field indicates the ARP packet type. The value 1 indicates ARP request packets and the value 2 indicates ARP reply packets.

    • If the device does not send any ARP request packet, rectify the fault according to IP Address Scanning Occurs.
    • If the device does not receive any ARP reply packet, the ARP reply packets sent by the remote device may be discarded by the CPCAR mechanism. Go to step 3.
    • If the device receives ARP reply packets, go to step 5.

  3. Check whether ARP reply packets are discarded.

    • Run the display cpu-defend statistics packet-type arp-reply command to view statistics about ARP reply packets.

      If the Drop value keeps increasing, the rate of ARP reply packets exceeds the CPCAR. Run the packet-type command to increase the CPCAR for ARP reply packets.

    • Run the display this command in the interface view and system view to check whether a rate limit is set for ARP packets.

      If the rate limit is set and the rate of ARP packets is high, ARP reply packets may be discarded. Run the arp anti-attack rate-limit command to increase the rate limit.

  4. Check that the remote device correctly receives ARP request packets and sends ARP reply packets.

    If the remote device is a Huawei device, perform step 2 on the device. If the remote device is a non-Huawei device, see the manual of the device.

  5. If the fault persists, collect the following information and contact technical support personnel:

    • Results of the preceding troubleshooting procedure
    • Configuration files, log files, and alarm files of the devices

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Updated: 2019-05-10

Document ID: EDOC1000079719

Views: 455060

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