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Troubleshooting Guide

CloudEngine 16800, 12800, 12800E, 8800, 7800, 6800, and 5800 Series Switches

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Troubleshooting Procedure

Troubleshooting Procedure


After commands are configured to troubleshoot faults, pay attention to the configuration validation mode to ensure that the configurations take effect. Unless otherwise specified, this manual defaults to the two-phase validation mode.

  • In immediate validation mode, the configuration takes effect immediately after you run a command and press Enter.
  • In two-phase validation mode, you must run the commit command after commands are configured to commit the configuration.

Save the results of each troubleshooting step, so you can provide related information to Huawei technical support if your troubleshooting fails.

If you use eDesk to manage your network, you can use Layer 2 loop detection of eDesk to rapidly locate and solve loop problems.


  1. Determine loops.

    Determine loops based on the following phenomena.

    • Storms of data packets occur on the interface.
      <HUAWEI> display interface brief | include up
      PHY: Physical
      *down: administratively down
      ^down: standby
      (l): loopback
      (s): spoofing
      (b): BFD down
      (e): ETHOAM down
      (d): Dampening Suppressed
      (p): port alarm down
      (dl): DLDP down
      InUti/OutUti: input utility rate/output utility rate
      Interface                   PHY   Protocol InUti OutUti   inErrors  outErrors
      10GE2/0/3                   up    up         70%    70%          0          0
      10GE2/0/5                   up    up         70%    70%          0          0
      MEth0/0/0                   up    up       0.01%  0.01%          0          0
      NULL0                       up    up(s)       0%     0%          0          0

      Compare bandwidth usage of interface traffic with that of normal services. If bandwidth usage of interface traffic is much larger than that of normal services, a loop may occur.

      • If a broadcast storm occurs on only one interface, a self-loop may occur or a loop may occur on the downstream device.
      • If a broadcast storm occurs on two interfaces, a loop may occur between interfaces.
      • If a broadcast storm occurs on more interfaces, a self-loop may occur, and a loop may occur on the downstream device or between interfaces.
    • Check whether MAC address flapping occurs.
      • Query logs to check MAC address flapping records on the interface.

        Query the log.log file or run the display logbuffer command. The following information indicates that there are MAC address flapping records, indicating that a loop may occur on the corresponding interface.

        Sep 15 2013 15:23:58
        A8_CE12808_1 %%01FEI/4/hwMflpVlanLoopAlarm_active(l):CID=0x807f047e-alarmID=0x095e0012;MAC flapping detected, VlanId = 310, MacAddress = 0016-3e00-0464, Original-Port = Eth-Trunk49, Flapping port = Eth-Trunk33,-. Please check the network to which the interface learning a flapping MAC address is connected.
      • Run the display mac-address flapping command in any view to query MAC address flapping records on the interface.

        MoveNum indicates the MAC address flapping count in a specified time range. If the value of MoveNum is large, many MAC address flappings occur. A loop may occur. Rectify the fault on the interface.

    • The protocol status is unstable.

      When a loop occurs, packets of some protocols such as OSPF are lost or looped back to the local device, or there are multiple copies of replicated packets. As a result, the protocol status may become unstable. If there are many logs about the preceding information, a loop may occur.

      Sep 16 2013 10:55:56 A8_CE12808_1 %%01OSPF/6/NBR_CHANGE(l):CID=0x808304c7;Neighbor changes event: neighbor status changed. (ProcessId=1, NbrIpAddr=, NbrEvent=1-Way, NbrPreviousState=ExStart, NbrCurrentState=Init)
      Sep 16 2013 10:55:56 A8_CE12808_1 %%01OSPF/6/NBR_CHANGE(l):CID=0x808204c3;Neighbor changes event: neighbor status changed. (ProcessId=1, NbrIpAddr=, NbrEvent=2WayReceived, NbrPreviousState=Init, NbrCurrentState=ExStart)
    • Protocol packets such as ARP packets sent to the CPU are suppressed and discarded.

      When many packets are sent to the CPU due to a loopback, the packets may be suppressed. You can run the display cpu-defend statistics packet-type arp all command to query statistics. If there are many discarded packets, a loop may occur.

      <HUAWEI> display cpu-defend statistics packet-type arp all
      Statistics(packets) on slot 2 :                                                 
      PacketType               Total Passed        Total Dropped   Last Dropping Time 
                          Last 5 Min Passed   Last 5 Min Dropped                      
      arp                             34515             14346678   -                  
                                      34515                 1678                      
    • Use loopback detection (LBDT) to detect loops.

      Enable LBDT on the corresponding interface and in a VLAN. The device periodically sends LBDT packets. When the local interface receives the sent LBDT packets, a loop occurs. You can configure LBDT on an interface and in a VLAN according to the actual situation, and run the display loopback-detect command to check loops.

  2. Eliminate loops.

    Loops seriously affect the network performance and even cause service exceptions, so loops need to be eliminated immediately. You can use the following measures to eliminate loops:

    • Physical connection errors may cause loops. Onsite engineers need to check the network and remove redundant network cables or fibers. During fault location on the live network, shut down the interface to disconnect the link.

      Exercise caution to prevent service interruptions when you shut down an interface.

    • It is difficult to perform physical operations during fault location on the live network. In most situations, perform configurations to eliminate loops. For example, you can shut down an interface or remove an interface from the VLAN where loops occur.

      In addition, other features may cause loops. For example, an exception occurs in ring network protocols such as STP and Smart Link. As a result, loops cannot be eliminated correctly. You need to rectify faults of other features. Go to 3.

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

    • Results of the preceding troubleshooting procedure

    • Configuration file, logs, and alarms of the device

Updated: 2020-01-07

Document ID: EDOC1000060766

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