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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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MSTP Topology Change Leads to Service Interruption

MSTP Topology Change Leads to Service Interruption

Common Causes

When the topology on an MSTP network changes, services are interrupted.

This fault is commonly caused by one of the following:
  • MSTP is incorrectly configured.
  • Physical links flap, triggering a large number of TC messages.
  • An MSTP-aware device receives MSTP TC messages from clients or transparently-transmitted MSTP TC messages.

Troubleshooting Flowchart

Changing MSTP topology leads to service interruption on the network shown in Figure 16-3.

Figure 16-3  Networking diagram of MSTP

The troubleshooting roadmap is as follows:
  • Check that the MSTP status is correct.
  • Check whether the device has received TC messages.
  • Check that no physical interface on the device alternates between Up and Down.
  • Check that the MSTP convergence mode is Normal.

Figure 16-4 shows the troubleshooting flowchart.

Figure 16-4  Troubleshooting flowchart for service interruption due to changes in MSTP topology

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 the status of interfaces on MSTP devices.

    Check the role of each MSTP-enabled port in each instance.

    On the network shown in Figure 16-3, there is only one MSTP ring, which means that each instance can have only one blocked interface. Run the display stp brief command on each device to check whether the status of each port is normal.

    Run the display stp brief command in any view to check the MSTP status on Router1. As shown in Figure 16-3, in instances 0 and 1, Router1 functions as a root bridge, and all ports on Router1 are designated ports. In instance 2, one port on Router1 is a designated port, and the other port is a root port. Both ports are in the Forwarding state.

    [Router1] display stp brief
     MSTID      Port           Role  STP State       Protection	
       0        Ethernet2/0/1  DESI  FORWARDING      NONE
       0        Ethernet2/0/2  DESI  FORWARDING      NONE
       1        Ethernet2/0/1  DESI  FORWARDING      NONE
       1        Ethernet2/0/2  DESI  FORWARDING      NONE
       2        Ethernet2/0/1  ROOT  FORWARDING      NONE
       2        Ethernet2/0/2  DESI  FORWARDING      NONE
    

    Run the display stp brief command in any view to check the MSTP status on Router2. As shown in Figure 16-3, in instances 2, Router2 functions as a root bridge, and all ports on Router2 are designated ports. In other instances, one port on Router2 is a designated port, and the other port is a root port. Both of them are in the Forwarding state.

    [Router2] display stp brief
     MSTID      Port           Role  STP State       Protection	
       0        Ethernet2/0/1  ROOT  FORWARDING      NONE
       0        Ethernet2/0/2  DESI  FORWARDING      NONE
       1        Ethernet2/0/1  ROOT  FORWARDING      NONE
       1        Ethernet2/0/2  DESI  FORWARDING      NONE
       2        Ethernet2/0/1  DESI  FORWARDING      NONE
       2        Ethernet2/0/2  DESI  FORWARDING      NONE
    

    Run the display stp brief command in any view to check the MSTP status on Router3. As shown in Figure 16-3, in instance 2, one port on Router3 is an Alternate port and the other port is a root port. The Alternate port is blocked and in the Discarding state. In other instances, one port on Router3 is a designated port and the other port is a root port. Both of them are in the Forwarding state.

    [Router3] display stp brief
     MSTID      Port           Role  STP State       Protection	
       0        Ethernet2/0/1  DEST  FORWARDING      NONE
       0        Ethernet2/0/2  ROOT  FORWARDING      NONE
       1        Ethernet2/0/1  DEST  FORWARDING      NONE
       1        Ethernet2/0/2  ROOT  FORWARDING      NONE
       2        Ethernet2/0/1  ALTE  DISCARDING      NONE
       2        Ethernet2/0/2  ROOT  FORWARDING      NONE
    

    Run the display stp brief command in any view to check the MSTP status on Router4. As shown in Figure 16-3, in instance 0, one port on Router4 is an Alternate port, and the other port is a root port. The Alternate port is blocked and in the Discarding state. In instance 2, one port on Router4 is a designated port, and the other port is a root port. Both of them are in the Forwarding state.

    [Router4] display stp brief
     MSTID      Port           Role  STP State       Protection	
       0        Ethernet2/0/1  ALTE  DISCARDING      NONE
       0        Ethernet2/0/2  ROOT  FORWARDING      NONE
       1        Ethernet2/0/1  ALTE  DISCARDING      NONE
       1        Ethernet2/0/2  ROOT  FORWARDING      NONE
       2        Ethernet2/0/1  DESI  FORWARDING      NONE
       2        Ethernet2/0/2  ROOT  FORWARDING      NONE
    

    • On the network shown in Figure 16-3, each instance has only one port in the Discarding state and the other port is in the Forwarding state. If several ports are in the Discarding state, an MSTP calculation error occurs. To solve this problem, go to Step 6.

    • If the MSTP status is correct, go to Step 2.

  2. Check that the MSTP configuration is correct.

    Run the display stp region-configuration command to view mappings between VLANs and instances.

    [] display stp region-configuration
    Oper Configuration:
       Format selector :0
       Region name     :huawei
       Revision level  :0
    
    
       Instance   Vlans Mapped
          0       21 to 4094
          1       1 to 10
          2       11 to 20

    • Check whether mappings between VLANs and instances are correct. If a mapping is incorrect, run the instance command to map the VLAN to a specified spanning tree instance. Run the active region-configuration command to activate the mapping between the VLAN and instance configured (using the instance command).

    Run the display current-configuration command to view the MSTP configuration in the configuration file of the device.

    • Check whether MSTP is disabled on the interfaces that connect to user terminals or the interfaces are configured as edge interfaces.
    • Check whether interfaces are added to VLANs correctly. For VLAN configurations, see "VLAN Configuration" in the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 Configuration Guide - lan.
    • If the MSTP configuration is correct, go to Step 3.
  3. Check that no MSTP recalculation was performed.

    Run the display stp command in any view to check whether the device received TC messages.

    [Router1] display stp 
    -------[CIST Global Info][Mode MSTP]-------
    CIST Bridge         :57344.00e0-fc00-1597
    Bridge Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
    CIST Root/ERPC      :0    .0018-826f-fc7a / 20000
    CIST RegRoot/IRPC   :57344.00e0-fc00-1597 / 0
    CIST RootPortId     :128.2
    BPDU-Protection     :disabled
    TC or TCN received  :0
    TC count per hello  :0
    STP Converge Mode   :Normal
    Time since last TC :2 days 14h:16m:15s    
     
    -------[MSTI 1 Global Info]-------
    MSTI Bridge ID      :4096.00e0-fc00-1597
    MSTI RegRoot/IRPC   :4096.00e0-fc00-1597 / 0
    MSTI RootPortId     :0.0
    Master Bridge       :57344.00e0-fc00-1597
    Cost to Master      :0
    TC received         :0
    TC count per hello  :2
    

    • If the values of TC or TCN received, TC count per hello, TC received, and TC count per hello fields in the command output increase, the device has received TC messages, and the network topology has changed. View the log messages MSTP/6/SET_PORT_DISCARDING and MSTP/6/SET_PORT_FORWARDING to check whether the role of an MSTP-enabled port changed.

      • If the port role did not change, go to Step 4.

      • If the port role changed, go to Step 6.

    • If the values of the TC or TCN received, TC count per hello, TC received, and TC count per hello fields in the command output are 0s, the device does not receive any TC message. Please contact technical support personnel.

  4. Check that no interface on the device alternates between Up and Down.

    View the log message IFNET/4/IF_STATE to check whether an MSTP-enabled port alternates between Up and Down.

    • If an MSTP-enabled interface alternates between Up and Down, the interface flaps. If a physical interface frequently alternates between Up and Down, the MSTP status of the device on the network becomes unsteady. As a result, a large number of TC messages are generated, ARP entries and MAC entries are frequently deleted, and services are interrupted. Run the shutdown command on the flapping interface. If services are not restored after the interface is shut down, go to Step 5.

    • If no interface flaps, go to Step 5.

  5. Check that the MSTP convergence mode is Normal.

    Run the display stp command in any view to check the MSTP convergence mode of the device.

    [Router1] display stp
    -------[CIST Global Info][Mode MSTP]-------
    CIST Bridge         :57344.00e0-fc00-1597
    Bridge Times        :Hello 2s MaxAge 20s FwDly 15s MaxHop 20
    CIST Root/ERPC      :0    .0018-826f-fc7a / 20000
    CIST RegRoot/IRPC   :57344.00e0-fc00-1597 / 0
    CIST RootPortId     :128.2
    BPDU-Protection     :disabled
    TC or TCN received  :0
    TC count per hello  :0
    STP Converge Mode   :Normal
    Time since last TC :2 days 14h:16m:15s
     
    -------[MSTI 1 Global Info]-------
    MSTI Bridge ID      :4096.00e0-fc00-1597
    MSTI RegRoot/IRPC   :4096.00e0-fc00-1597 / 0
    MSTI RootPortId     :0.0
    Master Bridge       :57344.00e0-fc00-1597
    Cost to Master      :0
    TC received         :0
    TC count per hello  :2
    

    • If the convergence mode is Normal, go to Step 6.

    • If the convergence mode is Fast, run the stp converge normal command to change the convergence mode to Normal. If services are not restored after the convergence mode is changed, go to Step 6.

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

    • Results of the preceding troubleshooting procedure

    • Configuration files, log files, and alarm files of the device

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Updated: 2019-05-10

Document ID: EDOC1000079719

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