Troubleshooting: Link Switchover or Revertive Switchover Occurs

Common Causes

• The active AC fails.
• The faulty active AC recovers.
• The active and standby ACs have different priorities.
• The IP addresses of active and standby ACs are different.

Troubleshooting Flowchart

Troubleshooting Procedure (Web NMS)

1. Check whether the link connected to the active AC is faulty.

   An active/standby link switchover occurs when the active AC becomes faulty or the link between the AC and AP is faulty.

   1. Check whether the AC is faulty and cannot be accessed.
   2. Ping the AP from the AC to check whether the link between the AC and AP is normal.

      If the ping operation fails, the link between the AC and AP is not connected.

      Choose Diagnosis > Diagnosis Tool > ping and check the test result.

2. Check whether the faulty AC recovers.

   This is a normal situation where services are switched back to the recovered active AC.

   1. Check the onsite environment. Check whether the faulty AC recovers and whether the AC is the active AC.

      Determine whether the AC fails and recovers based on information collected onsite.

   2. If the AC recovers, log in the AC to check the IP address of the standby AC. If the IP address is configured and is the IP address of the AC where the switchover occurs, the recovered AC is the active AC. The specified configuration in the AP system profile takes precedence over the global configuration on the AC.

      Choose Configuration > Backup Settings > Backup Settings > Backup Configuration to check information, such as the dual-link backup status, AC switchback status, AC priority, and standby AC's IP address.

      Choose Configuration > AP Config > Profile> AP > AP System Profile to check information, such as the AC priority and standby AC's IP address in the bound AP system profile.

3. Check whether the active and standby ACs have the same priority.

   If the active and standby ACs have the same priority, the AP switches to the AC with a smaller IP address.

   For details on how to check the AC's priority, see step 2.

   Choose Configuration > AC Config > Basic Config > AC Configuration to check the IP address of the AC. If you select IP Address for AC source address, the value is displayed. If you select VLANIF for AC source address, check the IP address of the VLANIF interface.

4. Check whether two ACs start successively and have different priorities.

   If the standby AC starts later and has a higher priority than the active AC, a link switchover is triggered.

   1. Check whether the standby AC starts later and has a higher priority than the active AC.
      • Check the device running time to determine whether the standby AC starts later.
      • For details on how to check the AC's priority, see step 2.
   2. If the standby AC starts later than the active AC but two ACs have the same priority, go to step 5.

5. Check whether two ACs start successively and have the same priority.

   If the standby AC starts later, has the same priority as the active AC, but has a smaller IP address, a link switchover is triggered.

   1. Check whether the standby AC starts later but has the same priority as the active AC.
      • Check the device running time to determine whether the standby AC starts later.
      • For details on how to check the AC's priority, see step 2.
   2. If the active and standby ACs have the same priority, check whether the active AC has a smaller IP address. If the IP address of the active AC is larger than the IP address of the standby AC, go to step 6.

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

   The log file can be exported through the web NMS. For details about diagnosis commands or file operations, see the following section.

   Choose Maintenance > Log >View AC Logs > Export and export AC logs.

Troubleshooting Procedure (CLI)

1. Check whether the link connected to the active AC is faulty.

   When the active AC fails or the link between the AC and AP fails, services are switched between links.

   1. Check whether the AC is faulty and cannot be accessed.
   2. Perform the ping operation to check whether the link between the AC and AP works properly.

      If the ping operation fails, the link between the AC and AP is not connected.

      Run the Ping command to check the test result.

      <AC6605> ping 10.1.15.252
        PING 10.1.15.252: 56  data bytes, press CTRL_C to break
          Request time out 
          Request time out 
          Request time out 
          Request time out 
          Request time out 
        
        --- 10.1.15.252 ping statistics ---  
          5 packet(s) transmitted  
          0 packet(s) received 
          100.00% packet loss 

2. Check whether the faulty AC recovers.

   This is a normal situation where services are switched back to the recovered active AC.

   1. Check the AC status and check whether the faulty active AC recovers.

      Determine whether the AC fails and recovers based on information collected onsite.

   2. If the AC recovers, log in the AC to check the IP address of the standby AC. If the IP address is configured and is the IP address of the AC where the switchover occurs, the recovered AC is the active AC. The specified configuration in the AP system profile takes precedence over the global configuration on the AC.

      Run the display ac protect command to check the dual-link backup status, AC switchback status, and AC priority and standby AC's IP address in the WLAN view.

      [AC20] display ac protect 
      ------------------------------------------------------------ 
      Protect state             : disable 
      Protect AC                : - 
      Priority                  : 0 
      Protect restore           : enable 
      Coldbackup kickoff station: disable
      ------------------------------------------------------------ 

      Run the display ap-system-profile profile-name command to check the AC priority and standby AC's IP address in the AP system profile view.

      [AC20] display ap-system-profile name default
      ------------------------------------------------------------------------------ 
      AC priority                   : -
      Protect AC IP address         : -
      AP management VLAN            : -
      Keep service                  : disable 
      Keep service allow new access : disable 
      Temporary management switch   : disable 

3. Check whether the active and standby ACs have the same priority.

   If the active and standby ACs have the same priority, the AP switches to the AC with a smaller IP address.

   For details on how to check the AC's priority, see step 2.

   Run the display capwap configuration command to check the IP address of the AC. Check the value of Source ip-address.

   [AC20] display capwap configuration
     ------------------------------------------------------------ 
     Source interface                            : - 
     Source ip-address                           : 10.1.1.111 
     Echo interval(seconds)                      : 25
     Echo times                                  : 6
     Control priority(server to client)          : 7
     Control priority(client to server)          : 7
     Control-link DTLS encrypt                   : disable
     DTLS PSK value                              : ******
     PSK mandatroy match switch                  : enable
     Control-link inter-controller DTLS encrypt  : disable
     Inter-controller DTLS PSK value             : ******
     IPv6 status                                 : disable 
     ------------------------------------------------------------

4. Check whether two ACs start successively and have different priorities.

   If the standby AC starts later and has a higher priority than the active AC, a link switchover is triggered.

   1. Check whether the standby AC starts later and has a higher priority than the active AC.
      • Check the device running time to determine whether the standby AC starts later.
      • For details on how to check the AC's priority, see step 2.
   2. If the standby AC starts later than the active AC but two ACs have the same priority, go to step 5.

5. Check whether two ACs start successively and have the same priority.

   If the standby AC starts later, has the same priority as the active AC, but has a smaller IP address, a link switchover is triggered.

   1. Check whether the standby AC starts later but has the same priority as the active AC.
      • Check the device running time to determine whether the standby AC starts later.
      • For details on how to check the AC's priority, see step 2.
   2. If the active and standby ACs have the same priority, check whether the active AC has a smaller IP address. If the IP address of the active AC is larger than the IP address of the standby AC, go to step 6.

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

   Run the following commands to collect device information.

   Command	Function
   <AC6605>save logfile	Save diagnosis logs.
   [AC6605-diagnose]info-center create logbook xx.xml	Create a dictionary file of diagnosis logs.

   Access the logfile folder and export log.log, log.dlg, and created dictionary file xx.xml.

Troubleshooting Cases

Problem description:

The active link works properly but link switchover is still triggered.

Networking description:

The AP sets up links with AC1 and AC2 through the S9300. AC1 is the active AC, whereas AC2 is the standby AC.

Fault Analysis:

• The link between the AP and AC1 works properly and the two ACs are all started before the AP goes online. Normally, a link switchover does not occur.
• The two ACs have the same priority.
• AC2's IP address is smaller than AC1's.

Procedure:

1. Check whether AC1 is faulty or recovers from a fault.

   If neither of the receding situations occurs, go to the next step.

2. Check AC priority.

   If the two ACs have the same priority, go to step 3.

3. Check the IP addresses of the two ACs.

   AC2's IP address is smaller than AC1's. The AP switches links based on the revertive switchover algorithm. It first compares the two ACs' IP addresses and then switches traffic to the AC with a smaller IP address. Since AC2's IP address is smaller than AC1's, the AP performs a revertive switchover.

Summary:

• This fault occurs because the algorithm to choose an active AC is inconsistent with the revertive switchover algorithm.

  In old versions, the AP selects the active AC based on the following sequence: priority, load, and AC's IP address. That is, the AP preferentially goes online on the AC with a higher priority. If the two ACs have the same priority, the AP selects the AC with a smaller load. If the AC load is also the same, the AP connects to the AC with a smaller IP address.

  The AP determines whether to perform a revertive switchover based on AC priority and IP address (AC priority > IP address).

• Based on the algorithm to choose an active AC, the AP selects AC1 as the active AC to go online. Since AC2 has a smaller IP address, the AP switches traffic back to AC2 according to the revertive switchover algorithm. Consequently, the fault occurs.

  The inconsistency in the two algorithms has been modified. Currently, the AP performs a revertive switchover only according to the AC priority.