An Incorrect Active AC Is Selected in a Dual-Link Backup Scenario

Symptom

In a dual-link backup scenario, an incorrect active AC is selected.

An AC is specified as the active AC during the network planning. However, this specified AC is not the active AC based on the algorithm used by an AP to select the active AC.

During problem diagnosis, the active AC refers to the specified one unless otherwise stated.

Possible Causes

• The dual-link backup function is disabled.

  This cause may be neglected easily because the user routinely checks the AC priority, load, and IP address rather than checking whether dual-link backup is enabled. However, the AP preferentially goes online on the AC enabled with the dual-link backup function.

• The IP address of the standby AC is not configured globally or in the AP view.

  The user may have enabled the dual-link backup function using commands but does not configure the IP address of the standby AC. Consequently, the AC does not deliver the dual-link backup configuration to the AP, which makes the AP mistakenly consider that the AC is not enabled with dual-link backup.

• The AC is heavily loaded.
• The priority of the standby AC is configured in the AP view but is lower than that of the other AC.

Procedure

1. Check whether the dual-link backup function is enabled on the active AC.
   • If so, go to step 2.
   • If not, enable the dual-link backup function.

     Run the display wlan ac protect command on the active AC, and check whether the dual-link backup function is enabled. If not, run the ac protect enable command to enable the dual-link backup function.

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

2. Check whether the IP address of the standby AC is configured on the active AC.
   1. Check the configured IP address of the standby AC on the active AC by referring to step 1.
   2. Check the actual IP address of the standby AC.

      Run the display capwap configuration command on the standby AC to check the IP address. If an IP address is configured as the source IP address is an IP address, the IP address is directly displayed. If a VLANIF address is configured as the source interface, the IP address of the VLANIF address is displayed.

      [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
        ------------------------------------------------------------

   3. Check whether the IP addresses in 2.a and 2.b are the same.
      • If so, go to step 3.
      • If not, run the ac protect protect-ac command to change the standby AC's IP address configured on the active AC to the same as the standby AC's IP address.

3. Check the priorities of the active AC and the other AC.
   The specified configuration in the AP system profile takes precedence over the global configuration on the AC.

   1. Check the priority of the active AC.

      Run the display ac protect command to check the AC priority in the WLAN view.

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

   2. Run the display ap-system-profile name profile-name command to check the AC priority in the AP system profile view. The specified configuration in the AP system profile takes precedence over the global configuration on the AC.

      [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 the priority of the other AC.

      Check the priority of the other AC by referring to 3.a and 3.b.

   4. Compare the priority of the active AC with that of the other AC.
      • If the priority of the active AC is higher, go to step 5.
      • If the priority of the other AC is higher, the AP selects the AC with a higher priority to go online.

4. Check the load of the AC when the AP is online, and determine whether the AP selects the correct active AC based on the load.

   The AC that allows more APs to be connected is the active AC. If the two ACs allow the same number of APs to be connected, the AC that allows more STAs to be connected is the active AC. Determine the number of allowed devices based on specifications and the number of online devices.

   Number of allowed APs = Maximum number of access APs – Number of online APs

   Number of allowed STAs = Maximum number of access STAs – Number of online STAs

   1. Check the number of online devices on the active AC.

      Run the display ap all command to check the number of online APs.

      [AC20] display ap all
      Total AP information:
      nor  : normal          [1] 
      --------------------------------------------------------------------------------
      ----------
      ID   MAC            Name   Group     IP            Type            State STA Upt
      ime                                                                             
      --------------------------------------------------------------------------------
      ----------                                                                      
      0    4cf2-bff9-16a0 area_1 ap-group1 10.23.100.254 AP4130DN        nor   1   4D:
      22H:6M:28S 
      --------------------------------------------------------------------------------
      ---------- -

      Run the display access user command to check the number of online STAs.

      [AC20] display access-user 
       ------------------------------------------------------------------------------ 
       UserID Username                IP address       MAC            Status 
       ------------------------------------------------------------------------------ 
       18     88e3abb371ee            10.23.101.254    88e3-abb3-71ee Open 
       ------------------------------------------------------------------------------ 
       Total: 1, printed: 1 

   2. Check the load of the other AC.

      Check the load of the other AC by referring to 4.a.

   3. Compare the load of the active AC and that of the other AC.
      • If the load of the active AC is heavier, go to step 5.
      • If the load of the other AC is heavier, the AP selects the AC with heavier load to go online.

5. Collect the following information and contact technical support personnel.
   • Results of the preceding troubleshooting procedure
   • Configuration file, logs, and alarms of the device