Reliability Issues

Fault Symptom

The active and standby ACs have different configurations.

Procedure

1. Check whether configurations excluding the AC priority in the WLAN view are the same on the active and standby ACs.

   Error-prone configuration: If configurations excluding the AC priority in the WLAN view are different on the active and standby ACs, services will become faulty or the AC states will become incorrect after an active/standby switchover.

   Suggestion: Ensure the same WLAN configurations (excluding the AC priority) on the active and standby ACs.

Fault Symptom

In VRRP HSB scenarios, configurations delivered to APs do not take effect.

Procedure

1. Check the VRRP configuration on the master and backup ACs and verify that the VRRP virtual IP address is used as the CAPWAP source address.

   Error-prone configuration: The AC does not use the VRRP virtual IP address as the CAPWAP source address.

   #
   interface Vlanif100
    ip address 10.23.100.1 255.255.255.0
    vrrp vrid 1 virtual-ip 10.23.100.3
    admin-vrrp vrid 1
    vrrp vrid 1 priority 120
    vrrp vrid 1 preempt-mode timer delay 1800
    dhcp select interface
    dhcp server excluded-ip-address 10.23.100.2
   #
   capwap source ip-address 10.23.100.1  //The CAPWAP source address is not set to the same as the VRRP virtual IP address (10.23.100.3).

   Suggestion: In VRRP HSB scenarios, use the VRRP virtual IP address as the CAPWAP source IP address on the ACs.

Fault Symptom

A network fault occurs when multiple backup modes are configured.

Procedure

1. Check whether VRRP and dual-link backup modes are both configured.

   Error-prone configuration: Multiple backup modes are configured on the same AC, causing a network fault.

   [AC] display current-configuration | include vrrp
   [AC] display current-configuration | include ap protect

   Suggestion: It is recommended that only one backup mode be configured and redundant configurations of other backup modes be deleted.

Fault Symptom

HSB is configured incorrectly.

Procedure

1. Check whether HSB is correctly configured for VRRP and dual-link backup.

   Error-prone configuration: HSB is incorrectly configured in HSB scenarios.

   Data backup in HSB scenarios is implemented through the HSB mechanism. When the active device fails, service traffic can be switched to the standby device only if the standby AC has the same session entries as the active device. Otherwise, a session interruption will occur. The active and standby devices use the HSB mechanism to ensure the consistency of session entries.

   HSB provides two types of public services: HSB service and HSB group, which need to be bound in different HSB scenarios:

   • For VRRP HSB, the HSB group needs to be bound.
   • For dual-link HSB, the HSB service needs be bound.

   Suggestion: Configure HSB correctly as required.

Fault Symptom

A revertive switchover error occurs due to incorrect active/standby parameter settings.

Procedure

1. Check the recovery delay time of the VRRP group on the master and backup ACs.

   Error-prone configuration: The recovery delay of the VRRP group is improperly configured.

   When an interface or a BFD session associated with a VRRP group alternates between Up and Down states, the VRRP group status may flap, causing user traffic loss. To solve this problem, set a delay before a VRRP group recovers. A VRRP group then responds to the interface or BFD session Up event only after the delay expires.

   [AC] display current-configuration | include recover
   vrrp recover-delay 30

   Suggestion: Set the VRRP group recovery delay to 60 seconds on the master and backup ACs.

2. Check the VRRP preemption delay on the master and backup ACs.

   Error-prone configuration: If the backup in a VRRP group does not receive VRRP Advertisement packets from the master within a specified period of time, the backup becomes the master. On an unstable network, even if the master is working properly, the backup may not receive packets from the master because of network congestion. In this case, the VRRP group status flaps, causing traffic loss. You are advised to set the preemption delay of the backup in a VRRP group to 0, configure the master in preemption mode, and set the preemption delay to be longer than 1800s. These settings allow a period of time for status synchronization between the uplink and downlink on devices in a VRRP group on an unstable network. If the preceding settings are not used, two masters may coexist and user devices may learn an incorrect master address, interrupting traffic.

   #
   interface Vlanif100
    ip address 10.23.100.1 255.255.255.0
    vrrp vrid 1 virtual-ip 10.23.100.3
    admin-vrrp vrid 1
    vrrp vrid 1 priority 120
    vrrp vrid 1 preempt-mode timer delay 1800
    dhcp select interface
    dhcp server excluded-ip-address 10.23.100.2
   #

   Suggestion: Set the preemption delay of the master and backup ACs to 1800s.