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Case Study: VRRP Switchback Fails Due to a Short Recovery Delay of the VRRP Group
Symptom
As shown in the following figure, two ACs work in VRRP HSB mode. After the master AC restarts, the VRRP switchback delay does not take effect.
Relevant Alarms and Logs
None
Cause Analysis
A VRRP status exception occurs due to the VRRP switchover timeout, leading to a switchback exception.
Procedure
- Check whether the VRRP configuration, master/backup status, and HSB status on the master and backup ACs are normal.
- Run the display current-configuration and display vrrp interface vlanif220 commands. It is found that the VRRP configuration is correct and the master/backup status is normal.Master AC:
interface Vlanif220 ip address 10.23.201.3 255.255.255.0 vrrp vrid 1 virtual-ip 10.23.201.1 admin-vrrp vrid 1 vrrp vrid 1 priority 200 vrrp vrid 1 preempt-mode timer delay 1800
Backup AC:interface Vlanif220 ip address 10.23.201.4 255.255.255.0 vrrp vrid 1 virtual-ip 10.23.201.1 admin-vrrp vrid 1 vrrp vrid 1 priority 150
- Run the display hsb-group 0 command. The command output shows that the HSB status is normal.
[AC1] display hsb-group 0 Hot Standby Group Information: ---------------------------------------------------------- HSB-group ID : 0 Vrrp Group ID : 1 Vrrp Interface : Vlanif220 Service Index : 0 Group Vrrp Status : Master Group Status : Active Group Backup Process : Realtime Peer Group Device Name : AC2 Peer Group Software Version : V200R019C00 Group Backup Modules : Access-user DHCP AP ---------------------------------------------------------- [AC2] display hsb-group 0 Hot Standby Group Information: ---------------------------------------------------------- HSB-group ID : 0 Vrrp Group ID : 1 Vrrp Interface : Vlanif220 Service Index : 0 Group Vrrp Status : Backup Group Status : Inactive Group Backup Process : Realtime Peer Group Device Name : AC1 Peer Group Software Version : V200R019C00 Group Backup Modules : Access-user DHCP AP ----------------------------------------------------------
- Run the display current-configuration and display vrrp interface vlanif220 commands. It is found that the VRRP configuration is correct and the master/backup status is normal.
- Restart the master AC to reproduce the fault. Run the display vrrp command. The command output shows an exception of the status switchover
<AC1> display vrrp state-change interface vlanif 220 vrid 1 Time SourceState DestState Reason ----------------------------------------------------------------------------------- 2012-01-27 15:29:45 Backup Master Protocol timer expired 2012-01-27 15:29:42 Initialize Backup Interface UP
- Based on the preceding analysis, it is suspected that a VRRP status exception occurs due to the VRRP switchover timeout, leading to a switchback exception. Run the vrrp recover-delay 60 command to set the recovery delay of the VRRP group to 60s. Then the problem is solved.
Suggestion and Summary
The vrrp recover-delay command is used to set the recovery delay of a VRRP group. By default, the recovery delay of a VRRP group is 0 seconds. When a device in a VRRP group restarts, the VRRP status may flap. It is recommended that the delay be set based on the actual networking.