Fault Symptom
Router A and Router B are connected with a switch through Eth-Trunk sub-interfaces. VRRP is run on the Eth-Trunk sub-interfaces. The VRRP status of Router B is Master and the VRRP status of Router A is Backup. VRRP adopts the non-preemption mode.
After the configuration, it is found that the backup device preempts to be the master device. After Router B is restarted or the shutdown and undo shutdown commands are run on the Eth-Trunk sub-interface of Router B, the backup device still preempts to be the master device.
Fault Analysis
1. Check the log information on Router B.
a. After Router B is restarted or the interface connecting Router B to the switch is shut down, VRRP enters the Init state.
VRRP/4/STATEWARNING(l): Virtual Router state CREATED changed to INITIALIZE, because of create INITIALIZE. (Interface=Eth-Trunk11.200, VrId=200)
b. After the interface connecting Router B to the switch goes Up, VRRP enters the Backup state.
VRRP/4/STATEWARNING(l): Virtual Router state INITIALIZE changed to BACKUP, because of interface UP. (Interface=Eth-Trunk11.200, VrId=200)
c. After the VRRP timer times out, VRRP enters the Master state.
VRRP/4/STATEWARNING(l): Virtual Router state BACKUP changed to MASTER, because of protocol timer expired. (Interface=Eth-Trunk11.200, VrId=200)
2. The preceding information shows that VRRP preemption does not occur. Because Router B does not receive any VRRP packet from the Router A , after the VRRP timer times out, Router B considers that there is no master on the network, and thus enters the master state.
3. Check the information about Router A and the switch. You can find that Router A sends VRRP packets but the switch does not forward the VRRP packets to Router B. View the log information of the switch. You can find that the interface connecting the switch to Router B is not in the Forwarding time during the timeout period of the VRRP timer and thus discards the packets.
As defined in STP, after the interface becomes Up, the interface enters the Forwarding state after 50s. As a result, the VRRP packets are discarded, and it is shown that Router B preempts to be the Master device.
Procedure
1. Adjust the STP parameters of the switch so that the interface connecting the switch to Router B can immediately enter the Forwarding after going Up.
After the preceding operations, the backup device does not preempt to be the master device. Thus, the fault is rectified.
Summary
VRRP has the following modes:
· Preemption mode: In this mode, if the backup device receives a VRRP packet carrying a priority lower than the priority of the backup device, the backup device preempts to be the master device.
· Non-preemption mode: In this mode, the backup device does not preempt to be the master device.
The non-preemption mode, however, does not mean that the backup device does not become the master device. After the link between router B and the switch goes Down or Up, the interface connecting the switch to router B does not enter the Forwarding state immediately. As a result, VRRP packets are not forwarded in time. Consequently, the VRRP timer times out, VRRP master/slave switchover occurs, and there are two master devices on the network.
Therefore, when deploying VRRP, fully consider the network environment.
