Topology is as attachment. S9306-A is VRRP master device, VRRP PRI is 110，configure preemption delay as 30s；9306-B is VRRP backup device，PRI keeps as default 100，it does not configure preemption delay. C4948 pure layer 2，S9306 VRRP heartbeat run in C4948 line link. Take the master device power off, the backup device can replace in 3s, connecting PC ping external network，there is only one lost the packet；when reboot 9306-A，there are 8 packet lost.
Take the VRRP master device reboot, VRRP return cutting speed is slow.
1. Enhance VRRP preemption delay time continually, enhance from 30s to 90s, the failure remains.
2. Check S9306 log, there are the related content with VRRP in the process of device start:
Sep 17 2010 17:38:09 JZ-DST-QS9306-1 %%01IFNET/4/LINKNO_STATE(l): The line protocol on the interface Vlanif150 has entered the UP state.
Sep 17 2010 17:38:09 JZ-DST-QS9306-1 %%01VRRP/4/STATEWARNING(l): Virtual Router state INITIALIZE changed to BACKUP, because of interface UP. (Interface=Vlanif150, VrId=11)
Sep 17 2010 17:38:14 JZ-DST-QS9306-1 %%01VRRP/4/STATEWARNING(l): Virtual Router state BACKUP changed to MASTER, because of protocol timer expired. (Interface=Vlanif150, VrId=11)
Sep 17 2010 17:38:44 JZ-DST-QS9306-1 %%01VRRP/4/STATEWARNING(l): Virtual Router state BACKUP changed to MASTER, because of priority calculation. (Interface=Vlanif150, VrId=11)
3. Device became the VRRP master device after it set the VLANIF UP, the period is 5s, preemption delay has not effect. 30s later, device calculated the PRI again, take it as VRRP master device continually.
4. The device VRRP module did not receive VRRP packet forwarded through C4948 by backup device in 30s, device became the master because time delay, preemption delay did not work, it works normally only when the devcice receive the same VRRP team protocol packet and compare the PRI.
5. Downstream C4948 switch did not forward VRRP packet in 30s, the reason is peer vendor switch all the ports default enable spanning tree protocol, after S9306-A closed, C4948 device interface down, the interface will access to forwarding state only when spanning tree protocol convergenced after the interface be UP. So the S9306 device cannot receive VRRP packet in the interface up time 30s, the preemption delay did not effect.
6. The physic topology did not exist loop, so close the spanning tree protocol of C4948, VRRP becomes normal, it debars the failure.
Check the state of VRRP, master device has been preemption, ISIS and BGP of S9306 did not convergence completely. It leaded VRRP master device is on S9306-A， but there is no route through external network, cause the packet lost, put up the slow speed of return cutting.it judged that VRRP preemption delay of VRRP master device did not work normally.