Do I have to preempt both routers

williamsdo · ‎02-11-2008

We have a large enterprise network and our routers and switches are running HRSP. We were told the preempt command should be added to the interface of both the primary and the standby router. We have checked our configuration and notice that the preempt command is only on the primary routers. My question is if we configuer the priorty command to set a primary router and a standby router, does the priorty statement have any control on which router will be the primary after a failuer and recovery? if not when the preempt command is only on the router with the higest priorty will the standby router reinstate control to the primary after a failuer and recovery of the router with the higest priorty?

I am asking this question now so if configuration changes are needed on our network I would like to do them now before any outages. Thank you all for your responses.

Edison Ortiz · ‎02-11-2008

You only need it on the Primary. The Primary is the router usually taking over another current HSRP router. The Secondary only takes over when there isn't another HSRP router in the group, no preempt is needed there.

However, it doesn't hurt having it on both routers and actually is needed when you have 3 HSRP routers in a HSRP group.

HTH,

__

Edison.

Jon Marshall · ‎02-11-2008

Hi

Preempt allows the router with it configured to take over the active role if it has a higher priority than the other router.

So do you need it on both routers. Not necessarily because you may only want the active to be able to preempt. Indeed in many scenarios you only really want the router with the higher priority to preempt.

Where preemption is needed on both routers is if you are decreasing the priority based on an external event eg. you could be tracking an interface on the active router. The active router has a priority of 120 and the standby 110. The tracked interface goes down and the active router decrements it's priority by 20.

But if the standby router does not have preemption it will not take over.

HTH

Jon

williamsdo · ‎02-11-2008

Thank you both for your responses, look like I may have to add the preempt to both the primary and the standby routers. It's better to be safe than sorry or out of a job :-)

DW

aravindhs · ‎02-12-2008

Jon

I can appreciate your comment on this. I was always thinking why 'preempt' is required on the secondary router. But, when I added it the tracking and hence the hsrp started working fine.

Cheers

Arav