HSRP behaviour if the preempt delay is not finished

[paolo.acquaviva]

Hello all,

I have the following scenario:

-  Two router configured with HSRP in LAN interface.

- HSRP preempt is configured (300 seconds delay).

- The HSRP ex-standby router is active, after a while the HSRP ex-active router goes up.

- Then, the tracked link on HSRP ex-standby router goes down before the preempt delay is finished.

In these conditions, I have the doubt about the HSRP behaviour, I mean, if the HSRP active router waits the preempt delay before takes over or not.

Thank you very much.

Best regards.

Paolo

[Richard Burts]

Paolo

I am not sure that I fully understand your question so I would like to make sure that my understanding is close to what you meant. I think I understand that you have router A that is configured with higher priority to be the active router in HSRP and have router B that is configured with lower priority to be the standby router. I believe that you indicate that router A failed and that router B took over as active router. I believe that router A has returned to service and with higher priority will preempt and take over as active router, after the preempt delay. I believe that you indicate that a tracked interface on router B goes down and the priority of router B is even lower than it was. And the question is whether that has any change in router A and its becoming active.

If my understanding of your question is correct then the answer is that router A will continue to wait until the delay period of 300 is completed before it becomes the active router.

Note that it would be different situation if router B fails and goes out of service. In that case router A immediately becomes the active router. But if router A is going to preempt the currently active router then it will wait for the complete delay period.

I found this article about HSRP preempt delay to be helpful. You might be interested in what it has to say.

http://www.netcraftsmen.net/component/content/article/68-network-infrastructure/1051-hsrp-preempt-delay.html

HTH

Rick

[paolo.acquaviva]

Hello Rick,

Thank you for your quick answer. You get the point.

I have the last doubt. If on router B the LAN interface fails the behaviour is like the case in which the router B goes down. Isn't it?

Best regards.

Paolo

[Richard Burts · Accepted solution]

Paolo

Yes if the LAN interface of router B fails then the HSRP hello messages are not transmitted, just like if the whole router goes down. And when router A realizes that the HSRP hello messages have stopped then it knows that it has lost its HSRP peer and will immediately take over as the HSRP active router.

HTH

Rick

[paolo.acquaviva]

Hello Rick,

Thanks a lot.

Kind Regard.

Paolo

[Richard Burts]

Paolo

I am glad that my explanation was helpful. Thank you for using the rating system to mark this question as answered. It makes the forum more useful when people can read a question and can know that an answer was found. Your marking has contributed to that process.

HTH

Rick