Monday, December 24, 2012

HSRP Preemption On Standby Router - Required Or Not ?

Often I ask this question to CCNPs during interviews - "Do we require PREEMPT command on HSRP Standby router or not ? "

And often candidates either reply "NO" or looks Struggling.

Although Short answer is "YES". But here is the detailed explanation using a test bed.

For those which are new to HSRP. I would recommend first read following posts from Gr8 CCNP Intructor Chris Bryant, CCIE#12933


http://www.thebryantadvantage.com/CCNPCertificationBCMSNExamHSRPInterfaceTracking.htm

http://www.thebryantadvantage.com/CCNPCertificationExamBCMSNHSRPPriorityActive.htm

http://www.thebryantadvantage.com/CCNPCertificationBCMSNExamHSRPMACAddress.htm


Now lets get started with topology details later followed by Detailed Explanation using Test Bed:




















Further Readings:




 
HTH...
Deepak Arora
EVIL CCIE



2 comments:

Anonymous said...

The answer can be No if there is no track object condition on the primary router.

In reality, campus network there is not object track on the primary distribution router as it normally has local ethernet connection to the core. It's more likely the whole primary route goes down rather than an uplink fibre/cable cut and between the two distribution routers there are direct layer2 connections.

You can say Yes in Lab but Say No is not incorrect either.

Anonymous said...

I agree that the test bed is not that explainatory. I would say that preemption is required because :

1 - You want that your network works as you have designed it and as it has been documented.
2 - It is easier to monitor and operate : if Router2 is handling traffic, then you know your network is in trouble
3 - If you change the design (add a core layer for instance), it is far easier if the behaviour of the existing network is deterministic.