Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

HSRP standby preempt delay

What would be a recommended value given STP connection delays and using ospf?

3 REPLIES

Re: HSRP standby preempt delay

Bear in mind this is a general rule and there are exceptions to all - based on the particular design.

Given the fact HSRP failover has occurred, an interface/router will have gone down. As a result, I want the failover to the other HSRP peer to be as quick as possible (ie make the delay as low as possible). HSRP failover will by default be about 10 seconds (after 3 missed hellos), enough time for OSPF to have done it's reconvergence. OSPF probably will have reconverged before HSRP anyway, so you don't want to slow things down any more (i.e. if it's just an interface down on the active HSRP, then the active router will still receive the OSPF routes from the standby and forward the packets over to the standby and out to the destination before the HSRP fails over - I have had production environments failover in about 6 seconds).

As for STP, that can take anywhere from 20 to 50 seconds, so I hope that most networks are relying on L3 protocols for failover, and not L2 STP in the core/distribution layers. If it is STP failover, then serious consideration should be given on how to change. STP blocks should be local, small as possible, in most cases. Depends on the design and nature of the failure, the active HSRP router could forward traffic over to the peer HSRP, so again, I want it ready as soon as possible, certainly before STP reconverges.

Hope that helps.

Steve

Community Member

Re: HSRP standby preempt delay

What you describe covers when a HSRP active unit fails. What I am looking for is when the that failed unit recovers after a reload. What would be a recommended preempt delay value be to cover STP & ospf convergance.

Re: HSRP standby preempt delay

Again, it will take HSRP longer to fail back over than it will OSPF. HSRP will have to go through it's states (listen, speak etc) before it fails back over, OSPF will be quicker (based on my experience with OSPF and EIGRP).

Steve

1238
Views
2
Helpful
3
Replies
CreatePlease to create content