[c-nsp] HSRP failover/failback question

[Robert Williams]

Hi,

The 'preempt delay' element means that it won't go active for xxx seconds _if_ there is a lower priority instance already visible. However - if the other instance is _not_ visible, then it goes active immediately.

In your case, I suspect there was a layer-2 adjacency issue (maybe an STP re-convergence) which meant that it couldn't see the hellos from the other (now active) unit and thus there was a double-active scenario. Then, after STP had converged your secondary unit saw higher priority (and active) hellos and thus immediately went into the backup role again. Leaving your primary unit to blackhole until it re-converged it's IGP.

The resolution will depend on the rest of your infrastructure between the two units, maybe tune STP timers to be quicker than HSRP initial failures.

Also, there is a keyword for 'reload' delay under preempt, which is separate to the one you are using, which maybe will also apply during a failover event?

(config-if)#standby 0 preempt delay reload ?
  <0-3600>  Number of seconds for reload delay

Hope that helps!



Robert Williams
Custodian Data Centre
Email: Robert at CustodianDC.com
http://www.CustodianDC.com

-----Original Message-----
From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Randy
Sent: 01 August 2014 21:16
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] HSRP failover/failback question

I've got an HSRP setup between two 6500's.   Today the primary active
router's sup took a dump and failed over to the standby.   The blip
caused the standby router to take over the HSRP gateway on each VLAN as
expected.   However once the failover was complete on the primary router
it *immediately* took over the GW's again.   And of course, before it
had a full routing table so there was several minutes of blackholing.
I thought we'd be protected from this with the following config, but I
guess not:

PRIMARY ROUTER VLAN X:
  standby version 2
  standby 0 ip x.x.x.x
  standby 0 priority 150
  standby 0 preempt delay minimum 600

SECONDARY ROUTER VLAN X:
  standby version 2
  standby 0 ip x.x.x.x
  standby 0 preempt delay minimum 600

What am I missing?

Thanks!

~Randy



_______________________________________________
cisco-nsp mailing list  cisco-nsp at puck.nether.net
https://puck.nether.net/mailman/listinfo/cisco-nsp
archive at http://puck.nether.net/pipermail/cisco-nsp/