we've implemented together with one of our customers hsrp with tuned timers for "faster-than-default" hsrp convergence.
The hsrp pair consists of two cisco 7600 routers, either equiped with a sup720. Both Routers have the full internet routing table loaded
(they are Provider-Edge routers).
we use following timer settings:
standby 31 timers msec 50 msec 500
Initially everything seems to work fine, but after running this configuration for some time we can see a "state flapping" on the standby
Oct 2 21:10:10.655: %STANDBY-6-STATECHANGE: Vlan351 Group 51 state Standby -> Active
Oct 2 21:10:10.655: %STANDBY-6-STATECHANGE: Vlan357 Group 57 state Standby -> Active
Oct 2 21:10:10.687: %STANDBY-6-STATECHANGE: Vlan357 Group 57 state Active -> Speak
Oct 2 21:10:10.695: %STANDBY-6-STATECHANGE: Vlan351 Group 51 state Active -> Speak
it seems that the standby router doesn't get the hello packet within the holdtime of 500msecs and assumes that the hsrp active is down (and than
change to active). after additional ~300msec (see log output) the former standby again receives a hello from the "true" active router.
(-> the active router never changes its sate to standby)
so for me the standby router doesn't receive hellos from the active router for 800msec (500msecs holdtime + 300msec from the log output). we can
eliminate the possibility that all the hellos within the 800msec are dropped on the cross-link between the c76, because the utilization of this
link is about 5%. for me it seems that the active router doesn't send hsrp hellos for 800msecs.
has anyone experience with tuning hsrp timers? what about our setting with hello 50 / hold 500 msecs? are these timers too aggressive?
i've read in the docu that if the holdtime values is less than 250 milliseconds, a Cisco 7200 platforms or better should be used. As we use a
Cisco 7600, this recommandation is over-fulfilled (?)
i already wrote, these routers have the full internet routing table loaded. can this maybe the problem in our case?
it's very interesting, that our customer has the same hsrp configuration as showed above on other c7600s which doesn't have the full routing
tabel loaded - there is no problem with the state-flapping.
i would be thankful for every advise you give,