HSRP state machine

Raptien

Understanding and Troubleshooting HSRP Problems in Catalyst Switch Networks - Cisco Systems




On this diagram there is a transition from listen directly to active. The code references an event where a router in the listen state receives a lower priority hello from the active router, and subsequently enters active state itself by sending a coup message etc.

But the router in the standby state also does the same thing, so how would this work without a disagreement on which router is active?

stuh84

Raptien wrote: »

On this diagram there is a transition from listen directly to active. The code references an event where a router in the listen state receives a lower priority hello from the active router, and subsequently enters active state itself by sending a coup message etc.

But the router in the standby state also does the same thing, so how would this work without a disagreement on which router is active?

You've kinda answered your own question. Given that you should be setting priorities, one that comes in with a lower priority will be usurped, whereas one with a higher priority won't be.

So if you had say 3 routers, one with a priority 200, one with a priority 150, and another with priority 120, and the one with a priority 200 has just dropped to 100 (say, a tracking statement or something), then the one with priority 150 picks up as it hears a lower priority hello. The one with a priority 120 doesn't, as it hears the lower priority hello from the first router, but a higher priority from the second router.

That diagram seems a bit....like its missing something, as it only really says the states that something goes through, it doesn't seem complete in the messages that are exchanged. Put it this way, I've never seen a standby router take over from something of higher priority from itself in normal operation.