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Wednesday, July 4, 2012

VRRP active and backup Router behavior

On VRRP it says when you config timer on master then backup router also follows those hello timers. But when we config the advertise  timer on master then both routers R1 and R2 becomes master and they show different timers .Can you please let us know why this happens?

The virtual address in vrrp can be assigned as the physical address of a real interface. In other words, if you have 192.168.7.1 as in R1, then you can assign 192.168.7.1 as the vIP unlike with HSRP where it has to be different. When vrrp is assigned a virtual address that's equal to the real address, that router becomes the master. If the router were to go down, preemption is automatically enabled by default in vrrp and causes the router with the next higher priority to take over. The problem that I think you're seeing is that there's no real ip of 192.168.7.3 being used. In that case, neither of these are really being seen as the master of the group. So because of this, since both priorities are the same, the next check is going to be the highest ip address of the group will become the master. If you want to change this behavior, you can set the priority of the one that you want as the primary to something higher than 100 and it will take over as master after your configured time of 60 seconds.

The timers between the routers in the group need to match. The master is the router that controls the timers, so when you change the timer on the master you can learn the timers on the backup or set the timer to the same interval as the other router. The default is 1 second for advertisement. From what I see, if you change the backups timer, it becomes master. Now with 2 masters, you can't change the other (original master) timer to learn from the original master because it seems that the priority and highest address still comes into play. With the original master, you'd have to send the different timer or change your priority to prefer the other router as master before sending the timer from it. On the other router (whichever backup you want) you would need to either learn (vrrp timers learn) or set your timer manually to the timer that's being sent from the master.


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