Keepalived configuration for VRRP

Question

I am trying to understand if there is a relation between garp_master_delay and advert_int. In all the configurations I saw, advert_int was less than garp_master_delay.

• Is there any reason for this?
• Are those independent of each other or is there any ordering requirement between the two?

VRRP RFC does not seem to mention anything on this.

Solution

They aren't really related, per se - the advert_int controls the interval between advertisements in normal operation, whereas the garp_master_delay controls how long after taking master state a node should sent gratuitous ARP (to notify devices that it now controls those IPs at a new MAC address to override their ARP caches). You'd tune the two for different reasons.

Comments

[Abhishek Chanda]

Thanks for the explanation. Shouldn't it make more sense for garp_master_delay to be 1s or less? That way all devices will know about the master sooner. Why does it default to 5s, which looks like a larger value?

[ravi yarlagadda]

@AbhishekChanda My guess is the rather conservative default is for compatibility reasons. In a case where you're failing back and forth rapidly (usually due to communication problems between the VRRP nodes) you don't want both nodes spewing GARP constantly - I've seen network devices start completely ignoring ARP from an offending IP address in those kinds of cases.

[Clint]

This exact thing happened to us. Primary failed, secondary took over, primary came back up really quickly and we had conflicting arp tables everywhere. It took a few minutes to diagnose which sucked...