This value reports how often, in milliseconds, the router sends VRRP heartbeat advertisements when the faster, sub-second Fast VRRP mode is active in place of the standard once-per-second timer. Network admins read it to gauge how quickly a VRRP backup router will notice a failed master and take over forwarding for the shared virtual IP. For example, a reported value of 30 would mean advertisements go out every 30 milliseconds, letting a backup cut over in well under a second instead of the several seconds standard VRRP would take.