This read-write value sets, in seconds, how long the backed-up router has to signal before it's considered inoperational and this interface begins operating as its backup. An admin tunes this to control how quickly a failover triggers after the main router stops responding, balancing responsiveness against false positives from brief network blips. For example, setting this to 15 means three missed polls at a five-second poll interval would need to elapse before failover to backup mode occurs.