Interface Monitoring

When a unit does not receive hello messages on a monitored interface for 15 seconds, it runs interface tests. If one of the interface tests fails for an interface, but this same interface on the other unit continues to successfully pass traffic, then the interface is considered to be failed, and the device stops running tests.

If the threshold you define for the number of failed interfaces is met (see Devices > Device Management > High Availability > Failover Trigger Criteria), and the active unit has more failed interfaces than the standby unit, then a failover occurs. If an interface fails on both units, then both interfaces go into the “Unknown” state and do not count towards the failover limit defined by failover interface policy.

An interface becomes operational again if it receives any traffic. A failed device returns to standby mode if the interface failure threshold is no longer met.

If an interface has IPv4 and IPv6 addresses configured on it, the device uses the IPv4 addresses to perform the health monitoring. If an interface has only IPv6 addresses configured on it, then the device uses IPv6 neighbor discovery instead of ARP to perform the health monitoring tests. For the broadcast ping test, the device uses the IPv6 all nodes address (FE02::1).