In an active/standby high-availability mode, what causes a standby unit to assume the active role?

Hashed unit ID is used for device identification or election priority in some clustering implementations, but it is not the trigger mechanism that causes a standby unit to assume the active role upon failure.

Management MAC address is an administrative identifier used to reach a device for management purposes and plays no role in active/standby failover triggering.

Resource utilization metrics drive load-balancing decisions in active/active configurations, not the binary failover event in an active/standby pair.

Heartbeat detection works by having the standby unit listen for periodic keepalive packets from the active unit; when the standby stops receiving heartbeats within a configured timeout window, it concludes that the active unit has failed and promotes itself to the active role, ensuring service continuity without manual intervention.