The devices in an HA pair can be assigned a device priority value to indicate a preference for which device should assume the active role and manage traffic upon failover. If you need to use a specific device in the HA pair for actively securing traffic, you must enable the preemptive behavior on both the firewalls and assign a device priority value for each device. The device with the lower numerical value, and therefore higher priority, is designated as active and manages all traffic on the network. The other device is in a passive state, and synchronizes configuration and state information with the active device so that it is ready to transition to an active state should a failure occur.

By default, preemption is disabled on the firewalls and must be enabled on both devices. When enabled, the preemptive behavior allows the firewall with the higher priority (lower numerical value) to resume as active after it recovers from a failure. When preemption occurs, the event is logged in the system logs.