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.