ZyXEL Communications VPN Series Handbook page 740

Device HA Pro License
The Device HA Pro feature is license required. You must register both of your devices
on the myZyXEL.com server first. Then make sure the Device HA Pro license is available
on both of your devices.
Behavior of the Device HA Pro
The behavior of the Device HA Pro includes a heartbeat link to monitor the
"activate" device's interface status. If one of the monitored interfaces is dead or
fails, the "passive" device's status will become "activate". (This means only 1
device's status can be "activate" at a time.)
Be aware that the Device HA status of the devices might constantly change due
to the network environment situation. In the current firmware design, Device HA
Pro will not fallback when the primary device interface is working normally again.
Device-HA Pro Setting Screen
A. Enable configuration provisioning on the activated device
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