What factor make a device Active and another Standby, and when Active become standby does it become Active again once a network is stable (or anything that make it standby earlier)
This very much depends on your configuration. According to KB:
The BIG-IP system initiates failover according to any of several events that you define. These events fall into these categories:System fail-safe
Thanks for the answer
But i still won't understand how do i make one device as Active.. what config need to be done.