The correct answer is A . In a FortiNAC-F 1+1 HA deployment, failover from primary to secondary is automatic, but failback to the primary is not automatic . The study guide states that if the primary device or its network connectivity fails, the secondary assumes control automatically, but restoration of a failed-over HA deployment is a manual administrator-driven process. It further explains that after the cause of the failover is resolved, the administrator must use the Resume Control button to transfer control back to the primary server.
That means when the primary comes back online, it does not immediately take over again. The pair can resume HA communication, but the secondary remains the in-control node until an administrator deliberately returns control to the primary. Option B is wrong because FortiNAC-F 1+1 HA is active-passive, not load- balanced. Option C is wrong because the restored primary does not power itself down for maintenance.
Option D is a trap: five failed heartbeats are used in failure detection and gateway validation logic, not as an automatic failback timer. The exam point is simple: automatic failover, manual failback .