NSE4 Failover threshold Practice Question
A FortiGate administrator notices that the HA cluster is frequently failing over even though no hardware failure has occurred. The heartbeat link shows some packet loss. What is the best action to reduce unnecessary failovers?
⚠ Common exam trap
NSE4 often tests the misconception that lowering the heartbeat interval improves HA responsiveness, but it actually increases sensitivity to packet loss and can cause more failovers.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the failover threshold
The failover threshold (also called heartbeat loss threshold) determines how many consecutive heartbeat packets must be missed before a failover is triggered. By increasing this threshold, the FortiGate will tolerate more packet loss on the heartbeat link before declaring a failure, thus reducing unnecessary failovers caused by transient network issues. This directly addresses the root cause: intermittent packet loss on the heartbeat link. Lowering the interval would make the problem worse, and changing HA mode or disabling session sync does not affect failover sensitivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Lower the heartbeat interval
Why it's wrong here
Lowering the heartbeat interval makes the HA members send heartbeat packets more often, which shortens the time over which consecutive missed heartbeats are counted. During any transient network congestion or burst loss on the HA link, a brief interruption will be interpreted as a failed primary, causing the cluster to initiate an unnecessary failover. This action increases failover sensitivity and actually raises the frequency of failovers instead of reducing it, so it is incorrect.
- ✗
Change HA mode to active-active
Why it's wrong here
Switching the HA mode to active-active does not alter how the HA heartbeat is transmitted or how the failover decision is made; the heartbeat timer and missed-heartbeat threshold remain unchanged. Active-active merely changes the traffic-processing behavior by allowing both units to handle data plane traffic simultaneously, which adds complexity like session ownership negotiation. Since the root cause of frequent failovers is heartbeat sensitivity, active-active does not address that root cause and therefore will not resolve the problem.
- ✓
Increase the failover threshold
Why this is correct
The failover threshold (often called the missed-heartbeat threshold) specifies how many consecutive heartbeat packets from the primary must be lost before the secondary unit declares a failover. Increasing this threshold from the default of 3 to a larger value allows the cluster to tolerate small bursts of packet loss or a momentary HA link issue without triggering a failover. This directly reduces spurious failovers while still detecting a true primary outage if the primary remains silent for a longer period, making it the correct corrective action.
- ✗
Disable session synchronization
Why it's wrong here
Disabling session synchronization stops the replication of the session table from the primary to the standby unit, so if a failover does occur, all existing TCP and UDP sessions will be dropped. This setting has no effect on the HA heartbeat process or the failover timer, and therefore it does not reduce the frequency of failovers at all. In fact, it makes each failover more disruptive because established user connections cannot be gracefully preserved, so it is not a valid solution.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Fortinet exam blueprint
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