The answer is NPU offloading enabled on the primary FortiGate. This is the most likely cause because when NPU offloading is active, the network processor handles session establishment and forwarding directly in hardware, bypassing the CPU. Since session synchronization for HA failover relies on the CPU to capture and transmit session state to the backup unit, any session that was offloaded to the NPU may never be logged in the session table for sync, causing those TCP connections to drop after a failover. On the Fortinet NSE 4 Network Security Professional exam, this question tests your understanding of the interaction between hardware acceleration and HA session synchronization—a common trap is assuming heartbeat or sync settings are misconfigured when the real issue is that offloaded sessions are invisible to the sync process. Remember the memory tip: “If the NPU holds the session, the backup gets no impression.”
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are troubleshooting a FortiGate HA cluster (active-passive) and notice that after a failover, some existing TCP sessions are not being maintained. The hbdev heartbeat interfaces are configured correctly, and session synchronization is enabled. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Why wrong: Maintenance mode prevents the backup from taking over; it would not cause session loss during failover.
B
NPU offloading is enabled on the primary FortiGate
NPU offloading can cause sessions to be offloaded to hardware and not fully synced to the backup unit. Disabling NPU offloading ensures all sessions are synced.
C
The HA uptime monitor is not configured
Why wrong: HA uptime monitor affects failover triggers but not session sync.
D
Session pickup is not enabled in the HA configuration
Why wrong: Session pickup is not a separate setting; session synchronization is what maintains sessions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
NPU offloading is enabled on the primary FortiGate
In FortiGate HA, session synchronization relies on NPU offloaded sessions being re-synced. If the NPU offloading was enabled on the primary, sessions might not be fully synced to the backup. Disabling NPU offloading on the primary ensures all sessions are handled by the CPU and thus properly synced.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The secondary unit is in maintenance mode
Why it's wrong here
Maintenance mode prevents the backup from taking over; it would not cause session loss during failover.
✓
NPU offloading is enabled on the primary FortiGate
Why this is correct
NPU offloading can cause sessions to be offloaded to hardware and not fully synced to the backup unit. Disabling NPU offloading ensures all sessions are synced.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The HA uptime monitor is not configured
Why it's wrong here
HA uptime monitor affects failover triggers but not session sync.
✗
Session pickup is not enabled in the HA configuration
Why it's wrong here
Session pickup is not a separate setting; session synchronization is what maintains sessions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the NSE4 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: NPU offloading is enabled on the primary FortiGate — In FortiGate HA, session synchronization relies on NPU offloaded sessions being re-synced. If the NPU offloading was enabled on the primary, sessions might not be fully synced to the backup. Disabling NPU offloading on the primary ensures all sessions are handled by the CPU and thus properly synced.
What should I do if I get this NSE4 question wrong?
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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