The answer is to enable session synchronization between cluster members. In an active-passive FortiGate HA deployment, the passive unit maintains no awareness of existing TCP sessions unless session synchronization is explicitly configured via `config system ha session-sync`. Without this, after a failover the new active unit has no session state information, causing established TCP sessions to be dropped as if the connection never existed. On the Fortinet NSE 4 Network Security Professional exam, this scenario tests your understanding of HA session persistence versus device-level failover—a common trap is assuming that HA alone preserves sessions, when in fact session synchronization is a separate, required setting. Remember the key distinction: HA handles device redundancy, but session synchronization handles stateful session continuity. A useful memory tip is “sync or sink”—without session sync, your TCP sessions sink after failover.
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A company is deploying a FortiGate HA cluster in active-passive mode across two data centers. The network team reports that after a failover, some existing TCP sessions are dropped. Which configuration change should be applied to maintain session persistence during failover?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable session synchronization between cluster members
In an active-passive HA cluster, session synchronization (config.sys ha session-sync) ensures that TCP session state information is replicated from the active unit to the passive unit. Without this, the passive unit has no knowledge of existing sessions after a failover, causing them to be dropped. Enabling session synchronization allows the new active unit to continue forwarding traffic for established sessions seamlessly.
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.
✓
Enable session synchronization between cluster members
Why this is correct
Session sync shares session state between primary and secondary, maintaining sessions during failover.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable NAT inspection on the firewall policy
Why it's wrong here
Disabling NAT inspection is unrelated to session persistence.
✗
Configure gratuitous ARP on the virtual IP
Why it's wrong here
Gratuitous ARP updates MAC tables but does not preserve sessions.
✗
Increase the heartbeat interval to 2 seconds
Why it's wrong here
Increasing heartbeat interval may delay failover detection, not preserve sessions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse gratuitous ARP (which handles Layer 2 updates) with session persistence, assuming that updating MAC tables is sufficient to maintain TCP sessions, but session state must be replicated at Layer 4.
Detailed technical explanation
How to think about this question
Session synchronization in FortiGate HA uses a dedicated heartbeat interface (or a separate sync interface) to replicate session table entries via UDP port 703. The synchronization includes TCP sequence numbers, window sizes, and state (e.g., ESTABLISHED, FIN_WAIT). In real-world scenarios, without session sync, even a brief failover can cause critical applications like database connections or VoIP calls to reset, leading to user-visible outages.
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.
TExam Day Tips
→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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Enable session synchronization between cluster members — In an active-passive HA cluster, session synchronization (config.sys ha session-sync) ensures that TCP session state information is replicated from the active unit to the passive unit. Without this, the passive unit has no knowledge of existing sessions after a failover, causing them to be dropped. Enabling session synchronization allows the new active unit to continue forwarding traffic for established sessions seamlessly.
What should I do if I get this NSE4 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator configures two FortiGate units in an active-passive HA cluster. After a failover, some existing TCP sessions are dropped. What is the most likely reason for this behavior?
medium
✓ A.Session synchronization is not enabled
B.The failover time is too slow
C.The FortiGate units are running different firmware versions
D.The HA cluster is using a virtual MAC address
Why A: In an active-passive HA cluster, session synchronization must be explicitly enabled to replicate TCP session state from the primary unit to the backup unit. Without session sync, the backup unit has no knowledge of existing TCP sessions after a failover, causing those sessions to be dropped because the new primary cannot match incoming packets to any session table entry.
Variation 2. An administrator configures an HA cluster of two FortiGates in active-passive mode. The cluster is synchronized, but after a failover, some existing TCP sessions are dropped. What is the most likely cause?
hard
A.The heartbeat interface is configured as a dedicated management interface
✓ B.Session synchronization (session-pickup) is disabled
C.The cluster is operating in NAT mode
D.The cluster is using a virtual MAC address for the HA interface
Why B: Session synchronization (session-pickup) is required for active-passive HA clusters to replicate TCP session state from the primary FortiGate to the secondary. When disabled, the backup unit has no knowledge of existing sessions after a failover, causing those sessions to be dropped because the new primary cannot match incoming packets to any session table entry.
Last reviewed: Jun 11, 2026
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This NSE4 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE4 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.