The answer is that session synchronization is not enabled between cluster members. In an active-active asymmetric routing scenario, each FortiGate in the HA cluster may handle only one direction of a traffic flow—for example, one unit processes the client-to-server request while a different unit sees the server-to-client response. Without session synchronization, the unit receiving the response has no matching session entry and therefore drops the packet, even though the original forward packet was allowed by policy. This concept is central to the Fortinet NSE 4 Network Security Professional exam, where you must understand how strict session pickup and session sync work together to maintain stateful inspection across cluster members. A common trap is assuming that active-active HA inherently shares session state—it does not unless explicitly configured. Memory tip: “One-way traffic, two-way drop—sync your sessions or the response will stop.”
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 FortiGate in an active-active HA cluster is experiencing asymmetric routing. The administrator runs 'diagnose debug flow' on a packet from a client to a server. The flow trace shows the packet is allowed by policy, but the response is dropped. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The session synchronization is not enabled between cluster members
In active-active HA, asymmetric routing can cause session state issues because each unit may see only one direction of traffic. Without session synchronization and strict session pickup, the unit receiving the response may not have the session and drops it.
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 TTL of the packet is too low
Why it's wrong here
TTL issues would affect both directions, not just the response.
✗
The HA mode should be changed to active-passive
Why it's wrong here
Changing mode may help but the root cause is lack of session sync; active-active can work with proper configuration.
✗
The policy on the secondary unit has a different schedule
Why it's wrong here
Policy differences could cause issues, but asymmetric routing typically points to session synchronization problems.
✓
The session synchronization is not enabled between cluster members
Why this is correct
Session sync ensures all cluster members share session state, preventing drops due to asymmetric routing.
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.
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.
High Availability and Diagnostics — This question tests High Availability and Diagnostics — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The session synchronization is not enabled between cluster members — In active-active HA, asymmetric routing can cause session state issues because each unit may see only one direction of traffic. Without session synchronization and strict session pickup, the unit receiving the response may not have the session and drops it.
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.
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. In an active-active HA cluster, the administrator notices that traffic is not being load-balanced evenly across both units. What is the most likely cause?
medium
✓ A.The load balance method is set to 'none'
B.The heartbeat interface speed is mismatched
C.The load balance method is set to 'source-ip' which naturally causes imbalance
D.The cluster is using active-passive mode
Why A: In active-active HA, load balancing requires a load-balance method (like source IP hash or round-robin). Without a proper method, traffic may not distribute evenly.
Variation 2. A FortiGate HA cluster is set to active-active mode. The administrator notices that session synchronization is enabled but some sessions are not being synced between cluster units. Which of the following is a likely cause for incomplete session synchronization in active-active mode?
medium
A.The cluster is using unicast heartbeat
✓ B.The 'set session-sync-id' is not configured or mismatched between cluster units
C.The heartbeat interface speed is set to 1 Gbps
D.The HA override is enabled
Why B: Option A is correct. In active-active HA, session synchronization must be set to 'all' or 'group' to sync sessions; the default may only sync specific sessions. The 'session-sync-id' must match on all units.
Variation 3. In an active-active HA cluster, which of the following must be identical on both FortiGate units?
easy
A.HA priority
B.Management IP address
✓ C.Virtual cluster ID
D.Hostname
Why C: In an active-active HA cluster, the virtual cluster ID must be identical on both FortiGate units because it defines the cluster group and ensures that only units with the same ID can form an HA cluster. This ID is used in heartbeat packets to verify cluster membership and prevent accidental merging of separate clusters. Without a matching virtual cluster ID, the units will not recognize each other as part of the same HA group.
Variation 4. A company has two FortiGate units in an active-active HA cluster. They want to ensure that sessions initiated from the internet through a virtual IP are synchronized to the peer unit in case of failover. Which HA setting is required?
medium
A.Enable 'set ha-mgmt-status enable' on the WAN interface
B.Set 'set schedule' to 'round-robin' for the VIP
C.Configure the same virtual IP on both units
✓ D.Enable 'session-pickup' under config system ha
Why D: In active-active HA, session synchronization is enabled by default for TCP sessions, but for UDP and other protocols, session sync needs to be explicitly enabled. However, the question is about ensuring sessions are synchronized. The key setting is 'session-pickup' which enables session synchronization for all protocols. Also, for active-active, 'session-pickup-connectionless' should be enabled for UDP and ICMP. But the most direct answer is to enable session-pickup globally.
Variation 5. In an active-active HA cluster, what is the purpose of the 'session sync' configuration?
hard
A.To synchronize configuration changes between cluster members
B.To balance the number of sessions across cluster members
✓ C.To replicate session state so that if one unit fails, another can take over without interruption
D.To synchronize the time between cluster members
Why C: Session sync ensures that sessions are shared between cluster units so that any unit can handle traffic for a given session.
Variation 6. In an active-active HA cluster, session synchronization is configured. A new session is created on the primary unit. When does the secondary unit learn about this session?
hard
A.During the next heartbeat interval
B.After the session is closed
✓ C.Within a few milliseconds to seconds after creation
D.Immediately upon session creation
Why C: In active-active HA with session sync, sessions are synchronized periodically (every few seconds) or immediately depending on configuration. By default, sessions are synced every 200ms or when the session changes state.
Last reviewed: Jun 21, 2026
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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.
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