The answer is that the session is in a half-open TCP SYN_SENT state, waiting for a SYN-ACK response. This is because protocol 6 indicates TCP, and the proto_state=01 value specifically represents the TCP SYN_SENT phase—the very first step of the three-way handshake where the client has sent a SYN but has not yet received a reply. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this output tests your ability to interpret session diagnostics and recognize abnormal session states; a common trap is assuming a long duration (3600 seconds) means an established session, but the proto_state flag reveals it is stuck in the handshake. Remember the mnemonic: “01 = One-way sent, no reply yet” to quickly decode half-open sessions in the field.
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 admin runs 'diagnose sys session filter dport 443' and then 'diagnose sys session list'. The output shows a session with 'proto=6 proto_state=01 duration=3600 expire=3599'. What does this indicate about the session?
The session is in a half-open state, waiting for SYN-ACK
proto_state=01 corresponds to SYN_SENT. This indicates the client sent a SYN but has not received a SYN-ACK, so the session is stuck in a half-open state.
B
The session is closing with a FIN flag
Why wrong: Closing states would show different values like FIN_WAIT or TIME_WAIT.
C
The session is fully established and transferring data
Why wrong: An established TCP session would have proto_state=02 (ESTABLISHED).
D
The session was blocked by a firewall policy
Why wrong: Blocked sessions would not appear in the session table; they are denied and not tracked.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The session is in a half-open state, waiting for SYN-ACK
Protocol 6 is TCP, proto_state=01 indicates TCP SYN_SENT state (the first step of the three-way handshake). Duration and expire are in seconds. The session has been open for 3600 seconds (1 hour) and will expire in 3599 seconds, which is unusual for a TCP session that should have completed handshake quickly. This suggests the session is stuck in SYN_SENT, likely due to no SYN-ACK response.
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 session is in a half-open state, waiting for SYN-ACK
Why this is correct
proto_state=01 corresponds to SYN_SENT. This indicates the client sent a SYN but has not received a SYN-ACK, so the session is stuck in a half-open state.
Related concept
Read the scenario before looking for a memorised answer.
✗
The session is closing with a FIN flag
Why it's wrong here
Closing states would show different values like FIN_WAIT or TIME_WAIT.
✗
The session is fully established and transferring data
Why it's wrong here
An established TCP session would have proto_state=02 (ESTABLISHED).
✗
The session was blocked by a firewall policy
Why it's wrong here
Blocked sessions would not appear in the session table; they are denied and not tracked.
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.
Trap categories for this question
Command / output trap
Closing states would show different values like FIN_WAIT or TIME_WAIT.
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 is in a half-open state, waiting for SYN-ACK — Protocol 6 is TCP, proto_state=01 indicates TCP SYN_SENT state (the first step of the three-way handshake). Duration and expire are in seconds. The session has been open for 3600 seconds (1 hour) and will expire in 3599 seconds, which is unusual for a TCP session that should have completed handshake quickly. This suggests the session is stuck in SYN_SENT, likely due to no SYN-ACK response.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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