The answer is that the session is still being established and has not completed the TCP three-way handshake. This is because `proto_state=01` in a FortiGate session table indicates the TCP SYN-SENT state, meaning the initial SYN packet has been sent out but the corresponding SYN-ACK reply has not yet been received, leaving the handshake incomplete. On the Fortinet NSE 4 Network Security Professional exam, this output from `diagnose sys session` tests your ability to read session states and understand TCP connection phases, often appearing as a distractor where candidates mistakenly think `proto_state=01` means an established or closing session. A common trap is confusing `01` with a normal established state, but remember that established TCP sessions show `proto_state=10` (ESTABLISHED), not `01`. For a quick memory tip, think of `01` as the "one-way" state—only the first SYN has traveled, so the connection is still in limbo.
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. 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.
An administrator runs 'diagnose sys session filter dport 443' and sees the following output:
proto=6 proto_state=01 duration=3600 expire=3599
What does this indicate about the session?
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 the process of being established and has not completed the TCP three-way handshake
The output shows `proto=6` (TCP), `proto_state=01`, `duration=3600`, and `expire=3599`. In FortiGate session diagnostics, `proto_state=01` for TCP indicates the session is in the SYN-SENT state, meaning the initial SYN packet has been sent but the three-way handshake (SYN-ACK) has not yet been received. The session has been active for 3600 seconds but has not yet completed establishment, which is why the correct answer is A.
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 the process of being established and has not completed the TCP three-way handshake
Why this is correct
proto_state=01 means the first SYN has been sent but no SYN-ACK received, indicating the handshake is incomplete.
Related concept
Read the scenario before looking for a memorised answer.
✗
The session is a UDP session because the proto_state is 01
The session has been closed and is being removed from the session table
Why it's wrong here
A closing session would have a different state, not SYN_SENT.
✗
The session is fully established and has been active for 3600 seconds
Why it's wrong here
proto_state=01 indicates SYN_SENT, not established (which would be 02 or higher).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see `duration=3600` and assume the session is fully established and active, but they overlook that `proto_state=01` indicates the TCP handshake is incomplete, not an established connection.
Detailed technical explanation
How to think about this question
In FortiGate's session table, `proto_state` values for TCP correspond to the TCP state machine: 01=SYN-SENT, 02=ESTABLISHED, 03=FIN-WAIT-1, etc. The `duration` field shows how long the session has existed, while `expire` is the remaining time before timeout. A session stuck in SYN-SENT for 3600 seconds indicates a potential issue like asymmetric routing or a firewall dropping the SYN-ACK, which can cause session table exhaustion if not cleared. This diagnostic command (`diagnose sys session filter dport 443`) is commonly used to troubleshoot HTTPS connectivity issues.
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 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — 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 the process of being established and has not completed the TCP three-way handshake — The output shows `proto=6` (TCP), `proto_state=01`, `duration=3600`, and `expire=3599`. In FortiGate session diagnostics, `proto_state=01` for TCP indicates the session is in the SYN-SENT state, meaning the initial SYN packet has been sent but the three-way handshake (SYN-ACK) has not yet been received. The session has been active for 3600 seconds but has not yet completed establishment, which is why the correct answer is A.
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 runs 'diagnose sys session filter dport 443' and sees the following output:
proto=6 proto_state=01 duration=3600 expire=3599
What does this indicate about the session?
medium
A.The session is experiencing packet loss
B.The session is a UDP connection
✓ C.The session has been active for 3600 seconds and will expire in 3599 seconds
D.The session is blocked by a firewall policy
Why C: The output shows 'duration=3600' and 'expire=3599', which directly indicate the session has been active for 3600 seconds (1 hour) and will expire in 3599 seconds. The 'proto=6' confirms TCP (protocol 6), and 'proto_state=01' indicates an established TCP session. This is a standard FortiGate session diagnostic display.
Variation 2. An administrator uses 'diagnose sys session list' and sees the following output for a session: 'proto=6 proto_state=01 duration=3600 expire=3599'. The session is for HTTPS traffic. What does 'proto_state=01' typically indicate in FortiGate?
hard
A.The session is being NATted
B.The session is fully established and active
✓ C.The session is in the initial connection setup phase (SYN_SENT)
D.The session is being inspected by a security profile
Why C: In FortiGate, 'proto_state=01' for TCP (proto=6) indicates the session is in the SYN_SENT phase, meaning the initial SYN packet has been sent but the three-way handshake is not yet complete. For HTTPS traffic, this shows the session is still in the connection setup stage, not fully established. The 'duration' and 'expire' values reflect the time since the session was created and the remaining timeout, which is typical for an incomplete handshake.
Last reviewed: Jun 24, 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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