The correct answer is that proto_state=01 indicates the session is in SYN_SENT state and the three-way handshake is not yet complete. This is because proto=6 identifies the protocol as TCP, and proto_state=01 corresponds to the hexadecimal value 0x01, which FortiGate maps to the TCP SYN_SENT state—meaning the client has sent a SYN packet but has not yet received a SYN-ACK from the server. On the Fortinet NSE 4 Network Security Professional exam, this output from the diagnose sys session filter command tests your ability to interpret session table entries and understand TCP state transitions; a common trap is confusing proto_state=01 with an established session, but remember that an established TCP session would show proto_state=0b (0x0B for ESTABLISHED). To lock this in, use the memory tip: “01 is just one step—SYN sent, handshake not done.”
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.
You run the following command on a FortiGate: 'diagnose sys session filter dport 443' and see:
proto=6 proto_state=01 duration=3600 expire=3599
What does this output indicate?
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 SYN_SENT state and the three-way handshake is not yet complete
The output shows `proto=6`, which indicates TCP, and `proto_state=01`, which corresponds to the TCP state SYN_SENT (0x01). This means the session has sent a SYN but has not yet received a SYN-ACK, so the three-way handshake is incomplete. The `duration=3600` and `expire=3599` indicate the session has been tracked for 3600 seconds and will expire in 3599 seconds, but the state confirms it is not yet established.
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 SYN_SENT state and the three-way handshake is not yet complete
Why this is correct
proto_state=01 for TCP indicates SYN_SENT. The handshake is incomplete.
Related concept
Read the scenario before looking for a memorised answer.
✗
The session is using UDP and the duration is 3600 seconds
The session is being torn down and will expire in 3599 seconds
Why it's wrong here
Expire shows remaining lifetime, not teardown.
✗
The session is fully established and has been active for 3600 seconds
Why it's wrong here
State 01 is not established; established state is typically 06 or 0x10.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see `duration=3600` and `expire=3599` and assume the session is established and about to expire, but the `proto_state=01` (SYN_SENT) clearly indicates the handshake is incomplete, not that the session is active or being torn down.
Trap categories for this question
Command / output trap
Expire shows remaining lifetime, not teardown.
Detailed technical explanation
How to think about this question
In FortiGate's session table, `proto_state` uses a bitmask derived from the Linux TCP state machine: 0x01 is TCP_SYN_SENT, 0x02 is TCP_ESTABLISHED, 0x03 is TCP_SYN_RECV, etc. The `diagnose sys session filter dport 443` command filters sessions by destination port 443 (HTTPS), and the output reveals that the session is still in the handshake phase. This is critical for troubleshooting connectivity issues where clients fail to complete the TCP handshake due to firewall policies, asymmetric routing, or server unresponsiveness.
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 SYN_SENT state and the three-way handshake is not yet complete — The output shows `proto=6`, which indicates TCP, and `proto_state=01`, which corresponds to the TCP state SYN_SENT (0x01). This means the session has sent a SYN but has not yet received a SYN-ACK, so the three-way handshake is incomplete. The `duration=3600` and `expire=3599` indicate the session has been tracked for 3600 seconds and will expire in 3599 seconds, but the state confirms it is not yet established.
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.
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Question Discussion
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