The correct answer is that the session is a TCP connection to port 443 that was just established and will expire in about one hour. This is because `proto=6` indicates TCP, `proto_state=01` maps to the TCP ESTABLISHED state, and `expire=3599` seconds means the session has nearly its full 3600-second timeout remaining, confirming it was just created. On the Fortinet NSE 4 Network Security Professional exam, interpreting `diagnose sys session list` output tests your ability to read real-time session data and understand TCP state codes, a common troubleshooting skill. A frequent trap is confusing `proto_state=01` with a closing state like FIN_WAIT, but remember that state `01` always means ESTABLISHED. For a quick memory tip, think of the number 1 as “one active connection”—if the state is 01, the session is up and running.
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. 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 CLI command on a FortiGate:
diagnose sys session filter dport 443
diagnose sys session list
And you see the output:
proto=6 proto_state=01 duration=3600 expire=3599
What does this 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 a TCP connection to port 443 that was just established and will expire in about 1 hour
The command `diagnose sys session filter dport 443` filters sessions to destination port 443, and `diagnose sys session list` displays matching sessions. The output shows `proto=6`, which is the protocol number for TCP, and `expire=3599` seconds, indicating the session will expire in about 1 hour (3600 seconds total). The `proto_state=01` corresponds to TCP state ESTABLISHED, meaning the session is active and just established, not closing. Therefore, option C is correct.
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.
State 01 indicates TCP state SYN_SENT or similar, not CLOSE.
✓
The session is a TCP connection to port 443 that was just established and will expire in about 1 hour
Why this is correct
Duration 3600 seconds (1 hour) and expire 3599 seconds (almost 1 hour left) indicates a new session.
Related concept
Read the scenario before looking for a memorised answer.
✗
The session has been active for 1 hour and has 1 second remaining before expiry
Why it's wrong here
Duration is 3600 seconds, but expire is 3599, so it will expire in 3599 seconds, not 1 second.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse `duration` (time since session started) with `expire` (time remaining), or misinterpret `proto=6` as UDP because port 443 is commonly associated with HTTPS/TLS, but the protocol field explicitly shows TCP.
Trap categories for this question
Similar concept trap
State 01 indicates TCP state SYN_SENT or similar, not CLOSE.
Detailed technical explanation
How to think about this question
In FortiGate's session table, `proto_state` values are derived from TCP state machine transitions (RFC 793), where 01 = ESTABLISHED, 02 = SYN_SENT, 03 = SYN_RECV, etc. The `expire` counter decrements from the session's idle timeout (default 3600 seconds for TCP), and when it reaches 0, the session is removed. This is critical for troubleshooting long-lived connections like HTTPS (port 443) where premature expiry can cause application timeouts.
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: The session is a TCP connection to port 443 that was just established and will expire in about 1 hour — The command `diagnose sys session filter dport 443` filters sessions to destination port 443, and `diagnose sys session list` displays matching sessions. The output shows `proto=6`, which is the protocol number for TCP, and `expire=3599` seconds, indicating the session will expire in about 1 hour (3600 seconds total). The `proto_state=01` corresponds to TCP state ESTABLISHED, meaning the session is active and just established, not closing. Therefore, option C is correct.
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. You run the following command on a FortiGate:
```
diagnose sys session filter dport 443
diagnose sys session list
```
The output shows:
```
proto=6 proto_state=01 duration=3600 expire=3599
```
What does this indicate?
medium
✓ A.The session has been established for 3600 seconds and has 3599 seconds remaining before timeout.
B.The session is using TCP state 01 (SYN_SENT) and is still in the process of establishing.
C.The session has been idle for 3600 seconds and will expire in 3599 seconds.
D.The session is using UDP protocol and will expire in 3599 seconds.
Why A: Option A is correct because the output shows `duration=3600` and `expire=3599`, which indicate the session has been active for 3600 seconds and has 3599 seconds remaining before timeout. The `proto=6` confirms TCP (protocol 6), and `proto_state=01` represents the TCP state for an established connection (ESTABLISHED), not a handshake state.
Variation 2. You run the following diagnose command on a FortiGate and see the output:
diagnose sys session filter dport 443
diagnose sys session list
... proto=6 proto_state=01 duration=3600 expire=3599 ...
What does the 'proto_state=01' indicate?
hard
A.The session is UDP, indicated by proto_state 01
✓ B.The session is in a half-open state (SYN_SENT)
C.The session has been fully established
D.The session is being terminated
Why B: In FortiGate session diagnostics, 'proto_state=01' for a TCP session (proto=6) indicates the session is in a half-open state, specifically SYN_SENT, meaning the initial SYN packet has been sent but the three-way handshake has not yet completed. This is a transient state before the session becomes fully established (proto_state=02).
Variation 3. You run the following CLI command on a FortiGate: 'diagnose sys session filter dport 443' and see this output:
proto=6 proto_state=01 duration=3600 expire=3599
What does this indicate?
hard
A.The session is a TCP connection that has been active for 1 hour and will expire in 3599 seconds
✓ B.The session is using TCP and has been open for 3600 seconds with a remaining lifetime of 3599 seconds, indicating it is a long-lived session
C.The session is UDP (proto=6 is TCP? Actually proto=6 is TCP) and the output indicates an ICMP error
D.There is a problem because the session duration equals the expire time, meaning it will be removed immediately
Why B: Option B is correct because the output shows a TCP session (proto=6) with a duration of 3600 seconds (1 hour) and an expire value of 3599 seconds, meaning the session has been active for 3600 seconds and will be removed in 3599 seconds if no further traffic is seen. This indicates a long-lived session, typical for persistent connections like HTTPS, where the session timer resets with each packet.
Last reviewed: Jun 24, 2026
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