NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 diagnose command on a FortiGate and see the output:
diagnose sys session filter dport 443
diagnose sys session list
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 (SYN_SENT)
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).
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 UDP, indicated by proto_state 01
Why it's wrong here
UDP sessions have proto=17; proto=6 indicates TCP. proto_state 01 is not for UDP.
✓
The session is in a half-open state (SYN_SENT)
Why this is correct
Correct. proto_state=01 corresponds to TCP SYN_SENT.
Related concept
Read the scenario before looking for a memorised answer.
✗
The session has been fully established
Why it's wrong here
Established sessions typically show proto_state=06 (ESTABLISHED) or 08 (close).
✗
The session is being terminated
Why it's wrong here
Termination states include FIN_WAIT, TIME_WAIT, etc., not 01.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'proto_state=01' with a fully established session because they see 'duration' and 'expire' values that look normal, not realizing that a half-open TCP session can still have a duration counter if the initial SYN was sent.
Trap categories for this question
Command / output trap
Established sessions typically show proto_state=06 (ESTABLISHED) or 08 (close).
Detailed technical explanation
How to think about this question
The proto_state field maps directly to the TCP state machine as defined in RFC 793; value 01 corresponds to SYN_SENT, value 02 to ESTABLISHED, and values like 04 to FIN_WAIT. This is critical for troubleshooting connectivity issues where sessions remain in SYN_SENT due to firewall rules blocking SYN-ACK responses, or when asymmetric routing prevents handshake completion. In real-world scenarios, a high number of sessions stuck in proto_state=01 often indicates a misconfigured load balancer or a DDoS SYN flood attack.
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 in a half-open state (SYN_SENT) — 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).
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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