Interpreting proto_state=01 in FortiGate Session Table
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?
⚠ Common exam trap
Test-takers frequently confuse 'proto_state=01' with a fully established session because they see 'duration' and 'expire' values and assume the session is active, but the state code explicitly indicates the handshake is incomplete.
Answer choices
Why each option matters
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 initial connection setup phase (SYN_SENT)
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.
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 being NATted
Why it's wrong here
Network Address Translation (NAT) operates at the IP/port translation layer and is applied to outgoing packets, but it does not modify the TCP protocol state field in Fortinet's session table. The proto_state value (e.g., 0x01) is a kernel-level representation of the TCP state machine, not a NAT indicator. Even if a session is NATted, its proto_state reflects the TCP handshake status, so a value of 01 cannot be attributed to NAT. Thus this option is incorrect.
- ✗
The session is fully established and active
Why it's wrong here
A fully established and active TCP session would have completed the three-way handshake, and Fortinet's session table would reflect that by showing a proto_state other than 01—typically 0x1e (30) when the session is in the established/active state. A proto_state of 0x01 specifically indicates the initial SYN_SENT phase, where the client has sent a SYN but has not yet received a SYN-ACK. Seeing 01 means the connection setup is still in progress, not that the session is fully established. Therefore, this option is incorrect.
- ✓
The session is in the initial connection setup phase (SYN_SENT)
Why this is correct
The proto_state value 0x01 in the output of 'diagnose sys session list' corresponds to the TCP SYN_SENT state, which occurs during the initial connection setup phase. In this phase, the initiator has transmitted a SYN packet and is awaiting the peer's SYN-ACK response, meaning the three-way handshake is incomplete. This is precisely why the session is not fully established and why this is the correct answer.
- ✗
The session is being inspected by a security profile
Why it's wrong here
Security profile inspection (such as antivirus, IPS, or application control) occurs after the TCP session has been successfully established and operates at the application layer. The proto_state field in the session list is managed by the TCP engine and is completely independent of whether a security profile is applied; it only tracks TCP state transitions. Therefore, an inspection action would not cause proto_state to be 01, making this option incorrect.
Visual reference
Go deeper
Related to this question
About these practice questions
This NSE4 question is part of Courseiva's 773-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.