Interpreting proto_state=01 in FortiGate Session Table
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?
Quick Answer
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.
⚠ Common exam trap
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.
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 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.
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.
- ✗
The session is a UDP session because the proto_state is 01
Why it's wrong here
proto=6 indicates TCP, not UDP.
- ✗
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).
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Same concept, more angles
2 more ways this is tested on NSE4
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.
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.