NSE7 Troubleshooting and Diagnostics Practice Question
An administrator is troubleshooting an IPsec VPN tunnel that fails to establish. The administrator runs 'diagnose vpn ike log' and sees the message 'no matching proposal found'. What is the MOST likely cause?
⚠ Common exam trap
Watch out — candidates often confuse Phase 1 proposal mismatches with pre-shared key errors or firewall policy issues, but the IKE log message 'no matching proposal found' is a specific RFC 2409 notification that occurs before authentication, so only mismatched encryption, hash, or DH group parameters can cause it.
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 Phase 1 parameters (encryption, authentication, DH group) do not match between peers
The 'no matching proposal found' message in the IKE log indicates that the FortiGate received a proposal from the remote peer during Phase 1 negotiation, but none of the offered combinations of encryption, authentication, and Diffie-Hellman group matched its own configured Phase 1 parameters. Since IKE uses a proposal/response exchange, a mismatch in any of these attributes causes the negotiation to fail before any further steps, such as authentication or policy lookup, can occur.
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 remote gateway's IP address is unreachable
Why it's wrong here
Unreachable peer would result in timeout, not proposal mismatch.
- ✓
The Phase 1 parameters (encryption, authentication, DH group) do not match between peers
Why this is correct
'No matching proposal found' indicates that during IKE negotiation, the two peers could not agree on a common set of Phase 1 parameters.
- ✗
The firewall policy allowing the VPN traffic is missing or has the wrong interface
Why it's wrong here
A missing policy would cause a different error, such as 'no policy' or 'policy denied'.
- ✗
The pre-shared key is incorrect on one side
Why it's wrong here
Incorrect PSK would cause authentication failure, not proposal mismatch.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
About these practice questions
One of 940 original NSE7 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE7 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 NSE7 exam.