NSE7 Troubleshooting and Diagnostics Practice Question
An administrator is troubleshooting an IPsec VPN tunnel that fails to establish. The Phase 1 status shows 'init' and the debug output indicates 'no suitable proposal found'. The remote peer is a third-party VPN device. Which of the following is the MOST likely cause?
⚠ Common exam trap
Many candidates confuse 'no suitable proposal' with a pre-shared key mismatch, but the error occurs earlier in the IKE exchange before authentication begins, so it must be a proposal parameter mismatch.
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 IKE version or encryption algorithm does not match between the peers
The 'no suitable proposal found' error in Phase 1 indicates that the IKE proposal parameters (such as encryption algorithm, hash algorithm, Diffie-Hellman group, or IKE version) do not match between the FortiGate and the third-party peer. Since the status is 'init', the peers have exchanged initial packets but cannot agree on a common proposal, which is a classic proposal mismatch issue. A pre-shared key mismatch would typically cause an authentication failure later in Phase 1, not a 'no suitable proposal' error.
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 pre-shared key is incorrect on one side
Why it's wrong here
An incorrect PSK would cause authentication failure after proposal match, not a proposal mismatch.
- ✗
The remote peer's IP address is not reachable
Why it's wrong here
If the remote were unreachable, the status would show 'Idle' or 'connecting', not a proposal error.
- ✓
The IKE version or encryption algorithm does not match between the peers
Why this is correct
Proposal mismatch is caused by incompatible IKE parameters like encryption, hash, or DH group.
- ✗
The firewall policy allowing the VPN traffic is missing
Why it's wrong here
A missing policy would prevent traffic from reaching the VPN process, resulting in a different debug message.
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.
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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.