NSE7 Troubleshooting and Diagnostics Practice Question
A site-to-site IPsec VPN tunnel is failing. The administrator runs 'diagnose vpn ike config' and sees that phase 1 parameters are correct. However, phase 2 negotiation fails with 'no proposal chosen'. What is the MOST likely cause?
⚠ Common exam trap
Many exam-takers confuse phase 1 and phase 2 failures, assuming any 'no proposal chosen' error relates to IKE phase 1, when in fact the error message specifically indicates a phase 2 proposal mismatch after phase 1 has successfully completed.
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 2 encryption/authentication algorithms do not match between peers
The 'no proposal chosen' error in phase 2 indicates that the IPsec security association (SA) parameters—specifically the encryption algorithm, authentication algorithm, or Diffie-Hellman group—do not match between the two peers. Since the administrator confirmed phase 1 is correct via 'diagnose vpn ike config', the issue is isolated to phase 2 proposal mismatch, making option B the most likely cause.
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
Why it's wrong here
PSK mismatch causes phase 1 failure, not phase 2.
- ✓
The phase 2 encryption/authentication algorithms do not match between peers
Why this is correct
Phase 2 negotiation fails when proposals do not match.
- ✗
The firewall policy allowing IKE traffic is missing
Why it's wrong here
This would prevent phase 1 from starting.
- ✗
The remote gateway IP address is wrong
Why it's wrong here
This would cause phase 1 failure.
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.