NSE4 Authentication and VPN Practice Question
An administrator is troubleshooting an IPsec VPN tunnel that is not establishing. The Phase 1 status shows 'down'. Which TWO commands can help diagnose the issue? (Choose TWO.)
⚠ Common exam trap
Many exam-takers confuse 'diagnose vpn tunnel list' (which shows only the status) with a diagnostic tool that reveals the root cause, when in fact it provides no insight into the IKE negotiation process or error details.
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
✓
diagnose debug application ike -1
The 'diagnose debug application ike -1' command enables real-time IKE (Internet Key Exchange) debugging, which is essential for troubleshooting Phase 1 failures. This command captures IKEv1/v2 negotiation messages, including proposals, pre-shared key mismatches, and authentication errors, directly showing why the tunnel is down.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
diagnose npu np6 ipsec-sa list
Why it's wrong here
Shows hardware offload SA, not helpful for negotiation issues.
- ✗
diagnose sys session clear
Why it's wrong here
Clears sessions, not a diagnostic command for IKE.
- ✓
diagnose debug application ike -1
Why this is correct
Enables IKE debugging at the highest level.
- ✗
diagnose vpn tunnel list
Why it's wrong here
Shows tunnel status but not detailed debug information.
- ✓
diagnose vpn ike log-filter
Why this is correct
Filters IKE logs to specific peers.
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
Courseiva writes every NSE4 question from scratch — 282 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or 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.