NSE7 Advanced VPN and Zero Trust Practice Question
A network administrator is troubleshooting an IPsec VPN tunnel between two FortiGates. The tunnel is up but traffic is not passing. The administrator runs 'diagnose vpn ike gateway list' and sees that the IKE SA has been established. However, 'diagnose vpn tunnel list' shows no IPsec SA entries. What is the most likely cause?
⚠ Common exam trap
NSE7 often tests the distinction between Phase 1 and Phase 2 failures, so candidates may incorrectly blame firewall policies or pre-shared keys when the IKE SA is already up, missing that Phase 2 mismatch is the cause of missing IPsec SAs.
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 proposal (encryption, authentication, etc.) does not match between peers
If the IKE SA is established but no IPsec SA entries appear in 'diagnose vpn tunnel list', the most likely cause is a Phase 2 proposal mismatch. Phase 1 (IKE SA) negotiates the secure channel, while Phase 2 (IPsec SA) negotiates the actual tunnel parameters. If the encryption, authentication, or other Phase 2 settings do not match, the IPsec SA will fail to establish, even though Phase 1 is up.
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 firewall policies are not configured to allow traffic through the tunnel
Why it's wrong here
Firewall policies control whether traffic is permitted to enter the tunnel, but they do not create IPsec SAs. The absence of IPsec SA entries points to Phase 2 negotiation failure, which occurs before policy enforcement. Policies would be the culprit if SAs existed but traffic was silently dropped.
- ✓
The phase 2 proposal (encryption, authentication, etc.) does not match between peers
Why this is correct
A phase 2 mismatch prevents the IPsec SA from being negotiated, so Quick Mode fails while the IKE SA stays up. That matches the stem exactly: `diagnose vpn ike gateway list` shows an established IKE SA, but `diagnose vpn tunnel list` shows no IPsec SA entries. Phase 1 selectors and proposals are not the constraint here.
- ✗
The pre-shared key on both sides does not match
Why it's wrong here
A pre-shared key mismatch would prevent Phase 1 from completing, so the IKE SA would never appear in 'diagnose vpn ike gateway list'. Since the IKE SA is established, authentication succeeded. PSK errors are the classic cause when Phase 1 itself fails to come up.
- ✗
The interface MTU is set too low
Why it's wrong here
Low MTU may cause fragmentation issues but would not prevent IPsec SA creation.
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
This NSE7 question is part of Courseiva's 718-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Fortinet exam blueprint
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.