NSE7 Advanced VPN and Zero Trust Practice Question
A FortiGate administrator is troubleshooting an IKEv2 VPN tunnel that fails to establish. The remote peer logs show 'no acceptable proposal' error. Which TWO possible causes should the administrator check?
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 phase1 encryption algorithm or integrity algorithm is mismatched
The 'no acceptable proposal' error occurs when the two peers cannot agree on a set of parameters. Common causes are mismatched encryption/integrity algorithms (phase1 proposal) or mismatched Diffie-Hellman groups.
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 peer's IP address is unreachable
Why it's wrong here
Unreachability would cause timeout, not proposal rejection.
- ✓
The phase1 encryption algorithm or integrity algorithm is mismatched
Why this is correct
If the local and remote proposals do not have a common algorithm, negotiation fails with 'no acceptable proposal'.
- ✗
The local FortiGate has the wrong IKE version configured
Why it's wrong here
IKE version mismatch would cause a different error (e.g., 'no acceptable proposal' could appear if one side expects IKEv1 and the other IKEv2, but typically the error is more specific.
- ✗
The remote peer's pre-shared key is incorrect
Why it's wrong here
A pre-shared key mismatch causes authentication failure after proposal negotiation, not a proposal error.
- ✓
The Diffie-Hellman group configured is not supported by both peers
Why this is correct
DH group is part of the proposal; if mismatched, negotiation fails.
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
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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.