NSE7 Troubleshooting and Diagnostics Practice Question
An admin is troubleshooting an IPsec VPN tunnel that is failing phase 2. The IKE debug shows 'no matching proposal'. Which TWO settings should the admin verify on both sides? (Choose two.)
⚠ Common exam trap
A common mix-up: candidates confuse phase 1 and phase 2 parameters, incorrectly selecting pre-shared key (option D) or gateway IPs (option E) as causes for a phase 2 proposal mismatch, when in fact only the IPsec SA parameters (encryption, authentication, PFS) are negotiated in phase 2.
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
✓
Encryption algorithm (e.g., AES128, AES256)
In IPsec phase 2, the IKE debug message 'no matching proposal' indicates a mismatch in the security association (SA) parameters used to establish the IPsec SA. The encryption algorithm (option B) is a core component of the IPsec proposal that must match exactly on both peers. Perfect Forward Secrecy (PFS) using a Diffie-Hellman group (option C) is also negotiated during phase 2; if one side requires PFS and the other does not, or if the DH groups differ, phase 2 will fail with this 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.
- ✗
Dead Peer Detection interval
Why it's wrong here
DPD is not part of phase 2 proposal.
- ✓
Encryption algorithm (e.g., AES128, AES256)
Why this is correct
Part of phase 2 proposal.
- ✓
Diffie-Hellman group for PFS
Why this is correct
PFS is negotiated in phase 2; mismatched DH groups cause failure.
- ✗
Pre-shared key
Why it's wrong here
PSK is used in phase 1 only.
- ✗
Local and remote gateway IP addresses
Why it's wrong here
These are phase 1 settings.
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.