NSE7 Advanced VPN and Zero Trust Practice Question
A network administrator is troubleshooting an IPsec VPN tunnel between two FortiGates. The tunnel is established but traffic is not passing. The administrator runs 'diagnose vpn ike log' and sees 'no matching policy for this IPsec SA'. What is the most likely cause?
⚠ Common exam trap
The trap is conflating IKE negotiation failures (PSK mismatch, phase2 selector mismatch) with traffic-forwarding failures — candidates see 'IPsec SA' in the log and assume the SA itself is broken, when the message actually points to a missing firewall policy, not a VPN parameter problem.
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
✓
There is no firewall policy allowing traffic from the local network to the remote network via the VPN tunnel interface
The log message 'no matching policy for this IPsec SA' on a FortiGate means the IKE/IPsec SA was negotiated successfully but no firewall policy matches the traffic that needs to traverse the tunnel. In FortiOS, a firewall policy with the tunnel interface as the outgoing interface (and matching source/destination) is required for traffic to be encrypted and forwarded. Without it, the tunnel stays up but no data flows.
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 phase2 selectors do not match between peers
Why it's wrong here
Phase2 selector mismatches cause the tunnel to fail negotiation or drop traffic as not matching the SA, but the log line specifically flags policy lookup, not selector comparison. The error indicates no firewall policy permits the decrypted traffic, so a policy must be added to allow it.
- ✓
There is no firewall policy allowing traffic from the local network to the remote network via the VPN tunnel interface
Why this is correct
The log indicates the IKE SA negotiated selectors but no firewall policy permits that traffic. FortiGate requires an explicit policy matching source, destination and the VPN tunnel interface; without it, packets are dropped before entering the tunnel.
- ✗
The pre-shared key is mismatched
Why it's wrong here
A mismatched pre-shared key causes phase1 authentication to fail, so the tunnel never establishes and no IPsec SA is created. It is tempting because PSK errors are a frequent VPN fault, and they would be the cause when the log shows phase1 negotiation failure rather than a policy mismatch.
- ✗
The tunnel interface is administratively down
Why it's wrong here
An administratively down tunnel interface prevents traffic forwarding, but the IKE log would not report a policy-matching failure for an established SA. It is tempting because interface state is a routine check, and it would be correct when the tunnel shows as down or no SA exists at all.
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 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.