NSE7 Advanced VPN and Zero Trust Practice Question
A FortiGate administrator is configuring an IPsec VPN with IKEv2 between two sites. The administrator wants to ensure that only specific subnets are allowed over the tunnel and that the tunnel uses strong encryption. After configuring phase1 and phase2, the administrator notices that the tunnel is up, but traffic from a subnet that should be allowed is not passing. The administrator runs 'diagnose vpn tunnel list' and sees that the tunnel is established. What is the most likely reason for the traffic not passing?
⚠ Common exam trap
The trap here is assuming that an established tunnel guarantees traffic will pass, overlooking that phase2 selectors must match the actual traffic subnets.
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 phase2 selectors do not match the local and remote subnets exactly as configured in the firewall address objects.
Phase2 selectors must match the actual traffic subnets. If they do not, the FortiGate will not encrypt and send that traffic over the tunnel. Even with the tunnel up, mismatched selectors cause traffic to be dropped or routed elsewhere. The other options would either prevent tunnel establishment or are not relevant to the symptom.
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 the local and remote subnets exactly as configured in the firewall address objects.
Why this is correct
In IPsec VPN, phase2 selectors define the traffic that is allowed over the tunnel. If the local and remote subnets configured in phase2 do not match the actual source and destination addresses of the traffic, the FortiGate will not route that traffic into the tunnel. This is a common misconfiguration. Even if the tunnel is up, mismatched selectors will cause traffic to be dropped or sent unencrypted, depending on routing. The administrator should verify that the phase2 selectors exactly match the subnets defined in the firewall policies and address objects.
- ✗
The dead peer detection (DPD) is disabled, causing the tunnel to become stale.
Why it's wrong here
DPD is used to detect if a peer is no longer responding. If DPD is disabled, the tunnel might remain up even if the peer is unreachable, but in this scenario, the tunnel is established and presumably the peer is reachable. DPD being disabled would not prevent traffic from passing if the peer is up. The issue is more likely a configuration mismatch in the phase2 selectors or routing.
- ✗
The encryption algorithm used in phase2 is not supported by the remote peer.
Why it's wrong here
If the encryption algorithm were unsupported, the phase2 negotiation would fail, and the tunnel would not establish. Since the tunnel is up, the encryption algorithms are compatible. The issue is more likely related to traffic selectors or routing. The administrator should check the phase2 proposal settings, but if the tunnel is established, the algorithms are not the problem.
- ✗
The firewall policy allowing the traffic does not have NAT enabled.
Why it's wrong here
NAT is typically not required for site-to-site IPsec VPNs unless there is overlapping subnets or specific requirements. In most cases, NAT should be disabled to preserve original source IP addresses. Enabling NAT would actually change the source IP, which might break communication if the remote site expects the original subnet. Therefore, the absence of NAT is not the cause of the traffic not passing; it is usually the correct configuration.
Visual reference
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 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.