NSE7 Troubleshooting and Diagnostics Practice Question
A FortiGate administrator is troubleshooting a VPN tunnel that is up but no traffic passes through. The Phase 2 selectors match. The administrator runs 'diagnose vpn tunnel list' and sees that the tunnel has '0 bytes' in both directions. What is the MOST likely cause?
⚠ Common exam trap
Many exam-takers assume a 'tunnel is up' means traffic should flow, but FortiGate separates control plane (IKE/SA negotiation) from data plane (routing/policy); the tunnel being up only confirms Phase 1 and Phase 2 SAs exist, not that traffic is routed into the tunnel.
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 static route for the remote subnet does not point to the VPN tunnel interface
When a VPN tunnel is up but shows 0 bytes in both directions, it indicates that the control plane (IKE/IPsec SA negotiation) succeeded, but the data plane has no traffic. The most likely cause is that the static route for the remote subnet does not point to the VPN tunnel interface (e.g., 'tunnel.1'), so the FortiGate does not know to send traffic into the tunnel. Without a correct route, packets destined for the remote subnet are dropped or sent out the wrong interface, resulting in zero bytes on the tunnel.
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 policy is not configured to allow traffic through the tunnel
Why it's wrong here
If the policy were missing, the tunnel would still show traffic attempts (blocked). Zero bytes means no traffic reaches the tunnel.
- ✓
The static route for the remote subnet does not point to the VPN tunnel interface
Why this is correct
Without proper routing, traffic is not sent to the tunnel.
- ✗
The IPsec SA rekey interval is too short
Why it's wrong here
Rekey interval would not cause zero bytes; it would cause periodic renegotiation.
- ✗
The NAT traversal is not enabled
Why it's wrong here
NAT traversal affects tunnel establishment, not traffic flow after tunnel is up.
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 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.