Question 981 of 940
NSE7 Troubleshooting and Diagnostics Practice Question
An administrator is troubleshooting a VPN tunnel that is not coming up. The remote peer is a third-party device. Which THREE actions should be taken to diagnose the issue?
⚠ Common exam trap
A common mix-up: candidates confuse post-tunnel routing checks (Option E) with pre-tunnel connectivity checks, or they assume firewall port blocking (Option B) is a direct diagnostic step rather than a prerequisite to verify after other checks fail.
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
✓
Ensure that the pre-shared key matches on both sides.
IPsec IKE (Internet Key Exchange) uses the pre-shared key (PSK) during authentication phase 1 (Main Mode or Aggressive Mode). If the PSK does not match on both peers, the IKE SA will fail to establish, and the VPN tunnel will not come up. This is a fundamental prerequisite for any IPsec VPN, and mismatched PSKs are a common misconfiguration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ensure that the pre-shared key matches on both sides.
Why this is correct
Mismatched PSK is a common cause of tunnel failure.
- ✗
Confirm that UDP ports 500 and 4500 are not blocked by any firewall.
Why it's wrong here
This should be checked, but it's not one of the three most direct actions for a tunnel not coming up; it's more about network path.
- ✓
Verify that the remote peer's IP address is reachable via ping.
Why this is correct
Basic connectivity must exist before IKE negotiation.
- ✓
Check the IPSec VPN logs with 'diag debug application ike -1'.
Why this is correct
IKE debug shows detailed negotiation steps.
- ✗
Review the routing table to ensure the remote subnet is reachable through the tunnel interface.
Why it's wrong here
This is relevant after the tunnel is established.
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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Last reviewed: Jun 11, 2026
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.
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