NSE7 Advanced VPN and Zero Trust Practice Question
A FortiGate administrator is configuring an IPsec VPN tunnel to a remote site that is behind a NAT device. The administrator notices that the tunnel establishes, but traffic intermittently fails. Which setting should be adjusted to improve reliability?
⚠ Common exam trap
The trap here is attributing intermittent failures to DPD or encryption settings, when the root cause is often NAT session timeout that can be mitigated with NAT-T and keepalives.
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
✓
Enable NAT traversal (NAT-T) and set the keepalive frequency.
When an IPsec peer is behind NAT, the NAT device may close the UDP session if no traffic is sent for a period. Enabling NAT traversal (NAT-T) encapsulates IPsec packets in UDP, and setting a keepalive frequency ensures that periodic packets are sent to keep the NAT mapping alive. This prevents intermittent tunnel failures caused by NAT session timeouts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable Dead Peer Detection (DPD) with a shorter interval.
Why it's wrong here
DPD is used to detect dead peers, but it does not address intermittent traffic failures caused by NAT. While a shorter DPD interval can help detect failures faster, it does not solve the underlying NAT traversal issue that causes the intermittent failures. DPD is more about failure detection than prevention.
- ✗
Configure the remote gateway as a dynamic DNS hostname.
Why it's wrong here
Using a dynamic DNS hostname helps when the remote peer's IP changes, but it does not solve intermittent failures caused by NAT. If the peer is behind NAT with a stable public IP, dynamic DNS is not necessary. The issue is likely NAT session timeout, which requires NAT-T and keepalives.
- ✓
Enable NAT traversal (NAT-T) and set the keepalive frequency.
Why this is correct
NAT traversal (NAT-T) encapsulates IPsec packets in UDP to allow them to pass through NAT devices. The keepalive frequency setting sends periodic keepalive packets to maintain the NAT mapping and prevent the NAT session from timing out. This is crucial for reliability when a peer is behind NAT, as it keeps the UDP port open and avoids intermittent failures due to NAT session expiration.
- ✗
Set the IPsec phase-1 proposal to use AES-256 encryption.
Why it's wrong here
Changing the encryption algorithm to AES-256 does not affect NAT traversal or reliability. While AES-256 is strong encryption, it does not address the NAT-related issues that cause intermittent traffic failures. The problem is not about encryption strength but about maintaining the NAT mapping.
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.