This NSE4 practice question tests your understanding of authentication and vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An administrator is configuring a dialup IPsec VPN for remote users. Which two settings must be configured on the FortiGate to allow clients to connect?
Enable XAuth for user authentication.
Why wrong: XAuth is not required for basic connectivity.
Enable Dead Peer Detection.
Why wrong: DPD is optional.
Enable mode-cfg on the Phase 1 interface.
Mode-cfg provides client configuration.
Enable NAT traversal.
Why wrong: NAT-T is only needed if clients are behind NAT.
Create an IP pool for the remote clients.
IP pool assigns IP addresses to clients.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Enable mode-cfg on the Phase 1 interface.
Option C is correct because mode-config (mode-cfg) on the Phase 1 interface is required to push network configuration parameters (such as DNS, WINS, and the virtual IP address) to remote IPsec VPN clients. This setting enables the FortiGate to act as a server in a dialup VPN scenario, dynamically assigning IP addresses and other settings to clients without requiring static configuration on each client.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Enable XAuth for user authentication.
Why it's wrong here
XAuth is not required for basic connectivity.
Enable Dead Peer Detection.
Why it's wrong here
DPD is optional.
Enable mode-cfg on the Phase 1 interface.
Why this is correct
Mode-cfg provides client configuration.
Related concept
Read the scenario before looking for a memorised answer.
Enable NAT traversal.
Why it's wrong here
NAT-T is only needed if clients are behind NAT.
Create an IP pool for the remote clients.
Why this is correct
IP pool assigns IP addresses to clients.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often assume XAuth or NAT traversal are mandatory for dialup IPsec, but the FortiGate specifically requires mode-cfg and an IP pool to dynamically assign client addresses and complete the tunnel setup.
Detailed technical explanation
Mode-config (RFC 3947) works by extending IKE Phase 1 to exchange configuration attributes (e.g., INTERNAL_IP4_ADDRESS, INTERNAL_IP4_DNS) between the VPN gateway and client. The IP pool assigned to the dialup interface provides the actual IP addresses that are leased to remote clients, and without both mode-cfg and an IP pool, the client cannot obtain a routable IP address to communicate over the tunnel. In real-world deployments, failing to configure either setting results in clients being unable to complete Phase 1 or Phase 2 negotiations, as the client expects to receive an IP address from the gateway.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Authentication and VPN — This question tests Authentication and VPN — Read the scenario before looking for a memorised answer..
The correct answer is: Enable mode-cfg on the Phase 1 interface. — Option C is correct because mode-config (mode-cfg) on the Phase 1 interface is required to push network configuration parameters (such as DNS, WINS, and the virtual IP address) to remote IPsec VPN clients. This setting enables the FortiGate to act as a server in a dialup VPN scenario, dynamically assigning IP addresses and other settings to clients without requiring static configuration on each client.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
This NSE4 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 NSE4 exam.
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