NSE4 Firewall Policies and NAT Practice Question
A FortiGate administrator wants to ensure that traffic from the internal network to an external FTP server uses a specific source IP address (203.0.113.10). The internal network uses RFC 1918 addresses. Which NAT configuration should be used?
⚠ Common exam trap
Many candidates confuse VIP (inbound destination NAT) with source NAT (SNAT), leading candidates to select Option B, even though the requirement is for outbound traffic from internal clients to use a specific source IP.
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
✓
Policy-based NAT using an IP pool with type 'Overload' and the IP address 203.0.113.10
Policy-based NAT with an IP pool type 'Overload' (PAT) allows multiple internal hosts to share the single public IP 203.0.113.10 for outbound traffic. This meets the requirement to translate RFC 1918 source addresses to a specific source IP when accessing an external FTP server, while preserving port multiplexing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Policy-based NAT using an IP pool set to 'Fixed Port Range'
Why it's wrong here
A Fixed Port Range IP pool is used to translate a source address range to a fixed port range, not to translate all session traffic to a single specific IP. This pool type is designed for scenarios requiring port preservation or mapping, but it does not allow you to specify 203.0.113.10 as a single egress IP. Thus, it cannot guarantee that all traffic from the internal server will appear to originate from that exact address.
- ✗
Virtual IP (VIP) mapping the internal server to 203.0.113.10
Why it's wrong here
A Virtual IP (VIP) is a destination NAT object that translates inbound traffic destined to a public IP into an internal server address. It does not perform source translation on outbound sessions; VIPs are applied in the 'incoming interface' direction of a policy, not for outbound source IP masquerading. Since the requirement is to change the source IP for outbound traffic, a VIP is not the correct tool.
- ✗
Central SNAT with dynamic IP pool
Why it's wrong here
Central SNAT is a valid method, but the option specifies a 'dynamic IP pool,' which typically means a pool of multiple addresses. Unless that pool is restricted to a single address and uses Overload, dynamic allocation will not guarantee that all sessions egress with 203.0.113.10. For a fixed single source IP, a policy-based SNAT with an Overload pool is the straightforward and intended configuration.
- ✓
Policy-based NAT using an IP pool with type 'Overload' and the IP address 203.0.113.10
Why this is correct
Policy-based NAT with an IP pool of type Overload performs source NAT by translating the source address of all matching sessions to the single IP defined in the pool. Since the pool contains only 203.0.113.10, every outbound session from the internal server will appear to originate from that exact IP using PAT (port address translation). This directly meets the requirement of ensuring all traffic from the server uses 203.0.113.10 as the source IP.
Visual reference
Go deeper
Related to this question
About these practice questions
Courseiva writes every NSE4 question from scratch — 282 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.