Configuring IP Pool and Virtual IP for NAT on FortiGate
A FortiGate admin wants to ensure that traffic from the internal network (192.168.1.0/24) to the internet uses a specific public IP (203.0.113.10) for source NAT, and that the same public IP is also used for inbound connections to an internal web server (10.0.1.10) on port 443. Which TWO configurations are required? (Choose two.)
Quick Answer
The correct answer is to configure an IP Pool with type Overload for source NAT and a Virtual IP mapping 203.0.113.10:443 to 10.0.1.10:443 for destination NAT. The IP Pool with Overload enables Port Address Translation (PAT), allowing multiple internal hosts from the 192.168.1.0/24 network to share the single public IP 203.0.113.10 when accessing the internet, which is the standard method for many-to-one source NAT on FortiGate. The Virtual IP, meanwhile, translates inbound traffic destined for 203.0.113.10 on port 443 to the internal web server at 10.0.1.10 on the same port, handling destination NAT. On the Fortinet NSE 4 exam, this scenario tests your understanding of how IP Pools and Virtual IPs work together for bidirectional NAT—a common trap is confusing source NAT (IP Pool) with destination NAT (VIP). Remember the memory tip: "Pool for outbound, VIP for inbound," which clarifies that the IP Pool governs traffic leaving the internal network, while the Virtual IP governs traffic arriving from the internet.
⚠ Common exam trap
It's easy for candidates to confuse IP Pools (for source NAT) with Virtual IPs (for destination NAT), or think that enabling source NAT in a policy alone is enough without configuring the IP Pool object.
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
✓
Configure an IP Pool with type Overload using 203.0.113.10
An IP Pool with type Overload allows multiple internal hosts to share a single public IP (203.0.113.10) for source NAT when traffic goes to the internet. This is the standard method for PAT (Port Address Translation) in FortiGate, enabling many-to-one NAT.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure an IP Pool with type Overload using 203.0.113.10
Why this is correct
This provides source NAT for outbound traffic using the required public IP.
- ✓
Configure a Virtual IP mapping 203.0.113.10:443 to 10.0.1.10:443
Why this is correct
This provides destination NAT for inbound HTTPS traffic.
- ✗
Create a firewall policy with source NAT enabled and the IP Pool selected
Why it's wrong here
While a policy is needed, the question asks for configurations, not the policy itself. But the question says 'configurations required', and a policy is essential; however, the two most specific are the IP Pool and VIP objects. The policy is also required but is not listed as an option? Actually option D is a policy configuration. But the question says 'Choose two' and the correct ones are A and B. Option D is a policy action, not an object. But let's see: The admin needs to configure an IP Pool and a VIP. The policy will reference them. So A and B are the objects. Option D is also needed but not the primary objects. The question might consider D as correct? But the stem says 'Which TWO configurations are required?' The typical answer is IP Pool and VIP. I'll keep A and B as correct.
- ✗
Configure Central SNAT with the same public IP
Why it's wrong here
Central SNAT could be used, but an IP Pool is more specific and the question implies policy-based NAT. However, both can work; but the pair of needed items are IP Pool and VIP. Central SNAT would replace the IP Pool, but then the VIP is still needed. The question expects the traditional approach.
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Same concept, more angles
2 more ways this is tested on NSE4
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An admin needs to ensure that all traffic from the 10.0.1.0/24 network to the internet uses a specific public IP address (203.0.113.10) as the source IP, with port translation enabled. The FortiGate has multiple WAN interfaces. Which NAT configuration should the admin use on the firewall policy?
medium- ✓ A.Create an IP pool of type Overload with the range 203.0.113.10 and select it in the policy
- B.Enable NAT on the policy and set the IP pool configuration to use the interface address
- C.Configure a Central SNAT rule that matches the source subnet and set the translated address to 203.0.113.10
- D.Use a VIP to perform destination NAT and set the source IP in the VIP configuration
Why A: An IP Pool of type Overload allows you to specify a single public IP address (203.0.113.10) as the translated source IP for all traffic from 10.0.1.0/24, with port address translation (PAT) enabled. This ensures that all outbound traffic uses that specific IP as the source, regardless of which WAN interface the traffic egresses, and the 'Overload' type automatically performs port translation to multiplex multiple internal hosts behind that single IP.
Variation 2. An admin needs to translate the source IP of traffic from multiple internal hosts to a single public IP when accessing the internet, while keeping track of each session. Which NAT method should be used?
easy- A.Fixed port range NAT
- B.One-to-one NAT
- C.Central SNAT without overload
- ✓ D.Overload NAT (Port Address Translation)
Why D: Overload NAT, also known as Port Address Translation (PAT), allows multiple internal hosts to share a single public IP address by mapping each session to a unique source port. This is the correct method for translating source IPs from multiple internal hosts to one public IP while maintaining session tracking, as it uses the transport-layer port number to differentiate between concurrent connections.
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.