The answer is that no additional step is needed because the FortiGate automatically performs reverse NAT for established sessions. When a VIP translates the destination of incoming traffic from the public IP 203.0.113.10 to the internal server 192.168.1.10, the server replies with its private IP as the source. The FortiGate then automatically reverses that translation, rewriting the source back to the VIP’s public IP before forwarding the response to the external user—this is the core of the “FortiGate VIP reverse NAT automatic response” mechanism. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this concept tests your understanding that VIPs handle inbound and reply traffic transparently; a common trap is assuming you need a separate source NAT policy for replies. The key memory tip: “VIPs are two-way streets—they translate both directions automatically for sessions they initiate.”
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. 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.
A FortiGate administrator is configuring a Virtual IP (VIP) to allow external users to access an internal web server (192.168.1.10) using the public IP 203.0.113.10 on port 80. The admin creates a VIP with mapped IP 192.168.1.10 and port 80. A firewall policy is created from WAN to DMZ with destination set to the VIP. External users report that they can access the web server. What additional step is needed to allow the internal server to respond correctly?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
No additional step is needed; the FortiGate automatically performs reverse NAT for established sessions
When traffic arrives at the VIP, the destination is translated to the internal server IP. The internal server sends its response with source IP 192.168.1.10, which the FortiGate must translate back to the VIP IP (203.0.113.10) before sending to the external user. This reverse translation happens automatically if the policy is correctly configured. However, if the internal server needs to initiate outbound connections (not just respond), additional policies may be needed. The question asks about the response: no additional step is needed because the FortiGate automatically performs reverse NAT for sessions initiated through the VIP.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
No additional step is needed; the FortiGate automatically performs reverse NAT for established sessions
Why this is correct
FortiGate tracks the session and translates the response packets back to the VIP address.
Related concept
Static NAT maps one inside address to one outside address.
✗
Create a second VIP for the return traffic
Why it's wrong here
Reverse NAT is automatic; no separate VIP is needed.
✗
Add a policy from DMZ to WAN allowing the internal server to reply
Why it's wrong here
Return traffic is part of the same session; no separate policy is required for replies.
✗
Configure static routing on the internal server to route through the FortiGate
Why it's wrong here
The internal server must have the FortiGate as default gateway, but the question assumes basic connectivity.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
Firewall Policies and NAT — This question tests Firewall Policies and NAT — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: No additional step is needed; the FortiGate automatically performs reverse NAT for established sessions — When traffic arrives at the VIP, the destination is translated to the internal server IP. The internal server sends its response with source IP 192.168.1.10, which the FortiGate must translate back to the VIP IP (203.0.113.10) before sending to the external user. This reverse translation happens automatically if the policy is correctly configured. However, if the internal server needs to initiate outbound connections (not just respond), additional policies may be needed. The question asks about the response: no additional step is needed because the FortiGate automatically performs reverse NAT for sessions initiated through the VIP.
What should I do if I get this NSE4 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related NSE4 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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