- A
Ensure that a static route exists to the internet via the WAN interface
Why wrong: The traffic is coming from the internet, so this route is likely already present.
- B
Check if the public DNS resolution for the domain is correct
Why wrong: DNS is not related to this issue; the traffic is already reaching the FortiGate.
- C
Confirm that the firewall policy's destination is set to the internal web server's IP address (or the VIP's mapped IP)
After DNAT, the destination IP changes to the internal server. The firewall policy must allow traffic to that internal IP. If the policy's destination is set to the VIP's public IP, it may not match post-DNAT. The correct approach is to set the destination to the mapped IP address.
- D
Verify that the firewall policy allowing the traffic has the correct source interface (WAN)
The policy must have the ingress interface set to the interface where the traffic arrives (usually WAN). If it is set to internal, the policy won't match.
- E
Recreate the virtual IP object with a different port
Why wrong: The VIP configuration is likely correct since the debug shows DNAT is happening.
Quick Answer
The answer is to verify that the firewall policy allowing the traffic has the correct source interface (WAN) and the correct destination (the VIP’s mapped internal IP). This is correct because the debug output shows the traffic is successfully forwarded to the internal server via port2 after DNAT, but then hits a policy deny, meaning the Virtual IP translation worked but no valid firewall policy exists to permit the post-DNAT session. On the Fortinet NSE 4 exam, this scenario tests your understanding of the VIP-to-policy flow: the VIP translates the destination, but a separate policy must explicitly allow the traffic from the WAN interface to the real server IP. A common trap is assuming a VIP alone grants access, or misconfiguring the policy’s destination as the public IP instead of the mapped private IP. Remember the memory tip: “VIP translates, policy permits—check the interface and the real destination.”
NSE4 High Availability and Diagnostics Practice Question
This NSE4 practice question tests your understanding of high availability and diagnostics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 troubleshooting an issue where users cannot access an internal web server via the internet through a FortiGate. The FortiGate has a virtual IP (VIP) configured for the web server. The administrator runs 'diagnose debug flow filter daddr <public-ip>' and 'diagnose debug flow trace start 100'. The output shows 'msg: forward to x.x.x.x via intf port2' but then 'msg: policy deny'. Which TWO actions should the administrator take to resolve the issue? (Choose two.)
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
Confirm that the firewall policy's destination is set to the internal web server's IP address (or the VIP's mapped IP)
The debug shows that traffic is being forwarded to the internal server (via port2) but then denied by policy. This means the traffic is matching the VIP and being DNATed, but the firewall policy that should allow the traffic is either missing, disabled, or configured incorrectly. The administrator should check the firewall policy that handles the traffic after DNAT. Common issues: the policy's source interface is not the incoming interface (should be the WAN interface), or the policy's destination is not the internal server's IP (should be the original destination or the VIP destination). Option A and D are correct: ensure the policy has the correct source interface (WAN) and that the destination is set to the VIP's mapped IP (or the VIP itself). Option B is wrong because the issue is not DNS. Option C is wrong because adding a route to the internet won't help. Option E is wrong because the VIP is already configured.
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.
- ✗
Ensure that a static route exists to the internet via the WAN interface
Why it's wrong here
The traffic is coming from the internet, so this route is likely already present.
- ✗
Check if the public DNS resolution for the domain is correct
Why it's wrong here
DNS is not related to this issue; the traffic is already reaching the FortiGate.
- ✓
Confirm that the firewall policy's destination is set to the internal web server's IP address (or the VIP's mapped IP)
Why this is correct
After DNAT, the destination IP changes to the internal server. The firewall policy must allow traffic to that internal IP. If the policy's destination is set to the VIP's public IP, it may not match post-DNAT. The correct approach is to set the destination to the mapped IP address.
Related concept
Static NAT maps one inside address to one outside address.
- ✓
Verify that the firewall policy allowing the traffic has the correct source interface (WAN)
Why this is correct
The policy must have the ingress interface set to the interface where the traffic arrives (usually WAN). If it is set to internal, the policy won't match.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
Recreate the virtual IP object with a different port
Why it's wrong here
The VIP configuration is likely correct since the debug shows DNAT is happening.
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.
Trap categories for this question
Command / output trap
The VIP configuration is likely correct since the debug shows DNAT is happening.
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.
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High Availability and Diagnostics — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
High Availability and Diagnostics — This question tests High Availability and Diagnostics — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Confirm that the firewall policy's destination is set to the internal web server's IP address (or the VIP's mapped IP) — The debug shows that traffic is being forwarded to the internal server (via port2) but then denied by policy. This means the traffic is matching the VIP and being DNATed, but the firewall policy that should allow the traffic is either missing, disabled, or configured incorrectly. The administrator should check the firewall policy that handles the traffic after DNAT. Common issues: the policy's source interface is not the incoming interface (should be the WAN interface), or the policy's destination is not the internal server's IP (should be the original destination or the VIP destination). Option A and D are correct: ensure the policy has the correct source interface (WAN) and that the destination is set to the VIP's mapped IP (or the VIP itself). Option B is wrong because the issue is not DNS. Option C is wrong because adding a route to the internet won't help. Option E is wrong because the VIP is already configured.
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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Last reviewed: Jun 21, 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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