The answer is that no NAT policy is configured for internal users. This is correct because the FortiGate’s successful ping to 8.8.8.8 proves the default route and upstream connectivity are working, but internal users behind NAT cannot access the internet since their private IP addresses are not being translated to the FortiGate’s public IP. Without a NAT policy—or a firewall policy with NAT enabled—the ISP gateway drops the packets as unroutable private addresses. On the Fortinet NSE 4 exam, this scenario tests your understanding that reachability from the FortiGate itself does not guarantee NAT is in place for internal traffic; it is a common trap to assume routing alone solves the problem. Remember the memory tip: “Ping from the box, not from the user—check NAT before you accuse the route.”
NSE4 System and Network Administration Practice Question
This NSE4 practice question tests your understanding of system and network administration. 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.
A FortiGate administrator is troubleshooting a problem where users cannot access the Internet. The FortiGate has a default route pointing to the ISP gateway. The administrator runs 'execute ping 8.8.8.8' from the FortiGate CLI and it succeeds. However, internal users behind NAT are unable to reach external servers. Which is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
No NAT policy is configured for internal users
The administrator confirmed that the FortiGate itself can reach the Internet (ping 8.8.8.8 succeeds), so the default route and basic connectivity are working. However, internal users behind NAT cannot reach external servers, which indicates that traffic from internal users is either not being translated or is being blocked. The most likely cause is that no NAT policy (or firewall policy with NAT enabled) exists to perform source NAT for internal users, so their private IP addresses are not translated to the FortiGate's public IP, and the ISP gateway drops the packets because private addresses are not routable on the Internet.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The default route is incorrectly configured
Why it's wrong here
The ping succeeds, so the default route works for the FortiGate itself.
✗
An implicit deny policy is blocking traffic from internal to external
Why it's wrong here
An implicit deny would block all traffic including the ping from the FortiGate.
✓
No NAT policy is configured for internal users
Why this is correct
Without NAT, internal source IPs are not translated, so return traffic may be dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
External access profile is set to read-only
Why it's wrong here
External access profiles control admin access, not user traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a successful ping from the FortiGate CLI proves end-to-end connectivity for all users, but they overlook that NAT translation is required for internal private IPs to reach the Internet.
Detailed technical explanation
How to think about this question
In FortiGate, NAT is not automatically applied to all traffic; it must be explicitly configured either in the firewall policy (by enabling NAT) or via a central NAT policy. Without NAT, internal private IP addresses (e.g., 192.168.x.x) are sent unmodified to the ISP, which will drop them because RFC 1918 addresses are not routable on the public Internet. The 'execute ping' command uses the FortiGate's own IP (typically the WAN interface IP), which is already public or is NATed implicitly by the FortiGate's own routing, so it succeeds even when internal user traffic fails.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
System and Network Administration — This question tests System and Network Administration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: No NAT policy is configured for internal users — The administrator confirmed that the FortiGate itself can reach the Internet (ping 8.8.8.8 succeeds), so the default route and basic connectivity are working. However, internal users behind NAT cannot reach external servers, which indicates that traffic from internal users is either not being translated or is being blocked. The most likely cause is that no NAT policy (or firewall policy with NAT enabled) exists to perform source NAT for internal users, so their private IP addresses are not translated to the FortiGate's public IP, and the ISP gateway drops the packets because private addresses are not routable on the Internet.
What should I do if I get this NSE4 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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