The answer is the implicit deny policy at the end of the policy list. This entry is identified by its reserved ID of 2000000000, which FortiGate uses specifically for the default deny rule that matches all traffic from any source to any destination, as shown by the src-addr and dst-addr ranges of 0.0.0.0-255.255.255.255. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this question tests your ability to interpret diagnose firewall iprope output and distinguish the implicit deny from user-created policies; a common trap is confusing the ID 2000000000 with a normal policy ID, but remember that only the implicit deny uses this specific high-numbered identifier. To lock it in, use the mnemonic: "Two billion denies all, the last rule to fall."
NSE4 Firewall Policies and NAT Practice Question
This NSE4 practice question tests your understanding of firewall policies and nat. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 admin runs the command 'diagnose firewall iprope list 100000' and sees the following output:
id=2000000000 action=deny flag=0x0 src-interface=any dst-interface=any proto=0 src-addr=0.0.0.0-255.255.255.255 dst-addr=0.0.0.0-255.255.255.255
What does this entry represent?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The implicit deny policy at the end of the policy list
The ID 2000000000 is reserved for the implicit deny policy. It matches all traffic from any interface to any interface and denies. This is the last rule checked.
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.
The implicit deny policy at the end of the policy list
Why this is correct
The implicit deny has a fixed ID of 2000000000 and denies all unmatched traffic.
Related concept
Static NAT maps one inside address to one outside address.
✗
A user-created deny policy that blocks all traffic
Why it's wrong here
User-created policies have IDs below 2000000000 (e.g., 1-65534).
✗
A NAT policy that translates all addresses
Why it's wrong here
NAT policies are not shown in 'firewall iprope list'.
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
NAT policies are not shown in 'firewall iprope list'.
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: The implicit deny policy at the end of the policy list — The ID 2000000000 is reserved for the implicit deny policy. It matches all traffic from any interface to any interface and denies. This is the last rule checked.
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.
About these practice questions
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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 administrator runs 'diagnose firewall iprope list 100000' and sees 'action=deny' entries for traffic that should be allowed. The policy list shows an allow policy with ID 1 for that traffic. What is the most likely cause of the deny?
medium
A.The traffic is being blocked by a local-in policy
B.The implicit deny rule is being triggered because the policy is disabled
✓ C.The firewall policy is not installed in the kernel due to an error
D.A security profile is dropping the traffic after the policy matches
Why C: The 'diagnose firewall iprope list 100000' command displays the kernel-level firewall policy list. If the policy list shows an allow policy (ID 1) but the kernel entries show 'action=deny', it indicates that the policy was not successfully installed into the kernel's connection tracking or firewall engine. This typically occurs due to a policy installation error, such as a configuration inconsistency or a failure during the commit process, causing the kernel to fall back to a default deny action for that traffic.
Last reviewed: Jun 21, 2026
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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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