- A
A
Why wrong: Allowing from inside to DMZ would permit internal users to access the web server, not external users.
- B
B
This rule permits external users to initiate connections to the web server in the DMZ on port 80.
- C
C
Why wrong: Allowing from DMZ to inside is not needed for external access and could pose a security risk.
- D
D
Why wrong: A deny rule from outside to inside would block all incoming traffic, defeating the purpose.
Question 110 of 520
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company wants to allow external users to access a web server located in the DMZ. The firewall has three interfaces: inside, outside, and DMZ. Which firewall rule is necessary?
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
✓
B
Option B is correct because it allows traffic from the outside (external users) to the DMZ web server while keeping the inside network protected. In a three-legged firewall setup, the necessary rule permits inbound HTTP/HTTPS traffic from the outside interface to the DMZ interface, typically with a destination IP of the web server and port 80/443. This ensures external access is isolated from the internal network, adhering to the principle of least privilege.
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.
- ✗
A
Why it's wrong here
Allowing from inside to DMZ would permit internal users to access the web server, not external users.
When this WOULD be correct
Option A would be correct in a scenario where the question asks for a rule to allow internal users (inside interface) to access a web server in the DMZ, or to allow DMZ servers to initiate outbound connections to the internet.
- ✓
B
Why this is correct
This rule permits external users to initiate connections to the web server in the DMZ on port 80.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
C
Why it's wrong here
Allowing from DMZ to inside is not needed for external access and could pose a security risk.
When this WOULD be correct
Option C would be correct in a scenario where the question asks for a rule to allow the DMZ web server to initiate outbound connections to the internet (e.g., for updates), requiring a rule from DMZ to outside.
- ✗
D
Why it's wrong here
A deny rule from outside to inside would block all incoming traffic, defeating the purpose.
When this WOULD be correct
Option D would be correct if the question asked for a rule to allow internal users to access the web server in the DMZ, requiring traffic from the inside interface to the DMZ interface.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓BCorrect answer▾
Why this is correct
This rule permits external users to initiate connections to the web server in the DMZ on port 80.
✗AWrong answer — click to see why▾
Why this is wrong here
Option A is wrong because it does not specify a rule that allows traffic from the outside interface to the DMZ interface for the web server. The correct rule must permit inbound traffic from outside to DMZ, typically with destination port 80/443.
★ When this WOULD be the correct answer
Option A would be correct in a scenario where the question asks for a rule to allow internal users (inside interface) to access a web server in the DMZ, or to allow DMZ servers to initiate outbound connections to the internet.
Why candidates choose this
Candidates may confuse the direction of traffic, thinking that a rule from inside to DMZ is needed for external access, or they may misread the question and assume internal users are the target audience.
✗CWrong answer — click to see why▾
Why this is wrong here
Option C is wrong because it likely suggests a rule that does not properly allow traffic from the outside interface to the DMZ web server, such as allowing traffic from the DMZ to outside or misconfiguring source/destination zones.
★ When this WOULD be the correct answer
Option C would be correct in a scenario where the question asks for a rule to allow the DMZ web server to initiate outbound connections to the internet (e.g., for updates), requiring a rule from DMZ to outside.
Why candidates choose this
Candidates may confuse the direction of traffic or think that a rule allowing traffic from DMZ to outside is needed for external access, misunderstanding the flow of inbound vs. outbound rules.
✗DWrong answer — click to see why▾
Why this is wrong here
Option D is wrong because the question requires a rule allowing external users to access a web server in the DMZ, which typically involves allowing traffic from the outside interface to the DMZ interface. Option D likely specifies a different direction or incorrect source/destination.
★ When this WOULD be the correct answer
Option D would be correct if the question asked for a rule to allow internal users to access the web server in the DMZ, requiring traffic from the inside interface to the DMZ interface.
Why candidates choose this
Candidates may confuse the direction of traffic, thinking that external access requires a rule from DMZ to outside, or they may misremember standard firewall rule placement for DMZ servers.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the direction of traffic flow, mistakenly selecting a rule that allows inside-to-DMZ traffic (Option A) thinking it enables external access, when in fact external users initiate from the outside interface.
Detailed technical explanation
How to think about this question
In a three-interface firewall (inside, outside, DMZ), stateful inspection tracks connection states; the rule for outside-to-DMZ must be paired with a corresponding implicit or explicit rule allowing return traffic. Real-world scenarios often require additional rules for NAT (e.g., static NAT mapping the web server’s public IP to its private DMZ IP) and application-layer inspection (e.g., for HTTP/HTTPS) to prevent protocol anomalies. The DMZ acts as a buffer zone, so traffic from the DMZ to the inside is typically blocked by default to contain breaches.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: B — Option B is correct because it allows traffic from the outside (external users) to the DMZ web server while keeping the inside network protected. In a three-legged firewall setup, the necessary rule permits inbound HTTP/HTTPS traffic from the outside interface to the DMZ interface, typically with a destination IP of the web server and port 80/443. This ensures external access is isolated from the internal network, adhering to the principle of least privilege.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jun 11, 2026
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