- A
A) Port forwarding (DNAT) rule
Correct. Port forwarding translates the destination IP and port of incoming traffic from the public IP to the private IP of the web server, allowing external access.
- B
B) Allow rule with source any, destination 10.0.0.5, port 443
Why wrong: Incorrect. An allow rule alone does not change the destination IP. The incoming packet's destination is 203.0.113.10, not 10.0.0.5, so the server would not receive the traffic without address translation.
- C
C) Access control list on the internal interface
Why wrong: Incorrect. An ACL on the internal interface could be used to control traffic within the LAN, but it does not enable external traffic to reach the internal server.
- D
D) VPN rule to require remote access VPN
Why wrong: Incorrect. While a VPN would provide secure access, the scenario does not mention a VPN. The goal is to allow access directly via the internet without requiring a VPN.
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 security administrator is configuring a firewall to allow remote employees to access the company's internal web server (port 443) from the internet. The web server has an internal IP address of 10.0.0.5. The firewall has a public IP of 203.0.113.10. Which type of firewall rule should be created?
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
A) Port forwarding (DNAT) rule
A port forwarding (DNAT) rule is required because the web server uses a private RFC 1918 IP address (10.0.0.5), which is not routable on the public internet. The firewall must translate the destination IP from its public address (203.0.113.10) to the internal server's private address, allowing inbound traffic on port 443 to reach the correct internal host.
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) Port forwarding (DNAT) rule
Why this is correct
Correct. Port forwarding translates the destination IP and port of incoming traffic from the public IP to the private IP of the web server, allowing external access.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
B) Allow rule with source any, destination 10.0.0.5, port 443
Why it's wrong here
Incorrect. An allow rule alone does not change the destination IP. The incoming packet's destination is 203.0.113.10, not 10.0.0.5, so the server would not receive the traffic without address translation.
- ✗
C) Access control list on the internal interface
Why it's wrong here
Incorrect. An ACL on the internal interface could be used to control traffic within the LAN, but it does not enable external traffic to reach the internal server.
When this WOULD be correct
This option would be correct if the question asked about controlling outbound traffic from the internal network to the internet, such as restricting which internal users can access external web servers on port 443.
- ✗
D) VPN rule to require remote access VPN
Why it's wrong here
Incorrect. While a VPN would provide secure access, the scenario does not mention a VPN. The goal is to allow access directly via the internet without requiring a VPN.
When this WOULD be correct
A VPN rule would be correct if the scenario required secure, encrypted access to the entire internal network or multiple services, and the organization policy mandated that all remote access must go through a VPN for security compliance.
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.
✓A) Port forwarding (DNAT) ruleCorrect answer▾
Why this is correct
Correct. Port forwarding translates the destination IP and port of incoming traffic from the public IP to the private IP of the web server, allowing external access.
✗C) Access control list on the internal interfaceWrong answer — click to see why▾
Why this is wrong here
An access control list on the internal interface would only control traffic already inside the network, not allow inbound connections from the internet to the internal web server. The firewall must translate the public IP to the private IP, which DNAT does.
★ When this WOULD be the correct answer
This option would be correct if the question asked about controlling outbound traffic from the internal network to the internet, such as restricting which internal users can access external web servers on port 443.
Why candidates choose this
Candidates may think ACLs are the standard way to permit traffic, but they overlook that ACLs alone cannot handle the address translation needed for inbound traffic from the internet to a private IP.
✗D) VPN rule to require remote access VPNWrong answer — click to see why▾
Why this is wrong here
The question asks for a firewall rule to allow remote employees to access the internal web server from the internet. A VPN rule is not required for simple port forwarding; it would be an unnecessary complication and not the direct solution for allowing access via port 443.
★ When this WOULD be the correct answer
A VPN rule would be correct if the scenario required secure, encrypted access to the entire internal network or multiple services, and the organization policy mandated that all remote access must go through a VPN for security compliance.
Why candidates choose this
Candidates may think that remote access always requires a VPN for security, overlooking that a simple DNAT rule with proper firewall policies can securely expose a single service like HTTPS.
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 a simple 'allow' rule with the necessary NAT translation, failing to realize that without DNAT, the firewall has no way to forward the packet to the private IP address of the internal server.
Trap categories for this question
Scenario analysis trap
Incorrect. While a VPN would provide secure access, the scenario does not mention a VPN. The goal is to allow access directly via the internet without requiring a VPN.
Detailed technical explanation
How to think about this question
Destination NAT (DNAT) rewrites the destination IP address and port of incoming packets at the firewall's external interface before the routing decision is made. In a typical implementation, the firewall maintains a NAT table that maps the public IP:port (203.0.113.10:443) to the private IP:port (10.0.0.5:443), and the return traffic undergoes reverse NAT automatically. A common real-world pitfall is forgetting to also create a corresponding allow rule in the firewall's security policy for the translated traffic, which can cause the connection to fail even with correct DNAT configuration.
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 practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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: A) Port forwarding (DNAT) rule — A port forwarding (DNAT) rule is required because the web server uses a private RFC 1918 IP address (10.0.0.5), which is not routable on the public internet. The firewall must translate the destination IP from its public address (203.0.113.10) to the internal server's private address, allowing inbound traffic on port 443 to reach the correct internal host.
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.
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Last reviewed: Jun 11, 2026
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