The correct choice is to allow inbound HTTP, HTTPS, SMTP, and DNS to the DMZ. This is the most appropriate firewall rule because a DMZ acts as a buffer zone between the untrusted internet and your internal network, so you must apply the principle of least privilege by permitting only the essential protocols that public-facing servers require to function. Web servers need HTTP and HTTPS, while email servers need SMTP, and both rely on DNS for name resolution; blocking everything else prevents attackers from exploiting unnecessary open ports. On the ISC2 Certified in Cybersecurity CC exam, this question tests your understanding of DMZ segmentation and inbound traffic filtering, often appearing as a scenario where a trap answer includes allowing all traffic or permitting common but dangerous protocols like FTP or Telnet. A solid memory tip is to think of the acronym “WEDS” — Web, Email, DNS — and remember that only these specific services should ever cross the internet-to-DMZ boundary.
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 network administrator is configuring a DMZ for a company's web and email servers. Which firewall rule is most appropriate for traffic from the internet to the DMZ?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allow inbound HTTP, HTTPS, SMTP, and DNS to DMZ
Option B is correct because a DMZ must selectively permit essential services from the internet to the public-facing servers while blocking all other inbound traffic. HTTP (80), HTTPS (443), SMTP (25), and DNS (53) are the standard protocols required for web and email servers to function. This rule implements the principle of least privilege by allowing only the necessary traffic to the DMZ.
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.
✗
Deny all inbound traffic to DMZ but allow outbound
Why it's wrong here
This would prevent external users from accessing the servers.
✓
Allow inbound HTTP, HTTPS, SMTP, and DNS to DMZ
Why this is correct
These are the required services for web and email servers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Allow inbound only to the web server on ports 80 and 443
Why it's wrong here
This does not allow email traffic (SMTP, POP3) to the email server.
✗
Allow all inbound traffic to DMZ
Why it's wrong here
Allowing all inbound traffic defeats the purpose of a DMZ.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the misconception that a DMZ should allow only web traffic (HTTP/HTTPS) and forget that email servers require SMTP and DNS, leading candidates to choose option C instead of the more complete option B.
Detailed technical explanation
How to think about this question
In a typical DMZ architecture, the firewall uses stateful inspection to track connections; for SMTP, the firewall must allow inbound TCP port 25 to the mail server, but often also permits outbound SMTP for relaying. DNS traffic to the DMZ may be UDP port 53 for queries and TCP port 53 for zone transfers, and the rule should specify both. A common real-world scenario is that the DMZ also hosts a reverse proxy, which terminates TLS and forwards HTTP/HTTPS to internal servers, requiring the firewall to allow only the proxy's IP as the destination.
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 analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
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: Allow inbound HTTP, HTTPS, SMTP, and DNS to DMZ — Option B is correct because a DMZ must selectively permit essential services from the internet to the public-facing servers while blocking all other inbound traffic. HTTP (80), HTTPS (443), SMTP (25), and DNS (53) are the standard protocols required for web and email servers to function. This rule implements the principle of least privilege by allowing only the necessary traffic to the DMZ.
What should I do if I get this CC 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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