- A
Place all three services in the same DMZ subnet and use host-based firewalls to restrict traffic.
Why wrong: Host-based firewalls can be misconfigured or bypassed; a single subnet does not provide network-level isolation.
- B
Create two DMZ subnets: one for the web server and API gateway, and another for the database server.
Why wrong: The web server and API gateway share a subnet, allowing unnecessary direct access from web to database if the API gateway is compromised.
- C
Place the web server in a DMZ subnet, the API gateway in a separate DMZ subnet, and the database server on the internal network.
Why wrong: Placing the database on the internal network exposes it to internal threats and complicates firewall rules for encrypted traffic.
- D
Create three separate DMZ subnets: one for the web server, one for the API gateway, and one for the database server, with firewall rules allowing only required traffic.
This provides defense in depth; each tier is isolated, and only specific ports/protocols are allowed between them.
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. 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 security architect is designing a new DMZ for an e-commerce platform. The DMZ must host a web server, an API gateway, and a database server. The architect needs to minimize the attack surface while ensuring the web server can communicate with the API gateway, and the API gateway can communicate with the database. Which network segmentation approach best meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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
Create three separate DMZ subnets: one for the web server, one for the API gateway, and one for the database server, with firewall rules allowing only required traffic.
Option D is correct because it implements the principle of least privilege through network segmentation. By placing each service in its own DMZ subnet with firewall rules that allow only the required traffic (e.g., HTTP/HTTPS from web to API, SQL from API to database), the attack surface is minimized. This prevents lateral movement if one service is compromised, as an attacker cannot directly reach the database from the web server or the API gateway from 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.
- ✗
Place all three services in the same DMZ subnet and use host-based firewalls to restrict traffic.
Why it's wrong here
Host-based firewalls can be misconfigured or bypassed; a single subnet does not provide network-level isolation.
- ✗
Create two DMZ subnets: one for the web server and API gateway, and another for the database server.
Why it's wrong here
The web server and API gateway share a subnet, allowing unnecessary direct access from web to database if the API gateway is compromised.
- ✗
Place the web server in a DMZ subnet, the API gateway in a separate DMZ subnet, and the database server on the internal network.
Why it's wrong here
Placing the database on the internal network exposes it to internal threats and complicates firewall rules for encrypted traffic.
- ✓
Create three separate DMZ subnets: one for the web server, one for the API gateway, and one for the database server, with firewall rules allowing only required traffic.
Why this is correct
This provides defense in depth; each tier is isolated, and only specific ports/protocols are allowed between them.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that placing the database server on the internal network (Option C) is acceptable, but in a DMZ design, any server that must be accessed from a DMZ should remain in the DMZ to avoid exposing internal network resources to potential compromise.
Detailed technical explanation
How to think about this question
In a three-tier DMZ architecture, each tier (web, application, database) should reside in its own subnet with stateful firewall rules that permit only specific protocols (e.g., TCP/443 for HTTPS, TCP/3306 for MySQL) and deny all other traffic by default. This aligns with the NIST SP 800-41 guidelines for DMZ design and prevents an attacker from pivoting from a compromised web server to the database without traversing multiple firewall zones. Real-world implementations often use VLANs or VXLANs with ACLs to enforce this segmentation.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this CAS-004 question test?
Security Architecture — This question tests Security Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create three separate DMZ subnets: one for the web server, one for the API gateway, and one for the database server, with firewall rules allowing only required traffic. — Option D is correct because it implements the principle of least privilege through network segmentation. By placing each service in its own DMZ subnet with firewall rules that allow only the required traffic (e.g., HTTP/HTTPS from web to API, SQL from API to database), the attack surface is minimized. This prevents lateral movement if one service is compromised, as an attacker cannot directly reach the database from the web server or the API gateway from the internet.
What should I do if I get this CAS-004 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: "best", "minimum / minimize". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 30, 2026
This CAS-004 practice question is part of Courseiva's free CompTIA 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 CAS-004 exam.
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