- A
Use security groups on web servers allowing 0.0.0.0/0 on ports 80/443, and on app servers allowing the web servers' CIDR block
Why wrong: Allowing the entire CIDR is not least-privilege; should reference the security group.
- B
Use a Network ACL on the public subnet allowing inbound ports 80 and 443 from 0.0.0.0/0, and security groups on web and app servers with the app servers' security group referencing the web servers' security group
This provides least-privilege with stateful security groups and stateless NACL.
- C
Use a single Network ACL for both public and private subnets with allow rules for ports 80 and 443
Why wrong: NACLs are stateless; a single NACL would not provide least-privilege.
- D
Use a single Network ACL on the private subnet allowing inbound ports 80 and 443 from the public subnet CIDR
Why wrong: NACL would not distinguish between web server traffic and internet traffic that bypasses web servers.
Quick Answer
The correct choice is to use a Network ACL on the public subnet allowing inbound ports 80 and 443 from 0.0.0.0/0, paired with security groups on the web and app servers where the app servers’ security group references the web servers’ security group as its source. This design achieves least-privilege access by leveraging security group chaining, a stateful mechanism that automatically tracks connection state and eliminates the need to manage ephemeral ports or explicit CIDR ranges for return traffic. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how to combine stateless Network ACLs for broad subnet-level filtering with stateful security groups for granular, identity-based control—a critical distinction for PCI DSS compliance. A common trap is choosing a solution that uses NACLs for internal traffic, which breaks stateful tracking and forces manual ephemeral port management. Remember the memory tip: “NACLs block the neighborhood, security groups guard the door.”
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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.
A financial services company must meet PCI DSS compliance requirements. They have a VPC with public and private subnets. The web servers in the public subnets must only accept traffic from the internet on ports 80 and 443. The application servers in the private subnets must only accept traffic from the web servers. Which network design ensures least-privilege access?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
Use a Network ACL on the public subnet allowing inbound ports 80 and 443 from 0.0.0.0/0, and security groups on web and app servers with the app servers' security group referencing the web servers' security group
Option B is correct because it uses security groups for stateful, least-privilege access control. The web servers' security group allows inbound ports 80 and 443 from 0.0.0.0/0, and the app servers' security group references the web servers' security group as the source, ensuring only traffic from the web servers is permitted. This design leverages security group chaining, which automatically handles return traffic and avoids the need for explicit CIDR management, aligning with PCI DSS least-privilege requirements.
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.
- ✗
Use security groups on web servers allowing 0.0.0.0/0 on ports 80/443, and on app servers allowing the web servers' CIDR block
Why it's wrong here
Allowing the entire CIDR is not least-privilege; should reference the security group.
- ✓
Use a Network ACL on the public subnet allowing inbound ports 80 and 443 from 0.0.0.0/0, and security groups on web and app servers with the app servers' security group referencing the web servers' security group
Why this is correct
This provides least-privilege with stateful security groups and stateless NACL.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a single Network ACL for both public and private subnets with allow rules for ports 80 and 443
Why it's wrong here
NACLs are stateless; a single NACL would not provide least-privilege.
- ✗
Use a single Network ACL on the private subnet allowing inbound ports 80 and 443 from the public subnet CIDR
Why it's wrong here
NACL would not distinguish between web server traffic and internet traffic that bypasses web servers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often default to using Network ACLs for subnet-level control, forgetting that security groups provide stateful, instance-level filtering with the ability to reference other security groups, which is more aligned with least-privilege and PCI DSS requirements.
Detailed technical explanation
How to think about this question
Security groups are stateful, meaning that if you allow inbound traffic, the return outbound traffic is automatically permitted regardless of outbound rules, which simplifies compliance with PCI DSS requirement 1.2.1 (restrict inbound traffic). In contrast, Network ACLs are stateless and require explicit inbound and outbound rules, which can lead to misconfigurations if not carefully managed. In a real-world scenario, using security group references allows dynamic scaling of web servers without updating ACL rules, as the app servers' security group automatically includes any new web server instances that are members of the referenced security group.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a Network ACL on the public subnet allowing inbound ports 80 and 443 from 0.0.0.0/0, and security groups on web and app servers with the app servers' security group referencing the web servers' security group — Option B is correct because it uses security groups for stateful, least-privilege access control. The web servers' security group allows inbound ports 80 and 443 from 0.0.0.0/0, and the app servers' security group references the web servers' security group as the source, ensuring only traffic from the web servers is permitted. This design leverages security group chaining, which automatically handles return traffic and avoids the need for explicit CIDR management, aligning with PCI DSS least-privilege requirements.
What should I do if I get this ANS-C01 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: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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 24, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.
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