- A
Use a VPN between the web and application tiers and between application and database tiers.
Why wrong: VPN adds unnecessary complexity for intra-VPC communication.
- B
Place all tiers in the same private subnet and use security groups for isolation.
Why wrong: Same subnet does not provide network isolation; security groups alone are not enough for best practice.
- C
Place web tier in public subnets, application and database tiers in private subnets. Use security groups to allow only necessary traffic between tiers.
Security groups provide stateful filtering and are best practice for tier isolation.
- D
Place all tiers in public subnets and use network ACLs to restrict traffic.
Why wrong: Public subnets expose resources; network ACLs are stateless and complex.
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 company is designing a network for a three-tier application that must be PCI DSS compliant. The web tier must be accessible from the internet, the application tier must only be accessible from the web tier, and the database tier must only be accessible from the application tier. All tiers are in the same VPC. What is the MOST secure way to implement this?
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
Place web tier in public subnets, application and database tiers in private subnets. Use security groups to allow only necessary traffic between tiers.
Option A is correct because separate public and private subnets with security groups restricting traffic between tiers provide the required isolation. Option B is wrong because network ACLs are stateless and harder to manage for this use case. Option C is wrong because a single subnet does not provide isolation. Option D is wrong because a VPN is unnecessary for intra-VPC traffic.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 a VPN between the web and application tiers and between application and database tiers.
Why it's wrong here
VPN adds unnecessary complexity for intra-VPC communication.
- ✗
Place all tiers in the same private subnet and use security groups for isolation.
Why it's wrong here
Same subnet does not provide network isolation; security groups alone are not enough for best practice.
- ✓
Place web tier in public subnets, application and database tiers in private subnets. Use security groups to allow only necessary traffic between tiers.
Why this is correct
Security groups provide stateful filtering and are best practice for tier isolation.
Related concept
CIDR notation defines the prefix length.
- ✗
Place all tiers in public subnets and use network ACLs to restrict traffic.
Why it's wrong here
Public subnets expose resources; network ACLs are stateless and complex.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place web tier in public subnets, application and database tiers in private subnets. Use security groups to allow only necessary traffic between tiers. — Option A is correct because separate public and private subnets with security groups restricting traffic between tiers provide the required isolation. Option B is wrong because network ACLs are stateless and harder to manage for this use case. Option C is wrong because a single subnet does not provide isolation. Option D is wrong because a VPN is unnecessary for intra-VPC traffic.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 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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