- A
Place all tiers in public subnets and use security groups to control traffic between tiers.
Why wrong: Incorrect: public subnets expose app and DB to internet, not secure.
- B
Place the web tier in public subnets with an internet gateway, and the application and database tiers in private subnets. Use security groups to allow traffic from the web tier to the application tier, and from the application tier to the database tier.
Correct design: public subnet with IGW for web, private subnets for app and DB, security groups restrict traffic.
- C
Place all tiers in the same subnet and use network ACLs to restrict traffic between tiers.
Why wrong: Incorrect: single subnet cannot isolate tiers; subnets are in the same VPC but traffic flows through route tables and security groups.
- D
Place the web tier in a private subnet and use a NAT gateway for outbound internet access. Place the application and database tiers in public subnets.
Why wrong: Incorrect: web tier needs inbound internet access, private subnet cannot receive internet traffic without a load balancer in a public subnet.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 company is deploying a multi-tier web application in a VPC. The web tier must be accessible from the internet, while the application tier must only be accessible from the web tier. The database tier must only be accessible from the application tier. Which design 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.
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 the web tier in public subnets with an internet gateway, and the application and database tiers in private subnets. Use security groups to allow traffic from the web tier to the application tier, and from the application tier to the database tier.
Option A is correct because using public subnets for the web tier with an internet gateway and private subnets for the application and database tiers with security groups restricting traffic between tiers is the standard design. Option B is wrong because placing all tiers in public subnets exposes the application and database tiers to the internet. Option C is wrong because placement of tiers does not depend on CIDR blocks but on subnet types and route tables. Option D is wrong because using a single security group for all tiers cannot enforce tier-to-tier access restrictions.
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.
- ✗
Place all tiers in public subnets and use security groups to control traffic between tiers.
Why it's wrong here
Incorrect: public subnets expose app and DB to internet, not secure.
- ✓
Place the web tier in public subnets with an internet gateway, and the application and database tiers in private subnets. Use security groups to allow traffic from the web tier to the application tier, and from the application tier to the database tier.
Why this is correct
Correct design: public subnet with IGW for web, private subnets for app and DB, security groups restrict traffic.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
Place all tiers in the same subnet and use network ACLs to restrict traffic between tiers.
Why it's wrong here
Incorrect: single subnet cannot isolate tiers; subnets are in the same VPC but traffic flows through route tables and security groups.
- ✗
Place the web tier in a private subnet and use a NAT gateway for outbound internet access. Place the application and database tiers in public subnets.
Why it's wrong here
Incorrect: web tier needs inbound internet access, private subnet cannot receive internet traffic without a load balancer in a public subnet.
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 Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place the web tier in public subnets with an internet gateway, and the application and database tiers in private subnets. Use security groups to allow traffic from the web tier to the application tier, and from the application tier to the database tier. — Option A is correct because using public subnets for the web tier with an internet gateway and private subnets for the application and database tiers with security groups restricting traffic between tiers is the standard design. Option B is wrong because placing all tiers in public subnets exposes the application and database tiers to the internet. Option C is wrong because placement of tiers does not depend on CIDR blocks but on subnet types and route tables. Option D is wrong because using a single security group for all tiers cannot enforce tier-to-tier access restrictions.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". 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?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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