- A
Place the web tier in a public subnet and the application tier in a private subnet, and configure security groups to allow inbound traffic to the application tier only from the web tier's security group.
This achieves isolation with minimal overhead.
- B
Create two VPCs: one for the web tier with a public subnet, and one for the application tier with a private subnet, and connect them using VPC peering.
Why wrong: VPC peering adds complexity; single VPC is simpler.
- C
Place the web tier in a public subnet and the application tier in a private subnet with a NAT gateway for outbound access, and use security groups to allow traffic from the web tier.
Why wrong: NAT gateway is unnecessary and adds cost; no outbound access required.
- D
Place both tiers in the same public subnet, and use a network ACL to restrict traffic from the web tier to the application tier.
Why wrong: Public subnets have direct internet access, violating isolation.
ANS-C01 Network Implementation Practice Question
This ANS-C01 practice question tests your understanding of network implementation. 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 deploying a multi-tier web application on AWS. The web tier runs on EC2 instances behind an Application Load Balancer (ALB), and the application tier runs on EC2 instances that connect to an RDS MySQL Multi-AZ DB instance. The application tier must be isolated from the internet and only accessible from the web tier. Which network implementation meets these requirements with the LEAST administrative overhead?
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
Place the web tier in a public subnet and the application tier in a private subnet, and configure security groups to allow inbound traffic to the application tier only from the web tier's security group.
Option C is correct because placing the web tier in a public subnet and the application tier in a private subnet with security groups allowing traffic only from the web tier is the standard design for multi-tier web applications with minimal overhead. Option A is wrong because using a network ACL alone would not isolate the application tier from the internet; a private subnet is needed. Option B is wrong because a NAT gateway is unnecessary for outbound access from the application tier (not required) and adds cost. Option D is wrong because using a different VPC and VPC peering adds complexity.
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 the web tier in a public subnet and the application tier in a private subnet, and configure security groups to allow inbound traffic to the application tier only from the web tier's security group.
Why this is correct
This achieves isolation with minimal overhead.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
Create two VPCs: one for the web tier with a public subnet, and one for the application tier with a private subnet, and connect them using VPC peering.
Why it's wrong here
VPC peering adds complexity; single VPC is simpler.
- ✗
Place the web tier in a public subnet and the application tier in a private subnet with a NAT gateway for outbound access, and use security groups to allow traffic from the web tier.
- ✗
Place both tiers in the same public subnet, and use a network ACL to restrict traffic from the web tier to the application tier.
Why it's wrong here
Public subnets have direct internet access, violating isolation.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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 a public subnet and the application tier in a private subnet, and configure security groups to allow inbound traffic to the application tier only from the web tier's security group. — Option C is correct because placing the web tier in a public subnet and the application tier in a private subnet with security groups allowing traffic only from the web tier is the standard design for multi-tier web applications with minimal overhead. Option A is wrong because using a network ACL alone would not isolate the application tier from the internet; a private subnet is needed. Option B is wrong because a NAT gateway is unnecessary for outbound access from the application tier (not required) and adds cost. Option D is wrong because using a different VPC and VPC peering adds complexity.
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: "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?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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