- A
Use a single public subnet for all tiers and control access with security groups.
Why wrong: All instances would have public IPs, exposing app and database to the internet.
- B
Use private subnets for all tiers and a NAT gateway for internet access from the web tier. Use security groups to control traffic.
Why wrong: No inbound internet access to web tier unless an ALB is in a public subnet.
- C
Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.
The ALB in public subnet provides inbound access; private subnets isolate tiers.
- D
Use a VPN connection from the on-premises network to access all tiers.
Why wrong: This does not address internet access for the web tier.
- E
Use public subnets for the web tier, private subnets for the application tier, and isolated subnets (no route to internet) for the database tier. Use security groups to allow traffic only from the web to app and app to database.
This provides proper isolation and access control.
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 designing a multi-tier 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 be isolated from all other tiers except the application tier. Which TWO network architectures meet these requirements? (Choose TWO.)
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 public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.
Options B and D are correct. Option B uses public subnets for web, private subnets for app, and isolated subnets for database, with security groups controlling access. Option D uses a single private subnet with security groups and an ALB in a public subnet to expose the web tier. Option A is wrong because a single public subnet does not isolate tiers. Option C is wrong because placing all tiers in private subnets with a NAT gateway does not provide inbound access from the internet. Option E is wrong because a VPN connection is not needed.
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 single public subnet for all tiers and control access with security groups.
Why it's wrong here
All instances would have public IPs, exposing app and database to the internet.
- ✗
Use private subnets for all tiers and a NAT gateway for internet access from the web tier. Use security groups to control traffic.
Why it's wrong here
No inbound internet access to web tier unless an ALB is in a public subnet.
- ✓
Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.
Why this is correct
The ALB in public subnet provides inbound access; private subnets isolate tiers.
Related concept
CIDR notation defines the prefix length.
- ✗
Use a VPN connection from the on-premises network to access all tiers.
Why it's wrong here
This does not address internet access for the web tier.
- ✓
Use public subnets for the web tier, private subnets for the application tier, and isolated subnets (no route to internet) for the database tier. Use security groups to allow traffic only from the web to app and app to database.
Why this is correct
This provides proper isolation and access control.
Related concept
CIDR notation defines the prefix length.
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: Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers. — Options B and D are correct. Option B uses public subnets for web, private subnets for app, and isolated subnets for database, with security groups controlling access. Option D uses a single private subnet with security groups and an ALB in a public subnet to expose the web tier. Option A is wrong because a single public subnet does not isolate tiers. Option C is wrong because placing all tiers in private subnets with a NAT gateway does not provide inbound access from the internet. Option E is wrong because a VPN connection is not needed.
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
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