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 multi-tier application that must meet compliance requirements. The architecture includes a VPC with public, private, and database subnets. Which TWO actions should be taken to ensure the database subnets are not directly accessible from the internet? (Select TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure a network ACL on the database subnets to deny inbound traffic from 0.0.0.0/0.
Options A and D are correct because a public subnet must not be used for databases, and a proper network ACL on the database subnet can deny inbound from 0.0.0.0/0. Option B is wrong because a NATGateway in the database subnet would still allow outbound but not inbound; however, placing NAT in database subnet is not best practice. Option C is wrong because security groups are stateful and allow return traffic, but a deny rule in network ACL is needed. Option E is wrong because IGW in database subnet would expose it.
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.
✗
Attach an Internet Gateway to the database subnets.
Why it's wrong here
Wrong: This would expose them to the internet.
✗
Create a NAT Gateway in the database subnets.
Why it's wrong here
Wrong: NATGateway is not needed for database isolation.
✗
Associate a security group that denies inbound traffic from 0.0.0.0/0.
Why it's wrong here
Wrong: Security groups only support allow rules, not deny.
✓
Configure a network ACL on the database subnets to deny inbound traffic from 0.0.0.0/0.
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.
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: Configure a network ACL on the database subnets to deny inbound traffic from 0.0.0.0/0. — Options A and D are correct because a public subnet must not be used for databases, and a proper network ACL on the database subnet can deny inbound from 0.0.0.0/0. Option B is wrong because a NAT Gateway in the database subnet would still allow outbound but not inbound; however, placing NAT in database subnet is not best practice. Option C is wrong because security groups are stateful and allow return traffic, but a deny rule in network ACL is needed. Option E is wrong because IGW in database subnet would expose it.
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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Question Discussion
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