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 has a VPC with a CIDR block of 10.0.0.0/16. It needs to create a secondary CIDR block for additional subnets that must not overlap with the existing CIDR. Which CIDR block should be used?
172.16.0.0/16
Why wrong: This is a valid private CIDR but not the best answer as it is in a different private range; however, the question does not restrict to 10.0.0.0/8; but option C is more straightforward.
10.0.0.0/16
Why wrong: Same as existing CIDR, cannot be added as secondary.
10.0.0.0/8
Why wrong: This overlaps with the existing 10.0.0.0/16.
10.1.0.0/16
This does not overlap and is a valid private CIDR.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
10.1.0.0/16
VPC secondary CIDR blocks must not overlap with the primary CIDR. Option C (10.1.0.0/16) is in the 10.0.0.0/8 range but does not overlap with 10.0.0.0/16. Option A overlaps (10.0.0.0/8 includes 10.0.0.0/16). Option B overlaps (10.0.0.0/16 same). Option D (172.16.0.0/16) is valid but not in the 10.0.0.0/8 range; however, VPC can have any private CIDR, but the question implies a secondary CIDR that is not overlapping; Option C is correct because it is a common practice to use a different /16 within the 10.0.0.0/8.
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
For each option: why learners choose it and why it is or isn't the right answer here.
172.16.0.0/16
Why it's wrong here
This is a valid private CIDR but not the best answer as it is in a different private range; however, the question does not restrict to 10.0.0.0/8; but option C is more straightforward.
10.0.0.0/16
Why it's wrong here
Same as existing CIDR, cannot be added as secondary.
10.0.0.0/8
Why it's wrong here
This overlaps with the existing 10.0.0.0/16.
10.1.0.0/16
Common exam traps
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
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.
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
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
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
Network Design — This question tests Network Design — CIDR notation defines the prefix length..
The correct answer is: 10.1.0.0/16 — VPC secondary CIDR blocks must not overlap with the primary CIDR. Option C (10.1.0.0/16) is in the 10.0.0.0/8 range but does not overlap with 10.0.0.0/16. Option A overlaps (10.0.0.0/8 includes 10.0.0.0/16). Option B overlaps (10.0.0.0/16 same). Option D (172.16.0.0/16) is valid but not in the 10.0.0.0/8 range; however, VPC can have any private CIDR, but the question implies a secondary CIDR that is not overlapping; Option C is correct because it is a common practice to use a different /16 within the 10.0.0.0/8.
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.
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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