This ANS-C01 practice question tests your understanding of network design. 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 has a VPC with a CIDR of 10.0.0.0/16 and needs to peer with another VPC that has CIDR 10.0.0.0/16. What is the issue and how can it be resolved?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPCs have overlapping CIDRs, so they cannot be directly peered. You must re-IP one VPC or use a NAT solution.
Option C is correct because overlapping CIDRs prevent VPC Peering. Option A is wrong because VPC Peering does not require non-overlapping CIDRs for established connections but for new ones it's a limitation. Option B is wrong because Transit Gateway also does not support overlapping CIDRs without NAT. Option D is wrong because Direct Connect also requires non-overlapping CIDRs.
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.
✗
The VPCs can be peered if you enable DNS resolution.
Use a Transit Gateway to connect the VPCs, which supports overlapping CIDRs.
Why it's wrong here
Wrong: Transit Gateway also requires unique CIDRs.
✗
Use a Direct Connect Gateway to connect the VPCs, which ignores CIDR overlap.
Why it's wrong here
Wrong: Direct Connect Gateway also requires unique ranges.
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 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
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: The VPCs have overlapping CIDRs, so they cannot be directly peered. You must re-IP one VPC or use a NAT solution. — Option C is correct because overlapping CIDRs prevent VPC Peering. Option A is wrong because VPC Peering does not require non-overlapping CIDRs for established connections but for new ones it's a limitation. Option B is wrong because Transit Gateway also does not support overlapping CIDRs without NAT. Option D is wrong because Direct Connect also requires non-overlapping CIDRs.
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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