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 with CIDR 10.0.0.0/16. They plan to use a transit gateway to connect the VPCs. What is the correct approach to handle the overlapping CIDR ranges?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a new VPC with a non-overlapping CIDR and migrate resources from one of the existing VPCs.
Transit gateways do not perform NAT or resolve overlapping CIDR conflicts between attached VPCs. When two VPCs have identical CIDR blocks (10.0.0.0/16), the transit gateway cannot route traffic correctly because it cannot distinguish between the two networks. The only viable solution is to create a new VPC with a non-overlapping CIDR and migrate resources from one of the existing VPCs, eliminating the conflict at the network layer.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Create a new VPC with a non-overlapping CIDR and migrate resources from one of the existing VPCs.
Why this is correct
This resolves the overlap by eliminating it.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create a VPC peering connection and use a smaller subnet CIDR for traffic filtering.
Why it's wrong here
VPC peering does not allow overlapping CIDRs.
✗
Use a transit gateway with network address translation (NAT) to translate one VPC CIDR to a non-overlapping range.
Configure the transit gateway with equal-cost multipath (ECMP) to load balance traffic between the overlapping CIDRs.
Why it's wrong here
ECMP does not resolve overlap.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a transit gateway can perform NAT or otherwise magically handle overlapping CIDRs, but in reality, AWS transit gateways are pure Layer-3 routers that require unique destination prefixes for correct forwarding.
Detailed technical explanation
How to think about this question
Under the hood, a transit gateway uses a route table to direct traffic based on destination CIDR. With overlapping CIDRs, the route table would contain two identical entries, causing the transit gateway to either reject the second attachment or unpredictably route traffic to one VPC. In practice, this is a common issue when merging organizations or connecting environments with legacy addressing, and the only AWS-native solution is to re-IP one of the VPCs using a new CIDR block (e.g., 10.1.0.0/16) and migrate resources, as AWS does not support overlapping VPC CIDRs in any direct peering or transit gateway configuration.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a new VPC with a non-overlapping CIDR and migrate resources from one of the existing VPCs. — Transit gateways do not perform NAT or resolve overlapping CIDR conflicts between attached VPCs. When two VPCs have identical CIDR blocks (10.0.0.0/16), the transit gateway cannot route traffic correctly because it cannot distinguish between the two networks. The only viable solution is to create a new VPC with a non-overlapping CIDR and migrate resources from one of the existing VPCs, eliminating the conflict at the network layer.
What should I do if I get this ANS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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