- A
Use an AWS Site-to-Site VPN connection
Why wrong: VPN does not resolve overlapping IPs.
- B
Establish VPC peering between the two VPCs
Why wrong: VPC peering does not support overlapping CIDRs.
- C
Use an AWS Transit Gateway with a transit gateway attachment and configure NAT on the transit gateway to translate IPs
Transit Gateway can perform NAT to resolve overlapping CIDRs.
- D
Use an AWS Direct Connect private virtual interface
Why wrong: Direct Connect does not address overlapping IPs.
Question 1,117 of 1,705
How to Connect Overlapping VPCs Using Transit Gateway NAT
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 block of 10.0.0.0/16 and needs to connect to a partner's VPC with CIDR 10.0.0.0/16. The VPCs are in the same Region. What is the best solution?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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 an AWS Transit Gateway with a transit gateway attachment and configure NAT on the transit gateway to translate IPs
Option C is correct because when two VPCs have overlapping CIDR blocks (both 10.0.0.0/16), VPC peering and Direct Connect cannot resolve the IP conflict, as they require non-overlapping address spaces. An AWS Transit Gateway with NAT attachments can translate IP addresses at the transit gateway level, allowing traffic to flow between overlapping VPCs by mapping source/destination IPs to non-conflicting ranges. This solution provides a scalable, managed way to handle overlapping CIDRs without complex manual routing.
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.
- ✗
Use an AWS Site-to-Site VPN connection
- ✗
Establish VPC peering between the two VPCs
Why it's wrong here
VPC peering does not support overlapping CIDRs.
- ✓
Use an AWS Transit Gateway with a transit gateway attachment and configure NAT on the transit gateway to translate IPs
- ✗
Use an AWS Direct Connect private virtual interface
Why it's wrong here
Direct Connect does not address overlapping IPs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that VPC peering or VPN can handle overlapping CIDRs by simply adding routes, but the trap is that overlapping IPs cause routing ambiguity and packet loss, requiring NAT at the transit gateway or a middlebox appliance to resolve the conflict.
Detailed technical explanation
How to think about this question
AWS Transit Gateway supports Network Address Translation (NAT) on attachments via the 'transit gateway NAT' feature, which can perform IP translation between VPCs with overlapping CIDRs. Under the hood, the transit gateway uses a NAT table to map source IPs from one VPC to a different IP range before forwarding traffic to the other VPC, and reverse translation on return traffic. This is critical in mergers, acquisitions, or multi-account architectures where legacy VPCs cannot be renumbered.
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 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.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
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: Use an AWS Transit Gateway with a transit gateway attachment and configure NAT on the transit gateway to translate IPs — Option C is correct because when two VPCs have overlapping CIDR blocks (both 10.0.0.0/16), VPC peering and Direct Connect cannot resolve the IP conflict, as they require non-overlapping address spaces. An AWS Transit Gateway with NAT attachments can translate IP addresses at the transit gateway level, allowing traffic to flow between overlapping VPCs by mapping source/destination IPs to non-conflicting ranges. This solution provides a scalable, managed way to handle overlapping CIDRs without complex manual routing.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Same concept, more angles
1 more ways this is tested on ANS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a VPC with a CIDR block of 10.0.0.0/16. The company needs to peer with another VPC that has a CIDR block of 10.0.0.0/16. What should the network engineer do to enable connectivity between the two VPCs?
easy- ✓ A.Use an AWS Transit Gateway with Network Address Translation (NAT) to resolve overlapping CIDRs.
- B.Use an internet gateway to route traffic between the VPCs.
- C.Create a VPC peering connection and add routes in both route tables.
- D.Create a VPC peering connection and use a network address translation (NAT) device.
Why A: Option A is correct because when two VPCs have overlapping CIDR blocks (both 10.0.0.0/16), a standard VPC peering connection cannot be established due to route table conflicts. An AWS Transit Gateway can be used with Network Address Translation (NAT) to translate the overlapping IP addresses, enabling connectivity between the VPCs by allowing traffic to be routed through the Transit Gateway with NAT applied to resolve the address conflict.
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Last reviewed: Jul 4, 2026
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
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