- A
Use VPC peering between the existing VPC and a new VPC with a non-overlapping CIDR, then route traffic through the new VPC.
Why wrong: This still requires the existing VPC to connect to on-premises, and the overlapping issue remains.
- B
Create a new VPC with a non-overlapping CIDR such as 172.16.0.0/16 and migrate resources.
Why wrong: The company may not want to migrate resources; also, the question implies using the existing VPC.
- C
Assign IPv6 CIDR to the existing VPC, use IPv6 for all resources, and connect over Direct Connect using IPv6.
IPv6 addresses do not overlap with the on-premises IPv4 space, providing unique addressing.
- D
Use AWS Transit Gateway with a Network Address Translation (NAT) attachment to translate the VPC CIDR.
Why wrong: Transit Gateway does not provide NAT; you would need a separate NAT instance or appliance.
Using IPv6 to Avoid IP Overlap with On-Premises Over Direct Connect
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 an IPv4 CIDR block of 10.0.0.0/16. It needs to connect to an on-premises data center over AWS Direct Connect. The on-premises network uses the 10.0.0.0/8 address space. The company cannot change the on-premises addressing. Which solution will allow connectivity without overlapping IP addresses?
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
Assign IPv6 CIDR to the existing VPC, use IPv6 for all resources, and connect over Direct Connect using IPv6.
Option C is correct because assigning an IPv6 CIDR to the existing VPC and using IPv6 for all resources avoids the IPv4 address overlap with the on-premises 10.0.0.0/8 network. AWS Direct Connect supports both IPv4 and IPv6 traffic, so you can establish a BGP session over IPv6 and route IPv6 traffic between the VPC and on-premises, completely bypassing the conflicting IPv4 address space.
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 VPC peering between the existing VPC and a new VPC with a non-overlapping CIDR, then route traffic through the new VPC.
Why it's wrong here
This still requires the existing VPC to connect to on-premises, and the overlapping issue remains.
- ✗
Create a new VPC with a non-overlapping CIDR such as 172.16.0.0/16 and migrate resources.
Why it's wrong here
The company may not want to migrate resources; also, the question implies using the existing VPC.
- ✓
Assign IPv6 CIDR to the existing VPC, use IPv6 for all resources, and connect over Direct Connect using IPv6.
Why this is correct
IPv6 addresses do not overlap with the on-premises IPv4 space, providing unique addressing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use AWS Transit Gateway with a Network Address Translation (NAT) attachment to translate the VPC CIDR.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume Direct Connect only works with IPv4 or that overlapping IPv4 addresses can be resolved with NAT or Transit Gateway, but the exam tests the understanding that IPv6 is a clean way to avoid IPv4 overlap without changing the existing VPC CIDR.
Detailed technical explanation
How to think about this question
When using IPv6 with Direct Connect, you must configure a virtual interface (VIF) with IPv6 BGP peering and ensure that the on-premises router supports IPv6. The VPC's IPv6 CIDR is globally unique (from AWS's 2600:1f16::/28 pool), so there is no overlap risk. In a real-world scenario, this approach is ideal when on-premises addressing cannot be changed, but it requires that all VPC resources support IPv6 (e.g., dual-stack EC2 instances, IPv6-enabled ALB/NLB) and that the on-premises network has IPv6 routing enabled.
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
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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: Assign IPv6 CIDR to the existing VPC, use IPv6 for all resources, and connect over Direct Connect using IPv6. — Option C is correct because assigning an IPv6 CIDR to the existing VPC and using IPv6 for all resources avoids the IPv4 address overlap with the on-premises 10.0.0.0/8 network. AWS Direct Connect supports both IPv4 and IPv6 traffic, so you can establish a BGP session over IPv6 and route IPv6 traffic between the VPC and on-premises, completely bypassing the conflicting IPv4 address space.
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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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 an IPv4 CIDR block of 10.0.0.0/16. It needs to connect to an on-premises data center via AWS Direct Connect. The on-premises network uses 10.0.0.0/8. Which action should the network engineer take to avoid IP address overlap?
easy- A.Use a NAT gateway to translate the VPC addresses when connecting to on-premises.
- B.Use AWS Direct Connect gateway to automatically handle overlapping IPs.
- C.Add a secondary CIDR block to the VPC and use it for resources that need to connect to on-premises.
- ✓ D.Create a new VPC with a non-overlapping CIDR block, such as 172.16.0.0/16, and migrate resources.
Why D: Option D is correct because the VPC CIDR 10.0.0.0/16 is a subset of the on-premises 10.0.0.0/8, creating an overlap that prevents Direct Connect routing. AWS does not support overlapping IP spaces across a Direct Connect virtual interface; the only viable solution is to use a non-overlapping CIDR (e.g., 172.16.0.0/16) for the VPC and migrate resources to it.
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Last reviewed: Jun 24, 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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