ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
Watch out — candidates often 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.
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.
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.
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.
- ✗
Use AWS Transit Gateway with a Network Address Translation (NAT) attachment to translate the VPC CIDR.
Why it's wrong here
Transit Gateway does not provide NAT; you would need a separate NAT instance or appliance.
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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: 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.