ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
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.
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
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.
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
Why it's wrong here
VPN does not resolve overlapping IPs.
- ✗
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
Why this is correct
Transit Gateway can perform NAT to resolve overlapping CIDRs.
- ✗
Use an AWS Direct Connect private virtual interface
Why it's wrong here
Direct Connect does not address overlapping IPs.
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Same concept, more angles
1 more way 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: 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.
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.