ANS-C01 Network Design Practice Question
A company has a Direct Connect connection with a private VIF to a VPC. The VPC has a virtual private gateway attached. The on-premises network advertises a specific route 10.0.0.0/16, but the VPC uses the same CIDR 10.0.0.0/16. The company requires connectivity to the VPC from on-premises but cannot change the VPC CIDR. What is the most cost-effective solution?
⚠ Common exam trap
AWS often tests the misconception that Direct Connect or VPC peering can handle overlapping CIDRs, but the trap here is that only a Transit Gateway with route table separation (or a similar overlay mechanism like VPN with BGP communities) can resolve CIDR conflicts without changing the network addressing.
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
✓
Create a Transit Gateway with a VPN attachment to on-premises and use route table separation.
A Transit Gateway with a VPN attachment allows you to use route table separation to isolate the overlapping CIDR (10.0.0.0/16) between the on-premises network and the VPC. By creating separate route tables for the VPN attachment and the VPC attachment, you can control traffic flow and avoid routing conflicts without changing the VPC CIDR. This is the most cost-effective solution as it leverages existing VPN connectivity and avoids the expense of migrating workloads or provisioning additional infrastructure.
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 on-premises network and the VPC.
Why it's wrong here
VPC peering does not support overlapping CIDRs.
- ✗
Set up a Direct Connect Gateway and attach the VPC and on-premises networks.
Why it's wrong here
Direct Connect Gateway still requires unique CIDRs.
- ✓
Create a Transit Gateway with a VPN attachment to on-premises and use route table separation.
Why this is correct
Transit Gateway can manage overlapping CIDRs with multiple route tables.
- ✗
Create a new VPC with a different CIDR and migrate workloads.
Why it's wrong here
Migration is disruptive and not the most cost-effective.
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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.