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 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?
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.
Option C is correct because 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.
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 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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Transit Gateway supports multiple route tables, enabling you to isolate traffic between attachments. In this scenario, you can create a route table for the VPN attachment that points to the VPC attachment for specific routes, and a separate route table for the VPC attachment that does not propagate the overlapping on-premises route, effectively breaking the routing loop. This approach leverages BGP over the VPN to exchange routes, and the Transit Gateway's route table association and propagation rules allow fine-grained control, similar to how you would use separate VRF instances in MPLS networks.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Create a Transit Gateway with a VPN attachment to on-premises and use route table separation. — Option C is correct because 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.
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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Question Discussion
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