- A
Create a more specific route in the VPC route table for the on-premises CIDR.
Why wrong: Overlap still causes ambiguity.
- B
Enable route propagation on the VPC route tables.
Why wrong: Does not resolve overlap.
- C
Use a VPN connection with static routes instead of BGP.
Why wrong: Does not resolve overlapping CIDRs.
- D
Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16.
Eliminates the overlap.
Question 1,137 of 1,705
ANS-C01 Network Design Practice Question
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 a CIDR of 10.0.0.0/16 and needs to connect to an on-premises network with CIDR 10.0.0.0/8. The company wants to use AWS Site-to-Site VPN. What configuration change is required to avoid routing conflicts?
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
✓
Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16.
The VPC CIDR 10.0.0.0/16 is a subset of the on-premises CIDR 10.0.0.0/8. AWS Site-to-Site VPN cannot route traffic correctly when the VPC and on-premises networks have overlapping IP ranges because the VPN connection relies on distinct destination prefixes. The only way to eliminate the conflict is to change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16, ensuring no IP address overlap between the two networks.
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.
- ✗
Create a more specific route in the VPC route table for the on-premises CIDR.
Why it's wrong here
Overlap still causes ambiguity.
- ✗
Enable route propagation on the VPC route tables.
Why it's wrong here
Does not resolve overlap.
- ✗
Use a VPN connection with static routes instead of BGP.
Why it's wrong here
Does not resolve overlapping CIDRs.
- ✓
Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16.
Why this is correct
Eliminates the overlap.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates think they can override the conflict with a more specific route or by switching to static routes, but they overlook that the VPC's local route is always more specific than any VPN route for overlapping prefixes, making the conflict unresolvable without changing the VPC CIDR.
Detailed technical explanation
How to think about this question
AWS Site-to-Site VPN uses IPsec tunnels and relies on distinct destination CIDRs in the route table to forward traffic. When VPC CIDR 10.0.0.0/16 overlaps with on-premises 10.0.0.0/8, the VPC's local route (10.0.0.0/16) takes precedence over any VPN route (10.0.0.0/8) because the local route is more specific. This means traffic destined for on-premises hosts within the 10.0.0.0/8 range that falls outside the VPC's /16 will be dropped or misrouted. In real-world scenarios, overlapping CIDRs often require renumbering one side or using advanced techniques like NAT or Transit Gateway with multiple TGW attachments, but for a simple Site-to-Site VPN, a non-overlapping CIDR is mandatory.
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
What to study next
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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: Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16. — The VPC CIDR 10.0.0.0/16 is a subset of the on-premises CIDR 10.0.0.0/8. AWS Site-to-Site VPN cannot route traffic correctly when the VPC and on-premises networks have overlapping IP ranges because the VPN connection relies on distinct destination prefixes. The only way to eliminate the conflict is to change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16, ensuring no IP address overlap between the two networks.
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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Last reviewed: Jun 24, 2026
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