Quick Answer
The answer is to change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16. This is required because the existing VPC CIDR of 10.0.0.0/16 is a subset of the on-premises CIDR 10.0.0.0/8, and AWS Site-to-Site VPN cannot route traffic when destination prefixes overlap—the VPN relies on distinct, non-conflicting IP spaces in its route tables. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of IP address planning and the immutable nature of VPC CIDRs; once a VPC is created, you cannot shrink or modify its primary CIDR block, so the only fix is to create a new VPC or add a secondary CIDR that does not conflict. A common trap is assuming you can use VPC peering or NAT to resolve the overlap, but those solutions do not fix the fundamental routing conflict for VPN traffic. Memory tip: “If your VPC is a subset of on-prem, you must reset—change the block, don’t try to unlock.”
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?
Create a more specific route in the VPC route table for the on-premises CIDR.
Why wrong: Overlap still causes ambiguity.
Enable route propagation on the VPC route tables.
Why wrong: Does not resolve overlap.
Use a VPN connection with static routes instead of BGP.
Why wrong: Does not resolve overlapping CIDRs.
Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16.
Eliminates the overlap.
Answer choices
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
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
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
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Design — study guide chapter
Learn the concepts, then practise the questions
Network Design practice questions
Targeted practice on this topic area only
All ANS-C01 questions
1,705 questions across all exam domains
AWS Certified Advanced Networking Specialty ANS-C01 study guide
Full concept coverage aligned to exam objectives
ANS-C01 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise ANS-C01 questions linked to Network Management and Operations.
Practise ANS-C01 questions linked to Network Security, Compliance and Governance.
Practise ANS-C01 questions linked to Network Design.
Practise ANS-C01 questions linked to Network Implementation.
Practise ANS-C01 questions linked to ANS-C01 fundamentals.
Practise ANS-C01 questions linked to ANS-C01 scenario.
Practise ANS-C01 questions linked to ANS-C01 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
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 CIDR 10.0.0.0/16 and needs to connect to an on-premises network with CIDR 10.0.0.0/8. They plan to use AWS Direct Connect with a private virtual interface. What should they do to resolve the overlapping CIDR conflict?
easyWhy C: Option C is correct because AWS does not support network address translation (NAT) for overlapping CIDRs on a Direct Connect private virtual interface. The only way to resolve the conflict is to change the VPC CIDR to a non-overlapping range (e.g., 172.16.0.0/16) and recreate the VPC, as the VPC CIDR cannot be modified after creation. This ensures that routes between the VPC and on-premises network do not conflict.
Keep practising
Last reviewed: Jun 24, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.