ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
Many exam-takers 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.
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.
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.
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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?
easy- A.Create a VPN connection with dynamic routing and use BGP to advertise the VPC CIDR.
- B.Create a VPC peering connection between the VPC and the on-premises network.
- ✓ C.Change the VPC CIDR to a non-overlapping range, such as 172.16.0.0/16, and re-create the VPC with the new CIDR.
- D.Use a NAT Gateway in the VPC to translate the on-premises IP addresses.
Why C: 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.
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.