ANS-C01 Network Design Practice Question
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?
⚠ Common exam trap
A common mix-up: candidates assume NAT or VPN can magically resolve overlapping IP ranges, but AWS Direct Connect private VIFs require non-overlapping CIDRs for proper routing, and no AWS service (including NAT Gateway or VPN) can translate on-premises IPs in this context.
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, and re-create the VPC with the new CIDR.
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.
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 VPN connection with dynamic routing and use BGP to advertise the VPC CIDR.
Why it's wrong here
BGP does not resolve overlapping CIDRs; routes with overlapping prefixes cause conflicts.
- ✗
Create a VPC peering connection between the VPC and the on-premises network.
Why it's wrong here
VPC peering does not support overlapping CIDR ranges.
- ✓
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.
Why this is correct
The only solution is to use non-overlapping IP address ranges.
- ✗
Use a NAT Gateway in the VPC to translate the on-premises IP addresses.
Why it's wrong here
NAT Gateway translates private IPs from the VPC to the internet, not for overlapping CIDRs.
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Written by Johnson Ajibi, MSc IT Security
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