ANS-C01 Network Design Practice Question
A company has a VPC with an IPv4 CIDR of 10.0.0.0/16 and needs to connect to an on-premises network via AWS Direct Connect. The on-premises network uses 10.0.0.0/16. Which solution allows connectivity without IP overlap?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that Direct Connect alone can handle overlapping IPs by using static routes or BGP communities, but without NAT or address translation, overlapping CIDRs cause asymmetric routing and unreachability.
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
✓
Create a new VPC with a non-overlapping CIDR, connect both VPCs via Transit Gateway, and use NAT on the Transit Gateway attachment to the on-premises network.
When both the VPC and on-premises network use the same 10.0.0.0/16 CIDR, direct connectivity is impossible due to overlapping IP ranges. By creating a new VPC with a non-overlapping CIDR, connecting both VPCs via Transit Gateway, and applying NAT on the Transit Gateway attachment to the on-premises network, traffic from the original VPC can be source-NATed to the new VPC's range before being forwarded to on-premises, resolving the overlap. This allows the on-premises network to receive traffic with unique IPs, avoiding routing conflicts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Establish a VPC peering connection between the VPC and on-premises network.
Why it's wrong here
VPC peering does not support overlapping CIDRs.
- ✗
Use AWS Direct Connect with a private VIF and static routes to route traffic.
Why it's wrong here
Direct Connect cannot resolve IP overlap; routes will conflict.
- ✓
Create a new VPC with a non-overlapping CIDR, connect both VPCs via Transit Gateway, and use NAT on the Transit Gateway attachment to the on-premises network.
Why this is correct
Transit Gateway with NAT attachment allows IP translation to resolve overlap.
- ✗
Deploy a NAT instance in the VPC to translate on-premises IPs.
Why it's wrong here
A single NAT instance is a bottleneck and does not scale for all traffic.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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