ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR of 10.0.0.0/16 and needs to peer with another VPC that has CIDR 10.0.0.0/16. What is the issue and how can it be resolved?
⚠ Common exam trap
Test-takers frequently assume a Transit Gateway or Direct Connect Gateway can magically handle overlapping CIDRs, but AWS requires unique CIDRs for direct routing between VPCs unless you introduce NAT or translation layers.
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
✓
The VPCs have overlapping CIDRs, so they cannot be directly peered. You must re-IP one VPC or use a NAT solution.
VPC peering requires non-overlapping CIDR blocks because the route tables in each VPC must have distinct destination prefixes to route traffic correctly. When both VPCs use 10.0.0.0/16, the routes are identical, causing ambiguity and preventing the peering connection from being established. The only resolution is to change the CIDR of one VPC or use a NAT-based solution to translate addresses.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The VPCs can be peered if you enable DNS resolution.
Why it's wrong here
Wrong: Overlapping CIDRs block peering regardless.
- ✓
The VPCs have overlapping CIDRs, so they cannot be directly peered. You must re-IP one VPC or use a NAT solution.
Why this is correct
Correct: Overlapping CIDRs are not allowed.
- ✗
Use a Transit Gateway to connect the VPCs, which supports overlapping CIDRs.
Why it's wrong here
Wrong: Transit Gateway also requires unique CIDRs.
- ✗
Use a Direct Connect Gateway to connect the VPCs, which ignores CIDR overlap.
Why it's wrong here
Wrong: Direct Connect Gateway also requires unique ranges.
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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.