ANS-C01 Network Implementation Practice Question
A company is troubleshooting connectivity between two VPCs (VPC-A and VPC-B) that are peered together. Both VPCs are in the same region. VPC-A has a CIDR of 10.0.0.0/16 and VPC-B has a CIDR of 10.0.0.0/16. The peering connection is established and the route tables are updated. However, EC2 instances in VPC-A cannot ping EC2 instances in VPC-B. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that security groups or route table entries are the primary cause of connectivity issues in VPC peering, when in fact overlapping CIDR blocks create a fundamental routing conflict that overrides all other configurations.
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 CIDR blocks.
VPC peering requires non-overlapping CIDR blocks because the VPCs must have unique IP address spaces for routing to work correctly. Since both VPC-A and VPC-B use the same CIDR 10.0.0.0/16, the route tables cannot distinguish between the two VPCs, causing traffic to be misrouted or dropped. This is the most likely cause of the ping failure, as overlapping CIDRs prevent proper destination-based routing in the VPC peering connection.
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 route tables do not have routes to the private IP addresses of the instances.
Why it's wrong here
Routes to the CIDR are present, but overlapping CIDRs cause ambiguity.
- ✓
The VPCs have overlapping CIDR blocks.
Why this is correct
Overlapping CIDRs prevent proper routing in VPC peering.
- ✗
The security groups in VPC-B do not allow inbound ICMP traffic from VPC-A.
Why it's wrong here
While true, the primary issue is overlapping CIDRs; even with open security groups, routing would fail.
- ✗
The VPCs are in different regions and peering does not work across regions.
Why it's wrong here
The question states same region.
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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.