ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR block of 10.0.0.0/16. They have three subnets: Subnet A (10.0.1.0/24) in us-east-1a, Subnet B (10.0.2.0/24) in us-east-1b, and Subnet C (10.0.3.0/24) in us-east-1c. The company has deployed a set of EC2 instances in Subnet A that need to access an Amazon S3 bucket. The company wants to ensure that traffic to S3 does not traverse the internet and remains within the AWS network. The VPC has a VPC endpoint for S3 (gateway type) created and associated with the route table for Subnet A. However, the instances are unable to access the S3 bucket. What is the MOST likely cause?
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 route table for Subnet A does not have a route for the S3 prefix list pointing to the VPC endpoint.
A gateway VPC endpoint for S3 is only accessible from the subnet whose route table has a route to the endpoint. The route table for Subnet A must have a route for the S3 prefix list pointing to the VPC endpoint. If that route is missing, traffic will not use the endpoint. Option A is incorrect because a VPC endpoint does not require an internet gateway. Option C is incorrect because a gateway endpoint does not use security groups; it uses endpoint policies. Option D is incorrect because the endpoint policy does not need to be explicitly attached to the bucket; the bucket policy must grant access to the VPC endpoint.
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 VPC does not have an internet gateway attached.
Why it's wrong here
A gateway endpoint does not require an internet gateway; it uses the AWS private network.
- ✓
The route table for Subnet A does not have a route for the S3 prefix list pointing to the VPC endpoint.
Why this is correct
Without this route, traffic from Subnet A to S3 does not use the endpoint.
- ✗
The S3 bucket policy does not allow access from the VPC endpoint.
Why it's wrong here
The bucket policy may need to allow access, but the most likely cause is the missing route.
- ✗
The VPC endpoint is not associated with a security group that allows outbound traffic to S3.
Why it's wrong here
Gateway endpoints do not use security groups.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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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.