ANS-C01 Network Implementation Practice Question
A network engineer is troubleshooting connectivity from an EC2 instance in a private subnet to an S3 bucket. The VPC has a VPC endpoint for S3 configured. The instance can access the internet via a NAT Gateway. Which configuration is MOST likely causing the connection to S3 to fail?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that a VPC endpoint automatically routes traffic without a route table entry, leading candidates to overlook the required route and instead blame the bucket policy or the instance's public IP.
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 the private subnet is missing a route to the S3 VPC endpoint.
For an EC2 instance in a private subnet to use a VPC endpoint for S3, the subnet's route table must include a route with the S3 endpoint's prefix list as the destination and the VPC endpoint ID as the target. Without this route, traffic destined for S3 will be sent to the NAT Gateway instead, which may fail if the instance lacks a public IP or if the NAT Gateway's route table or security groups block the traffic. Option B correctly identifies this missing route as the most likely cause.
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 S3 VPC endpoint is in a different Availability Zone than the instance.
Why it's wrong here
VPC endpoints are regional and work across AZs.
- ✓
The route table for the private subnet is missing a route to the S3 VPC endpoint.
Why this is correct
Without a route to the endpoint, traffic goes via NAT Gateway, which may be blocked.
- ✗
The S3 bucket policy does not allow access from the VPC endpoint.
Why it's wrong here
This would cause an access denied error, not a connectivity failure.
- ✗
The EC2 instance does not have a public IP address.
Why it's wrong here
Private instances do not need public IP for VPC endpoint access.
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.