ANS-C01 Network Implementation Practice Question
Exhibit
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::my-bucket/*",
"Condition": {
"IpAddress": {
"aws:SourceIp": "10.0.0.0/16"
}
}
}
]
}Refer to the exhibit. A company has an S3 bucket with the bucket policy shown. An EC2 instance in a VPC with CIDR 10.0.0.0/16 tries to retrieve an object from the bucket using the S3 console, but receives an 'Access Denied' error. The instance's security group allows all outbound traffic. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that the `aws:SourceIp` condition evaluates the private IP of the EC2 instance, when in reality it evaluates the source IP of the IP packet as seen by S3, which after NAT is the public IP of the NAT Gateway.
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 EC2 instance is accessing the S3 bucket through a NAT Gateway, so the source IP is the public IP of the NAT Gateway, which does not match the condition.
The bucket policy uses the `aws:SourceIp` condition to restrict access to requests originating from the specific IP range 10.0.0.0/16. However, when the EC2 instance accesses S3 through a NAT Gateway, the source IP seen by S3 is the public IP of the NAT Gateway, not the private IP of the instance. Since the NAT Gateway's public IP does not fall within the 10.0.0.0/16 range, the condition fails and S3 returns an 'Access Denied' error.
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 EC2 instance is accessing the S3 bucket through a NAT Gateway, so the source IP is the public IP of the NAT Gateway, which does not match the condition.
Why this is correct
The IP condition requires the source IP to be within the VPC CIDR, but via NAT the source IP is the NAT's public IP.
- ✗
The bucket policy does not allow the s3:GetObject action.
Why it's wrong here
The policy explicitly allows s3:GetObject.
- ✗
The bucket policy does not specify a principal, so it defaults to deny.
Why it's wrong here
Principal: '*' allows all principals.
- ✗
The condition aws:SourceIp is too restrictive and blocks all traffic.
Why it's wrong here
The condition is valid; the issue is the IP mismatch.
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.