- A
The security group outbound rule does not allow traffic to the S3 prefix list.
Correct: The security group must have an outbound rule allowing HTTPS traffic to the S3 prefix list ID. The default 'all traffic' rule does not suffice.
- B
The VPC endpoint is not associated with the route table.
Why wrong: Incorrect: The VPC endpoint is already associated with the route table, as stated in the scenario.
- C
The route table does not have a route to a NAT gateway.
Why wrong: Incorrect: A NAT gateway is not required for S3 access when using a VPC gateway endpoint.
- D
The S3 bucket policy does not allow access from the VPC endpoint.
Why wrong: Incorrect: The bucket policy may need to allow access from the VPC endpoint, but the most likely cause given the all-outbound security group is the missing prefix list rule.
ANS-C01 VPC Gateway Endpoint Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: vPC Gateway Endpoint. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security engineer is troubleshooting connectivity between an EC2 instance in a private subnet and an S3 bucket. The instance has a VPC gateway endpoint for S3, and the route table has a route to the endpoint. The security group for the instance allows all outbound traffic. However, the instance cannot access the S3 bucket. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 security group outbound rule does not allow traffic to the S3 prefix list.
Although the security group allows all outbound traffic to 0.0.0.0/0, this rule does not apply to traffic destined for the S3 prefix list when using a VPC gateway endpoint. Gateway endpoints require a security group rule that explicitly allows HTTPS traffic to the S3 prefix list ID. Without this rule, traffic is blocked. Option A is correct. Option B is incorrect because the VPC endpoint is indeed associated with the route table. Option C is incorrect because a NAT gateway is not needed for S3 access via the endpoint. Option D is incorrect because the bucket policy is not the issue; the security group rule is missing.
Key principle: VPC Gateway 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 security group outbound rule does not allow traffic to the S3 prefix list.
- ✗
The VPC endpoint is not associated with the route table.
Why it's wrong here
Incorrect: The VPC endpoint is already associated with the route table, as stated in the scenario.
- ✗
The route table does not have a route to a NAT gateway.
- ✗
The S3 bucket policy does not allow access from the VPC endpoint.
Why it's wrong here
Incorrect: The bucket policy may need to allow access from the VPC endpoint, but the most likely cause given the all-outbound security group is the missing prefix list rule.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many assume that an 'allow all' outbound security group rule is sufficient for accessing S3 via a gateway endpoint, but the destination must be the prefix list ID.
Trap categories for this question
Scenario analysis trap
Incorrect: The VPC endpoint is already associated with the route table, as stated in the scenario.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- VPC Gateway Endpoint
- Prefix List
- Security Group Rule
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
VPC Gateway Endpoint
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 |
What to study next
Got this wrong? Here's your next step.
Review vPC Gateway Endpoint, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — VPC Gateway Endpoint.
What is the correct answer to this question?
The correct answer is: The security group outbound rule does not allow traffic to the S3 prefix list. — Although the security group allows all outbound traffic to 0.0.0.0/0, this rule does not apply to traffic destined for the S3 prefix list when using a VPC gateway endpoint. Gateway endpoints require a security group rule that explicitly allows HTTPS traffic to the S3 prefix list ID. Without this rule, traffic is blocked. Option A is correct. Option B is incorrect because the VPC endpoint is indeed associated with the route table. Option C is incorrect because a NAT gateway is not needed for S3 access via the endpoint. Option D is incorrect because the bucket policy is not the issue; the security group rule is missing.
What should I do if I get this ANS-C01 question wrong?
Review vPC Gateway Endpoint, then practise related ANS-C01 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
VPC Gateway Endpoint
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Last reviewed: Jun 20, 2026
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