- A
The NAT Gateway's security group does not allow outbound HTTPS traffic.
Why wrong: NAT Gateways do not have security groups; they are not associated with security groups. This option is factually incorrect.
- B
The NACL for the private subnet blocks inbound traffic from S3.
Why wrong: The NACL for the private subnet allows inbound ephemeral ports from 0.0.0.0/0, which covers return traffic from S3. This is not the issue.
- C
The private subnet's route table does not have a route to the NAT Gateway.
If the private subnet's route table lacks a route to the NAT Gateway (0.0.0.0/0 -> NAT Gateway), outbound traffic to S3 will fail. This is the most common cause when an instance in a private subnet cannot reach the internet.
- D
The S3 bucket policy denies access from the VPC.
Why wrong: S3 bucket policies are evaluated separately and are not typically the cause if the instance cannot reach S3 at all. The problem is at the network layer.
ANS-C01 NAT Gateway Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: nAT Gateway. 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 company has a VPC with public and private subnets. An EC2 instance in a private subnet needs to access an S3 bucket. The VPC has a NAT Gateway in the public subnet. The security group for the EC2 instance allows outbound HTTPS to 0.0.0.0/0. The NACL for the private subnet allows outbound HTTPS to 0.0.0.0/0 and inbound ephemeral ports from 0.0.0.0/0. The instance still cannot reach S3. 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 private subnet's route table does not have a route to the NAT Gateway.
The most likely cause is that the private subnet's route table does not have a route to the NAT Gateway. Without a default route (0.0.0.0/0) pointing to the NAT Gateway, traffic destined for the internet (including S3) will not be forwarded to the NAT Gateway and will be dropped. Option A is incorrect because NAT Gateways do not have security groups; they are managed by network ACLs and route tables. Option B is incorrect because the NACL inbound rule allows ephemeral ports, which is sufficient for return traffic from S3. Option D is incorrect as there is no indication the bucket policy is restrictive.
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 NAT Gateway's security group does not allow outbound HTTPS traffic.
Why it's wrong here
NAT Gateways do not have security groups; they are not associated with security groups. This option is factually incorrect.
- ✗
The NACL for the private subnet blocks inbound traffic from S3.
Why it's wrong here
The NACL for the private subnet allows inbound ephemeral ports from 0.0.0.0/0, which covers return traffic from S3. This is not the issue.
- ✓
The private subnet's route table does not have a route to the NAT Gateway.
Why this is correct
If the private subnet's route table lacks a route to the NAT Gateway (0.0.0.0/0 -> NAT Gateway), outbound traffic to S3 will fail. This is the most common cause when an instance in a private subnet cannot reach the internet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
- ✗
The S3 bucket policy denies access from the VPC.
Why it's wrong here
S3 bucket policies are evaluated separately and are not typically the cause if the instance cannot reach S3 at all. The problem is at the network layer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
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
- NAT Gateway
- Route Table
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
NAT Gateway
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 nAT Gateway, then practise related ANS-C01 questions on the same topic to reinforce the concept.
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Network Management and Operations — study guide chapter
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Management and Operations — This question tests Network Management and Operations — NAT Gateway.
What is the correct answer to this question?
The correct answer is: The private subnet's route table does not have a route to the NAT Gateway. — The most likely cause is that the private subnet's route table does not have a route to the NAT Gateway. Without a default route (0.0.0.0/0) pointing to the NAT Gateway, traffic destined for the internet (including S3) will not be forwarded to the NAT Gateway and will be dropped. Option A is incorrect because NAT Gateways do not have security groups; they are managed by network ACLs and route tables. Option B is incorrect because the NACL inbound rule allows ephemeral ports, which is sufficient for return traffic from S3. Option D is incorrect as there is no indication the bucket policy is restrictive.
What should I do if I get this ANS-C01 question wrong?
Review nAT Gateway, 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?
NAT Gateway
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Last reviewed: Jun 20, 2026
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