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Network Implementation →easyMultiple ChoiceObjective-mapped

ANS-C01 Network Implementation Practice Question

This ANS-C01 practice question tests your understanding of network implementation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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 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?

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.

A
The S3 VPC endpoint is in a different Availability Zone than the instance.
Why wrong: VPC endpoints are regional and work across AZs.
B
The route table for the private subnet is missing a route to the S3 VPC endpoint.
Without a route to the endpoint, traffic goes via NAT Gateway, which may be blocked.
C
The S3 bucket policy does not allow access from the VPC endpoint.
Why wrong: This would cause an access denied error, not a connectivity failure.
D
The EC2 instance does not have a public IP address.
Why wrong: Private instances do not need public IP for VPC endpoint access.

Full breakdown with real-world context →

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.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.

Common exam traps

Common exam trap: answer the scenario, not the keyword

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.

Detailed technical explanation

How to think about this question

VPC endpoints for S3 use a prefix list (e.g., com.amazonaws.us-east-1.s3) as the destination in the route table, which directs traffic to the endpoint's elastic network interface rather than the internet. The NAT Gateway's route table must also have a route to the S3 prefix list if the private subnet's route table points to the NAT Gateway for 0.0.0.0/0; otherwise, traffic will be dropped. In practice, this misconfiguration often causes intermittent failures when the NAT Gateway's public IP is blocked by S3 bucket policies or when the instance tries to resolve S3 endpoints via public DNS.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

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

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 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.

What should I do if I get this ANS-C01 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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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.