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.
Refer to the exhibit. The bucket policy shown is applied to an S3 bucket. A VPC endpoint for S3 is created in a VPC with CIDR 10.0.0.0/16. An EC2 instance in the VPC tries to access an object in the bucket using the VPC endpoint. The request fails. What is the most likely reason?
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The condition uses aws:SourceIp, which does not work with VPC endpoint traffic.
The condition in the bucket policy uses aws:SourceIp, but when traffic goes through a VPC endpoint, the source IP is the private IP of the instance, which is not evaluated by aws:SourceIp. Instead, aws:SourceVpce should be used. Option A (IAM role) is not shown; Option B (DNS) is unlikely; Option C (route table) is not the issue.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 bucket policy does not allow s3:ListBucket.
Why it's wrong here
Only GetObject is needed to retrieve an object; ListBucket is not required.
✓
The condition uses aws:SourceIp, which does not work with VPC endpoint traffic.
Why this is correct
aws:SourceIp is not applicable for VPC endpoint requests; use aws:SourceVpce instead.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The EC2 instance does not have an IAM role that allows s3:GetObject.
Why it's wrong here
The bucket policy allows all principals, so IAM is not required.
✗
The VPC endpoint does not have a route table associated with the instance's subnet.
Why it's wrong here
The route table association is needed for Gateway endpoints but not for Interface endpoints; however, the condition is the primary issue.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Implementation — This question tests Network Implementation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The condition uses aws:SourceIp, which does not work with VPC endpoint traffic. — The condition in the bucket policy uses aws:SourceIp, but when traffic goes through a VPC endpoint, the source IP is the private IP of the instance, which is not evaluated by aws:SourceIp. Instead, aws:SourceVpce should be used. Option A (IAM role) is not shown; Option B (DNS) is unlikely; Option C (route table) is not the issue.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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