The answer is the VPC endpoint policy missing s3:ListBucket permission. While the endpoint policy allows s3:GetObject, the AWS CLI’s cp or sync commands first perform a ListBucket call to enumerate objects before downloading them; without that permission, the CLI fails even if the IAM role grants GetObject. This scenario tests your understanding of how VPC Gateway Endpoint policies interact with IAM—both must allow the required actions, and the CLI’s implicit dependency on ListBucket is a classic trap on the ANS-C01 exam. A common mistake is assuming IAM alone suffices, but the endpoint policy acts as an additional guard. Remember: the endpoint policy is a resource-based policy that must explicitly permit every API call the client makes, not just the final data operation. Memory tip: “List before Get”—the CLI always lists before it fetches, so your endpoint policy must allow both.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Network Topology
A CloudFormation stack created a VPC Gateway Endpoint for S3 with the above policy. An EC2 instance in the VPC is unable to download objects from the S3 bucket using the AWS CLI. The instance has an IAM role with s3:GetObject permission. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VPC Endpoint policy does not allow s3:ListBucket, which is needed for the CLI to list objects.
Option B is correct because the VPC Endpoint policy allows only s3:GetObject, but the CLI often requires s3:ListBucket to list objects, and also the endpoint policy must be combined with IAM; the instance role may not have the correct permissions. Option A is wrong because the endpoint policy allows GetObject. Option C is wrong because Gateway Endpoints do not use security groups. Option D is wrong because the route table must have a route to the endpoint, but the question implies it's configured.
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 security group associated with the VPC Endpoint blocks traffic.
Why it's wrong here
Gateway Endpoints do not have security groups; they are managed by route tables and endpoint policies.
✗
The VPC Endpoint policy does not allow s3:GetObject.
Why it's wrong here
It does allow s3:GetObject.
✓
The VPC Endpoint policy does not allow s3:ListBucket, which is needed for the CLI to list objects.
Why this is correct
The CLI often lists objects first, requiring ListBucket permission.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The route table for the private subnet does not have a route to the VPC Endpoint.
Why it's wrong here
If the route were missing, the request would not reach the endpoint; but the issue is likely policy-related.
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 Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The VPC Endpoint policy does not allow s3:ListBucket, which is needed for the CLI to list objects. — Option B is correct because the VPC Endpoint policy allows only s3:GetObject, but the CLI often requires s3:ListBucket to list objects, and also the endpoint policy must be combined with IAM; the instance role may not have the correct permissions. Option A is wrong because the endpoint policy allows GetObject. Option C is wrong because Gateway Endpoints do not use security groups. Option D is wrong because the route table must have a route to the endpoint, but the question implies it's configured.
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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