ANS-C01 Network Security, Compliance and Governance 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. 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 security engineer created the S3 bucket policy shown. After applying it, users from the 10.0.0.0/16 network (VPC CIDR) are able to access objects, but external users from 203.0.113.0/24 receive 'Access Denied' even though they are using HTTPS. What is the likely cause?
The VPC endpoint policy for the S3 endpoint restricts access to the bucket.
Even if the bucket policy allows, the VPC endpoint policy can deny access, especially for external IPs routed through the endpoint?
B
The policy only allows 's3:GetObject' but the users are trying to list objects.
Why wrong: The stem says they are trying to access objects, not list.
C
The policy does not include a 'Deny' statement for non-IP ranges.
Why wrong: The policy is permissive; it allows specified IPs, but other traffic is implicitly denied by default, so this is not the issue.
D
The S3 bucket has 'Block public access' enabled, which overrides the policy.
Why wrong: If public access is blocked, the policy would be ignored, but the internal users are accessing, so public access is likely not fully blocked.
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 for the S3 endpoint restricts access to the bucket.
The bucket policy allows access from both the VPC CIDR (10.0.0.0/16) and the external IP range (203.0.113.0/24) when using HTTPS. However, external users are likely accessing the bucket through a VPC endpoint (e.g., Gateway Endpoint), not directly over the internet. When traffic goes through a VPC endpoint, the effective policy is the intersection of the bucket policy and the VPC endpoint policy. If the VPC endpoint policy restricts access (e.g., denies all or requires specific source VPCs), then even though the bucket policy allows the external IP, the endpoint policy denies it. This explains the 'Access Denied' for external users who are routed through the VPC endpoint. Option A correctly identifies this cause. Options B, C, and D are incorrect because the bucket policy itself is not the issue; the problem lies with the additional restriction imposed by the VPC endpoint policy.
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 VPC endpoint policy for the S3 endpoint restricts access to the bucket.
Why this is correct
Even if the bucket policy allows, the VPC endpoint policy can deny access, especially for external IPs routed through the endpoint?
The policy only allows 's3:GetObject' but the users are trying to list objects.
Why it's wrong here
The stem says they are trying to access objects, not list.
✗
The policy does not include a 'Deny' statement for non-IP ranges.
Why it's wrong here
The policy is permissive; it allows specified IPs, but other traffic is implicitly denied by default, so this is not the issue.
✗
The S3 bucket has 'Block public access' enabled, which overrides the policy.
Why it's wrong here
If public access is blocked, the policy would be ignored, but the internal users are accessing, so public access is likely not fully blocked.
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.
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 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 for the S3 endpoint restricts access to the bucket. — The bucket policy allows access from both the VPC CIDR (10.0.0.0/16) and the external IP range (203.0.113.0/24) when using HTTPS. However, external users are likely accessing the bucket through a VPC endpoint (e.g., Gateway Endpoint), not directly over the internet. When traffic goes through a VPC endpoint, the effective policy is the intersection of the bucket policy and the VPC endpoint policy. If the VPC endpoint policy restricts access (e.g., denies all or requires specific source VPCs), then even though the bucket policy allows the external IP, the endpoint policy denies it. This explains the 'Access Denied' for external users who are routed through the VPC endpoint. Option A correctly identifies this cause. Options B, C, and D are incorrect because the bucket policy itself is not the issue; the problem lies with the additional restriction imposed by the VPC endpoint policy.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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