The answer is that the aws:SourceIp condition key evaluates the request’s public IP address, but traffic originating from within a VPC uses private IP addresses, causing the condition to fail. When you apply an S3 bucket policy with aws:SourceIp to restrict access to a specific VPC CIDR range, the condition checks the source IP as seen at the internet edge—typically the NAT gateway or internet gateway’s public IP—not the private IP of the EC2 instance or resource inside the VPC. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of how condition keys map to network layers; a common trap is assuming aws:SourceIp works for private IPs when it only evaluates public-facing IPs. To control VPC access, you must use aws:SourceVpce or aws:VpcSourceIp with a VPC endpoint policy instead. Memory tip: “SourceIp sees the street address, not the room number—private IPs are inside the building.”
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. 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.
An IAM policy is attached to an S3 bucket to allow access from a specific VPC CIDR range. However, users from the VPC are receiving 'Access Denied' errors when trying to access objects in the bucket. 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 key 'aws:SourceIp' evaluates the public IP address, but the VPC uses private IP addresses
The condition uses 'aws:SourceIp' which checks the public IP of the request, not the private IP. Since the VPC uses private IPs, the condition fails. Option B is wrong because the policy does not specify sourceVpce. Option C is wrong because the policy does not enforce HTTPS. Option D is wrong because the IAM role does not affect the source IP check.
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 users are assuming an IAM role that does not have permission to access S3
Why it's wrong here
The IAM role would override the bucket policy; but the bucket policy condition is the issue.
✓
The condition key 'aws:SourceIp' evaluates the public IP address, but the VPC uses private IP addresses
Why this is correct
'aws:SourceIp' checks the public IP of the client, not the private IP.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The condition key 'aws:SourceIp' evaluates the public IP address, but the VPC uses private IP addresses — The condition uses 'aws:SourceIp' which checks the public IP of the request, not the private IP. Since the VPC uses private IPs, the condition fails. Option B is wrong because the policy does not specify sourceVpce. Option C is wrong because the policy does not enforce HTTPS. Option D is wrong because the IAM role does not affect the source IP check.
What should I do if I get this DOP-C02 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 DOP-C02 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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Question Discussion
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