The answer is that the EC2 instance’s source IP is not in the allowed IP range. This is because the S3 bucket policy contains two separate allow statements: one using the aws:SourceIp condition key to restrict access to the 203.0.113.0/24 CIDR, and another using the aws:SourceVpc condition key to allow requests from vpc-12345. However, the aws:SourceVpc condition is only evaluated when the request arrives through a VPC endpoint—either a Gateway or Interface endpoint—and not when the EC2 instance accesses S3 over the internet using its public IP. Since the instance’s public IP of 198.51.100.10 falls outside the allowed IP range, the first statement denies access, and the second statement does not apply, resulting in an implicit deny. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of how condition keys interact with network paths, a common trap where candidates assume SourceVpc works for any VPC-originated traffic. Remember: SourceVpc only triggers via a VPC endpoint, not via the internet gateway. A useful memory tip is “VPC endpoint or bust”—if the traffic doesn’t hit a VPC endpoint, SourceVpc is ignored.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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. A company has attached this bucket policy to an S3 bucket. An EC2 instance in VPC vpc-12345 is trying to access the bucket but is getting access denied. The EC2 instance has a public IP of 198.51.100.10. 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 EC2 instance's source IP is not in the allowed IP range
Option B is correct. The policy has two allow statements: one for source IP range and one for source VPC. The EC2 instance's source IP (198.51.100.10) is not in the allowed IP range (203.0.113.0/24). The second statement allows requests from the VPC, but the condition aws:SourceVpc is only present when the request comes through a VPC endpoint (Gateway or Interface endpoint). If the EC2 instance accesses S3 via the internet (public IP), the aws:SourceVpc condition is not satisfied, so the second statement does not apply. The first statement does not allow the IP, resulting in implicit deny. Option A is wrong because the policy allows GetObject. Option C is wrong because the policy does not require both conditions. Option D is wrong because there is no explicit deny.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 policy does not have an explicit allow for the instance's IP
Why it's wrong here
There is an implicit deny, but the explicit allow is conditional; the condition is not met.
✓
The EC2 instance's source IP is not in the allowed IP range
Why this is correct
The instance has a different public IP; the IP condition is not met, and the VPC condition only applies if accessed via VPC endpoint.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
Both conditions must be met for access
Why it's wrong here
The statements are separate; either condition can allow access.
✗
The EC2 instance does not have the s3:GetObject permission
Why it's wrong here
The bucket policy grants s3:GetObject; the instance's IAM role may also need permission, but the policy is permissive for the actions.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related ANS-C01 ACL questions on filtering logic and placement.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The EC2 instance's source IP is not in the allowed IP range — Option B is correct. The policy has two allow statements: one for source IP range and one for source VPC. The EC2 instance's source IP (198.51.100.10) is not in the allowed IP range (203.0.113.0/24). The second statement allows requests from the VPC, but the condition aws:SourceVpc is only present when the request comes through a VPC endpoint (Gateway or Interface endpoint). If the EC2 instance accesses S3 via the internet (public IP), the aws:SourceVpc condition is not satisfied, so the second statement does not apply. The first statement does not allow the IP, resulting in implicit deny. Option A is wrong because the policy allows GetObject. Option C is wrong because the policy does not require both conditions. Option D is wrong because there is no explicit deny.
What should I do if I get this ANS-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related ANS-C01 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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