- A
Flow Logs are published to an S3 bucket instead of CloudWatch Logs.
Why wrong: Publishing to S3 does not cause missing traffic; both destinations capture the same data.
- B
The traffic uses UDP protocol.
Why wrong: Flow Logs capture UDP traffic, so this is not a cause of missing logs.
- C
The traffic is blocked by a security group rule.
Why wrong: Flow Logs capture both accepted and rejected traffic (provided the log format includes the action field), so a security group rule blocking traffic would still be logged as rejected.
- D
The traffic is to or from the Amazon DNS server (169.254.169.253).
By default, traffic to/from the Amazon DNS server is not logged; this is the likely cause of missing expected traffic.
Question 885 of 1,748
SCS-C02 VPC Flow Logs Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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. A key principle to apply: vPC Flow Logs. 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 company has a VPC with multiple subnets and uses VPC Flow Logs to capture network traffic. The security team notices that some expected traffic is not appearing in the logs. What is a likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The traffic is to or from the Amazon DNS server (169.254.169.253).
VPC Flow Logs do not capture traffic to or from the Amazon DNS server (169.254.169.253) by default. This is because the DNS server is a well-known AWS internal service and capturing that traffic is unnecessary. Therefore, if expected traffic involves the DNS server, it will not appear in the logs. Option A is incorrect because Flow Logs can be published to either CloudWatch Logs or S3, but the destination does not cause missing logs. Option B is incorrect because Flow Logs capture UDP traffic as well as TCP. Option C is incorrect because Flow Logs capture all accepted traffic regardless of security group rules; they log both accepted and rejected traffic (though rejected traffic is logged only if the log format includes the 'action' field and the rule allows logging).
Key principle: VPC Flow Logs
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Flow Logs are published to an S3 bucket instead of CloudWatch Logs.
Why it's wrong here
Publishing to S3 does not cause missing traffic; both destinations capture the same data.
- ✗
The traffic uses UDP protocol.
Why it's wrong here
Flow Logs capture UDP traffic, so this is not a cause of missing logs.
- ✗
The traffic is blocked by a security group rule.
Why it's wrong here
Flow Logs capture both accepted and rejected traffic (provided the log format includes the action field), so a security group rule blocking traffic would still be logged as rejected.
- ✓
The traffic is to or from the Amazon DNS server (169.254.169.253).
Why this is correct
By default, traffic to/from the Amazon DNS server is not logged; this is the likely cause of missing expected traffic.
Related concept
VPC Flow Logs
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- VPC Flow Logs
- Amazon DNS Server
- Flow Log Destinations
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
VPC Flow Logs
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 vPC Flow Logs, then practise related SCS-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — VPC Flow Logs.
What is the correct answer to this question?
The correct answer is: The traffic is to or from the Amazon DNS server (169.254.169.253). — VPC Flow Logs do not capture traffic to or from the Amazon DNS server (169.254.169.253) by default. This is because the DNS server is a well-known AWS internal service and capturing that traffic is unnecessary. Therefore, if expected traffic involves the DNS server, it will not appear in the logs. Option A is incorrect because Flow Logs can be published to either CloudWatch Logs or S3, but the destination does not cause missing logs. Option B is incorrect because Flow Logs capture UDP traffic as well as TCP. Option C is incorrect because Flow Logs capture all accepted traffic regardless of security group rules; they log both accepted and rejected traffic (though rejected traffic is logged only if the log format includes the 'action' field and the rule allows logging).
What should I do if I get this SCS-C02 question wrong?
Review vPC Flow Logs, then practise related SCS-C02 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
VPC Flow Logs
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Last reviewed: Jun 20, 2026
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