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Security Logging and Monitoring →hardMultiple ChoiceObjective-mapped

SCS-C02 Security Logging and Monitoring Practice Question

This SCS-C02 practice question tests your understanding of security logging and monitoring. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 is investigating a potential data exfiltration incident. They suspect that an EC2 instance was compromised and used to transfer large amounts of data from an S3 bucket to an external IP address. The engineer has enabled VPC Flow Logs for the subnet where the EC2 instance resides, but the logs are not capturing traffic to the external IP. 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.

A
The EC2 instance's security group is blocking the traffic.
Why wrong: Incorrect. Security groups filter traffic but do not prevent flow logs from capturing it; flow logs log both accepted and rejected traffic.
B
VPC Flow Logs only capture rejected traffic.
Why wrong: Incorrect. VPC Flow Logs capture both accepted and rejected traffic, not only rejected.
C
VPC Flow Logs only capture traffic to and from other VPC resources.
Why wrong: Incorrect. VPC Flow Logs capture traffic to any IP address, including external IPs, provided the flow log is configured on the appropriate subnet or ENI.
D
The traffic is routed through a NAT gateway, and flow logs are not enabled on the NAT gateway's subnet.
Correct. When traffic from an EC2 instance to an external IP is routed through a NAT gateway, the flow logs on the instance's subnet will only show traffic to the NAT gateway's private IP. To capture the external traffic, flow logs must be enabled on the subnet hosting the NAT gateway.

Full breakdown with real-world context →

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 routed through a NAT gateway, and flow logs are not enabled on the NAT gateway's subnet.

Option D is correct because VPC Flow Logs capture traffic at the subnet or ENI level. If traffic from an EC2 instance to an external IP is routed through a NAT gateway, the flow logs on the EC2 instance's subnet will only show traffic to the NAT gateway, not the external IP. To capture the external traffic, flow logs must be enabled on the subnet where the NAT gateway resides. Option A is incorrect because Security Groups do not affect flow log capture; they filter traffic but flow logs log both accepted and rejected traffic. Option B is incorrect because VPC Flow Logs capture all traffic, not just rejected. Option C is incorrect because flow logs capture traffic to any IP, not just other VPC resources.

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 EC2 instance's security group is blocking the traffic.
Why it's wrong here
Incorrect. Security groups filter traffic but do not prevent flow logs from capturing it; flow logs log both accepted and rejected traffic.
✗
VPC Flow Logs only capture rejected traffic.
Why it's wrong here
Incorrect. VPC Flow Logs capture both accepted and rejected traffic, not only rejected.
✗
VPC Flow Logs only capture traffic to and from other VPC resources.
Why it's wrong here
Incorrect. VPC Flow Logs capture traffic to any IP address, including external IPs, provided the flow log is configured on the appropriate subnet or ENI.
✓
The traffic is routed through a NAT gateway, and flow logs are not enabled on the NAT gateway's subnet.
Why this is correct
Correct. When traffic from an EC2 instance to an external IP is routed through a NAT gateway, the flow logs on the instance's subnet will only show traffic to the NAT gateway's private IP. To capture the external traffic, flow logs must be enabled on the subnet hosting the NAT gateway.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.

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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this SCS-C02 question test?

Security Logging and Monitoring — This question tests Security Logging and Monitoring — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The traffic is routed through a NAT gateway, and flow logs are not enabled on the NAT gateway's subnet. — Option D is correct because VPC Flow Logs capture traffic at the subnet or ENI level. If traffic from an EC2 instance to an external IP is routed through a NAT gateway, the flow logs on the EC2 instance's subnet will only show traffic to the NAT gateway, not the external IP. To capture the external traffic, flow logs must be enabled on the subnet where the NAT gateway resides. Option A is incorrect because Security Groups do not affect flow log capture; they filter traffic but flow logs log both accepted and rejected traffic. Option B is incorrect because VPC Flow Logs capture all traffic, not just rejected. Option C is incorrect because flow logs capture traffic to any IP, not just other VPC resources.

What should I do if I get this SCS-C02 question wrong?

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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