- A
Network ACLs
NACLs are stateless firewalls applied at the subnet level.
- B
IAM policies
Why wrong: IAM policies control access to AWS APIs, not network traffic.
- C
Amazon CloudWatch alarms
Why wrong: CloudWatch alarms monitor metrics and trigger actions, but do not control traffic.
- D
AWS Key Management Service (KMS)
Why wrong: KMS manages encryption keys, not network traffic.
- E
Security groups
Security groups act as virtual firewalls for EC2 instances.
Question 1,255 of 1,748
SCS-C02 Infrastructure Security 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. 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.
Which TWO of the following are valid ways to control inbound traffic to an EC2 instance? (Select TWO.)
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
✓
Network ACLs
Network ACLs (NACLs) are a valid method to control inbound traffic to an EC2 instance because they act as a stateless firewall at the subnet level. Each NACL rule evaluates inbound traffic based on source IP, protocol, and port, and rules are processed in order from lowest to highest number. Since NACLs are stateless, you must explicitly allow both inbound and outbound traffic for a response to return.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Network ACLs
Why this is correct
NACLs are stateless firewalls applied at the subnet level.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
IAM policies
Why it's wrong here
IAM policies control access to AWS APIs, not network traffic.
- ✗
Amazon CloudWatch alarms
Why it's wrong here
CloudWatch alarms monitor metrics and trigger actions, but do not control traffic.
- ✗
AWS Key Management Service (KMS)
Why it's wrong here
KMS manages encryption keys, not network traffic.
- ✓
Security groups
Why this is correct
Security groups act as virtual firewalls for EC2 instances.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse IAM policies with network-level controls, mistakenly thinking IAM can filter traffic, or they assume CloudWatch alarms can block traffic when they only trigger notifications or auto-scaling actions.
Detailed technical explanation
How to think about this question
Security groups are stateful, meaning if you allow inbound traffic on port 443, the outbound return traffic is automatically permitted regardless of outbound rules. In contrast, NACLs are stateless and require explicit outbound rules for ephemeral ports (typically 1024-65535) to allow return traffic. A common real-world scenario is troubleshooting connectivity where a security group allows inbound HTTP but the NACL blocks the ephemeral response port, causing timeouts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Visual reference
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Network ACLs — Network ACLs (NACLs) are a valid method to control inbound traffic to an EC2 instance because they act as a stateless firewall at the subnet level. Each NACL rule evaluates inbound traffic based on source IP, protocol, and port, and rules are processed in order from lowest to highest number. Since NACLs are stateless, you must explicitly allow both inbound and outbound traffic for a response to return.
What should I do if I get this SCS-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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