- A
Use VPC peering to isolate the database subnet from the application subnet.
Why wrong: VPC peering connects VPCs; it does not prevent lateral movement within the same VPC.
- B
Deploy AWS WAF in front of the ALB to block known malicious IPs.
Why wrong: WAF protects against web exploits but does not prevent lateral movement after compromise.
- C
Create a network ACL for the private subnet that denies outbound traffic from the EC2 instances to the database subnet.
Why wrong: Network ACLs are stateless and apply to the entire subnet, potentially blocking legitimate traffic.
- D
Implement a host-based firewall on each EC2 instance to restrict outbound connections to only the database endpoint.
This provides fine-grained control over outbound traffic from the application.
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.
A company runs a critical application on EC2 instances in an Auto Scaling group across multiple Availability Zones. The application uses an Application Load Balancer (ALB) to distribute traffic. The security team has implemented a security group for the ALB that allows inbound HTTPS from 0.0.0.0/0 and a security group for the EC2 instances that allows inbound HTTP from the ALB's security group. Recently, the company experienced a security incident where an attacker exploited a vulnerability in the application to gain access to an EC2 instance and then moved laterally to the database. The database is in a private subnet and uses a security group that allows inbound traffic from the EC2 instance security group on port 3306 (MySQL). The security team wants to prevent lateral movement in the future. Which of the following is the MOST effective course of action?
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
Implement a host-based firewall on each EC2 instance to restrict outbound connections to only the database endpoint.
Option C is correct because implementing a host-based firewall (e.g., AWS Systems Manager Agent with a firewall policy) on each EC2 instance can restrict outbound connections from the application to only necessary destinations, preventing lateral movement. Option A (network ACLs) can block traffic at the subnet level but are not as granular for individual instances. Option B (VPC peering) is not relevant. Option D (AWS WAF) protects against web exploits but does not prevent lateral movement after compromise.
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.
- ✗
Use VPC peering to isolate the database subnet from the application subnet.
Why it's wrong here
VPC peering connects VPCs; it does not prevent lateral movement within the same VPC.
- ✗
Deploy AWS WAF in front of the ALB to block known malicious IPs.
Why it's wrong here
WAF protects against web exploits but does not prevent lateral movement after compromise.
- ✗
Create a network ACL for the private subnet that denies outbound traffic from the EC2 instances to the database subnet.
Why it's wrong here
Network ACLs are stateless and apply to the entire subnet, potentially blocking legitimate traffic.
- ✓
Implement a host-based firewall on each EC2 instance to restrict outbound connections to only the database endpoint.
Why this is correct
This provides fine-grained control over outbound traffic from the application.
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 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.
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?
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Implement a host-based firewall on each EC2 instance to restrict outbound connections to only the database endpoint. — Option C is correct because implementing a host-based firewall (e.g., AWS Systems Manager Agent with a firewall policy) on each EC2 instance can restrict outbound connections from the application to only necessary destinations, preventing lateral movement. Option A (network ACLs) can block traffic at the subnet level but are not as granular for individual instances. Option B (VPC peering) is not relevant. Option D (AWS WAF) protects against web exploits but does not prevent lateral movement after compromise.
What should I do if I get this SCS-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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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Last reviewed: Jun 20, 2026
This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.
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