- A
Use network ACLs with inbound rules that reference the prefix list of the previous tier's subnets.
Why wrong: NACLs do not support referencing prefix lists or security groups; they only support CIDR blocks.
- B
Use network ACLs with inbound rules that allow traffic from the previous tier's subnet CIDR.
Why wrong: NACLs are stateless and require separate rules for inbound and outbound traffic, increasing overhead.
- C
Use security groups with inbound rules that allow traffic from the previous tier's public IP addresses.
Why wrong: Using public IPs for internal traffic is not recommended; it's insecure and adds administrative burden.
- D
Use security groups with inbound rules that reference the security group of the previous tier.
Security groups are stateful and can reference other security groups, simplifying rule management.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 designing a network architecture for a multi-tier application. The web tier must be accessible from the internet, while the application tier should only be accessible from the web tier, and the database tier only from the application tier. All tiers are in the same VPC. Which configuration meets these requirements with minimal administrative overhead?
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
Use security groups with inbound rules that reference the security group of the previous tier.
Option B is correct because security group rules can reference other security groups by ID, allowing traffic between tiers without managing IP addresses. Option A is wrong because NACLs are stateless and require explicit allow rules for return traffic, adding complexity. Option C is wrong because using public IPs for internal communication is unnecessary and insecure. Option D is wrong because prefix lists are used for IP address management, not for allowing traffic between security groups.
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 network ACLs with inbound rules that reference the prefix list of the previous tier's subnets.
Why it's wrong here
NACLs do not support referencing prefix lists or security groups; they only support CIDR blocks.
- ✗
Use network ACLs with inbound rules that allow traffic from the previous tier's subnet CIDR.
Why it's wrong here
NACLs are stateless and require separate rules for inbound and outbound traffic, increasing overhead.
- ✗
Use security groups with inbound rules that allow traffic from the previous tier's public IP addresses.
Why it's wrong here
Using public IPs for internal traffic is not recommended; it's insecure and adds administrative burden.
- ✓
Use security groups with inbound rules that reference the security group of the previous tier.
Why this is correct
Security groups are stateful and can reference other security groups, simplifying rule management.
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.
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: Use security groups with inbound rules that reference the security group of the previous tier. — Option B is correct because security group rules can reference other security groups by ID, allowing traffic between tiers without managing IP addresses. Option A is wrong because NACLs are stateless and require explicit allow rules for return traffic, adding complexity. Option C is wrong because using public IPs for internal communication is unnecessary and insecure. Option D is wrong because prefix lists are used for IP address management, not for allowing traffic between security groups.
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.
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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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