- A
Use security groups for all tiers; add an inbound rule to the database security group allowing traffic from the web security group on port 3306.
Security groups are stateful and can reference other security groups, reducing overhead. This is correct.
- B
Use security groups for all tiers; add an inbound rule to the web security group allowing internet traffic on port 443, and add an outbound rule to the web security group allowing traffic to the database security group on port 3306.
Why wrong: This allows outbound from web to database, but inbound to database must be allowed on the database security group. The outbound rule on the web SG alone is insufficient because the database SG controls inbound.
- C
Use security groups for the web tier and network ACLs for the database tier; add an inbound rule to the database network ACL allowing traffic from the web subnet CIDR on port 3306.
Why wrong: Using network ACLs adds overhead due to stateless filtering and managing IP addresses. Not optimal.
- D
Use security groups for the web tier and network ACLs for the database tier; add an inbound rule to the database network ACL allowing all traffic from the web security group.
Why wrong: Network ACLs cannot reference security groups; they use IP addresses. Also, allowing all traffic is overly permissive.
Quick Answer
The correct choice is to use security groups for all tiers, with an inbound rule on the database security group referencing the web security group on port 3306. This approach minimizes administrative overhead because security groups are stateful and support logical referencing, meaning you can allow traffic based on other security groups rather than hard-coding IP addresses or CIDR blocks. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the security group reference database concept and the trade-offs between stateful and stateless controls. A common trap is defaulting to network ACLs for private subnets, but that would require managing explicit rules for return traffic and IP changes, increasing overhead. Remember the key distinction: security groups are stateful and support logical references, while network ACLs are stateless and require explicit bidirectional rules. Memory tip: “SG references = no IP guesswork; NACL stateless = double the rules.”
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 is designing a VPC with public and private subnets. The web servers in the public subnets must be accessible from the internet on port 443, but the database servers in the private subnets should only be accessible from the web servers on port 3306. Which combination of security group rules and network ACL rules should be used to meet these requirements with the least administrative overhead?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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 for all tiers; add an inbound rule to the database security group allowing traffic from the web security group on port 3306.
Option C is correct because security groups are stateful and can reference other security groups, allowing you to allow inbound traffic from the web security group to the database security group without needing to manage IP addresses. Network ACLs are stateless and would require explicit allow rules for return traffic, increasing overhead. Options A and B use network ACLs for the database tier, which is less efficient. Option D is incorrect because it allows all traffic from the web security group, which is more permissive than necessary.
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 security groups for all tiers; add an inbound rule to the database security group allowing traffic from the web security group on port 3306.
Why this is correct
Security groups are stateful and can reference other security groups, reducing overhead. This is correct.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
- ✗
Use security groups for all tiers; add an inbound rule to the web security group allowing internet traffic on port 443, and add an outbound rule to the web security group allowing traffic to the database security group on port 3306.
Why it's wrong here
This allows outbound from web to database, but inbound to database must be allowed on the database security group. The outbound rule on the web SG alone is insufficient because the database SG controls inbound.
- ✗
Use security groups for the web tier and network ACLs for the database tier; add an inbound rule to the database network ACL allowing traffic from the web subnet CIDR on port 3306.
Why it's wrong here
Using network ACLs adds overhead due to stateless filtering and managing IP addresses. Not optimal.
- ✗
Use security groups for the web tier and network ACLs for the database tier; add an inbound rule to the database network ACL allowing all traffic from the web security group.
Why it's wrong here
Network ACLs cannot reference security groups; they use IP addresses. Also, allowing all traffic is overly permissive.
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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Infrastructure Security — study guide chapter
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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 for all tiers; add an inbound rule to the database security group allowing traffic from the web security group on port 3306. — Option C is correct because security groups are stateful and can reference other security groups, allowing you to allow inbound traffic from the web security group to the database security group without needing to manage IP addresses. Network ACLs are stateless and would require explicit allow rules for return traffic, increasing overhead. Options A and B use network ACLs for the database tier, which is less efficient. Option D is incorrect because it allows all traffic from the web security group, which is more permissive than necessary.
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.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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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