- A
Use network ACLs to block all inbound traffic to the private subnets.
Why wrong: Network ACLs are stateless and would block return traffic; security groups are more appropriate.
- B
Configure security group rules to allow inbound traffic from the web server security group to the database security group.
This allows targeted traffic between web and database servers.
- C
Do not add a route to an internet gateway in the route table for the private subnets.
This ensures the private subnets have no direct internet access.
- D
Attach an internet gateway to the VPC and route the private subnets to it.
Why wrong: This would give the private subnets internet access, which is not desired.
- E
Add a NAT gateway in the public subnet and route the private subnets to it.
Why wrong: This would give the private subnets outbound internet access, which is not required.
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 VPC with public and private subnets. The VPC will host web servers in public subnets and database servers in private subnets. The web servers need to send traffic to the database servers, and the database servers must not have direct internet access. Which TWO configurations should the engineer implement?
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
Configure security group rules to allow inbound traffic from the web server security group to the database security group.
Option A is correct because security group rules can allow traffic between web and database servers based on the security group ID. Option D is correct because a NAT gateway is not needed for private subnets that don't need internet access; however, the database servers must not have internet access, so a NAT gateway should not be used. Actually, the correct combination is A and C: Use security group rules (A) and ensure no route to an internet gateway for private subnets (C). Option E is also correct? No, E is about NAT gateway which would give internet access. So correct: A and C.
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 to block all inbound traffic to the private subnets.
Why it's wrong here
Network ACLs are stateless and would block return traffic; security groups are more appropriate.
- ✓
Configure security group rules to allow inbound traffic from the web server security group to the database security group.
Why this is correct
This allows targeted traffic between web and database servers.
Related concept
CIDR notation defines the prefix length.
- ✓
Do not add a route to an internet gateway in the route table for the private subnets.
Why this is correct
This ensures the private subnets have no direct internet access.
Related concept
CIDR notation defines the prefix length.
- ✗
Attach an internet gateway to the VPC and route the private subnets to it.
Why it's wrong here
This would give the private subnets internet access, which is not desired.
- ✗
Add a NAT gateway in the public subnet and route the private subnets to it.
Why it's wrong here
This would give the private subnets outbound internet access, which is not required.
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: Configure security group rules to allow inbound traffic from the web server security group to the database security group. — Option A is correct because security group rules can allow traffic between web and database servers based on the security group ID. Option D is correct because a NAT gateway is not needed for private subnets that don't need internet access; however, the database servers must not have internet access, so a NAT gateway should not be used. Actually, the correct combination is A and C: Use security group rules (A) and ensure no route to an internet gateway for private subnets (C). Option E is also correct? No, E is about NAT gateway which would give internet access. So correct: A and C.
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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