The correct answer is to ensure the database subnets lack a route to an Internet Gateway and to create a security group for the database instances that allows inbound traffic only from the web servers' security group. This works because securing database subnets from internet access requires a two-layer defense: the subnet’s route table must not have a default route (0.0.0.0/0) pointing to an Internet Gateway, which physically blocks inbound internet traffic at the network layer, and the security group acts as a virtual firewall at the instance level, explicitly restricting inbound traffic to only the trusted source—the web server security group. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of defense-in-depth for private subnets, often appearing as a multi-select question where common traps include confusing security groups with network ACLs (which are stateless and less precise) or mistakenly assigning public IPs. A key memory tip is “no route, no public IP, and lock the group”—if a subnet has no IGW route and its instances have no public IP, they are unreachable from the internet, and the security group then fine-tunes allowed traffic.
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.
Exhibit
Which TWO actions should a security engineer take to secure a VPC that contains a public-facing web application?
A security engineer is configuring a VPC for a web application. The VPC has public and private subnets. The web servers are in public subnets and the database servers are in private subnets. The engineer wants to ensure that the database servers are not accessible from the internet. Which two actions should the engineer take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ensure the route table for the database subnets does not have a default route to an Internet Gateway.
Option A and Option D are correct. The database subnets should not have a route to the Internet Gateway, and their security group should only allow traffic from the web servers' security group. Option B is unnecessary; network ACLs are stateless and can be used, but security groups are sufficient. Option C is incorrect because assigning public IPs would expose them. Option E is incorrect because a NAT gateway is for outbound internet access, not inbound.
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.
✗
Place the database instances in a public subnet with a NAT gateway.
Configure a network ACL on the database subnets to deny all inbound traffic.
Why it's wrong here
This would block all traffic, including from web servers.
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.
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: Ensure the route table for the database subnets does not have a default route to an Internet Gateway. — Option A and Option D are correct. The database subnets should not have a route to the Internet Gateway, and their security group should only allow traffic from the web servers' security group. Option B is unnecessary; network ACLs are stateless and can be used, but security groups are sufficient. Option C is incorrect because assigning public IPs would expose them. Option E is incorrect because a NAT gateway is for outbound internet access, not inbound.
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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Question Discussion
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