The correct answer is to use a NAT gateway in a public subnet for outbound traffic from private subnets and to apply a security group to the RDS database for fine-grained access control. A NAT gateway enables instances in private subnets to initiate outbound internet connections—such as for software updates—while blocking any unsolicited inbound traffic, preserving the subnet’s isolation. A security group acts as a virtual stateful firewall for the RDS instance, allowing you to restrict inbound connections to only the necessary application servers. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of layered network security and common misconfigurations: a common trap is placing an internet gateway in a private subnet, which would directly expose instances, or using a single subnet, which defeats isolation entirely. Remember the mnemonic “NAT out, SG in” to recall that NAT gateways handle outbound-only traffic from private subnets, while security groups control inbound access to specific resources.
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 security engineer is designing a VPC with private and public subnets. Which TWO actions improve network security? (Choose two.)
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 to restrict traffic to the database from only the application tier.
Options A and D are correct. Option A is correct because a NATgateway in a public subnet allows outbound internet for private instances without inbound access. Option D is correct because a security group on the RDS database allows fine-grained control. Option B is wrong because an internet gateway in a private subnet would expose instances. Option C is wrong because a public subnet allows direct internet access. Option E is wrong because a single subnet defeats isolation.
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 a single subnet for all resources to simplify network rules.
Why it's wrong here
Single subnet lacks segmentation and security boundaries.
✓
Use security groups to restrict traffic to the database from only the application tier.
Why this is correct
Security groups provide stateful firewall rules for instance-level security.
Internet gateway should be in public subnet to allow inbound/outbound internet.
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.
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 to restrict traffic to the database from only the application tier. — Options A and D are correct. Option A is correct because a NAT gateway in a public subnet allows outbound internet for private instances without inbound access. Option D is correct because a security group on the RDS database allows fine-grained control. Option B is wrong because an internet gateway in a private subnet would expose instances. Option C is wrong because a public subnet allows direct internet access. Option E is wrong because a single subnet defeats isolation.
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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