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Database Security →easyMultiple ChoiceObjective-mapped

DBS-C01 Database Security Practice Question

This DBS-C01 practice question tests your understanding of database security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 using Amazon RDS for MySQL and needs to restrict access to the database to only specific Amazon EC2 instances in the same VPC. Which security mechanism should be used?

A
Configure a DB security group that allows inbound traffic from the EC2 security groups.
This option is incorrect because DB security groups are only applicable in EC2-Classic, not in a VPC. In a VPC, you should use a VPC security group to control traffic to the RDS instance.
B
Create an IAM policy that allows the EC2 instances to connect to the RDS instance.
Why wrong: This option is incorrect because IAM policies govern permissions for AWS API calls (e.g., to create or modify RDS instances), not network-level access to the database.
C
Create a DB subnet group that includes only the subnets where the EC2 instances reside.
Why wrong: This option is incorrect because a DB subnet group determines which subnets an RDS instance can be deployed in; it does not provide inbound traffic control.
D
Modify the network ACL for the DB subnet to allow traffic from the EC2 instances' IP addresses.
Why wrong: This option is incorrect because network ACLs are stateless, operate at the subnet level, and cannot be used to restrict access to specific instances. They also do not support referencing security groups.

Full breakdown with real-world context →

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 a DB security group that allows inbound traffic from the EC2 security groups.

In a VPC, RDS instances use VPC security groups to control inbound traffic, not DB security groups. DB security groups are only used in the EC2-Classic platform, which is not applicable here. Option A is incorrect because it references DB security groups. Option B is incorrect because IAM policies control API access, not network connectivity. Option C is incorrect because subnet groups define subnets for deployment, not security rules. Option D is incorrect because network ACLs are stateless, apply to entire subnets, and cannot reference security groups or specific instances. The correct mechanism is to configure a VPC security group that allows inbound traffic from the EC2 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.

✓
Configure a DB security group that allows inbound traffic from the EC2 security groups.
Why this is correct
This option is incorrect because DB security groups are only applicable in EC2-Classic, not in a VPC. In a VPC, you should use a VPC security group to control traffic to the RDS instance.
Related concept
CIDR notation defines the prefix length.
✗
Create an IAM policy that allows the EC2 instances to connect to the RDS instance.
Why it's wrong here
This option is incorrect because IAM policies govern permissions for AWS API calls (e.g., to create or modify RDS instances), not network-level access to the database.
✗
Create a DB subnet group that includes only the subnets where the EC2 instances reside.
Why it's wrong here
This option is incorrect because a DB subnet group determines which subnets an RDS instance can be deployed in; it does not provide inbound traffic control.
✗
Modify the network ACL for the DB subnet to allow traffic from the EC2 instances' IP addresses.
Why it's wrong here
This option is incorrect because network ACLs are stateless, operate at the subnet level, and cannot be used to restrict access to specific instances. They also do not support referencing security groups.

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.

Visual reference

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 DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DBS-C01 question test?

Database Security — This question tests Database Security — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Configure a DB security group that allows inbound traffic from the EC2 security groups. — In a VPC, RDS instances use VPC security groups to control inbound traffic, not DB security groups. DB security groups are only used in the EC2-Classic platform, which is not applicable here. Option A is incorrect because it references DB security groups. Option B is incorrect because IAM policies control API access, not network connectivity. Option C is incorrect because subnet groups define subnets for deployment, not security rules. Option D is incorrect because network ACLs are stateless, apply to entire subnets, and cannot reference security groups or specific instances. The correct mechanism is to configure a VPC security group that allows inbound traffic from the EC2 security groups.

What should I do if I get this DBS-C01 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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