- A
Modify the VPC security group to allow inbound traffic on the database port from the specific CIDR, and ensure the DB instance is publicly accessible with the correct security group.
The security group acts as a firewall for the DB instance, and the PubliclyAccessible setting allows it to have a public IP.
- B
Modify the DB subnet group to include only subnets from the allowed CIDR.
Why wrong: The DB subnet group determines which subnets the DB instance can be placed in, but does not filter incoming traffic.
- C
Add a rule to the network ACL to allow inbound traffic from the CIDR.
Why wrong: Network ACLs are associated with subnets, not directly with the DB instance, and are less precise than security groups.
- D
Set the rds.force_ssl parameter to force encrypted connections from the allowed CIDR.
Why wrong: This parameter enforces SSL, not network access control.
DBS-C01 Database Security Practice Question
This DBS-C01 practice question tests your understanding of database 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 has an Amazon RDS for Oracle DB instance that is publicly accessible. They want to restrict access to only a specific CIDR block. Which two actions must be taken together?
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
Modify the VPC security group to allow inbound traffic on the database port from the specific CIDR, and ensure the DB instance is publicly accessible with the correct security group.
Option C is correct because the security group must allow inbound from the specific CIDR, and the DB instance must be publicly accessible. Option A is wrong because subnet assignment is not directly for access control. Option B is wrong because NACLs are stateless and not typically used for RDS access control. Option D is wrong because the DB parameter group does not control network access.
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.
- ✓
Modify the VPC security group to allow inbound traffic on the database port from the specific CIDR, and ensure the DB instance is publicly accessible with the correct security group.
- ✗
Modify the DB subnet group to include only subnets from the allowed CIDR.
Why it's wrong here
The DB subnet group determines which subnets the DB instance can be placed in, but does not filter incoming traffic.
- ✗
Add a rule to the network ACL to allow inbound traffic from the CIDR.
Why it's wrong here
Network ACLs are associated with subnets, not directly with the DB instance, and are less precise than security groups.
- ✗
Set the rds.force_ssl parameter to force encrypted connections from the allowed CIDR.
Why it's wrong here
This parameter enforces SSL, not network access control.
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 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: Modify the VPC security group to allow inbound traffic on the database port from the specific CIDR, and ensure the DB instance is publicly accessible with the correct security group. — Option C is correct because the security group must allow inbound from the specific CIDR, and the DB instance must be publicly accessible. Option A is wrong because subnet assignment is not directly for access control. Option B is wrong because NACLs are stateless and not typically used for RDS access control. Option D is wrong because the DB parameter group does not control network access.
What should I do if I get this DBS-C01 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 DBS-C01 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
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