This DBS-C01 practice question tests your understanding of database 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 audit reveals that an Amazon RDS for MySQL DB instance is accessible from the internet. The security team requires that the database be accessible only from a specific set of application servers within the same VPC. Which solution should be implemented?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Modify the DB instance's security group to allow inbound traffic only from the application servers' security group.
Option B is correct because a security group with an inbound rule that references the application servers' security group restricts access to only those instances. Option A is wrong because network ACLs are stateless and block all traffic if not correctly configured, but security groups are more appropriate for instance-level access. Option C is wrong because changing the subnet to private and using a bastion host is unnecessary if the app servers are in the same VPC. Option D is wrong because enabling encryption does not restrict 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 DB instance's security group to allow inbound traffic only from the application servers' security group.
Why this is correct
Security group references allow traffic from instances with that security group.
Apply a network ACL that denies inbound traffic from 0.0.0.0/0 and allows from the application servers' IP range.
Why it's wrong here
Network ACLs are stateless and would require additional rules for return traffic; security groups are preferred.
✗
Enable encryption at rest on the DB instance to prevent unauthorized access.
Why it's wrong here
Encryption does not control network access.
✗
Move the DB instance to a private subnet and configure a bastion host for access.
Why it's wrong here
This adds complexity; the app servers are in the same VPC.
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.
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 DB instance's security group to allow inbound traffic only from the application servers' security group. — Option B is correct because a security group with an inbound rule that references the application servers' security group restricts access to only those instances. Option A is wrong because network ACLs are stateless and block all traffic if not correctly configured, but security groups are more appropriate for instance-level access. Option C is wrong because changing the subnet to private and using a bastion host is unnecessary if the app servers are in the same VPC. Option D is wrong because enabling encryption does not restrict 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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Question Discussion
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