- A
Modify the DB instance's security group to allow inbound traffic only from the application servers' security group.
Security group references allow traffic from instances with that security group.
- B
Apply a network ACL that denies inbound traffic from 0.0.0.0/0 and allows from the application servers' IP range.
Why wrong: Network ACLs are stateless and would require additional rules for return traffic; security groups are preferred.
- C
Enable encryption at rest on the DB instance to prevent unauthorized access.
Why wrong: Encryption does not control network access.
- D
Move the DB instance to a private subnet and configure a bastion host for access.
Why wrong: This adds complexity; the app servers are in the same VPC.
Question 1,247 of 1,730
Restricting RDS Access to Application Servers Using Security Groups
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 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 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 DB instance's security group to allow inbound traffic only from the application servers' security group.
Option A is correct because modifying the DB instance's security group to allow inbound traffic only from the application servers' security group restricts access to only those instances, using the security group as a source for a more dynamic and manageable solution. Option B is incorrect because network ACLs are stateless and apply at the subnet level, not the instance level, and allowing from the application servers' IP range is less flexible and secure than using security group references. Option C is incorrect because enabling encryption at rest protects data at rest but does not control network access. Option D is incorrect because moving to a private subnet and using a bastion host is unnecessary when the application servers are in the same VPC; a security group rule is simpler and more appropriate.
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.
Related concept
CIDR notation defines the prefix length.
- ✗
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.
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: Modify the DB instance's security group to allow inbound traffic only from the application servers' security group. — Option A is correct because modifying the DB instance's security group to allow inbound traffic only from the application servers' security group restricts access to only those instances, using the security group as a source for a more dynamic and manageable solution. Option B is incorrect because network ACLs are stateless and apply at the subnet level, not the instance level, and allowing from the application servers' IP range is less flexible and secure than using security group references. Option C is incorrect because enabling encryption at rest protects data at rest but does not control network access. Option D is incorrect because moving to a private subnet and using a bastion host is unnecessary when the application servers are in the same VPC; a security group rule is simpler and more appropriate.
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.
About these practice questions
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Same concept, more angles
1 more ways this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is deploying a new Amazon RDS for MySQL database in a VPC. The database must be accessible only from an application server running in the same VPC. The security team also wants to ensure that the database is not accessible from the internet. Which TWO configurations are required? (Choose TWO.)
easy- A.Place the DB instance in a public subnet.
- B.Modify the DB parameter group to restrict network access.
- ✓ C.Configure the security group to allow inbound traffic only from the application server's security group.
- ✓ D.Set the DB instance to be not publicly accessible.
- E.Configure a network ACL to deny inbound traffic from 0.0.0.0/0.
Why C: To meet the requirements, two configurations are needed. First, the DB instance must be set to not publicly accessible (Option D) to ensure it cannot be reached from the internet. Second, the security group associated with the DB instance must allow inbound traffic only from the application server's security group (Option C), which restricts access to resources within the VPC. Option A is incorrect because placing the DB instance in a public subnet would expose it to the internet. Option B is incorrect because the DB parameter group controls database engine settings, not network access. Option E is incorrect because network ACLs are stateless and a rule denying all inbound traffic would block legitimate traffic as well; security groups are the appropriate mechanism for this scenario.
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Last reviewed: Jun 20, 2026
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