- A
Use a network ACL on the private subnet that allows MySQL traffic from the EC2 instances' IP addresses.
Why wrong: Network ACLs are stateless and require both inbound and outbound rules; they are less secure than security groups.
- B
Set up a VPN connection between the EC2 instances and the RDS instance.
Why wrong: VPN is unnecessary for traffic within the same VPC.
- C
Use a security group for the RDS instance that allows inbound MySQL traffic from the security group of the EC2 instances.
Security group rules can reference other security groups, providing instance-level access control.
- D
Enable IAM database authentication for the RDS instance and require EC2 instances to use IAM credentials.
Why wrong: IAM authentication controls user access, not network-level access.
Quick Answer
The correct answer is to use a security group for the RDS instance that allows inbound MySQL traffic from the security group of the EC2 instances. This works because security groups act as a virtual firewall at the instance level, and referencing another security group as a source creates a tightly scoped, stateful rule that permits traffic only from any EC2 instance associated with that specific group—regardless of IP address changes. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding of granular network segmentation within a VPC, often appearing as a trap where candidates mistakenly choose network ACLs, which are stateless and require explicit inbound and outbound rules, or IAM database authentication, which handles user credentials rather than network access. A common memory tip for RDS access control with security groups is “group-to-group, not IP-to-IP”—think of it as a VIP list for your database, where only members of the EC2 security group are allowed in, making it the most secure and manageable approach for in-VPC traffic.
ANS-C01 Network Security, Compliance and Governance Practice Question
This ANS-C01 practice question tests your understanding of network security, compliance and governance. 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 MySQL database in a private subnet. The database should only be accessible from a specific fleet of EC2 instances in the same VPC. Which combination of security controls should be used to meet this requirement?
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
Use a security group for the RDS instance that allows inbound MySQL traffic from the security group of the EC2 instances.
Option A is correct because a security group on the RDS instance that allows inbound traffic from the security group of the EC2 instances restricts access to only those instances. Option B is wrong because network ACLs are stateless and less granular. Option C is wrong because IAM database authentication is for user authentication, not network access. Option D is wrong because a VPN connection is not needed for in-VPC 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.
- ✗
Use a network ACL on the private subnet that allows MySQL traffic from the EC2 instances' IP addresses.
Why it's wrong here
Network ACLs are stateless and require both inbound and outbound rules; they are less secure than security groups.
- ✗
Set up a VPN connection between the EC2 instances and the RDS instance.
Why it's wrong here
VPN is unnecessary for traffic within the same VPC.
- ✓
Use a security group for the RDS instance that allows inbound MySQL traffic from the security group of the EC2 instances.
Why this is correct
Security group rules can reference other security groups, providing instance-level access control.
Related concept
CIDR notation defines the prefix length.
- ✗
Enable IAM database authentication for the RDS instance and require EC2 instances to use IAM credentials.
Why it's wrong here
IAM authentication controls user access, not network-level access.
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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use a security group for the RDS instance that allows inbound MySQL traffic from the security group of the EC2 instances. — Option A is correct because a security group on the RDS instance that allows inbound traffic from the security group of the EC2 instances restricts access to only those instances. Option B is wrong because network ACLs are stateless and less granular. Option C is wrong because IAM database authentication is for user authentication, not network access. Option D is wrong because a VPN connection is not needed for in-VPC access.
What should I do if I get this ANS-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 ANS-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
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.
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