- A
Add a security group rule allowing inbound traffic from 203.0.113.0/24
Why wrong: This is necessary but not sufficient; there is no network path from that IP range to the private subnet.
- B
Create an AWS Site-to-Site VPN connection and update route tables to route the on-premises CIDR to the virtual private gateway
A VPN provides a secure tunnel from on-premises to the VPC, and route tables direct traffic to the VPN gateway.
- C
Assign a public IP address to the RDS instance
Why wrong: Assigning a public IP would expose the database to the internet, which is not desired and may not be allowed for security reasons.
- D
Modify the network ACL of the private subnet to allow inbound traffic from 203.0.113.0/24
Why wrong: Same as A; a network path must exist first.
Quick Answer
The answer is to create an AWS Site-to-Site VPN connection and update the route tables to route the on-premises CIDR to the virtual private gateway. This is correct because an RDS instance in a private subnet has no public endpoint, so a direct internet path is impossible; instead, a dedicated network link like a VPN or Direct Connect establishes a secure tunnel between the on-premises network and the VPC. The security group must also allow inbound traffic from the on-premises CIDR, but without the route table entry pointing to the virtual private gateway, traffic will never reach the RDS instance. On the ANS-C01 exam, this scenario tests your understanding that private RDS access requires both a Layer 3 path (routing) and a Layer 4 rule (security group), and a common trap is thinking a security group rule alone suffices. Memory tip: think “Route first, then rule”—the network path must exist before the firewall can allow traffic.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 company needs to allow a specific IP address range (203.0.113.0/24) to access an Amazon RDS database in a private subnet. The RDS instance is deployed in a VPC with no public access. Which configuration step is required?
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
Create an AWS Site-to-Site VPN connection and update route tables to route the on-premises CIDR to the virtual private gateway
RDS instances in a private subnet are not directly accessible from the internet. To allow access from an on-premises network, a VPN or Direct Connect connection is needed. The security group must allow inbound traffic from the on-premises CIDR, and the route tables must route traffic to the VPN/Direct Connect. Simply adding a security group rule does not provide connectivity; a network path is required.
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.
- ✗
Add a security group rule allowing inbound traffic from 203.0.113.0/24
Why it's wrong here
This is necessary but not sufficient; there is no network path from that IP range to the private subnet.
- ✓
Create an AWS Site-to-Site VPN connection and update route tables to route the on-premises CIDR to the virtual private gateway
- ✗
Assign a public IP address to the RDS instance
Why it's wrong here
Assigning a public IP would expose the database to the internet, which is not desired and may not be allowed for security reasons.
- ✗
Modify the network ACL of the private subnet to allow inbound traffic from 203.0.113.0/24
Why it's wrong here
Same as A; a network path must exist first.
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 Design — This question tests Network Design — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create an AWS Site-to-Site VPN connection and update route tables to route the on-premises CIDR to the virtual private gateway — RDS instances in a private subnet are not directly accessible from the internet. To allow access from an on-premises network, a VPN or Direct Connect connection is needed. The security group must allow inbound traffic from the on-premises CIDR, and the route tables must route traffic to the VPN/Direct Connect. Simply adding a security group rule does not provide connectivity; a network path is required.
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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