- A
Disable the 'Publicly accessible' option for the RDS instances.
Why wrong: This is a good practice, but if the instance has a public IP via a subnet, it could still be accessible. The question asks for VPC-level actions.
- B
Create a network ACL that denies all inbound traffic from 0.0.0.0/0.
Why wrong: Network ACLs are stateless and would also affect outbound traffic; also, security groups are more appropriate.
- C
Remove the route to an internet gateway from the private subnet's route table.
Without a route to an internet gateway, traffic cannot reach the internet.
- D
Ensure that the RDS instances are launched in a private subnet without a public IP address.
Without a public IP, the instances are not directly reachable from the internet.
- E
Configure the security group for the RDS instances to deny all inbound traffic.
Why wrong: This would block all inbound traffic, but the question is about internet access; internal traffic may be needed.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 a VPC with a public subnet and a private subnet. The private subnet hosts Amazon RDS instances. The security team wants to ensure that the RDS instances are not accessible from the internet. Which TWO actions should be taken?
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
Remove the route to an internet gateway from the private subnet's route table.
Options A and D are correct because removing internet gateway routes and not assigning public IPs prevent internet access. Option B is wrong because restricting security group inbound rules is important, but alone it may not prevent internet access if there is a public IP. Option C is wrong because network ACLs are stateless and can be used, but they are not as precise as security groups for this purpose. Option E is wrong because RDS can have public accessibility disabled, but that is not a VPC-level action.
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.
- ✗
Disable the 'Publicly accessible' option for the RDS instances.
Why it's wrong here
This is a good practice, but if the instance has a public IP via a subnet, it could still be accessible. The question asks for VPC-level actions.
- ✗
Create a network ACL that denies all inbound traffic from 0.0.0.0/0.
Why it's wrong here
Network ACLs are stateless and would also affect outbound traffic; also, security groups are more appropriate.
- ✓
Remove the route to an internet gateway from the private subnet's route table.
- ✓
Ensure that the RDS instances are launched in a private subnet without a public IP address.
Why this is correct
Without a public IP, the instances are not directly reachable from the internet.
Related concept
CIDR notation defines the prefix length.
- ✗
Configure the security group for the RDS instances to deny all inbound traffic.
Why it's wrong here
This would block all inbound traffic, but the question is about internet access; internal traffic may be needed.
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: Remove the route to an internet gateway from the private subnet's route table. — Options A and D are correct because removing internet gateway routes and not assigning public IPs prevent internet access. Option B is wrong because restricting security group inbound rules is important, but alone it may not prevent internet access if there is a public IP. Option C is wrong because network ACLs are stateless and can be used, but they are not as precise as security groups for this purpose. Option E is wrong because RDS can have public accessibility disabled, but that is not a VPC-level action.
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
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