The answer is to create a service control policy (SCP) that denies ec2:RunInstances when a public IP is requested, unless the launch occurs within an allowed VPC. This works because SCPs operate at the AWS Organizations root or OU level, providing a centralized guardrail that prevents EC2 public IP assignment across accounts without requiring per-account IAM changes. The key technical lever is the ec2:AssociatePublicIpAddress condition key, which lets you inspect the launch request for a public IP parameter and conditionally deny it based on the VPC ID. On the ANS-C01 exam, this scenario tests your understanding of preventive versus detective controls—Config and CloudTrail are detective, while SCPs are preventive. A common trap is assuming IAM policies alone suffice, but they must be applied individually per account, making SCPs the only scalable solution for multi-account enforcement. Memory tip: SCPs are the “bouncer” at the organization door, checking for public IPs before any instance gets inside the VPC.
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 is using AWS Organizations with multiple accounts. The security team wants to ensure that no EC2 instance in any account can be launched with a public IP address unless it is in a specific VPC. Which solution will meet this requirement?
Create a service control policy (SCP) that denies ec2:RunInstances if the request includes an association with a public IP address, unless the VPC is the allowed one.
Correct: SCPs can enforce restrictions across all accounts in the organization.
B
Create an IAM policy that denies ec2:RunInstances if the subnet is not in the allowed VPC, and attach it to all IAM users.
Why wrong: Wrong: IAM policies are per-account and not organization-wide.
C
Enable AWS CloudTrail and create a CloudWatch Events rule to stop any instance with a public IP.
Why wrong: Wrong: CloudTrail logs, does not prevent.
D
Use AWS Config rules to detect non-compliant instances and automatically terminate them.
Why wrong: Wrong: Config detects after launch, does not prevent.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a service control policy (SCP) that denies ec2:RunInstances if the request includes an association with a public IP address, unless the VPC is the allowed one.
Option B is correct because an SCP can be applied at the root OU to deny the ec2:RunInstances action if the request includes a parameter to assign a public IP address, using a condition key like ec2:AssociatePublicIpAddress. Option A is wrong because IAM policies need to be applied in each account individually. Option C is wrong because Config can detect but not prevent. Option D is wrong because CloudTrail logs but does not prevent.
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.
✓
Create a service control policy (SCP) that denies ec2:RunInstances if the request includes an association with a public IP address, unless the VPC is the allowed one.
Why this is correct
Correct: SCPs can enforce restrictions across all accounts in the organization.
Create an IAM policy that denies ec2:RunInstances if the subnet is not in the allowed VPC, and attach it to all IAM users.
Why it's wrong here
Wrong: IAM policies are per-account and not organization-wide.
✗
Enable AWS CloudTrail and create a CloudWatch Events rule to stop any instance with a public IP.
Why it's wrong here
Wrong: CloudTrail logs, does not prevent.
✗
Use AWS Config rules to detect non-compliant instances and automatically terminate them.
Why it's wrong here
Wrong: Config detects after launch, does not prevent.
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.
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: Create a service control policy (SCP) that denies ec2:RunInstances if the request includes an association with a public IP address, unless the VPC is the allowed one. — Option B is correct because an SCP can be applied at the root OU to deny the ec2:RunInstances action if the request includes a parameter to assign a public IP address, using a condition key like ec2:AssociatePublicIpAddress. Option A is wrong because IAM policies need to be applied in each account individually. Option C is wrong because Config can detect but not prevent. Option D is wrong because CloudTrail logs but does not prevent.
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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