The answer is to use IAM roles on the subnet resource and the organizational policy constraint `compute.restrictVpcSubnetworks`. Granting the `compute.subnetUser` IAM role to a service project directly controls which projects can launch VM instances in that specific subnet, making it a precise method to restrict subnet usage in a Shared VPC. The organizational policy constraint, meanwhile, enforces a blanket restriction at the folder or project level, preventing any VM from using subnets outside a defined allowlist. On the Google Professional Cloud Network Engineer exam, this question tests your ability to differentiate between IAM-based resource-level controls and organization policy-based guardrails—a common trap is confusing the `compute.subnetUser` role with broader network roles like `compute.networkUser`. Remember the memory tip: IAM says "who can use this subnet," while the org policy says "which subnets can be used at all."
PCNE Practice Question: Designing, planning, and prototyping a GCP network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. 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 uses Shared VPC. They want to restrict which service project's VMs can use a specific subnet. Which TWO methods can achieve this? (Choose TWO.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use IAM roles on the subnet resource to grant 'compute.subnetUser' to specific service projects.
Option B is correct because IAM roles on a subnet resource allow you to grant the `compute.subnetUser` role to specific service projects, which controls which projects can create VM instances in that subnet. This is a direct method to restrict subnet usage within a Shared VPC environment, as the role grants permission to use the subnet without granting broader network access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 VPC network peering.
Why it's wrong here
Peering connects VPCs but does not restrict subnet access.
✓
Use IAM roles on the subnet resource to grant 'compute.subnetUser' to specific service projects.
Why this is correct
This IAM role controls which projects can use the subnet.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use firewall rules to deny traffic from other service projects.
Why it's wrong here
Firewall rules do not prevent VM creation in the subnet.
✗
Use network tags on VMs and associate the subnet with those tags.
Why it's wrong here
Subnets do not have network tags; tags are on VMs and do not restrict subnet usage.
✓
Use organizational policy constraints like 'compute.restrictVpcSubnetworks'.
Why this is correct
This policy can limit subnets available to projects in the organization.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules or network tags can control subnet access, when in fact they only control traffic flow or VM-level attributes, not the authorization to use a subnet resource.
Detailed technical explanation
How to think about this question
Under the hood, the `compute.subnetUser` IAM role grants the `compute.subnetworks.use` permission, which is evaluated at the subnet resource level in the Shared VPC host project. When a service project attempts to create a VM, the GCP IAM system checks if the service project's compute service account has this permission on the target subnet, ensuring that only authorized projects can use that subnet. In real-world scenarios, this allows fine-grained segmentation, such as granting a development service project access to a 'dev-subnet' while denying access to a 'prod-subnet', without needing separate VPCs.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use IAM roles on the subnet resource to grant 'compute.subnetUser' to specific service projects. — Option B is correct because IAM roles on a subnet resource allow you to grant the `compute.subnetUser` role to specific service projects, which controls which projects can create VM instances in that subnet. This is a direct method to restrict subnet usage within a Shared VPC environment, as the role grants permission to use the subnet without granting broader network access.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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