The answer is to configure Cloud NAT with a specific network tag and assign that tag only to VMs in authorized service projects. This works because Cloud NAT applies its source network address translation based on VM-level tags, not at the project level; when the NAT gateway is created in the host project with a designated tag, only instances bearing that tag can use the gateway’s IP addresses for outbound traffic. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of Shared VPC isolation and the fact that tags are the only native mechanism to limit NAT access to specific service projects—a common trap is assuming you can restrict NAT by project ID or IAM roles alone. Remember the mnemonic: “Tag the VM, not the project” to avoid confusing network tags with project-level permissions.
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. 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 uses Shared VPC with multiple service projects. They want to ensure that only specific service projects can use the Cloud NAT configured in the host project. What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure Cloud NAT with a specific network tag and assign that tag only to VMs in authorized service projects.
Cloud NAT can be restricted to specific VMs using network tags. By configuring the Cloud NAT gateway in the host project with a specific network tag, and then assigning that tag only to the VM instances in authorized service projects, only those tagged VMs can use the NAT gateway. This ensures that only specific service projects (via their tagged VMs) can leverage the Cloud NAT, while all other VMs in the shared VPC are excluded.
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.
✓
Configure Cloud NAT with a specific network tag and assign that tag only to VMs in authorized service projects.
Why this is correct
This is the standard method to restrict Cloud NAT usage.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use firewall rules to restrict traffic from service projects.
Why it's wrong here
Firewall rules do not control which VMs use Cloud NAT.
✗
Use VPC Service Controls to restrict access.
Why it's wrong here
VPC Service Controls prevent data exfiltration but do not control NAT access.
✗
Configure IAM roles on the Cloud NAT resource to allow only specific projects.
Why it's wrong here
IAM roles on Cloud NAT do not control which VMs can use it at the network level.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume IAM is the correct way to restrict access to a Cloud NAT resource, but Cloud NAT does not have an IAM resource—it is a regional service that is controlled via network tags or subnet-level configuration, not IAM permissions.
Detailed technical explanation
How to think about this question
Under the hood, Cloud NAT uses a set of NAT IP addresses and applies source network address translation (SNAT) for outbound connections. When a network tag is specified in the Cloud NAT configuration, only VM instances that have that tag in their network interface will have their outbound traffic translated by the NAT gateway. This tag-based filtering is evaluated at the time of packet processing by the Cloud NAT's data plane, allowing fine-grained control without requiring separate NAT gateways per project. In a real-world scenario, this is critical for multi-tenant environments where you want to allow only certain service projects (e.g., those handling external API calls) to use the NAT, while others use direct internet access via external IPs.
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: Configure Cloud NAT with a specific network tag and assign that tag only to VMs in authorized service projects. — Cloud NAT can be restricted to specific VMs using network tags. By configuring the Cloud NAT gateway in the host project with a specific network tag, and then assigning that tag only to the VM instances in authorized service projects, only those tagged VMs can use the NAT gateway. This ensures that only specific service projects (via their tagged VMs) can leverage the Cloud NAT, while all other VMs in the shared VPC are excluded.
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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