The answer is that the service project is missing the compute.networkUser role on the host project. This is required because Shared VPC architecture separates network resources (owned by the host project) from compute resources (owned by service projects); even if a subnet’s IAM policy grants compute.instanceAdmin to a service project’s service account, that account still needs the compute.networkUser role at the host project level to attach the subnet’s network interface to a VM. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of the layered permission model in Shared VPC, where subnet-level IAM controls access to a specific subnet, but the host-project-level role is the gatekeeper for using any subnet in that VPC. A common trap is assuming subnet IAM alone is sufficient, but the networkUser role is the foundational prerequisite. Memory tip: think “NetworkUser first, then subnet IAM” — you must be invited to the network before you can use a specific room.
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An organization uses Shared VPC with multiple service projects. They want to allow a service project to create a VM in a subnet that belongs to the host project. The subnet has an IAM policy that grants the compute.instanceAdmin role to the service project's service account. However, the service project is unable to create VMs in that subnet. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service project is missing the compute.networkUser role on the host project.
In addition to subnet-level IAM, the service project must have the compute.networkUser role on the host project to use the Shared VPC. Option A is correct. Option B is wrong because the subnet IAM is sufficient for subnet access once the network user role is granted. Option C is wrong because service project's own IAM does not grant access to host project resources. Option D is wrong because quota is not the issue here.
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.
✗
The subnet IAM policy does not include the service project's service account.
Why it's wrong here
It does, but the network user role is also needed.
✗
The subnet is out of IP addresses.
Why it's wrong here
IP exhaustion is possible but less likely given the context.
✗
The service project does not have the compute.instanceAdmin role on itself.
Why it's wrong here
Instance admin role in service project is for creating VMs, but network access requires host project permissions.
✓
The service project is missing the compute.networkUser role on the host project.
Why this is correct
The compute.networkUser role is required to use the host project's VPC networks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The service project is missing the compute.networkUser role on the host project. — In addition to subnet-level IAM, the service project must have the compute.networkUser role on the host project to use the Shared VPC. Option A is correct. Option B is wrong because the subnet IAM is sufficient for subnet access once the network user role is granted. Option C is wrong because service project's own IAM does not grant access to host project resources. Option D is wrong because quota is not the issue here.
What should I do if I get this PCNE 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 PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An organization uses Shared VPC with multiple service projects. They want to ensure that only certain service projects can use a specific subnet. How can this be achieved?
hard
A.Use VPC subnet secondary IP ranges.
✓ B.Use IAM roles on the subnet to grant access to specific service projects.
C.Use VPC Network Tags on the VM instances.
D.Use VPC firewall rules with service accounts to restrict access.
Why B: Option A is correct because Shared VPC subnet-level IAM allows granting access to specific service projects. Option B is wrong because firewall rules with service accounts control traffic, not subnet access. Option C is wrong because network tags are used for firewall rules, not subnet permissions. Option D is wrong because secondary IP ranges do not control project access.
Last reviewed: Jun 24, 2026
Question Discussion
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This PCNE practice question is part of Courseiva's free Google Cloud 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 PCNE exam.
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