The answer is that the host project administrator must create the firewall rule in the host project. This is correct because in a Shared VPC architecture, firewall rules are defined and managed exclusively at the host project level, not within individual service projects. The shared VPC network is a host-project-level resource, so only the host project administrator holds the compute.firewalls.create permission required to write rules that apply to instances across all attached service projects. On the Google Professional Cloud Security Engineer exam, this concept frequently appears in scenarios testing your understanding of IAM delegation and resource hierarchy—a common trap is assuming a service project network admin can manage firewall rules independently. Remember the memory tip: "Firewall rules follow the network, not the instance; the host project owns the network, so the host admin owns the rules."
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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 a host project and several service projects. A network administrator in a service project wants to create a firewall rule that allows traffic from a specific source CIDR to a Compute Engine instance in the service project. What is the correct way to achieve this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Request the host project administrator to create the firewall rule in the host project.
In a Shared VPC architecture, firewall rules are a host-project-level resource. Service project administrators cannot create or manage firewall rules that apply to resources in the shared VPC network; only the host project administrator has the necessary permissions. Therefore, to allow traffic from a specific source CIDR to a Compute Engine instance in a service project, the host project administrator must create the firewall rule in the host project, targeting the instance's tags or service account.
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.
✗
Create the firewall rule in the service project targeting the instance's tags.
Why it's wrong here
Firewall rules for a shared VPC network must be created in the host project.
✗
Create a firewall rule in the service project using the instance's service account.
Why it's wrong here
Firewall rules are applied to network interfaces, not service accounts, and service projects cannot create rules for shared VPC.
✗
Use VPC Flow Logs to generate a recommendation and apply it in the service project.
Why it's wrong here
VPC Flow Logs do not create firewall rules, and service projects cannot apply rules to shared VPC.
✓
Request the host project administrator to create the firewall rule in the host project.
Why this is correct
In Shared VPC, the host project owns the firewall rules for the shared VPC network.
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 service project administrators have full control over networking resources in a Shared VPC, when in fact firewall rules and other network-level configurations are exclusively managed in the host project.
Detailed technical explanation
How to think about this question
Under the hood, Shared VPC uses Identity and Access Management (IAM) roles such as Compute Network Admin (roles/compute.networkAdmin) at the host project level to control firewall rule creation. The service project's network is actually the host project's VPC network, so any firewall rule applied to that network must originate from the host project. A real-world scenario is a multi-tenant environment where each service project has its own Compute Engine instances but shares a common VPC; the host project admin must centrally manage all firewall rules to ensure consistent security policies across tenants.
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.
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Request the host project administrator to create the firewall rule in the host project. — In a Shared VPC architecture, firewall rules are a host-project-level resource. Service project administrators cannot create or manage firewall rules that apply to resources in the shared VPC network; only the host project administrator has the necessary permissions. Therefore, to allow traffic from a specific source CIDR to a Compute Engine instance in a service project, the host project administrator must create the firewall rule in the host project, targeting the instance's tags or service account.
What should I do if I get this PCSE 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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