The correct approach is to create a firewall rule in the host project that denies egress to all destinations except the allowed IPs, and apply it to the service project's VMs via service accounts. This works because in a Shared VPC, all firewall rules are defined and enforced at the host project level, not within individual service projects, making the host project the only place where egress traffic can be effectively controlled. The deny-all rule with a lower priority is paired with a higher-priority allow rule scoped to specific external IPs and targeted to the service accounts of the VMs that need restricted egress. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding that service projects cannot create their own egress firewall rules in a Shared VPC—a common trap is thinking you can apply rules directly in the service project. Remember the mnemonic: "Host rules, service accounts, deny then allow."
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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 a Shared VPC in Google Cloud with multiple service projects. The security team wants to restrict egress traffic from a specific service project to only allowed external IP addresses. The network project hosts the VPC. What is the best approach?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Why wrong: Private Google Access is for access to Google APIs, not general egress.
B
Use VPC Service Controls to restrict egress.
Why wrong: VPC Service Controls prevent data exfiltration to Google services, not external IPs.
C
Create a firewall rule in the service project's VPC that denies egress.
Why wrong: Service projects do not have their own VPC in Shared VPC; they use the host's VPC.
D
Create a firewall rule in the host project that denies egress to all destinations except the allowed IPs, and apply it to the service project's VMs via service accounts.
Firewall rules in host project can target service projects VMs by service account.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a firewall rule in the host project that denies egress to all destinations except the allowed IPs, and apply it to the service project's VMs via service accounts.
In a Shared VPC, firewall rules are defined in the host project and apply to VM instances in service projects. Option D correctly creates a deny-all egress rule in the host project, then uses a higher-priority allow rule for specific external IPs, scoped to service accounts of the target VMs. This ensures egress traffic from the specific service project is restricted at the VPC firewall level, which is the only effective way to control outbound traffic in a Shared VPC architecture.
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 Private Google Access to restrict egress.
Why it's wrong here
Private Google Access is for access to Google APIs, not general egress.
✗
Use VPC Service Controls to restrict egress.
Why it's wrong here
VPC Service Controls prevent data exfiltration to Google services, not external IPs.
✗
Create a firewall rule in the service project's VPC that denies egress.
Why it's wrong here
Service projects do not have their own VPC in Shared VPC; they use the host's VPC.
✓
Create a firewall rule in the host project that denies egress to all destinations except the allowed IPs, and apply it to the service project's VMs via service accounts.
Why this is correct
Firewall rules in host project can target service projects VMs by service account.
Clue confirmation
The clue word "best" in the question point toward this answer.
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 can be created in service projects within a Shared VPC, but the correct understanding is that all firewall rules must be managed in the host project, and service accounts are the mechanism to scope rules to specific VMs.
Detailed technical explanation
How to think about this question
Shared VPC firewall rules are hierarchical: they are evaluated in the host project and apply to all instances in attached service projects. Egress rules are stateful, meaning return traffic is automatically allowed for established connections. When using service accounts in firewall rule targets, the rule applies only to VMs running with that service account, enabling fine-grained control per project or workload. This approach leverages Google Cloud's implicit 'deny all egress' default, which can be overridden by explicit allow rules with higher priority.
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: Create a firewall rule in the host project that denies egress to all destinations except the allowed IPs, and apply it to the service project's VMs via service accounts. — In a Shared VPC, firewall rules are defined in the host project and apply to VM instances in service projects. Option D correctly creates a deny-all egress rule in the host project, then uses a higher-priority allow rule for specific external IPs, scoped to service accounts of the target VMs. This ensures egress traffic from the specific service project is restricted at the VPC firewall level, which is the only effective way to control outbound traffic in a Shared VPC architecture.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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