- A
Priority 1000: Allow ingress from 10.0.1.0/24 to VMs with tag 'app-b' on TCP 443.
This allows the desired inter-service-project traffic on TCP 443.
- B
Priority 2000: Deny ingress from 0.0.0.0/0 to all VMs on all protocols.
This blocks all other ingress traffic (including default-allow-internal) because priority 2000 is higher than the default 65535.
- C
Priority 1000: Allow ingress from IAP forwarding ranges to all VMs on all protocols.
Why wrong: This would allow all protocols from IAP, which is too broad and unnecessary; only TCP 22 is needed.
- D
Priority 1000: Allow egress from VMs in service project A to service project B's VMs on TCP 443.
Why wrong: Egress rules are not needed because the default egress allow will suffice; the ingress rule already permits the destination VMs to receive traffic.
- E
Priority 900: Allow ingress from IAP forwarding ranges (35.235.240.0/20) to all VMs on TCP 22.
This permits SSH access via IAP, overriding the deny rule for TCP 22.
Quick Answer
The correct answer involves creating three firewall rules in the host project: a high-priority ingress allow rule from 10.0.1.0/24 to tagged 'app-b' VMs on TCP 443, a lower-priority deny-all ingress rule for inter-service-project traffic, and an allow rule from IAP forwarding ranges 35.235.240.0/20 to all VMs on TCP 22. This works because in Shared VPC, all firewall rules are defined at the host project level and apply uniformly across service projects, so the specific allow rule permits the desired communication while the broader deny rule blocks everything else, and the IAP rule ensures SSH access remains open for management. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of Shared VPC firewall rule hierarchy and the critical distinction that IAP uses a fixed source range, not your VPC’s internal IPs. A common trap is forgetting that deny rules must have a lower priority than allow rules to function correctly, or assuming IAP rules belong in service projects. Memory tip: “Allow specific, deny all, then IAP for fallback.”
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 uses Shared VPC with a host project and multiple service projects. The security team wants to enforce that only specific VMs in service project A (using IP range 10.0.1.0/24) can communicate with specific VMs in service project B (tagged as 'app-b') on TCP port 443, and all other inter-service-project traffic should be blocked. Additionally, VMs should still be accessible via IAP TCP forwarding (SSH) on TCP port 22. Which three firewall rules should be created in the host project? (Choose three.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Priority 1000: Allow ingress from 10.0.1.0/24 to VMs with tag 'app-b' on TCP 443.
Option A is correct because it creates an ingress firewall rule in the host project that allows traffic from the specific IP range 10.0.1.0/24 (VMs in service project A) to VMs tagged 'app-b' in service project B on TCP port 443. In Shared VPC, all firewall rules are defined in the host project and apply to all service projects, so this rule enforces the required communication while the deny rule (Option B) blocks all other inter-service-project traffic. The IAP rule (Option E) is needed to allow SSH access via IAP TCP forwarding, which uses the source range 35.235.240.0/20 on TCP port 22.
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.
- ✓
Priority 1000: Allow ingress from 10.0.1.0/24 to VMs with tag 'app-b' on TCP 443.
Why this is correct
This allows the desired inter-service-project traffic on TCP 443.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Priority 2000: Deny ingress from 0.0.0.0/0 to all VMs on all protocols.
Why this is correct
This blocks all other ingress traffic (including default-allow-internal) because priority 2000 is higher than the default 65535.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Priority 1000: Allow ingress from IAP forwarding ranges to all VMs on all protocols.
Why it's wrong here
This would allow all protocols from IAP, which is too broad and unnecessary; only TCP 22 is needed.
- ✗
Priority 1000: Allow egress from VMs in service project A to service project B's VMs on TCP 443.
Why it's wrong here
Egress rules are not needed because the default egress allow will suffice; the ingress rule already permits the destination VMs to receive traffic.
- ✓
Priority 900: Allow ingress from IAP forwarding ranges (35.235.240.0/20) to all VMs on TCP 22.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that egress rules are needed for inter-service-project communication, when in fact ingress rules on the destination VMs are sufficient, and that IAP rules must be scoped to only TCP 22, not all protocols.
Detailed technical explanation
How to think about this question
In Shared VPC, firewall rules are hierarchical and evaluated in the host project, applying to all service project VMs. The deny rule (Option B) with priority 2000 acts as a catch-all to block all inter-service-project traffic, but it must be placed at a lower priority than the allow rules (priority 1000) to ensure the specific allow rules take precedence. IAP TCP forwarding uses a specific source IP range (35.235.240.0/20) and requires an ingress allow rule on TCP port 22; using 'all protocols' would expose other ports unnecessarily. The tag 'app-b' is a network tag applied to VMs in service project B, which the firewall rule matches for targeted access.
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.
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FAQ
Questions learners often ask
What does this PCSE question test?
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: Priority 1000: Allow ingress from 10.0.1.0/24 to VMs with tag 'app-b' on TCP 443. — Option A is correct because it creates an ingress firewall rule in the host project that allows traffic from the specific IP range 10.0.1.0/24 (VMs in service project A) to VMs tagged 'app-b' in service project B on TCP port 443. In Shared VPC, all firewall rules are defined in the host project and apply to all service projects, so this rule enforces the required communication while the deny rule (Option B) blocks all other inter-service-project traffic. The IAP rule (Option E) is needed to allow SSH access via IAP TCP forwarding, which uses the source range 35.235.240.0/20 on TCP port 22.
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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Last reviewed: Jun 30, 2026
This PCSE 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 PCSE exam.
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