- A
Delete the VPC peering connection between the Staging and Production VPCs.
Why wrong: Deleting a non-existent peering between Staging and Production is irrelevant; they are only peered to Shared Services, so this action does nothing.
- B
Set up a Cloud VPN between each spoke VPC and the Shared Services VPC to enable transitive routing.
Correct. Cloud VPN enables transitive routing between hub and spokes, allowing the hub to forward inter-spoke traffic through the firewall appliance.
- C
Configure static routes in each spoke VPC with a next hop to the firewall appliance's internal IP for the destination VPC's subnet ranges.
Correct when combined with Option B. Static routes in each spoke force traffic to the other spoke’s subnet range through the firewall’s internal IP, ensuring inspection.
- D
Remove the default route (0.0.0.0/0) from the spoke VPCs to prevent direct internet access.
Why wrong: Removing the default route would break outbound internet access via Cloud NAT, as spokes need the default route to reach the NAT gateway in Shared Services.
- E
Enable the export of custom routes from the Shared Services VPC to the peered VPCs.
Why wrong: Exporting custom routes from Shared Services to peered VPCs does not enable transitive routing because peering does not support it; routes are not propagated further. This alone cannot make the hub a transit point.
PCNE Transitive routing Practice Question
This PCNE practice question tests your understanding of implementing network security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: transitive routing. 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 designing a secure multi-VPC architecture in Google Cloud. They have three VPCs: Production, Staging, and Shared Services. The Shared Services VPC hosts a Cloud NAT for outbound internet access and a set of managed instance groups. The Production and Staging VPCs are peered to the Shared Services VPC. The company wants to ensure that: (1) instances in Staging cannot initiate connections to instances in Production, (2) instances in Production cannot initiate connections to instances in Staging, (3) all VPCs can communicate with Shared Services, and (4) traffic between VPCs must be inspected by a firewall appliance in Shared Services. Which TWO actions should the company take?
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
Set up a Cloud VPN between each spoke VPC and the Shared Services VPC to enable transitive routing.
In Google Cloud, VPC peering does not support transitive routing. Therefore, to route traffic between the spoke VPCs (Production and Staging) through the firewall appliance in Shared Services, you must establish Cloud VPN connections between each spoke and the hub (Option B). This enables dynamic route exchange and allows the hub to forward inter-spoke traffic. Additionally, you need to configure static routes in each spoke VPC with a next hop to the firewall appliance's internal IP (Option C) to ensure that traffic destined for the other spoke is sent through the firewall for inspection. Together, these actions satisfy all requirements: spokes cannot communicate directly (no direct peering), all VPCs reach Shared Services via peering, and inter-VPC traffic is inspected by the firewall.
Key principle: Transitive routing
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Delete the VPC peering connection between the Staging and Production VPCs.
Why it's wrong here
Deleting a non-existent peering between Staging and Production is irrelevant; they are only peered to Shared Services, so this action does nothing.
- ✓
Set up a Cloud VPN between each spoke VPC and the Shared Services VPC to enable transitive routing.
- ✓
Configure static routes in each spoke VPC with a next hop to the firewall appliance's internal IP for the destination VPC's subnet ranges.
Why this is correct
Correct when combined with Option B. Static routes in each spoke force traffic to the other spoke’s subnet range through the firewall’s internal IP, ensuring inspection.
Related concept
Transitive routing
- ✗
Remove the default route (0.0.0.0/0) from the spoke VPCs to prevent direct internet access.
Why it's wrong here
Removing the default route would break outbound internet access via Cloud NAT, as spokes need the default route to reach the NAT gateway in Shared Services.
- ✗
Enable the export of custom routes from the Shared Services VPC to the peered VPCs.
Why it's wrong here
Exporting custom routes from Shared Services to peered VPCs does not enable transitive routing because peering does not support it; routes are not propagated further. This alone cannot make the hub a transit point.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates may mistakenly think that VPC peering with custom route export (Option E) enables transitive routing through a hub, but Google Cloud explicitly does not support transitive peering. Cloud VPN or Network Connectivity Center is required for hub-and-spoke transit.
Detailed technical explanation
How to think about this question
VPC peering in Google Cloud does not support transitive routing, meaning that if Production and Staging are both peered to Shared Services, they cannot communicate with each other through Shared Services unless explicit routes are configured. By adding static routes in each spoke VPC with a next hop to the firewall appliance's internal IP (e.g., 10.0.0.2), traffic is forced through the firewall, which can inspect and enforce security policies. This approach leverages the fact that VPC peering allows custom route exchange when route export is enabled, enabling the firewall to act as a central inspection point.
KKey Concepts to Remember
- Transitive routing
- Hub-and-spoke architecture
- Cloud VPN
- Static route next hop
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
Transitive routing
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review transitive routing, then practise related PCNE questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this PCNE question test?
Implementing network security — This question tests Implementing network security — Transitive routing.
What is the correct answer to this question?
The correct answer is: Set up a Cloud VPN between each spoke VPC and the Shared Services VPC to enable transitive routing. — In Google Cloud, VPC peering does not support transitive routing. Therefore, to route traffic between the spoke VPCs (Production and Staging) through the firewall appliance in Shared Services, you must establish Cloud VPN connections between each spoke and the hub (Option B). This enables dynamic route exchange and allows the hub to forward inter-spoke traffic. Additionally, you need to configure static routes in each spoke VPC with a next hop to the firewall appliance's internal IP (Option C) to ensure that traffic destined for the other spoke is sent through the firewall for inspection. Together, these actions satisfy all requirements: spokes cannot communicate directly (no direct peering), all VPCs reach Shared Services via peering, and inter-VPC traffic is inspected by the firewall.
What should I do if I get this PCNE question wrong?
Review transitive routing, then practise related PCNE questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Transitive routing
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Last reviewed: Jun 11, 2026
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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