- A
Configure a managed VPN between the hub and each spoke, and enable dynamic routing
Using a managed VPN with dynamic routing (e.g., Cloud Router with BGP) allows the hub to advertise routes between spokes.
- B
Enable 'Export custom routes' on the hub VPC and 'Import custom routes' on the spoke VPCs
Why wrong: Custom routes export/import does not enable transitive routing across peering connections.
- C
Use a shared VPC instead of VPC Network Peering
Why wrong: Shared VPC allows central management but does not inherently enable transitive routing between service projects without additional configuration.
- D
Create a peering connection between each pair of spokes
Why wrong: This would work but defeats the purpose of a hub-and-spoke design and increases complexity.
Quick Answer
The answer is to configure a managed VPN between the hub and each spoke with dynamic routing. This is required because VPC Network Peering does not support transitive routing by default—traffic from one spoke cannot flow through the hub to another spoke without an explicit routing overlay. By deploying Cloud VPN tunnels with BGP between the hub and each spoke, you create a routed network where the hub can forward traffic between spokes, effectively achieving the desired hub-and-spoke transitive routing. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding of VPC peering’s non-transitive nature, a common trap where candidates assume peering alone enables spoke-to-spoke communication. A useful memory tip: “Peering is point-to-point, not transitive—VPN with BGP bridges the gap.”
PCNE Practice Question: Designing, planning, and prototyping a GCP network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 wants to implement a hub-and-spoke network topology in Google Cloud using VPC Network Peering. The hub VPC hosts shared services and the spoke VPCs host application workloads. They need to ensure that spokes can communicate with each other through the hub. Which additional configuration is required?
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
Configure a managed VPN between the hub and each spoke, and enable dynamic routing
VPC Network Peering does not support transitive routing by default. To enable spoke-to-spoke communication through the hub, you must configure a managed VPN (Cloud VPN) between the hub and each spoke with dynamic routing (BGP). This creates a routed overlay that allows the hub to forward traffic between spokes, effectively achieving transitive routing.
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.
- ✓
Configure a managed VPN between the hub and each spoke, and enable dynamic routing
- ✗
Enable 'Export custom routes' on the hub VPC and 'Import custom routes' on the spoke VPCs
Why it's wrong here
Custom routes export/import does not enable transitive routing across peering connections.
- ✗
Use a shared VPC instead of VPC Network Peering
Why it's wrong here
Shared VPC allows central management but does not inherently enable transitive routing between service projects without additional configuration.
- ✗
Create a peering connection between each pair of spokes
Why it's wrong here
This would work but defeats the purpose of a hub-and-spoke design and increases complexity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume exporting/importing custom routes (Option B) can enable transitive routing, but VPC Network Peering explicitly forbids transitive routing regardless of route propagation settings.
Detailed technical explanation
How to think about this question
VPC Network Peering is a non-transitive, point-to-point connection that does not support routing traffic from one peering link to another (RFC 1918 isolation). Cloud VPN with BGP (using dynamic routing) establishes a Layer 3 overlay where the hub acts as a BGP route reflector, advertising spoke prefixes to other spokes via BGP updates, enabling transitive routing. In practice, this design is often used for centralized inspection (e.g., firewall appliances) where the hub must forward traffic between spokes.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
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FAQ
Questions learners often ask
What does this PCNE question test?
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a managed VPN between the hub and each spoke, and enable dynamic routing — VPC Network Peering does not support transitive routing by default. To enable spoke-to-spoke communication through the hub, you must configure a managed VPN (Cloud VPN) between the hub and each spoke with dynamic routing (BGP). This creates a routed overlay that allows the hub to forward traffic between spokes, effectively achieving transitive routing.
What should I do if I get this PCNE 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 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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