The answer is to create a Cloud Router per VPC, each with its own VLAN attachment on the same Dedicated Interconnect. This configuration is correct because each VLAN attachment is a Layer 2 boundary that maps to exactly one Cloud Router and one VPC, meaning a single attachment cannot be shared across multiple VPCs. By provisioning a dedicated Cloud Router and VLAN attachment for each VPC, you establish separate BGP sessions over the same physical interconnect, allowing multiple VPCs in a single project to communicate with on-premises while maintaining isolated routing domains. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of the one-to-one relationship between VLAN attachments and VPCs—a common trap is assuming a single attachment can serve multiple VPCs. Remember the memory tip: “One VPC, one VLAN, one Cloud Router” to avoid sharing what cannot be shared.
PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. 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 has multiple VPCs in Google Cloud that need to communicate with an on-premises network through a single Dedicated Interconnect. All VPCs are in the same project. What is the most efficient way to enable connectivity from all VPCs to on-premises?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a Cloud Router per VPC, each with its own VLAN attachment on the same Interconnect
Option C is correct because each VPC requires its own Cloud Router and VLAN attachment to establish a dedicated BGP session over the same Dedicated Interconnect. This allows multiple VPCs in the same project to share a single physical interconnect while maintaining separate Layer 3 routing domains. A single VLAN attachment cannot be shared across VPCs, as each attachment is associated with exactly one Cloud Router and one VPC.
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 a separate Interconnect for each VPC
Why it's wrong here
This is costly and inefficient; a single Interconnect can serve multiple VPCs.
✗
Create a single VLAN attachment and use it for all VPCs
Why it's wrong here
A VLAN attachment can only be attached to one VPC.
✓
Create a Cloud Router per VPC, each with its own VLAN attachment on the same Interconnect
Why this is correct
Each VPC gets its own Cloud Router and VLAN attachment, allowing all to use the same Interconnect.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use VPC Network Peering to connect VPCs and attach one VPC to Interconnect
Why it's wrong here
Peering does not support transitive routing for Interconnect.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a single VLAN attachment can be shared across multiple VPCs, but in Google Cloud, each VLAN attachment is a per-VPC resource that requires its own Cloud Router and BGP session.
Detailed technical explanation
How to think about this question
Each VLAN attachment on a Dedicated Interconnect corresponds to a unique 802.1q VLAN ID and a BGP session with the on-premises router. Cloud Routers manage dynamic route exchange via BGP, and each VPC must have its own Cloud Router to handle its own set of routes and BGP sessions. In a scenario with overlapping IP ranges, separate VLAN attachments prevent route conflicts and allow independent traffic engineering.
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.
Implementing hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a Cloud Router per VPC, each with its own VLAN attachment on the same Interconnect — Option C is correct because each VPC requires its own Cloud Router and VLAN attachment to establish a dedicated BGP session over the same Dedicated Interconnect. This allows multiple VPCs in the same project to share a single physical interconnect while maintaining separate Layer 3 routing domains. A single VLAN attachment cannot be shared across VPCs, as each attachment is associated with exactly one Cloud Router and one VPC.
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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Question Discussion
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