- A
No impact on either VPC
Why wrong: Dev VPC will have issues with the overlapping subnet.
- B
Prod VPC loses connectivity to the on-premises network
Why wrong: Prod's routes to on-prem are separate; no impact.
- C
Prod VPC can now communicate with Dev VPC via on-prem
Why wrong: Peering is non-transitive; routes not exchanged.
- D
Dev VPC cannot communicate with on-prem due to overlap
Overlapping subnets cause routing issues for Dev VPC to on-prem.
Question 629 of 982
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. 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 has two VPCs (Prod and Dev) that are peered. Both VPCs have routes to an on-premises network via separate Cloud VPN tunnels. The on-prem network has routes to both VPCs. The Dev VPC recently added a subnet that overlaps with an on-prem subnet. What is the likely impact on the Prod VPC?
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
✓
Dev VPC cannot communicate with on-prem due to overlap
When the Dev VPC adds a subnet that overlaps with an on-premises subnet, Cloud VPN routes for that overlapping prefix become ambiguous. GCP Cloud Router uses dynamic routing (BGP) and will prefer the more specific route, but if the prefixes are identical, the route to the on-premises network via the Dev VPN tunnel may be withdrawn or become unreachable due to the conflict. This directly impacts the Dev VPC's ability to communicate with the on-premises network over the VPN, while the Prod VPC, with its non-overlapping subnet, remains unaffected.
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.
- ✗
No impact on either VPC
Why it's wrong here
Dev VPC will have issues with the overlapping subnet.
- ✗
Prod VPC loses connectivity to the on-premises network
Why it's wrong here
Prod's routes to on-prem are separate; no impact.
- ✗
Prod VPC can now communicate with Dev VPC via on-prem
Why it's wrong here
Peering is non-transitive; routes not exchanged.
- ✓
Dev VPC cannot communicate with on-prem due to overlap
Why this is correct
Overlapping subnets cause routing issues for Dev VPC to on-prem.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume overlapping subnets in one VPC will break all VPN connectivity across peered VPCs, but in reality, each VPC's VPN tunnel is independent, and only the VPC with the overlapping subnet loses connectivity to the on-premises network.
Detailed technical explanation
How to think about this question
Under the hood, Cloud VPN with dynamic routing uses BGP to exchange routes. When a VPC subnet overlaps with an on-premises subnet, GCP's Cloud Router may install a more specific or conflicting route, causing the BGP session to withdraw the overlapping prefix or leading to asymmetric routing. In a real-world scenario, this often results in the overlapping VPC losing connectivity to the on-premises network for that subnet range, while other VPCs with non-overlapping ranges remain unaffected. The key subtlety is that overlapping subnets do not propagate across VPC peering; they only affect the VPC where the overlap exists.
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.
Visual reference
What to study next
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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: Dev VPC cannot communicate with on-prem due to overlap — When the Dev VPC adds a subnet that overlaps with an on-premises subnet, Cloud VPN routes for that overlapping prefix become ambiguous. GCP Cloud Router uses dynamic routing (BGP) and will prefer the more specific route, but if the prefixes are identical, the route to the on-premises network via the Dev VPN tunnel may be withdrawn or become unreachable due to the conflict. This directly impacts the Dev VPC's ability to communicate with the on-premises network over the VPN, while the Prod VPC, with its non-overlapping subnet, remains unaffected.
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.
About these practice questions
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Last reviewed: Jul 4, 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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