- A
Use Cloud NAT to allow the frontend to reach the backend via the internet.
Why wrong: Cloud NAT provides outbound internet access, not internal connectivity between VPCs, and would expose traffic to the internet.
- B
Use an internal TCP/UDP load balancer in the backend VPC and configure the frontend to send traffic to the load balancer's internal IP.
Why wrong: An internal load balancer is used to distribute traffic within a VPC or across peered VPCs, but it would only be needed if the backend had multiple instances; however, direct peering is simpler and sufficient.
- C
Place both frontend and backend instances in the same VPC but different subnets, and use firewall rules to allow traffic.
Why wrong: This would work, but the question implies they are in different VPCs. It is a valid design but not the best answer given the scenario of separate VPCs.
- D
Set up VPC Network Peering between the frontend VPC and the backend VPC.
VPC peering enables private IP communication across VPCs without requiring external IPs or gateways, meeting the requirement of internal-only communication.
Quick Answer
The correct answer is to set up VPC Network Peering between the frontend VPC and the backend VPC. This configuration is required because VPC Network Peering enables direct internal IP communication between two separate VPC networks without needing a VPN, gateway, or public internet access, which perfectly satisfies the requirement for frontend and backend instances to communicate using only internal IP addresses. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of when to use peering versus Shared VPC or Cloud VPN—a common trap is assuming Shared VPC is needed, but peering is the correct choice when the tiers are in entirely separate VPC projects or networks and you need simple, low-latency internal routing. A helpful memory tip: if the tiers are in different VPCs but need private, direct connectivity, think “peer, not share” for isolated internal communication.
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.
A company is deploying a multi-tier application on Google Cloud. The frontend tier runs in a managed instance group behind a global external HTTP(S) load balancer. The backend tier runs on Compute Engine instances in a different VPC subnet. The frontend instances must communicate with the backend instances using internal IP addresses only. Which configuration should the network engineer use?
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 VPC Network Peering between the frontend VPC and the backend VPC.
Option D is correct because VPC Network Peering allows two separate VPC networks to communicate using internal IP addresses without traversing the internet or requiring a VPN. Since the frontend and backend are in different VPCs (implied by the need for peering), peering enables direct internal IP connectivity between the frontend instances and the backend instances, satisfying the requirement for internal-only communication.
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.
- ✗
Use Cloud NAT to allow the frontend to reach the backend via the internet.
Why it's wrong here
Cloud NAT provides outbound internet access, not internal connectivity between VPCs, and would expose traffic to the internet.
- ✗
Use an internal TCP/UDP load balancer in the backend VPC and configure the frontend to send traffic to the load balancer's internal IP.
Why it's wrong here
An internal load balancer is used to distribute traffic within a VPC or across peered VPCs, but it would only be needed if the backend had multiple instances; however, direct peering is simpler and sufficient.
- ✗
Place both frontend and backend instances in the same VPC but different subnets, and use firewall rules to allow traffic.
Why it's wrong here
This would work, but the question implies they are in different VPCs. It is a valid design but not the best answer given the scenario of separate VPCs.
- ✓
Set up VPC Network Peering between the frontend VPC and the backend VPC.
Why this is correct
VPC peering enables private IP communication across VPCs without requiring external IPs or gateways, meeting the requirement of internal-only communication.
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 may assume placing instances in the same VPC (Option C) is the simplest solution, but the question explicitly implies the frontend and backend are in separate VPCs, making VPC Network Peering the correct choice for internal IP communication across VPCs.
Trap categories for this question
Scenario analysis trap
This would work, but the question implies they are in different VPCs. It is a valid design but not the best answer given the scenario of separate VPCs.
Detailed technical explanation
How to think about this question
VPC Network Peering uses the Google Cloud internal infrastructure to route traffic between VPCs using RFC 1918 addresses, with no bandwidth limits or single points of failure. When peering is established, routes are automatically exchanged, allowing instances in one VPC to reach instances in the other VPC directly via internal IPs. A key subtlety is that peering is not transitive; if you need communication across multiple VPCs, you must set up direct peering between each pair, or use a hub-and-spoke model with a network appliance.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
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Designing, planning, and prototyping a GCP network — study guide chapter
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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: Set up VPC Network Peering between the frontend VPC and the backend VPC. — Option D is correct because VPC Network Peering allows two separate VPC networks to communicate using internal IP addresses without traversing the internet or requiring a VPN. Since the frontend and backend are in different VPCs (implied by the need for peering), peering enables direct internal IP connectivity between the frontend instances and the backend instances, satisfying the requirement for internal-only communication.
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: 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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