The correct design is to use three separate VPCs for each tier and connect them using VPC peering. This approach enforces strict segmentation by isolating each tier into its own network boundary: the web tier VPC gets a public subnet with an internet gateway, the application tier VPC is peered only to the web tier (with no internet gateway), and the database tier VPC is peered only to the application tier (with no public IPs). On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of VPC peering as a tool for transitive isolation—a common trap is assuming a single VPC with firewall rules provides equivalent security, but that still exposes the database to lateral movement risks. The key insight is that peering is non-transitive, so traffic cannot hop from web to database without passing through the application tier. Memory tip: think “three rings, two bridges”—each tier is a separate ring, and peering only connects adjacent rings, never skipping one.
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. 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 is deploying a multi-tier web application on Google Cloud. The web tier must be accessible from the internet, while the application tier should only be accessible from the web tier. The database tier must not have any public IP addresses. Which VPC design should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use three separate VPCs for each tier and connect them using VPC peering.
Option B is correct because using three separate VPCs with VPC peering enforces strict network segmentation: the web tier VPC has a public subnet with an internet gateway, the application tier VPC is peered only to the web tier VPC (no internet gateway), and the database tier VPC is peered only to the application tier VPC (no public IPs). This design ensures that the database tier has no public IP addresses and is only reachable through the application tier, meeting all security requirements.
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 a Shared VPC with separate subnets in different projects for each tier.
Why it's wrong here
Shared VPC is for multi-project environments, not for tier isolation within one organization.
✓
Use three separate VPCs for each tier and connect them using VPC peering.
Why this is correct
Separate VPCs provide full isolation; peering allows controlled communication.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single VPC and connect the database tier via Cloud VPN to on-premises.
Why it's wrong here
Cloud VPN does not address isolation between tiers within a VPC.
✗
Use a single VPC with separate subnets for each tier and configure firewall rules to restrict traffic.
Why it's wrong here
Single VPC does not provide network isolation at the VPC level; firewall rules alone can be misconfigured.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that firewall rules alone can prevent public IP assignment, but the trap here is that firewall rules control traffic, not the existence of a public IP address on a resource; the database tier must have no public IP at all, which requires a VPC design that prohibits internet gateway routes.
Detailed technical explanation
How to think about this question
VPC peering uses the RFC 1918 address space to route traffic between VPCs without requiring a VPN or gateway, and each peered VPC retains its own firewall rules and routing tables. In this design, the database tier VPC must not have a default route to the internet (0.0.0.0/0 via internet gateway), ensuring no public IPs are needed or used. A real-world scenario where this matters is in PCI DSS compliance, where cardholder data must be isolated from public-facing tiers; using separate VPCs with peering provides a clean audit boundary.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use three separate VPCs for each tier and connect them using VPC peering. — Option B is correct because using three separate VPCs with VPC peering enforces strict network segmentation: the web tier VPC has a public subnet with an internet gateway, the application tier VPC is peered only to the web tier VPC (no internet gateway), and the database tier VPC is peered only to the application tier VPC (no public IPs). This design ensures that the database tier has no public IP addresses and is only reachable through the application tier, meeting all security requirements.
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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