The answer is to separate each application tier into its own subnet, use Private Google Access for private API connectivity, and implement VPC firewall rules with least privilege. This design is correct because subnet-level segmentation allows you to apply granular ingress and egress controls between web, app, and database tiers, ensuring only necessary traffic—like web-to-app on TCP 8080 or app-to-database on TCP 3306—is permitted while all other traffic is denied by default. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of VPC design best practices for multi-tier applications, often appearing as a multi-select question where common traps include choosing a single shared subnet or relying on public IPs for database access. A useful memory tip is “Subnets, Private, and Rules”—think of slicing tiers into separate subnets, keeping API calls private, and locking down traffic with firewall rules.
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 is planning to migrate to Google Cloud and needs to design a VPC network for a multi-tier application (web, app, database). Which THREE best practices should they follow? (Choose THREE.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create separate subnets for each tier and use firewall rules to control traffic between them.
Option C is correct because separating each application tier into its own subnet allows you to apply VPC firewall rules to control ingress and egress traffic between tiers based on source and destination CIDR ranges or service accounts. This follows the principle of least privilege, ensuring that only necessary traffic (e.g., web-to-app on TCP port 8080, app-to-database on TCP port 3306) is permitted, while all other traffic is denied by default.
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 one subnet for all tiers to simplify routing.
Why it's wrong here
This reduces security and makes firewall rules more complex.
✗
Use instance-level firewalls instead of VPC firewall rules.
Why it's wrong here
Instance-level firewalls are harder to manage; VPC firewall rules are central and scalable.
✓
Create separate subnets for each tier and use firewall rules to control traffic between them.
Why this is correct
Segmentation improves security and manageability.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use Cloud Armor to protect the web tier.
Why this is correct
Cloud Armor provides DDoS protection and WAF capabilities.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use Private Google Access for instances to reach Google APIs privately.
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that instance-level firewalls are a best practice for multi-tier security in GCP, but the correct approach is to use VPC firewall rules with subnet segmentation and service account or tag-based controls for centralized, scalable traffic management.
Detailed technical explanation
How to think about this question
VPC firewall rules in GCP are stateful and evaluated in order of priority (0–65535), with an implied deny-all at the end. When you create separate subnets for web, app, and database tiers, you can use firewall rules with source_tags or target_tags to enforce micro-segmentation without relying on IP addresses that may change. For example, you can allow HTTP(S) traffic from the internet to instances tagged 'web', then allow traffic from 'web' to 'app' on a specific port, and from 'app' to 'db' on another port, while blocking all other cross-tier traffic.
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.
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: Create separate subnets for each tier and use firewall rules to control traffic between them. — Option C is correct because separating each application tier into its own subnet allows you to apply VPC firewall rules to control ingress and egress traffic between tiers based on source and destination CIDR ranges or service accounts. This follows the principle of least privilege, ensuring that only necessary traffic (e.g., web-to-app on TCP port 8080, app-to-database on TCP port 3306) is permitted, while all other traffic is denied by default.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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