The answer is to use a NAT instance with an external IP in the host project and route traffic from service projects. This design is correct because a NAT instance, deployed as a centralized egress point in the host project, allows the network administration team to attach a static external IP for centralized outbound IP control, while each service project retains autonomy to manage its own Cloud NAT configurations for internal traffic. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of the trade-off between managed Cloud NAT and self-managed NAT instances within a Shared VPC hierarchy—a common trap is assuming Cloud NAT alone can delegate IP control to a central team, but Cloud NAT’s IP is per-region and per-project, not centrally managed. The key insight is that a NAT instance decouples IP ownership from NAT management. Memory tip: “Instance for IP, Cloud NAT for autonomy”—the instance owns the static IP, the service projects own their NAT 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. 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.
An organization is using Shared VPC with 100 service projects. They want to allow each service project to manage its own Cloud NAT, but the network administration team wants to control the outbound IP addresses used. What is the best design?
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
✓
Use a NAT instance with an external IP in the host project and route traffic from service projects
Option B is correct because a NAT instance in the host project allows the network administration team to control the outbound IP addresses (by attaching a static external IP to the instance) while service projects can manage their own Cloud NAT configurations for outbound traffic. The NAT instance acts as a centralized egress point, and service project traffic is routed to it via custom routes or policy-based routing, meeting both requirements: service project autonomy for NAT management and centralized IP control.
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 single Cloud NAT in the host project and share it
Why it's wrong here
Service projects cannot manage or configure this NAT.
✓
Use a NAT instance with an external IP in the host project and route traffic from service projects
Why this is correct
Network team controls the IP, service projects can manage routes to use it.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create Cloud NAT in each service project with the same external IPs
Why it's wrong here
Same external IP cannot be used across projects; IPs must be reserved per project.
✗
Use Private Google Access with Cloud NAT in the host project
Why it's wrong here
Private Google Access does not provide general internet access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that Cloud NAT can be shared across VPCs or service projects, or that multiple Cloud NATs can reuse the same external IP, leading candidates to pick Option A or C without realizing Cloud NAT's per-VPC and per-region scope and IP uniqueness constraints.
Detailed technical explanation
How to think about this question
Under the hood, a NAT instance uses IP forwarding and iptables (or similar) to perform source NAT (SNAT), rewriting source IPs to the instance's external IP. Service projects must have routes (e.g., default route via the NAT instance's internal IP) and firewall rules to allow traffic. In contrast, Cloud NAT is a managed service using Andromeda software-defined networking, which cannot be delegated per service project for IP control. A real-world scenario is a multi-tenant SaaS provider where each tenant (service project) needs to configure NAT rules (e.g., port ranges) but the provider must enforce a single egress IP for whitelisting.
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.
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: Use a NAT instance with an external IP in the host project and route traffic from service projects — Option B is correct because a NAT instance in the host project allows the network administration team to control the outbound IP addresses (by attaching a static external IP to the instance) while service projects can manage their own Cloud NAT configurations for outbound traffic. The NAT instance acts as a centralized egress point, and service project traffic is routed to it via custom routes or policy-based routing, meeting both requirements: service project autonomy for NAT management and centralized IP control.
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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