- A
Create a firewall rule in the host project that denies all egress traffic except to the Cloud NAT IP
Why wrong: Firewall rules cannot force traffic through NAT; they only allow/deny. NAT is configured on Cloud Router.
- B
Set the instances to use a custom route with next-hop as the Cloud NAT IP address
Why wrong: Cloud NAT is not a next-hop; it's a function of Cloud Router. Custom routes cannot point to a NAT IP.
- C
Configure a Cloud NAT on the Cloud Router in the host project for the subnet that is shared with the service project
Correct: In Shared VPC, the host project owns the subnets. Cloud NAT on the host project's router for those subnets will handle egress for all instances in those subnets, including those from service projects.
- D
Configure a Cloud NAT in each service project and associate it with the subnet that the instances use
Why wrong: This would create separate NATs, not centralized. The goal is a single NAT in the host project.
Quick Answer
The answer is to configure a Cloud NAT on the Cloud Router in the host project for the subnet that is shared with the service project. This works because Cloud NAT is always tied to a specific subnet and Cloud Router, and in a Shared VPC architecture, the host project owns the subnets and the Cloud Router, so any Compute Engine instances in service projects attached to that shared subnet will automatically use the host project’s NAT IP for outbound traffic. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of how Shared VPC decouples network ownership from compute resources—a common trap is trying to configure NAT in the service project, which would create a separate, non-centralized egress path. Remember the key rule: in Shared VPC, the host project owns the network resources, so all centralized egress controls must live there. Memory tip: “Host owns the route, service just sends the packet.”
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. 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.
Your organization uses Shared VPC with a host project and several service projects. You need to ensure that all egress traffic from Compute Engine instances in a service project is routed through a centralized Cloud NAT in the host project. What is the required configuration?
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
Configure a Cloud NAT on the Cloud Router in the host project for the subnet that is shared with the service project
Option C is correct because a Cloud NAT configured on the Cloud Router in the host project for the shared subnet allows all Compute Engine instances in service projects attached to that subnet to use the host project's NAT IP for outbound traffic. This is the only way to centralize egress traffic through the host project's Cloud NAT while respecting Shared VPC architecture, as the NAT is tied to the subnet and Cloud Router in the host project.
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 firewall rule in the host project that denies all egress traffic except to the Cloud NAT IP
- ✗
Set the instances to use a custom route with next-hop as the Cloud NAT IP address
Why it's wrong here
Cloud NAT is not a next-hop; it's a function of Cloud Router. Custom routes cannot point to a NAT IP.
- ✓
Configure a Cloud NAT on the Cloud Router in the host project for the subnet that is shared with the service project
Why this is correct
Correct: In Shared VPC, the host project owns the subnets. Cloud NAT on the host project's router for those subnets will handle egress for all instances in those subnets, including those from service projects.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Configure a Cloud NAT in each service project and associate it with the subnet that the instances use
Why it's wrong here
This would create separate NATs, not centralized. The goal is a single NAT in the host project.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that a Cloud NAT must be configured in the same project as the instances, but in Shared VPC, the NAT is configured in the host project for the shared subnet, and service project instances automatically use it without any additional configuration.
Detailed technical explanation
How to think about this question
Cloud NAT uses Andromeda, Google Cloud's software-defined networking stack, to perform source network address translation (SNAT) for outbound packets. The NAT is configured on a Cloud Router in the host project and associated with a specific subnet; when instances in a service project send traffic to the internet, the VPC routes the packet to the Cloud Router, which translates the source IP to the NAT IP address. A subtle behavior is that Cloud NAT does not support destination NAT (DNAT) for inbound traffic, and it requires the subnet's primary IP range to be non-overlapping with the NAT IP range to avoid asymmetric routing.
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.
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FAQ
Questions learners often ask
What does this PCSE question test?
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a Cloud NAT on the Cloud Router in the host project for the subnet that is shared with the service project — Option C is correct because a Cloud NAT configured on the Cloud Router in the host project for the shared subnet allows all Compute Engine instances in service projects attached to that subnet to use the host project's NAT IP for outbound traffic. This is the only way to centralize egress traffic through the host project's Cloud NAT while respecting Shared VPC architecture, as the NAT is tied to the subnet and Cloud Router in the host project.
What should I do if I get this PCSE 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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Last reviewed: Jun 30, 2026
This PCSE 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 PCSE exam.
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