The answer is that the Cloud NAT is not in the same region as the new service project's instances. Cloud NAT is a regional resource, meaning it only provides outbound internet access to virtual machine instances located within the same Google Cloud region where the Cloud NAT gateway is configured. Since the Cloud NAT was deployed in us-central1, instances in europe-west1 cannot use it, regardless of matching network tags or Shared VPC configuration. This scenario tests your understanding of Cloud NAT regional scope in Shared VPC, a critical concept for the Google Professional Cloud Network Engineer exam, which often includes trap answers involving network tags or service project permissions. A common mistake is assuming tags alone enable connectivity, but the gateway’s regional boundary is the decisive factor. Remember: Cloud NAT is region-locked, not tag-locked—think “same region, same route.”
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. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 uses a Shared VPC with a host project and multiple service projects. They have deployed Cloud NAT in the host project's network to provide internet access for service project instances. The Cloud NAT is configured to use a network tag 'nat'. Instances in service projects that have the tag 'nat' can reach the internet. A new service project is added and its instances are created with the same tag 'nat' in a subnet in europe-west1. However, these instances cannot reach the internet. Other service project instances with the tag 'nat' in us-central1 work fine. The Cloud NAT is deployed in us-central1. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Cloud NAT is not in the same region as the new service project's instances.
Cloud NAT is a regional resource; it only provides outbound internet access to instances within the same region. Since the Cloud NAT is deployed in us-central1, instances in europe-west1 cannot use it, regardless of their network tag. The instances in the new service project must have a Cloud NAT deployed in europe-west1 to reach the internet.
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.
✗
The Cloud NAT's UDP timeout is too short.
Why it's wrong here
Timeout would not prevent all connectivity.
✗
The firewall rules in the host project block traffic from the new service project's subnets.
Why it's wrong here
Firewall rules are not the issue; the region mismatch is.
✓
The Cloud NAT is not in the same region as the new service project's instances.
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The new service project's instances are not tagged with 'nat'.
Why it's wrong here
They are tagged as stated.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume Cloud NAT is a global resource or that network tags alone ensure connectivity, overlooking the critical regional scope of Cloud NAT and the fact that it must be deployed in the same region as the instances it serves.
Detailed technical explanation
How to think about this question
Cloud NAT is implemented as a regional managed service using Cloud Routers and NAT gateways. Each region requires its own Cloud NAT configuration because the NAT gateway's external IP addresses and forwarding rules are bound to that region's VPC subnet. Under the hood, Cloud NAT uses Andromeda (Google's network virtualization stack) to perform source NAT (SNAT) for outbound packets, and the regional scope is enforced by the underlying network infrastructure. In a real-world scenario, if you have workloads in multiple regions, you must deploy a Cloud NAT in each region where outbound internet access is needed.
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: The Cloud NAT is not in the same region as the new service project's instances. — Cloud NAT is a regional resource; it only provides outbound internet access to instances within the same region. Since the Cloud NAT is deployed in us-central1, instances in europe-west1 cannot use it, regardless of their network tag. The instances in the new service project must have a Cloud NAT deployed in europe-west1 to reach the internet.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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