The answer is a region mismatch between the subnet and the Cloud NAT gateway. This is correct because Cloud NAT is a regional resource that applies only to instances within its configured region and VPC network; if the subnet containing the instance resides in a different region than the NAT gateway, the gateway cannot route traffic for that subnet, leaving the instance without internet access even though it is in the correct zone. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding that Cloud NAT operates at the regional level, not the zonal level, and a common trap is assuming that as long as the instance’s zone matches the NAT’s region, it will work—overlooking the subnet’s region. Remember the memory tip: “NAT is regional, subnet is regional—if they don’t match, traffic won’t dispatch.”
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. 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.
An engineer creates a Cloud NAT configuration as shown in the exhibit. The test-instance is created without an external IP address. However, the instance cannot reach the internet. 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 subnet subnet-a is in a region different from us-central1
Option A is correct because Cloud NAT is a regional resource that applies to all instances within a given region. The exhibit shows subnet-a is in a different region than us-central1, so the NAT gateway cannot route traffic from instances in that subnet. Even though the instance is in us-central1, the subnet's region mismatch means the NAT configuration does not apply, leaving the instance without internet access.
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 subnet subnet-a is in a region different from us-central1
Why this is correct
Cloud NAT covers only subnets in the same region as the NAT router. If subnet-a is in another region, it is not covered.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Cloud Router is not in the same zone as the instance
Why it's wrong here
Cloud Router is regional, not zonal; region us-central1 covers all zones in that region.
✗
A firewall rule is blocking outbound traffic from the instance
Why it's wrong here
By default, VPC firewall allows outbound connections; no explicit rule is mentioned.
✗
Logging is enabled but not configured to send logs to Cloud Logging
Why it's wrong here
Logging is optional and does not affect connectivity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that Cloud NAT is zonal or that Cloud Router must be in the same zone as the instance, but the key trap here is that candidates overlook the regional scope of Cloud NAT and assume subnet location is irrelevant.
Detailed technical explanation
How to think about this question
Cloud NAT uses a Cloud Router to dynamically learn routes and perform source NAT (SNAT) for instances without external IPs. The NAT gateway is regional, meaning it only handles traffic from instances in the same region, regardless of their zone. If a subnet is in a different region, the NAT gateway cannot see the instance's traffic, and the instance remains unable to reach the internet because it lacks an external IP and no NAT is applied.
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.
Configuring network services — This question tests Configuring network services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The subnet subnet-a is in a region different from us-central1 — Option A is correct because Cloud NAT is a regional resource that applies to all instances within a given region. The exhibit shows subnet-a is in a different region than us-central1, so the NAT gateway cannot route traffic from instances in that subnet. Even though the instance is in us-central1, the subnet's region mismatch means the NAT configuration does not apply, leaving the instance without internet access.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses Cloud NAT to enable outbound connectivity for private VMs. They notice that some VMs are not able to reach a specific external IP range. The VMs have no tags or service accounts. What is the most likely cause?
easy
A.Cloud NAT requires each VM to have a unique external IP address.
B.The VMs need a default route pointing to the NAT gateway.
C.A static route must be created for the external IP range via the NAT gateway.
✓ D.The VMs might be in a different subnet than the one where Cloud NAT is configured.
Why D: Option C is correct because Cloud NAT uses the source IP address of the VM to determine which NAT IP to use, and if the VM is not in the subnet where Cloud NAT is configured, it won't use that NAT. Option A is wrong because Cloud NAT does not require a default route via the NAT gateway; it works with dynamic routes. Option B is wrong because there is no static route requirement. Option D is wrong because Cloud NAT does use unique external IPs per VM if configured, but that wouldn't block traffic.
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This PCNE 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 PCNE exam.
Question Discussion
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