Cloud NAT Region Subnet Mismatch: Troubleshooting Tips

Exhibit

Refer to the exhibit.

```
gcloud compute routers create nat-router \
    --network=my-vpc \
    --region=us-central1

gcloud compute routers nats create nat-config \
    --router=nat-router \
    --region=us-central1 \
    --nat-external-ip-pool=ip-address-1 \
    --nat-all-subnet-ip-ranges \
    --enable-logging

gcloud compute instances create test-instance \
    --zone=us-central1-a \
    --network=my-vpc \
    --subnet=subnet-a \
    --no-address
```

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?

Quick Answer

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.”

⚠ Common exam trap

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.

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

✓

The subnet subnet-a is in a region different from us-central1

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.

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.
✗
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.

Visual reference

About these practice questions

Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →

How Courseiva writes practice questions · Editorial policy

Same concept, more angles

1 more way this is tested on PCNE

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: The most likely cause is that the VMs are in a subnet that does not have Cloud NAT configured. Cloud NAT is configured on a per-subnet basis, and only VMs in subnets with Cloud NAT enabled can use it for outbound traffic. Option A is incorrect because Cloud NAT does not require each VM to have a unique external IP; it uses a pool of NAT IPs. Option B is incorrect because VMs already have a default route (0.0.0.0/0) via the default internet gateway, and Cloud NAT works with that route; there is no need for a route pointing to the NAT gateway. Option C is incorrect because no static route is needed for specific external IP ranges; Cloud NAT uses the default route and performs source NAT for all outbound traffic.

Last reviewed: Jun 30, 2026

Question Discussion

Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.

Loading comments…

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.