PCNE Implementing VPC Instances Practice Question
An engineer needs to provide outbound internet access to a set of Compute Engine instances that do not have external IP addresses. The instances are in a VPC subnet with a Cloud NAT configured. However, the instances still cannot reach the internet. The engineer verified that Cloud NAT is configured on the same region and VPC as the instances. What is the most likely cause?
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 instances are not tagged with the correct network tag used in the Cloud NAT configuration
Cloud NAT requires the instances to have the 'allow NAT' network tag or service account configured in the NAT gateway rules. If the instances are not tagged or the service account is not specified, traffic is not forwarded.
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 firewall rules block all outbound traffic from the subnet
Why it's wrong here
Firewall rules are stateful and allow outbound traffic by default, but Cloud NAT still requires proper tagging.
- ✗
The instances are using a custom network that does not support Cloud NAT
Why it's wrong here
Cloud NAT works with custom VPC networks.
- ✓
The instances are not tagged with the correct network tag used in the Cloud NAT configuration
Why this is correct
Cloud NAT uses tags or service accounts to determine which instances can use it for outbound connectivity.
- ✗
The Cloud NAT gateway uses dynamic port allocation, which is disabled
Why it's wrong here
Dynamic port allocation is the default and does not affect connectivity.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.