PCNE Implementing VPC Instances Practice Question
An engineer is troubleshooting outbound connectivity from a Compute Engine instance that has no external IP. The instance needs to reach an external service on the internet. Cloud NAT is configured on the VPC network. However, the instance cannot connect. 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
✓
Egress firewall rules are blocking the traffic
For Cloud NAT to work, the instance must be in a subnet for which a Cloud NAT gateway is configured, and the instance should not have an external IP. Additionally, firewall rules must allow egress traffic. The most common issue is missing egress firewall rules or incorrect NAT configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Private Google Access is not enabled
Why it's wrong here
Private Google Access is for Google APIs, not general internet access.
- ✗
The instance has an external IP assigned
Why it's wrong here
If an instance has an external IP, it doesn't use Cloud NAT; but the scenario says no external IP.
- ✓
Egress firewall rules are blocking the traffic
Why this is correct
Correct. Even with Cloud NAT, egress firewall rules must allow the traffic; by default, egress is allowed, but if custom rules are applied, they might deny.
- ✗
The Cloud NAT gateway is in a different region than the instance
Why it's wrong here
Cloud NAT is regional; if the instance is in a subnet in a different region, it won't use that NAT.
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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.