PCNE Implementing VPC Instances Practice Question
A company has a VPC with a subnet in us-central1. Compute Engine instances in that subnet have no external IPs but need to reach the internet for software updates. The engineer configured Cloud NAT with the default settings. However, instances fail to reach the internet. 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
✓
An egress firewall rule is missing that allows traffic from the instances to the internet via NAT.
Cloud NAT requires that the instances are allowed egress traffic to the internet. Without a suitable egress firewall rule, NAT traffic is blocked. The default firewall rules only allow egress to Google APIs (private.googleapis.com) but not to general internet destinations. A firewall rule allowing egress to 0.0.0.0/0 on the appropriate ports is required.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Cloud NAT is not configured in the correct region.
Why it's wrong here
The NAT gateway must be in the same region as the instances. The scenario mentions us-central1, which should be fine.
- ✓
An egress firewall rule is missing that allows traffic from the instances to the internet via NAT.
Why this is correct
Firewall rules control egress traffic; Cloud NAT does not bypass them. A rule allowing egress to 0.0.0.0/0 is needed.
- ✗
Private Google Access is enabled on the subnet, which overrides Cloud NAT.
Why it's wrong here
Private Google Access does not affect general internet access via NAT.
- ✗
The Cloud NAT router is not attached to the correct VPC network.
Why it's wrong here
If it were not attached, NAT wouldn't work at all. The issue is likely firewall-related.
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JA
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.