PCNE Implementing VPC Instances Practice Question
A company uses Cloud NAT with a static NAT IP address. They notice that connections from their instances are failing after a few minutes. 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 Cloud NAT gateway is using dynamic port allocation and running out of ports
Cloud NAT by default uses dynamic port allocation and releases ports after a timeout. With static NAT IP, if port exhaustion occurs or if the connection idle timeout is too low, connections may drop.
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 instance's external IP is conflicting with the NAT IP
Why it's wrong here
Instances with external IPs bypass NAT, so no conflict.
- ✗
The NAT IP address is not whitelisted on the target
Why it's wrong here
Whitelisting is a network-level issue, but the symptom suggests port allocation.
- ✓
The Cloud NAT gateway is using dynamic port allocation and running out of ports
Why this is correct
With many connections, ports can be exhausted, causing failures.
- ✗
The VPC network has a firewall rule blocking egress
Why it's wrong here
If egress were blocked, connections would fail immediately, not after minutes.
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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.