PCNE Implementing a Virtual Private Cloud Practice Question
A developer created a Compute Engine instance in the default VPC network. The instance needs to communicate with an on-premises server over a Cloud VPN tunnel. The developer configured the VPN tunnel but the instances cannot ping the on-premises server. What is the most likely cause?
⚠ Common exam trap
Google Cloud often tests the misconception that a configured VPN tunnel automatically allows all traffic, when in reality firewall rules (ingress) and routes must be explicitly configured to permit communication between VPC and on-premises networks.
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 firewall rules in the VPC are blocking ingress traffic from the on-premises network.
By default, the default VPC includes firewall rules that allow outbound traffic but restrict inbound traffic. Even though the Cloud VPN tunnel is established, the VPC firewall rules block ingress traffic from the on-premises network (e.g., ICMP for ping). To allow communication, a firewall rule must explicitly permit ingress traffic from the on-premises IP range or the remote tunnel IP.
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 IP range overlaps with the on-premises network.
Why it's wrong here
Default VPC uses Auto mode subnets with non-overlapping ranges; overlap is unlikely but would cause routing issues, not firewall.
- ✗
The instance has IP forwarding disabled.
Why it's wrong here
IP forwarding is required only for instances acting as routers, not for general communication.
- ✗
The default VPC does not have a default route to the internet.
Why it's wrong here
Default VPC has a default route (0.0.0.0/0) to the internet via the default internet gateway.
- ✓
The firewall rules in the VPC are blocking ingress traffic from the on-premises network.
Why this is correct
Default firewall rules allow only certain ingress; ICMP from on-premises is not allowed by default.
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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.