PCNE Implementing VPC Instances Practice Question
A company has deployed a network appliance (e.g., firewall) as a Compute Engine instance with two NICs: NIC0 for management and NIC1 for data traffic. The appliance must forward traffic from instances in subnet A to subnet B. The engineer has enabled IP forwarding on the appliance. What additional configuration is required on the VPC for the appliance to route traffic between subnets?
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
✓
Create a route in the VPC with destination subnet B and next hop set to the appliance's internal IP address.
For a Compute Engine instance to forward traffic between subnets, it must act as a router. The VPC needs a custom route that sends traffic destined for subnet B to the appliance's IP (or NIC) as the next hop. Without this route, the VPC's default routing will deliver traffic directly between subnets, bypassing the appliance. Also, the appliance's NIC1 must be in the same VPC and the firewall rules must allow the traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the appliance's guest OS to enable packet forwarding by setting net.ipv4.ip_forward=1.
Why it's wrong here
This is already required by enabling IP forwarding on the instance, but the VPC still needs a route.
- ✗
Create a firewall rule allowing egress from the appliance to both subnets.
Why it's wrong here
Firewall rules are necessary but not sufficient; routing must be configured.
- ✗
Attach the appliance to a Cloud Router and configure BGP sessions.
Why it's wrong here
Cloud Router is for dynamic routing with VPNs or Dedicated Interconnect, not for simple subnet-to-subnet forwarding.
- ✓
Create a route in the VPC with destination subnet B and next hop set to the appliance's internal IP address.
Why this is correct
This custom route directs traffic to the appliance for forwarding.
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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.