PCNE Load balancer routing Practice Question
A company has deployed an HTTP load balancer with a backend service configured to use an unmanaged instance group. Users report that traffic is not reaching the backend instances. The backend instances are healthy and have proper firewall rules allowing traffic from the load balancer. What step should the network engineer take to resolve the issue?
⚠ Common exam trap
Candidates may mistakenly focus on health check firewall rules when the actual issue is a missing route for the load balancer's traffic.
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
✓
Add a route for the load balancer's IP range.
The load balancer sends traffic to backend instances using their internal IP addresses. If there is no route from the load balancer's frontend IP range to the subnet containing the backend instances, traffic will be dropped. Adding a route for the load balancer's IP range ensures that packets can reach the instances. Since the problem states firewall rules are already proper, Option A (health check firewall rules) is unnecessary. Health checks are already configured (Option B is not needed). Instances do not require external IPs (Option C). Therefore, the correct step is to add the missing route.
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 a firewall rule to allow health check probes from the load balancer's health check ranges.
Why it's wrong here
Incorrect. Firewall rules for health checks are not needed because the problem states firewall rules are already proper for load balancer traffic.
- ✗
Enable HTTP health check on the backend service.
Why it's wrong here
Incorrect. HTTP health check is already enabled on the backend service; enabling again will not resolve the issue.
- ✗
Assign an external IP address to each backend instance.
Why it's wrong here
Incorrect. Backend instances only need internal IPs; external IPs are not required for load balancer communication.
- ✓
Add a route for the load balancer's IP range.
Why this is correct
Correct. A missing route for the load balancer's IP range prevents traffic from reaching the backend instances. Adding the route resolves the issue.
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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.