PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company has deployed an internal HTTP Load Balancer (ILB) in us-west1 within a Shared VPC. The host project contains the ILB's forwarding rule and the backend service. The backend instances are Compute Engine VMs running in a service project in us-east1. The health checks for the ILB are consistently failing with 'unhealthy' status. The firewall rules in the host project allow ingress from the Google Cloud health checker ranges (130.211.0.0/22 and 35.191.0.0/16) on TCP port 80 to all VMs in the VPC. The backend VMs are running a web server listening on port 80. What is the most likely cause of the health check failures?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ILB's forwarding rule and backends are in different regions.
The internal HTTPLoad Balancer (ILB) in Google Cloud requires that the forwarding rule, backend service, and backend instances all reside in the same region. In this scenario, the ILB is deployed in us-west1, but the backend VMs are in us-east1. Cross-region backends are not supported for ILBs, causing health checks to fail because the load balancer cannot route traffic or verify health across regions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 ILB's forwarding rule and backends are in different regions.
Why this is correct
ILB requires backends to be in the same region as the forwarding rule; otherwise health checks fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The health checker firewall rule is not applied to the service project.
Why it's wrong here
Firewall rules in the host project apply to all VMs in the VPC, including those in service projects.
✗
The backend VMs are not in the same project as the ILB.
Why it's wrong here
Shared VPC allows backend VMs in different service projects; this is not an issue.
✗
The backend VMs do not have the correct IAM permissions for the ILB.
Why it's wrong here
IAM permissions are not required for backends to respond to health checks.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that health check failures are always due to firewall rules or IAM, when the real issue is the regional constraint of internal load balancers.
Detailed technical explanation
How to think about this question
Google Cloud ILBs are regional resources that use a proxy-based architecture in the same region to forward traffic. Health check probes originate from Google's health checker IP ranges (130.211.0.0/22 and 35.191.0.0/16) and must reach the backend VMs within the same region; cross-region health checks are not supported because the load balancer's control plane does not establish health-check sessions across regions. This is distinct from external load balancers, which can have backends in multiple regions via global load balancing.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Configuring network security — This question tests Configuring network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The ILB's forwarding rule and backends are in different regions. — The internal HTTP Load Balancer (ILB) in Google Cloud requires that the forwarding rule, backend service, and backend instances all reside in the same region. In this scenario, the ILB is deployed in us-west1, but the backend VMs are in us-east1. Cross-region backends are not supported for ILBs, causing health checks to fail because the load balancer cannot route traffic or verify health across regions.
What should I do if I get this PCSE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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