The answer is that the backend must have a public IP address or be accessible via the internet, and it must allow inbound traffic from Google’s health check IP ranges. This is required because a Global External HTTP(S) Load Balancer operates as a proxy; its frontend uses Google’s public IP ranges (specifically 35.191.0.0/16 and 130.211.0.0/22) to send health probes to the backend. If these probes are blocked by a firewall or the backend lacks internet-facing connectivity, the load balancer will mark the backend as unhealthy and stop forwarding user traffic. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding of proxy-based load balancing versus pass-through load balancing—a common trap is assuming internal backends can be used without additional configuration. Remember, external backends must be reachable from the internet and explicitly allow Google’s health check sources. A useful memory tip: think of the health check ranges as the “35.191 and 130.211 gatekeepers”—if they can’t knock, traffic won’t flow.
PCNE Practice Question: Designing, planning, and prototyping a GCP network
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which THREE of the following are requirements for implementing a Global External HTTP(S) Load Balancer with an external backend?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The backend must support health checks from the load balancer's health check IP ranges.
Option B is correct because Global External HTTP(S) Load Balancers use Google's frontend (proxying) IP ranges to send health checks to backends. The backend must allow inbound traffic from these specific health check IP ranges (e.g., 35.191.0.0/16 and 130.211.0.0/22) to receive health probes; otherwise, the load balancer will mark the backend as unhealthy and stop forwarding traffic.
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 backend must be configured with Private Google Access.
Why it's wrong here
Private Google Access is for VMs without external IPs to reach Google APIs.
✓
The backend must support health checks from the load balancer's health check IP ranges.
Why this is correct
Health checks are required for proper traffic routing.
Related concept
Read the scenario before looking for a memorised answer.
✗
The backend must have an SSL certificate installed.
Why it's wrong here
SSL certificates are only needed for HTTPS backends.
✓
Firewall rules must allow traffic from the load balancer's IP ranges.
Read the scenario before looking for a memorised answer.
✓
The backend must have a public IP address or be accessible via internet.
Why this is correct
Global external load balancer requires internet connectivity to backends.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between health check IP ranges and load balancer forwarding IP ranges, causing candidates to confuse which IP ranges must be allowed in firewall rules for external backends.
Detailed technical explanation
How to think about this question
The Global External HTTP(S) Load Balancer operates as a reverse proxy: it terminates client TLS at the Google Front End (GFE), then forwards requests to backends over HTTP or HTTPS. Health checks are sent from GFE IP ranges (35.191.0.0/16, 130.211.0.0/22) and must be allowed by firewall rules; if the backend is external (e.g., on-premises or another cloud), it must also have a public IP or be reachable via internet, and firewall rules must permit traffic from the load balancer's IP ranges (not just health check ranges) for actual user traffic.
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.
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backend must support health checks from the load balancer's health check IP ranges. — Option B is correct because Global External HTTP(S) Load Balancers use Google's frontend (proxying) IP ranges to send health checks to backends. The backend must allow inbound traffic from these specific health check IP ranges (e.g., 35.191.0.0/16 and 130.211.0.0/22) to receive health probes; otherwise, the load balancer will mark the backend as unhealthy and stop forwarding traffic.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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