- A
Create an ingress firewall rule that allows traffic from the load balancer's health check ranges and uses a service account filter to allow traffic from the cloud-services service account (used by the load balancer).
This ensures that only traffic from the load balancer's health check probes and the load balancer itself (via service account) reaches the backend instances.
- B
Create an ingress firewall rule allowing all traffic from 0.0.0.0/0 with a target tag applied to the backend instances.
Why wrong: This would allow traffic from any source, not just the load balancer, exposing the instances.
- C
Create an ingress firewall rule that denies all traffic except from the load balancer's frontend IP address.
Why wrong: The load balancer's frontend IP is a virtual IP and does not appear as the source IP in packets reaching the backend; this would not work.
- D
Create an ingress firewall rule allowing traffic from the health check ranges (35.191.0.0/16, 130.211.0.0/22) and the load balancer's source IP ranges (e.g., 130.211.0.0/22) to the backend instances.
Why wrong: This approach is not recommended because the load balancer's source IP ranges can vary and are not guaranteed; using service account filters is more reliable.
Quick Answer
The correct choice is to create an ingress firewall rule that uses a service account filter to allow traffic from the cloud-services service account, combined with the load balancer’s health check ranges. This approach is correct because Cloud Load Balancing forwards traffic to backend instances using the cloud-services service account as its identity, so filtering by that service account inherently permits all legitimate load balancer traffic—including health check probes—without needing to hardcode ever-changing IP ranges like 35.191.0.0/16 and 130.211.0.0/22. On the Google Professional Cloud Network Engineer exam, this question tests your understanding of identity-based firewall rules versus traditional IP-based rules, a common trap where candidates default to static IP ranges and miss the more scalable, secure service account filter. The key insight is that service account filters decouple access control from network topology, making them ideal for globally distributed applications. Memory tip: think “service account, not spreadsheet”—let the cloud manage the IPs, not your firewall rules.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 a globally distributed application on Google Cloud using Cloud Load Balancing and managed instance groups across multiple regions. They need to restrict access to the application's backend instances so that only traffic from the load balancer's health check ranges and the load balancer's source IP addresses is allowed. Which firewall rule configuration should be used?
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 an ingress firewall rule that allows traffic from the load balancer's health check ranges and uses a service account filter to allow traffic from the cloud-services service account (used by the load balancer).
Option A is correct because it uses a service account filter to allow traffic from the cloud-services service account, which is the identity used by Cloud Load Balancing to forward traffic to backend instances. This ensures that only traffic originating from the load balancer (including health check probes) is permitted, while also automatically covering the health check ranges (35.191.0.0/16, 130.211.0.0/22) without needing to hardcode IP ranges. This approach is more secure and scalable than IP-based rules, as it avoids the risk of IP range changes and provides identity-based access control.
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.
- ✓
Create an ingress firewall rule that allows traffic from the load balancer's health check ranges and uses a service account filter to allow traffic from the cloud-services service account (used by the load balancer).
Why this is correct
This ensures that only traffic from the load balancer's health check probes and the load balancer itself (via service account) reaches the backend instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create an ingress firewall rule allowing all traffic from 0.0.0.0/0 with a target tag applied to the backend instances.
Why it's wrong here
This would allow traffic from any source, not just the load balancer, exposing the instances.
- ✗
Create an ingress firewall rule that denies all traffic except from the load balancer's frontend IP address.
Why it's wrong here
The load balancer's frontend IP is a virtual IP and does not appear as the source IP in packets reaching the backend; this would not work.
- ✗
Create an ingress firewall rule allowing traffic from the health check ranges (35.191.0.0/16, 130.211.0.0/22) and the load balancer's source IP ranges (e.g., 130.211.0.0/22) to the backend instances.
Why it's wrong here
This approach is not recommended because the load balancer's source IP ranges can vary and are not guaranteed; using service account filters is more reliable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that you can simply allow the load balancer's frontend IP address, but the trap here is that the frontend IP is a virtual IP that never appears as the source IP in packets reaching the backend—instead, the source IP is the load balancer's internal IP or health check ranges, so candidates must understand the difference between frontend and backend traffic flows.
Detailed technical explanation
How to think about this question
Cloud Load Balancing uses the cloud-services service account (or the Google APIs service account in some configurations) to originate traffic to backend instances, and health checks are sent from the ranges 35.191.0.0/16 and 130.211.0.0/22. By using a service account filter in the firewall rule, you leverage Google Cloud's identity-aware firewall, which is more resilient to IP range changes and provides granular control; this is especially important in multi-region deployments where the load balancer's source IPs may vary. In practice, if you only use IP-based rules, you might miss traffic from newer health check ranges or from load balancers using different forwarding paths, leading to dropped traffic or security gaps.
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.
- →
Implementing network security — study guide chapter
Learn the concepts, then practise the questions
- →
Implementing network security practice questions
Targeted practice on this topic area only
- →
All PCNE questions
497 questions across all exam domains
- →
Google Professional Cloud Network Engineer study guide
Full concept coverage aligned to exam objectives
- →
PCNE practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related PCNE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Designing, planning, and prototyping a GCP network practice questions
Practise PCNE questions linked to Designing, planning, and prototyping a GCP network.
Implementing hybrid interconnectivity practice questions
Practise PCNE questions linked to Implementing hybrid interconnectivity.
Configuring network services practice questions
Practise PCNE questions linked to Configuring network services.
Implementing network security practice questions
Practise PCNE questions linked to Implementing network security.
Implementing a Virtual Private Cloud practice questions
Practise PCNE questions linked to Implementing a Virtual Private Cloud.
PCNE fundamentals practice questions
Practise PCNE questions linked to PCNE fundamentals.
PCNE scenario practice questions
Practise PCNE questions linked to PCNE scenario.
PCNE troubleshooting practice questions
Practise PCNE questions linked to PCNE troubleshooting.
Practice this exam
Start a free PCNE practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this PCNE question test?
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create an ingress firewall rule that allows traffic from the load balancer's health check ranges and uses a service account filter to allow traffic from the cloud-services service account (used by the load balancer). — Option A is correct because it uses a service account filter to allow traffic from the cloud-services service account, which is the identity used by Cloud Load Balancing to forward traffic to backend instances. This ensures that only traffic originating from the load balancer (including health check probes) is permitted, while also automatically covering the health check ranges (35.191.0.0/16, 130.211.0.0/22) without needing to hardcode IP ranges. This approach is more secure and scalable than IP-based rules, as it avoids the risk of IP range changes and provides identity-based access control.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 30, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.