Quick Answer
The answer is to configure Cloud Armor with an IP allowlist and attach it to the Cloud Load Balancer. This is correct because Cloud Armor acts as a web application firewall (WAF) that evaluates incoming traffic against security policies before it reaches the load balancer; by defining an allowlist rule with specific source IP ranges, all other traffic is implicitly denied at the edge, enforcing access control without modifying backend instance configurations. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of how Cloud Armor integrates with Cloud Load Balancing for perimeter security, often appearing as a distractor against options like VPC firewall rules or IAM permissions, which cannot filter traffic at the load balancer level. A common trap is assuming backend instance firewalls suffice, but Cloud Armor’s allowlist is the only method that blocks traffic before it consumes load balancer resources. Memory tip: think “Armor at the door, not the room”—Cloud Armor guards the load balancer entry point, not the backend instances.
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 wants to ensure that only traffic from specific source IP ranges can reach a Cloud Load Balancer. How should they enforce this?
Use IAP.
Why wrong: IAP is for user access, not IP filtering for load balancer.
Configure Cloud Armor with IP allowlist.
Cloud Armor can filter traffic to the load balancer based on source IP.
Set up Cloud NAT.
Why wrong: Cloud NAT is for outbound traffic from instances.
Use VPC firewall rules on the load balancer's backend.
Why wrong: Firewall rules on backend instances do not filter traffic to the load balancer itself.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Configure Cloud Armor with IP allowlist.
Cloud Armor is a web application firewall (WAF) that can be attached to a Cloud Load Balancer to filter incoming traffic based on IP addresses, including allowlisting specific source IP ranges. This directly meets the requirement to restrict access to the load balancer by source IP without affecting backend instance configurations.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use IAP.
Why it's wrong here
IAP is for user access, not IP filtering for load balancer.
Configure Cloud Armor with IP allowlist.
Why this is correct
Cloud Armor can filter traffic to the load balancer based on source IP.
Related concept
Read the scenario before looking for a memorised answer.
Set up Cloud NAT.
Why it's wrong here
Cloud NAT is for outbound traffic from instances.
Use VPC firewall rules on the load balancer's backend.
Why it's wrong here
Firewall rules on backend instances do not filter traffic to the load balancer itself.
Common exam traps
The trap here is that candidates confuse VPC firewall rules (which apply to VM instances) with Cloud Armor (which applies to the load balancer frontend), leading them to incorrectly select Option D.
Detailed technical explanation
Cloud Armor security policies are evaluated at the Google Front End (GFE) before traffic reaches the load balancer, allowing IP allowlisting to block unwanted traffic at the edge. The allowlist is defined using CIDR notation (e.g., 203.0.113.0/24) and can be combined with other rules like rate limiting or OWASP signatures. In a real-world scenario, this is critical for exposing a load balancer only to a corporate VPN CIDR while blocking all other internet traffic.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Implementing network security — This question tests Implementing network security — Read the scenario before looking for a memorised answer..
The correct answer is: Configure Cloud Armor with IP allowlist. — Cloud Armor is a web application firewall (WAF) that can be attached to a Cloud Load Balancer to filter incoming traffic based on IP addresses, including allowlisting specific source IP ranges. This directly meets the requirement to restrict access to the load balancer by source IP without affecting backend instance configurations.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 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.
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