- A
Create a VPC firewall rule that allows traffic from 203.0.113.0/24 to the load balancer's forwarding rule IP.
Why wrong: VPC firewall rules evaluate traffic to instance network interfaces, not to load balancer IPs. Also, internal load balancer IP is not reachable from the internet.
- B
Assign a public IP to the internal load balancer and restrict access using Google Cloud Armor.
Why wrong: Internal load balancers cannot have public IPs; Cloud Armor only works with external load balancers.
- C
Configure a Cloud VPN tunnel between on-premises and VPC, then create a firewall rule allowing the corporate IP range to the internal load balancer's backend instances.
This provides secure connectivity and allows fine-grained access control.
- D
Use Google Cloud Armor with IP allowlisting on the internal load balancer.
Why wrong: Cloud Armor is not supported on internal HTTP(S) load balancers.
Quick Answer
The correct answer is to configure a Cloud VPN tunnel between on-premises and the VPC, then create a firewall rule allowing the corporate IP range to the internal load balancer's backend instances. This is correct because an internal HTTP(S) load balancer operates with a private IP address that is only reachable from within the same VPC or through a hybrid connectivity solution like Cloud VPN or Cloud Interconnect; since the corporate office has a static public IP range, the only secure way to bridge that on-premises network to the internal load balancer is via an encrypted VPN tunnel, which extends the VPC and allows VPC firewall rules to control access. On the Google Professional Cloud Security Engineer exam, this scenario tests your understanding of internal load balancer architecture and hybrid networking—a common trap is to mistakenly try to apply a firewall rule directly to the load balancer’s forwarding rule or to use Cloud NAT, neither of which can make a private IP publicly routable. Remember the key principle: internal load balancers are never directly exposed to the internet; to secure access from on-premises, you must first extend the network, then filter at the backend. Memory tip: “VPN first, then firewall—private IPs need a bridge, not a gate.”
PCSE Configuring network security Practice Question
This PCSE practice question tests your understanding of configuring network security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 web application on Compute Engine instances in a managed instance group behind an internal HTTP(S) load balancer. The application needs to be accessible only from the corporate office, which has a static public IP range of 203.0.113.0/24. The load balancer is in us-central1. What is the most secure way to restrict access?
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
Configure a Cloud VPN tunnel between on-premises and VPC, then create a firewall rule allowing the corporate IP range to the internal load balancer's backend instances.
Option C is correct because an internal HTTP(S) load balancer has a private IP address that is only reachable from within the same VPC or via Cloud VPN / Cloud Interconnect. To allow access from a corporate office with a static public IP range, you must establish a Cloud VPN tunnel to extend the VPC network to the on-premises network, then create a firewall rule that permits traffic from the corporate IP range to the internal load balancer's backend instances. This ensures traffic traverses an encrypted tunnel and is subject to VPC firewall controls, providing the most secure and architecturally correct solution.
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 a VPC firewall rule that allows traffic from 203.0.113.0/24 to the load balancer's forwarding rule IP.
Why it's wrong here
VPC firewall rules evaluate traffic to instance network interfaces, not to load balancer IPs. Also, internal load balancer IP is not reachable from the internet.
- ✗
Assign a public IP to the internal load balancer and restrict access using Google Cloud Armor.
Why it's wrong here
Internal load balancers cannot have public IPs; Cloud Armor only works with external load balancers.
- ✓
Configure a Cloud VPN tunnel between on-premises and VPC, then create a firewall rule allowing the corporate IP range to the internal load balancer's backend instances.
Why this is correct
This provides secure connectivity and allows fine-grained access control.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Google Cloud Armor with IP allowlisting on the internal load balancer.
Why it's wrong here
Cloud Armor is not supported on internal HTTP(S) load balancers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that internal load balancers can be secured with Cloud Armor or that VPC firewall rules can filter traffic based on source public IPs when the destination is a private IP, but in reality, internal load balancers are only reachable from within the VPC or via hybrid connectivity like Cloud VPN.
Detailed technical explanation
How to think about this question
An internal HTTP(S) load balancer operates at the application layer (HTTP/HTTPS) and uses Envoy-based proxies that run in the same VPC, with a private IP address from a subnet in the same region. Traffic from on-premises must be routed through a Cloud VPN tunnel (using IPsec with IKEv2) or Cloud Interconnect, which encapsulates the packets and presents them as VPC-internal traffic. The firewall rule must allow traffic from the corporate IP range (203.0.113.0/24) to the backend instances' health check ports and the load balancer's proxy-only subnet, ensuring that only authenticated VPN traffic reaches the application.
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
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FAQ
Questions learners often ask
What does this PCSE question test?
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: Configure a Cloud VPN tunnel between on-premises and VPC, then create a firewall rule allowing the corporate IP range to the internal load balancer's backend instances. — Option C is correct because an internal HTTP(S) load balancer has a private IP address that is only reachable from within the same VPC or via Cloud VPN / Cloud Interconnect. To allow access from a corporate office with a static public IP range, you must establish a Cloud VPN tunnel to extend the VPC network to the on-premises network, then create a firewall rule that permits traffic from the corporate IP range to the internal load balancer's backend instances. This ensures traffic traverses an encrypted tunnel and is subject to VPC firewall controls, providing the most secure and architecturally correct solution.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCSE 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 PCSE exam.
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