The correct answer is to change the source IP range in the firewall rule to the VPN gateway's public IP address. This works because the SSH connection originates from the VPN gateway's public-facing interface over the internet, so the firewall must match the source IP as seen by the target VM—the gateway's public, internet-routable address, not its internal IP. On the Google Professional Cloud Network Engineer exam, this tests your understanding of how firewall rules evaluate source IPs for traffic arriving from the internet, a common trap being to mistakenly use the gateway's internal IP, which is not routable over the internet and would never match the incoming packet's source. Remember the key distinction: external traffic always carries the public IP as its source, so your firewall source filter must mirror that. A useful memory tip is "public in, public out"—if traffic arrives from the internet, the source IP in the rule must be a public IP.
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. 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 a VPC with a firewall rule that allows SSH (tcp:22) from 0.0.0.0/0. They want to restrict SSH access to only the public IP address of their Cloud VPN gateway. How should they modify the firewall rule?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the source IP range to the VPN gateway's public IP address.
The firewall rule currently allows SSH from any source IP (0.0.0.0/0). To restrict access to only the Cloud VPNgateway, you must change the source IP range to the gateway's public IP address, because the SSH connection originates from the VPN gateway's public-facing interface over the internet. Internal IP addresses are not routable over the internet and would not match the source of the incoming SSH 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.
✗
Use Cloud Armor to block all SSH except from the VPN IP.
Change the source IP range to the VPN gateway's public IP address.
Why this is correct
Restricts SSH to traffic coming from the VPNgateway.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use IAP Tunneling instead of SSH firewall rules.
Why it's wrong here
IAP Tunneling is a different approach, not a firewall rule modification.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that internal IPs can be used as source ranges for internet-originating traffic, leading candidates to choose Option B instead of recognizing that the source IP of the SSH connection is the VPNgateway's public IP.
Detailed technical explanation
How to think about this question
Cloud VPN gateways have both a public (external) IP address for the internet-facing tunnel endpoint and an internal IP address for the VPC network. When an administrator initiates an SSH connection from the on-premises side through the VPN tunnel, the source IP seen by the VPC firewall is the public IP of the VPN gateway, not the internal IP. The firewall rule's source range must match the actual source IP of the incoming packets, which is the gateway's public IP. This is a common point of confusion because internal IPs are used for routing within the VPC, but external traffic arrives with the public IP as the source.
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: Change the source IP range to the VPN gateway's public IP address. — The firewall rule currently allows SSH from any source IP (0.0.0.0/0). To restrict access to only the Cloud VPN gateway, you must change the source IP range to the gateway's public IP address, because the SSH connection originates from the VPN gateway's public-facing interface over the internet. Internal IP addresses are not routable over the internet and would not match the source of the incoming SSH 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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