PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing 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 uses VPC Service Controls to protect a managed service (e.g., BigQuery) within a service perimeter. Developers need to access the service from an on-premises network via a Cloud VPN tunnel with a specific IP address. However, access is being denied. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The on-premises source IP is not included in the allowed external IP addresses list in the perimeter.
VPC Service Controls enforce access to managed services like BigQuery by restricting which source IPs can reach the service. When accessing from on-premises via Cloud VPN, the source IP seen by the service is the on-premises client's IP, not the VPN gateway's IP. If that on-premises source IP is not explicitly added to the allowed external IP addresses list in the service perimeter, access is denied, even though the VPN tunnel is established.
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 project containing the VPN tunnel is not in the same perimeter.
Why it's wrong here
The VPN tunnel's project does not need to be in the perimeter.
✗
The VM instances in the perimeter do not have public IP addresses.
Why it's wrong here
Private IP access is allowed within perimeter.
✓
The on-premises source IP is not included in the allowed external IP addresses list in the perimeter.
Why this is correct
VPC Service Controls can restrict by source IP; the on-prem IP must be allowed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Cloud VPN tunnel is not using IKEv2.
Why it's wrong here
IKE version does not affect VPC Service Controls.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that placing the VPN tunnel's project inside the service perimeter or using a specific IKE version is required, when the real issue is that VPC Service Controls evaluate the source IP of the original client, not the VPN gateway, and that IP must be explicitly allowed.
Detailed technical explanation
How to think about this question
VPC Service Controls use a context-aware access model where the 'allowed external IP addresses' list in the perimeter acts as a source IP allowlist for requests coming from outside Google Cloud. When traffic arrives via Cloud VPN, the source IP is the on-premises client's IP, not the VPN gateway's internal IP, because the VPN tunnel encapsulates the original packet. This means the perimeter's IP-based restriction must include the actual on-premises source IPs, not just the VPN tunnel's endpoints.
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 — 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: The on-premises source IP is not included in the allowed external IP addresses list in the perimeter. — VPC Service Controls enforce access to managed services like BigQuery by restricting which source IPs can reach the service. When accessing from on-premises via Cloud VPN, the source IP seen by the service is the on-premises client's IP, not the VPN gateway's IP. If that on-premises source IP is not explicitly added to the allowed external IP addresses list in the service perimeter, access is denied, even though the VPN tunnel is established.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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