PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 Identity-Aware Proxy (IAP) to secure access to Compute Engine VMs. Users report that they can SSH into some VMs but not others, even though they have the IAP-secured Tunnel User role. Both VMs are in the same project and have the same network tags. What is the most likely reason?
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 VMs that can be accessed have external IP addresses; the others only have internal IP addresses.
Option C is correct because IAP for TCP forwarding requires the target VM to have an external IP address (or be accessible via a Cloud NAT with specific routing) for the IAP service to establish the tunnel. Without an external IP, the IAP tunnel cannot reach the VM, even if the user has the IAP-secured Tunnel User role and the firewall rules allow ingress from IAP's IP ranges (35.235.240.0/20).
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.
✗
Firewall rules allow ingress from IAP's IP ranges only for some VMs.
Why it's wrong here
Firewall rules should allow IAP ranges for all VMs with IAP.
✗
The VMs are in different zones with different DNS resolution.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume IAP works with any VM in the project as long as firewall rules and IAM roles are correct, overlooking the requirement for an external IP address (or Cloud NAT) for the IAP tunnel to reach the VM.
Detailed technical explanation
How to think about this question
IAP for TCP forwarding works by creating a tunnel from the user's device through the IAP service to the VM's external IP address on port 22 (or 3389 for RDP). The VM must have an external IP (even if ephemeral) or be behind a Cloud NAT with appropriate routes so that the IAP service can reach it; internal-only VMs cannot be targeted because IAP does not have a path to private IPs. This is a common pitfall when designing secure bastionless access, as teams often assume IAP works with internal IPs alone.
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 VMs that can be accessed have external IP addresses; the others only have internal IP addresses. — Option C is correct because IAP for TCP forwarding requires the target VM to have an external IP address (or be accessible via a Cloud NAT with specific routing) for the IAP service to establish the tunnel. Without an external IP, the IAP tunnel cannot reach the VM, even if the user has the IAP-secured Tunnel User role and the firewall rules allow ingress from IAP's IP ranges (35.235.240.0/20).
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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