The answer is that the user's source IP is being translated by a NAT or proxy, so it doesn't match the allowed range. Cloud Armor evaluates the source IP as seen by the External HTTP(S) Load Balancer, which may be the proxy or NAT gateway address rather than the original client IP, causing the deny rule to match even when the logs show the allowed range. This scenario tests your understanding of how Cloud Armor source IP translation proxy NAT affecting rule matching can break IP-based restrictions, a common trap on the Google Professional Cloud Network Engineer exam where engineers forget that load balancers can receive traffic through intermediate devices like Cloud NAT or third-party proxies. The key insight is that `source.ip` in Cloud Armor rules refers to the IP address of the packet arriving at the load balancer, not the original client. Memory tip: think of Cloud Armor as seeing the "last hop" IP, not the "first mile" IP.
PCNE Implementing network security Practice Question
This PCNE practice question tests your understanding of implementing network security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 behind an External HTTP(S) Load Balancer with Cloud Armor. They want to restrict access to a specific URL path /admin to only users from a specific IP range (198.51.100.0/24). The engineer creates a Cloud Armor security policy with two rules: Rule 1 (priority 1000) with match expression "request.path == '/admin' && inIpRange(source.ip, '198.51.100.0/24')" and action "allow". Rule 2 (priority 2147483647) with match "request.path == '/admin'" and action "deny". After testing, users from the allowed IP range receive a 403 error when accessing /admin. The Cloud Armor logs show that the request was denied. The engineer confirms that the policy is attached to the backend service and that the source IP in the logs matches the allowed range. What is the most likely cause of the denial?
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 user's source IP is being translated by a NAT or proxy, so it doesn't match the allowed range.
Option C is correct because the most likely cause is that the user's source IP is being translated by a NAT or proxy before reaching the load balancer. Cloud Armor evaluates the source IP as seen by the load balancer, which may differ from the original client IP if traffic passes through an intermediate device. The logs confirm the source IP matches the allowed range, but if the request arrives via a proxy, the actual source IP in the packet could be the proxy's IP, not the user's, causing the deny rule to match.
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 allow rule is missing a condition to also check the request path because the path condition is not supported in Cloud Armor.
Why it's wrong here
Cloud Armor supports path matching in rule conditions.
✗
The allow rule's condition is incorrect because it should use "origin.ip" instead of "source.ip".
Why it's wrong here
source.ip is the correct field for the client IP.
✓
The user's source IP is being translated by a NAT or proxy, so it doesn't match the allowed range.
Why this is correct
This is the most likely cause; the actual source IP seen by the load balancer is different.
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 allow rule's priority is 1000, which is lower than the deny rule, but the deny rule still overrides.
Why it's wrong here
Lower priority number means higher priority, so the allow rule is evaluated first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that the source IP in Cloud Armor logs is always the original client IP, when in reality it is the IP of the last hop before the load balancer, which can be a NAT or proxy.
Detailed technical explanation
How to think about this question
Cloud Armor evaluates rules in priority order, and the source IP is the IP address of the immediate sender as seen by the load balancer. If a proxy or NAT device is between the client and the load balancer, the source IP in the packet is the proxy's IP, not the client's. To preserve the original client IP, you must use the X-Forwarded-For header (if supported by the proxy) and configure Cloud Armor to evaluate that header via the 'origin.remote_ip' attribute or a custom header match. This is a common pitfall in environments with CDNs, WAFs, or corporate proxies.
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 user's source IP is being translated by a NAT or proxy, so it doesn't match the allowed range. — Option C is correct because the most likely cause is that the user's source IP is being translated by a NAT or proxy before reaching the load balancer. Cloud Armor evaluates the source IP as seen by the load balancer, which may differ from the original client IP if traffic passes through an intermediate device. The logs confirm the source IP matches the allowed range, but if the request arrives via a proxy, the actual source IP in the packet could be the proxy's IP, not the user's, causing the deny rule to match.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.