The answer is the origin server sending a Cache-Control: private header, which directly prevents Cloud CDN from caching the content. This header explicitly instructs intermediate caches, including CDN edge nodes, not to store the response, forcing every user request to travel all the way back to the regional backend in us-west1. As a result, European users experience high latency due to the transcontinental round trip, while US users see good performance from a shorter path. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding that enabling Cloud CDN is not enough—the origin must also permit caching by omitting private or setting Cache-Control: public with a max-age directive. A common trap is assuming Premium Tier or a global load balancer automatically caches everything. Remember the memory tip: “Private means no cache—your users pay the distance price.”
PCNE Configuring network services Practice Question
This PCNE practice question tests your understanding of configuring network services. 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 has deployed a Global External Application Load Balancer with Premium Tier and enables Cloud CDN. Users in Europe report high latency, while users in the US have good performance. The backend is a regional NEG in us-west1. 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 origin server is sending 'Cache-Control: private' headers, preventing Cloud CDN from caching.
Option D is correct because Cloud CDN cannot cache responses that include a 'Cache-Control: private' header. This header instructs intermediate caches (including CDN nodes) not to store the response, forcing all requests to go to the origin server in us-west1. Users in Europe experience high latency because their requests must traverse the long distance to the US origin, while US users benefit from shorter paths. Enabling Cloud CDN alone does not guarantee caching; the origin must also allow caching by omitting 'private' or setting appropriate 'Cache-Control: public' and 'max-age' directives.
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 load balancer is using Premium Tier, which routes to the nearest backend; the backend is only in us-west1.
Why it's wrong here
Global load balancer does route to the nearest healthy backend, but CDN should cache; latency is due to lack of caching.
✗
Cloud CDN is not enabled on the load balancer.
Why it's wrong here
The scenario states Cloud CDN is enabled.
✗
The load balancer is using Standard Tier, which does not support global anycast.
Why it's wrong here
The scenario explicitly says Premium Tier is used.
✓
The origin server is sending 'Cache-Control: private' headers, preventing Cloud CDN from caching.
Why this is correct
Cloud CDN respects origin cache headers; private or no-store headers prevent caching, so all requests hit the backend.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that enabling Cloud CDN automatically caches all content, when in reality the origin's cache-control headers dictate cacheability, and 'Cache-Control: private' is a common reason for CDN bypass.
Trap categories for this question
Scenario analysis trap
The scenario states Cloud CDN is enabled.
Detailed technical explanation
How to think about this question
Cloud CDN relies on the origin server's cache-control headers to determine cacheability. The 'Cache-Control: private' header, defined in RFC 7234, explicitly forbids shared caches (like CDN edge nodes) from storing the response. Even with Cloud CDN enabled, if the origin sends this header, each request from Europe must be forwarded to the us-west1 backend, bypassing any edge caching. A common real-world scenario is a web application that sets 'private' for user-specific content (e.g., dashboards), inadvertently preventing CDN caching for all responses, including static assets that could be cached.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Configuring network services — This question tests Configuring network services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The origin server is sending 'Cache-Control: private' headers, preventing Cloud CDN from caching. — Option D is correct because Cloud CDN cannot cache responses that include a 'Cache-Control: private' header. This header instructs intermediate caches (including CDN nodes) not to store the response, forcing all requests to go to the origin server in us-west1. Users in Europe experience high latency because their requests must traverse the long distance to the US origin, while US users benefit from shorter paths. Enabling Cloud CDN alone does not guarantee caching; the origin must also allow caching by omitting 'private' or setting appropriate 'Cache-Control: public' and 'max-age' directives.
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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