The answer is that VPC Flow Logs use sampling, and high-throughput traffic can cause logs to be dropped or reduced. This occurs because Flow Logs are not a packet-by-packet capture; they sample a subset of network flows, and when an instance handles extremely high traffic volumes, the sampling rate may be lowered or logs may be omitted entirely to manage resource consumption. On the Google Professional Cloud Network Engineer exam, this concept tests your understanding that Flow Logs are a best-effort monitoring tool, not a complete audit trail—a common trap is assuming that enabling logs on a subnet guarantees every packet is recorded. Remember the memory tip: “High traffic, low logs—sampling skips the floods.”
PCNE Implementing a Virtual Private Cloud Practice Question
This PCNE practice question tests your understanding of implementing a virtual private cloud. 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 Flow Logs for traffic analysis. They notice that logs are missing for a specific Compute Engine instance that handles high traffic. The subnet has Flow Logs enabled. 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
✓
Flow Logs are sampled and may drop high-throughput traffic.
VPC Flow Logs use sampling; high throughput can lead to sampling reduction or dropped logs.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 instance is using Private Google Access.
Why it's wrong here
Private Google Access does not affect Flow Logs.
✓
Flow Logs are sampled and may drop high-throughput traffic.
Why this is correct
Flow Logs sample traffic, and at high throughput, sampling rate may be reduced or logs dropped.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The instance's network interface has an external IP.
Why it's wrong here
External IP does not prevent Flow Logs from being generated.
✗
The instance is in a different region from the log sink.
Why it's wrong here
Log sink region is independent; Flow Logs are generated at the subnet level.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
Implementing a Virtual Private Cloud — This question tests Implementing a Virtual Private Cloud — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Flow Logs are sampled and may drop high-throughput traffic. — VPC Flow Logs use sampling; high throughput can lead to sampling reduction or dropped logs.
What should I do if I get this PCNE question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related PCNE subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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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.
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