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Managing, Monitoring, and Optimising Network Operations →mediumMultiple ChoiceObjective-mapped

PCNE Practice Question: Managing, Monitoring, and Optimising Network Operations

This PCNE practice question tests your understanding of managing, monitoring, and optimising network operations. 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.

An engineer notices that VPC Flow Logs are enabling on a subnet but only a fraction of traffic is logged. 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.

A
The log export filter is too restrictive
Why wrong: Log export filters apply to the destination, not sampling.
B
Default sampling rate of 50% is applied
Default sampling rate is 50%, so half the flows are logged.
C
The subnet has an insufficient sampling rate set to 0.5
Why wrong: Sampling rate is 0.5 by default, meaning 50% of flows.
D
Flow Logs only log TCP traffic
Why wrong: Flow Logs log TCP, UDP, ICMP, etc.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Default sampling rate of 50% is applied

VPC Flow Logs use sampling by default (50%) to reduce cost and volume. This means only half of the flows are logged.

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 log export filter is too restrictive
Why it's wrong here
Log export filters apply to the destination, not sampling.
✓
Default sampling rate of 50% is applied
Why this is correct
Default sampling rate is 50%, so half the flows are logged.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The subnet has an insufficient sampling rate set to 0.5
Why it's wrong here
Sampling rate is 0.5 by default, meaning 50% of flows.
✗
Flow Logs only log TCP traffic
Why it's wrong here
Flow Logs log TCP, UDP, ICMP, etc.

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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.

Visual reference

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.

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FAQ

Questions learners often ask

What does this PCNE question test?

Managing, Monitoring, and Optimising Network Operations — This question tests Managing, Monitoring, and Optimising Network Operations — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Default sampling rate of 50% is applied — VPC Flow Logs use sampling by default (50%) to reduce cost and volume. This means only half of the flows are logged.

What should I do if I get this PCNE question wrong?

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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Last reviewed: Jul 4, 2026

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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.