FE Electrical & Computer Practice Question Solution included after investigation
CASE E-038 · FE

The /27 Network That Could Not Fit 40 Devices

The subnet looked large enough from the address range. The usable host count said otherwise.

▶ INTERACTIVE CASE FILE • 5–10 MIN • CLICK TO INVESTIGATE

Inspect, commit, prove, fix, and sign off.

Case E-038 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A lab needs addresses for 40 IPv4 devices on one subnet. The proposed network is 192.168.10.0/27. The planner sees 32 addresses in the block and assumes the subnet is close enough. During deployment, addresses run out. Calculate the usable host capacity, identify the design error, and choose the smallest larger prefix that can support at least 40 hosts.

Computer Networks Electrical & Computer Design Verification Root Cause Analysis Safe Correction
E-038
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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DEBRIEF (LOCKED)

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Find the root cause, confirm the fix, and see how this connects to the exam.

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🔒Exam takeawayComplete the case
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

The /27 subnet could not support 40 host devices.

What was assumed

All addresses in the block were treated as usable hosts.

Corrected model

Calculate total addresses from host bits, then subtract network and broadcast addresses for conventional IPv4 host capacity.

QUICK ANSWER

An IPv4 /27 prefix leaves 5 host bits, so the block contains 2^5=32 total addresses. Reserving the network and broadcast addresses leaves 30 usable host addresses. A /26 provides 62 usable hosts and can support 40 devices.

ENGINEERING TAKEAWAY

For a conventional IPv4 subnet, total addresses are 2^(32-prefix), and usable host addresses are total minus 2.

CASE QUESTIONS

Questions this case should settle.

How many usable hosts are in a /27 subnet?

30 usable hosts in a conventional IPv4 subnet.

What prefix can support at least 40 hosts?

A /26 provides 62 usable host addresses.

NEXT FE PRACTICE QUESTION

The Router That Ignored the Shorter-Looking Route

Computer Networks · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.