IT & cloud certifications · course 45 of 105

Subnetting Without a Calculator

Subnet IPv4 on paper, exam-style: masks and binary, any subnet’s network, broadcast and usable range, then equal splits, VLSM (subnets of different sizes) and route summaries.

4 modules

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What it teaches

Subnetting on paper, in the style of certification-exam and interview questions: masks and prefix lengths, binary, counting hosts, block sizes, then everything about one subnet (network, broadcast, usable range, “same subnet?”, private or not), then design: equal splits, sizing for a host count, VLSM and route summaries. The AI asks 3 questions, places you, shows a short card per module, then gives you one problem at a time and checks your answer against keys computed by script, naming the slip when it’s a common one (“that’s the next subnet’s network address; the broadcast is one before it”).

How long

47 items. Simulated runs: about 30 rounds for a beginner who gets almost everything right, 70-75 for one who misses a lot, 11-17 if you already know the basics, plus a 12-item final (not timed with a real person). The tutor gives a one-line save code at the end of each session.

The modules

4 modules, drilled one item at a time.

M0
The words
Concept questions
M1
Masks, binary and counting
Maths
M2
Everything about one subnet
Maths
M3
Splitting, sizing and summarising
Maths

Before it teaches, it asks

1
What’s this for: an exam (Network+, CCNA, something else), a job, or curiosity? Have you subnetted before, even a little?
AI voice (ElevenLabs)
2
How many usable hosts are in a /27?
3
192.168.10.77/26: what’s the broadcast address?

What’s exact, and what isn’t

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Straight from the course’s own notes.

Computed by script: All 37 maths keys, with Python’s ipaddress module or plain integer maths, each matched to a hand-written answer; the network, broadcast, mask and host-count keys also get a bit-maths cross-check; 33 of the 37 listed wrong answers are reproduced by applying the slip, the other 4 are only checked to differ from the key.
Sourced: Definitions (address length, prefix, broadcast, private ranges, /31, loopback, link-local) from the IETF RFCs (791, 1878, 1918, 3021, 3927, 4632, 6890) and the Python ipaddress docs, plus one Wikipedia line for Microsoft’s APIPA name; short quotes matched word for word on 2026-10-10. The block-size, VLSM and summarisation methods are standard hand methods checked by script, not quoted from a source.
Simplified on purpose: IPv4 only; “usable hosts” uses the classic rule (network and broadcast reserved), with /31 point-to-point links as the stated exception.
Not in it yet: IPv6, wildcard masks, routing, VLANs, NAT.