Subnetting Practice: unlimited questions for CCNA and Network+

Randomly generated subnetting questions with instant marking and the full working, from the same engine that powers the calculator — so the answer it marks you against is provably the right one.

Answers that are provably rightquestions and answers both come from the calculator's tested engine, so it cannot mark a correct answer wrong.
The working, every timeget one wrong and see the steps — mask, host bits, the AND — not just a red cross.
Nine question typesnetwork and broadcast address, first and last host, usable hosts, mask, wildcard, next subnet and prefix length.
Three difficultiesoctet boundaries to start, then the CCNA range, then the prefixes that cross an octet awkwardly.
Timed, with a streakthe exam gives you about a minute per question, so this counts your seconds too.
Unlimited and freequestions are generated, not a fixed bank, so you never run out or memorise the set.

Stuck on one? The subnet cheat sheet has every prefix, and the subnet calculator shows the whole breakdown.

Subnetting question generator

Questions are generated, not drawn from a bank, so you cannot run out or learn the set. Every answer is computed by the calculator's own engine and checked against an independent derivation in the test suite, which matters more than it sounds: a practice tool that marks a right answer wrong is worse than none when you are revising and have no way to tell who is mistaken.

Question 1

What is the last usable host address?

Given198.51.151.236/30

Also for subnetting

ToolSubnet calculatorNetwork and broadcast address, usable range, masks and host counts for one network or a hundred, with VLSM splitting and route aggregation.ReferenceSubnet cheat sheetEvery CIDR prefix with its mask, wildcard and host count — /0 to /32 for IPv4 and /0 to /128 for IPv6. Filterable, and it prints on one page.

Subnetting practice: unlimited questions, marked instantly, with the working

Subnetting is not a topic you understand once — it is a skill you get fast at, and the only way to get fast is repetition against a clock. This tool generates subnetting questions endlessly, marks them the moment you answer, and shows the steps every time, so a wrong answer teaches you something instead of just costing you a mark.

Answers you can actually trust

Every other practice site either hard-codes its question bank or computes answers in a second implementation written for the quiz. Both are how a practice tool ends up marking a correct answer wrong — which is worse than useless when you are revising and have no way to tell which of you is mistaken. Here the question and the answer both come from the engine that powers the subnet calculator, and the test suite re-derives thousands of generated answers from scratch to prove the two agree.

Nine question types, covering the whole syllabus

Network address, broadcast address, first usable host, last usable host, usable host count, subnet mask, wildcard mask, the next subnet of the same size, and the prefix length behind a given mask. These are the forms real CCNA and Network+ questions take, and drilling them separately is the fastest way to find the one that keeps catching you out.

Three difficulties, because /19 is harder than /24

Warm up stays on octet boundaries and the first two splits, which is where the pattern becomes visible. CCNA uses /22 through /30, the range exam questions actually live in. Hard adds the prefixes that cross an octet boundary in an awkward place — /11, /13, /17, /19, /21 — plus /31 and /32, the two special cases that trip up people who have only ever memorised a table.

The block-size method, which is what the working shows

Converting to binary for every question is too slow for an exam. The method worth learning is block sizes: subtract the interesting octet of the mask from 256, and that is how far apart the networks are. A /26 is 255.255.255.192, so 256 - 192 = 64, and the networks start at 0, 64, 128 and 192. The broadcast address is one below the next network, and the usable hosts sit between the two. Learn the eight mask values — 128, 192, 224, 240, 248, 252, 254, 255 — and almost all the arithmetic disappears. The working shown after each question walks this path, not the binary one.

Timed, because the exam is

You get roughly a minute per question in the real thing, and subnetting questions are the ones where people lose time they need elsewhere. Each question here is timed and the panel keeps your score, your current streak and your average seconds per question, so you can see the speed improving rather than guessing at it.

Use it alongside the reference, then stop needing the reference

When a question catches you out, the subnet cheat sheet has every prefix with its mask, wildcard and host count, and any question can be opened in the full calculator to see the complete breakdown. The point of practising, though, is to reach the stage where you do not open either — and the average-time counter is how you tell you are getting there.

Subnetting questions, answered

How do you find the network address of an IP?

AND the address with its subnet mask, which in practice means setting every host bit to 0. For 192.168.10.77/26 the mask is 255.255.255.192, so the block size in the last octet is 64. The blocks start at 0, 64, 128 and 192, and 77 falls in the one starting at 64 — so the network address is 192.168.10.64.

The block-size shortcut is faster than binary and is what most people use under exam time pressure: 256 minus the interesting octet of the mask gives the block size, then count up in that size until you pass your address.

What is the fastest way to subnet in your head?

Work with block sizes rather than binary. Subtract the interesting octet of the mask from 256 to get the block size: a /26 mask of 255.255.255.192 gives 256 - 192 = 64. Networks then start at every multiple of that size, the broadcast address is one below the next network, and the usable range sits between them.

Learning the eight mask values by heart — 128, 192, 224, 240, 248, 252, 254, 255 — and their matching block sizes of 128, 64, 32, 16, 8, 4, 2, 1 removes almost all the arithmetic. The rest is practice, which is what this tool is for.

How much subnetting is on the CCNA exam?

Subnetting underpins the IP addressing section of the CCNA and appears throughout the exam rather than sitting in one block of questions — you need it to answer configuration, troubleshooting and design questions too. The same is true of CompTIA Network+.

The practical constraint is speed: with roughly a minute per question on average, you cannot afford to convert to binary each time. That is why this tool times you and shows your average, not just whether you were right.

What is the broadcast address of a subnet?

The last address in the block: every host bit set to 1. It is the address that reaches every host on that subnet, and it cannot be assigned to a device, which is why a subnet always has two fewer usable hosts than total addresses.

The quick method is to find the network address, add the block size, and subtract one. For 192.168.10.64/26 the block size is 64, so the next network is 192.168.10.128 and the broadcast is 192.168.10.127.

Are these subnetting questions free?

Yes, entirely, with no account and no limit. Questions are generated rather than drawn from a fixed bank, so you cannot exhaust them or memorise the set, and everything runs in your browser — nothing you type is uploaded and the page keeps working offline once loaded.

Why does a /31 have two usable addresses?

RFC 3021 defines a /31 on a point-to-point link as having no network or broadcast address, so both of its two addresses are assignable. Under the ordinary rule both would be reserved, leaving the prefix useless.

It appears in the hard difficulty here because exam questions and real designs both use it: a /31 links two routers using half the addresses a /30 would. A /32 is the related special case — a single host route, with one usable address.