Subnetting practice
Speed comes from drilling one conversion until it's reflex — not from grinding mixed question sets. Pick a mode, answer as fast as you can, and misses pause on a worked solution that shows the block-size shortcut. Free, endless, no signup.
The modes
The block-size method in 20 seconds
Memorize the eight mask octets — 128, 192, 224, 240, 248, 252, 254, 255 — and every subnetting question becomes arithmetic:
- Find the block size: 256 minus the interesting mask octet. For /26 (255.255.255.192): 256 − 192 = 64.
- Count the blocks: subnets start at 0, 64, 128, 192.
- Place the address: 192.168.1.154 falls in the 128 block → network 192.168.1.128, broadcast one below the next block → 192.168.1.191, usable hosts .129–.190.
The Network ID and Broadcast & range modes above drill exactly this loop until it takes seconds.
Subnetting is one objective of many
The N10-009 exam has five domains. Take the free 25-question diagnostic to see where you actually stand — and get a daily plan built from your weak spots.
Take the free diagnosticNot ready to sign up? Try the free Network+ practice test — no account needed.
Frequently asked questions
How do I get faster at subnetting?
Drill one conversion at a time until it's reflex, then stack the next — that's why this tool is organized as modes instead of mixed questions. Learn the mask octets cold (128, 192, 224, 240, 248, 252, 254, 255), then use the block-size method: subtract the interesting mask octet from 256 and count in blocks. Exam-ready pace is roughly 30 seconds per question, which the timer here tracks for you.
What is the magic number (block size) method?
Take the mask octet that isn't 0 or 255 and subtract it from 256 — that's your block size. For /26 (mask 255.255.255.192): 256 − 192 = 64, so subnets start at 0, 64, 128, 192. Any address falls in the block at or below it: 192.168.1.154 sits in the 128 block, so the network is 192.168.1.128 and the broadcast is one below the next block, 192.168.1.191. No binary needed once the mask octets are memorized.
Do I need subnetting for Network+ and Security+?
Network+ (N10-009) tests subnetting directly — mask and prefix questions, usable-host math, and it appears inside performance-based questions. Security+ assumes you can read CIDR notation and recognize network boundaries in firewall rules and logs. CCNA leans on the same skills even harder, so the drills transfer.
Should I practice subnetting in binary or with shortcuts?
Both, in that order. Binary mode builds the mental model — why 192 means two network bits. The block-size shortcut is what you'll actually use under exam time pressure. If you can convert octets to binary and recite the block sizes, every subnetting question becomes arithmetic.
Is this subnetting practice really free?
Yes — every mode, unlimited questions, no account. A free CertBench account adds the full Network+ question bank with spaced repetition, a 25-question diagnostic, and a readiness score.