Quiz · CCNA · Network+

Subnetting practice.

Unlimited random subnetting questions with instant checking and a short explanation after every answer.

How to practise subnetting effectively

Subnetting becomes quick only with repetition. Work through a few questions a day, say your reasoning out loud, and use the explanation to find the step you got wrong. Check the answer with the IP subnet calculator when you are unsure, and keep the subnet cheat sheet handy until the block sizes are memorised.

The block-size method

Convert the prefix to a mask and find the octet where the mask is neither 255 nor 0 (the “interesting octet”).
Block size = 256 − mask value in that octet. For /26 (255.255.255.192) the block size is 64.
The network address is the largest multiple of the block size that is ≤ the IP’s value in that octet.
The broadcast address is the next network address minus 1.
Usable hosts run from network + 1 to broadcast − 1.

Host 192.168.1.130/26
Block size  = 256 − 192 = 64   (networks at 0, 64, 128, 192)
Network     = 192.168.1.128
Broadcast   = 192.168.1.191
Usable      = 192.168.1.129 – 192.168.1.190  (62 hosts)

Powers of two to memorise

Host bits	Addresses	Usable	CIDR
2	4	2	/30
3	8	6	/29
4	16	14	/28
5	32	30	/27
6	64	62	/26
7	128	126	/25
8	256	254	/24

Ready to go deeper? Read subnetting explained, then try variable-length planning with the VLSM calculator.

Frequently asked questions

How can I practise subnetting online?

Use the quiz above: it generates random subnetting questions (network address, broadcast address, usable hosts, subnet mask, first and last host) and checks your answers instantly with an explanation of each step.

What is the fastest way to subnet in your head?

Find the “interesting octet” (the one where the mask is not 0 or 255), compute the block size as 256 minus the mask value, then find the multiple of that block size just below the IP address. That multiple is the network address.

What subnetting questions are common in exams?

CCNA-style questions ask for the network address, broadcast address, number of hosts, the subnet a host belongs to, the mask needed for N hosts, and how many subnets you get when borrowing bits.

How many bits should I borrow to get N subnets?

Borrow n bits where 2^n ≥ the number of subnets you need. Borrowing 3 bits from a /24 gives 8 subnets of /27.