Subnetting Explained: A Step-by-Step Method
Subnetting is splitting one IP network into smaller ones by borrowing host bits. The fast way is the block-size method: block size = 256 − the interesting octet of the mask. Find the block, and the network, broadcast and host range fall out instantly — no binary needed under exam pressure.
The block-size method in 4 steps
- Find the block size: 256 minus the mask value in the "interesting" octet. For /26 the mask is 255.255.255.192, so block = 256 − 192 = 64.
- List the networks: count up in block-size steps — 0, 64, 128, 192.
- Find which block your IP falls in: 192.168.1.130 with /26 sits in the 128 block, so the network is 192.168.1.128.
- Broadcast = next network − 1: next block is 192, so broadcast = 192.168.1.191, and usable hosts are .129 to .190.
Usable hosts formula
Usable hosts = 2^(host bits) − 2. A /26 has 6 host bits → 2^6 − 2 = 62 usable hosts. The "− 2" removes the network address and the broadcast address, which can't be assigned to devices. Practise instantly with our subnet calculator, then test yourself on the CCNA practice test.
Why subnetting matters for the exam and the job
Subnetting is roughly a quarter of CCNA questions and comes up in almost every networking interview. On the job it decides how you carve address space for VLANs, sites and point-to-point links. Master it until you can subnet any address in under 30 seconds — that speed is what separates confident engineers. See also VLSM for variable-length subnetting.
Frequently asked questions
What is subnetting in simple words?
Subnetting divides one large IP network into several smaller networks by borrowing bits from the host portion. It improves organisation, security and efficient use of address space.
What is the easiest way to subnet?
The block-size method: block size = 256 minus the subnet mask value in the interesting octet. Count up in blocks to find your network, then broadcast is the next network minus one.
How many hosts are in a /26?
62 usable hosts. A /26 has 6 host bits, so 2^6 − 2 = 62 (subtracting the network and broadcast addresses).
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