Learning path
From reading a mask to splitting a network, with one method, a calculator to check yourself, and random practice questions that show the working.
Subnetting is a skill you build by doing questions, not by reading about it. This path gives you one method, the block size, and then five kinds of practice question, from turning a prefix into a mask to deciding whether two hosts share a subnet.
Each practice question has a Show me how button that walks through the working. Use it freely at first; move on from a step when you can answer five in a row without it.
One table and one method that answers every question here. Keep it open in another tab.
Type a few addresses from networks you know and see the network, mask and range it gives.
Turning /26 into 255.255.255.192 and back quickly is what everything else builds on.
The core skill: network, first and last usable, broadcast and host count from one address.
How you choose a prefix when you plan a new segment.
Borrowing bits to carve one block into equal subnets.
The first question behind "it can reach the gateway but not the server next to it".
See how addressing turns up in certification questions.
The same method in the cloud. Azure keeps five addresses in every subnet for itself, not two.
