First off, to understand any solution even if the solution is provided by someone else you must first understand the whole problem. If i just gave you a number, lets say the number 22. How did I derive at that number? Did I add 11+11 or did I add 7+15? None the less, understanding the problem is going to ultimately help you understand how I provided you with the correct solution. This not only applies to subnetting but also everything in life.

So lets take a little journey back in time to the early days of the internet. Back when IPv6 was still considered classful. To understand what classful is, you first need to understand a little binary so lets tackle that first.

Computers operate by executing chucks of data in binary. Binary in a nutshell is a 1 or 0. On or Off, Voltage or No Voltage… Beer or no beer… haha jk

A bit which is a single 1 or 0 is the smallest numerical value a computer can use. A byte which is a collection of 8 Bits is what defines the decimal notation.

Back to binary, Lets take 8 sections. |X|X|X|X|X|X|X|X| Each one of these X’s have a special value. Take a look again below how that value is derived;

|128|64|32|16|8|4|2|1|

So if we want to make the number 22 in Binary, you would add a 1 to the places that add up to 22 but a 0 in other spots.

00010110 = 16+4+2 = 20

The same concept applies to larger numbers all the way up to 255 which is all 1’s and starting with 0 which is all 0’s.