Binary Number System (2-based Number System)
The most difficult part of understanding subnetting is probably the math (the calculation). As you can see from the links above, subnetting involves binary numbers. Yes, you are required to understand at least the basic of binary number system in order to understand subnetting process.
Binary number system is used by any computers based on their nature of “on” and “off” state. Unfortunately we humans are used to decimal number system, hence create a gap. This gap leads to some kind of confusion to those who are just learning networking and subnetting.
But no worries! There is an easier way to understand subnetting with less theory and more practical approach. The key is to keep using decimal number system with binary number system in mind.
Before we begin, you need to refresh your math on power. Following is an illustration.
2^0 = 1
2^1 = 2
2^2 = 2 x 2 = 4
2^3 = 2 x 2 x 2 = 8
2^4 = 2 x 2 x 2 x 2 = 16
2^5 = 32
2^6 = 64
2^7 = 128
2^8 = 256
Binary system number is based on power of two (2^n). This number system shows that you can only double the current number to have the next bigger number. This number system also shows that you can only halve the current number to have the previous number. The Binary system number hence introduces the concept of half-and-double size.
To explore further, check out the following table. On the table, note that the next bigger number is always double the size of the current number. From different approach, the previous number is always half size of the current number.
As you may see, there is no other way to have the next bigger number of the current number but to double size of current number. Similarly, there is no other way to have one smaller number of the current number but to halve size the current number. The interval between one number and the next or between one number and the previous is always based on the power of two. Keep in mind that this half-and-double size concept is the very basic of subnetting as you will later find out.