Class A: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0

8.20.15.1 = 00001000.00010100.00001111.00000001
255.0.0.0 = 11111111.00000000.00000000.00000000

Subnetting

Subnetting is a process of breaking large network in small networks known as subnets. Subnetting happens when we extend default boundary of subnet mask. Basically we borrow host bits to create networks. Let's take a example

Being a network administrator you are asked to create two networks, each will host 30 systems.

Single class C IP range can fulfill this requirement, still you have to purchase 2 class C IP range, one for each network. Single class C range provides 256 total addresses and we need only 30 addresses, this will waste 226 addresses. These unused addresses would make additional route advertisements slowing down the network.

With subnetting you only need to purchase single range of class C. You can configure router to take first 26 bits instead of default 24 bits as network bits. In this case we would extend default boundary of subnet mask and borrow 2 host bits to create networks. By taking two bits from the host range and counting them as network bits, we can create two new subnets, and assign hosts them. As long as the two new network bits match in the address, they belong to the same network. You can change either of the two bits, and you would be in a new subnet.

Advantage of Subnetting

• Subnetting breaks large network in smaller networks and smaller networks are easier to manage.
• Subnetting reduces network traffic by removing collision and broadcast traffic, that overall improve performance.
• Subnetting allows you to apply network security polices at the interconnection between subnets.
• Subnetting allows you to save money by reducing requirement for IP range.

Subnetting math

Subnetting process involves binary math calculation. Computers communicate with each other's in binary language. To succeed in any kind of networking career, you might be fluent in binary math calculation. Subnetting needs two type of calculation, convert decimal to binary and convert binary to decimal.

Binary system works exactly same as decimal system, except the base number. Base number is 2 in binary system and 10 in decimal system. To calculate decimal equivalent value of a binary number, you have to replace base value 10 with 2. Binary numbers are displayed in columns and each position in binary system has double value than the position in right. From earlier section of this article you know that each number of an IP address is made from eight individual bits known as octet. So you should remember at least eight decimal equivalent value from binary position.

Binary value of 117 is 01110101.

Convert binary in decimal

To convert a binary in decimal we will follow above method in reverse mode. We will find the decimal value of on binary bit position and add them. For example convert 10101010 binary number in decimal.

Target binary number 10101010

Move direction From Left ===========================> to Right

Decimal value of 10101010 is 170 [ 128+0+32+0+8+0+2+0 ]