# Subnet mask, Slash Notion and Mathematical formula for IP subnetting Made easy.

For us to subnet very well both in real world and in CCNA exam it is important that you get conversant with subnet mask in octect form, bit form, binary form and also in slash notions. Finally, using some sort of formula can help in saving time while solving subnetting questions in CCNA exams. In this tutorial we are going to explore all these , it might be length but it’s worth reading through.

First we will write out subnet mask in octet, convert them to binary and then put I the slash notions appropriately.
Our daily chart here 128 64 32 16 8 4 2 1

Note: 8bits makes one octet, with that in mind let’s gets going down.

11111111.0000000.00000000.00000000 =255.0.0.0 in slash notion we have slash /8 hence we have

8bits turned on
11111111.10000000.00000000.00000000 =255.128.0.0/9 9bits on
11111111.11000000.00000000.00000000 =255.192.0.0/10 10 bits on.
11111111.11100000.00000000.00000000 =255.224.0.0/11 11 bits on
11111111.11110000.00000000.00000000 = 255.240.0.0/12 12bit on.
11111111.11111.000.00000000.00000000 = 255.248.0.0/13 13 bits on.
11111111.11111100.00000000.00000000 = 255.252.0.0/14 14 bits on.
11111111.11111110.00000000.00000000 = 255.254.0.0/15 15 bits on
11111111.11111111.00000000.00000000 = 255.255.0.0/16 16 bits on
Class B
11111111.11111111.10000000.00000000 =255.255.128.0/17 17bits on

11111111.11111111.11000000.00000000 =255.255.192.0/18 18 bits on.

11111111.11111111.11100000.00000000 =255.255.224.0/19 19 bits on

11111111.11111111.11110000.00000000 = 255.255.240.0/20 20bit on.

11111111.11111111.11111000.00000000 = 255.255.248.0/21 21 bits on.

11111111.11111111.11111100.00000000 = 255.255.252.0/22 22 bits on.

11111111.11111111.11111110.00000000 = 255.255.254.0/23 23 bits on

11111111.11111111.11111111.00000000 = 255.255.255.0/24 24 bits on

Class C
11111111.11111111.10000000.00000000 =255.255.255.128 /25 25bits on

11111111.11111111.11000000.00000000 =255.255.255.192/26 26 bits on.

11111111.11111111.11100000.00000000 =255.255.255.224/27 27 bits on

11111111.11111111.11110000.00000000 = 255.255.255.240/28 28bit on.

11111111.11111111.11111000.00000000 = 255.255.255.248/29 29 bits on.

11111111.11111111.11111100.00000000 = 255.255.255.252/30 30 bits on.

11111111.11111111.11111110.00000000 = 255.255.255.255/31 31 bits on

With this in place and in mind you can be very fast while creating network and host on your network even in your CCNA exam another method to determine the number of host and networks in while building a network is t use this mathematical formular (2*) where * is equal to the number of bits, with this you can find your network ranges. (2*)-2 with this fromular you can find your network host ranges. We will be solving with this formular in our upcoming post.