Subnetting in 5 minutes

192.168.1.7 is an IP in IPV4 standard
IPV4 networks have 32bits.
Each 8bit is a Network ID.
Each Network ID represent number between 0-255

There are 4 basic classes A , B C, D
The first ID or 8 bits is network class
0-127 - Class A
128 - 191 Class B
192 -  223 Class C
223 + Class D & E kept for research purpose

Class First Network ID Last Network ID
Class A 1.0.0.0 126.0.0.0
Class B 128.0.0.0 191.255.0.0
Class C 192.0.0.0 223.255.255.0

If we have a class C network
The first 3 numbers are network ID  192.168.1
The last number is host ID
First host id (0) is network id and last (255 broadcast id) not used
So in the network we have host ids from
192.168.1.1 - 192.168.1.254 we can have 254 hosts (computers or devices)
We do sub netting to separate network traffic , like partitioning  house.
we can make 2 networks each having 254/2 - 1*2  hosts
or make 4 networks having  254/4 - 1 *4

Every time we break the network the first and last host IDs are used as subnets network ID and broadcast ID.

Broadcast address used to send data to all hosts.
So they cant be used  as host IDs..
A disadvantage of subnetting is reducing of usable IPs in a network.

In order to tell the network how many computers we have in the subnet we use a subnet mask. Another number which tells how many subnet networks have been created.
When we have 254 computers in a class C network we use
255.255.255.0 as subnet mask so 192.168.1.1- 192.168.1.255 ips available to us.
When we break the network into two subnets. We have to put a boundry between them by changing the subnet mask.

Here subnet mask borrow one bit from host ID
so subnet mask becomes 255.255.255.128
The IP range of sub network A now is 192.168.1.1- 192.168.1.126
The IP range of sub network B now is 192.168.1.129- 192.168.1.253
The first and last IP of each subnet used for subnetworkid and broadcast address.

Check here
http://www.subnet-calculator.com/

 In detail http://ict.shilpa64.lk