What is subnetting? Why is it used?

If definitions are helpful to you, use these vocabulary terms to get you started:

• Address—The unique number ID assigned to one host or interface in a network.

• Subnet—A portion of a network sharing a particular subnet address.

• Subnet mask—A32-bit combination used to describe which portion of an address refers to the subnet and which part refers to the host.

• Interface—A network connection.

You could read this Link

A subnetwork, or subnet, is a logically visible subdivision of an IP network.[1] The practice of dividing a network into two or more networks is called subnetting.

it is used to efficiently allocate address space.

Further read here:

http://en.wikipedia.org/wiki/Subnetwork

Subnetting is division of a network into subnetworks. Subnetting is actually efficient use of IP addresses and used because IP addresses were running short. It's practically done by using Hosts bits as Network bits for creating creating more subnetworks. For instance if an IP address of class A is assigned to an organization and they required just few hundred computers(hosts) so other million IP addresses will be wasted by the organization. So that's why IP addresses subnetting is quite handy.

besm alah alrahman alrahim

a network may have small networks inside of it ( thats call sub )

suppose you where in a company that has2 department one for acounting and the other for purchacing

and you want to make a network for this company ?

you will make2 subnetwork from one network

the1st subnet have10 computer as an example so you will give every computer an IP address that is as an example192 .168 .1 . ?

the question mark here is the number you give to each computer , the192 .168 .1 are called the subnet address 

for the other department you will give it another subnet number like192 .168 .2 . ?

the question mark here is the number you give to each computer , the192 .168 .2 are called the subnet address 

we understand that as human but how can computer understand that ?

computer understand it as calculations numbers 

so if the PC want to now the subnet number (that is192.168.1) he must have something to extract those number so what PC do ?

PC multiplay the whole number of192.168.1.? with255.255.255.0 as an example here only

that multiplication not done as human but in what thay called OR and AND gates (electronics componnents) the255 look like you multiplay with one and the0 look like0 so when you multiplay255.255.255.0 with192.168.1. ? yoy will have192.168.1.0 (thats the number of the subnetwork

the same thing done with the other subnetwork (192.168.2. ?) so you will have192.168.2.0

the255.255.255.0 called subnet mask some time called routing prefix (/24) that mask extract subnetworks from what thay called host ( the computers numbers at that subnetwork [the question mark we use for them previously ] )  

the2 subnetworks connected to each other if we want that through a router (some time through rouuting swiths ) the exact name Gateway 

router (or routing swithch ) orgnise the work between the2 department

i wich i give you some help (as i could)

this link for more information :

http://en.wikipedia.org/wiki/Subnetwork