We know how to find the valid host range in Class A, Class B and Class C network by the value of 0 and 1 in the IP address. But it is only for the one network, if we take one address and want to create 4 or 6 other network form this single network. Is it possible? Yes it is possible by the method called ‘Subnetting’.
Subnettig allow to create logical network form a single address block. In the Subnet a group of IP addresses that have same value in the first part of the IP address allowing routing to identify the group by the initial part of the IP address.IP addresses in the same subnet exists on the same network medium and these are not separated from each other by any routers and IP address in the different network are separated to each other by at least one router. Subnet is the short form of Subnetwork.
Adding the Subnetwork in the IP address creates an intermediate level in the IP addressing system. Now we have three levels in the IP address- Network id, Subnet id and the Host id.The Network id is the first level, it defines the network. The second level is the Subnet id it define the physical subnetwork and the third level is Host id, it define connection of the host to the subnetwork.
There are number of reason to create the subnets-
1. It reduces the network traffic. In routers most traffic stay on the local network and only packet to other network to reach the destination will pass through the router. Router created broadcast domain. The more the broadcast domain less the network traffic on each network segment.
2. It is easier to identify the problem in a smaller network than a large single network.
3. In WAN a single large network over the long distance can create problems in every area but multiple smaller networks are more efficient to solve the problems.
How to create subnetworks-
We can create a subnet by take borrow some bits from the host part of the IP address in any class ip address. The more host bit borrowed the more subnet we can define and for each borrowed bit from the host part, the number of subnetworks is double. For example if we borrow 1 bit from the host part it define two subnets and if we borrow 2 bits it define 4 subnets.
