There is a scarcity of network addresses today.
A viable solution to creating new network addresses is to divide the 32-bit address in a process called subnetting.
The process entails modifying the IP address by using the host (or client portion) address bits as network address bits.
A more technical evaluation is that a subnet mask
is applied to filter the bits not used in the network address.
A subnet mask is a 32-bit number, written in dotted decimal form, in much the same way an IP address is displayed. For example
only hosts IP addresses that are on the same subnet and can communicate with others without a router.
Subnetting is used when a company has more computers than can be connected to its network; it is also used as a traffic reduction mechanism. However, all devices on the subnet must be programmed with the correct mask value in order for the network to function properly.
To subnet an IP network, you use a subnet mask, which splits IP networks into subgroups of networks or subnetworks by filtering unwanted bits
so that only usable bits remain. Before using subnet masks, you must perform a decimal-to-binary conversion of the IP address.
A subnet mask identifies how the bits of an IP address are used. In binary terms, 0 and 1 are the only functional digits.
In binary notation, a 0 (zero) indicates that the bit is a host bit. A 1 (one) indicates that the bit is a network bit.
A subnet mask defines the network, the subnet, and the host.
The table below provides the default masks for IP address classes A to C.