A subnet or the sub network is a logical and visible subdivision of the IP network. In fact, dividing the network in to two or more networks is known as the subnetting process.
In fact, the subnet is the responsible for delivering the datagrams to the certain range of the IP address. However, it is an extension of this concept of the splitting fields that are in the A, B and C classes. In addition to that, the network part can also be extended to include some bit from the part of the host. As the way, the counting of bits that are interpreted as the subnet number is called as the subnet mask or the net mask. In fact, this is the 32 bit number and it can specify the bit mask for the network of the IP address.
However, the subnets are only divided by the owner of the network who is also known as the network administrators. In fact, the subnets are created often to reflect the active boundaries like physical, administrative and geographical and the power over each subnet is delegated to some contact person.