A subnet splits a network into sections. The IP address contains the network identifier and the host identifier. The subnet mask determines the size of the host identifier.
For example, the IPv4 address 192.168.0.1 with the subnet 255.255.0.0 has the first two bytes (192.168) as the network identifier and the rest as the host identifier (0.1), allowing for or computers. Using a subnet mask of 255.0.0.0 allows for or computers.
Classless Inter-Domain Routing (CIDR
This is a shorthand for the subnet mask. The network 192.168.0.0 with subnet 255.255.0.0 is written 192.168.0.0/16, with the /16 representing the 2 bytes/ 16 bits of the mask.