Class B is the middle ground. This presents a problem. If you intend to develop an intranet with IP addresses, refer to Kinnaman and Ballew for a discussion on how to choose the best classes to meet your needs. The first level domain is assigned to an organization. The organization is free to further divide the domain name in any way it sees fit.
Most organizations divide their networks into subnets, or networks within networks.
Subnetworking allows multiple network segments to be created within a single IP network address space. For example, an organization with a Class B address could divide its one address into 254 sub-networks of 254 devices each rather than one network of 65,534 devices. This is done through the use of routers and subnet masks . A subnet mask is essentially a filter. The router that is handling network 128.205 knows the message is intended for something on its network and sends it to subnet 99.