7.2. What Is a Subnet?

Subnets work exactly like classful networks in that they require a router to get to other networks and have a network address, a directed broadcast address, and a specific set of hosts. To quote from RFC 917:

We discuss the utility of “subnets” of Internet networks, which are logically visible sub-sections of a single Internet network. For administrative or technical reasons, many organizations have chosen to divide one Internet network into several subnets, instead of acquiring a set of Internet network numbers.