Subdividing a Network into Subnets

Subdividing a Network into Subnets

Class A networks contain more than 16,000,000 IP addresses, and Class B networks contain more than 65,000 addresses. Out of context, those might seem like large numbers. When you consider the fact that all hosts in the same IP network cannot be separated from each other by a router, the numbers end up looking huge. These days, LANs with more than a few hundred devices on them are unusual, and single LANs with more than 1000 devices are extremely rare. If you use a Class A or even a Class B network for all the devices on a LAN, many IP addresses will go unused.

Subnetting provides one solution by reducing a lot of the waste. Subnetting refers to a process by which the network engineer in charge of a particular TCP/IP network number, in effect, changes the rules. Next, the chapter shows you an example in which lots of IP addresses are wasted, followed by the same general example, with subnetting being used to reduce waste.