The subnetting of IP addresses can help to make better use of IP address space, for example on expansion of a network. It also allows IP addresses on networks to be divided into multiple smaller networks or subnets. The addresses for the subnets are derived from the main network address by applying a subnet mask, and as such belong to that organisation. Effective use of subnets may remove the need to obtain additional address space. Subnets also provide some advantages over one large network:
Computers have a unique hardware address that is allocated to the network interface when the machine is manufactured. When a computer is connected to a LAN, the Address Resolution Protocol provides a mapping of IP addresses to the hardware or MAC address.
The method of allocating address space according to need is known as CIDR. Further information about this strategy may be found in RFC 1519, Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy.