A computer on the Internet is identified by its IP address. In order to
avoid address conflicts, IP addresses are publicly registered with the
Network Information Centre (NIC). Computers on private TCP/IP LANs
however do not need public addresses, since they do not need to be
accessed by the public. For this reason, the NIC has reserved certain
addresses that will never be registered publicly.
A subnet is an identifiably separate part of an
organization's network. Typically, a subnet may represent all the
machines at one geographic location, in one building, or on the same
local area network (LAN).
Network designers employ subnets as a way to partition networks into logical segments for greater ease of administration