DHCP

The Dynamic Host Configuration Protocol (DHCP) is an autoconfiguration protocol used on IP networks. Computers that are connected to IP networks must be configured before they can communicate with other computers on the network. DHCP allows a computer to be configured automatically, eliminating the need for intervention by a network administrator. It also provides a central database for keeping track of computers that have been connected to the network. This prevents two computers from accidentally being configured with the same IP address.

http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol

see Internet Protocol Suite