System Admins should thank the ghost in the firm , DHCP. Which assigns you IP whenever you connect a machine to the network. it is a protocol for delivering host-specific configuration parameters from a DHCP server to a host and also provides a mechanism for allocation of network addresses to hosts.

 

It Guarantees that any specific network address will not be in use by more than one DHCP client at a time. Make sure you retain your IP on system reboot and Automatically assign the configuration parameters.

 

it works on DORA Process. Discover, offer, Request and Acknowledge. The client will broadcast the Discover message. Server will offer an IP on return, Client will then send a Request message to get that IP and server will end the process by sending an Ack. DHCP is not all about DORA. Its an Ocean.

 

Refer RFC 2131 for more details.