IP address
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
An IP address serves two principal functions: host or network interface identification and location addressing.
Network interface layer security
When a client system without an IP address enters a network it will request an IP address from the resident DHCP server. The DHCP server will reserve an IP address (so anyone else asking for one is not granted this one) and it will send that IP address to the device along with a lease identifying how long the address will be valid. Normally, from this point, the device will respond by confirming the IP address with the DHCP server and the DHCP server finally responds with an acknowledgement.