An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."
The header of each IP packet sent over the Internet must contain the IP address of both the destination server or website and of the sender (the client). The Domain Name System (DNS) translates domain names to the corresponding destination IP address, identifying the computer or device where the services or resources requested by a client are located. Both the source address and the destination address may be changed in transit by a network address translation device.
The sender's IP address is available to the server (which may log it or block it) and becomes the destination address when the server responds to a client request. Geolocation software can use a device's IP address to deduce its geolocation to determine the country and even the city and post/ZIP code,[6] organization, or user the IP address has been assigned to, and then to determine a device's actual location. A sender wanting to remain anonymous to the server may use a proxy server, which substitutes that server's IP address, as far as the destination server is aware, in place of the true source address. When the destination server responds to the proxy server, it would forward it on to the true client—ie., change the IP address to that of the originator of the request. A reverse DNS lookup involves the querying of DNS to determine the domain name associated with an IP address