Internet Protocol, or IP, is the method that governs how computers share data across the Internet. When one computer sends data, such as an email or a web form, its message gets parsed into small packets that contain the sending computer's Internet address, the receiving computer's address, and part of the message. Internet Protocol serves several basic functions.
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IP packet headers contain addresses that identify the sending computer and the receiving computer. Routers use this information to guide each packet across communication networks and connect the sending and receiving computers.
Internet Protocol keeps track of the way messages between computers are broken into packets. Since most messages are too big to fit in one packet, and since packets aren't sent in any organized order, they must be reassembled as they arrive at the recipient. IP dictates how packets are reassembled into usable messages.
Each IP packet contains a self-destructive counter that limits its lifetime. If a packet's defined lifetime expires, the packet is destroyed so that the Internet doesn't get overloaded with broken packets wandering aimlessly.
IP includes optional features such as allowing the sending computer to decide the path its packets take to get to the receiving computer, to trace the path they take or to include added security in the packets.