Internet Protocol

The Internet Protocol (IP) is a protocol (computer) used for communicating across a heterogeneous network. It is the protocol on which the Internet is built. Internet Protocol version 4 (IPv4) has been the standard for many years, but Internet Protocol version 6 (IPv6) is the newer standard.

Addressing

Every IP packet has a source address and a destination address. Within the routing domain in which these addresses are used, the addresses must be unique. In the global Internet, blocks of addresses are delegated from the Internet Assigned Numbers Authority, part of the Internet Corporation for Names and Numbers, which further delegates blocks of addresses to Regional Internet Registries at a roughly continental level.

Intranets have no need to have addresses unique with respect to the global Internet, and, indeed, there are blocks in IPv4 and IPv6 that are defined not to be routable in the global system. One way to extend the lifetime of the increasingly scarce IPv4 address space is to use "registered" IPv4 addresses only on the Internet-facing side of network address translators, and use private space in the enterprise side.

Extranets may use private space if the address administration does not become overwhelming; extranets of the size of U.S. military networks such as NIPRNET, SIPRNET and JWICS have unique address space that is delegated by military administrators. In practice, there is no conflict even if every address on the public Internet were duplicated, because the secure networks have an "air gap" to the Internet; there is no direct connectivity at the IP level.

Transmission medium agnostic

IP architects call it "agnostic" as to the underlying data link protocol managing shared access to the medium, physical protocol managing the access of single devices to the medium, and to the transmission medium,. It commonly runs over multimegabit or gigabit links, but has been demonstrated to operate, in conjunction with the Transmission Control Protocol, over avian media (i.e., carrier pigeons). IP provides computers with communicable addresses that are globally unique.

IP is a connectionless protocol and provides best-effort delivery for its data payload, making no guarantees with respect to reliability. Without notification to either the sender or receiver, packets may become corrupted, lost, reordered, or duplicated. This design reduces the complexity of Internet routers. When reliable delivery is needed, the Internet Protocol Suite has mechanisms at the end-to-end (e.g., Transmission Control Protocol) or application (e.g., Remote Procedure Call) levels.