Internet Protocol

The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking and essentially establishes the Internet. IP is a connectionless, best-effort delivery protocol; it does not guarantee delivery, nor does it assure proper sequencing or avoidance of duplicate packets. These functions are left to higher-layer protocols, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

IP provides an addressing system that identifies both the host network and the specific host on that network, using IP addresses. The two main versions in use are IPv4 and IPv6. IPv4 uses 32-bit addresses and is the backbone of the modern Internet, while IPv6 uses 128-bit addresses and was developed to address the exhaustion of IPv4 address space.

Features

IP is designed to operate over any heterogeneous network, from Ethernet to Wi-Fi to satellite links. Key features include:

Packet switching: Data is broken into packets (datagrams) that are routed independently through the network.
Best-effort delivery: No guarantees of delivery, ordering, or error correction are provided by IP itself.
Fragmentation and reassembly: If a datagram is too large for the next network's maximum transmission unit (MTU), IP can fragment it and reassemble at the destination.
Time to Live (TTL): A hop limit field that prevents packets from looping indefinitely.
Header checksum: In IPv4, a header checksum protects against corruption, but it is recalculated at each hop; IPv6 omits this in favor of relying on layer‑2 and higher‑layer checksums.

IP is stateless; each packet is processed independently. For reliable, ordered delivery, upper-layer protocols like TCP add state and retransmission.

History

The Internet Protocol was developed in the 1970s as part of the DARPA research program. A key early specification was RFC 791, published in September 1981 by the Internet Engineering Task Force (IETF). This document defined IPv4 and formalized the protocol's basic functions. The success of the ARPANET and its transition to the Internet led to widespread adoption of IP.

By the 1990s, the explosive growth of the Internet made IPv4 address exhaustion imminent. In response, the IETF developed IPv6, formalized in RFC 2460 (1998) and later updated. IPv6 offers a vastly larger address space, simplified header structure, built-in IPsec support, and improved multicast and anycast capabilities. As of the 2020s, IPv6 deployment has increased but still lags behind IPv4 in overall traffic share.

Internet Protocol