By the early 1990s it was clear the Internet would outgrow IPv4. The original Internet Protocol used a 32-bit address field, allowing roughly four billion addresses, and the rapid commercial growth of the network made exhaustion a foreseeable certainty. The IETF launched an effort known as IP Next Generation (IPng) to design a replacement. The result was Internet Protocol Version 6, first specified by Stephen E. Deering of Xerox PARC and Robert M. Hinden of Ipsilon Networks in RFC 1883, published in December 1995. The document opens by stating that it “specifies version 6 of the Internet Protocol (IPv6), also sometimes referred to as IP Next Generation or IPng.”
The central change is the address. IPv6 uses 128-bit addresses, an increase from IPv4’s 32 bits that expands the theoretical address space from about 4.3 billion to roughly 3.4 times 10 to the 38th power. Addresses are written as eight groups of four hexadecimal digits separated by colons, with rules for compressing runs of zeros. The vast space was meant not only to end the prospect of exhaustion but also to restore the end-to-end addressing model that IPv4 scarcity had eroded through workarounds like Network Address Translation.
Beyond the larger address, IPv6 simplified the packet header. The base header is fixed in size, and optional fields that complicated IPv4 processing were moved into a chain of extension headers placed between the base header and the upper-layer payload. Routers no longer fragment packets in transit; path MTU discovery is expected of the sender instead. These choices were intended to make forwarding faster and more predictable in high-speed routers.
RFC 1883 was revised by RFC 2460 in December 1998, which became the long-standing reference for the protocol. After nearly two decades of deployment experience, the IETF folded accumulated errata and clarifications into RFC 8200, published in July 2017 by the same authors, Deering and Hinden. RFC 8200 obsoletes RFC 2460 and carries the designation STD 86, marking IPv6 as a full Internet Standard rather than a draft track specification.
Deployment of IPv6 was slow for many years because IPv4, supplemented by NAT and CIDR-based address conservation, kept functioning long past the point where exhaustion had been predicted. Adoption accelerated only as regional registries actually ran out of IPv4 blocks and as mobile carriers and large content providers found dual-stack and IPv6-only operation cheaper than maintaining ever-larger NAT layers. The protocol now carries a substantial and growing share of global traffic, the practical end of a transition that the 1995 specification set in motion.