The five-layer TCP/IP model 5. Application layer DHCP · DNS · FTP · Gopher · HTTP · NFS · NTP · (more) 4. Transport layer TCP · UDP · DCCP · SCTP · RTP · RSVP · IGMP · IS-IS · IGRP · EIGRP 2. Data Link layer PPP · SLIP 1. Physical layer RS-232 · V.35· V.34· I.430· I.431· T1· E1· 10BASE-T· 100BASE-TX· POTS· SONET· DSL· 802.11a/b/g/n PHY This box: view • talk • edit This article is about the data-oriented protocol. For the set of communications protocols, see Internet protocol suite. The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. IP is a network layer protocol in use today is IPv4; this version of the protocol is assigned version 4. IPv4 is described in RFC-791 (1981). IPv6 is the proposed successor to IPv4 whose most prominent change is the addressing. IPv4 uses 32-bit addresses (~4 billion addresses) while IPv6 uses 128-bit addresses (~3.4×1038 addresses). Although adoption of IPv6 has been slow, as of 2008, all United States government systems must support IPv6 (if only at the backbone level). [3] Version numbers 0 through 3 were development versions of IPv4 used between 1977 and 1979. Version number 5 was used by the Internet Stream Protocol (IST), an experimental stream protocol. Version numbers 6 through 9 were assigned to experimental protocols designed to replace IPv4: SIPP (known nowadays as IPv6),