It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks.

In March 1982, the US Department of Defense decided on the Internet Protocol Suite (TCP/IP) as the standard for all military computer networking.

They are most often written in dot-decimal notation, which consists of four octets of the address expressed individually in decimal numbers and separated by periods.

For example, the quad-dotted IP address in the illustration (172.16.254.1) represents the 32-bit decimal number 2886794753, which in hexadecimal format is 0xAC10FE01.

CIDR notation combines the address with its routing prefix in a compact format, in which the address is followed by a slash character (/) and the count of leading consecutive 1 bits in the routing prefix (subnet mask).

This division was made more flexible with the introduction of variable-length subnet masks (VLSM) in RFC 1109 in 1987.

In 1993, based on this work, RFC 1517 introduced Classless Inter-Domain Routing (CIDR),[7] which expressed the number of bits (from the most significant) as, for instance, /24, and the class-based scheme was dubbed classful, by contrast.

Each RIR maintains a publicly searchable WHOIS database that provides information about IP address assignments.

The Internet Engineering Task Force (IETF) and IANA have restricted from general use various reserved IP addresses for special purposes.

Additionally, encapsulated packets may be encrypted for transmission across public networks to secure the data.

Microsoft created an implementation called Automatic Private IP Addressing (APIPA), which was deployed on millions of machines and became a de facto standard.

Many years later, in May 2005, the IETF defined a formal standard in RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.

Packets received on a non-loopback interface with a loopback source or destination address must be dropped.

[20] Hosts on the Internet are usually known by names, e.g., www.example.com, not primarily by their IP address, which is used for routing and network interface identification.

The use of domain names requires translating, called resolving, them to addresses and vice versa.

When a link is unnumbered, a router-id is used, a single IP address borrowed from a defined (normally a loopback) interface.

In the 1980s, it became apparent that the pool of available IPv4 addresses was depleting at a rate that was not initially anticipated in the original design of the network.

[25] The main market forces that accelerated address depletion included the rapidly growing number of Internet users, who increasingly used mobile computing devices, such as laptop computers, personal digital assistants (PDAs), and smart phones with IP data services.

The threat of exhaustion motivated the introduction of a number of remedial technologies, such as: By the mid-1990s, NAT was used pervasively in network access provider systems, along with strict usage-based allocation policies at the regional and local Internet registries.

The primary address pool of the Internet, maintained by IANA, was exhausted on 3 February 2011, when the last five blocks were allocated to the five RIRs.

[26][27] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition technologies to IPv6, which is to be allocated under a restricted policy.

[28] The long-term solution to address exhaustion was the 1998 specification of a new version of the Internet Protocol, IPv6.

With the phase-out of the 6bone experimental network starting in 2004, permanent formal deployment of IPv6 commenced in 2006.

[30] Completion of IPv6 deployment is expected to take considerable time,[31] so that intermediate transition technologies are necessary to permit hosts to participate in the Internet using both versions of the protocol.

Typically the link layer encapsulates IP packets in frames with a CRC footer that detects most errors.

The design accommodates networks of diverse physical nature; it is independent of the underlying transmission technology used in the link layer.

In IPv4, this function was placed at the Internet Layer and is performed in IPv4 routers limiting exposure to these issues by hosts.

When the receiver has all fragments, they can be reassembled in the correct sequence according to the offsets to form the original datagram.

In order to properly deliver an IP packet to the destination host on a link, hosts and routers need additional mechanisms to make an association between the hardware address[b] of network interfaces and IP addresses.

This article was adapted from the following source under a CC BY 4.0 license (2022) : Michel Bakni; Sandra Hanbo (9 December 2022).