Internet Protocol
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The Internet Protocol (IP) is the network layer
communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A communications system or communication system is a collection of individual telecommunications network ...
in the
Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A commu ...
for relaying
datagram A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication Connectionless communication, often referred to a ...
s across network boundaries. Its
routing Routing is the process of selecting a path for traffic in a network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 American film * ''Network'' (2019 film), an Indian film * ''Network'' ...

routing
function enables
internetworking Internetworking is the practice of interconnecting multiple computer networks, such that any pair of Host (network), hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting sy ...
, and essentially establishes the
Internet The Internet (Capitalization of Internet, or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''network of networks'' t ...

Internet
. IP has the task of delivering packets from the source
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host (19 ...
to the destination host solely based on the
IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.RFC 760, ''DOD Standard Internet Protocol'', DARPA, Information Sciences Institut ...
es in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information. Historically, IP was the
connectionless Connectionless communication, often referred to as CL-mode communication,Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for St ...
datagram service in the original Transmission Control Program introduced by
Vint Cerf Vinton Gray Cerf (; born June 23, 1943) is an American Internet pioneer and is recognized as one of "List of Internet pioneers, the fathers of the Internet", sharing this title with TCP/IP co-developer Bob Kahn. He has received honorary degrees ...

Vint Cerf
and
Bob Kahn Robert Elliot Kahn (born December 23, 1938) is an American electrical engineer, who, along with Vint Cerf Vinton Gray Cerf (; born June 23, 1943) is an American Internet pioneer and is recognized as one of "List of Internet pioneers, the fa ...
in 1974, which was complemented by a connection-oriented service that became the basis for the
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the e ...
(TCP). The Internet protocol suite is therefore often referred to as ''TCP/IP''. The first major version of IP,
Internet Protocol Version 4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routi ...

Internet Protocol Version 4
(IPv4), is the dominant protocol of the Internet. Its successor is
Internet Protocol Version 6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic a ...

Internet Protocol Version 6
(IPv6), which has been in increasing deployment on the public Internet since c. 2006.


Function

The Internet Protocol is responsible for addressing host interfaces, encapsulating data into datagrams (including fragmentation and reassembly) and routing datagrams from a source host interface to a destination host interface across one or more IP networks. For these purposes, the Internet Protocol defines the format of packets and provides an addressing system. Each datagram has two components: a
header Header may refer to: Computers and engineering * Header (computing)In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the h ...
and a
payload Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scienti ...
. The
IP header An IP header is header information at the beginning of an Internet Protocol (IP) packet. An IP packet is the smallest message entity exchanged via the Internet Protocol across an IP network. IP packets consist of a header for addressing and routin ...
includes source IP address, destination IP address, and other metadata needed to route and deliver the datagram. The payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation. IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into
subnetwork A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to the same subnet are addressed with an identical ...
s, involving the designation of network prefixes. IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed
routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theor ...
s, either interior gateway protocols or
exterior gateway protocol The Exterior Gateway Protocol (EGP) was a routing protocol used to connect different autonomous system (Internet), autonomous systems on the Internet from the mid-1980s until the mid-1990s, when it was replaced by Border Gateway Protocol (BGP). Hi ...
s, as needed for the topology of the network.


Version history

In May 1974, the
Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operations center in ...
(IEEE) published a paper entitled "A Protocol for Packet Network Intercommunication". The paper's authors,
Vint Cerf Vinton Gray Cerf (; born June 23, 1943) is an American Internet pioneer and is recognized as one of "List of Internet pioneers, the fathers of the Internet", sharing this title with TCP/IP co-developer Bob Kahn. He has received honorary degrees ...

Vint Cerf
and
Bob Kahn Robert Elliot Kahn (born December 23, 1938) is an American electrical engineer, who, along with Vint Cerf Vinton Gray Cerf (; born June 23, 1943) is an American Internet pioneer and is recognized as one of "List of Internet pioneers, the fa ...
, described an
internetworking Internetworking is the practice of interconnecting multiple computer networks, such that any pair of Host (network), hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology. The resulting sy ...
protocol for sharing resources using
packet switching In telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads or el ...
among
network nodeIn telecommunications network A telecommunications network is a group of nodes interconnected by links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switchi ...
s. A central control component of this model was the "Transmission Control Program" that incorporated both connection-oriented links and datagram services between hosts. The monolithic Transmission Control Program was later divided into a modular architecture consisting of the
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the e ...
and
User Datagram Protocol In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (networkin ...
at the
transport layer In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (netw ...
and the Internet Protocol at the
internet layer The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport network packets from the originating host across network boundaries; if necessary, to the destin ...
. The model became known as the ''Department of Defense (DoD) Internet Model'' and ''
Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A commu ...
'', and informally as ''TCP/IP''. IP versions 1 to 3 were experimental versions, designed between 1973 and 1978. The following
Internet Experiment NoteAn Internet Experiment Note (IEN) is a sequentially numbered document in a series of technical publications issued by the participants of the early development work groups that created the precursors of the modern Internet The Internet (Ca ...
(IEN) documents describe version 3 of the Internet Protocol, prior to the modern version of IPv4:
IEN 2
(''Comments on Internet Protocol and TCP''), dated August 1977 describes the need to separate the TCP and Internet Protocol functionalities (which were previously combined.) It proposes the first version of the IP header, using 0 for the version field.
IEN 26
(''A Proposed New Internet Header Format''), dated February 1978 describes a version of the IP header that uses a 1-bit version field.
IEN 28
(''Draft Internetwork Protocol Description Version 2''), dated February 1978 describes IPv2.
IEN 41
(''Internetwork Protocol Specification Version 4''), dated June 1978 describes the first protocol to be called IPv4. The IP header is different from the modern IPv4 header.
IEN 44
(''Latest Header Formats''), dated June 1978 describes another version of IPv4, also with a header different from the modern IPv4 header.
IEN 54
(''Internetwork Protocol Specification Version 4''), dated September 1978 is the first description of IPv4 using the header that would be standardized in . The dominant internetworking protocol in the
Internet Layer The internet layer is a group of internetworking methods, protocols, and specifications in the Internet protocol suite that are used to transport network packets from the originating host across network boundaries; if necessary, to the destin ...
in use is
IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routi ...

IPv4
; the number 4 identifies the protocol version, carried in every IP datagram. IPv4 is described in (1981). Version number 5 was used by the
Internet Stream Protocol The Internet Stream Protocol (ST) is a family of experimental protocols first defined in Internet Experiment Note IEN-119 in 1979, and later substantially revised in RFC 1190 (ST-II) and RFC 1819 (ST2+). The protocol uses the version number 5 in th ...
, an experimental streaming protocol that was not adopted. The successor to IPv4 is
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. It ...

IPv6
. IPv6 was a result of several years of experimentation and dialog during which various protocol models were proposed, such as TP/IX (), PIP () and TUBA (TCP and UDP with Bigger Addresses, ). Its most prominent difference from version 4 is the size of the addresses. While IPv4 uses
32 bits 32-bit microcomputers are computers in which 32-bit microprocessors are the norm. Range for storing integers A 32-bit register can store 232 different values. The range (computer programming), range of integer values that can be stored in 32 bit ...
for addressing, yielding c. 4.3
billion A billion is a number with two distinct definitions: *1,000,000,000 1,000,000,000 (one billion, short scale; one thousand million or milliard, yard, long scale) is the natural number In mathematics, the natural numbers are those used for ...
() addresses, IPv6 uses
128-bit While there are currently no mainstream general-purpose processors built to operate on 128-bit ''integers'' or addresses, a number of processors do have specialized ways to operate on 128-bit chunks of data. The IBM System/370 could be considered ...
addresses providing ca. addresses. Although adoption of IPv6 has been slow, , most countries in the world show significant adoption of IPv6, with over 35% of Google's traffic being carried over IPv6 connections. The assignment of the new protocol as IPv6 was uncertain until due diligence assured that IPv6 had not been used previously. Other Internet Layer protocols have been assigned version numbers, such as 7 (''IP/TX''), 8 and 9 (''historic''). Notably, on April 1, 1994, the
IETF The Internet Engineering Task Force (IETF) is an open standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SSO) is an organization whose primary function ...
published an
April Fools' Day April Fools' Day or April Fool's Day is an annual custom on April 1 consisting of practical jokes and hoaxes. Jokesters often expose their actions by shouting "April Fool!" at the recipient. Mass media can be involved in these pranks, which may ...
joke about IPv9. IPv9 was also used in an alternate proposed address space expansion called TUBA. A 2004 Chinese proposal for an "IPv9" protocol appears to be unrelated to all of these, and is not endorsed by the IETF.


Reliability

The design of the Internet protocol suite adheres to the
end-to-end principle The end-to-end principle is a design framework in computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resource ...
, a concept adapted from the
CYCLADES The Cyclades ( el, Κυκλάδες ) are an island group in the Aegean Sea The Aegean Sea ; tr, Ege Denizi is an elongated Bay, embayment of the Mediterranean Sea located between Europe's Geography of Europe, Balkan peninsula and Asia ...

CYCLADES
project. Under the end-to-end principle, the network infrastructure is considered inherently unreliable at any single network element or transmission medium and is dynamic in terms of the availability of links and nodes. No central monitoring or performance measurement facility exists that tracks or maintains the state of the network. For the benefit of reducing network complexity, the intelligence in the network is purposely located in the end nodes. As a consequence of this design, the Internet Protocol only provides
best-effort delivery Best-effort delivery describes a network service in which the network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 American film * ''Network'' (2019 film), an Indian film * ''Network'' ( ...
and its service is characterized as unreliable. In network architectural parlance, it is a
connectionless protocol Connectionless communication, often referred to as CL-mode communication,Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for St ...
, in contrast to
connection-oriented communication Connection-oriented communication is a network communication mode in telecommunications and computer networking, where a communication session or a semi-permanent connection is established before any useful data can be transferred, enabling the ab ...
. Various fault conditions may occur, such as
data corruption Image:Data loss of image file.JPG, Photo data corruption; in this case, a result of a failed data recovery from a hard disk drive Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or proce ...
,
packet loss Packet loss occurs when one or more packet (information technology), packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless netw ...

packet loss
and duplication. Because routing is dynamic, meaning every packet is treated independently, and because the network maintains no state based on the path of prior packets, different packets may be routed to the same destination via different paths, resulting in
out-of-order delivery In computer networking A computer network is a group of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of op ...
to the receiver. All fault conditions in the network must be detected and compensated by the participating end nodes. The
upper layer protocol In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (networkin ...
s of the Internet protocol suite are responsible for resolving reliability issues. For example, a host may
buffer Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Buffering agent, the weak acid or base in a buffer solution * Lysis buffer, in cell biology * Metal ion buffer * M ...
network data to ensure correct ordering before the data is delivered to an application. IPv4 provides safeguards to ensure that the header of an IP packet is error-free. A routing node discards packets that fail a header
checksum A checksum is a small-sized block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Car ...

checksum
test. Although the
Internet Control Message Protocol The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rule ...
(ICMP) provides notification of errors, a routing node is not required to notify either end node of errors. IPv6, by contrast, operates without header checksums, since current
link layer In computer networking, the link layer is the lowest Abstraction layer, layer in the Internet protocol suite, the networking architecture of the Internet. The link layer is the group of methods and communications protocols confined to the link th ...
technology is assumed to provide sufficient error detection.


Link capacity and capability

The dynamic nature of the Internet and the diversity of its components provide no guarantee that any particular path is actually capable of, or suitable for, performing the data transmission requested. One of the technical constraints is the size of data packets possible on a given link. Facilities exist to examine the
maximum transmission unit In computer networking A computer network is a set of computers sharing resources located on or provided by Node (networking), network nodes. The computers use common communication protocols over digital signal, digital Interconnection, inter ...
(MTU) size of the local link and
Path MTU Discovery Path MTU Discovery (PMTUD) is a standardized technique in computer networking for determining the maximum transmission unit, maximum transmission unit (MTU) size on the network path between two Internet Protocol (IP) hosts, usually with the goal o ...
can be used for the entire intended path to the destination. The IPv4 internetworking layer automatically fragments a datagram into smaller units for transmission when the link MTU is exceeded. IP provides re-ordering of fragments received out of order. An IPv6 network does not perform fragmentation in network elements, but requires end hosts and higher-layer protocols to avoid exceeding the path MTU. The
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main communications protocol, protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the e ...
(TCP) is an example of a protocol that adjusts its segment size to be smaller than the MTU. The
User Datagram Protocol In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (networkin ...
(UDP) and ICMP disregard MTU size, thereby forcing IP to fragment oversized datagrams.


Security

During the design phase of the
ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switching In telecommunications, packet switching is a method of grouping data that is transmitted over a digital network into '' packets''. Packets are ...
and the early Internet, the security aspects and needs of a public, international network could not be adequately anticipated. Consequently, many Internet protocols exhibited vulnerabilities highlighted by network attacks and later security assessments. In 2008, a thorough security assessment and proposed mitigation of problems was published. The IETF has been pursuing further studies.


See also

*
ICANN The Internet Corporation for Assigned Names and Numbers (ICANN ) is an American multistakeholder group and nonprofit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or no ...

ICANN
*
IP routing IP routing is the field of routing methodologies of Internet Protocol (IP) packets within and across IP networks. This involves not only protocols and technologies but includes the policies of the worldwide organization and configuration of Intern ...
*
List of IP protocol numbers This is a list of the IP protocol numbers found in the field ''Protocol'' of the IPv4 header and the ''Next Header'' field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately ...
*
Next-generation network The next-generation network (NGN) is a body of key architectural changes in telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of ...

Next-generation network


References


External links

* * {{Authority control Internet layer protocols Internet