Internet Protocol (IP) is the principal communications protocol in
Internet protocol suite
Internet protocol suite for relaying packets across network
boundaries. Its routing function enables internetworking, and
essentially establishes the Internet.
IP has the task of delivering packets from the source host to the
destination host solely based on the IP addresses 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
Historically, IP was the connectionless datagram service in the
original Transmission Control Program introduced by
Vint Cerf and Bob
Kahn in 1974; the other being the connection-oriented Transmission
Control Protocol (TCP). The
Internet protocol suite
Internet protocol suite is therefore often
referred to as TCP/IP.
The first major version of IP,
Internet Protocol Version 4 (IPv4), is
the dominant protocol of the Internet. Its successor is Internet
Protocol Version 6 (IPv6).
2 Version history
4 Link capacity and capability
6 See also
8 External links
Sample encapsulation of application data from UDP to a Link protocol
Internet Protocol is responsible for addressing hosts,
encapsulating data into datagrams (including fragmentation and
reassembly) and routing datagrams from a source host to a destination
host across one or more IP networks. For these purposes, the
Internet Protocol defines the format of packets and provides an
Each datagram has two components: a header and a payload. The IP
header 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
subnetworks, 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 protocols, either
interior gateway protocols or exterior gateway protocols, as needed
for the topology of the network.
In May 1974, the Institute of Electrical and Electronic Engineers
(IEEE) published a paper entitled "A Protocol for Packet Network
Intercommunication". The paper's authors,
Vint Cerf and Bob Kahn,
described an internetworking protocol for sharing resources using
packet switching among network nodes. 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
User Datagram Protocol at the transport layer and the Internet
Protocol at the network layer. The model became known as the
Department of Defense (DoD)
Internet Model and
suite, and informally as TCP/IP.
IP versions 0 to 3 were experimental versions, used between 1977 and
1979. The following
Internet Experiment Note (IEN) documents describe
versions 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
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
IEN 44 (Latest Header Formats), dated June 1978 describes another
version of IPv4, also with a header different from the modern IPv4
IEN 54 (
Internetwork Protocol Specification Version 4), dated
September 1978 is the first description of
IPv4 using the header that
would be standardized in RFC 760.
The dominant internetworking protocol in the
Internet Layer in use
today is IPv4; the number 4 is the protocol version number carried in
every IP datagram.
IPv4 is described in RFC 791 (1981).
Version 5 was used by the
Internet Stream Protocol, an experimental
The successor to
IPv4 is IPv6.
IPv6 was a result of several years of
experimentation and dialog during which various protocol models were
proposed, such as TP/IX (RFC 1475), PIP (RFC 1621) and TUBA (TCP and
UDP with Bigger Addresses, RFC 1347). Its most prominent difference
from version 4 is the size of the addresses. While
IPv4 uses 32 bits
for addressing, yielding c. 4.3 billion
IPv6 uses 128-bit
addresses providing ca. 340 undecillion, or
7038340000000000000♠3.4×1038 addresses. Although adoption of IPv6
has been slow, as of June 2008[update], all United States government
systems have demonstrated basic infrastructure support for IPv6.
The assignment of the new protocol as
IPv6 was uncertain until due
diligence revealed that
IPv6 had not yet been used previously.
Other protocol proposals named IPv9 and IPv8 briefly surfaced, but had
no affiliation with any international standards body, and have had no
support. However, on April 1, 1994, the
IETF published an April
Fools' Day joke about IPv9.
The design of the
Internet protocol suite
Internet protocol suite adheres to the end-to-end
principle, a concept adapted from the
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 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 and its service is characterized as unreliable.
In network architectural language, it is a connectionless protocol, in
contrast to connection-oriented communication. Various error
conditions may occur, such as data corruption, 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 to the receiver.
All error conditions in the network must be detected and compensated
by the participating end nodes. The upper layer protocols of the
Internet protocol suite
Internet protocol suite are responsible for resolving reliability
issues. For example, a host may buffer network data to ensure correct
ordering before the data is delivered to an application.
IPv4 provides safeguards to ensure that the IP packet header is
error-free. A routing node calculates a checksum for a packet. If the
checksum is bad, the routing node discards the packet. Although the
Internet Control Message Protocol (ICMP) allows such notification, the
routing node is not required to notify either end node of these
errors. By contrast, in order to increase performance, and since
current link layer technology is assumed to provide sufficient error
IPv6 header has no checksum to protect it.
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 allowed on a
given link. Facilities exist to examine the maximum transmission unit
(MTU) size of the local link and
Path MTU Discovery can be used for
the entire intended path to the destination.
IPv4 internetworking layer has the ability to automatically
fragment the original datagram into smaller units for transmission. In
this case, IP provides re-ordering of fragments delivered out of
IPv6 network does not perform fragmentation or
reassembly, and as per the end-to-end principle, requires end stations
and higher-layer protocols to avoid exceeding the network's MTU.
Transmission Control Protocol
Transmission Control Protocol (TCP) is an example of a protocol
that adjusts its segment size to be smaller than the MTU. The User
Datagram Protocol (UDP) and ICMP disregard MTU size, thereby forcing
IP to fragment oversized datagrams.
During the design phase of the ARPANET and the early Internet, the
security aspects and needs of a public, international network could
not be adequately anticipated. Consequently, many
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.
Information technology portal
List of IP protocol numbers
IP forwarding algorithm
^ Charles M. Kozierok, The TCP/IP Guide
^ Vinton G. Cerf, Robert E. Kahn, "A Protocol for Packet Network
Intercommunication", IEEE Transactions on Communications, Vol. 22, No.
5, May 1974 pp. 637–648
^ CIO council adds to
IPv6 transition primer Archived 2006-07-01 at
the Wayback Machine., gcn.com
^ Mulligan, Geoff. "It was almost IPv7". O'Reilly. O'Reilly Media.
Retrieved 4 July 2015.
^ Leyden, John (6 July 2004). "China disowns IPv9 hype".
theregister.co.uk. The Register. Retrieved 4 May 2014.
^ RFC 1606: A Historical Perspective On The Usage Of IP Version 9.
April 1, 1994.
^ RFC 1726 section 6.2
^ RFC 2460
^ Siyan, Karanjit. Inside TCP/IP, New Riders Publishing, 1997.
^ Bill Cerveny (2011-07-25). "
IPv6 Fragmentation". Arbor Networks.
^ Parker, Don (2 November 2010). "Basic Journey of a Packet".
symantec.com. Symantec. Retrieved 4 May 2014.
^ Fernando Gont (July 2008), Security Assessment of the Internet
Protocol (PDF), CPNI, archived from the original (PDF) on
^ F. Gont (July 2011). Security Assessment of the
version 4. doi:10.17487/RFC6274. RFC 6274.
Look up internet protocol in Wiktionary, the free dictionary.
Internet Protocol at Curlie (based on DMOZ)
Manfred Lindner. "IP Technology" (PDF). Retrieved 2018-02-11.
Manfred Lindner. "IP Routing" (PDF). Retrieved 2018-02-11.