The Internet Protocol (IP) is the principal communications protocol used for relaying datagrams (also known as network packets) across an internetwork using the Internet Protocol Suite. Responsible for routing packets across network boundaries, it is the primary protocol that establishes the Internet.

IP is the primary protocol in the Internet Layer of the Internet Protocol Suite and has the task of delivering datagrams from the source host to the destination host solely based on the addresses. For this purpose, IP defines datagram structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram source and destination.

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 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), which is increasing in use.

Function[link]

The Internet Protocol is responsible for addressing hosts and routing datagrams (packets) from a source host to the destination host across one or more IP networks. For this purpose the Internet Protocol defines an addressing system that has two functions: identifying hosts and providing a logical location service. This is accomplished by defining standard datagrams and a standard addressing system.

Datagram construction[link]

Sample encapsulation of application data from UDP to a Link protocol frame

Each datagram has two components, a header and a payload. The IP header is tagged with the source IP address, destination IP address, and other meta-data needed to route and deliver the datagram. The payload is the data to be transported. This process of nesting data payloads in a packet with a header is called encapsulation.

IP addressing and routing[link]

Perhaps the most complex aspects of IP are IP addressing and routing. Addressing refers to how end hosts are assigned IP addresses and how subnetworks of IP host addresses are divided and grouped. IP routing is performed by all hosts, but most importantly by routers, which typically use either interior gateway protocols (IGPs) or external gateway protocols (EGPs) to decide how to move datagrams among networks.

IP routing is also common in local networks. For example, Ethernet switches sold today support IP multicast.^[1] These switches use IP addresses and Internet Group Management Protocol for control of the multicast routing but use MAC addresses for the actual routing.

Reliability[link]

The design principles of the Internet protocols assume that the network infrastructure is inherently unreliable at any single network element or transmission medium and that it 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 mostly located in the end nodes of each data transmission, cf. end-to-end principle. Routers in the transmission path simply forward packets to the next known local gateway matching the routing prefix for the destination address.

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 connection-less protocol, in contrast to so-called connection-oriented modes of transmission. The lack of reliability permits various error conditions, such as data corruption, packet loss and duplication, as well as out-of-order packet delivery. Since routing is dynamic for every packet and the network maintains no state of the path of prior packets, it is possible that some packets are routed on a longer path to their destination, resulting in improper sequencing at the receiver.

The only assistance that IPv4 provides regarding unreliability is 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. The routing node does not have to notify either end node, although the Internet Control Message Protocol (ICMP) allows such notification. In contrast, IPv6 abandons checksums in favor of faster routing.

Upper layer protocols are responsible for resolving reliability issues. For example, an upper layer protocol may cache data to make sure that it is in the correct order, before giving the data to an application.

In addition to issues of reliability, the dynamic nature and the diversity of the Internet and its components provide no guarantee that any particular path is actually capable of, or suitable for, performing the data transmission requested, even if the path is available and reliable. One of the technical constraints is the size of data packets allowed on a given link. An application must assure that it uses proper transmission characteristics. Some of this responsibility lies also in the upper layer protocols between application and IP. Facilities exist to examine the maximum transmission unit (MTU) size of the local link, as well as for the entire projected path to the destination when using IPv6. The IPv4 internetworking layer has the capability to automatically fragment the original datagram into smaller units for transmission. In this case, IP does provide re-ordering of fragments delivered out-of-order.^[2]

Transmission Control Protocol (TCP) is an example of a protocol that will adjust its segment size to be smaller than the MTU. User Datagram Protocol (UDP) and Internet Control Message Protocol (ICMP) disregard MTU size, thereby forcing IP to fragment oversized datagrams.^[3]

Version history[link]

In May 1974, the Institute of Electrical and Electronic Engineers (IEEE) published a paper entitled "A Protocol for Packet Network Intercommunication."^[4] The paper's authors, Vint Cerf and Bob Kahn, described an internetworking protocol for sharing resources using packet-switching among the nodes. A central control component of this model was the "Transmission Control Program" (TCP) 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 at the connection-oriented layer and the Internet Protocol at the internetworking (datagram) layer. The model became known informally as TCP/IP, although formally referenced as the Internet Protocol Suite.

The Internet Protocol is one of the elements that define the Internet. 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).

The successor to IPv4 is IPv6. Its most prominent modification from version 4 is the addressing system. IPv4 uses 32-bit addresses (c. 4 billion, or 4.3×10⁹, addresses) while IPv6 uses 128-bit addresses (c. 340 undecillion, or 3.4×10³⁸ addresses). Although adoption of IPv6 has been slow, as of June 2008, all United States government systems have demonstrated basic infrastructure support for IPv6 (if only at the backbone level).^[5]

IP versions 0 to 3 were development versions of IPv4 and were used between 1977 and 1979.^{[citation needed]} Version 5 was used by the Internet Stream Protocol, an experimental streaming protocol. Version numbers 6 through 9 were proposed for various protocol models designed to replace IPv4: SIPP (Simple Internet Protocol Plus, known now as IPv6), TP/IX (RFC 1475), PIP (RFC 1621) and TUBA (TCP and UDP with Bigger Addresses, RFC 1347).

Other protocol proposals named IPv9 and IPv8 briefly surfaced, but have no support.^[6]

On April 1, 1994, the IETF published an April Fool's Day joke about IPv9.^[7]

Vulnerabilities[link]

This section requires expansion.

The Internet Protocol is vulnerable to a variety of attacks. A thorough vulnerability assessment, along with proposed mitigations, was published in 2008,^[8] and is currently being pursued within the IETF.^[9]

See also[link]

	Computer networking portal
	Computer Science portal

References[link]

External links[link]

Look up internet protocol in Wiktionary, the free dictionary.

• Internet Protocol at the Open Directory Project
• RFC 791
• Data Communication Lectures of Manfred Lindner - Part IP Technology Basics
• Data Communication Lectures of Manfred Lindner - Part IP Technology Details
• Data Communication Lectures of Manfred Lindner - Part IPv6
• IPv6.com - Knowledge Center for Next Generation Internet IPv6

Wikisource has original text related to this article: Protocol I

Protocol I is a 1977 amendment protocol to the Geneva Conventions relating to the protection of victims of international armed conflicts. It reaffirms the international laws of the original Geneva Conventions of 1949, but adds clarifications and new provisions to accommodate developments in modern international warfare that have taken place since the Second World War.

As of 11 May 2011, it had been ratified by 170 countries,^[1] with the United States, Israel, Iran, Pakistan, and Turkey being notable exceptions. However, the United States, Iran, and Pakistan signed it on 12 December 1977 with the intention of ratifying it. According to an appeal by the International Committee of the Red Cross in 1997, a number of the articles contained in both protocols are recognized as rules of customary international law valid for all states, whether or not they have ratified them.^[2]

Summary of Provisions[link]

Protocol I is an extensive document, containing 102 articles. Following is a basic overview of the protocol.^[3] For a comprehensive listing of all provisions, consult the original text^[4] and the commentary.^[5] In general, the protocol reaffirms the provisions of the original four Geneva Conventions. However, the following additional protections are added.

• Articles 51 and 54 outlaw indiscriminate attacks on civilian populations, and destruction of food, water, and other materials needed for survival. Indiscriminate attacks include directly attacking civilian (non-military) targets, but also using technology such as biological weapons, nuclear weapons and land mines, whose scope of destruction cannot be limited.^[5] A total war that does not distinguish between civilian and military targets is considered a war crime.
• Articles 56 and 53 outlaw attacks on dams, dikes, nuclear generating stations, and places of worship. The first three are "works and installations containing dangerous forces" and may be attacked but only in ways that do not threaten to release the dangerous forces (i.e., it is permissible to attempt to capture them but not to try to destroy them).
• Articles 76 and 77, 15 and 79 provide special protections for women, children, and civilian medical personnel, and provide measures of protection for journalists.
• Article 77 forbids conscription of children under age 15 into the armed forces. It does allow, however, for persons under the age of 15 to participate voluntarily.^[5]
• Articles 43 and 44 clarify the military status of members of guerrilla forces. Combatant and prisoner of war status is granted to members of dissident forces when under the command of a central authority. Such combatants cannot conceal their allegiance; they must be recognizable as combatants while preparing for or during an attack.
• Article 35 bans weapons that "cause superfluous injury or unnecessary suffering," as well as means of warfare that "cause widespread, long-term, and severe damage to the natural environment."
• Article 85 states that it is a war crime to use one of the protective emblems recognized by the Geneva Conventions to deceive the opposing forces (perfidy).
• Articles 17 and 81 authorize the ICRC, national societies, or other impartial humanitarian organizations to provide assistance to the victims of war.

See also[link]

• Command responsibility
• Geneva Conventions
• List of parties to the Geneva Conventions
• First Geneva Convention of 1864, on the treatment of battlefield casualties.
• Jus in bello
• Targeted killing

References[link]

External links[link]

• Full text of Protocol I
• List of countries that have signed but not yet ratified Protocol I
• International Review of the Red Cross, 1997 – No. 320 Special issue: 20th anniversary of the 1977 Additional Protocols
• 1977 Additional Protocols – short bibliography (by ICRC)
• "New rules for victims of armed conflicts, Commentary on the two 1977 Protocols additional to the Geneva Conventions of 1949", by M. Bothe, K.J.Partsch, W.A. Solf, Pub: Martinus Nijhoff The Hague/Boston/London, 1982, ISBN 90-247-2537-2
• U.S. President Ronald Reagan's message to the Senate on Protocols I & II