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Internet Protocol 

From Wikipedia, the free encyclopediaThis article is about a specific protocol technology. For the entire set of Internet relatedprotocols, see Internet Protocol Suite. 

Internet Protocol Suite in operation between two hosts connected via two routers and thecorresponding layers used at each hop

The Internet Protocol (IP) is the principal communications protocol used for relayingdatagrams (packets) across an internetwork using the Internet Protocol Suite. Responsible forrouting 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 their addresses. 

For this purpose, IP defines addressing methods and structures for datagram encapsulation. Historically, IP was the connectionless datagram service in the original Transmission ControlProgram introduced by Vint Cerf  and Bob Kahn in 1974, the other being the connection-orientedTransmission Control Protocol (TCP). The Internet Protocol Suite is therefore often referred toas TCP/IP.

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The first major version of IP, now referred to as Internet Protocol Version 4 (IPv4) is thedominant protocol of the Internet, although the successor, Internet Protocol Version 6 (IPv6) is inactive, growing deployment worldwide.

Contents

[hide] 

  1 Function   2 Reliability   3 IP addressing and routing   4 Version history   5 Reference diagrams   6 Vulnerabilities   7 See also   8 References   9 External links 

[edit] Function

Internet protocol suite

Application layer

  BGP 

  DHCP 

  DNS 

  FTP 

  HTTP 

  IMAP 

  IRC 

  LDAP 

  MGCP   NNTP 

  NTP 

  POP 

  RIP 

  RPC 

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  RTP 

  SIP 

  SMTP 

  SNMP 

  SOCKS   SSH 

  Telnet 

  TLS/SSL 

  XMPP 

  (more) 

Transport layer

  TCP   UDP 

  DCCP 

  SCTP 

  RSVP 

  ECN 

  (more) 

Internet layer

  IP 

o  IPv4 

o  IPv6 

  ICMP 

  ICMPv6 

  IGMP 

  IPsec 

  (more) 

Link layer  

  ARP/InARP 

  NDP 

  OSPF 

  Tunnels 

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o  L2TP 

  PPP 

  Media access control 

o  Ethernet 

o  DSL o  ISDN 

o  FDDI 

  (more) 

v ·  d ·  e 

The Internet Protocol is responsible for addressing hosts and routing datagrams (packets) from asource 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. Addresses identify hosts andprovide a logical location service. Each packet is tagged with a header that contains the meta-data for the purpose of delivery. This process of tagging is also called encapsulation.

[edit] Reliability

The design principles of the Internet protocols assume that the network infrastructure isinherently unreliable at any single network element or transmission medium and that it isdynamic in terms of availability of links and nodes. No central monitoring or performancemeasurement 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 theend nodes of each data transmission, cf. end-to-end principle. Routers in the transmission pathsimply forward packets to the next known local gateway matching the routing prefix for thedestination address.

As a consequence of this design, the Internet Protocol only provides  best effort delivery and itsservice 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 data corruption, packet loss and duplication, aswell as out-of-order packet delivery. Since routing is dynamic for every packet and the networkmaintains no state of the path of prior packets, it is possible that some packets are routed on alonger path to their destination, resulting in improper sequencing at the receiver.

The only assistance that the Internet Protocol provides in Version 4 (IPv4) is to ensure that the IPpacket header is error-free through computation of a checksum at the routing nodes. This has theside-effect of discarding packets with bad headers on the spot. In this case no notification isrequired to be sent to either end node, although a facility exists in the Internet Control MessageProtocol (ICMP) to do so.

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IPv6, on the other hand, has abandoned the use of IP header checksums for the benefit of rapidforwarding through routing elements in the network.

The resolution or correction of any of these reliability issues is the responsibility of an upperlayer protocol. For example, to ensure in-order delivery the upper layer may have to cache data

until it can be passed to the application.In addition to issues of reliability, this dynamic nature and the diversity of the Internet and itscomponents 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 thetechnical constraints is the size of data packets allowed on a given link. An application mustassure that it uses proper transmission characteristics. Some of this responsibility lies also in theupper layer protocols between application and IP. Facilities exist to examine the maximumtransmission unit (MTU) size of the local link, as well as for the entire projected path to thedestination when using IPv6. The IPv4 internetworking layer has the capability to automaticallyfragment the original datagram into smaller units for transmission. In this case, IP does provide

re-ordering of fragments delivered out-of-order.

[1]

 Transmission Control Protocol (TCP) is an example of a protocol that will adjust its segment sizeto be smaller than the MTU. User Datagram Protocol (UDP) and Internet Control MessageProtocol (ICMP) disregard MTU size thereby forcing IP to fragment oversized datagrams.[2] 

[edit] IP addressing and routing

Perhaps the most complex aspects of IP are IP addressing and routing. Addressing refers to howend hosts become assigned IP addresses and how subnetworks of IP host addresses are dividedand grouped together. IP routing is performed by all hosts, but most importantly by internetwork

routers, which typically use either interior gateway protocols (IGPs) or external gatewayprotocols (EGPs) to help make IP datagram forwarding decisions across IP connected networks.

IP routing is also common in local networks. For example, Ethernet switches sold today supportIP multicast.[3] These switches primarily use IP addresses but also support MAC addresses forcompatibility with older layer 2 Ethernet switches.

[edit] Version history

In May 1974, the Institute of Electrical and Electronic Engineers (IEEE) published a paper

entitled "A Protocol for Packet Network Interconnection."

[4]

 The paper's authors, Vint Cerf  andBob Kahn, described an internetworking protocol for sharing resources using packet-switchingamong the nodes. A central control component of this model was the "Transmission ControlProgram" (TCP) that incorporated both connection-oriented links and datagram services betweenhosts. The monolithic Transmission Control Program was later divided into a modulararchitecture consisting of the Transmission Control Protocol at the connection-oriented layer andthe Internet Protocol at the internetworking (datagram) layer. The model became knowninformally as TCP/IP, although formally referenced as the Internet Protocol Suite. 

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The Internet Protocol is one of the determining elements that define the Internet. The dominantinternetworking protocol in the Internet Layer in use today is IPv4; with number 4 assigned asthe formal 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 addressingsystem. 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 infrastructuresupport for IPv6 (if only at the backbone level).[5] 

Version numbers 0 through 3 were development versions of IPv4 used between 1977 and1979.[citation needed ] Version number 5 was used by the Internet Stream Protocol, an experimentalstreaming protocol. Version numbers 6 through 9 were proposed for various protocol modelsdesigned to replace IPv4: SIPP (Simple Internet Protocol Plus, known now as IPv6), TP/IX (RFC1475), PIP (RFC 1621) and TUBA (TCP and UDP with Bigger Addresses, RFC 1347). Version

number 6 was eventually chosen as the official assignment for the successor Internet protocol,subsequently standardized as IPv6. 

A humorous Request for Comments that made an IPv9 protocol center of its storyline waspublished on April 1, 1994 by the IETF.[6] It was intended as an April Fool's Day  joke. Otherprotocol proposals named "IPv9" and "IPv8" have also briefly surfaced, though these came withlittle or no support from the wider industry and academia.[7] 

[edit] Reference diagrams

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

[edit] Vulnerabilities

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 withinthe IETF.[9] 

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[edit] See also

Computer networking portal  

Computer Science portal  

  Outline of the Internet   List of Internet topics   All IP   ATM   Connectionless protocol   Flat IP   Geolocation software   IANA   Internet   Internet Protocol Suite   Internet Stream Protocol   ip - the ip structure for the C programming language   IP address   IP fragmentation   IPv4 (including packet structure)   IPv4 address exhaustion   IPv6 (and packet structure)   List of IP protocol numbers   Packet   TCP and UDP port numbers   TDM   Transmission Control Protocol 

[edit] References

1.  ^ Siyan, Karanjit. Inside TCP/IP, New Riders Publishing, 1997. ISBN 1-56205-714-6 2.  ^ Basic Journey of a Packet 3.  ^ Netgear ProSafe XSM7224S reference manual4.  ^ Vinton G. Cerf, Robert E. Kahn, "A Protocol for Packet Network Intercommunication",

IEEE Transactions on Communications, Vol. 22, No. 5, May 1974 pp. 637-6485.  ^ CIO council adds to IPv6 transition primer, gcn.com

6. 

^ RFC 1606: A Historical Perspective On The Usage Of IP Version 9. April 1, 1994.7.  ^ Theregister.com 8.  ^ Security Assessment of the Internet Protocol (IP)[dead link ] 9.  ^ Security Assessment of the Internet Protocol version 4 (IPv4) 

[edit] External links

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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 

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