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This article is from:

All text is available under the terms of the GNU Free Documentation License: 

IP address

From Wikipedia, the free encyclopedia


An IP address (Internet Protocol address) is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)—in simpler terms, a computer address. Any participating network device—including routers, computers, time-servers, printers, Internet fax machines, and some telephones—can have their own unique address. Also, many people can find personal information through IP addresses.

An IP address can also be thought of as the equivalent of a street address or a phone number (compare: VoIP (voice over (the) internet protocol)) for a computer or other network device on the Internet. Just as each street address and phone number uniquely identifies a building or telephone, an IP address can uniquely identify a specific computer or other network device on a network.

An IP address can appear to be shared by multiple client devices either because they are part of a shared hosting web server environment or because a proxy server (e.g., an ISP or anonymizer service) acts as an intermediary agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request. The analogy to telephone systems would be the use of predial numbers (proxy) and extensions (shared).

IP addresses are managed and created by the Internet Assigned Numbers Authority. IANA generally allocates super-blocks to Regional Internet Registries, who in turn allocate smaller blocks to Internet service providers and enterprises.

IP versions

The Internet Protocol has two primary versions in use. Each version has its own definition of an IP address. Because of its prevalence, "IP address" typically refers to those defined by IPv4.

IP version 4

Main article: IPv4 (Addressing)

IPv4 only uses 32-bit (4 byte) addresses, which limits the address space to 4,294,967,296 (232) possible unique addresses. However, many are reserved for special purposes, such as private networks (~18 million addresses) or multicast addresses (~1 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses, and as the number of addresses available is consumed, an IPv4 address shortage appears to be inevitable in the long run. This limitation has helped stimulate the push towards IPv6, which is currently in the early stages of deployment and is currently the only contender to replace IPv4.

Example: (Loopback)

IP version 5

Main article: IPv5

What would be considered IPv5 existed only as an experimental non-IP real time streaming protocol called ST2, described in RFC 1819. In keeping with standard UNIX release conventions, all odd-numbered versions are considered experimental, and this version was never intended to be implemented, thus not abandoned. RSVP has replaced it to some degree.

IP version 6

Main article: IPv6 (Addressing)

IPv6 is the new standard protocol for the Internet. Windows Vista and an increasing range of Linux distibutions include native support for the protocol, but it is not yet widely deployed elsewhere.

Addresses are 128 bits (16 bytes) wide, which, even with a generous assignment of netblocks, will more than suffice for the foreseeable future. In theory, there would be exactly 2128, or about 3.403 × 1038 unique host interface addresses. Further, this large address space will be sparsely populated, which makes it possible to again encode more routing information into the addresses themselves.

One source[1] notes that there will exist "roughly 5,000 addresses for every square micrometer of the Earth's surface". This enormous magnitude of available IP addresses will be sufficiently large for the indefinite future, even though mobile phones, cars and all types of personal devices are coming to rely on the Internet for everyday purposes.

Example: 2001:0db8:85a3:08d3:1319:8a2e:0370:7334

IP version 6 private addresses

Just as there are addresses for private, or internal networks in IPv4 (one example being the - range), there are blocks of addresses set aside in IPv6 for private addresses. Addresses starting with FE80: are called link-local addresses and are routable only on your local link area. This means that if several hosts connect to each other through a hub or switch then they would communicate through their link-local IPv6 address.

Early designs specified an address range used for "private" addressing, with prefix FEC0:, however this is no longer the case. These are called site-local addresses and are routable within a particular site, analogously to IPv4 private addresses. Neither site- nor link-local address ranges are routable over the internet.

With IPv6, virtually every device in the world can have an IP address: cars, refrigerators, lawnmowers and so on. If one's refrigerator stopped working, for example, a repair specialist could identify the problem without ever visiting in person. Depending on the severity of the problem it might even be possible to make repairs remotely.

IP address legality in Europe

It is important to note that unlike the US, under European Union law IP Addresses are considered to be personal data as defined by article 2(a) of Directive 95/46/EC " 'personal data' shall mean any information relating to an identified or identifiable natural person ('data subject'); an identifiable person is one who can be identified, directly or indirectly, in particular by reference to an identification number or to one or more factors specific to his physical, physiological, mental, economic, cultural or social identity; " Also see Directive 2006/24/EC.

In association with Time Codes, IP Addressing information will always identify unique ISP account holders unless there is translation of that information.

It is important that this significant difference in legal status be understood, because Websites that provide for third-party interception of IP addressing information and Traffic Data, without Website visitor consent, are committing a criminal offence in the UK by virtue of the Regulation of Investigatory Powers Act 2000, where through the requirements of European Council Decision 2005/222/JHA such Website owners face serious sanctions, including the winding up of their businesses, being debarred from running a business, and more than 2 years imprisonment.

  • Directive 95/46/EC
  • Directive 2006/24/EC
  • European Council Framework Decision 2005/222/JHA
  • the Regulation of Investigatory Powers Act 2000

To access EU documents it may be necessary to register with the Eur-Lex Website at

See also

  • Ping
  • IP Multicast
  • MAC address
  • Regional Internet Registry
    • African Network Information Center
    • American Registry for Internet Numbers
    • RIPE Network Coordination Centre
    • Asia-Pacific Network Information Centre
    • Latin American and Caribbean Internet Addresses Registry
  • Subnet address
  • Geolocation
  • Geolocation software
  • Country IP database
  • Geo (marketing)
  • Honeypot
  • Data mining
  • IP address spoofing
  • Help:Page history: your IP in the Wikipedia page histories.
  • Private network

External links

  • IP at the Open Directory Project (suggest site)
  • Articles on CircleID about IP addressing
  • IP-Address Management on LANs — article in Byte magazine
  • Understanding IP Addressing: Everything You Ever Wanted To Know


  • IPv4 addresses: RFC 791, RFC 1519, RFC 1918
  • IPv6 addresses: RFC 4291


  1. ^ Article in MIT magazine Technology Review introducing IPv6
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