IP address 14921 225938136 2008-07-16T02:52:33Z Amnuay 2298836 /* IPv4 address networks */ {{citations missing|article|date=November 2007}} An [[Internet Protocol]] ('''IP''') '''address''' is a numerical identification ([[logical address]]) that is assigned to devices participating in a [[computer network]] utilizing the [[Internet Protocol]] for communication between its nodes.<ref name="rfc760">RFC 760, {{cite web |url=http://www.ietf.org/rfc/rfc0760.txt |title=DOD Standard Internet Protocol |accessdate=2008-07-08 |work=DARPA Request For Comments |publisher=[[Internet Engineering Task Force]] |date=January 1980}}</ref> Although IP addresses are stored as [[binary number]]s, they are often displayed in more [[human-readable]] notations, such as 192.168.100.1 (for [[IPv4]]), and 2001:db8:0:1234:0:567:1:1 (for [[IPv6]]). The role of the IP address has been characterized as follows: "A [[hostname|name]] indicates what we seek. An address indicates where it is. A route indicates how to get there." <ref name="rfc791">RFC 791, {{cite web |url=http://www.ietf.org/rfc/rfc791.txt |title=Internet Protocol |accessdate=2008-07-08 |work=DARPA Request For Comments |publisher=[[Internet Engineering Task Force]] |pages=6 |date=September 1981 }}</ref> Originally, an IP address was defined as a [[32-bit]] number<ref name="rfc760" /> and this system, now named [[IPv4|Internet Protocol Version 4]] (IPv4), is still in use today. However, due to the enormous growth of the Internet and the resulting depletion of the address space, a new addressing system ([[IPv6]]), using 128 bits for the address, had to be developed.<ref name="rfc1883">RFC 1883, {{cite web |url=http://www.ietf.org/rfc/rfc1883.txt |title=Internet Protocol, Version 6 (IPv6) Specification |accessdate=2008-07-08 |work=DARPA Request For Comments |publisher=[[Internet Engineering Task Force]] |date=December 1995}}</ref> IPv6 is now being deployed across the world; in many places it coexists with the old standard and is transmitted over the same hardware and network links. The Internet Protocol also is responsible for [[routing]] data [[packet (information technology)|packet]]s between networks, and IP addresses specify the locations of the source and destination nodes in the [[Network topology|topology]] of the [[routing]] system. For this purpose, some of the bits in an IP address are used to designate a [[subnetwork]]. (In [[Classless Inter-Domain Routing|CIDR]] notation, the number of bits used for the subnet follows the IP address. E.g. ''192.168.100.1/16'') An IP address can be ''private'', for use on a [[Local area network|LAN]], or ''public'', for use on the Internet or other [[Wide area network|WAN]]. In early specifications, IP addresses were intended to be uniquely assigned to a particular computer or device.{{Fact|date=July 2008}} However, it was found that this was not always necessary as [[private network]]s developed and address space needed to be conserved ([[IPv4 address exhaustion]]). RFC 1918 specifies private address spaces that may be reused by anyone; today, such private networks typically access the Internet through [[Network Address Translation]] (NAT). In addition, technologies such as [[anycast]] addressing have been developed to allow multiple hosts at the same IP address but in different portions of the Internet to service requests by network clients. The global IP address space is managed by the [[Internet Assigned Numbers Authority]] (IANA). IANA works in cooperation with five [[Regional Internet Registries]] (RIRs) to allocate IP address blocks to [[Local Internet Registry|Local Internet Registries]] (Internet service providers) and other entities. ==IP versions== The Internet Protocol (IP) has two versions currently in use (see [[Internet Protocol#Version history|IP version history]] for details). Each version has its own definition of an IP address. Because of its prevalence, "IP address" typically refers to those defined by [[IPv4]]. [[Image:Ipv4 address.svg|right|300px|thumb|An illustration of an IP address (version 4), in both [[dot-decimal notation]] and [[binary numeral system|binary]].]] ===IP version 4 addresses=== {{main|IPv4#Addressing}} IPv4 uses 32-[[bit]] (4-[[byte]]) addresses, which limits the [[address space]] to 4,294,967,296 (2<sup>32</sup>) possible unique addresses. However, some are reserved for special purposes such as [[private network]]s (~18 million addresses) or [[multicast address]]es (~270 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#Exhaustion|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. IPv4 addresses are usually represented in [[dot-decimal notation|dotted-decimal notation]] (four numbers, each ranging from 0 to 255, separated by dots, e.g. 147.132.42.18). Each range from 0 to 255 can be represented by 8 bits, and is therefore called an ''[[octet (computing)|octet]]''. It is possible, although less common, to write IPv4 addresses in [[binary numeral system|binary]] or [[hexadecimal]]. When converting, each octet is treated as a separate number. (So 255.255.0.0 in dot-decimal would be FF.FF.00.00 in hexadecimal.) ====IPv4 address networks ==== In the early stages of development of the Internet protocol, <ref name="rfc760" /> IP addresses were interpreted as structures of network numbers and host numbers, with the highest order octet (first eight bits) of an IP address designating the "network number", and the rest of the bits (called the "rest" field) used for host numbering within a network. This method soon proved inadequate as local area networks developed that were not part of the larger networks already designated by a network number. In [[1981]] IP protocol specification was revised with the introduction of the [[classful network]] architecture. <ref name="rfc791" /> Classful network design allowed for a larger number of individual allocations. The first three bits of the most significant octet of an IP address were used to imply the "class" of the address instead of just the network number and, depending on the class derived, the network designation was based on octet boundary segments of the entire address. The following table gives an overview of this system. {| class="wikitable" |- |- ! Class ! First octet in binary ! Range of first octet ! Network ID ! Host ID ! Possible number of networks ! Possible number of hosts |- ! A | 0XXXXXXX | 0 - 127 | a | b.c.d | 128 = (2<sup>7</sup>) | 16,777,214 = (2<sup>24</sup> - 2) |- ! B | 10XXXXXX | 128 - 191 | a.b | c.d | 16,384 = (2<sup>14</sup>) | 65,534 = (2<sup>16</sup> - 2) |- ! C | 110XXXXX | 192 - 223 | a.b.c | d | 2,097,152 = (2<sup>21</sup>) | 254 = (2<sup>8</sup> - 2) |} For details on design and use see '[[Subnetwork]]' and '[[classful network]]'. While being a successful developmental stage, classful network design proved [[Scalability|unscalable]] in the rapid expansion of the Internet and was abandoned in [[1993]] when [[Classless Inter-Domain Routing]] (CIDR) was introduced (RFC 1517, RFC 1518, RFC 1519) to define a new concept of allocation of IP address blocks and new methods of routing protocol packets using IPv4 addresses. CIDR is based on variable-length subnet masking (VLSM) to allow allocation on arbitrary-length prefixes. Today, remnants of classful network concepts are used only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask). ====IPv4 private addresses==== {{main|Private network}} Computers not connected to the Internet (e.g., factory machines that communicate with each other via TCP/IP) need not have globally-unique IP addresses. Three ranges of IPv4 addresses for [[private network]]s, one range for each [[classful network|class]], were reserved in RFC 1918; these addresses are not routed on the Internet, and thus need not be coordinated with an IP address registry. {| class="wikitable" ! IANA Reserved Private Network Ranges ! Start of range ! End of range ! Total addresses |- ! 24-bit Block (/8 prefix, A) | 10.0.0.0 | 10.255.255.255 | 16,777,216 |- ! 20-bit Block (/12 prefix, B) | 172.16.0.0 | 172.31.255.255 | 1,048,576 |- ! 16-bit Block (/16 prefix, C) | 192.168.0.0 | 192.168.255.255 | 65,536 |- |} Each block may be used as needed by anyone and typically a network administrator will divide a block into [[subnetwork|subnets]]; for example, many [[residential gateway|home routers]] automatically use a default address range of 192.168.0.0 - 192.168.0.255 (192.168.0.0/24). === IP version 6 addresses === {{main|IPv6#Addressing}} [[Image:Ipv6 address.svg|right|300px|thumb|An illustration of an IP address (version 6), in [[hexadecimal]] and [[binary]].]] IPv6 is the next generation of the Internet Protocol, designed to replace IPv4 on the Internet.<ref name="rfc1883" /> Addresses are 128 [[bits]] (16 [[bytes]]) wide, which, even with a generous assignment of network blocks, will more than suffice for the foreseeable future. The new address space provides a maximum of 2<sup>128</sup>, or about 3.403 &times; 10<sup>38</sup> unique addresses. The utilization of this large address space is designed in a fashion that provides more efficient route aggregation across the network world-wide. Example of an IPv6 address: 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 Writing for ''[[Technology Review]]'' in 2004, [[Simson Garfinkel]] wrote that there will exist "roughly 5,000 addresses for every square [[Micrometre|micrometer]] of the Earth's surface".<ref name=Garfinkel>{{cite news|author=Garfinkel, Simson|title=Internet 6.0|url=http://www.technologyreview.com/Infotech/13426/?a=f|date=[[January 7]], [[2004]]|publisher=Masschusetts Institute of Technology via Technology Review|accessdate=2007-11-12}}</ref> 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. The above statement, however, involves a common misconception about the IPv6 architecture. Its large address space is not intended to provide unique addresses for every possible point. Rather, the addressing architecture is such that it allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for providing efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in [[classless inter-domain routing]] (CIDR). [[Windows Vista]], [[Apple Computer]]'s [[Mac OS X]], all modern [[Linux distribution]]s<ref>{{cite web |url=http://www.ipv6.org/impl/linux.html |title=Linux IPv6 Implementation |accessdate=2008-06-06 |publisher=ipv6.org |date=2003-03-20 }}</ref>, and an increasing range of other operating systems include native support for the protocol, but it is not yet widely deployed in other devices. ==== IPv6 private addresses ==== Just as there are addresses for private, or internal networks in IPv4, there are blocks of addresses set aside in IPv6 for private addresses. In IPv6, these are referred to as unique local addresses (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block. The addresses include a 40-bit pseudorandom number that minimize the risk of address collisions if sites merge or packets are misrouted. Early designs (RFC 3513) used a different block for this purpose (fec0::), dubbed site-local addresses. However, the definition of what constituted 'sites' was unclear, and the poorly defined address structure created ambiguities for routing. The address range specification was abandoned and must no longer be used in new systems. Addresses starting with fe80: are called link-local addresses and are routable only in the local link area. The addresses are assigned automatically by the operating system's IP layer for each network interface. This provides instant network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have an instant communication path via their link-local IPv6 address. None of the private address prefixes may be routed in the public Internet. ==IP address subnetworks== {{main|Subnetwork}} [[subnetwork|Subnetting]] is a technique that can be used in both IPv4 and IPv6 networks. The IP address is divided into two parts: the ''network address'' and the ''host address''. The [[subnetwork#Binary subnet masks|subnet mask]] determines how the IP address is divided into network and host parts. As an alternative to the ''subnet mask'', [[CIDR]] notation can also be used. In CIDR notation, the IP address is followed by a slash and the number of bits used to designate the prefix length, i.e., the network part. For example, a typical IP address and its subnet mask may be '''192.0.2.1''' and '''255.255.255.0''', respectively. The CIDR notation for the same IP address and subnet is '''192.0.2.1/24''', because the first 24 bits of the IP address indicate the [[subnetwork]]. ==Static and dynamic IP addresses== When a computer is manually configured to use the same IP address each time it powers up, this is known as a ''Static IP address''. In contrast, in situations when the computer's IP address is assigned automatically, it is known as a ''Dynamic IP address.'' ===Method of assignment=== Static IP addresses are manually assigned to a computer by an administrator. The exact procedure varies according to platform. This contrasts with dynamic IP addresses, which are assigned either randomly (by the computer itself, as in [[Zeroconf]]), or assigned by a server using [[Dynamic Host Configuration Protocol]] (DHCP). Even though IP addresses assigned using DHCP may stay the same for long periods of time, they can generally change. In some cases, a network administrator may implement dynamically assigned static IP addresses. In this case, a DHCP server is used, but it is specifically configured to always assign the same IP address to a particular computer, and never to assign that IP address to another computer. This allows static IP addresses to be configured in one place, without having to specifically configure each computer on the network in a different way. In the absence of both an administrator (to assign a static IP address) and a DHCP server, the operating system may assign itself an IP address using state-less autoconfiguration methods, such as [[Zeroconf]]. These IP addresses are known as [[link-local address]]es. For IPv4, link-local addresses are in the 169.254.0.0/16 address range. In [[IPv6]], every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the fe80::/64 subnet. ===Uses of dynamic addressing=== Dynamic IP Addresses are most frequently assigned on LANs and broadband networks by [[Dynamic Host Configuration Protocol]] (DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows many devices to share limited address space on a network if only some of them will be online at a particular time. In most current desktop operating systems, dynamic IP configuration is enabled by default so that a user does not need to manually enter any settings to connect to a network with a DHCP server. DHCP is not the only technology used to assigning dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the [[Point-to-Point Protocol]]. ===Uses of static addressing=== Static addressing is essential in some infrastructure situations, such as finding the [[Domain Name Service]] directory host that will translate [[Domain name system|domain names]] to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a [[time to live]], or [[Domain Name System#Caching time|caching time]], after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072). == Modifications to IP addressing == === IP blocking and firewalls === {{main|IP blocking|Firewall}} [[Firewall]]s are common on today's Internet. For increased network security, they control access to [[private network]]s based on the public IP of the client. Whether using a [[blacklist (computing)|blacklist]] or a [[whitelist]], the IP address that is blocked is the perceived public IP address of the client, meaning that if the client is using a [[proxy server]] or [[Network Address Translation|NAT]], blocking one IP address might block many individual people. === IP address translation === {{main|Network Address Translation}} IP addresses can appear to be shared by multiple client devices either because they are part of a [[shared hosting]] [[web server]] environment or because an IPv4 [[network address translator]] (NAT) or [[proxy server]] 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]]. A common practice is to have a NAT hide a large number of IP addresses in a [[private network]]. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses<ref>Comer pg.394</ref>. Most commonly, the NAT device maps TCP or UDP port numbers on the outside to individual private addresses on the inside. Just as there may be site-specific extensions on a telephone number, the port numbers are site-specific extensions to an IP address. In small home networks, NAT functions are usually performed by a [[residential gateway]] device, typically one marketed as a "router". In this scenario, the computers connected to the router would have 'private' IP addresses and the router would have a 'public' address to communicate with the Internet. This type of router allows several computers to share one public IP address. ==See also== <div style="-moz-column-count:3; column-count:3;"> *[[Classful network]] *[[Country IP database]] *[[Data mining]] *[[Geo (marketing)]] *[[Geolocation]] *[[Geolocation software]] *[[Help:Page history]]: your IP in the Wikipedia page histories. *[[Honeypot (computing)|Honeypot]] *[[Internet]] *[[IP address spoofing]] *[[IP blocking]] *[[IP Multicast]] *[[IP2Location]] *[[List of assigned /8 IP address blocks]] *[[MAC address]] *[[PING]] *[[Private network]] *[[Provider Aggregatable Address Space]] *[[Provider Independent Address Space]] *[[Regional Internet Registry]] **[[AfriNIC|African Network Information Center]] **[[American Registry for Internet Numbers]] **[[Asia-Pacific Network Information Centre]] **[[Latin American and Caribbean Internet Addresses Registry]] **[[RIPE NCC|RIPE Network Coordination Centre]] *[[Subnetwork|Subnet address]] *[[Virtual IP address]] </div> ==References== *{{cite book | last =Comer | first =Douglas | title =Internetworking with TCP/IP:Principles, Protocols, and Architectures --4th ed. | publisher =Prentice Hall | date =2000 | location =Upper Saddle River, NJ | url =http://www.cs.purdue.edu/homes/dec/netbooks.html | doi = | id = | isbn =0-13-018380-6 }} {{reflist}} <!-- Before you add new external links here, please make sure it points to information about IP addresses, and not to services offering IP location, etc. Especially, simple IP lookup tools are a dime a dozen and this article has decided not to list any of them. Please discuss new additions on the talk page first so your link won't be treated as yet another spam. Thank you. --> ==External links== * {{dmoz|Computers/Internet/Protocols/IP/|IP}} which includes sites that let you find your IP address <!-- Please do not add links for finding out your IP address. This article is *about* IP addresses, not a newbie guide on how to find yours. The above DMOZ link should be a good starting point. As the majority of external links added here end up being removed, you are HIGHLY advised to take it up on the TALK PAGE before adding a link. --> *[http://www.circleid.com/topics/ip_addressing Articles on CircleID about IP addressing] *[http://www.byte.com/art/9602/sec16/art4.htm IP-Address Management on LANs] &mdash; article in ''[[Byte (magazine)|Byte]]'' magazine *[http://www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf Understanding IP Addressing: Everything You Ever Wanted To Know] *[http://corz.org/comms/hardware/router/static.ip.address.php How to get a static IP address - clear instructions for all the major platforms] *[http://www.ip2location.com/ip2location-internet-ip-address-2008-report.aspx Internet IP Address Allocation by Country 2008 Report] ===RFCs=== * IPv4 addresses: RFC 791, RFC 1519, RFC 1918, RFC 2071, RFC 2072 * IPv6 addresses: RFC 4291, RFC 4192 [[Category:Network addressing]] [[Category:Internet Protocol|Address]] [[af:IP-adres]] [[als:IP-Adresse]] [[ar:عنوان آي.بي]] [[an:Adreza IP]] [[frp:Adrèce IP]] [[br:Ennegañ IP]] [[ca:Adreça IP]] [[cs:IP adresa]] [[da:IP-adresse]] [[de:IP-Adresse]] [[et:IP-aadress]] [[el:Διεύθυνση IP]] [[es:Dirección IP]] [[eo:IP-adreso]] [[eu:IP helbide]] [[fa:نشانی پروتکل اینترنت]] [[fo:IP-adressa]] [[fr:Adresse IP]] [[ga:Seoladh IP]] [[gu:IP address]] [[ko:IP 주소]] [[hr:IP broj]] [[id:Alamat IP]] [[is:Vistfang]] [[it:Indirizzo IP]] [[he:כתובת IP]] [[ka:IP-მისამართი]] [[lt:IP adresas]] [[li:IP-adres]] [[ln:Limelo lia protokɔ́le ya ɛtɛrnɛ́tɛ]] [[hu:IP-cím]] [[mi:Nohoanga kawa ipurangi]] [[ms:Alamat IP]] [[nl:IP-adres]] [[ja:IPアドレス]] [[no:IP-adresse]] [[nn:IP-adresse]] [[oc:Adreça IP]] [[pl:Adres IP]] [[pt:Endereço IP]] [[ksh:IP-Nummer]] [[ro:Adresă IP]] [[ru:IP-адрес]] [[sq:Adresa IP]] [[scn:Nnirizzu IP]] [[sk:IP adresa]] [[sl:IP-naslov]] [[sr:ИП адреса]] [[sh:IP adresa]] [[fi:IP-osoite]] [[sv:IP-adress]] [[ta:இ.நெறி முகவரி]] [[kab:Tansa IP]] [[th:หมายเลขไอพี]] [[vi:Địa chỉ IP]] [[tr:IP adresi]] [[uk:IP-адреса]] [[ur:دستورشبکی پتا]] [[yi:IP אדרעס]] [[bat-smg:IP adrėsas]] [[zh:IP地址]]