Difference between revisions of "IP адрес"

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IP адресът е уникален номер, много наподобяващ телефонен номер, който се използва от машини (обикновено компютри), за да се свързват едни с други, когато изпращат информация през Интернет или локална мрежа, използвайки Интернет протокол (IP). Той позволява на машините, които предават информацията, да знаят къде да я изпращат, а на машините, които получават информацията, да знаят, че тя идва от желаното местоназначение.
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== Термини ==
  
Интернет протоколът (IP) разпознава логическите интерфейси на хостове по номер, наричан IP адрес. В дадена мрежа този номер трябва да е уникален за всеки от хостовете, които осъществяват връзки в тази мрежа. Доставчиците на Интернет услуги понякога дават на някои потребители на Интернет и име на хост в допълнение към техния цифров IP адрес.
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*LIR - local Internet Registry
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*RIR - regional Internet registry
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*[[IPv6]] - Интернет протокол версия 6
  
IP адресите на потребителите, които сърфират в световната мрежа (World Wide Web,) се използват при осъществявaне на връзките им със сървърите на уеб сайтовете. Също така, в заглавната част на съобщенията от електронната поща обикновено се записват IP адресите на пощенските сървъри, откъдето изпращаме пощата. В зависимост от връзката на даден потребител с Интернет, IP адресът може да бъде един и същ всеки път, когато той се свързва с Интернет – статичен IP адрес, или различен за всяка сесия (но първата му част си остава същата) – динамичен IP адрес.
 
  
IP адресите служат не само за уникалното обозначаване на интерфейсите на хостовете, но и за маршрутизиране, поради което голяма част от тях са неизползваеми или запазени...
 
IP версия 4 [редактиране]
 
Основна статия: IPv4
 
Адресиране [редактиране]
 
  
При IPv4, понастоящем стандартен протокол за Интернет, IP адресите са съставени от 32 бита, което прави теоретично 4 294 967 296 (над 4 милиарда) уникални адреси за интерфейси на хостове. На практика обаче, адресното пространство не се оползотворява напълно поради проблемите на маршрутизирането, така че има натиск за разширяване на адресния обхват чрез IP версия 6 (вижте по-долу).
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An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2]
  
IPv4 адресите обикновено се отбелязват като четворка числа, разделени с точки, т.е. четири байта (по 8 бита), разделени с точки и написани като десетични числа. Например, хостът, известен като www.bg.wikipedia.org, понастоящем има номер [3482223596] (десетично число), което се записва като 207.142.131.204. Тези числа се получават чрез преобразуване в бройна система с основа 256:
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The designers of the Internet Protocol defined an IP address as a 32-bit number[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new version of IP (IPv6), using 128 bits for the address, was developed in 1995.[3] IPv6 was standardized as RFC 2460 in 1998,[4] and its deployment has been ongoing since the mid-2000s.
  
3482223596 = 207*2563+142*2562+131*2561+236*2560. Преобразуването на името „www.wikipedia.org“ в съответния номер е направено от DNS-сървърите.
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IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).
  
Първоначално IPv4 адресите са имали само две части (пълнокласна мрежа). По-късно частите стават три: част за мрежа, част подмрежова и част за хост, в тази последователност. Обаче с появата на безкласово вътредомейноново маршрутизиране (CIDR) това вече не е валидно и адресът може да има произволен брой йерархични нива. (За момента няма наложил се превод на Classless Inter-Domain Routing). Технически погледнато, това става възможно още при появата на подмрежите, тъй като даден сайт може да има повече от едно ниво на подмрежи в рамките на съответния клас IP адреси).
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The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.Contents  [hide]
Даване на IP адрес [редактиране]
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1 IP versions
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1.1 IPv4 addresses
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1.1.1 IPv4 subnetting
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1.1.2 IPv4 private addresses
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1.2 IPv4 address exhaustion
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1.3 IPv6 addresses
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1.3.1 IPv6 private addresses
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2 IP subnetworks
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3 IP address assignment
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3.1 Methods
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3.2 Uses of dynamic addressing
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3.2.1 Sticky dynamic IP address
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3.3 Address autoconfiguration
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3.4 Uses of static addressing
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4 Public addresses
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5 Modifications to IP addressing
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5.1 IP blocking and firewalls
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5.2 IP address translation
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6 Diagnostic tools
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7 See also
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8 References
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9 External links
  
IP адресите не се дават произволно. Нуждаещата се организация, примерно доставчик на Интернет услуги, подава заявка за „блок IP адреси“ (netblock) до някоя регистрираща организация, например Американски регистър за Интернет номера (ARIN). Блокът IP адреси съдържа множество адреси, които организацията е свободна да разпределя по свое усмотрение. Ако организацията, привърши адресите от заделеното ѝ адресно пространство, може да подаде заявка за друг „блок IP адреси“.
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IP versions
  
Например, ARIN са заделили адресите от 64.78.200.0 до 64.78.207.255 на Verado, Inc. От своя страна Verado заделя адресите от 64.78.205.0 до 64.78.205.15 на Bomis. А Bomis пък дава точно определен адрес, 64.78.205.6, на интерфейса на хоста, носещ името www.wikipedia.com.
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Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.
Изчерпване [редактиране]
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IPv4 addresses
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Main article: IPv4#Addressing
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Decomposition of an IPv4 address from dot-decimal notation to its binary value.
  
Някои групи адреси са заделени чрез RFC 1918 за частни IP адреси. Това означава, че тези адреси са достъпни за употреба от който и да е потребител, поради което едни и същи IP адреси от RFC 1918 могат да се използват в много мрежи. Обаче тези адреси не подлежат на маршрутизиране в Интернет. Те са широко използвани поради недостиг на регистрируеми (реални) IP адреси. Мрежи, които използват такива адреси, се нуждаят от превод на мрежовите адреси (NAT), за да се свържат с Интернет.
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In IPv4 an address consists of 32 bits which limits the address space to 4294967296 (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses).
  
Въпреки редицата мерки за икономисване на IPv4 адресите (като например, използване на NAT и частни IP адреси), броят на 32-битовите IP адреси е недостатъчен, за да поеме бъдещото разрастване на Интернет. Поради тази причина вече има общо съгласие, че в близките 5 до 15 години трябва да се възприеме 128-битова схема за адресиране в Интернет.
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IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations.
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IPv4 subnetting
  
Вижте също: Изчерпване на IPv4 адресите
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In the early stages of development of the Internet Protocol,[1] network administrators interpreted an IP address in two parts: network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier and were used for host numbering within a network.
IP версия 5 [редактиране]
 
  
Какво е щяло да се разбира под IPv5, е съществувало само като експериментален не-IP поточен протокол в реално време, наречен ST2 (Internet Stream Protocol version 2), описан в RFC 1819. Този протокол е използвал числото 5 в полето за версия в хедъра на IP протокола, затова и версията се представя като IPv5. Въпреки това той никога не е бил самостоятелна версия на самия IP протокол. Този протокол е изоставен в полза на RSVP (виж. Интегрирани услуги).
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This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.[2]
IP версия 6 [редактиране]
 
Основна статия: IPv6
 
  
При IPv6, новият (но все още не широко използван) стандартен протокол за Интернет, адресите са 128-битови, което означава, че дори и при щедро даване на „нетблокове“, ще са достатъчни в обозримото бъдеще. Теоретично уникалните адреси са 18 445 618 199 572 250 625 (точно 264, или около 1,845*1019). Това огромно адресно пространство ще бъде рядко населено, което прави възможно отново да се кодира повече информация за маршрутизирането в самите адреси.
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Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the class of the address. Three classes (A, B, and C) were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (B and C). The following table gives an overview of this now obsolete system.
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Historical classful network architectureClass Leading bits in address (binary) Range of first octet (decimal) Network ID format Host ID format Number of networks Number of addresses per network
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A 0 0–127 a b.c.d 27 = 128 224 = 16777216
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B 10 128–191 a.b c.d 214 = 16384 216 = 65536
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C 110 192–223 a.b.c d 221 = 2097152 28 = 256
  
Адресът от версия 6 се записва с осем 4-цифрени (16-битови) шестнадесетични числа, разделени с двоеточия. Един низ от нули може да се прескочи, така че 1080::800:0:417A е същото, което и 1080:0:0:0:0:800:0:417A.
 
  
Глобалните уникални IPv6 адреси се състоят от две части: 64-битова маршрутизираща част, следвана от 64-битов идентификатор на хоста.
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Classful network design served its purpose in the startup stage of the Internet, but it lacked scalability in the face of the rapid expansion of the network in the 1990s. The class system of the address space was replaced with Classless Inter-Domain Routing (CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes.
  
„Нетблоковете“ се характеризират като модерна алтернатива на IPv4: мрежов номер, следван от наклонена надясно черта и броят на съответните битове в мрежовия номер (с десетично число). Пример: 12AB::CD30:0:0:0:0/60 включва всички адреси, започващи с 12AB00000000CD3.
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Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.
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IPv4 private addresses
  
Освен по-голямото адресно пространство, IPv6 има много други подобрения спрямо IPv4, като автоматично преномериране и повишена сигурност чрез задължително използване на стандарта IPsec.
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Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.
  
Допълнителна информация: Internet RFC, включително RFC 791, RFC 1519 (IPv4 адреси), и RFC 2373 (IPv6 адреси).
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Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.
  
Да вземем за пример IP адреса 207.142.131.236. Получаването на тези числа от домейн адреси, написани в една по-разбираема за човека форма, като например www.wikipedia.org, се извършва от Система за имена на домейни (DNS). Този процес е известен като преобразуване на имената на домейни към IP адрес. (Забележка: Система за имена на домейни е общо понятие, обхващащо всичките Сървъри за имена на домейни)
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Today, when needed, such private networks typically connect to the Internet through network address translation (NAT).
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IANA-reserved private IPv4 network ranges Start End No. of addresses
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24-bit block (/8 prefix, 1 × A) 10.0.0.0 10.255.255.255 16777216
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20-bit block (/12 prefix, 16 × B) 172.16.0.0 172.31.255.255 1048576
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16-bit block (/16 prefix, 256 × C) 192.168.0.0 192.168.255.255 65536
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Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255 (192.168.0.0/24).
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IPv4 address exhaustion
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IPv4 address exhaustion is the decreasing supply of unallocated Internet Protocol Version 4 (IPv4) addresses available at the Internet Assigned Numbers Authority (IANA) and the regional Internet registries (RIRs) for assignment to end users and local Internet registries, such as Internet service providers. IANA's primary address pool was exhausted on 3 February 2011, when the last 5 blocks were allocated to the 5 RIRs.[5][6] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, intended to be allocated in a restricted process.[7]
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IPv6 addresses
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Main article: IPv6 address
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Decomposition of an IPv6 address from hexadecimal representation to its binary value.
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The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, intended to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6 (IPv6) in 1995.[3][4] The address size was increased from 32 to 128 bits or 16 octets. This, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2128, or about 3.403×1038 unique addresses.
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The new design is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 264 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or renumbering.
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The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in CIDR.
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Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over IP (VoIP) and multimedia equipment, and network peripherals.
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IPv6 private addresses
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Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are 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 which is divided into two /8 blocks with different implied policies. The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.[8]
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Early designs used a different block for this purpose (fec0::), dubbed site-local addresses.[9] However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. This address range specification was abandoned and must not be used in new systems.[10]
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Addresses starting with fe80:, called link-local addresses, are assigned to interfaces for communication on the link only. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have a communication path via their link-local IPv6 address. This feature is used in the lower layers of IPv6 network administration (e.g. Neighbor Discovery Protocol).
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None of the private address prefixes may be routed on the public Internet.
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IP subnetworks
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IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the network prefix and the host identifier, or interface identifier (IPv6). The subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts.
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The term subnet mask is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 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 network and subnet.
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IP address assignment
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Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a dynamic IP address.
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Methods
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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 by the computer interface or host software 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. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure.
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In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less auto-configuration methods, such as Zeroconf.
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Uses of dynamic addressing
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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 assign dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol.
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Sticky dynamic IP address
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A sticky dynamic IP address is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address which seldom changes. The addresses are usually assigned with DHCP. Since the modems are usually powered on for extended periods of time, the address leases are usually set to long periods and simply renewed. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.
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Address autoconfiguration
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RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the block fe80::/10.
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These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.
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When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses.
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Uses of static addressing
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Some infrastructure situations have to use static addressing, such as when finding the Domain Name System (DNS) host that will translate 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 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).
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Public addresses
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A public IP address, in common parlance, is synonymous with a globally routable unicast IP address.[citation needed]
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Both IPv4 and IPv6 define address ranges that are reserved for private networks and link-local addressing. The term public IP address often used excludes these types of addresses.

Latest revision as of 12:48, 22 January 2013

Термини

  • LIR - local Internet Registry
  • RIR - regional Internet registry
  • IPv6 - Интернет протокол версия 6


An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2]

The designers of the Internet Protocol defined an IP address as a 32-bit number[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new version of IP (IPv6), using 128 bits for the address, was developed in 1995.[3] IPv6 was standardized as RFC 2460 in 1998,[4] and its deployment has been ongoing since the mid-2000s.

IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).

The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.Contents [hide] 1 IP versions 1.1 IPv4 addresses 1.1.1 IPv4 subnetting 1.1.2 IPv4 private addresses 1.2 IPv4 address exhaustion 1.3 IPv6 addresses 1.3.1 IPv6 private addresses 2 IP subnetworks 3 IP address assignment 3.1 Methods 3.2 Uses of dynamic addressing 3.2.1 Sticky dynamic IP address 3.3 Address autoconfiguration 3.4 Uses of static addressing 4 Public addresses 5 Modifications to IP addressing 5.1 IP blocking and firewalls 5.2 IP address translation 6 Diagnostic tools 7 See also 8 References 9 External links

IP versions

Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5. IPv4 addresses Main article: IPv4#Addressing

Decomposition of an IPv4 address from dot-decimal notation to its binary value.

In IPv4 an address consists of 32 bits which limits the address space to 4294967296 (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses).

IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal, octal, or binary representations. IPv4 subnetting

In the early stages of development of the Internet Protocol,[1] network administrators interpreted an IP address in two parts: network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated as the network number and the remaining bits were called the rest field or host identifier and were used for host numbering within a network.

This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of classful network architecture.[2]

Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the class of the address. Three classes (A, B, and C) were defined for universal unicast addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (B and C). The following table gives an overview of this now obsolete system. Historical classful network architectureClass Leading bits in address (binary) Range of first octet (decimal) Network ID format Host ID format Number of networks Number of addresses per network A 0 0–127 a b.c.d 27 = 128 224 = 16777216 B 10 128–191 a.b c.d 214 = 16384 216 = 65536 C 110 192–223 a.b.c d 221 = 2097152 28 = 256


Classful network design served its purpose in the startup stage of the Internet, but it lacked scalability in the face of the rapid expansion of the network in the 1990s. The class system of the address space was replaced with Classless Inter-Domain Routing (CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes.

Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions. IPv4 private addresses

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved.

Computers not connected to the Internet, such as factory machines that communicate only with each other via TCP/IP, need not have globally unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.

Today, when needed, such private networks typically connect to the Internet through network address translation (NAT). IANA-reserved private IPv4 network ranges Start End No. of addresses 24-bit block (/8 prefix, 1 × A) 10.0.0.0 10.255.255.255 16777216 20-bit block (/12 prefix, 16 × B) 172.16.0.0 172.31.255.255 1048576 16-bit block (/16 prefix, 256 × C) 192.168.0.0 192.168.255.255 65536


Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255 (192.168.0.0/24). IPv4 address exhaustion

IPv4 address exhaustion is the decreasing supply of unallocated Internet Protocol Version 4 (IPv4) addresses available at the Internet Assigned Numbers Authority (IANA) and the regional Internet registries (RIRs) for assignment to end users and local Internet registries, such as Internet service providers. IANA's primary address pool was exhausted on 3 February 2011, when the last 5 blocks were allocated to the 5 RIRs.[5][6] APNIC was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, intended to be allocated in a restricted process.[7] IPv6 addresses Main article: IPv6 address

Decomposition of an IPv6 address from hexadecimal representation to its binary value.

The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, intended to replace IPv4 on the Internet, was eventually named Internet Protocol Version 6 (IPv6) in 1995.[3][4] The address size was increased from 32 to 128 bits or 16 octets. This, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2128, or about 3.403×1038 unique addresses.

The new design is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 264 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or renumbering.

The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is not the need to have complex address conservation methods as used in CIDR.

Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers, voice over IP (VoIP) and multimedia equipment, and network peripherals. IPv6 private addresses

Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are 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 which is divided into two /8 blocks with different implied policies. The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.[8]

Early designs used a different block for this purpose (fec0::), dubbed site-local addresses.[9] However, the definition of what constituted sites remained unclear and the poorly defined addressing policy created ambiguities for routing. This address range specification was abandoned and must not be used in new systems.[10]

Addresses starting with fe80:, called link-local addresses, are assigned to interfaces for communication on the link only. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have a communication path via their link-local IPv6 address. This feature is used in the lower layers of IPv6 network administration (e.g. Neighbor Discovery Protocol).

None of the private address prefixes may be routed on the public Internet. IP subnetworks

IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the network prefix and the host identifier, or interface identifier (IPv6). The subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts.

The term subnet mask is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 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 network and subnet. IP address assignment

Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a dynamic IP address. Methods

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 by the computer interface or host software 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. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure.

In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less auto-configuration methods, such as Zeroconf. 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 assign dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the Point-to-Point Protocol. Sticky dynamic IP address

A sticky dynamic IP address is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address which seldom changes. The addresses are usually assigned with DHCP. Since the modems are usually powered on for extended periods of time, the address leases are usually set to long periods and simply renewed. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address. Address autoconfiguration

RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the block fe80::/10.

These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. These addresses are not routable and like private addresses cannot be the source or destination of packets traversing the Internet.

When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft created an implementation that is called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a de facto standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled Dynamic Configuration of IPv4 Link-Local Addresses. Uses of static addressing

Some infrastructure situations have to use static addressing, such as when finding the Domain Name System (DNS) host that will translate 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 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). Public addresses

A public IP address, in common parlance, is synonymous with a globally routable unicast IP address.[citation needed]

Both IPv4 and IPv6 define address ranges that are reserved for private networks and link-local addressing. The term public IP address often used excludes these types of addresses.