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Prefix aggregation </div> </a> <ul id="toc-Prefix_aggregation-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> 7 See also </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> 8 References </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> 9 Further reading </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item 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Available in 27 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-27" aria-hidden="true" > 27 languages </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AA%D9%88%D8%AC%D9%8A%D9%87_%D8%A8%D9%8A%D9%86_%D9%86%D8%B7%D8%A7%D9%82%D9%8A_%D8%BA%D9%8A%D8%B1_%D8%B5%D9%86%D9%81%D9%8A" title="توجيه بين نطاقي غير صنفي – Arabic" lang="ar" hreflang="ar" data-title="توجيه بين نطاقي غير صنفي" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target">العربية</a></li><li class="interlanguage-link interwiki-an mw-list-item"><a href="https://an.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Aragonese" lang="an" hreflang="an" data-title="Classless Inter-Domain Routing" data-language-autonym="Aragonés" data-language-local-name="Aragonese" class="interlanguage-link-target">Aragonés</a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Catalan" lang="ca" hreflang="ca" data-title="Classless Inter-Domain Routing" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target">Català</a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Czech" lang="cs" hreflang="cs" data-title="Classless Inter-Domain Routing" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target">Čeština</a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – German" lang="de" hreflang="de" data-title="Classless Inter-Domain Routing" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target">Deutsch</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Spanish" lang="es" hreflang="es" data-title="Classless Inter-Domain Routing" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-fr badge-Q70893996 mw-list-item" title=""><a href="https://fr.wikipedia.org/wiki/CIDR" title="CIDR – French" lang="fr" hreflang="fr" data-title="CIDR" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target">Français</a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/CIDR" title="CIDR – Korean" lang="ko" hreflang="ko" data-title="CIDR" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target">한국어</a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/CIDR" title="CIDR – Croatian" lang="hr" hreflang="hr" data-title="CIDR" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target">Hrvatski</a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Indonesian" lang="id" hreflang="id" data-title="Classless Inter-Domain Routing" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target">Bahasa Indonesia</a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Italian" lang="it" hreflang="it" data-title="Classless Inter-Domain Routing" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target">Italiano</a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Bezklases_starpdom%C4%93nu_mar%C5%A1rut%C4%93%C5%A1ana" title="Bezklases starpdomēnu maršrutēšana – Latvian" lang="lv" hreflang="lv" data-title="Bezklases starpdomēnu maršrutēšana" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target">Latviešu</a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/CIDR" title="CIDR – Macedonian" lang="mk" hreflang="mk" data-title="CIDR" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target">Македонски</a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Dutch" lang="nl" hreflang="nl" data-title="Classless Inter-Domain Routing" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target">Nederlands</a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Japanese" lang="ja" hreflang="ja" data-title="Classless Inter-Domain Routing" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target">日本語</a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Classless Inter-Domain Routing" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target">Norsk bokmål</a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Polish" lang="pl" hreflang="pl" data-title="Classless Inter-Domain Routing" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target">Polski</a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Roteamento_entre_dom%C3%ADnios_sem_classes" title="Roteamento entre domínios sem classes – Portuguese" lang="pt" hreflang="pt" data-title="Roteamento entre domínios sem classes" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target">Português</a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%91%D0%B5%D1%81%D0%BA%D0%BB%D0%B0%D1%81%D1%81%D0%BE%D0%B2%D0%B0%D1%8F_%D0%B0%D0%B4%D1%80%D0%B5%D1%81%D0%B0%D1%86%D0%B8%D1%8F" title="Бесклассовая адресация – Russian" lang="ru" hreflang="ru" data-title="Бесклассовая адресация" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target">Русский</a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Simple English" lang="en-simple" hreflang="en-simple" data-title="Classless Inter-Domain Routing" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target">Simple English</a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/CIDR" title="CIDR – Serbian" lang="sr" hreflang="sr" data-title="CIDR" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target">Српски / srpski</a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Luokaton_reititys" title="Luokaton reititys – Finnish" lang="fi" hreflang="fi" data-title="Luokaton reititys" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target">Suomi</a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Swedish" lang="sv" hreflang="sv" data-title="Classless Inter-Domain Routing" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target">Svenska</a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/S%C4%B1n%C4%B1fs%C4%B1z_alanlar_aras%C4%B1_y%C3%B6nlendirme" title="Sınıfsız alanlar arası yönlendirme – Turkish" lang="tr" hreflang="tr" data-title="Sınıfsız alanlar arası yönlendirme" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target">Türkçe</a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/CIDR" title="CIDR – Ukrainian" lang="uk" hreflang="uk" data-title="CIDR" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target">Українська</a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Classless_Inter-Domain_Routing" title="Classless Inter-Domain Routing – Vietnamese" lang="vi" hreflang="vi" data-title="Classless Inter-Domain Routing" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target">Tiếng Việt</a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a 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class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Method for IP address allocation and routing</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"CIDR" redirects here. For other uses, see <a href="/wiki/CIDR_(disambiguation)" class="mw-disambig" title="CIDR (disambiguation)">CIDR (disambiguation)</a>.</div> Classless Inter-Domain Routing (CIDR <a href="/wiki/Help:IPA/English" title="Help:IPA/English">/ˈsaɪdər, ˈsɪ-/</a>) is a method for allocating <a href="/wiki/IP_address" title="IP address">IP addresses</a> for <a href="/wiki/IP_routing" title="IP routing">IP routing</a>. The <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</a> introduced CIDR in 1993 to replace the previous <a href="/wiki/Classful_network" title="Classful network">classful network</a> addressing architecture on the <a href="/wiki/Internet" title="Internet">Internet</a>. Its goal was to slow the growth of <a href="/wiki/Routing_table" title="Routing table">routing tables</a> on <a href="/wiki/Router_(computing)" title="Router (computing)">routers</a> across the Internet, and to help slow the rapid <a href="/wiki/IPv4_address_exhaustion" title="IPv4 address exhaustion">exhaustion of IPv4 addresses</a>.<a href="#cite_note-RFC_1518-1">[1]</a><a href="#cite_note-RFC_1519-2">[2]</a> IP addresses are described as consisting of two groups of <a href="/wiki/Bit" title="Bit">bits</a> in the address: the <a href="/wiki/Most_significant_bit" class="mw-redirect" title="Most significant bit">most significant bits</a> are the <a href="/wiki/Network_prefix" class="mw-redirect" title="Network prefix">network prefix</a>, which identifies a whole network or <a href="/wiki/Subnet" title="Subnet">subnet</a>, and the <a href="/wiki/Least_significant_bit" class="mw-redirect" title="Least significant bit">least significant</a> set forms the host identifier, which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies. Whereas classful network design for <a href="/wiki/IPv4" title="IPv4">IPv4</a> sized the network prefix as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses, under CIDR address space is allocated to <a href="/wiki/Internet_service_provider" title="Internet service provider">Internet service providers</a> and <a href="/wiki/End_user" title="End user">end users</a> on any address-bit boundary. In <a href="/wiki/IPv6" title="IPv6">IPv6</a>, however, the interface identifier has a fixed size of 64 bits by convention, and smaller subnets are never allocated to end users. CIDR is based on variable-length subnet masking (VLSM), in which network prefixes have variable length (as opposed to the fixed-length prefixing of the previous classful network design). The main benefit of this is that it grants finer control of the sizes of subnets allocated to organizations, hence slowing the exhaustion of IPv4 addresses from allocating larger subnets than needed. CIDR gave rise to a new way of writing IP addresses known as CIDR notation, in which an IP address is followed by a suffix indicating the number of bits of the prefix. Some examples of CIDR notation are the addresses 192.0.2.0/24 for IPv4 and 2001:db8::/32 for IPv6. Blocks of addresses having contiguous prefixes may be aggregated as <a href="/wiki/Supernet" class="mw-redirect" title="Supernet">supernets</a>, reducing the number of entries in the global routing table. <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Background">Background</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=1" title="Edit section: Background">edit</a>]</div> Each IP address consists of a network prefix followed by a <a href="/wiki/Host_(network)" title="Host (network)">host</a> identifier. In the <a href="/wiki/Classful_network" title="Classful network">classful network</a> architecture of <a href="/wiki/IPv4" title="IPv4">IPv4</a>, the three most significant bits of the 32-bit IP address defined the size of the network prefix for unicast networking, and determined the network class A, B, or C.<a href="#cite_note-rfc943-3">[3]</a> <table class="wikitable"> <tbody><tr> <th>Class </th> <th>Most-significant bits </th> <th>Network prefix size (bits) </th> <th>Host identifier size (bits) </th> <th>Address range </th></tr> <tr> <td>A </td> <td>0 </td> <td>8 </td> <td>24 </td> <td>0.0.0.0–127.255.255.255 </td></tr> <tr> <td>B </td> <td>10 </td> <td>16 </td> <td>16 </td> <td>128.0.0.0–191.255.255.255 </td></tr> <tr> <td>C </td> <td>110 </td> <td>24 </td> <td>8 </td> <td>192.0.0.0–223.255.255.255 </td></tr> <tr> <td>D(multicast) E(reserved) </td> <td>1110 1111 </td> <td>– </td> <td>– </td> <td>224.0.0.0–255.255.255.255 </td></tr></tbody></table> The advantage of this system is that the network prefix could be determined for any IP address without any further information. The disadvantage is that networks were usually too big or too small for most organizations to use, because only three sizes were available. The smallest allocation and routing block contained 28 = 256 addresses, larger than necessary for personal or department networks, but too small for most enterprises. The next larger block contained 216 = 65536 addresses, too large to be used efficiently even by large organizations. But for network users who needed more than 65536 addresses, the only other size (224) provided far too many, more than 16 million. This led to inefficiencies in address use as well as inefficiencies in routing, because it required a large number of allocated class-C networks with individual route announcements, being geographically dispersed with little opportunity for <a href="/wiki/Route_aggregation" class="mw-redirect" title="Route aggregation">route aggregation</a>. Within a decade after the invention of the <a href="/wiki/Domain_Name_System" title="Domain Name System">Domain Name System</a> (DNS), the classful network method was found not <a href="/wiki/Scalable" class="mw-redirect" title="Scalable">scalable</a>.<a href="#cite_note-RFC_1517-4">[4]</a> This led to the development of <a href="/wiki/Subnet" title="Subnet">subnetting</a> and CIDR. The formerly meaningful class distinctions based on the most-significant address bits were abandoned and the new system was described as classless, in contrast to the old system, which became known as classful. Routing protocols were revised to carry not just IP addresses, but also their subnet masks. Implementing CIDR required every host and router on the Internet to be reprogrammed in small ways—no small feat at a time when the Internet was entering a period of rapid growth. In 1993, the <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</a> published a new set of standards, <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1518">1518</a> and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1519">1519</a>, to define this new principle for allocating IP address blocks and routing IPv4 packets. An updated version, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4632">4632</a>, was published in 2006.<a href="#cite_note-RFC_4632-5">[5]</a> After a period of experimentation with various alternatives, Classless Inter-Domain Routing was based on variable-length subnet masking (VLSM), which allows each network to be divided into subnetworks of various power-of-two sizes, so that each subnetwork can be sized appropriately for local needs. Variable-length subnet masks were mentioned as one alternative in <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc950">950</a>.<a href="#cite_note-RFC_950_2.1-6">[6]</a> Techniques for grouping addresses for common operations were based on the concept of cluster addressing, first proposed by Carl-Herbert Rokitansky.<a href="#cite_note-7">[7]</a><a href="#cite_note-8">[8]</a> <div class="mw-heading mw-heading2"><h2 id="CIDR_notation">CIDR notation</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=2" title="Edit section: CIDR notation">edit</a>]</div> CIDR notation is a compact representation of an IP address and its associated network mask. The notation was invented by <a href="/wiki/Phil_Karn" title="Phil Karn">Phil Karn</a> in the 1980s.<a href="#cite_note-kantor-9">[9]</a><a href="#cite_note-simpson-10">[10]</a> CIDR notation specifies an IP address, a <a href="/wiki/Slash_(punctuation)" title="Slash (punctuation)">slash</a> ('/') character, and a decimal number. The decimal number is the count of consecutive leading 1-bits (from left to right) in the network mask. Each 1-bit denotes a bit of the address range which must remain identical to the given IP address. The IP address in CIDR notation is always represented according to the standards for IPv4 or IPv6. The address may denote a specific interface address (including a host identifier, such as 10.0.0.1/8), or it may be the beginning address of an entire network (using a host identifier of 0, as in 10.0.0.0/8 or its equivalent 10/8). CIDR notation can even be used with no IP address at all, e.g. when referring to a /24 as a generic description of an IPv4 network that has a 24-bit prefix and 8-bit host numbers. For example: <ul><li>198.51.100.14/24 represents the IPv4 address 198.51.100.14 and its associated network prefix 198.51.100.0, or equivalently, its subnet mask 255.255.255.0, which has 24 leading 1-bits.</li> <li>the IPv4 block 198.51.100.0/22 represents the 1024 IPv4 addresses from 198.51.100.0 to 198.51.103.255.</li> <li>the IPv6 block 2001:db8::/48 represents the block of IPv6 addresses from 2001:db8:0:0:0:0:0:0 to 2001:db8:0:ffff:ffff:ffff:ffff:ffff.</li> <li>::1/128 represents the IPv6 <a href="/wiki/Loopback" title="Loopback">loopback</a> address. Its prefix length is 128 which is the number of bits in the address.</li></ul> In IPv4, CIDR notation came into wide use only after the implementation of the method, which was documented using <a href="/wiki/Dotted-decimal" class="mw-redirect" title="Dotted-decimal">dotted-decimal</a> subnet mask specification after the slash, for example, 192.24.12.0/255.255.252.0.<a href="#cite_note-RFC_1519-2">[2]</a> Describing the network prefix width as a single number (192.24.12.0/22) was easier for network administrators to conceptualize and to calculate. It became gradually incorporated into later standards documents<a href="#cite_note-11">[11]</a><a href="#cite_note-12">[12]</a> and into network configuration interfaces. The number of addresses of a network may be calculated as 2address length − prefix length, where address length is 128 for IPv6 and 32 for IPv4. For example, in IPv4, the prefix length /29 gives: 232−29 = 23 = 8 addresses. <div class="mw-heading mw-heading2"><h2 id="Subnet_masks">Subnet masks</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=3" title="Edit section: Subnet masks">edit</a>]</div> A subnet mask is a <a href="/wiki/Bitmask" class="mw-redirect" title="Bitmask">bitmask</a> that encodes the prefix length associated with an IPv4 address or network in quad-dotted notation: 32 bits, starting with a number of 1-bits equal to the prefix length, ending with 0-bits, and encoded in four-part dotted-decimal format: 255.255.255.0. A subnet mask encodes the same information as a prefix length but predates the advent of CIDR. In CIDR notation, the prefix bits are always contiguous. Subnet masks were allowed by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc950">950</a><a href="#cite_note-RFC_950_2.1-6">[6]</a> to specify non-contiguous bits until <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4632">4632</a><a href="#cite_note-RFC_4632-5">[5]</a>: Section 5.1  stated that the mask must be left contiguous. Given this constraint, a subnet mask and CIDR notation serve exactly the same function. <div class="mw-heading mw-heading2"><h2 id="CIDR_blocks">CIDR blocks</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=4" title="Edit section: CIDR blocks">edit</a>]</div> CIDR is principally a bitwise, prefix-based standard for the representation of IP addresses and their routing properties. It facilitates routing by allowing blocks of addresses to be grouped into single routing table entries. These groups, commonly called CIDR blocks, share an initial sequence of bits in the binary representation of their IP addresses. IPv4 CIDR blocks are identified using a syntax similar to that of IPv4 addresses: a dotted-decimal address, followed by a slash, then a number from 0 to 32, i.e., a.b.c.d/n. The dotted decimal portion is the IPv4 address. The number following the slash is the prefix length, the number of shared initial bits, counting from the most-significant bit of the address. When emphasizing only the size of a network, the address portion of the notation is usually omitted. Thus, a /20 block is a CIDR block with an unspecified 20-bit prefix. An IP address is part of a CIDR block and is said to match the CIDR prefix if the initial n bits of the address and the CIDR prefix are the same. An IPv4 address is 32 bits so an n-bit CIDR prefix leaves 32 − n bits unmatched, meaning that 232−n IPv4 addresses match a given n-bit CIDR prefix. Shorter CIDR prefixes match more addresses, while longer prefixes match fewer. In the case of overlaid CIDR blocks, an address can match multiple CIDR prefixes of different lengths. CIDR is also used for <a href="/wiki/IPv6_address" title="IPv6 address">IPv6 addresses</a> and the syntax semantic is identical. The prefix length can range from 0 to 128, due to the larger number of bits in the address. However, by convention, a subnet on broadcast MAC layer networks always has 64-bit host identifiers.<a href="#cite_note-13">[13]</a> Larger prefixes (/127) are only used on some point-to-point links between routers, for security and policy reasons.<a href="#cite_note-14">[14]</a><figure class="mw-halign-right" typeof="mw:File"><a href="/wiki/File:IP_Address_Match.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/IP_Address_Match.svg/400px-IP_Address_Match.svg.png" decoding="async" width="400" height="394" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/IP_Address_Match.svg/600px-IP_Address_Match.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/7b/IP_Address_Match.svg/800px-IP_Address_Match.svg.png 2x" data-file-width="621" data-file-height="612" /></a><figcaption></figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Assignment_of_CIDR_blocks">Assignment of CIDR blocks</h3>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=5" title="Edit section: Assignment of CIDR blocks">edit</a>]</div> The <a href="/wiki/Internet_Assigned_Numbers_Authority" title="Internet Assigned Numbers Authority">Internet Assigned Numbers Authority</a> (IANA) issues to <a href="/wiki/Regional_Internet_registries" class="mw-redirect" title="Regional Internet registries">regional Internet registries</a> (RIRs) large, short-prefix CIDR blocks. However, a /8 (with over sixteen million addresses) is the largest block IANA will allocate. For example, 62.0.0.0/8 is administered by <a href="/wiki/RIPE_NCC" title="RIPE NCC">RIPE NCC</a>, the European RIR. The RIRs, each responsible for a single, large, geographic area, such as Europe or North America, subdivide these blocks and allocate subnets to local Internet registries (LIRs). Similar subdividing may be repeated several times at lower levels of delegation. End-user networks receive subnets sized according to their projected short-term need. Networks served by a single ISP are encouraged by <a href="/wiki/IETF" class="mw-redirect" title="IETF">IETF</a> recommendations to obtain IP address space directly from their ISP. Networks served by multiple ISPs, on the other hand, may obtain <a href="/wiki/Provider-independent_address_space" title="Provider-independent address space">provider-independent address space</a> directly from the appropriate RIR. <figure class="mw-halign-right" typeof="mw:File"><a href="/wiki/File:CIDR_Address.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/26/CIDR_Address.svg/400px-CIDR_Address.svg.png" decoding="async" width="400" height="220" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/26/CIDR_Address.svg/600px-CIDR_Address.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/26/CIDR_Address.svg/800px-CIDR_Address.svg.png 2x" data-file-width="800" data-file-height="440" /></a><figcaption></figcaption></figure> For example, in the late 1990s, the IP address 208.130.29.33 (since reassigned) was used by www.freesoft.org. An analysis of this address identified three CIDR prefixes. 208.128.0.0/11, a large CIDR block containing over 2 million addresses, had been assigned by <a href="/wiki/ARIN" class="mw-redirect" title="ARIN">ARIN</a> (the North American RIR) to <a href="/wiki/MCI_Communications" title="MCI Communications">MCI</a>. Automation Research Systems (ARS), a Virginia <a href="/wiki/Value-added_reseller" title="Value-added reseller">VAR</a>, leased an Internet connection from MCI and was assigned the 208.130.28.0/22 block, capable of addressing just over 1000 devices. ARS used a /24 block for its publicly accessible servers, of which 208.130.29.33 was one. All of these CIDR prefixes would be used, at different locations in the network. Outside MCI's network, the 208.128.0.0/11 prefix would be used to direct to MCI traffic bound not only for 208.130.29.33, but also for any of the roughly two million IP addresses with the same initial 11 bits. Within MCI's network, 208.130.28.0/22 would become visible, directing traffic to the leased line serving ARS. Only within the ARS corporate network would the 208.130.29.0/24 prefix have been used. <div class="mw-heading mw-heading3"><h3 id="IPv4_CIDR_blocks">IPv4 CIDR blocks</h3>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=6" title="Edit section: IPv4 CIDR blocks">edit</a>]</div> <table class="wikitable"> <tbody><tr> <th rowspan="2">Address format </th> <th rowspan="2">Difference to last address </th> <th rowspan="2">Mask </th> <th colspan="2">Addresses </th> <th rowspan="2">Relative to class A, B, C </th> <th rowspan="2">Restrictions on a, b, c and d (0..255 unless noted) </th> <th rowspan="2">Typical use </th></tr> <tr> <th>Decimal </th> <th>2n </th></tr> <tr> <td>a.b.c.d/32 </td> <td>+0.0.0.0 </td> <td>255.255.255.255 </td> <td style="text-align:right;">1 </td> <td style="text-align:right;">20 </td> <td style="text-align:right;"><style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style>1⁄256 C </td> <td> </td> <td>Host route </td></tr> <tr> <td>a.b.c.d/31 </td> <td>+0.0.0.1 </td> <td>255.255.255.254 </td> <td style="text-align:right;">2 </td> <td style="text-align:right;">21 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄128 C </td> <td>d = 0 ... (2n) ... 254 </td> <td>Point-to-point links (<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc3021">3021</a>) </td></tr> <tr> <td>a.b.c.d/30 </td> <td>+0.0.0.3 </td> <td>255.255.255.252 </td> <td style="text-align:right;">4 </td> <td style="text-align:right;">22 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄64 C </td> <td>d = 0 ... (4n) ... 252 </td> <td>Point-to-point links (glue network) </td></tr> <tr> <td>a.b.c.d/29 </td> <td>+0.0.0.7 </td> <td>255.255.255.248 </td> <td style="text-align:right;">8 </td> <td style="text-align:right;">23 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄32 C </td> <td>d = 0 ... (8n) ... 248 </td> <td>Smallest multi-host network </td></tr> <tr> <td>a.b.c.d/28 </td> <td>+0.0.0.15 </td> <td>255.255.255.240 </td> <td style="text-align:right;">16 </td> <td style="text-align:right;">24 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄16 C </td> <td>d = 0 ... (16n) ... 240 </td> <td rowspan="3">Small <a href="/wiki/LAN" class="mw-redirect" title="LAN">LAN</a> </td></tr> <tr> <td>a.b.c.d/27 </td> <td>+0.0.0.31 </td> <td>255.255.255.224 </td> <td style="text-align:right;">32 </td> <td style="text-align:right;">25 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄8 C </td> <td>d = 0 ... (32n) ... 224 </td></tr> <tr> <td>a.b.c.d/26 </td> <td>+0.0.0.63 </td> <td>255.255.255.192 </td> <td style="text-align:right;">64 </td> <td style="text-align:right;">26 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄4 C </td> <td>d = 0, 64, 128, 192 </td></tr> <tr> <td>a.b.c.d/25 </td> <td>+0.0.0.127 </td> <td>255.255.255.128 </td> <td style="text-align:right;">128 </td> <td style="text-align:right;">27 </td> <td style="text-align:right;"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027">1⁄2 C </td> <td>d = 0, 128 </td> <td rowspan="2">Large <a href="/wiki/LAN" class="mw-redirect" title="LAN">LAN</a> </td></tr> <tr> <td>a.b.c.0/24 </td> <td>+0.0.0.255 </td> <td>255.255.255.0 </td> <td style="text-align:right;">256 </td> <td style="text-align:right;">28 </td> <td style="text-align:right;">1 C </td> <td> </td></tr> <tr> <td>a.b.c.0/23 </td> <td>+0.0.1.255 </td> <td>255.255.254.0 </td> <td style="text-align:right;">512 </td> <td style="text-align:right;">29 </td> <td style="text-align:right;">2 C </td> <td>c = 0 ... (2n) ... 254 </td> <td> </td></tr> <tr> <td>a.b.c.0/22 </td> <td>+0.0.3.255 </td> <td>255.255.252.0 </td> <td style="text-align:right;">1,024 </td> <td style="text-align:right;">210 </td> <td style="text-align:right;">4 C </td> <td>c = 0 ... (4n) ... 252 </td> <td>Small business </td></tr> <tr> <td>a.b.c.0/21 </td> <td>+0.0.7.255 </td> <td>255.255.248.0 </td> <td style="text-align:right;">2,048 </td> <td style="text-align:right;">211 </td> <td style="text-align:right;">8 C </td> <td>c = 0 ... (8n) ... 248 </td> <td rowspan="2">Small <a href="/wiki/ISP" class="mw-redirect" title="ISP">ISP</a>/ large business </td></tr> <tr> <td>a.b.c.0/20 </td> <td>+0.0.15.255 </td> <td>255.255.240.0 </td> <td style="text-align:right;">4,096 </td> <td style="text-align:right;">212 </td> <td style="text-align:right;">16 C </td> <td>c = 0 ... (16n) ... 240 </td></tr> <tr> <td>a.b.c.0/19 </td> <td>+0.0.31.255 </td> <td>255.255.224.0 </td> <td style="text-align:right;">8,192 </td> <td style="text-align:right;">213 </td> <td style="text-align:right;">32 C </td> <td>c = 0 ... (32n) ... 224 </td> <td rowspan="3"><a href="/wiki/ISP" class="mw-redirect" title="ISP">ISP</a>/ large business </td></tr> <tr> <td>a.b.c.0/18 </td> <td>+0.0.63.255 </td> <td>255.255.192.0 </td> <td style="text-align:right;">16,384 </td> <td style="text-align:right;">214 </td> <td style="text-align:right;">64 C </td> <td>c = 0, 64, 128, 192 </td></tr> <tr> <td>a.b.c.0/17 </td> <td>+0.0.127.255 </td> <td>255.255.128.0 </td> <td style="text-align:right;">32,768 </td> <td style="text-align:right;">215 </td> <td style="text-align:right;">128 C </td> <td>c = 0, 128 </td></tr> <tr> <td>a.b.0.0/16 </td> <td>+0.0.255.255 </td> <td>255.255.0.0 </td> <td style="text-align:right;">65,536 </td> <td style="text-align:right;">216 </td> <td style="text-align:right;">256 C = B </td> <td> </td> <td> </td></tr> <tr> <td>a.b.0.0/15 </td> <td>+0.1.255.255 </td> <td>255.254.0.0 </td> <td style="text-align:right;">131,072 </td> <td style="text-align:right;">217 </td> <td style="text-align:right;">2 B </td> <td>b = 0 ... (2n) ... 254 </td> <td> </td></tr> <tr> <td>a.b.0.0/14 </td> <td>+0.3.255.255 </td> <td>255.252.0.0 </td> <td style="text-align:right;">262,144 </td> <td style="text-align:right;">218 </td> <td style="text-align:right;">4 B </td> <td>b = 0 ... (4n) ... 252 </td> <td> </td></tr> <tr> <td>a.b.0.0/13 </td> <td>+0.7.255.255 </td> <td>255.248.0.0 </td> <td style="text-align:right;">524,288 </td> <td style="text-align:right;">219 </td> <td style="text-align:right;">8 B </td> <td>b = 0 ... (8n) ... 248 </td> <td> </td></tr> <tr> <td>a.b.0.0/12 </td> <td>+0.15.255.255 </td> <td>255.240.0.0 </td> <td style="text-align:right;">1,048,576 </td> <td style="text-align:right;">220 </td> <td style="text-align:right;">16 B </td> <td>b = 0 ... (16n) ... 240 </td> <td> </td></tr> <tr> <td>a.b.0.0/11 </td> <td>+0.31.255.255 </td> <td>255.224.0.0 </td> <td style="text-align:right;">2,097,152 </td> <td style="text-align:right;">221 </td> <td style="text-align:right;">32 B </td> <td>b = 0 ... (32n) ... 224 </td> <td> </td></tr> <tr> <td>a.b.0.0/10 </td> <td>+0.63.255.255 </td> <td>255.192.0.0 </td> <td style="text-align:right;">4,194,304 </td> <td style="text-align:right;">222 </td> <td style="text-align:right;">64 B </td> <td>b = 0, 64, 128, 192 </td> <td> </td></tr> <tr> <td>a.b.0.0/9 </td> <td>+0.127.255.255 </td> <td>255.128.0.0 </td> <td style="text-align:right;">8,388,608 </td> <td style="text-align:right;">223 </td> <td style="text-align:right;">128 B </td> <td>b = 0, 128 </td> <td> </td></tr> <tr> <td>a.0.0.0/8 </td> <td>+0.255.255.255 </td> <td>255.0.0.0 </td> <td style="text-align:right;">16,777,216 </td> <td style="text-align:right;">224 </td> <td style="text-align:right;">256 B = A </td> <td> </td> <td>Largest <a href="/wiki/IANA" class="mw-redirect" title="IANA">IANA</a> block allocation </td></tr> <tr> <td>a.0.0.0/7 </td> <td>+1.255.255.255 </td> <td>254.0.0.0 </td> <td style="text-align:right;">33,554,432 </td> <td style="text-align:right;">225 </td> <td style="text-align:right;">2 A </td> <td>a = 0 ... (2n) ... 254 </td> <td> </td></tr> <tr> <td>a.0.0.0/6 </td> <td>+3.255.255.255 </td> <td>252.0.0.0 </td> <td style="text-align:right;">67,108,864 </td> <td style="text-align:right;">226 </td> <td style="text-align:right;">4 A </td> <td>a = 0 ... (4n) ... 252 </td> <td> </td></tr> <tr> <td>a.0.0.0/5 </td> <td>+7.255.255.255 </td> <td>248.0.0.0 </td> <td style="text-align:right;">134,217,728 </td> <td style="text-align:right;">227 </td> <td style="text-align:right;">8 A </td> <td>a = 0 ... (8n) ... 248 </td> <td> </td></tr> <tr> <td>a.0.0.0/4 </td> <td>+15.255.255.255 </td> <td>240.0.0.0 </td> <td style="text-align:right;">268,435,456 </td> <td style="text-align:right;">228 </td> <td style="text-align:right;">16 A </td> <td>a = 0 ... (16n) ... 240 </td> <td> </td></tr> <tr> <td>a.0.0.0/3 </td> <td>+31.255.255.255 </td> <td>224.0.0.0 </td> <td style="text-align:right;">536,870,912 </td> <td style="text-align:right;">229 </td> <td style="text-align:right;">32 A </td> <td>a = 0 ... (32n) ... 224 </td> <td> </td></tr> <tr> <td>a.0.0.0/2 </td> <td>+63.255.255.255 </td> <td>192.0.0.0 </td> <td style="text-align:right;">1,073,741,824 </td> <td style="text-align:right;">230 </td> <td style="text-align:right;">64 A </td> <td>a = 0, 64, 128, 192 </td> <td> </td></tr> <tr> <td>a.0.0.0/1 </td> <td>+127.255.255.255 </td> <td>128.0.0.0 </td> <td style="text-align:right;">2,147,483,648 </td> <td style="text-align:right;">231 </td> <td style="text-align:right;">128 A </td> <td>a = 0, 128 </td> <td> </td></tr> <tr> <td>0.0.0.0/0 </td> <td>+255.255.255.255 </td> <td>0.0.0.0 </td> <td style="text-align:right;">4,294,967,296 </td> <td style="text-align:right;">232 </td> <td style="text-align:right;">256 A </td> <td> </td> <td>Entire IPv4 Internet, <a href="/wiki/Default_route" title="Default route">default route</a>. </td></tr></tbody></table> In common usage, the first address in a subnet, all binary zero in the host identifier, is reserved for referring to the network itself, while the last address, all binary one in the host identifier, is used as a <a href="/wiki/Broadcast_address" title="Broadcast address">broadcast address</a> for the network; this reduces the number of addresses available for hosts by 2. As a result, a /31 network, with one binary digit in the host identifier, would be unusable, as such a subnet would provide no available host addresses after this reduction. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc3021">3021</a> creates an exception to the "host all ones" and "host all zeros" rules to make /31 networks usable for point-to-point links. /32 addresses (single-host network) must be accessed by explicit routing rules, as there is no room in such a network for a gateway. In routed subnets larger than /31 or /32, the number of available host addresses is usually reduced by two, namely the largest address, which is reserved as the broadcast address, and the smallest address, which identifies the network itself.<a href="#cite_note-RFC_922-15">[15]</a><a href="#cite_note-RFC_1812-16">[16]</a> <div class="mw-heading mw-heading3"><h3 id="IPv6_CIDR_blocks">IPv6 CIDR blocks</h3>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=7" title="Edit section: IPv6 CIDR blocks">edit</a>]</div> <table class="wikitable" style="text-align: center; margin-left: auto; margin-right: auto; border: none;"> <caption>IPv6 CIDR prefixes </caption> <tbody><tr> <th rowspan="2">Prefix size</th> <th colspan="3">Number of equivalent subnets</th> <th rowspan="2">Interface ID bits </th></tr> <tr> <th>/48</th> <th>/56</th> <th>/64 </th></tr> <tr> <td>/24</td> <td>16M</td> <td>4G</td> <td>1T</td> <td>104 </td></tr> <tr> <td>/25</td> <td>8M</td> <td>2G</td> <td>512G</td> <td>103 </td></tr> <tr> <td>/26</td> <td>4M</td> <td>1G</td> <td>256G</td> <td>102 </td></tr> <tr> <td>/27</td> <td>2M</td> <td>512M</td> <td>128G</td> <td>101 </td></tr> <tr> <td>/28</td> <td>1M</td> <td>256M</td> <td>64G</td> <td>100 </td></tr> <tr> <td>/29</td> <td>512K</td> <td>128M</td> <td>32G</td> <td>99 </td></tr> <tr> <td>/30</td> <td>256K</td> <td>64M</td> <td>16G</td> <td>98 </td></tr> <tr> <td>/31</td> <td>128K</td> <td>32M</td> <td>8G</td> <td>97 </td></tr> <tr> <td>/32</td> <td>64K</td> <td>16M</td> <td>4G</td> <td>96 </td></tr> <tr> <td>/33</td> <td>32K</td> <td>8M</td> <td>2G</td> <td>95 </td></tr> <tr> <td>/34</td> <td>16K</td> <td>4M</td> <td>1G</td> <td>94 </td></tr> <tr> <td>/35</td> <td>8K</td> <td>2M</td> <td>512M</td> <td>93 </td></tr> <tr> <td>/36</td> <td>4K</td> <td>1M</td> <td>256M</td> <td>92 </td></tr> <tr> <td>/37</td> <td>2K</td> <td>512K</td> <td>128M</td> <td>91 </td></tr> <tr> <td>/38</td> <td>1K</td> <td>256K</td> <td>64M</td> <td>90 </td></tr> <tr> <td>/39</td> <td>512</td> <td>128K</td> <td>32M</td> <td>89 </td></tr> <tr> <td>/40</td> <td>256</td> <td>64K</td> <td>16M</td> <td>88 </td></tr> <tr> <td>/41</td> <td>128</td> <td>32K</td> <td>8M</td> <td>87 </td></tr> <tr> <td>/42</td> <td>64</td> <td>16K</td> <td>4M</td> <td>86 </td></tr> <tr> <td>/43</td> <td>32</td> <td>8K</td> <td>2M</td> <td>85 </td></tr> <tr> <td>/44</td> <td>16</td> <td>4K</td> <td>1M</td> <td>84 </td></tr> <tr> <td>/45</td> <td>8</td> <td>2K</td> <td>512K</td> <td>83 </td></tr> <tr> <td>/46</td> <td>4</td> <td>1K</td> <td>256K</td> <td>82 </td></tr> <tr> <td>/47</td> <td>2</td> <td>512</td> <td>128K</td> <td>81 </td></tr> <tr> <td>/48</td> <td>1</td> <td>256</td> <td>64K</td> <td>80 </td></tr> <tr> <td>/49</td> <td></td> <td>128</td> <td>32K</td> <td>79 </td></tr> <tr> <td>/50</td> <td></td> <td>64</td> <td>16K</td> <td>78 </td></tr> <tr> <td>/51</td> <td></td> <td>32</td> <td>8K</td> <td>77 </td></tr> <tr> <td>/52</td> <td></td> <td>16</td> <td>4K</td> <td>76 </td></tr> <tr> <td>/53</td> <td></td> <td>8</td> <td>2K</td> <td>75 </td></tr> <tr> <td>/54</td> <td></td> <td>4</td> <td>1K</td> <td>74 </td></tr> <tr> <td>/55</td> <td></td> <td>2</td> <td>512</td> <td>73 </td></tr> <tr> <td>/56</td> <td></td> <td>1</td> <td>256</td> <td>72 </td></tr> <tr> <td>/57</td> <td></td> <td></td> <td>128</td> <td>71 </td></tr> <tr> <td>/58</td> <td></td> <td></td> <td>64</td> <td>70 </td></tr> <tr> <td>/59</td> <td></td> <td></td> <td>32</td> <td>69 </td></tr> <tr> <td>/60</td> <td></td> <td></td> <td>16</td> <td>68 </td></tr> <tr> <td>/61</td> <td></td> <td></td> <td>8</td> <td>67 </td></tr> <tr> <td>/62</td> <td></td> <td></td> <td>4</td> <td>66 </td></tr> <tr> <td>/63</td> <td></td> <td></td> <td>2</td> <td>65 </td></tr> <tr> <td>/64</td> <td></td> <td></td> <td>1</td> <td>64 </td></tr> <tr> <td colspan="5">K = 1,024 </td></tr> <tr> <td colspan="5">M = 1,048,576 </td></tr> <tr> <td colspan="5">G = 1,073,741,824 </td></tr> <tr> <td colspan="5">T = 1,099,511,627,776 </td></tr></tbody></table> The large address size of IPv6 permitted worldwide route summarization and guaranteed sufficient address pools at each site. The standard subnet size for IPv6 networks is a /64 block, which is required for the operation of <a href="/wiki/IPv6_stateless_address_autoconfiguration" class="mw-redirect" title="IPv6 stateless address autoconfiguration">stateless address autoconfiguration</a>.<a href="#cite_note-RFC_4862-17">[17]</a> At first, the IETF recommended in <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc3177">3177</a> as a best practice that all end sites receive a /48 address allocation,<a href="#cite_note-RFC_3177-18">[18]</a> but criticism and reevaluation of actual needs and practices has led to more flexible allocation recommendations in <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc6177">6177</a><a href="#cite_note-RFC_6177-19">[19]</a> suggesting a significantly smaller allocation for some sites, such as a /56 block for residential networks. This IPv6 subnetting reference lists the sizes for IPv6 <a href="/wiki/Subnetwork" class="mw-redirect" title="Subnetwork">subnetworks</a>. Different types of network links may require different subnet sizes.<a href="#cite_note-20">[20]</a> The subnet mask separates the bits of the network identifier prefix from the bits of the interface identifier. Selecting a smaller prefix size results in fewer number of networks covered, but with more addresses within each network.<a href="#cite_note-21">[21]</a> <pre>2001:0db8:0123:4567:89ab:cdef:1234:5678 |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||| |||128 Single end-points and <a href="/wiki/Loopback" title="Loopback">loopback</a> |||| |||| |||| |||| |||| |||| |||| |||127 Point-to-point links (inter-router) |||| |||| |||| |||| |||| |||| |||| ||124 |||| |||| |||| |||| |||| |||| |||| |120 |||| |||| |||| |||| |||| |||| |||| 116 |||| |||| |||| |||| |||| |||| |||112 |||| |||| |||| |||| |||| |||| ||108 |||| |||| |||| |||| |||| |||| |104 |||| |||| |||| |||| |||| |||| 100 |||| |||| |||| |||| |||| |||96 |||| |||| |||| |||| |||| ||92 |||| |||| |||| |||| |||| |88 |||| |||| |||| |||| |||| 84 |||| |||| |||| |||| |||80 |||| |||| |||| |||| ||76 |||| |||| |||| |||| |72 |||| |||| |||| |||| 68 |||| |||| |||| |||64 Single LAN; default prefix size for <a href="/wiki/IPv6#Stateless_address_autoconfiguration_(SLAAC)" title="IPv6">SLAAC</a> |||| |||| |||| ||60 Some (very limited) <a href="/wiki/6rd" class="mw-redirect" title="6rd">6rd</a> deployments (/60 = 16 /64 blocks) |||| |||| |||| |56 Minimal end sites assignment;<a href="#cite_note-RFC_6177-19">[19]</a> e.g. <a href="/wiki/Home_network" title="Home network">home network</a> (/56 = 256 /64 blocks) |||| |||| |||| 52 /52 block = 4096 /64 blocks |||| |||| |||48 Typical assignment for larger sites (/48 = 65536 /64 blocks) |||| |||| ||44 |||| |||| |40 |||| |||| 36 possible future <a href="/wiki/Local_Internet_registry" class="mw-redirect" title="Local Internet registry">local Internet registry</a> (LIR) extra-small allocations |||| |||32 LIR minimum allocations |||| ||28 LIR medium allocations |||| |24 LIR large allocations |||| 20 LIR extra large allocations |||16 ||12 <a href="/wiki/Regional_Internet_registry" title="Regional Internet registry">Regional Internet registry</a> (RIR) allocations from IANA<a href="#cite_note-22">[22]</a> |8 4 </pre> <div class="mw-heading mw-heading2"><h2 id="Numerical_interpretation">Numerical interpretation</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=8" title="Edit section: Numerical interpretation">edit</a>]</div> Topologically, the set of subnets described by CIDR represent a <a href="/wiki/Cover_(topology)" title="Cover (topology)">cover</a> of the corresponding address space. The interval described by the notation <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle X/n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>X</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle X/n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9621ac5e67b2a08f340f537aca5fc9e67c7ed13d" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.537ex; height:2.843ex;" alt="{\displaystyle X/n}"> numerically corresponds to addresses of the form (for IPv4) <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle [x\cdot 2^{32-n},x\cdot 2^{32-n}+2^{32-n}-1]}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mo stretchy="false">[</mo> <mi>x</mi> <mo>⋅</mo> <msup> <mn>2</mn> <mrow class="MJX-TeXAtom-ORD"> <mn>32</mn> <mo>−</mo> <mi>n</mi> </mrow> </msup> <mo>,</mo> <mi>x</mi> <mo>⋅</mo> <msup> <mn>2</mn> <mrow class="MJX-TeXAtom-ORD"> <mn>32</mn> <mo>−</mo> <mi>n</mi> </mrow> </msup> <mo>+</mo> <msup> <mn>2</mn> <mrow class="MJX-TeXAtom-ORD"> <mn>32</mn> <mo>−</mo> <mi>n</mi> </mrow> </msup> <mo>−</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle [x\cdot 2^{32-n},x\cdot 2^{32-n}+2^{32-n}-1]}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c3dfe784525655b1aab39369f3e9e87548965aff" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:31.099ex; height:3.176ex;" alt="{\displaystyle [x\cdot 2^{32-n},x\cdot 2^{32-n}+2^{32-n}-1]}">, where <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle X=x\cdot 2^{32-n}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>X</mi> <mo>=</mo> <mi>x</mi> <mo>⋅</mo> <msup> <mn>2</mn> <mrow class="MJX-TeXAtom-ORD"> <mn>32</mn> <mo>−</mo> <mi>n</mi> </mrow> </msup> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle X=x\cdot 2^{32-n}}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/95decca0ed16bf12808f9947163f99e2008dde83" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:13.391ex; height:2.676ex;" alt="{\displaystyle X=x\cdot 2^{32-n}}"> has the lower <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a601995d55609f2d9f5e233e36fbe9ea26011b3b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.395ex; height:1.676ex;" alt="{\displaystyle n}"> bits set to 0. (For IPv6, substitute 128.) For a fixed <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a601995d55609f2d9f5e233e36fbe9ea26011b3b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.395ex; height:1.676ex;" alt="{\displaystyle n}">, the set of all <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle X/n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>X</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle X/n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9621ac5e67b2a08f340f537aca5fc9e67c7ed13d" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.537ex; height:2.843ex;" alt="{\displaystyle X/n}"> subnets constitute a <a href="/wiki/Partition_of_a_set" title="Partition of a set">partition</a>, that is a cover of non-overlapping sets. Increasing <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a601995d55609f2d9f5e233e36fbe9ea26011b3b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.395ex; height:1.676ex;" alt="{\displaystyle n}"> yields finer and finer subpartitions. Thus two subnets <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle X/n}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>X</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>n</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle X/n}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9621ac5e67b2a08f340f537aca5fc9e67c7ed13d" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.537ex; height:2.843ex;" alt="{\displaystyle X/n}"> and <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle Y/m}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>Y</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>m</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle Y/m}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c2d5beab4f12c3090fed631387008a3d24af5b4e" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.976ex; height:2.843ex;" alt="{\displaystyle Y/m}"> are either disjoint or one is a subnet of the other. <div class="mw-heading mw-heading2"><h2 id="Prefix_aggregation">Prefix aggregation</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=9" title="Edit section: Prefix aggregation">edit</a>]</div> CIDR provides fine-grained <a href="/wiki/Routing_prefix_aggregation" class="mw-redirect" title="Routing prefix aggregation">routing prefix aggregation</a>. For example, if the first 20 bits of their network prefixes match, sixteen contiguous /24 networks can be aggregated and advertised to a larger network as a single /20 <a href="/wiki/Routing_table" title="Routing table">routing table</a> entry. This reduces the number of routes that have to be advertised. <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=10" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/Internet_protocol_suite" title="Internet protocol suite">Internet protocol suite</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=11" title="Edit section: References">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-RFC_1518-1"><a href="#cite_ref-RFC_1518_1-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFY._RekhterT._Li1993" class="citation cs1">Y. Rekhter; T. Li (September 1993). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1518">An Architecture for IP Address Allocation with CIDR</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1518">10.17487/RFC1518</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1518">1518</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=An+Architecture+for+IP+Address+Allocation+with+CIDR&rft.date=1993-09&rft_id=info%3Adoi%2F10.17487%2FRFC1518&rft.au=Y.+Rekhter&rft.au=T.+Li&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1518&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_1519-2">^ <a href="#cite_ref-RFC_1519_2-0">a</a> <a href="#cite_ref-RFC_1519_2-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFV._FullerT._LiJ._YuK._Varadhan1993" class="citation cs1">V. Fuller; T. Li; J. Yu; K. Varadhan (September 1993). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1519">Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1519">10.17487/RFC1519</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1519">1519</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Classless+Inter-Domain+Routing+%28CIDR%29%3A+an+Address+Assignment+and+Aggregation+Strategy&rft.date=1993-09&rft_id=info%3Adoi%2F10.17487%2FRFC1519&rft.au=V.+Fuller&rft.au=T.+Li&rft.au=J.+Yu&rft.au=K.+Varadhan&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1519&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-rfc943-3"><a href="#cite_ref-rfc943_3-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJ._ReynoldsJ._Postel1985" class="citation cs1">J. Reynolds; J. Postel, eds. (April 1985). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc943">Assigned Numbers</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC0943">10.17487/RFC0943</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc943">943</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Assigned+Numbers&rft.date=1985-04&rft_id=info%3Adoi%2F10.17487%2FRFC0943&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc943&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_1517-4"><a href="#cite_ref-RFC_1517_4-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFR._Hinden1993" class="citation cs1">R. Hinden, ed. (September 1993). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1517">Applicability Statement for the Implementation of Classless Inter-Domain Routing (CIDR)</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1517">10.17487/RFC1517</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1517">1517</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Applicability+Statement+for+the+Implementation+of+Classless+Inter-Domain+Routing+%28CIDR%29&rft.date=1993-09&rft_id=info%3Adoi%2F10.17487%2FRFC1517&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1517&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_4632-5">^ <a href="#cite_ref-RFC_4632_5-0">a</a> <a href="#cite_ref-RFC_4632_5-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFV._FullerT._Li2006" class="citation cs1">V. Fuller; T. Li (August 2006). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4632">Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC4632">10.17487/RFC4632</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4632">4632</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Classless+Inter-domain+Routing+%28CIDR%29%3A+The+Internet+Address+Assignment+and+Aggregation+Plan&rft.date=2006-08&rft_id=info%3Adoi%2F10.17487%2FRFC4632&rft.au=V.+Fuller&rft.au=T.+Li&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc4632&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_950_2.1-6">^ <a href="#cite_ref-RFC_950_2.1_6-0">a</a> <a href="#cite_ref-RFC_950_2.1_6-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJ._MogulJ._Postel1985" class="citation cs1">J. Mogul; J. Postel, eds. (August 1985). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc950#section-2.1">Internet Standard Subnetting Procedure</a>. sec. 2.1. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC0950">10.17487/RFC0950</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc950">950</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Internet+Standard+Subnetting+Procedure&rft.pages=sec.-2.1&rft.date=1985-08&rft_id=info%3Adoi%2F10.17487%2FRFC0950&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc950%26%23035%3Bsection-2.1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-7"><a href="#cite_ref-7">^</a> Carl-Herbert Rokitansky, "Internet Cluster Addressing Scheme and its Application to Public Data Networks", Proc. 9th International Conference on Computer Communication (ICCC' 88), pp. 482–491, Tel Aviv, Israel, October/November 1988 </li> <li id="cite_note-8"><a href="#cite_ref-8">^</a> <a rel="nofollow" class="external text" href="http://www.ietf.org/mail-archive/web/ietf/current/msg24136.html">Cluster Addressing and CIDR</a> in the mail archives of the IETF </li> <li id="cite_note-kantor-9"><a href="#cite_ref-kantor_9-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBrian_Kantor2018" class="citation web cs1">Brian Kantor (December 2018). <a rel="nofollow" class="external text" href="https://seclists.org/nanog/2018/Dec/334">"Re: Stupid Question maybe?"</a>. North American Network Operators Group. <q>/24 is certainly cleaner than 255.255.255.0. I seem to remember it was Phil Karn who in the early 80's suggested that expressing subnet masks as the number of bits from the top end of the address word was efficient, since subnet masks were always a series of ones followd by zeros with no interspersing, which was incorporated (or independently invented) about a decade later as CIDR a.b.c.d/n notation in RFC1519.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Re%3A+Stupid+Question+maybe%3F&rft.pub=North+American+Network+Operators+Group&rft.date=2018-12&rft.au=Brian+Kantor&rft_id=https%3A%2F%2Fseclists.org%2Fnanog%2F2018%2FDec%2F334&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-simpson-10"><a href="#cite_ref-simpson_10-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWilliam_Simpson2018" class="citation web cs1">William Simpson (December 2018). <a rel="nofollow" class="external text" href="https://seclists.org/nanog/2018/Dec/368">"Re: Stupid Question maybe?"</a>. North American Network Operators Group. <q>Actually, Brian is correct. Phil was w-a-y ahead of the times. But I don't remember him talking about it until the late '80s.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Re%3A+Stupid+Question+maybe%3F&rft.pub=North+American+Network+Operators+Group&rft.date=2018-12&rft.au=William+Simpson&rft_id=https%3A%2F%2Fseclists.org%2Fnanog%2F2018%2FDec%2F368&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-11"><a href="#cite_ref-11">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFT._PummillB._Manning1995" class="citation cs1">T. Pummill; B. Manning (December 1995). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1878">Variable Length Subnet Table For IPv4</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1878">10.17487/RFC1878</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1878">1878</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Variable+Length+Subnet+Table+For+IPv4&rft.date=1995-12&rft_id=info%3Adoi%2F10.17487%2FRFC1878&rft.au=T.+Pummill&rft.au=B.+Manning&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1878&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-12"><a href="#cite_ref-12">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFS._WilliamsonM._KostersD._BlackaJ._Singh1997" class="citation cs1">S. Williamson; M. Kosters; D. Blacka; J. Singh; K. Zeilstra (June 1997). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2167">Referral Whois (RWhois) Protocol V1.5</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC2167">10.17487/RFC2167</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2167">2167</a>. <q>IP networks are also lexically hierarchical labels using the Classless Inter-Domain Routing (CIDR) notation, but their hierarchy is not easily determined with simple text manipulation; for example, 198.41.0.0/22 is a part of 198.41.0.0/16, which is a part of 198.40.0.0/15.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Referral+Whois+%28RWhois%29+Protocol+V1.5&rft.date=1997-06&rft_id=info%3Adoi%2F10.17487%2FRFC2167&rft.au=S.+Williamson&rft.au=M.+Kosters&rft.au=D.+Blacka&rft.au=J.+Singh&rft.au=K.+Zeilstra&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc2167&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-13"><a href="#cite_ref-13">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCarpenterJiang2014" class="citation cs1">Carpenter, B.; Jiang, S. (February 2014). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc7136">Significance of IPv6 Interface Identifiers</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC7136">10.17487/RFC7136</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc7136">7136</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Significance+of+IPv6+Interface+Identifiers&rft.date=2014-02&rft_id=info%3Adoi%2F10.17487%2FRFC7136&rft.aulast=Carpenter&rft.aufirst=B.&rft.au=Jiang%2C+S.&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc7136&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-14"><a href="#cite_ref-14">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKohnoNitzanBushMatsuzaki2011" class="citation cs1">Kohno, M.; Nitzan, B.; Bush, R.; Matsuzaki, Y.; Colitti, L.; Narten, T. (April 2011). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc6164">Using 127-Bit IPv6 Prefixes on Inter-Router Links</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC6164">10.17487/RFC6164</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc6164">6164</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Using+127-Bit+IPv6+Prefixes+on+Inter-Router+Links&rft.date=2011-04&rft_id=info%3Adoi%2F10.17487%2FRFC6164&rft.aulast=Kohno&rft.aufirst=M.&rft.au=Nitzan%2C+B.&rft.au=Bush%2C+R.&rft.au=Matsuzaki%2C+Y.&rft.au=Colitti%2C+L.&rft.au=Narten%2C+T.&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc6164&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_922-15"><a href="#cite_ref-RFC_922_15-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFJ._Mogul1984" class="citation cs1">J. Mogul, ed. (October 1984). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc922#section-7">Broadcasting Internet Datagrams in the Presence of Subnets</a>. sec. 7. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC0922">10.17487/RFC0922</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc922">922</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Broadcasting+Internet+Datagrams+in+the+Presence+of+Subnets&rft.pages=sec.-7&rft.date=1984-10&rft_id=info%3Adoi%2F10.17487%2FRFC0922&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc922%26%23035%3Bsection-7&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_1812-16"><a href="#cite_ref-RFC_1812_16-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFF._Baker1995" class="citation cs1">F. Baker, ed. (June 1995). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1812#section-4.2.3.1">Requirements for IP Version 4 Routers</a>. sec. 4.2.3.1. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1812">10.17487/RFC1812</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1812">1812</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Requirements+for+IP+Version+4+Routers&rft.pages=sec.-4.2.3.1&rft.date=1995-06&rft_id=info%3Adoi%2F10.17487%2FRFC1812&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1812%26%23035%3Bsection-4.2.3.1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_4862-17"><a href="#cite_ref-RFC_4862_17-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/RFC_(identifier)" class="mw-redirect" title="RFC (identifier)">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4862">4862</a> </li> <li id="cite_note-RFC_3177-18"><a href="#cite_ref-RFC_3177_18-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation cs1"><a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc3177">IAB/IESG Recommendation on IPv6 Address Allocations to Sites</a>. IAB/IESG. September 2001. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC3177">10.17487/RFC3177</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc3177">3177</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IAB%2FIESG+Recommendation+on+IPv6+Address+Allocations+to+Sites&rft.pub=IAB%2FIESG&rft.date=2001-09&rft_id=info%3Adoi%2F10.17487%2FRFC3177&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc3177&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-RFC_6177-19">^ <a href="#cite_ref-RFC_6177_19-0">a</a> <a href="#cite_ref-RFC_6177_19-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFT._NartenG._HustonL._Roberts2011" class="citation cs1">T. Narten; G. Huston; L. Roberts (March 2011). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc6177">IPv6 Address Assignment to End Sites</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC6177">10.17487/RFC6177</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc6177">6177</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IPv6+Address+Assignment+to+End+Sites&rft.date=2011-03&rft_id=info%3Adoi%2F10.17487%2FRFC6177&rft.au=T.+Narten&rft.au=G.+Huston&rft.au=L.+Roberts&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc6177&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-20"><a href="#cite_ref-20">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.getipv6.info/index.php/IPv6_Addressing_Plans">"ARIN IPv6 Addressing Plans"</a>. Getipv6.info. 2016-03-25. Retrieved 2018-03-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=ARIN+IPv6+Addressing+Plans&rft.pub=Getipv6.info&rft.date=2016-03-25&rft_id=http%3A%2F%2Fwww.getipv6.info%2Findex.php%2FIPv6_Addressing_Plans&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-21"><a href="#cite_ref-21">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110203130851/http://ripe.net/info/info-services/addressing.html">"RIPE IP Allocation Rates"</a>. Archived from <a rel="nofollow" class="external text" href="https://www.ripe.net/info/info-services/addressing.html">the original</a> on 2011-02-03.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=RIPE+IP+Allocation+Rates&rft_id=https%3A%2F%2Fwww.ripe.net%2Finfo%2Finfo-services%2Faddressing.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> <li id="cite_note-22"><a href="#cite_ref-22">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xml">"IANA IPv6 unicast address assignments"</a>. Iana.org. Retrieved 2018-03-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=IANA+IPv6+unicast+address+assignments&rft.pub=Iana.org&rft_id=https%3A%2F%2Fwww.iana.org%2Fassignments%2Fipv6-unicast-address-assignments%2Fipv6-unicast-address-assignments.xml&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=12" title="Edit section: Further reading">edit</a>]</div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation cs1"><a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2317">Classless IN-ADDR.ARPA delegation</a>. March 1998. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC2317">10.17487/RFC2317</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2317">2317</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Classless+IN-ADDR.ARPA+delegation&rft.date=1998-03&rft_id=info%3Adoi%2F10.17487%2FRFC2317&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc2317&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation cs1"><a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1817">CIDR and Classful Routing</a>. August 1995. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.17487%2FRFC1817">10.17487/RFC1817</a>. <a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1817">1817</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=CIDR+and+Classful+Routing&rft.date=1995-08&rft_id=info%3Adoi%2F10.17487%2FRFC1817&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1817&rfr_id=info%3Asid%2Fen.wikipedia.org%3AClassless+Inter-Domain+Routing" class="Z3988"></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=Classless_Inter-Domain_Routing&action=edit&section=13" title="Edit section: External links">edit</a>]</div> <ul><li><a rel="nofollow" class="external text" href="https://www.cidr-report.org/as2.0/">CIDR Report</a> (updated daily)</li></ul>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Classless_Inter-Domain_Routing&oldid=1256755405">https://en.wikipedia.org/w/index.php?title=Classless_Inter-Domain_Routing&oldid=1256755405</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Internet_Standards" title="Category:Internet Standards">Internet Standards</a></li><li><a href="/wiki/Category:Internet_architecture" title="Category:Internet architecture">Internet architecture</a></li><li><a href="/wiki/Category:IP_addresses" title="Category:IP addresses">IP addresses</a></li><li><a href="/wiki/Category:Routing" title="Category:Routing">Routing</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_matches_Wikidata" title="Category:Short description matches Wikidata">Short description matches Wikidata</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 11 November 2024, at 11:57 (UTC).</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. 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