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vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Software_implementations"> <div class="vector-toc-text"> 5 Software implementations </div> </a> <button aria-controls="toc-Software_implementations-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Software implementations subsection </button> <ul id="toc-Software_implementations-sublist" class="vector-toc-list"> <li id="toc-Reference_implementation" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Reference_implementation"> <div class="vector-toc-text"> 5.1 Reference implementation </div> </a> <ul id="toc-Reference_implementation-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Windows_Time" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Windows_Time"> <div class="vector-toc-text"> 5.2 Windows Time </div> </a> <ul id="toc-Windows_Time-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-OpenNTPD" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#OpenNTPD"> <div class="vector-toc-text"> 5.3 OpenNTPD </div> </a> <ul id="toc-OpenNTPD-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-NTPsec" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#NTPsec"> <div class="vector-toc-text"> 5.4 NTPsec </div> </a> <ul id="toc-NTPsec-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-chrony" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#chrony"> <div class="vector-toc-text"> 5.5 chrony </div> </a> <ul id="toc-chrony-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Others" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Others"> <div class="vector-toc-text"> 5.6 Others </div> </a> <ul id="toc-Others-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Leap_seconds" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Leap_seconds"> <div class="vector-toc-text"> 6 Leap seconds </div> </a> <ul id="toc-Leap_seconds-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Security_concerns" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Security_concerns"> <div class="vector-toc-text"> 7 Security concerns </div> </a> <button aria-controls="toc-Security_concerns-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Security concerns subsection </button> <ul id="toc-Security_concerns-sublist" class="vector-toc-list"> <li id="toc-Secure_extensions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Secure_extensions"> <div class="vector-toc-text"> 7.1 Secure extensions </div> </a> <ul id="toc-Secure_extensions-sublist" class="vector-toc-list"> </ul> </li> </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"> 8 See also </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Notes"> <div class="vector-toc-text"> 9 Notes </div> </a> <ul id="toc-Notes-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"> 10 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"> 11 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 vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> 12 External links </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" > Toggle the table of contents </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading">Network Time Protocol</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 39 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-39" aria-hidden="true" > 39 languages </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Netwerktyd-protokol" title="Netwerktyd-protokol – Afrikaans" lang="af" hreflang="af" data-title="Netwerktyd-protokol" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target">Afrikaans</a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A8%D8%B1%D9%88%D8%AA%D9%88%D9%83%D9%88%D9%84_%D9%88%D9%82%D8%AA_%D8%A7%D9%84%D8%B4%D8%A8%D9%83%D8%A9" title="بروتوكول وقت الشبكة – Arabic" lang="ar" hreflang="ar" data-title="بروتوكول وقت الشبكة" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target">العربية</a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/NTP" title="NTP – Azerbaijani" lang="az" hreflang="az" data-title="NTP" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target">Azərbaycanca</a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/NTP" title="NTP – Belarusian" lang="be" hreflang="be" data-title="NTP" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target">Беларуская</a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%92%D1%80%D0%B5%D0%BC%D0%B5%D0%B2%D0%B8_%D0%BC%D1%80%D0%B5%D0%B6%D0%BE%D0%B2_%D0%BF%D1%80%D0%BE%D1%82%D0%BE%D0%BA%D0%BE%D0%BB" title="Времеви мрежов протокол – Bulgarian" lang="bg" hreflang="bg" data-title="Времеви мрежов протокол" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target">Български</a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Catalan" lang="ca" hreflang="ca" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Czech" lang="cs" hreflang="cs" data-title="Network Time Protocol" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target">Čeština</a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Danish" lang="da" hreflang="da" data-title="Network Time Protocol" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target">Dansk</a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – German" lang="de" hreflang="de" data-title="Network Time Protocol" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target">Deutsch</a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/V%C3%B5rguaja_protokoll" title="Võrguaja protokoll – Estonian" lang="et" hreflang="et" data-title="Võrguaja protokoll" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target">Eesti</a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Greek" lang="el" hreflang="el" data-title="Network Time Protocol" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target">Ελληνικά</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Spanish" lang="es" hreflang="es" data-title="Network Time Protocol" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Basque" lang="eu" hreflang="eu" data-title="Network Time Protocol" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target">Euskara</a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – French" lang="fr" hreflang="fr" data-title="Network Time Protocol" 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/%EB%84%A4%ED%8A%B8%EC%9B%8C%ED%81%AC_%ED%83%80%EC%9E%84_%ED%94%84%EB%A1%9C%ED%86%A0%EC%BD%9C" title="네트워크 타임 프로토콜 – Korean" lang="ko" hreflang="ko" data-title="네트워크 타임 프로토콜" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target">한국어</a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Indonesian" lang="id" hreflang="id" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Italian" lang="it" hreflang="it" data-title="Network Time Protocol" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target">Italiano</a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Hebrew" lang="he" hreflang="he" data-title="Network Time Protocol" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target">עברית</a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/NTP" title="NTP – Latvian" lang="lv" hreflang="lv" data-title="NTP" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target">Latviešu</a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/H%C3%A1l%C3%B3zati_id%C5%91_protokoll" title="Hálózati idő protokoll – Hungarian" lang="hu" hreflang="hu" data-title="Hálózati idő protokoll" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target">Magyar</a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%9C%D1%80%D0%B5%D0%B6%D0%B5%D0%BD_%D0%BF%D1%80%D0%BE%D1%82%D0%BE%D0%BA%D0%BE%D0%BB_%D0%B7%D0%B0_%D0%B2%D1%80%D0%B5%D0%BC%D0%B5" title="Мрежен протокол за време – Macedonian" lang="mk" hreflang="mk" data-title="Мрежен протокол за време" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target">Македонски</a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Protokol_Masa_Rangkaian" title="Protokol Masa Rangkaian – Malay" lang="ms" hreflang="ms" data-title="Protokol Masa Rangkaian" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target">Bahasa Melayu</a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Mongolian" lang="mn" hreflang="mn" data-title="Network Time Protocol" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target">Монгол</a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Dutch" lang="nl" hreflang="nl" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Japanese" lang="ja" hreflang="ja" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Polish" lang="pl" hreflang="pl" data-title="Network Time Protocol" 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/Network_Time_Protocol" title="Network Time Protocol – Portuguese" lang="pt" hreflang="pt" data-title="Network Time Protocol" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target">Português</a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Romanian" lang="ro" hreflang="ro" data-title="Network Time Protocol" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target">Română</a></li><li class="interlanguage-link interwiki-ru badge-Q17559452 badge-recommendedarticle mw-list-item" title="recommended article"><a href="https://ru.wikipedia.org/wiki/NTP" title="NTP – Russian" lang="ru" hreflang="ru" data-title="NTP" 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/Network_Time_Protocol" title="Network Time Protocol – Simple English" lang="en-simple" hreflang="en-simple" data-title="Network Time Protocol" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target">Simple English</a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/NTP_(tietotekniikka)" title="NTP (tietotekniikka) – Finnish" lang="fi" hreflang="fi" data-title="NTP (tietotekniikka)" 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/Network_Time_Protocol" title="Network Time Protocol – Swedish" lang="sv" hreflang="sv" data-title="Network Time Protocol" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target">Svenska</a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B9%80%E0%B8%AD%E0%B9%87%E0%B8%99%E0%B8%97%E0%B8%B5%E0%B8%9E%E0%B8%B5" title="เอ็นทีพี – Thai" lang="th" hreflang="th" data-title="เอ็นทีพี" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target">ไทย</a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Turkish" lang="tr" hreflang="tr" data-title="Network Time Protocol" 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/NTP" title="NTP – Ukrainian" lang="uk" hreflang="uk" data-title="NTP" 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/NTP" title="NTP – Vietnamese" lang="vi" hreflang="vi" data-title="NTP" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target">Tiếng Việt</a></li><li class="interlanguage-link interwiki-yo mw-list-item"><a href="https://yo.wikipedia.org/wiki/Network_Time_Protocol" title="Network Time Protocol – Yoruba" lang="yo" hreflang="yo" data-title="Network Time Protocol" data-language-autonym="Yorùbá" data-language-local-name="Yoruba" class="interlanguage-link-target">Yorùbá</a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E7%B6%B2%E8%B7%AF%E6%99%82%E9%96%93%E5%8D%94%E5%AE%9A" title="網路時間協定 – Chinese" lang="zh" hreflang="zh" data-title="網路時間協定" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target">中文</a></li> </ul> <div class="after-portlet after-portlet-lang"><a 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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">Not to be confused with <a href="/wiki/Daytime_Protocol" title="Daytime Protocol">Daytime Protocol</a>, <a href="/wiki/Time_Protocol" title="Time Protocol">Time Protocol</a>, or <a href="/wiki/NNTP" class="mw-redirect" title="NNTP">NNTP</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox vevent"><caption class="infobox-title summary">Network Time Protocol</caption><tbody><tr><td colspan="2" class="infobox-image"><a href="/wiki/File:Network_Time_Protocol_servers_and_clients.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/220px-Network_Time_Protocol_servers_and_clients.svg.png" decoding="async" width="220" height="197" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/330px-Network_Time_Protocol_servers_and_clients.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/440px-Network_Time_Protocol_servers_and_clients.svg.png 2x" data-file-width="470" data-file-height="420" /></a></td></tr><tr><th scope="row" class="infobox-label">International standard</th><td class="infobox-data"><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 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class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a></td></tr><tr><th scope="row" class="infobox-label">Developed by</th><td class="infobox-data"><a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a>, Harlan Stenn, Network Time Foundation</td></tr><tr><th scope="row" class="infobox-label">Introduced</th><td class="infobox-data">1985; 39 years ago (1985)</td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": 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class="mw-redirect" title="Open Network Computing Remote Procedure Call">ONC/RPC</a></li> <li><a href="/wiki/Real-time_Transport_Protocol" title="Real-time Transport Protocol">RTP</a></li> <li><a href="/wiki/Real_Time_Streaming_Protocol" class="mw-redirect" title="Real Time Streaming Protocol">RTSP</a></li> <li><a href="/wiki/Routing_Information_Protocol" title="Routing Information Protocol">RIP</a></li> <li><a href="/wiki/Session_Initiation_Protocol" title="Session Initiation Protocol">SIP</a></li> <li><a href="/wiki/Simple_Mail_Transfer_Protocol" title="Simple Mail Transfer Protocol">SMTP</a></li> <li><a href="/wiki/Simple_Network_Management_Protocol" title="Simple Network Management Protocol">SNMP</a></li> <li><a href="/wiki/Secure_Shell" title="Secure Shell">SSH</a></li> <li><a href="/wiki/Telnet" title="Telnet">Telnet</a></li> <li><a href="/wiki/Transport_Layer_Security" title="Transport Layer Security">TLS/SSL</a></li> <li><a href="/wiki/XMPP" title="XMPP">XMPP</a></li> <li><a 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class="sidebar-heading"> <a href="/wiki/Internet_layer" title="Internet layer">Internet layer</a></th></tr><tr><td class="sidebar-content"> <ul><li><a href="/wiki/Internet_Protocol" title="Internet Protocol">IP</a> <ul><li><a href="/wiki/IPv4" title="IPv4">v4</a></li> <li><a href="/wiki/IPv6" title="IPv6">v6</a></li></ul></li> <li><a href="/wiki/Internet_Control_Message_Protocol" title="Internet Control Message Protocol">ICMP</a> (<a href="/wiki/ICMPv6" title="ICMPv6">v6</a>)</li> <li><a href="/wiki/Neighbor_Discovery_Protocol" title="Neighbor Discovery Protocol">NDP</a></li> <li><a href="/wiki/Explicit_Congestion_Notification" title="Explicit Congestion Notification">ECN</a></li> <li><a href="/wiki/Internet_Group_Management_Protocol" title="Internet Group Management Protocol">IGMP</a></li> <li><a href="/wiki/IPsec" title="IPsec">IPsec</a></li> <li><a href="/wiki/Category:Internet_layer_protocols" title="Category:Internet layer protocols">more...</a></li></ul></td> </tr><tr><th class="sidebar-heading"> <a href="/wiki/Link_layer" title="Link layer">Link layer</a></th></tr><tr><td class="sidebar-content"> <ul><li><a href="/wiki/Address_Resolution_Protocol" title="Address Resolution Protocol">ARP</a></li> <li><a href="/wiki/Tunneling_protocol" title="Tunneling protocol">Tunnels</a></li> <li><a href="/wiki/Point-to-Point_Protocol" title="Point-to-Point Protocol">PPP</a></li> <li><a href="/wiki/Medium_access_control" title="Medium access control">MAC</a></li> <li><a href="/wiki/Category:Link_protocols" title="Category:Link protocols">more...</a></li></ul></td> </tr><tr><td class="sidebar-navbar"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Internet_protocol_suite" title="Template:Internet protocol suite"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Internet_protocol_suite" title="Template talk:Internet protocol suite"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Internet_protocol_suite" title="Special:EditPage/Template:Internet protocol suite"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> The Network Time Protocol (NTP) is a <a href="/wiki/Networking_protocol" class="mw-redirect" title="Networking protocol">networking protocol</a> for <a href="/wiki/Clock_synchronization" title="Clock synchronization">clock synchronization</a> between computer systems over <a href="/wiki/Packet-switched" class="mw-redirect" title="Packet-switched">packet-switched</a>, variable-<a href="/wiki/Network_latency" class="mw-redirect" title="Network latency">latency</a> data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by <a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a> of the <a href="/wiki/University_of_Delaware" title="University of Delaware">University of Delaware</a>. NTP is intended to <a href="/wiki/Synchronize" class="mw-redirect" title="Synchronize">synchronize</a> participating computers to within a few <a href="/wiki/Millisecond" title="Millisecond">milliseconds</a> of <a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">Coordinated Universal Time</a> (UTC).<a href="#cite_note-Mills2010-1">[1]</a>: 3  It uses the <a href="/wiki/Intersection_algorithm" title="Intersection algorithm">intersection algorithm</a>, a modified version of <a href="/wiki/Marzullo%27s_algorithm" title="Marzullo's algorithm">Marzullo's algorithm</a>, to select accurate <a href="/wiki/Time_server" title="Time server">time servers</a> and is designed to mitigate the effects of variable <a href="/wiki/Network_latency" class="mw-redirect" title="Network latency">network latency</a>. NTP can usually maintain time to within tens of milliseconds over the public <a href="/wiki/Internet" title="Internet">Internet</a>, and can achieve better than one millisecond accuracy in <a href="/wiki/Local_area_network" title="Local area network">local area networks</a> under ideal conditions. Asymmetric <a href="/wiki/Routing" title="Routing">routes</a> and <a href="/wiki/Network_congestion" title="Network congestion">network congestion</a> can cause errors of 100 ms or more.<a href="#cite_note-summary-2">[2]</a><a href="#cite_note-faq-3">[3]</a> The protocol is usually described in terms of a <a href="/wiki/Client%E2%80%93server_model" title="Client–server model">client–server model</a>, but can as easily be used in <a href="/wiki/Peer-to-peer" title="Peer-to-peer">peer-to-peer</a> relationships where both peers consider the other to be a potential time source.<a href="#cite_note-Mills2010-1">[1]</a>: 20  Implementations send and receive <a href="/wiki/Timestamp" title="Timestamp">timestamps</a> using the <a href="/wiki/User_Datagram_Protocol" title="User Datagram Protocol">User Datagram Protocol</a> (UDP) on <a href="/wiki/Port_number" class="mw-redirect" title="Port number">port number</a> 123.<a href="#cite_note-qNvGW-4">[4]</a><a href="#cite_note-rfc5905-5">[5]</a>: 16  They can also use <a href="/wiki/Broadcasting_(networking)" title="Broadcasting (networking)">broadcasting</a> or <a href="/wiki/Multicasting" class="mw-redirect" title="Multicasting">multicasting</a>, where clients passively listen to time updates after an initial round-trip calibrating exchange.<a href="#cite_note-faq-3">[3]</a> NTP supplies a warning of any impending <a href="/wiki/Leap_second" title="Leap second">leap second</a> adjustment, but no information about local <a href="/wiki/Time_zone" title="Time zone">time zones</a> or <a href="/wiki/Daylight_saving_time" title="Daylight saving time">daylight saving time</a> is transmitted.<a href="#cite_note-summary-2">[2]</a><a href="#cite_note-faq-3">[3]</a> The current protocol is version 4 (NTPv4),<a href="#cite_note-rfc5905-5">[5]</a> which is <a href="/wiki/Backward_compatible" class="mw-redirect" title="Backward compatible">backward compatible</a> with version 3.<a href="#cite_note-rfc1305-6">[6]</a> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=1" title="Edit section: History">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:DL_Mills-2.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3f/DL_Mills-2.jpg/170px-DL_Mills-2.jpg" decoding="async" width="170" height="349" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/3f/DL_Mills-2.jpg/255px-DL_Mills-2.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/3f/DL_Mills-2.jpg/340px-DL_Mills-2.jpg 2x" data-file-width="752" data-file-height="1544" /></a><figcaption>NTP was designed by <a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a>.</figcaption></figure> <table id="Container" role="presentation" class="toccolours searchaux" style="text-align:left;padding:0 0.5em;border-style:solid;float:left;clear:left;margin:0.3em 1.4em 0.8em 0;overflow:hidden;min-width:34.15em"><tbody><tr><td colspan="3" id="Title" style="padding:1em 1em 1em 1em"><div style="background-color:#77bb77;padding:0 0.2em 0 0.2em;font-weight:bold;text-align:center"><a href="/wiki/Request_for_Comments" title="Request for Comments">RFC</a> evolution for NTP</div></td></tr><tr style="vertical-align:top"><td id="Scale" style="padding:0;margin:0.7em 0 0.7em 0;width:4.2em;position:relative;float:left;font-size:100%;height:500px;border-right:1px solid #242020"><div style="float:right;position:absolute;right:-1px;top:500.00px;transform:translateY(-50%)">1980 —</div><div style="float:right;position:absolute;right:-1px;top:470.93px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:441.86px;transform:translateY(-50%)">1985 —</div><div style="float:right;position:absolute;right:-1px;top:412.79px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:383.72px;transform:translateY(-50%)">1990 —</div><div style="float:right;position:absolute;right:-1px;top:354.65px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:325.58px;transform:translateY(-50%)">1995 —</div><div style="float:right;position:absolute;right:-1px;top:296.51px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:267.44px;transform:translateY(-50%)">2000 —</div><div style="float:right;position:absolute;right:-1px;top:238.37px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:209.30px;transform:translateY(-50%)">2005 —</div><div style="float:right;position:absolute;right:-1px;top:180.23px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:151.16px;transform:translateY(-50%)">2010 —</div><div style="float:right;position:absolute;right:-1px;top:122.09px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:93.02px;transform:translateY(-50%)">2015 —</div><div style="float:right;position:absolute;right:-1px;top:63.95px;transform:translateY(-50%)">–</div><div style="float:right;position:absolute;right:-1px;top:34.88px;transform:translateY(-50%)">2020 —</div><div style="float:right;position:absolute;right:-1px;top:5.81px;transform:translateY(-50%)">–</div></td><td id="Timeline" class="toccolours notheme" style="padding:0px;margin:0.7em 0 0.7em 0;position:relative;font-size:100%;width:18em;height:500px;float:left;border:none;background-color:#bbeebb"><div class="notheme" style="font-size:100%;background-color:#6ca;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:406.977px;height:34.884px;left:0.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-17.442px;transform:translateY(-50%);z-index:5">v0, RFC 958<a href="#cite_note-rfc958-7">[7]</a></div></div><div class="notheme" style="font-size:100%;background-color:#ff9;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:395.349px;height:11.628px;left:0.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-5.814px;transform:translateY(-50%);z-index:5">v1, RFC 1059<a href="#cite_note-rfc1059-8">[8]</a></div></div><div class="notheme" style="font-size:100%;background-color:#6cf;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:360.465px;height:34.884px;left:0.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-17.442px;transform:translateY(-50%);z-index:5">v2, RFC 1119<a href="#cite_note-rfc1119-9">[9]</a></div></div><div class="notheme" style="font-size:100%;background-color:#c96;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:151.163px;height:209.302px;left:0.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-104.651px;transform:translateY(-50%);z-index:5">v3, RFC 1305<a href="#cite_note-rfc1305-6">[6]</a></div></div><div class="notheme" style="font-size:100%;background-color:#fcc;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:0.000px;height:151.163px;left:0.900em;width:16.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-75.581px;transform:translateY(-50%);z-index:5">v4, RFC 5905<a href="#cite_note-rfc5905-5">[5]</a></div></div><div class="notheme" style="font-size:100%;background-color:#96c;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:325.581px;height:34.884px;left:9.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-17.442px;transform:translateY(-50%);z-index:5">v3, RFC 1361<a href="#cite_note-rfc1361-10">[10]</a></div></div><div class="notheme" style="font-size:100%;background-color:#cc6;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:313.953px;height:11.628px;left:9.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-5.814px;transform:translateY(-50%);z-index:5">v3, RFC 1769<a href="#cite_note-rfc1769-11">[11]</a></div></div><div class="notheme" style="font-size:100%;background-color:#ccc;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:197.674px;height:116.279px;left:9.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-58.140px;transform:translateY(-50%);z-index:5">v4, RFC 2030<a href="#cite_note-rfc2030-12">[12]</a></div></div><div class="notheme" style="font-size:100%;background-color:#f66;border-style:none none;position:absolute;text-align:center;margin:0;padding:0;top:151.163px;height:46.512px;left:9.900em;width:7.200em"><div class="notheme" style="position:relative;text-align:center;vertical-align:middle;display:block;bottom:-23.256px;transform:translateY(-50%);z-index:5">v4, RFC 4330<a href="#cite_note-rfc4330-13">[13]</a></div></div></td><td id="Annotations" style="padding:0;margin:0.7em 0 0.7em 0;float:left;position:relative;width:10.25em;height:500px"><table role="presentation" style="position:absolute;z-index:15;top:488.372px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:green;display:block;line-height:105%;bottom:0">DCNET Internet Clock Service<a href="#cite_note-rfc778-14">[14]</a></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:360.465px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:blue;display:block;line-height:105%;bottom:0">SNTP</div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:151.163px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:blue;display:block;line-height:105%;bottom:0">SNTP merged</div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:81.395px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:red;display:block;line-height:105%;bottom:0">Ext. fields<a href="#cite_note-rfc7822-15">[15]</a></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:46.512px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:red;display:block;line-height:105%;bottom:0"><a href="/wiki/Message_authentication_code" title="Message authentication code">MAC</a> change<a href="#cite_note-rfc8573-16">[16]</a></div></td></tr></tbody></table><table role="presentation" style="position:absolute;z-index:15;top:23.256px;left:0em;transform:translateY(-50%);padding:0;margin:0;font-size:100%"><tbody><tr><td style="padding:0;text-align:left;vertical-align:middle">←</td><td style="padding:0;text-align:left;vertical-align:middle"><div style="z-index:10;font-size:90%;color:red;display:block;line-height:105%;bottom:0">Port randomization<a href="#cite_note-rfc9109-17">[17]</a></div></td></tr></tbody></table></td></tr><tr><td id="Caption" colspan="3" style="padding:0;margin:0 0.2em 0.7em 0.2em"><div id="Caption" class="toccolours" style="margin:0 0.5em;border-style:none;clear:both;text-align:center;width:31em"></div></td></tr></tbody></table> In 1979, network <a href="/wiki/Time_synchronization" class="mw-redirect" title="Time synchronization">time synchronization</a> technology was used in what was possibly the first public demonstration of <a href="/wiki/Internet" title="Internet">Internet</a> services running over a trans-Atlantic satellite network, at the <a href="/wiki/National_Computer_Conference" class="mw-redirect" title="National Computer Conference">National Computer Conference</a> in New York. The technology was later described in the 1981 Internet Engineering Note (IEN) 173<a href="#cite_note-ND7CF-18">[18]</a> and a public protocol was developed from it that was documented 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/rfc778">778</a>. The technology was first deployed in a local area network as part of the Hello routing protocol and implemented in the <a href="/wiki/Fuzzball_router" title="Fuzzball router">Fuzzball router</a>, an experimental operating system used in network prototyping, where it ran for many years. Other related network tools were available both then and now. They include the <a href="/wiki/Daytime_Protocol" title="Daytime Protocol">Daytime</a> and <a href="/wiki/Time_Protocol" title="Time Protocol">Time</a> protocols for recording the time of events, as well as the <a href="/wiki/ICMP_Timestamp" class="mw-redirect" title="ICMP Timestamp">ICMP Timestamp</a> messages and IP Timestamp option (<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/rfc781">781</a>). More complete synchronization systems, although lacking NTP's data analysis and clock disciplining algorithms, include the <a href="/wiki/Unix" title="Unix">Unix</a> daemon <a href="/wiki/Timed" title="Timed">timed</a>, which uses an election algorithm to appoint a server for all the clients;<a href="#cite_note-Y8SkT-19">[19]</a> and the Digital Time Synchronization Service (DTSS), which uses a hierarchy of servers similar to the NTP stratum model. In 1985, NTP version 0 (NTPv0) was implemented in both Fuzzball and Unix, and the NTP packet header and <a href="/wiki/Round-trip_delay" title="Round-trip delay">round-trip delay</a> and offset calculations, which have persisted into NTPv4, were documented 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/rfc958">958</a>. Despite the relatively slow computers and networks available at the time, accuracy of better than 100 <a href="/wiki/Millisecond" title="Millisecond">milliseconds</a> was usually obtained on Atlantic spanning links, with accuracy of tens of milliseconds on <a href="/wiki/Ethernet" title="Ethernet">Ethernet</a> networks. In 1988, a much more complete specification of the NTPv1 protocol, with associated algorithms, was published 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/rfc1059">1059</a>. It drew on the experimental results and clock filter algorithm documented 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/rfc956">956</a> and was the first version to describe the <a href="/wiki/Client%E2%80%93server" class="mw-redirect" title="Client–server">client–server</a> and <a href="/wiki/Peer-to-peer" title="Peer-to-peer">peer-to-peer</a> modes. In 1991, the NTPv1 architecture, protocol and algorithms were brought to the attention of a wider engineering community with the publication of an article by <a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a> in the <a href="/wiki/IEEE_Transactions_on_Communications" title="IEEE Transactions on Communications">IEEE Transactions on Communications</a>.<a href="#cite_note-AMYJK-20">[20]</a> In 1989, <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/rfc1119">1119</a> was published defining NTPv2 by means of a <a href="/wiki/State_machine" class="mw-redirect" title="State machine">state machine</a>, with <a href="/wiki/Pseudocode" title="Pseudocode">pseudocode</a> to describe its operation. It introduced a management protocol and <a href="/wiki/Digital_signature" title="Digital signature">cryptographic authentication</a> scheme which have both survived into NTPv4, along with the bulk of the algorithm. However the design of NTPv2 was criticized for lacking <a href="/wiki/Correctness_(computer_science)" title="Correctness (computer science)">formal correctness</a> by the DTSS community, and the clock selection procedure was modified to incorporate <a href="/wiki/Marzullo%27s_algorithm" title="Marzullo's algorithm">Marzullo's algorithm</a> for NTPv3 onwards.<a href="#cite_note-">[21]</a> In 1992, <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/rfc1305">1305</a> defined NTPv3. The RFC included an analysis of all sources of error, from the <a href="/wiki/Master_clock" title="Master clock">reference clock</a> down to the final client, which enabled the calculation of a <a href="/wiki/Software_metric" title="Software metric">metric</a> that helps choose the best server where several candidates appear to disagree. Broadcast mode was introduced. In subsequent years, as new features were added and algorithm improvements were made, it became apparent that a new protocol version was required.<a href="#cite_note-MillsES-22">[22]</a> In 2010, <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/rfc5905">5905</a> was published containing a proposed specification for NTPv4.<a href="#cite_note-E4akm-23">[23]</a> Following the retirement of Mills from the <a href="/wiki/University_of_Delaware" title="University of Delaware">University of Delaware</a>, the reference implementation is currently maintained as an <a href="/wiki/Open_source" title="Open source">open source</a> project led by Harlan Stenn.<a href="#cite_note-jZjhj-24">[24]</a><a href="#cite_note-MShrI-25">[25]</a> On the IANA side, a ntp (network time protocols) work group is in charge of reviewing proposed drafts.<a href="#cite_note-ntpwg-doc-26">[26]</a> The protocol has significantly progressed since NTPv4.<a href="#cite_note-E4akm-23">[23]</a> As of 2022<a class="external text" href="https://en.wikipedia.org/w/index.php?title=Network_Time_Protocol&action=edit">[update]</a>, three RFC documents describing updates to the protocol have been published,<a href="#cite_note-rfc5905-5">[5]</a> not counting the numerous peripheral standards such as NTS (<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/rfc8915">8915</a>).<a href="#cite_note-ntpwg-doc-26">[26]</a> Mills had mentioned plans for a "NTPv5" on his page, but one was never published.<a href="#cite_note-E4akm-23">[23]</a> An unrelated draft termed "NTPv5" by M. Lichvar of <a href="/wiki/Chrony" title="Chrony">chrony</a> was initiated in 2020 and includes security, accuracy, and scaling changes.<a href="#cite_note-27">[27]</a> <div class="mw-heading mw-heading3"><h3 id="SNTP">SNTP</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=2" title="Edit section: SNTP">edit</a>]</div> As NTP replaced the use of the old <a href="/wiki/Time_Protocol" title="Time Protocol">Time Protocol</a>, some use cases nevertheless found the full protocol too complicated. In 1992, Simple Network Time Protocol (SNTP) was defined to fill this niche. The SNTPv3 standard describes a way to use NTPv3, such that no storage of <a href="/wiki/State_(computer_science)" title="State (computer science)">state</a> over an extended period is needed. The topology becomes essentially the same as with the Time Protocol, as only one server is used.<a href="#cite_note-rfc1361-10">[10]</a> In 1996, SNTP was updated to SNTPv4<a href="#cite_note-rfc2030-12">[12]</a> with some features of the then-in-development NTPv4. The current version of SNTPv4 was merged into the main NTPv4 standard in 2010.<a href="#cite_note-rfc5905-5">[5]</a> SNTP is fully interoperable with NTP since it does not define a new protocol.<a href="#cite_note-">[28]</a>: §14  However, the simple algorithms provide times of reduced accuracy and thus it is inadvisable to sync time from an SNTP source.<a href="#cite_note-rfc4330-13">[13]</a> <div class="mw-heading mw-heading2"><h2 id="Clock_strata">Clock strata</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=3" title="Edit section: Clock strata">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Usno-amc.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/Usno-amc.jpg/220px-Usno-amc.jpg" decoding="async" width="220" height="114" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/45/Usno-amc.jpg/330px-Usno-amc.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/45/Usno-amc.jpg/440px-Usno-amc.jpg 2x" data-file-width="1197" data-file-height="618" /></a><figcaption>The <a href="/wiki/United_States_Naval_Observatory" title="United States Naval Observatory">U.S. Naval Observatory</a> Alternate Master Clock at <a href="/wiki/Schriever_Air_Force_Base" class="mw-redirect" title="Schriever Air Force Base">Schriever AFB (Colorado)</a> is a stratum 0 source for NTP</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Network_Time_Protocol_servers_and_clients.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/220px-Network_Time_Protocol_servers_and_clients.svg.png" decoding="async" width="220" height="197" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/330px-Network_Time_Protocol_servers_and_clients.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Network_Time_Protocol_servers_and_clients.svg/440px-Network_Time_Protocol_servers_and_clients.svg.png 2x" data-file-width="470" data-file-height="420" /></a><figcaption>Yellow arrows indicate a direct connection; red arrows indicate a network connection.</figcaption></figure> NTP uses a hierarchical, semi-layered system of time sources. Each level of this hierarchy is termed a stratum and is assigned a number starting with zero for the reference clock at the top. A server synchronized to a stratum n server runs at stratum n + 1. The number represents the distance from the reference clock and is used to prevent cyclical dependencies in the hierarchy. Stratum is not always an indication of quality or reliability; it is common to find stratum 3 time sources that are higher quality than other stratum 2 time sources.<a href="#cite_note-29">[a]</a> A brief description of strata 0, 1, 2 and 3 is provided below. <dl><dt>Stratum 0</dt> <dd>These are high-precision timekeeping devices such as <a href="/wiki/Atomic_clock" title="Atomic clock">atomic clocks</a>, <a href="/wiki/GNSS" class="mw-redirect" title="GNSS">GNSS</a> (including <a href="/wiki/GPS" class="mw-redirect" title="GPS">GPS</a>) or other <a href="/wiki/Radio_clock" title="Radio clock">radio clocks</a>, or a <a href="/wiki/Precision_Time_Protocol" title="Precision Time Protocol">PTP</a>-synchronized clock.<a href="#cite_note-30">[29]</a> They generate a very accurate <a href="/wiki/Pulse_per_second" class="mw-redirect" title="Pulse per second">pulse per second</a> signal that triggers an <a href="/wiki/Interrupt" title="Interrupt">interrupt</a> and timestamp on a connected computer. Stratum 0 devices are also known as reference clocks. NTP servers cannot advertise themselves as stratum 0. A stratum field set to 0 in NTP packet indicates an unspecified stratum.<a href="#cite_note-GPf8p-31">[30]</a></dd> <dt>Stratum 1</dt> <dd>These are computers whose <a href="/wiki/System_time" title="System time">system time</a> is synchronized to within a few microseconds of their attached stratum 0 devices. Stratum 1 servers may peer with other stratum 1 servers for <a href="/wiki/Sanity_check" title="Sanity check">sanity check</a> and backup.<a href="#cite_note-cisco-32">[31]</a> They are also referred to as primary time servers.<a href="#cite_note-summary-2">[2]</a><a href="#cite_note-faq-3">[3]</a></dd> <dt>Stratum 2</dt> <dd>These are computers that are synchronized over a network to stratum 1 servers. Often a stratum 2 computer queries several stratum 1 servers. Stratum 2 computers may also peer with other stratum 2 computers to provide more stable and robust time for all devices in the peer group.</dd> <dt>Stratum 3</dt> <dd>These are computers that are synchronized to stratum 2 servers. They employ the same algorithms for peering and data sampling as stratum 2, and can themselves act as servers for stratum 4 computers, and so on.</dd></dl> The upper limit for stratum is 15; stratum 16 is used to indicate that a device is unsynchronized. The NTP algorithms on each computer interact to construct a <a href="/wiki/Bellman%E2%80%93Ford" class="mw-redirect" title="Bellman–Ford">Bellman–Ford</a> shortest-path <a href="/wiki/Spanning_tree" title="Spanning tree">spanning tree</a>, to minimize the accumulated round-trip delay to the stratum 1 servers for all the clients.<a href="#cite_note-Mills2010-1">[1]</a>: 20  In addition to stratum, the protocol is able to identify the synchronization source for each server in terms of a reference identifier (refid). <table class="wikitable sortable"> <caption>Common time reference identifiers (refid) codes </caption> <tbody><tr> <th>Refid<a href="#cite_note-MIvTF-33">[32]</a></th> <th>Clock Source </th></tr> <tr> <td>GOES</td> <td>Geosynchronous Orbit Environment Satellite </td></tr> <tr> <td>GPS</td> <td><a href="/wiki/Global_Positioning_System" title="Global Positioning System">Global Positioning System</a> </td></tr> <tr> <td>GAL</td> <td><a href="/wiki/Galileo_(satellite_navigation)" title="Galileo (satellite navigation)">Galileo</a> Positioning System </td></tr> <tr> <td>PPS</td> <td>Generic pulse-per-second </td></tr> <tr> <td>IRIG</td> <td>Inter-Range Instrumentation Group </td></tr> <tr> <td>WWVB</td> <td>LF Radio <a href="/wiki/WWVB" title="WWVB">WWVB</a> Fort Collins, Colorado 60 kHz </td></tr> <tr> <td>DCF</td> <td>LF Radio <a href="/wiki/DCF77" title="DCF77">DCF77</a> Mainflingen, DE 77.5 kHz </td></tr> <tr> <td>HBG</td> <td>LF Radio <a href="/wiki/HBG_(time_signal)" title="HBG (time signal)">HBG</a> Prangins, HB 75 kHz (ceased operation) </td></tr> <tr> <td>MSF</td> <td>LF Radio <a href="/wiki/Time_from_NPL_(MSF)" title="Time from NPL (MSF)">MSF</a> Anthorn, UK 60 kHz </td></tr> <tr> <td>JJY</td> <td>LF Radio <a href="/wiki/JJY" title="JJY">JJY</a> Fukushima, JP 40 kHz, Saga, JP 60 kHz </td></tr> <tr> <td>LORC</td> <td>MF Radio <a href="/wiki/Loran-C" title="Loran-C">Loran-C</a> station, 100 kHz </td></tr> <tr> <td>TDF</td> <td><a href="/wiki/TDF_time_signal" class="mw-redirect" title="TDF time signal">MF Radio Allouis, FR 162 kHz</a> </td></tr> <tr> <td>CHU</td> <td>HF Radio <a href="/wiki/CHU_(radio_station)" title="CHU (radio station)">CHU</a> Ottawa, Ontario </td></tr> <tr> <td>WWV</td> <td>HF Radio <a href="/wiki/WWV_(radio_station)" title="WWV (radio station)">WWV</a> Fort Collins, Colorado </td></tr> <tr> <td>WWVH</td> <td>HF Radio <a href="/wiki/WWVH" title="WWVH">WWVH</a> Kauai, Hawaii </td></tr> <tr> <td>NIST</td> <td><a href="/wiki/NIST" class="mw-redirect" title="NIST">NIST</a> telephone modem </td></tr> <tr> <td>ACTS</td> <td>NIST telephone modem </td></tr> <tr> <td>USNO</td> <td>USNO telephone modem </td></tr> <tr> <td>PTB</td> <td>German PTB time standard telephone modem </td></tr> <tr> <td>MRS</td> <td>(Informal) Multi Reference Sources </td></tr> <tr> <td>GOOG</td> <td>(Unofficial) Google Refid used by Google NTP servers as time4.google.com </td></tr></tbody></table> For servers on stratum 2 and below, the refid is an encoded form of the upstream time server's IP address. For IPv4, this is simply the 32-bit address; for IPv6, it would be the first 32 bits of the MD5 hash of the source address. Refids serve to detect and prevent timing loops to the first degree.<a href="#cite_note-rfc5905-5">[5]</a> The refid field is filled with status words in the case of kiss-o'-death (KoD) packets, which tell the client to stop sending requests so that the server can rest.<a href="#cite_note-rfc5905-5">[5]</a> Some examples are INIT (initialization), STEP (step time change), and RATE (client requesting too fast).<a href="#cite_note-34">[33]</a> The program output may additionally use codes not transmitted in the packet to indicate error, such as XFAC to indicate a network disconnection.<a href="#cite_note-MIvTF-33">[32]</a> The IANA maintains a registry for refid source names and KoD codes. Informal assignments can still appear.<a href="#cite_note-35">[34]</a> <div class="mw-heading mw-heading2"><h2 id="Timestamps">Timestamps</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=4" title="Edit section: Timestamps">edit</a>]</div> The 64-bit <a href="/wiki/Fixed-point_arithmetic" title="Fixed-point arithmetic">binary fixed-point</a> timestamps used by NTP consist of a 32-bit part for seconds and a 32-bit part for fractional second, giving a time scale that <a href="/wiki/Integer_overflow" title="Integer overflow">rolls over</a> every 232 seconds (136 years) and a theoretical resolution of 2−32 seconds (233 picoseconds). NTP uses an <a href="/wiki/Epoch" title="Epoch">epoch</a> of January 1, 1900. Therefore, the first rollover occurs on February 7, 2036.<a href="#cite_note-mvUS1-36">[35]</a><a href="#cite_note-StevensFenner2004-37">[36]</a> NTPv4 introduces a 128-bit date format: 64 bits for the second and 64 bits for the fractional-second. The most-significant 32 bits of this format is the Era Number which resolves rollover ambiguity in most cases.<a href="#cite_note-bzRE9-38">[37]</a> According to Mills, "The 64-bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64-bit second value is enough to provide unambiguous time representation until the universe goes dim."<a href="#cite_note-FIILt-39">[38]</a><a href="#cite_note-40">[b]</a> <div class="mw-heading mw-heading2"><h2 id="Clock_synchronization_algorithm">Clock synchronization algorithm</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=5" title="Edit section: Clock synchronization algorithm">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:NTP-Algorithm.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8d/NTP-Algorithm.svg/220px-NTP-Algorithm.svg.png" decoding="async" width="220" height="103" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8d/NTP-Algorithm.svg/330px-NTP-Algorithm.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8d/NTP-Algorithm.svg/440px-NTP-Algorithm.svg.png 2x" data-file-width="463" data-file-height="216" /></a><figcaption>Round-trip delay time δ</figcaption></figure> A typical NTP client regularly <a href="/wiki/Polling_(computer_science)" title="Polling (computer science)">polls</a> one or more NTP servers. The client must compute its time offset and <a href="/wiki/Round-trip_delay" title="Round-trip delay">round-trip delay</a>. Time offset θ is positive or negative (client time > server time) difference in absolute time between the two clocks. It is defined by <math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \theta ={\frac {(t_{1}-t_{0})+(t_{2}-t_{3})}{2}},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>θ</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msub> <mo>−</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo stretchy="false">)</mo> <mo>+</mo> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> <mo>−</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </mfrac> </mrow> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \theta ={\frac {(t_{1}-t_{0})+(t_{2}-t_{3})}{2}},}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9a9ff4428ee0102d2c62b260df1b38b26989b383" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:25.387ex; height:5.676ex;" alt="{\displaystyle \theta ={\frac {(t_{1}-t_{0})+(t_{2}-t_{3})}{2}},}"> and the round-trip delay δ by <math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \delta ={(t_{3}-t_{0})-(t_{2}-t_{1})},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>δ</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msub> <mo>−</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo stretchy="false">)</mo> <mo>−</mo> <mo stretchy="false">(</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> <mo>−</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msub> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \delta ={(t_{3}-t_{0})-(t_{2}-t_{1})},}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/65338ea1460dfa5f67b959d315b2cfd47983218f" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:24.509ex; height:2.843ex;" alt="{\displaystyle \delta ={(t_{3}-t_{0})-(t_{2}-t_{1})},}"> where <ul><li>t0 is the client's timestamp of the request packet transmission,</li> <li>t1 is the server's timestamp of the request packet reception,</li> <li>t2 is the server's timestamp of the response packet transmission and</li> <li>t3 is the client's timestamp of the response packet reception.<a href="#cite_note-Mills2010-1">[1]</a>: 19 </li></ul> To derive the expression for the offset, note that for the request packet, <math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle t_{0}+\theta +\delta /2=t_{1}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo>+</mo> <mi>θ</mi> <mo>+</mo> <mi>δ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mn>2</mn> <mo>=</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle t_{0}+\theta +\delta /2=t_{1}}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/64f5c9a6ddc61f286ff5a58ffc276b994906a00c" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:17.031ex; height:2.843ex;" alt="{\displaystyle t_{0}+\theta +\delta /2=t_{1}}"> and for the response packet, <math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle t_{3}+\theta -\delta /2=t_{2}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msub> <mo>+</mo> <mi>θ</mi> <mo>−</mo> <mi>δ</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mn>2</mn> <mo>=</mo> <msub> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle t_{3}+\theta -\delta /2=t_{2}}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/7a0b6f9be48356814dd3c2086384f4375f8cfdcc" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:17.031ex; height:2.843ex;" alt="{\displaystyle t_{3}+\theta -\delta /2=t_{2}}"> Solving for θ yields the definition of the time offset. The values for θ and δ are passed through filters and subjected to statistical analysis ("mitigation"). <a href="/wiki/Outlier" title="Outlier">Outliers</a> are discarded and an estimate of time offset is derived from the best three remaining candidates. The clock frequency is then adjusted to reduce the offset gradually ("discipline"), creating a <a href="/wiki/Feedback_loop" class="mw-redirect" title="Feedback loop">feedback loop</a>.<a href="#cite_note-Mills2010-1">[1]</a>: 20  Accurate synchronization is achieved when both the incoming and outgoing routes between the client and the server have symmetrical nominal delay. If the routes do not have a common nominal delay, a <a href="/wiki/Systematic_bias" class="mw-redirect" title="Systematic bias">systematic bias</a> exists of half the difference between the forward and backward travel times. A number of approaches have been proposed to measure asymmetry,<a href="#cite_note-iL6pp-41">[39]</a> but among practical implementations only chrony seems to have one included.<a href="#cite_note-Ocilw-42">[40]</a><a href="#cite_note-43">[41]</a> <div class="mw-heading mw-heading2"><h2 id="Software_implementations">Software implementations</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=6" title="Edit section: Software implementations">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/Ntpd#Implementations" title="Ntpd">ntpd § Implementations</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Ntpq_-p_query.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Ntpq_-p_query.png/220px-Ntpq_-p_query.png" decoding="async" width="220" height="85" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Ntpq_-p_query.png/330px-Ntpq_-p_query.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Ntpq_-p_query.png/440px-Ntpq_-p_query.png 2x" data-file-width="628" data-file-height="244" /></a><figcaption>The NTP management protocol utility ntpq being used to query the state of a stratum 2 server.</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Reference_implementation">Reference implementation</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=7" title="Edit section: Reference implementation">edit</a>]</div> The NTP <a href="/wiki/Reference_implementation" title="Reference implementation">reference implementation</a>, along with the protocol, has been continuously developed for over 20 years. Backwards compatibility has been maintained as new features have been added. It contains several sensitive algorithms, especially to discipline the clock, that can misbehave when synchronized to servers that use different algorithms. The software has been <a href="/wiki/Ported" class="mw-redirect" title="Ported">ported</a> to almost every computing platform, including personal computers. It runs as a <a href="/wiki/Daemon_(computing)" title="Daemon (computing)">daemon</a> called <a href="/wiki/Ntpd" title="Ntpd">ntpd</a> under Unix or as a <a href="/wiki/Windows_service" title="Windows service">service</a> under Windows. Reference clocks are supported and their offsets are filtered and analysed in the same way as remote servers, although they are usually polled more frequently.<a href="#cite_note-Mills2010-1">[1]</a>: 15–19  This implementation was audited in 2017, finding 14 potential security issues.<a href="#cite_note-jAgTl-44">[42]</a> <div class="mw-heading mw-heading3"><h3 id="Windows_Time">Windows Time</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=8" title="Edit section: Windows Time">edit</a>]</div> All <a href="/wiki/Microsoft_Windows" title="Microsoft Windows">Microsoft Windows</a> versions since <a href="/wiki/Windows_2000" title="Windows 2000">Windows 2000</a> include the Windows Time service (W32Time),<a href="#cite_note-ciu7z-45">[43]</a> which has the ability to synchronize the computer clock to an NTP server. W32Time was originally implemented for the purpose of the <a href="/wiki/Kerberos_(protocol)" title="Kerberos (protocol)">Kerberos</a> version 5 authentication protocol, which required time to be within 5 minutes of the correct value to prevent <a href="/wiki/Replay_attack" title="Replay attack">replay attacks</a>. The network time server in Windows 2000 Server (and Windows XP) does not implement NTP disciplined synchronization, only locally disciplined synchronization with NTP/SNTP correction.<a href="#cite_note-gn3Ev-46">[44]</a> Beginning with <a href="/wiki/Windows_Server_2003" title="Windows Server 2003">Windows Server 2003</a> and <a href="/wiki/Windows_Vista" title="Windows Vista">Windows Vista</a>, the NTP provider for W32Time became compatible with a significant subset of NTPv3.<a href="#cite_note-AD2ab-47">[45]</a> Microsoft states that W32Time cannot reliably maintain time synchronization with one second accuracy.<a href="#cite_note-kb939322-48">[46]</a> If higher accuracy is desired, Microsoft recommends using a newer version of Windows or different NTP implementation.<a href="#cite_note-ihlx1-49">[47]</a> Beginning with <a href="/wiki/Windows_10" title="Windows 10">Windows 10</a> version 1607 and <a href="/wiki/Windows_Server_2016" title="Windows Server 2016">Windows Server 2016</a>, W32Time can be configured to reach time accuracy of 1 s, 50 ms or 1 ms under certain specified operating conditions.<a href="#cite_note-FvW7f-50">[48]</a><a href="#cite_note-kb939322-48">[46]</a><a href="#cite_note-51">[49]</a> <div class="mw-heading mw-heading3"><h3 id="OpenNTPD">OpenNTPD</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=9" title="Edit section: OpenNTPD">edit</a>]</div> In 2004, Henning Brauer of <a href="/wiki/OpenBSD" title="OpenBSD">OpenBSD</a> presented <a href="/wiki/OpenNTPD" title="OpenNTPD">OpenNTPD</a>, an NTPv3/SNTPv4<a href="#cite_note-52">[50]</a> implementation with a focus on security and encompassing a privilege separated design. Whilst it is aimed more closely at the simpler generic needs of OpenBSD users, it also includes some protocol security improvements while still being compatible with existing NTP servers. The simpler code base sacrifices accuracy, deemed unnecessary in this use case.<a href="#cite_note-accuracy-53">[51]</a> A portable version is available in Linux package repositories. <div class="mw-heading mw-heading3"><h3 id="NTPsec">NTPsec</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=10" title="Edit section: NTPsec">edit</a>]</div> NTPsec is a <a href="/wiki/Fork_(software_development)" title="Fork (software development)">fork</a> of the reference implementation that has been systematically <a href="/wiki/Hardening_(computing)" title="Hardening (computing)">security-hardened</a>. The fork point was in June 2015 and was in response to a series of compromises in 2014.<a href="#cite_note-54">[52]</a> The first production release shipped in October 2017.<a href="#cite_note-TLIYY-55">[53]</a> Between removal of unsafe features, removal of support for obsolete hardware, and removal of support for obsolete Unix variants, NTPsec has been able to pare away 75% of the original codebase, making the remainder easier to <a href="/wiki/Software_quality_assurance" title="Software quality assurance">audit</a>.<a href="#cite_note-Liska2016-56">[54]</a> A 2017 audit of the code showed eight security issues, including two that were not present in the original reference implementation, but NTPsec did not suffer from eight other issues that remained in the reference implementation.<a href="#cite_note-5CF55-57">[55]</a> <div class="mw-heading mw-heading3"><h3 id="chrony">chrony</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=11" title="Edit section: chrony">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Chrony" title="Chrony">chrony</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Chrony_4.1_screenshot.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Chrony_4.1_screenshot.png/220px-Chrony_4.1_screenshot.png" decoding="async" width="220" height="180" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Chrony_4.1_screenshot.png/330px-Chrony_4.1_screenshot.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Chrony_4.1_screenshot.png/440px-Chrony_4.1_screenshot.png 2x" data-file-width="648" data-file-height="529" /></a><figcaption>chronyc, showing sources and activity information. <a href="/wiki/Terminal_window" class="mw-redirect" title="Terminal window">Terminal window</a> under <a href="/wiki/Arch_Linux" title="Arch Linux">Arch Linux</a></figcaption></figure> <a href="/wiki/Chrony" title="Chrony">chrony</a> is an independent NTP implementation mainly sponsored by <a href="/wiki/Red_Hat" title="Red Hat">Red Hat</a>, who uses it as the default time program in their distributions.<a href="#cite_note-Q91Af-58">[56]</a> Being written from scratch, chrony has a simpler codebase allowing for better security<a href="#cite_note-kYgFj-59">[57]</a> and lower resource consumption.<a href="#cite_note-jR9Jg-60">[58]</a> It does not however compromise on accuracy, instead syncing faster and better than the reference ntpd in many circumstances. It is versatile enough for ordinary computers, which are unstable, go into sleep mode or have intermittent connection to the Internet. It is also designed for virtual machines, a more unstable environment.<a href="#cite_note-Both2018-61">[59]</a> Chrony has been evaluated as "trustworthy", with only a few incidents.<a href="#cite_note-tN0aV-62">[60]</a> It is able to achieve improved precision on LAN connections, using hardware timestamping on the network adapter.<a href="#cite_note-Ocilw-42">[40]</a> Support for Network Time Security (NTS) was added on version 4.0.<a href="#cite_note-63">[61]</a> chrony is available under <a href="/wiki/GNU_General_Public_License_version_2" class="mw-redirect" title="GNU General Public License version 2">GNU General Public License version 2</a>, was created by <a href="/w/index.php?title=Richard_Curnow&action=edit&redlink=1" class="new" title="Richard Curnow (page does not exist)">Richard Curnow</a> in 1997 and is currently maintained by <a href="/w/index.php?title=Miroslav_Lichvar&action=edit&redlink=1" class="new" title="Miroslav Lichvar (page does not exist)">Miroslav Lichvar</a>.<a href="#cite_note-jR9Jg-60">[58]</a> <div class="mw-heading mw-heading3"><h3 id="Others">Others</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=12" title="Edit section: Others">edit</a>]</div> <ul><li><style data-mw-deduplicate="TemplateStyles:r1238216509">.mw-parser-output .vanchor>:target~.vanchor-text{background-color:#b1d2ff}@media screen{html.skin-theme-clientpref-night .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .vanchor>:target~.vanchor-text{background-color:#0f4dc9}}</style>Ntimed was started by <a href="/wiki/Poul-Henning_Kamp" title="Poul-Henning Kamp">Poul-Henning Kamp</a> of <a href="/wiki/FreeBSD" title="FreeBSD">FreeBSD</a> in 2014 and abandoned in 2015.<a href="#cite_note-F7zIq-64">[62]</a> The implementation was sponsored by the <a href="/wiki/Linux_Foundation" title="Linux Foundation">Linux Foundation</a>.<a href="#cite_note-HA4P8-65">[63]</a></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238216509">systemd-timesyncd is the SNTP client built into <a href="/wiki/Systemd" title="Systemd">systemd</a>. It is used by <a href="/wiki/Debian" title="Debian">Debian</a> since version "bookworm"<a href="#cite_note-66">[64]</a> and the downstream Ubuntu.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Leap_seconds">Leap seconds</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=13" title="Edit section: Leap seconds">edit</a>]</div> On the day of a <a href="/wiki/Leap_second" title="Leap second">leap second</a> event, ntpd receives notification from either a <a href="/wiki/Configuration_file" title="Configuration file">configuration file</a>, an attached reference clock, or a remote server. Although the NTP clock is actually halted during the event, because of the requirement that time must appear to be <a href="/wiki/Monotonic_function" title="Monotonic function">strictly increasing</a>, any <a href="/wiki/Process_(computing)" title="Process (computing)">processes</a> that query the system time cause it to increase by a tiny amount, preserving the order of events. If a negative leap second should ever become necessary, it would be deleted with the sequence 23:59:58, 00:00:00, skipping 23:59:59.<a href="#cite_note-7hQhm-67">[65]</a> An alternative implementation, called leap smearing, consists in introducing the leap second incrementally during a period of 24 hours, from noon to noon in UTC time. This implementation is used by Google (both internally and on their public NTP servers), Amazon AWS,<a href="#cite_note-kYj2y-68">[66]</a> and Facebook.<a href="#cite_note-69">[67]</a> Chrony supports leap smear in <style data-mw-deduplicate="TemplateStyles:r886049734">.mw-parser-output .monospaced{font-family:monospace,monospace}</style>smoothtime and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734">leapsecmode configurations, but such use is not to be mixed with a public NTP pool as leap smear is non-standard and will throw off client calculation in a mix.<a href="#cite_note-70">[68]</a> <div class="mw-heading mw-heading2"><h2 id="Security_concerns">Security concerns</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=14" title="Edit section: Security concerns">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/NTP_server_misuse_and_abuse" title="NTP server misuse and abuse">NTP server misuse and abuse</a></div> Because adjusting system time is generally a privileged operation, part or all of NTP code has to be run with some privileges in order to support its core functionality. Only a few other security problems have been identified in the reference implementation of the NTP codebase, but those that appeared in 2009[<a href="/wiki/Wikipedia:Avoid_weasel_words" class="mw-redirect" title="Wikipedia:Avoid weasel words">which?</a>] were cause for significant concern.<a href="#cite_note-8pJKT-71">[69]</a><a href="#cite_note-DoZBy-72">[70]</a> The protocol has been undergoing revision and review throughout its history. The codebase for the reference implementation has undergone security audits from several sources for several years.<a href="#cite_note-ZD0x6-73">[71]</a> A <a href="/wiki/Stack_buffer_overflow" title="Stack buffer overflow">stack buffer overflow</a> exploit was discovered and patched in 2014.<a href="#cite_note-m0CJK-74">[72]</a> <a href="/wiki/Apple_Inc." title="Apple Inc.">Apple</a> was concerned enough about this vulnerability that it used its auto-update capability for the first time.<a href="#cite_note-zg08P-75">[73]</a> On systems using the reference implementation, which is running with root user's credential, this could allow unlimited access. Some other implementations, such as <a href="/wiki/OpenNTPD" title="OpenNTPD">OpenNTPD</a>, have smaller code base and adopted other mitigation measures like privilege separation, are not subject to this flaw.<a href="#cite_note-PW78Z-76">[74]</a> A 2017 security audit of three NTP implementations, conducted on behalf of the Linux Foundation's Core Infrastructure Initiative, suggested that both NTP<a href="#cite_note-VBrX5-77">[75]</a><a href="#cite_note-T0ZbX-78">[76]</a> and NTPsec<a href="#cite_note-YK5og-79">[77]</a> were more problematic than Chrony<a href="#cite_note-rPdf5-80">[78]</a> from a security standpoint.<a href="#cite_note-nPXeu-81">[79]</a> NTP servers can be susceptible to <a href="/wiki/Man-in-the-middle_attack" title="Man-in-the-middle attack">man-in-the-middle attacks</a> unless packets are cryptographically signed for authentication.<a href="#cite_note-cGifv-82">[80]</a> The computational overhead involved can make this impractical on busy servers, particularly during <a href="/wiki/Denial_of_service" class="mw-redirect" title="Denial of service">denial of service</a> attacks.<a href="#cite_note-7a6Kk-83">[81]</a> NTP message <a href="/wiki/Spoofing_attack" title="Spoofing attack">spoofing</a> from a man-in-the-middle attack can be used to alter clocks on client computers and allow a number of attacks based on bypassing of cryptographic key expiration.<a href="#cite_note-OcBCA-84">[82]</a> Some of the services affected by fake NTP messages identified are <a href="/wiki/Transport_Layer_Security" title="Transport Layer Security">TLS</a>, <a href="/wiki/DNSSEC" class="mw-redirect" title="DNSSEC">DNSSEC</a>, various caching schemes (such as DNS cache), <a href="/wiki/Border_Gateway_Protocol" title="Border Gateway Protocol">Border Gateway Protocol</a> (BGP), Bitcoin [<a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed">citation needed</a>]and a number of persistent login schemes.<a href="#cite_note-CjQpl-85">[83]</a><a href="#cite_note-PglM9-86">[84]</a> NTP has been used in <a href="/wiki/Distributed_denial_of_service_attack" class="mw-redirect" title="Distributed denial of service attack">distributed denial of service attacks</a>.<a href="#cite_note-ElmaH-87">[85]</a><a href="#cite_note-Eb0sO-88">[86]</a> A small query is sent to an NTP server with the return <a href="/wiki/IP_address_spoofing" title="IP address spoofing">IP address spoofed</a> to be the target address. Similar to the <a href="/wiki/DNS_amplification_attack" class="mw-redirect" title="DNS amplification attack">DNS amplification attack</a>, the server responds with a much larger reply that allows an attacker to substantially increase the amount of data being sent to the target. To avoid participating in an attack, NTP server software can be upgraded or servers can be configured to ignore external queries.<a href="#cite_note-wkYHy-89">[87]</a> <div class="mw-heading mw-heading3"><h3 id="Secure_extensions">Secure extensions</h3>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=15" title="Edit section: Secure extensions">edit</a>]</div> NTP itself includes support for authenticating servers to clients. NTPv3 supports a <a href="/wiki/Symmetric_key" class="mw-redirect" title="Symmetric key">symmetric key</a> mode, which is not useful against MITM. The <a href="/wiki/Public_key" class="mw-redirect" title="Public key">public key</a> system known as "autokey" in NTPv4 adapted from <a href="/wiki/IPSec" class="mw-redirect" title="IPSec">IPSec</a> offers useful authentication,<a href="#cite_note-cGifv-82">[80]</a> but is not practical for a busy server.<a href="#cite_note-7a6Kk-83">[81]</a> Autokey was also later found to suffer from several design flaws,<a href="#cite_note-90">[88]</a> with no correction published, save for a change in the <a href="/wiki/Message_authentication_code" title="Message authentication code">message authentication code</a>.<a href="#cite_note-rfc8573-16">[16]</a> Autokey should no longer be used.<a href="#cite_note-">[89]</a> Network Time Security (NTS) is a secure version of NTPv4 with <a href="/wiki/Transport_Layer_Security" title="Transport Layer Security">TLS</a> and <a href="/wiki/Authenticated_encryption" title="Authenticated encryption">AEAD</a>.<a href="#cite_note-92">[90]</a> The main improvement over previous attempts is that a separate "key establishment" server handles the heavy asymmetric cryptography, which needs to be done only once. If the server goes down, previous users would still be able to fetch time without fear of MITM.<a href="#cite_note-rfc8915-93">[91]</a> NTS is currently supported by several time servers,<a href="#cite_note-94">[92]</a><a href="#cite_note-95">[93]</a> including <a href="/wiki/Cloudflare" title="Cloudflare">Cloudflare</a>. It is supported by NTPSec and chrony.<a href="#cite_note-96">[94]</a> Microsoft also has an approach to authenticate NTPv3/SNTPv4 packets using a <a href="/wiki/Windows_domain" title="Windows domain">Windows domain</a> identity, known as MS-SNTP.<a href="#cite_note-97">[95]</a> This system is implemented in the reference ntpd and chrony, using <a href="/wiki/Samba_(software)" title="Samba (software)">samba</a> for the domain connection. <a href="#cite_note-comparison-98">[96]</a> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=16" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/Allan_variance" title="Allan variance">Allan variance</a> – Measure of frequency stability in clocks and oscillators</li> <li><a href="/wiki/Clock_network" title="Clock network">Clock network</a> – Set of clocks that are automatically synchronized to show the same time</li> <li><a href="/wiki/International_Atomic_Time" title="International Atomic Time">International Atomic Time</a> – Time standard based on atomic clocks</li> <li><a href="/wiki/IRIG_timecode" title="IRIG timecode">IRIG timecode</a> – Standard formats for transferring time information</li> <li><a href="/wiki/NITZ" title="NITZ">NITZ</a></li> <li><a href="/wiki/NTP_pool" title="NTP pool">NTP pool</a> – Dynamic collection of networked computers providing time synchronization</li> <li><a href="/wiki/Ntpdate" title="Ntpdate">Ntpdate</a> – A computer program to synchronize computer time</li> <li><a href="/wiki/Precision_Time_Protocol" title="Precision Time Protocol">Precision Time Protocol</a> – Network time synchronization protocol</li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=17" title="Edit section: Notes">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 reflist-lower-alpha"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-29"><a href="#cite_ref-29">^</a> Telecommunication systems use a different definition for <a href="/wiki/Synchronization_in_telecommunications" title="Synchronization in telecommunications">clock strata</a>. </li> <li id="cite_note-40"><a href="#cite_ref-40">^</a> 2−64 seconds is about <a href="/wiki/1_E-21_s" class="mw-redirect" title="1 E-21 s">54 zeptoseconds</a> (light would travel 16.26 picometers, or approximately 0.31 × <a href="/wiki/Bohr_radius" title="Bohr radius">Bohr radius</a>), and 264 seconds is about <a href="/wiki/1_E19_s_and_more" class="mw-redirect" title="1 E19 s and more">585 billion years</a>. </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=18" title="Edit section: References">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239543626"><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-Mills2010-1">^ <a href="#cite_ref-Mills2010_1-0">a</a> <a href="#cite_ref-Mills2010_1-1">b</a> <a href="#cite_ref-Mills2010_1-2">c</a> <a href="#cite_ref-Mills2010_1-3">d</a> <a href="#cite_ref-Mills2010_1-4">e</a> <a href="#cite_ref-Mills2010_1-5">f</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills2010" class="citation book cs1">David L. Mills (12 December 2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=pdTcJBfnbq8C&pg=PA12">Computer Network Time Synchronization: The Network Time Protocol</a>. Taylor & Francis. pp. 12–. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-8493-5805-0" title="Special:BookSources/978-0-8493-5805-0"><bdi>978-0-8493-5805-0</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140718092324/http://books.google.com/books?id=pdTcJBfnbq8C&pg=PA12">Archived</a> from the original on 18 July 2014. Retrieved 16 October 2016.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Computer+Network+Time+Synchronization%3A+The+Network+Time+Protocol&rft.pages=12-&rft.pub=Taylor+%26+Francis&rft.date=2010-12-12&rft.isbn=978-0-8493-5805-0&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DpdTcJBfnbq8C%26pg%3DPA12&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-summary-2">^ <a href="#cite_ref-summary_2-0">a</a> <a href="#cite_ref-summary_2-1">b</a> <a href="#cite_ref-summary_2-2">c</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.eecis.udel.edu/~mills/exec.html">"Executive Summary: Computer Network Time Synchronization"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20111102204926/http://www.eecis.udel.edu/~mills/exec.html">Archived</a> from the original on 2011-11-02. Retrieved 2011-11-21.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Executive+Summary%3A+Computer+Network+Time+Synchronization&rft_id=http%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fexec.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-faq-3">^ <a href="#cite_ref-faq_3-0">a</a> <a href="#cite_ref-faq_3-1">b</a> <a href="#cite_ref-faq_3-2">c</a> <a href="#cite_ref-faq_3-3">d</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.ntp.org/ntpfaq/NTP-s-algo.htm#Q-ACCURATE-CLOCK">"NTP FAQ"</a>. The NTP Project. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110906014530/http://www.ntp.org/ntpfaq/NTP-s-algo.htm#Q-ACCURATE-CLOCK">Archived</a> from the original on 2011-09-06. Retrieved 2011-08-27.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=NTP+FAQ&rft.pub=The+NTP+Project&rft_id=http%3A%2F%2Fwww.ntp.org%2Fntpfaq%2FNTP-s-algo.htm%23Q-ACCURATE-CLOCK&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-qNvGW-4"><a href="#cite_ref-qNvGW_4-0">^</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/port-numbers">"Port Numbers"</a>. The Internet Assigned Numbers Authority (IANA). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20010604223215/https://www.iana.org/assignments/port-numbers">Archived</a> from the original on 2001-06-04. Retrieved 2011-01-19.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Port+Numbers&rft.pub=The+Internet+Assigned+Numbers+Authority+%28IANA%29&rft_id=https%3A%2F%2Fwww.iana.org%2Fassignments%2Fport-numbers&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-rfc5905-5">^ <a href="#cite_ref-rfc5905_5-0">a</a> <a href="#cite_ref-rfc5905_5-1">b</a> <a href="#cite_ref-rfc5905_5-2">c</a> <a href="#cite_ref-rfc5905_5-3">d</a> <a href="#cite_ref-rfc5905_5-4">e</a> <a href="#cite_ref-rfc5905_5-5">f</a> <a href="#cite_ref-rfc5905_5-6">g</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._MillsJ._BurbankW._Kasch2010" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a>; J. Burbank; W. Kasch (August 2010). J. Martin (ed.). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">Network Time Protocol Version 4: Protocol and Algorithms Specification</a>. <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</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%2FRFC5905">10.17487/RFC5905</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc5905">5905</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+Version+4%3A+Protocol+and+Algorithms+Specification&rft.pub=Internet+Engineering+Task+Force&rft.date=2010-08&rft_id=info%3Adoi%2F10.17487%2FRFC5905&rft.issn=2070-1721&rft.au=D.+Mills&rft.au=J.+Burbank&rft.au=W.+Kasch&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc5905&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Proposed Standard. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">1305</a>, <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4330">4330</a>. Updated by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc7822">7822</a>, <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc8573">8573</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc9109">9109</a>. </li> <li id="cite_note-rfc1305-6">^ <a href="#cite_ref-rfc1305_6-0">a</a> <a href="#cite_ref-rfc1305_6-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills1992" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a> (March 1992). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">Network Time Protocol (Version 3) - Specification, Implementation and Analysis</a>. Network Working Group. <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%2FRFC1305">10.17487/RFC1305</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/rfc1305">1305</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28Version+3%29+-+Specification%2C+Implementation+and+Analysis&rft.pub=Network+Working+Group&rft.date=1992-03&rft_id=info%3Adoi%2F10.17487%2FRFC1305&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1305&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a>. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc958">958</a>, <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1059">1059</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1119">1119</a>. </li> <li id="cite_note-rfc958-7"><a href="#cite_ref-rfc958_7-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1985" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (September 1985). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc958">Network Time Protocol (NTP)</a>. Network Working Group. <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%2FRFC0958">10.17487/RFC0958</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/rfc958">958</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28NTP%29&rft.pub=Network+Working+Group&rft.date=1985-09&rft_id=info%3Adoi%2F10.17487%2FRFC0958&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc958&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1059">1059</a>, <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1119">1119</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">1305</a>. </li> <li id="cite_note-rfc1059-8"><a href="#cite_ref-rfc1059_8-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1988" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (July 1988). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1059">Network Time Protocol (Version 1) Specification and Implementation</a>. Network Working Group. <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%2FRFC1059">10.17487/RFC1059</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/rfc1059">1059</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28Version+1%29+Specification+and+Implementation&rft.pub=Network+Working+Group&rft.date=1988-07&rft_id=info%3Adoi%2F10.17487%2FRFC1059&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1059&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1119">1119</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">1305</a>. </li> <li id="cite_note-rfc1119-9"><a href="#cite_ref-rfc1119_9-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1989" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (September 1989). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1119">Network Time Protocol (Version 2) Specification and Implementation</a>. Network Working Group. <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%2FRFC1119">10.17487/RFC1119</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/rfc1119">1119</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28Version+2%29+Specification+and+Implementation&rft.pub=Network+Working+Group&rft.date=1989-09&rft_id=info%3Adoi%2F10.17487%2FRFC1119&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1119&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">1305</a>. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc958">958</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1059">1059</a>. </li> <li id="cite_note-rfc1361-10">^ <a href="#cite_ref-rfc1361_10-0">a</a> <a href="#cite_ref-rfc1361_10-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1992" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (August 1992). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1361">Type of Service in the Internet Protocol Suite</a>. Network Working Group. <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%2FRFC1361">10.17487/RFC1361</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/rfc1361">1361</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Type+of+Service+in+the+Internet+Protocol+Suite&rft.pub=Network+Working+Group&rft.date=1992-08&rft_id=info%3Adoi%2F10.17487%2FRFC1361&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1361&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1769">1769</a>. </li> <li id="cite_note-rfc1769-11"><a href="#cite_ref-rfc1769_11-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1995" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (March 1995). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1769">Simple Network Time Protocol (SNTP)</a>. Network Working Group. <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%2FRFC1769">10.17487/RFC1769</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/rfc1769">1769</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Simple+Network+Time+Protocol+%28SNTP%29&rft.pub=Network+Working+Group&rft.date=1995-03&rft_id=info%3Adoi%2F10.17487%2FRFC1769&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1769&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2030">2030</a>. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1361">1361</a>. </li> <li id="cite_note-rfc2030-12">^ <a href="#cite_ref-rfc2030_12-0">a</a> <a href="#cite_ref-rfc2030_12-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills1996" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (October 1996). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2030">Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI</a>. Network Working Group. <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%2FRFC2030">10.17487/RFC2030</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/rfc2030">2030</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Simple+Network+Time+Protocol+%28SNTP%29+Version+4+for+IPv4%2C+IPv6+and+OSI&rft.pub=Network+Working+Group&rft.date=1996-10&rft_id=info%3Adoi%2F10.17487%2FRFC2030&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc2030&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4330">4330</a>. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1769">1769</a>. </li> <li id="cite_note-rfc4330-13">^ <a href="#cite_ref-rfc4330_13-0">a</a> <a href="#cite_ref-rfc4330_13-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._Mills2006" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a> (January 2006). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc4330">Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI</a>. Network Working Group. <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%2FRFC4330">10.17487/RFC4330</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/rfc4330">4330</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Simple+Network+Time+Protocol+%28SNTP%29+Version+4+for+IPv4%2C+IPv6+and+OSI&rft.pub=Network+Working+Group&rft.date=2006-01&rft_id=info%3Adoi%2F10.17487%2FRFC4330&rft.au=D.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc4330&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. Obsoletes <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc2030">2030</a> and <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1769">1769</a>. Obsoleted by <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a>. </li> <li id="cite_note-rfc778-14"><a href="#cite_ref-rfc778_14-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD.L._Mills1981" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D.L. Mills</a> (April 1981). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc778">DCNET Internet Clock Service</a>. <a href="/wiki/IETF" class="mw-redirect" title="IETF">IETF</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%2FRFC0778">10.17487/RFC0778</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/rfc778">778</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=DCNET+Internet+Clock+Service&rft.pub=IETF&rft.date=1981-04&rft_id=info%3Adoi%2F10.17487%2FRFC0778&rft.au=D.L.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc778&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Historic. </li> <li id="cite_note-rfc7822-15"><a href="#cite_ref-rfc7822_15-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFT._MizrahiD._Mayer2016" class="citation cs1">T. Mizrahi; D. Mayer (March 2016). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc7822">Network Time Protocol Version 4 (NTPv4) Extension Fields</a>. <a href="/wiki/IETF" class="mw-redirect" title="IETF">IETF</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%2FRFC7822">10.17487/RFC7822</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc7822">7822</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+Version+4+%28NTPv4%29+Extension+Fields&rft.pub=IETF&rft.date=2016-03&rft_id=info%3Adoi%2F10.17487%2FRFC7822&rft.issn=2070-1721&rft.au=T.+Mizrahi&rft.au=D.+Mayer&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc7822&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Informational. Updates <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a>. </li> <li id="cite_note-rfc8573-16">^ <a href="#cite_ref-rfc8573_16-0">a</a> <a href="#cite_ref-rfc8573_16-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFA._MalhotraS._Goldberg2019" class="citation cs1">A. Malhotra; S. Goldberg (June 2019). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc8573">Message Authentication Code for the Network Time Protocol</a>. <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</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%2FRFC8573">10.17487/RFC8573</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc8573">8573</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Message+Authentication+Code+for+the+Network+Time+Protocol&rft.pub=Internet+Engineering+Task+Force&rft.date=2019-06&rft_id=info%3Adoi%2F10.17487%2FRFC8573&rft.issn=2070-1721&rft.au=A.+Malhotra&rft.au=S.+Goldberg&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc8573&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Proposed Standard. Updates <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a>. </li> <li id="cite_note-rfc9109-17"><a href="#cite_ref-rfc9109_17-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFF._GontG._GontM._Lichvar2021" class="citation cs1">F. Gont; G. Gont; M. Lichvar (August 2021). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc9109">Network Time Protocol Version 4: Port Randomization</a>. <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</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%2FRFC9109">10.17487/RFC9109</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc9109">9109</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+Version+4%3A+Port+Randomization&rft.pub=Internet+Engineering+Task+Force&rft.date=2021-08&rft_id=info%3Adoi%2F10.17487%2FRFC9109&rft.issn=2070-1721&rft.au=F.+Gont&rft.au=G.+Gont&rft.au=M.+Lichvar&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc9109&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Proposed Standard. Updates <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222">RFC <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">5905</a>. </li> <li id="cite_note-ND7CF-18"><a href="#cite_ref-ND7CF_18-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD.L._Mills1981" class="citation cs2">D.L. Mills (25 February 1981), <a rel="nofollow" class="external text" href="https://web.archive.org/web/19961230073104/http://www.cis.ohio-state.edu/htbin/ien/ien173.html">Time Synchronization in DCNET Hosts</a>, archived from <a rel="nofollow" class="external text" href="http://www.cis.ohio-state.edu/htbin/ien/ien173.html">the original</a> on 1996-12-30</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Time+Synchronization+in+DCNET+Hosts&rft.date=1981-02-25&rft.au=D.L.+Mills&rft_id=http%3A%2F%2Fwww.cis.ohio-state.edu%2Fhtbin%2Fien%2Fien173.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-Y8SkT-19"><a href="#cite_ref-Y8SkT_19-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation cs2"><a rel="nofollow" class="external text" href="http://www.skrenta.com/rt/man/timed.8.html">"TIMED(8)"</a>, UNIX System Manager's Manual, <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110722012159/http://www.skrenta.com/rt/man/timed.8.html">archived</a> from the original on 2011-07-22, retrieved 2017-09-12</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=UNIX+System+Manager%27s+Manual&rft.atitle=TIMED%288%29&rft_id=http%3A%2F%2Fwww.skrenta.com%2Frt%2Fman%2Ftimed.8.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-AMYJK-20"><a href="#cite_ref-AMYJK_20-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills1991" class="citation journal cs1">David L. Mills (October 1991). <a rel="nofollow" class="external text" href="http://www3.cs.stonybrook.edu/~jgao/CSE590-spring11/91-ntp.pdf">"Internet Time Synchronization: The Network Time Protocol"</a> (PDF). IEEE Transactions on Communications. 39 (10): 1482–1493. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1991ITCom..39.1482M">1991ITCom..39.1482M</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2F26.103043">10.1109/26.103043</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160610113047/http://www3.cs.stonybrook.edu/%7Ejgao/CSE590-spring11/91-ntp.pdf">Archived</a> (PDF) from the original on 2016-06-10. Retrieved 2017-11-06.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=IEEE+Transactions+on+Communications&rft.atitle=Internet+Time+Synchronization%3A+The+Network+Time+Protocol&rft.volume=39&rft.issue=10&rft.pages=1482-1493&rft.date=1991-10&rft_id=info%3Adoi%2F10.1109%2F26.103043&rft_id=info%3Abibcode%2F1991ITCom..39.1482M&rft.au=David+L.+Mills&rft_id=http%3A%2F%2Fwww3.cs.stonybrook.edu%2F~jgao%2FCSE590-spring11%2F91-ntp.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-0-21"><a href="#cite_ref-0_21-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills1992" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">David L. Mills</a> (March 1992). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc1305">Network Time Protocol (Version 3) - Specification, Implementation and Analysis</a>. Network Working Group. <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%2FRFC1305">10.17487/RFC1305</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/rfc1305">1305</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28Version+3%29+-+Specification%2C+Implementation+and+Analysis&rft.pub=Network+Working+Group&rft.date=1992-03&rft_id=info%3Adoi%2F10.17487%2FRFC1305&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc1305&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Obsolete. <q>The clock-selection procedure was modified to remove the first of the two sorting/discarding steps and replace with an algorithm first proposed by Marzullo and later incorporated in the Digital Time Service. These changes do not significantly affect the ordinary operation of or compatibility with various versions of NTP, but they do provide the basis for formal statements of correctness.</q> </li> <li id="cite_note-MillsES-22"><a href="#cite_ref-MillsES_22-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills2010" class="citation book cs1">David L. Mills (15 November 2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=BxTOBQAAQBAJ&pg=PA377">Computer Network Time Synchronization: The Network Time Protocol on Earth and in Space, Second Edition</a>. CRC Press. p. 377. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-4398-1464-2" title="Special:BookSources/978-1-4398-1464-2"><bdi>978-1-4398-1464-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Computer+Network+Time+Synchronization%3A+The+Network+Time+Protocol+on+Earth+and+in+Space%2C+Second+Edition&rft.pages=377&rft.pub=CRC+Press&rft.date=2010-11-15&rft.isbn=978-1-4398-1464-2&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DBxTOBQAAQBAJ%26pg%3DPA377&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-E4akm-23">^ <a href="#cite_ref-E4akm_23-0">a</a> <a href="#cite_ref-E4akm_23-1">b</a> <a href="#cite_ref-E4akm_23-2">c</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation cs2">"Future Plans", <a rel="nofollow" class="external text" href="https://www.eecis.udel.edu/~mills/ntp.html">Network Time Synchronization Research Project</a>, <a rel="nofollow" class="external text" href="https://web.archive.org/web/20141223013515/http://www.eecis.udel.edu/~mills/ntp.html">archived</a> from the original on 23 December 2014, retrieved 24 December 2014</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Future+Plans&rft.btitle=Network+Time+Synchronization+Research+Project&rft_id=https%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fntp.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-jZjhj-24"><a href="#cite_ref-jZjhj_24-0">^</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.informationweek.com/cloud/infrastructure-as-a-service/ntp-needs-money-is-a-foundation-the-answer/d/d-id/1319557">"NTP Needs Money: Is A Foundation The Answer?"</a>. <a href="/wiki/InformationWeek" title="InformationWeek">InformationWeek</a>. March 23, 2015. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150410033108/http://www.informationweek.com/cloud/infrastructure-as-a-service/ntp-needs-money-is-a-foundation-the-answer/d/d-id/1319557">Archived</a> from the original on April 10, 2015. Retrieved April 4, 2015.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=InformationWeek&rft.atitle=NTP+Needs+Money%3A+Is+A+Foundation+The+Answer%3F&rft.date=2015-03-23&rft_id=http%3A%2F%2Fwww.informationweek.com%2Fcloud%2Finfrastructure-as-a-service%2Fntp-needs-money-is-a-foundation-the-answer%2Fd%2Fd-id%2F1319557&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-MShrI-25"><a href="#cite_ref-MShrI_25-0">^</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.informationweek.com/it-life/ntps-fate-hinges-on-father-time/d/d-id/1319432?cmp=em-prog-na-na-newsltr_20150313_control&imm_mid=0ce65e&page_number=2">"NTP's Fate Hinges On 'Father Time'"</a>. <a href="/wiki/InformationWeek" title="InformationWeek">InformationWeek</a>. March 11, 2015. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150410021745/http://www.informationweek.com/it-life/ntps-fate-hinges-on-father-time/d/d-id/1319432?cmp=em-prog-na-na-newsltr_20150313_control&imm_mid=0ce65e&page_number=2">Archived</a> from the original on April 10, 2015. Retrieved April 4, 2015.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=InformationWeek&rft.atitle=NTP%27s+Fate+Hinges+On+%27Father+Time%27&rft.date=2015-03-11&rft_id=http%3A%2F%2Fwww.informationweek.com%2Fit-life%2Fntps-fate-hinges-on-father-time%2Fd%2Fd-id%2F1319432%3Fcmp%3Dem-prog-na-na-newsltr_20150313_control%26imm_mid%3D0ce65e%26page_number%3D2&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-ntpwg-doc-26">^ <a href="#cite_ref-ntpwg-doc_26-0">a</a> <a href="#cite_ref-ntpwg-doc_26-1">b</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://datatracker.ietf.org/wg/ntp/documents/">"Network Time Protocols (ntp): Documents"</a>. datatracker.ietf.org. Retrieved 27 December 2022.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=datatracker.ietf.org&rft.atitle=Network+Time+Protocols+%28ntp%29%3A+Documents&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fwg%2Fntp%2Fdocuments%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-27"><a href="#cite_ref-27">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLichvar2022" class="citation journal cs1">Lichvar, Miroslav (6 December 2022). <a rel="nofollow" class="external text" href="https://www.ietf.org/archive/id/draft-mlichvar-ntp-ntpv5-06.html">"Network Time Protocol Version 5"</a>. www.ietf.org.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=www.ietf.org&rft.atitle=Network+Time+Protocol+Version+5&rft.date=2022-12-06&rft.aulast=Lichvar&rft.aufirst=Miroslav&rft_id=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-mlichvar-ntp-ntpv5-06.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-2-28"><a href="#cite_ref-2_28-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFD._MillsJ._BurbankW._Kasch2010" class="citation cs1"><a href="/wiki/David_L._Mills" title="David L. Mills">D. Mills</a>; J. Burbank; W. Kasch (August 2010). J. Martin (ed.). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc5905">Network Time Protocol Version 4: Protocol and Algorithms Specification</a>. <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</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%2FRFC5905">10.17487/RFC5905</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc5905">5905</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+Version+4%3A+Protocol+and+Algorithms+Specification&rft.pub=Internet+Engineering+Task+Force&rft.date=2010-08&rft_id=info%3Adoi%2F10.17487%2FRFC5905&rft.issn=2070-1721&rft.au=D.+Mills&rft.au=J.+Burbank&rft.au=W.+Kasch&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc5905&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Proposed Standard. <q>Primary servers and clients complying with a subset of NTP, called the Simple Network Time Protocol (SNTPv4) [...], do not need to implement the mitigation algorithms [...] The fully developed NTPv4 implementation is intended for [...] servers with multiple upstream servers and multiple downstream servers [...] Other than these considerations, NTP and SNTP servers and clients are completely interoperable and can be intermixed [...]</q> </li> <li id="cite_note-30"><a href="#cite_ref-30">^</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.redhat.com/en/blog/combining-ptp-ntp-get-best-both-worlds">"Combining PTP with NTP to Get the Best of Both Worlds"</a>. www.redhat.com. <q>Programs from the linuxptp package can be used in a combination with an NTP daemon. A PTP clock on a NIC is synchronized by ptp4l and is used as a reference clock by chronyd or ntpd for synchronization of the system clock.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.redhat.com&rft.atitle=Combining+PTP+with+NTP+to+Get+the+Best+of+Both+Worlds&rft_id=https%3A%2F%2Fwww.redhat.com%2Fen%2Fblog%2Fcombining-ptp-ntp-get-best-both-worlds&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-GPf8p-31"><a href="#cite_ref-GPf8p_31-0">^</a> RFC 5905, p. 21 </li> <li id="cite_note-cisco-32"><a href="#cite_ref-cisco_32-0">^</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.cisco.com/en/US/tech/tk869/tk769/technologies_white_paper09186a0080117070.shtml">"Network Time Protocol: Best Practices White Paper"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20131001041853/http://www.cisco.com/en/US/tech/tk869/tk769/technologies_white_paper09186a0080117070.shtml">Archived</a> from the original on 1 October 2013. Retrieved 15 October 2013.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Network+Time+Protocol%3A+Best+Practices+White+Paper&rft_id=http%3A%2F%2Fwww.cisco.com%2Fen%2FUS%2Ftech%2Ftk869%2Ftk769%2Ftechnologies_white_paper09186a0080117070.shtml&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-MIvTF-33">^ <a href="#cite_ref-MIvTF_33-0">a</a> <a href="#cite_ref-MIvTF_33-1">b</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://nlug.ml1.co.uk/2012/01/ntpq-p-output/831">"'ntpq -p' output"</a>. NLUG.ML1.co.uk. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20181112141516/https://nlug.ml1.co.uk/2012/01/ntpq-p-output/831">Archived</a> from the original on 2018-11-12. Retrieved 2018-11-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=NLUG.ML1.co.uk&rft.atitle=%27ntpq+-p%27+output&rft_id=https%3A%2F%2Fnlug.ml1.co.uk%2F2012%2F01%2Fntpq-p-output%2F831&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-34"><a href="#cite_ref-34">^</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://docs.ntpsec.org/latest/decode.html#kiss">"Event Messages and Status Words"</a>. docs.ntpsec.org. <q>Refid codes are used in kiss-o'-death (KoD) packets, the reference identifier field in ntpq and ntpmon billboard displays and log messages.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=docs.ntpsec.org&rft.atitle=Event+Messages+and+Status+Words&rft_id=https%3A%2F%2Fdocs.ntpsec.org%2Flatest%2Fdecode.html%23kiss&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-35"><a href="#cite_ref-35">^</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/ntp-parameters/ntp-parameters.xhtml">"Network Time Protocol (NTP) Parameters"</a>. www.iana.org.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.iana.org&rft.atitle=Network+Time+Protocol+%28NTP%29+Parameters&rft_id=https%3A%2F%2Fwww.iana.org%2Fassignments%2Fntp-parameters%2Fntp-parameters.xhtml&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-mvUS1-36"><a href="#cite_ref-mvUS1_36-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills2012" class="citation web cs1">David L. Mills (12 May 2012). <a rel="nofollow" class="external text" href="https://www.eecis.udel.edu/~mills/y2k.html">"The NTP Era and Era Numbering"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20161026011515/https://www.eecis.udel.edu/~mills/y2k.html">Archived</a> from the original on 26 October 2016. Retrieved 24 September 2016.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+NTP+Era+and+Era+Numbering&rft.date=2012-05-12&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fy2k.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-StevensFenner2004-37"><a href="#cite_ref-StevensFenner2004_37-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFW._Richard_StevensBill_FennerAndrew_M._Rudoff2004" class="citation book cs1">W. Richard Stevens; Bill Fenner; Andrew M. Rudoff (2004). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=ptSC4LpwGA0C&pg=PA582">UNIX Network Programming</a>. Addison-Wesley Professional. pp. 582–. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-13-141155-5" title="Special:BookSources/978-0-13-141155-5"><bdi>978-0-13-141155-5</bdi></a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190330170620/https://books.google.com/books?id=ptSC4LpwGA0C&pg=PA582">Archived</a> from the original on 2019-03-30. Retrieved 2016-10-16.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=UNIX+Network+Programming&rft.pages=582-&rft.pub=Addison-Wesley+Professional&rft.date=2004&rft.isbn=978-0-13-141155-5&rft.au=W.+Richard+Stevens&rft.au=Bill+Fenner&rft.au=Andrew+M.+Rudoff&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DptSC4LpwGA0C%26pg%3DPA582&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-bzRE9-38"><a href="#cite_ref-bzRE9_38-0">^</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.lieberbiber.de/2017/03/14/a-look-at-the-year-20362038-problems-and-time-proofness-in-various-systems/">"A look at the Year 2036/2038 problems and time proofness in various systems"</a>. 14 March 2017. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180721014309/http://www.lieberbiber.de/2017/03/14/a-look-at-the-year-20362038-problems-and-time-proofness-in-various-systems/">Archived</a> from the original on 2018-07-21. Retrieved 2018-07-20.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=A+look+at+the+Year+2036%2F2038+problems+and+time+proofness+in+various+systems&rft.date=2017-03-14&rft_id=http%3A%2F%2Fwww.lieberbiber.de%2F2017%2F03%2F14%2Fa-look-at-the-year-20362038-problems-and-time-proofness-in-various-systems%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-FIILt-39"><a href="#cite_ref-FIILt_39-0">^</a> <a href="/wiki/University_of_Delaware" title="University of Delaware">University of Delaware</a> Digital Systems Seminar presentation by David Mills, 2006-04-26 </li> <li id="cite_note-iL6pp-41"><a href="#cite_ref-iL6pp_41-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGotohImamuraKaneko2002" class="citation conference cs1">Gotoh, T.; Imamura, K.; Kaneko, A. (2002). "Improvement of NTP time offset under the asymmetric network with double packets method". Conference Digest Conference on Precision Electromagnetic Measurements. Conference on Precision Electromagnetic Measurements. pp. 448–449. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FCPEM.2002.1034915">10.1109/CPEM.2002.1034915</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-7803-7242-5" title="Special:BookSources/0-7803-7242-5"><bdi>0-7803-7242-5</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=conference&rft.atitle=Improvement+of+NTP+time+offset+under+the+asymmetric+network+with+double+packets+method&rft.btitle=Conference+Digest+Conference+on+Precision+Electromagnetic+Measurements&rft.pages=448-449&rft.date=2002&rft_id=info%3Adoi%2F10.1109%2FCPEM.2002.1034915&rft.isbn=0-7803-7242-5&rft.aulast=Gotoh&rft.aufirst=T.&rft.au=Imamura%2C+K.&rft.au=Kaneko%2C+A.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-Ocilw-42">^ <a href="#cite_ref-Ocilw_42-0">a</a> <a href="#cite_ref-Ocilw_42-1">b</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLichvar2018" class="citation web cs1">Lichvar, Miroslav (18 September 2018). <a rel="nofollow" class="external text" href="https://chrony.tuxfamily.org/doc/4.3/chrony.conf.html#hwtimestamp">"chrony – chrony.conf(5)"</a>. Chrony project. Retrieved 2 August 2020. <q>This directive enables hardware timestamping of NTP packets sent to and received from the specified network interface.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Chrony+project&rft.atitle=chrony+%E2%80%93+chrony.conf%285%29&rft.date=2018-09-18&rft.aulast=Lichvar&rft.aufirst=Miroslav&rft_id=https%3A%2F%2Fchrony.tuxfamily.org%2Fdoc%2F4.3%2Fchrony.conf.html%23hwtimestamp&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-43"><a href="#cite_ref-43">^</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://git.tuxfamily.org/chrony/chrony.git/tree/sourcestats.c?h=4.3">"sourcestats.c, function estimate_asymmetry()"</a>. git.tuxfamily.org (chrony).</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=git.tuxfamily.org+%28chrony%29&rft.atitle=sourcestats.c%2C+function+estimate_asymmetry%28%29&rft_id=https%3A%2F%2Fgit.tuxfamily.org%2Fchrony%2Fchrony.git%2Ftree%2Fsourcestats.c%3Fh%3D4.3&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-jAgTl-44"><a href="#cite_ref-jAgTl_44-0">^</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://wiki.mozilla.org/images/e/ea/Ntp-report.pdf">"Pentest-Report NTP 01.2017"</a> (PDF). Cure53. 2017. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20181201232241/https://wiki.mozilla.org/images/e/ea/Ntp-report.pdf">Archived</a> (PDF) from the original on 2018-12-01. Retrieved 2019-07-03.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Pentest-Report+NTP+01.2017&rft.pub=Cure53&rft.date=2017&rft_id=https%3A%2F%2Fwiki.mozilla.org%2Fimages%2Fe%2Fea%2FNtp-report.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-ciu7z-45"><a href="#cite_ref-ciu7z_45-0">^</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://technet.microsoft.com/en-us/library/cc773061%28WS.10%29.aspx">"Windows Time Service Technical Reference"</a>. technet.microsoft.com. 2011-08-17. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110906143547/http://technet.microsoft.com/en-us/library/cc773061(WS.10).aspx">Archived</a> from the original on 2011-09-06. Retrieved 2011-09-19.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Windows+Time+Service+Technical+Reference&rft.pub=technet.microsoft.com&rft.date=2011-08-17&rft_id=https%3A%2F%2Ftechnet.microsoft.com%2Fen-us%2Flibrary%2Fcc773061%2528WS.10%2529.aspx&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-gn3Ev-46"><a href="#cite_ref-gn3Ev_46-0">^</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://support.ntp.org/bin/view/Support/WindowsTimeService">"Windows Time Service page at NTP.org"</a>. Support.NTP.org. 2008-02-25. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170514214217/http://support.ntp.org/bin/view/Support/WindowsTimeService">Archived</a> from the original on 2017-05-14. Retrieved 2017-05-01.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Support.NTP.org&rft.atitle=Windows+Time+Service+page+at+NTP.org&rft.date=2008-02-25&rft_id=https%3A%2F%2Fsupport.ntp.org%2Fbin%2Fview%2FSupport%2FWindowsTimeService&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-AD2ab-47"><a href="#cite_ref-AD2ab_47-0">^</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://technet.microsoft.com/en-us/library/cc773013%28WS.10%29.aspx">"How the Windows Time Service Works"</a>. technet.microsoft.com. 2010-03-12. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110924184432/http://technet.microsoft.com/en-us/library/cc773013(WS.10).aspx">Archived</a> from the original on 2011-09-24. 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Retrieved 2012-08-26.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=High+Accuracy+W32time+Requirements&rft.pub=Microsoft&rft.date=2007-10-23&rft.au=Ned+Pyle&rft_id=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Farchive%2Fblogs%2Faskds%2Fhigh-accuracy-w32time-requirements&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-FvW7f-50"><a href="#cite_ref-FvW7f_50-0">^</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://technet.microsoft.com/en-us/windows-server-docs/identity/ad-ds/get-started/windows-time-service/windows-2016-accurate-time">"Windows Server 2016 Accurate Time"</a>. technet.microsoft.com. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20161202233231/https://technet.microsoft.com/en-us/windows-server-docs/identity/ad-ds/get-started/windows-time-service/windows-2016-accurate-time">Archived</a> from the original on 2016-12-02. Retrieved 2016-12-07.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=technet.microsoft.com&rft.atitle=Windows+Server+2016+Accurate+Time&rft_id=https%3A%2F%2Ftechnet.microsoft.com%2Fen-us%2Fwindows-server-docs%2Fidentity%2Fad-ds%2Fget-started%2Fwindows-time-service%2Fwindows-2016-accurate-time&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-51"><a href="#cite_ref-51">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFdahavey" class="citation web cs1">dahavey. <a rel="nofollow" class="external text" href="https://docs.microsoft.com/en-us/windows-server/networking/windows-time-service/support-boundary">"Support boundary for high-accuracy time"</a>. docs.microsoft.com. Retrieved 2021-07-24.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=docs.microsoft.com&rft.atitle=Support+boundary+for+high-accuracy+time&rft.au=dahavey&rft_id=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Fwindows-server%2Fnetworking%2Fwindows-time-service%2Fsupport-boundary&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-52"><a href="#cite_ref-52">^</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://man.openbsd.org/ntpd">"ntpd(8) - OpenBSD manual pages"</a>. man.openbsd.org. <q>It implements the Simple Network Time Protocol version 4, as described in RFC 5905, and the Network Time Protocol version 3, as described in RFC 1305.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=man.openbsd.org&rft.atitle=ntpd%288%29+-+OpenBSD+manual+pages&rft_id=https%3A%2F%2Fman.openbsd.org%2Fntpd&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-accuracy-53"><a href="#cite_ref-accuracy_53-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFThe_OpenBSD_Project2006" class="citation web cs1">The OpenBSD Project (21 August 2006). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160205120110/http://www.openbsd.org/faq/faq6.html#OpenNTPDaccurate">"FAQ 6.12.1: 'But OpenNTPD isn't as accurate as the ntp.org daemon!'"</a>. The OpenBSD Project. Archived from <a rel="nofollow" class="external text" href="http://www.openbsd.org/faq/faq6.html#OpenNTPDaccurate">the original</a> on 2016-02-05. Retrieved 2020-05-14.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=The+OpenBSD+Project&rft.atitle=FAQ+6.12.1%3A+%27But+OpenNTPD+isn%27t+as+accurate+as+the+ntp.org+daemon%21%27&rft.date=2006-08-21&rft.au=The+OpenBSD+Project&rft_id=http%3A%2F%2Fwww.openbsd.org%2Ffaq%2Ffaq6.html%23OpenNTPDaccurate&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-54"><a href="#cite_ref-54">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRaymond2017" class="citation web cs1">Raymond, Eric S. (2017-03-30). <a rel="nofollow" class="external text" href="https://www.linuxjournal.com/content/ntpsec-secure-hardened-ntp-implementation">"NTPsec: a Secure, Hardened NTP Implementation | Linux Journal"</a>. <a href="/wiki/Linux_Journal" title="Linux Journal">Linux Journal</a>. <a rel="nofollow" class="external text" href="https://archive.today/20240126231434/https://www.linuxjournal.com/content/ntpsec-secure-hardened-ntp-implementation">Archived</a> from the original on 2024-01-26. Retrieved 2024-01-26.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Linux+Journal&rft.atitle=NTPsec%3A+a+Secure%2C+Hardened+NTP+Implementation+%7C+Linux+Journal&rft.date=2017-03-30&rft.aulast=Raymond&rft.aufirst=Eric+S.&rft_id=https%3A%2F%2Fwww.linuxjournal.com%2Fcontent%2Fntpsec-secure-hardened-ntp-implementation&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-TLIYY-55"><a href="#cite_ref-TLIYY_55-0">^</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://ntpsec.org">"The Secure Network Time Protocol (NTPsec) Distribution"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190113232124/https://ntpsec.org/">Archived</a> from the original on 2019-01-13. Retrieved 2019-01-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+Secure+Network+Time+Protocol+%28NTPsec%29+Distribution&rft_id=https%3A%2F%2Fntpsec.org&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-Liska2016-56"><a href="#cite_ref-Liska2016_56-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLiska2016" class="citation book cs1">Liska, Allan (December 10, 2016). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=AB-1DQAAQBAJ&pg=PA80">NTP Security: A Quick-Start Guide</a>. Apress. pp. 80–. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-4842-2412-0" title="Special:BookSources/978-1-4842-2412-0"><bdi>978-1-4842-2412-0</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=NTP+Security%3A+A+Quick-Start+Guide&rft.pages=80-&rft.pub=Apress&rft.date=2016-12-10&rft.isbn=978-1-4842-2412-0&rft.aulast=Liska&rft.aufirst=Allan&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DAB-1DQAAQBAJ%26pg%3DPA80&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-5CF55-57"><a href="#cite_ref-5CF55_57-0">^</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://wiki.mozilla.org/images/1/10/Ntpsec-report.pdf">"Pentest-Report NTPsec 01.2017"</a> (PDF). Cure53. 2017. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190704001204/https://wiki.mozilla.org/images/1/10/Ntpsec-report.pdf">Archived</a> (PDF) from the original on 2019-07-04. Retrieved 2019-07-03.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Pentest-Report+NTPsec+01.2017&rft.pub=Cure53&rft.date=2017&rft_id=https%3A%2F%2Fwiki.mozilla.org%2Fimages%2F1%2F10%2FNtpsec-report.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-Q91Af-58"><a href="#cite_ref-Q91Af_58-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLichvar2016" class="citation web cs1">Lichvar, Miroslav (20 July 2016). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160730091110/http://rhelblog.redhat.com/2016/07/20/combining-ptp-with-ntp-to-get-the-best-of-both-worlds/">"Combining PTP with NTP to Get the Best of Both Worlds"</a>. Red Hat Enterprise Linux Blog. <a href="/wiki/Red_Hat" title="Red Hat">Red Hat</a>. Archived from <a rel="nofollow" class="external text" href="http://rhelblog.redhat.com/2016/07/20/combining-ptp-with-ntp-to-get-the-best-of-both-worlds/">the original</a> on 30 July 2016. Retrieved 19 November 2017. <q>Starting with Red Hat Enterprise Linux 7.0 (and now in Red Hat Enterprise Linux 6.8) a more versatile NTP implementation is also provided via the chrony package</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Red+Hat+Enterprise+Linux+Blog&rft.atitle=Combining+PTP+with+NTP+to+Get+the+Best+of+Both+Worlds&rft.date=2016-07-20&rft.aulast=Lichvar&rft.aufirst=Miroslav&rft_id=http%3A%2F%2Frhelblog.redhat.com%2F2016%2F07%2F20%2Fcombining-ptp-with-ntp-to-get-the-best-of-both-worlds%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-kYgFj-59"><a href="#cite_ref-kYgFj_59-0">^</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/20171028123642/https://www.coreinfrastructure.org/news/blogs/2017/09/securing-network-time">"Securing Network Time"</a>. Core Infrastructure Initiative, a Linux Foundation Collaborative Project. Core Infrastructure Initiative. 27 September 2017. Archived from <a rel="nofollow" class="external text" href="https://www.coreinfrastructure.org/news/blogs/2017/09/securing-network-time">the original</a> on 28 October 2017. Retrieved 19 November 2017. <q>In sum, the Chrony NTP software stands solid and can be seen as trustworthy</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Core+Infrastructure+Initiative%2C+a+Linux+Foundation+Collaborative+Project&rft.atitle=Securing+Network+Time&rft.date=2017-09-27&rft_id=https%3A%2F%2Fwww.coreinfrastructure.org%2Fnews%2Fblogs%2F2017%2F09%2Fsecuring-network-time&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-jR9Jg-60">^ <a href="#cite_ref-jR9Jg_60-0">a</a> <a href="#cite_ref-jR9Jg_60-1">b</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/20091209115945/https://chrony.tuxfamily.org/">"chrony introduction"</a>. TuxFamily, a non-profit organization. chrony. Archived from <a rel="nofollow" class="external text" href="https://chrony.tuxfamily.org/">the original</a> on 9 December 2009. Retrieved 19 November 2017. <q>The software is supported on Linux, FreeBSD, NetBSD, macOS, and Solaris.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=TuxFamily%2C+a+non-profit+organization.&rft.atitle=chrony+introduction&rft_id=https%3A%2F%2Fchrony.tuxfamily.org%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-Both2018-61"><a href="#cite_ref-Both2018_61-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBoth" class="citation web cs1">Both, David. <a rel="nofollow" class="external text" href="https://opensource.com/article/18/12/manage-ntp-chrony">"Manage NTP with Chrony"</a>. Opensource.com. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190629174030/https://opensource.com/article/18/12/manage-ntp-chrony">Archived</a> from the original on 29 June 2019. Retrieved 29 June 2019.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Opensource.com&rft.atitle=Manage+NTP+with+Chrony&rft.aulast=Both&rft.aufirst=David&rft_id=https%3A%2F%2Fopensource.com%2Farticle%2F18%2F12%2Fmanage-ntp-chrony&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-tN0aV-62"><a href="#cite_ref-tN0aV_62-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHeiderich2017" class="citation web cs1">Heiderich, Mario (August 2017). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20171005123643/https://wiki.mozilla.org/images/e/e4/Chrony-report.pdf">"Pentest-Report Chrony 08.2017"</a> (PDF). Cure53.de Team. wiki.mozilla.org, AKA MozillaWiki or WikiMO. Archived from <a rel="nofollow" class="external text" href="https://wiki.mozilla.org/images/e/e4/Chrony-report.pdf">the original</a> (PDF) on 5 October 2017. Retrieved 19 November 2017. <q>Withstanding eleven full days of on-remote testing in August of 2017 means that Chrony is robust, strong, and developed with security in mind.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Cure53.de+Team&rft.atitle=Pentest-Report+Chrony+08.2017&rft.date=2017-08&rft.aulast=Heiderich&rft.aufirst=Mario&rft_id=https%3A%2F%2Fwiki.mozilla.org%2Fimages%2Fe%2Fe4%2FChrony-report.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-63"><a href="#cite_ref-63">^</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://git.tuxfamily.org/chrony/chrony.git/tree/NEWS?id=4.0#n6">"chrony/chrony.git - Official Git repository for the Chrony project"</a>. git.tuxfamily.org. Retrieved 2021-07-31.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=git.tuxfamily.org&rft.atitle=chrony%2Fchrony.git+-+Official+Git+repository+for+the+Chrony+project.&rft_id=https%3A%2F%2Fgit.tuxfamily.org%2Fchrony%2Fchrony.git%2Ftree%2FNEWS%3Fid%3D4.0%23n6&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-F7zIq-64"><a href="#cite_ref-F7zIq_64-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPoul-Henning" class="citation web cs1">Poul-Henning, Kamp. <a rel="nofollow" class="external text" href="http://phk.freebsd.dk/time/20140926">"20140926 – Playing with time again"</a>. PHK's Bikeshed. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20191220015844/http://phk.freebsd.dk/time/20140926/">Archived</a> from the original on 20 December 2019. Retrieved 4 June 2015.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=PHK%27s+Bikeshed&rft.atitle=20140926+%E2%80%93+Playing+with+time+again&rft.aulast=Poul-Henning&rft.aufirst=Kamp&rft_id=http%3A%2F%2Fphk.freebsd.dk%2Ftime%2F20140926&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-HA4P8-65"><a href="#cite_ref-HA4P8_65-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPoul-Henning" class="citation web cs1">Poul-Henning, Kamp. <a rel="nofollow" class="external text" href="https://github.com/bsdphk/Ntimed">"Network time synchronization software, NTPD replacement"</a>. ntimed git repository README file. Github. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150802090927/https://github.com/bsdphk/Ntimed/">Archived</a> from the original on 2 August 2015. Retrieved 4 June 2015.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=ntimed+git+repository+README+file&rft.atitle=Network+time+synchronization+software%2C+NTPD+replacement.&rft.aulast=Poul-Henning&rft.aufirst=Kamp&rft_id=https%3A%2F%2Fgithub.com%2Fbsdphk%2FNtimed&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-66"><a href="#cite_ref-66">^</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://anarc.at/blog/2022-01-23-chrony/">"Switching from OpenNTPd to Chrony - anarcat"</a>. anarc.at. <q>So in effect, systemd-timesyncd became the default NTP daemon in Debian in bookworm, which I find somewhat surprising.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=anarc.at&rft.atitle=Switching+from+OpenNTPd+to+Chrony+-+anarcat&rft_id=https%3A%2F%2Fanarc.at%2Fblog%2F2022-01-23-chrony%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-7hQhm-67"><a href="#cite_ref-7hQhm_67-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_Mills" class="citation web cs1">David Mills. <a rel="nofollow" class="external text" href="http://www.eecis.udel.edu/~mills/leap.html">"The NTP Timescale and Leap Seconds"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20130907021050/http://www.eecis.udel.edu/%7emills/leap.html">Archived</a> from the original on 7 September 2013. Retrieved 15 October 2013.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=The+NTP+Timescale+and+Leap+Seconds&rft.au=David+Mills&rft_id=http%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fleap.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-kYj2y-68"><a href="#cite_ref-kYj2y_68-0">^</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://developers.google.com/time/smear">"Google Developers Leap Smear"</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190404122431/https://developers.google.com/time/smear">Archived</a> from the original on 4 April 2019. Retrieved 4 April 2019.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Google+Developers+Leap+Smear&rft_id=https%3A%2F%2Fdevelopers.google.com%2Ftime%2Fsmear&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-69"><a href="#cite_ref-69">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFObleukhov2020" class="citation journal cs1">Obleukhov, Oleg (18 March 2020). <a rel="nofollow" class="external text" href="https://engineering.fb.com/2020/03/18/production-engineering/ntp-service/">"Building a more accurate time service at Facebook scale"</a>. Engineering at Meta.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Engineering+at+Meta&rft.atitle=Building+a+more+accurate+time+service+at+Facebook+scale&rft.date=2020-03-18&rft.aulast=Obleukhov&rft.aufirst=Oleg&rft_id=https%3A%2F%2Fengineering.fb.com%2F2020%2F03%2F18%2Fproduction-engineering%2Fntp-service%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-70"><a href="#cite_ref-70">^</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://chrony.tuxfamily.org/faq.html#_should_be_a_leap_smear_enabled_on_ntp_server">"chrony – Frequently Asked Questions"</a>. chrony.tuxfamily.org.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=chrony.tuxfamily.org&rft.atitle=chrony+%E2%80%93+Frequently+Asked+Questions&rft_id=https%3A%2F%2Fchrony.tuxfamily.org%2Ffaq.html%23_should_be_a_leap_smear_enabled_on_ntp_server&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-8pJKT-71"><a href="#cite_ref-8pJKT_71-0">^</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://support.ntp.org/security">"Security Notice"</a>. Support.NTP.org. 2009-12-10. Retrieved 2011-01-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Support.NTP.org&rft.atitle=Security+Notice&rft.date=2009-12-10&rft_id=http%3A%2F%2Fsupport.ntp.org%2Fsecurity&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988">[<a href="/wiki/Wikipedia:Link_rot" title="Wikipedia:Link rot">permanent dead link</a>‍] </li> <li id="cite_note-DoZBy-72"><a href="#cite_ref-DoZBy_72-0">^</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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-ntp">"Cisco IOS Software Network Time Protocol Packet Vulnerability"</a>. <a href="/wiki/Cisco_Systems" class="mw-redirect" title="Cisco Systems">Cisco Systems</a>. 23 September 2009. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200611155551/https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-ntp">Archived</a> from the original on 11 June 2020. Retrieved 11 June 2020.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Cisco+IOS+Software+Network+Time+Protocol+Packet+Vulnerability&rft.pub=Cisco+Systems&rft.date=2009-09-23&rft_id=https%3A%2F%2Ftools.cisco.com%2Fsecurity%2Fcenter%2Fcontent%2FCiscoSecurityAdvisory%2Fcisco-sa-20090923-ntp&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-ZD0x6-73"><a href="#cite_ref-ZD0x6_73-0">^</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://support.ntp.org/Main/CodeAudit">"Code Audit"</a>. Support.NTP.org. 2009-06-13. Retrieved 2011-01-12.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Support.NTP.org&rft.atitle=Code+Audit&rft.date=2009-06-13&rft_id=http%3A%2F%2Fsupport.ntp.org%2FMain%2FCodeAudit&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-m0CJK-74"><a href="#cite_ref-m0CJK_74-0">^</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://ics-cert.us-cert.gov/advisories/ICSA-14-353-01">"Network Time Protocol Vulnerabilities (Update C) | ICS-CERT"</a>. Ics-cert.us-cert.gov. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20141220002022/https://ics-cert.us-cert.gov/advisories/ICSA-14-353-01">Archived</a> from the original on 2014-12-20. Retrieved 2015-04-15.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Network+Time+Protocol+Vulnerabilities+%28Update+C%29+%26%23124%3B+ICS-CERT&rft.pub=Ics-cert.us-cert.gov&rft_id=https%3A%2F%2Fics-cert.us-cert.gov%2Fadvisories%2FICSA-14-353-01&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-zg08P-75"><a href="#cite_ref-zg08P_75-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCunningham2014" class="citation web cs1">Cunningham, Andrew (Dec 23, 2014). <a rel="nofollow" class="external text" href="https://arstechnica.com/apple/2014/12/apple-automatically-patches-macs-to-fix-severe-ntp-security-flaw/">"Apple automatically patches Macs to fix severe NTP security flaw"</a>. arstechnica. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150415002211/http://arstechnica.com/apple/2014/12/apple-automatically-patches-macs-to-fix-severe-ntp-security-flaw/">Archived</a> from the original on April 15, 2015. Retrieved Apr 29, 2015.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Apple+automatically+patches+Macs+to+fix+severe+NTP+security+flaw&rft.pub=arstechnica&rft.date=2014-12-23&rft.aulast=Cunningham&rft.aufirst=Andrew&rft_id=https%3A%2F%2Farstechnica.com%2Fapple%2F2014%2F12%2Fapple-automatically-patches-macs-to-fix-severe-ntp-security-flaw%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-PW78Z-76"><a href="#cite_ref-PW78Z_76-0">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFairhead2014" class="citation web cs1">Fairhead, Harry (23 December 2014). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20141224071634/http://www.i-programmer.info/news/149-security/8120-ntp-the-latest-open-source-security-problem.html">"NTP The Latest Open Source Security Problem"</a>. I Programmer. Archived from <a rel="nofollow" class="external text" href="http://www.i-programmer.info/news/149-security/8120-ntp-the-latest-open-source-security-problem.html">the original</a> on 24 December 2014. Retrieved 24 December 2014.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=NTP+The+Latest+Open+Source+Security+Problem&rft.pub=I+Programmer&rft.date=2014-12-23&rft.aulast=Fairhead&rft.aufirst=Harry&rft_id=http%3A%2F%2Fwww.i-programmer.info%2Fnews%2F149-security%2F8120-ntp-the-latest-open-source-security-problem.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-VBrX5-77"><a href="#cite_ref-VBrX5_77-0">^</a> <a rel="nofollow" class="external text" href="http://support.ntp.org/bin/view/Main/SecurityNotice">NTP SecurityNotice Page</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140219093152/http://support.ntp.org/bin/view/Main/SecurityNotice">Archived</a> 2014-02-19 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a> </li> <li id="cite_note-T0ZbX-78"><a href="#cite_ref-T0ZbX_78-0">^</a> <a rel="nofollow" class="external text" href="https://nvd.nist.gov/vuln/search/results?form_type=Advanced&results_type=overview&search_type=all&cpe_vendor=cpe%3A%2F%3Antp&cpe_product=cpe%3A%2F%3A%3Antp">NVD NIST Product Search NTP</a> </li> <li id="cite_note-YK5og-79"><a href="#cite_ref-YK5og_79-0">^</a> <a rel="nofollow" class="external text" href="https://nvd.nist.gov/vuln/search/results?form_type=Advanced&results_type=overview&search_type=all&cpe_vendor=cpe%3A%2F%3Antpsec&cpe_product=cpe%3A%2F%3A%3Antpsec">NVD NIST Product Search NTPsec</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200626160445/https://nvd.nist.gov/vuln/search/results?form_type=Advanced&results_type=overview&search_type=all&cpe_vendor=cpe%3A%2F%3Antpsec&cpe_product=cpe%3A%2F%3A%3Antpsec">Archived</a> 2020-06-26 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a> </li> <li id="cite_note-rPdf5-80"><a href="#cite_ref-rPdf5_80-0">^</a> <a rel="nofollow" class="external text" href="https://nvd.nist.gov/vuln/search/results?form_type=Advanced&results_type=overview&search_type=all&cpe_vendor=cpe%3A%2F%3Atuxfamily&cpe_product=cpe%3A%2F%3A%3Achrony">NVD NIST Product Search Chrony</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200626200844/https://nvd.nist.gov/vuln/search/results?form_type=Advanced&results_type=overview&search_type=all&cpe_vendor=cpe%3A%2F%3Atuxfamily&cpe_product=cpe%3A%2F%3A%3Achrony">Archived</a> 2020-06-26 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a> </li> <li id="cite_note-nPXeu-81"><a href="#cite_ref-nPXeu_81-0">^</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/20180203195701/https://www.linuxfoundation.org/blog/cii-audit-identifies-secure-ntp-implementation/">"CII Audit Identifies Most Secure NTP Implementation"</a>. 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Sundblad (September 2020). <a rel="nofollow" class="external text" href="https://datatracker.ietf.org/doc/html/rfc8915">Network Time Security for the Network Time Protocol</a>. <a href="/wiki/Internet_Engineering_Task_Force" title="Internet Engineering Task Force">Internet Engineering Task Force</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%2FRFC8915">10.17487/RFC8915</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/2070-1721">2070-1721</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/rfc8915">8915</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Security+for+the+Network+Time+Protocol&rft.pub=Internet+Engineering+Task+Force&rft.date=2020-09&rft_id=info%3Adoi%2F10.17487%2FRFC8915&rft.issn=2070-1721&rft.au=D.+Franke&rft.au=D.+Sibold&rft.au=K.+Teichel&rft.au=M.+Dansarie&rft.au=R.+Sundblad&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc8915&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> Proposed Standard. </li> <li id="cite_note-94"><a href="#cite_ref-94">^</a> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLanger2019" class="citation web cs1">Langer, Martin (2019-12-05). <a rel="nofollow" class="external text" href="https://weberblog.net/setting-up-nts-secured-ntp-with-ntpsec/">"Setting up NTS-Secured NTP with NTPsec"</a>. Weberblog.net. Retrieved 2021-08-19.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Weberblog.net&rft.atitle=Setting+up+NTS-Secured+NTP+with+NTPsec&rft.date=2019-12-05&rft.aulast=Langer&rft.aufirst=Martin&rft_id=https%3A%2F%2Fweberblog.net%2Fsetting-up-nts-secured-ntp-with-ntpsec%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-95"><a href="#cite_ref-95">^</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.netnod.se/time-and-frequency/how-to-use-nts">"How to use NTS | Netnod"</a>. Netnod. Retrieved 2021-08-19.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Netnod&rft.atitle=How+to+use+NTS+%7C+Netnod&rft_id=https%3A%2F%2Fwww.netnod.se%2Ftime-and-frequency%2Fhow-to-use-nts&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-96"><a href="#cite_ref-96">^</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://developers.cloudflare.com/time-services/nts/">"Network Time Security · Cloudflare Time Services docs"</a>. developers.cloudflare.com. 5 February 2024.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=developers.cloudflare.com&rft.atitle=Network+Time+Security+%C2%B7+Cloudflare+Time+Services+docs&rft.date=2024-02-05&rft_id=https%3A%2F%2Fdevelopers.cloudflare.com%2Ftime-services%2Fnts%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-97"><a href="#cite_ref-97">^</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://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-sntp/8106cb73-ab3a-4542-8bc8-784dd32031cc">"[MS-SNTP]: Network Time Protocol (NTP) Authentication Extensions"</a>. 24 June 2021.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=%26%2391%3BMS-SNTP%26%2393%3B%3A+Network+Time+Protocol+%28NTP%29+Authentication+Extensions&rft.date=2021-06-24&rft_id=https%3A%2F%2Flearn.microsoft.com%2Fen-us%2Fopenspecs%2Fwindows_protocols%2Fms-sntp%2F8106cb73-ab3a-4542-8bc8-784dd32031cc&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"> </li> <li id="cite_note-comparison-98"><a href="#cite_ref-comparison_98-0">^</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://chrony.tuxfamily.org/comparison.html">"Comparison of NTP implementations"</a>. chrony.tuxfamily.org. Retrieved 2019-10-08.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Comparison+of+NTP+implementations&rft.pub=chrony.tuxfamily.org&rft_id=https%3A%2F%2Fchrony.tuxfamily.org%2Fcomparison.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" 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=Network_Time_Protocol&action=edit&section=19" 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/rfc5907">Definitions of Managed Objects for Network Time Protocol Version 4 (NTPv4)</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%2FRFC5907">10.17487/RFC5907</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/rfc5907">5907</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Definitions+of+Managed+Objects+for+Network+Time+Protocol+Version+4+%28NTPv4%29&rft_id=info%3Adoi%2F10.17487%2FRFC5907&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc5907&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" 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/rfc5908">Network Time Protocol (NTP) Server Option for DHCPv6</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%2FRFC5908">10.17487/RFC5908</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/rfc5908">5908</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Network+Time+Protocol+%28NTP%29+Server+Option+for+DHCPv6&rft_id=info%3Adoi%2F10.17487%2FRFC5908&rft_id=https%3A%2F%2Fdatatracker.ietf.org%2Fdoc%2Fhtml%2Frfc5908&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=Network_Time_Protocol&action=edit&section=20" title="Edit section: External links">edit</a>]</div> <ul><li><a rel="nofollow" class="external text" href="https://www.ntp.org/">Official website</a> <a href="https://www.wikidata.org/wiki/Q217491#P856" title="Edit this at Wikidata"><img alt="Edit this at Wikidata" src="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/10px-OOjs_UI_icon_edit-ltr-progressive.svg.png" decoding="async" width="10" height="10" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/15px-OOjs_UI_icon_edit-ltr-progressive.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/8/8a/OOjs_UI_icon_edit-ltr-progressive.svg/20px-OOjs_UI_icon_edit-ltr-progressive.svg.png 2x" data-file-width="20" data-file-height="20" /></a></li> <li><a rel="nofollow" class="external text" href="http://support.ntp.org/bin/view/Servers/StratumOneTimeServers">Official Stratum One Time Servers list</a></li> <li><a rel="nofollow" class="external text" href="https://datatracker.ietf.org/wg/ntp/charter/">IETF NTP working group</a></li> <li><a rel="nofollow" class="external text" href="https://docs.microsoft.com/en-us/windows-server/networking/windows-time-service/accurate-time">Microsft Windows accurate time guide</a> and <a rel="nofollow" class="external text" href="https://docs.microsoft.com/en-us/windows-server/networking/windows-time-service/configuring-systems-for-high-accuracy?tabs=MinPollInterval">more</a></li> <li><a rel="nofollow" class="external text" href="https://www.ijs.si/time/">Time and NTP paper</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20190504164134/http://ntpsurvey.arauc.br/">NTP Survey 2005</a></li> <li><a rel="nofollow" class="external text" href="https://www.ietf.org/timezones/data/leap-seconds.list">Current NIST leap seconds file compatible with ntpd</a></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFDavid_L._Mills" class="citation cs2">David L. Mills, <a rel="nofollow" class="external text" href="https://www.eecis.udel.edu/~mills/database/papers/history.pdf">A Brief History of NTP Time: Confessions of an Internet Timekeeper</a> (PDF), retrieved 2021-02-07</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+Brief+History+of+NTP+Time%3A+Confessions+of+an+Internet+Timekeeper&rft.au=David+L.+Mills&rft_id=https%3A%2F%2Fwww.eecis.udel.edu%2F~mills%2Fdatabase%2Fpapers%2Fhistory.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ANetwork+Time+Protocol" class="Z3988"></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=Network_Time_Protocol&oldid=1258659528">https://en.wikipedia.org/w/index.php?title=Network_Time_Protocol&oldid=1258659528</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:Application_layer_protocols" title="Category:Application layer protocols">Application layer protocols</a></li><li><a href="/wiki/Category:Internet_Standards" title="Category:Internet Standards">Internet Standards</a></li><li><a href="/wiki/Category:Network_time-related_software" title="Category:Network time-related software">Network time-related software</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:All_articles_with_dead_external_links" title="Category:All articles with dead external links">All articles with dead external links</a></li><li><a href="/wiki/Category:Articles_with_dead_external_links_from_November_2023" title="Category:Articles with dead external links from November 2023">Articles with dead external links from November 2023</a></li><li><a href="/wiki/Category:Articles_with_permanently_dead_external_links" title="Category:Articles with permanently dead external links">Articles with permanently dead external links</a></li><li><a href="/wiki/Category:Webarchive_template_wayback_links" title="Category:Webarchive template wayback links">Webarchive template wayback links</a></li><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><li><a href="/wiki/Category:Articles_containing_potentially_dated_statements_from_2022" title="Category:Articles containing potentially dated statements from 2022">Articles containing potentially dated statements from 2022</a></li><li><a href="/wiki/Category:All_articles_containing_potentially_dated_statements" title="Category:All articles containing potentially dated statements">All articles containing potentially dated statements</a></li><li><a href="/wiki/Category:All_articles_with_specifically_marked_weasel-worded_phrases" title="Category:All articles with specifically marked weasel-worded phrases">All articles with specifically marked weasel-worded phrases</a></li><li><a href="/wiki/Category:Articles_with_specifically_marked_weasel-worded_phrases_from_July_2022" title="Category:Articles with specifically marked weasel-worded phrases from July 2022">Articles with specifically marked weasel-worded phrases from July 2022</a></li><li><a href="/wiki/Category:All_articles_with_unsourced_statements" title="Category:All articles with unsourced statements">All articles with unsourced statements</a></li><li><a href="/wiki/Category:Articles_with_unsourced_statements_from_April_2022" title="Category:Articles with unsourced statements from April 2022">Articles with unsourced statements from April 2022</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 20 November 2024, at 22:09 (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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