TCP Fast Open

<h2 id="history">History</h2>
The TFO proposal was originally presented in 2011<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a>
and was published as the experimental RFC 7413 in December 2014.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> TCP Fast Open shares the goal of bypassing the three-way handshake of TCP with an earlier proposal from 1994, called <a href="/facts/T%2fTCP/n7Mtzy90">T/TCP</a> (RFC 1644). In contrast to TCP Fast Open, T/TCP paid no attention to security,<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> opening a path for vulnerabilities and failing to gain traction.

<h2 id="characteristics">Characteristics</h2>
TFO implementations include the following:

<ul><li><a href="/facts/IPv4/bnQ5MEqm">IPv4</a> support for TFO was merged into the <a href="/facts/Linux_kernel_mainline/dlkduHuA">Linux kernel mainline</a> in kernel versions 3.6 (support for clients) and 3.7 (Dec 2012) (support for servers),<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> and was turned on by default in kernel version 3.13 (Jan 2014).<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> TFO support for <a href="/facts/IPv6/d4dg7kIL">IPv6</a> servers was merged in kernel version 3.16.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a></li>
<li><a href="/facts/FreeBSD/RKsFTm7F">FreeBSD</a> from version 10.3<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> (support for servers) and 12.0.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a><a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> (support for clients).</li>
<li><a href="/facts/Mozilla_Firefox/xez2zv8H">Mozilla Firefox</a> from version 58.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> The support was disabled by default due to network device compatibility issues with TFO and <a href="/facts/Transport_Layer_Security/pGy16TnA">TLS 1.3</a><a class="footnote-ref" id="fnref:15" href="#fn:15">15</a> and eventually removed in version 87.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a></li>
<li><a href="/facts/Google_Chrome/4INfWq37">Google Chrome</a> and <a href="/facts/Chromium_(web_browser)/F1S8sAEt">Chromium</a> browsers have support for TFO on <a href="/facts/Linux/9FvCKSTq">Linux</a>, including <a href="/facts/ChromeOS/zH0B5Xtk">ChromeOS</a> and <a href="/facts/Android_(operating_system)/nNyHb0xz">Android</a>.</li>
<li><a href="/facts/Exim/CRVTpcoY">Exim</a> <a href="/facts/Mail_transfer_agent/9SJG5sbb">mail transfer agent</a> (MTA) from version 4.88.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a></li>
<li><a href="/facts/Unbound_(DNS_server)/0WeDyewu">Unbound DNS Resolver</a> from version 1.5.10.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a></li>
<li><a href="/facts/BIND/Mj5qNIuW">BIND</a> <a href="/facts/Domain_Name_System/rfxdWFsj">Domain Name System</a> (DNS) from version 9.11.0.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a></li>
<li><a href="/facts/Knot_DNS/chqAjYjV">Knot DNS</a> from version 2.6.0.<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a></li>
<li><a href="/facts/Apple_Inc./oTJYta3k">Apple</a>'s <a href="/facts/IOS_9/jeF0FGnB">iOS 9</a> and <a href="/facts/OS_X_10.11/4NAIbG7c">OS X 10.11</a> both support TCP Fast Open, but it is not enabled for individual connections by default.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a></li>
<li><a href="/facts/Microsoft_Edge/BGoJEFX9">Microsoft Edge</a> supports TCP Fast Open since <a href="/facts/Windows_10/be9IHehJ">Windows 10</a> Preview build 14352.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a></li>
<li><a href="/facts/PowerDNS/EDoMFvEx">PowerDNS Recursor</a> supports TCP Fast Open from version 4.1.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a></li>
<li><a href="/facts/Dnsmasq/aJF9tQcp">dnsmasq</a> supports TCP-fastopen (RFC-7413) from version 2.81.<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a></li></ul>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/SPDY/2uH2Rbu5">SPDY</a></li>
<li><a href="/facts/SYN_cookies/xFWsxKv0">SYN cookies</a></li>
<li><a href="/facts/TCP_Cookie_Transactions/QdomRpuM">TCP Cookie Transactions</a></li>
<li><a href="/facts/0-RTT/pGy16TnA">0-RTT</a></li>
<li><a href="/facts/QUIC/nQt0oLRW">QUIC</a></li></ul>

<h2 id="bibliography">Bibliography</h2>
<ul><li>Rybczyńska, Marta (13 March 2020). <a href="https://lwn.net/Articles/814522/">"A QUIC look at HTTP/3"</a>. <a href="/facts/LWN.net/8uTsltvM">LWN.net</a>.</li>
<li>Sy, Erik; Mueller, Tobias; Burkert, Christian; Federrath, Hannes; Fischer, Mathias (2020). <a href="https://doi.org/10.2478%2Fpopets-2020-0027">"Enhanced Performance and Privacy for TLS over TCP Fast Open"</a>. Proceedings on Privacy Enhancing Technologies. 2020 (2): 271–287. <a href="/facts/ArXiv_(identifier)/H6EtgnBe">arXiv</a>:<a href="https://arxiv.org/abs/1905.03518">1905.03518</a>. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.2478%2Fpopets-2020-0027">10.2478/popets-2020-0027</a>.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://www.rfc-editor.org/rfc/rfc7413">7413</a> specification</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Kerrisk, Michael (2012-08-01). "TCP Fast Open: expediting web services". LWN.net. <a href="https://lwn.net/Articles/508865/" target="_blank">https://lwn.net/Articles/508865/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Rybczyńska 2020. - Rybczyńska, Marta (13 March 2020). "A QUIC look at HTTP/3". LWN.net. <a href="https://lwn.net/Articles/814522/" target="_blank">https://lwn.net/Articles/814522/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Sy et al. 2020, p. 275-279. - Sy, Erik; Mueller, Tobias; Burkert, Christian; Federrath, Hannes; Fischer, Mathias (2020). "Enhanced Performance and Privacy for TLS over TCP Fast Open". Proceedings on Privacy Enhancing Technologies. 2020 (2): 271–287. arXiv:1905.03518. doi:10.2478/popets-2020-0027. <a href="https://doi.org/10.2478%2Fpopets-2020-0027" target="_blank">https://doi.org/10.2478%2Fpopets-2020-0027</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Radhakrishnan S, Cheng Y, Chu J, Jain A, Raghavan B (2011-12-06). "TCP Fast Open" (PDF). ACM CoNEXT. <a href="http://conferences.sigcomm.org/co-next/2011/papers/1569470463.pdf" target="_blank">http://conferences.sigcomm.org/co-next/2011/papers/1569470463.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Cheng, Yuchung; Chu, Jerry; Radhakrishnan, Sivasankar & Jain, Arvind (December 2014). TCP Fast Open. IETF. doi:10.17487/RFC7413. RFC 7413. Retrieved 27 June 2022. <a href="https://datatracker.ietf.org/doc/html/rfc7413" target="_blank">https://datatracker.ietf.org/doc/html/rfc7413</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Cheng, Yuchung; Chu, Jerry; Radhakrishnan, Sivasankar & Jain, Arvind (December 2014). TCP Fast Open. IETF. doi:10.17487/RFC7413. RFC 7413. Retrieved 27 June 2022. <a href="https://datatracker.ietf.org/doc/html/rfc7413" target="_blank">https://datatracker.ietf.org/doc/html/rfc7413</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Kerrisk, Michael (2012-08-01). "TCP Fast Open: expediting web services". LWN.net. The client-side support has been merged for Linux 3.6 <a href="https://lwn.net/Articles/508865/" target="_blank">https://lwn.net/Articles/508865/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Vaughan-Nichols, Steven J (2012-12-11). "Linux 3.7 arrives, ARM developers rejoice". Linux and Open Source. ZDNet. Linux 3.7. TCP Fast Open will now be supported on servers <a href="https://www.zdnet.com/article/linux-3-7-arrives-arm-developers-rejoice/" target="_blank">https://www.zdnet.com/article/linux-3-7-arrives-arm-developers-rejoice/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">"Linux Kernel 3.13, Section 1.10. TCP Fast Open enabled by default". kernelnewbies.org. 19 January 2014. Retrieved 11 February 2014. <a href="http://kernelnewbies.org/Linux_3.13#head-159ff61ea3acfd67b88855e75dbbb140f8825c4a" target="_blank">http://kernelnewbies.org/Linux_3.13#head-159ff61ea3acfd67b88855e75dbbb140f8825c4a</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">"Linux Kernel 3.16, Section 1.4. TCP Fast Open server mode on IPv6 support". kernelnewbies.org. 3 August 2014. Retrieved 14 September 2014. <a href="http://kernelnewbies.org/Linux_3.16#head-93fbb9abc6149e9c3055322f27cdc3a8fcc198e6" target="_blank">http://kernelnewbies.org/Linux_3.16#head-93fbb9abc6149e9c3055322f27cdc3a8fcc198e6</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">"Implementation of server-side TCP Fast Open (TFO) [RFC7413]: MFC into stable/10 branch". 2015-12-28. <a href="https://svnweb.freebsd.org/base?view=revision&revision=292823" target="_blank">https://svnweb.freebsd.org/base?view=revision&revision=292823</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">"This is an implementation of the client side of TCP Fast Open (TFO) [RFC7413]". 2018-02-26. <a href="https://svnweb.freebsd.org/base?view=revision&revision=330001" target="_blank">https://svnweb.freebsd.org/base?view=revision&revision=330001</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"Enable TCP_FASTOPEN by default for FreeBSD 12". 2018-06-24. <a href="https://svnweb.freebsd.org/base?view=revision&revision=335610" target="_blank">https://svnweb.freebsd.org/base?view=revision&revision=335610</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">"1188435 - Support TCP Fast Open". 2017-05-05. <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1188435" target="_blank">https://bugzilla.mozilla.org/show_bug.cgi?id=1188435</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">"1398201 - Disable TCP Fast Open for 57". 2017-09-10. <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1398201" target="_blank">https://bugzilla.mozilla.org/show_bug.cgi?id=1398201</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">"1689604 - Remove TCP FastOpen". 2021-03-23. <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1689604" target="_blank">https://bugzilla.mozilla.org/show_bug.cgi?id=1689604</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">"Exim 4.88 released". 2016-12-25. <a href="https://lists.exim.org/lurker/message/20161225.101705.4bbe7ae8.en.html" target="_blank">https://lists.exim.org/lurker/message/20161225.101705.4bbe7ae8.en.html</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">"Unbound 1.5.10". Retrieved 2017-12-05. <a href="https://www.unbound.net/pipermail/unbound-users/2016-September/004466.html" target="_blank">https://www.unbound.net/pipermail/unbound-users/2016-September/004466.html</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">"Release Notes for BIND Version 9.11.0". 2016-10-05. <a href="https://ftp.isc.org/isc/bind9/9.11.0/RELEASE-NOTES-bind-9.11.0.html" target="_blank">https://ftp.isc.org/isc/bind9/9.11.0/RELEASE-NOTES-bind-9.11.0.html</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">"Knot DNS 2.6.0". 2017-09-29. <a href="https://gitlab.labs.nic.cz/knot/knot-dns/tags/v2.6.0" target="_blank">https://gitlab.labs.nic.cz/knot/knot-dns/tags/v2.6.0</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">"Your App and Next Generation Networks". Apple Inc. 2015. <a href="https://developer.apple.com/videos/wwdc/2015/?id=719" target="_blank">https://developer.apple.com/videos/wwdc/2015/?id=719</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">"Windows 10 build 14352 - New web platform features". Microsoft. Retrieved 2016-05-27. <a href="https://developer.microsoft.com/en-us/microsoft-edge/platform/changelog/desktop/14352/" target="_blank">https://developer.microsoft.com/en-us/microsoft-edge/platform/changelog/desktop/14352/</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">"Changelogs for 4.1.x". PowerDNS. 2017-12-04. <a href="https://doc.powerdns.com/recursor/changelog/4.1.html" target="_blank">https://doc.powerdns.com/recursor/changelog/4.1.html</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">Kelley, Simon (2019-03-10). "Support TCP fastopen on incoming and outgoing connections". <a href="http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=608aa9fcfca2ffeba40d78c7c4e0dcb50e0d5704" target="_blank">http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commitdiff;h=608aa9fcfca2ffeba40d78c7c4e0dcb50e0d5704</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
</ol>

TCP Fast Open open-in-new

TCP Fast Open