rfc8765xml2.original.xml   rfc8765.xml 
<?xml version="1.0" encoding="UTF-8"?> <?xml version='1.0' encoding='utf-8'?>
<!-- This template is for creating an Internet Draft using xml2rfc, <rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="std" conse
which is available here: http://xml.resource.org. --> nsus="true" docName="draft-ietf-dnssd-push-25" indexInclude="true" ipr="trust200
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [ 902" number="8765" prepTime="2020-06-22T20:57:32" scripts="Common,Latin" sortRef
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There has to be one entity for each item to be referenced. :lang="en">
An alternate method (rfc include) is described in the references. --> <link href="https://datatracker.ietf.org/doc/draft-ietf-dnssd-push-25" rel="pr
ev"/>
<!ENTITY RFC0020 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <link href="https://dx.doi.org/10.17487/rfc8765" rel="alternate"/>
ence.RFC.0020.xml"> <link href="urn:issn:2070-1721" rel="alternate"/>
<!ENTITY RFC0768 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <front>
ence.RFC.0768.xml"> <title abbrev="DNS Push Notifications">DNS Push Notifications</title>
<!ENTITY RFC0793 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <seriesInfo name="RFC" value="8765" stream="IETF"/>
ence.RFC.0793.xml"> <author fullname="Tom Pusateri" initials="T." surname="Pusateri">
<!ENTITY RFC1034 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <organization showOnFrontPage="true">Unaffiliated</organization>
ence.RFC.1034.xml"> <address>
<!ENTITY RFC1035 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <postal>
ence.RFC.1035.xml"> <street/>
<!ENTITY RFC1123 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <city>Raleigh</city>
ence.RFC.1123.xml"> <region>NC</region>
<!ENTITY RFC2119 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <code>27608</code>
ence.RFC.2119.xml"> <country>United States of America</country>
<!ENTITY RFC2136 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </postal>
ence.RFC.2136.xml"> <phone>+1 919 867 1330</phone>
<!ENTITY RFC2181 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <email>pusateri@bangj.com</email>
ence.RFC.2181.xml"> </address>
<!ENTITY RFC2308 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </author>
ence.RFC.2308.xml"> <author fullname="Stuart Cheshire" initials="S." surname="Cheshire">
<!ENTITY RFC3123 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <organization showOnFrontPage="true">Apple Inc.</organization>
ence.RFC.3123.xml"> <address>
<!ENTITY RFC2782 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <postal>
ence.RFC.2782.xml"> <street>One Apple Park Way</street>
<!ENTITY RFC4287 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <city>Cupertino</city>
ence.RFC.4287.xml"> <region>CA</region>
<!ENTITY RFC4953 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <code>95014</code>
ence.RFC.4953.xml"> <country>United States of America</country>
<!ENTITY RFC6066 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </postal>
ence.RFC.6066.xml"> <phone>+1 (408) 996-1010</phone>
<!ENTITY RFC6281 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <email>cheshire@apple.com</email>
ence.RFC.6281.xml"> </address>
<!ENTITY RFC6762 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </author>
ence.RFC.6762.xml"> <date month="06" year="2020"/>
<!ENTITY RFC6763 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <area>INT</area>
ence.RFC.6763.xml"> <workgroup>DNSSD</workgroup>
<!ENTITY RFC6824 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <keyword>Push notification</keyword>
ence.RFC.6824.xml"> <keyword>Asynchronous notification</keyword>
<!ENTITY RFC6886 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <abstract pn="section-abstract">
ence.RFC.6886.xml"> <t pn="section-abstract-1">The Domain Name System (DNS) was designed to re
<!ENTITY RFC6887 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer turn matching records
ence.RFC.6887.xml"> efficiently for queries for data that are relatively static. When those
<!ENTITY RFC6895 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer records change frequently, DNS is still efficient at returning the
ence.RFC.6895.xml"> updated results when polled, as long as the polling rate is not too
<!ENTITY RFC7413 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer high.
ence.RFC.7413.xml"> But, there exists no mechanism for a client to be asynchronously
<!ENTITY RFC7673 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer notified
ence.RFC.7673.xml"> when these changes occur. This document defines a mechanism for a
<!ENTITY RFC7719 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer client to be notified of such changes to DNS records, called DNS Push
ence.RFC.7719.xml"> Notifications.</t>
<!ENTITY RFC7766 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </abstract>
ence.RFC.7766.xml"> <boilerplate>
<!ENTITY RFC7858 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc=
ence.RFC.7858.xml"> "exclude" pn="section-boilerplate.1">
<!ENTITY RFC8010 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <name slugifiedName="name-status-of-this-memo">Status of This Memo</name
ence.RFC.8010.xml"> >
<!ENTITY RFC8011 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer <t pn="section-boilerplate.1-1">
ence.RFC.8011.xml"> This is an Internet Standards Track document.
<!ENTITY RFC8174 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </t>
ence.RFC.8174.xml"> <t pn="section-boilerplate.1-2">
<!ENTITY RFC8310 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer This document is a product of the Internet Engineering Task Force
ence.RFC.8310.xml"> (IETF). It represents the consensus of the IETF community. It has
<!ENTITY RFC8446 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer received public review and has been approved for publication by
ence.RFC.8446.xml"> the Internet Engineering Steering Group (IESG). Further
<!ENTITY RFC8490 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer information on Internet Standards is available in Section 2 of
ence.RFC.8490.xml"> RFC 7841.
<!ENTITY RFC8499 SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/bibxml/refer </t>
ence.RFC.8499.xml"> <t pn="section-boilerplate.1-3">
<!ENTITY I-D.ietf-tcpm-rack SYSTEM "https://xml2rfc.tools.ietf.org/public/rfc/b Information about the current status of this document, any
ibxml3/reference.I-D.ietf-tcpm-rack.xml"> errata, and how to provide feedback on it may be obtained at
]> <eref target="https://www.rfc-editor.org/info/rfc8765" brackets="non
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> e"/>.
<!-- used by XSLT processors --> </t>
<!-- For a complete list and description of processing instructions (PIs), </section>
please see http://xml.resource.org/authoring/README.html. --> <section anchor="copyright" numbered="false" removeInRFC="false" toc="excl
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might want to use. <name slugifiedName="name-copyright-notice">Copyright Notice</name>
(Here they are set differently than their defaults in xml2rfc v1.32) --> <t pn="section-boilerplate.2-1">
<?rfc strict="yes" ?> Copyright (c) 2020 IETF Trust and the persons identified as the
<!-- give errors regarding ID-nits and DTD validation --> document authors. All rights reserved.
<!-- control the table of contents (ToC) --> </t>
<?rfc toc="yes"?> <t pn="section-boilerplate.2-2">
<!-- generate a ToC --> This document is subject to BCP 78 and the IETF Trust's Legal
<?rfc tocdepth="4"?> Provisions Relating to IETF Documents
<!-- the number of levels of subsections in ToC. default: 3 --> (<eref target="https://trustee.ietf.org/license-info" brackets="none
<!-- control references --> "/>) in effect on the date of
<?rfc symrefs="yes"?> publication of this document. Please review these documents
<!-- use symbolic references tags, i.e, [RFC2119] instead of [1] --> carefully, as they describe your rights and restrictions with
<?rfc sortrefs="yes" ?> respect to this document. Code Components extracted from this
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(using these PIs as follows is recommended by the RFC Editor) --> warranty as described in the Simplified BSD License.
<?rfc compact="yes" ?> </t>
<!-- do not start each main section on a new page --> </section>
<?rfc subcompact="no" ?> </boilerplate>
<!-- keep one blank line between list items --> <toc>
<!-- end of list of popular I-D processing instructions --> <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" p
<rfc category="std" docName="draft-ietf-dnssd-push-25" ipr="trust200902"> n="section-toc.1">
<!-- category values: std, bcp, info, exp, and historic <name slugifiedName="name-table-of-contents">Table of Contents</name>
ipr values: trust200902, noModificationTrust200902, noDerivativesTrust200902 <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-to
, c.1-1">
or pre5378Trust200902 <li pn="section-toc.1-1.1">
you can add the attributes updates="NNNN" and obsoletes="NNNN" <t keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent
they will automatically be output with "(if approved)" --> ="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedCon
tent="" format="title" sectionFormat="of" target="name-introduction">Introductio
<!-- ***** FRONT MATTER ***** --> n</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
<front> n-toc.1-1.1.2">
<!-- The abbreviated title is used in the page header - it is only necessary <li pn="section-toc.1-1.1.2.1">
if the <t keepWithNext="true" pn="section-toc.1-1.1.2.1.1"><xref derive
full title is longer than 39 characters --> dContent="1.1" format="counter" sectionFormat="of" target="section-1.1"/>.  <xre
f derivedContent="" format="title" sectionFormat="of" target="name-requirements-
<title abbrev="DNS Push Notifications">DNS Push Notifications</title> language">Requirements Language</xref></t>
</li>
<!-- add 'role="editor"' below for the editors if appropriate --> <li pn="section-toc.1-1.1.2.2">
<t keepWithNext="true" pn="section-toc.1-1.1.2.2.1"><xref derive
<!-- Another author who claims to be an editor --> dContent="1.2" format="counter" sectionFormat="of" target="section-1.2"/>.  <xre
f derivedContent="" format="title" sectionFormat="of" target="name-fatal-errors"
<author fullname="Tom Pusateri" initials="T.J." surname="Pusateri"> >Fatal Errors</xref></t>
<organization>Unaffiliated</organization> </li>
</ul>
<address> </li>
<postal> <li pn="section-toc.1-1.2">
<street></street> <t pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter
<!-- Reorder these if your country does things differently --> " sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="titl
<city>Raleigh</city> e" sectionFormat="of" target="name-motivation">Motivation</xref></t>
<region>NC</region> </li>
<code>27608</code> <li pn="section-toc.1-1.3">
<country>USA</country> <t pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter
</postal> " sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="titl
<phone>+1 919 867 1330</phone> e" sectionFormat="of" target="name-overview">Overview</xref></t>
<email>pusateri@bangj.com</email> </li>
<!-- uri and facsimile elements may also be added --> <li pn="section-toc.1-1.4">
</address> <t pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter
</author> " sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="titl
<author fullname="Stuart Cheshire" initials="S." surname="Cheshire"> e" sectionFormat="of" target="name-state-considerations">State Considerations</x
<organization>Apple Inc.</organization> ref></t>
</li>
<address> <li pn="section-toc.1-1.5">
<postal> <t pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter
<street>One Apple Park Way</street> " sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="titl
<!-- Reorder these if your country does things differently --> e" sectionFormat="of" target="name-transport">Transport</xref></t>
<city>Cupertino</city> </li>
<region>CA</region> <li pn="section-toc.1-1.6">
<code>95014</code> <t pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter
<country>USA</country> " sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="titl
</postal> e" sectionFormat="of" target="name-protocol-operation">Protocol Operation</xref>
<phone>+1 (408) 996-1010</phone> </t>
<email>cheshire@apple.com</email> <ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
<!-- uri and facsimile elements may also be added --> n-toc.1-1.6.2">
</address> <li pn="section-toc.1-1.6.2.1">
</author> <t pn="section-toc.1-1.6.2.1.1"><xref derivedContent="6.1" forma
t="counter" sectionFormat="of" target="section-6.1"/>.  <xref derivedContent=""
<date year='2019' month='October' day='13'/> format="title" sectionFormat="of" target="name-discovery">Discovery</xref></t>
</li>
<!-- If the month and year are both specified and are the current ones, xml2r <li pn="section-toc.1-1.6.2.2">
fc will fill <t pn="section-toc.1-1.6.2.2.1"><xref derivedContent="6.2" forma
in the current day for you. If only the current year is specified, xml2r t="counter" sectionFormat="of" target="section-6.2"/>.  <xref derivedContent=""
fc will fill format="title" sectionFormat="of" target="name-dns-push-notification-subsc">DNS
in the current day and month for you. If the year is not the current one Push Notification SUBSCRIBE</xref></t>
, it is <ul bare="true" empty="true" indent="2" spacing="compact" pn="se
necessary to specify at least a month (xml2rfc assumes day="1" if not sp ction-toc.1-1.6.2.2.2">
ecified for the <li pn="section-toc.1-1.6.2.2.2.1">
purpose of calculating the expiry date). With drafts it is normally suf <t pn="section-toc.1-1.6.2.2.2.1.1"><xref derivedContent="6.
ficient to 2.1" format="counter" sectionFormat="of" target="section-6.2.1"/>.  <xref derive
specify just the year. --> dContent="" format="title" sectionFormat="of" target="name-subscribe-request">SU
BSCRIBE Request</xref></t>
<!-- Meta-data Declarations --> </li>
<li pn="section-toc.1-1.6.2.2.2.2">
<area>DNSSD</area> <t pn="section-toc.1-1.6.2.2.2.2.1"><xref derivedContent="6.
2.2" format="counter" sectionFormat="of" target="section-6.2.2"/>.  <xref derive
<workgroup>Internet Engineering Task Force</workgroup> dContent="" format="title" sectionFormat="of" target="name-subscribe-response">S
UBSCRIBE Response</xref></t>
<!-- WG name at the upper left corner of the doc, </li>
IETF is fine for individual submissions. </ul>
If this element is not present, the default is "Network Working Group", </li>
which is used by the RFC Editor as a nod to the history of the IETF. --> <li pn="section-toc.1-1.6.2.3">
<t pn="section-toc.1-1.6.2.3.1"><xref derivedContent="6.3" forma
<keyword>dns update push notification</keyword> t="counter" sectionFormat="of" target="section-6.3"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-dns-push-notification-updat">DNS
<!-- Keywords will be incorporated into HTML output Push Notification Updates</xref></t>
files in a meta tag but they have no effect on text or nroff <ul bare="true" empty="true" indent="2" spacing="compact" pn="se
output. If you submit your draft to the RFC Editor, the ction-toc.1-1.6.2.3.2">
keywords will be used for the search engine. --> <li pn="section-toc.1-1.6.2.3.2.1">
<t pn="section-toc.1-1.6.2.3.2.1.1"><xref derivedContent="6.
<abstract> 3.1" format="counter" sectionFormat="of" target="section-6.3.1"/>.  <xref derive
<t>The Domain Name System (DNS) was designed to return matching records dContent="" format="title" sectionFormat="of" target="name-push-message">PUSH Me
efficiently for queries for data that are relatively static. ssage</xref></t>
When those records change frequently, DNS is still efficient at returning </li>
the updated results when polled, as long as the polling rate is not too hig </ul>
h. </li>
But there exists no mechanism <li pn="section-toc.1-1.6.2.4">
for a client to be asynchronously notified when these changes occur. <t pn="section-toc.1-1.6.2.4.1"><xref derivedContent="6.4" forma
This document defines a mechanism for a client to be notified t="counter" sectionFormat="of" target="section-6.4"/>.  <xref derivedContent=""
of such changes to DNS records, called DNS Push Notifications.</t> format="title" sectionFormat="of" target="name-dns-push-notification-unsub">DNS
</abstract> Push Notification UNSUBSCRIBE</xref></t>
</front> <ul bare="true" empty="true" indent="2" spacing="compact" pn="se
ction-toc.1-1.6.2.4.2">
<middle> <li pn="section-toc.1-1.6.2.4.2.1">
<?rfc needLines="14" ?> <t pn="section-toc.1-1.6.2.4.2.1.1"><xref derivedContent="6.
<section title="Introduction"> 4.1" format="counter" sectionFormat="of" target="section-6.4.1"/>.  <xref derive
dContent="" format="title" sectionFormat="of" target="name-unsubscribe-message">
<t>Domain Name System (DNS) records may be updated using <xref target="RFC2 UNSUBSCRIBE Message</xref></t>
136">DNS Update</xref>. </li>
Other mechanisms such as a <xref target="DisProx">Discovery Proxy</xref> ca </ul>
n also generate changes to a DNS zone. </li>
This document specifies a protocol for DNS clients to subscribe to receive <li pn="section-toc.1-1.6.2.5">
asynchronous notifications of changes to RRsets of interest. It is immediately r <t pn="section-toc.1-1.6.2.5.1"><xref derivedContent="6.5" forma
elevant in the case of <xref target="RFC6763">DNS Service Discovery</xref> but i t="counter" sectionFormat="of" target="section-6.5"/>.  <xref derivedContent=""
s not limited to that use case, and provides a general DNS mechanism for DNS rec format="title" sectionFormat="of" target="name-dns-push-notification-recon">DNS
ord change notifications. Familiarity with the DNS protocol and DNS packet forma Push Notification RECONFIRM</xref></t>
ts is assumed <xref target="RFC1034"/> <xref target="RFC1035"/> <xref target="RF <ul bare="true" empty="true" indent="2" spacing="compact" pn="se
C6895"/>.</t> ction-toc.1-1.6.2.5.2">
<li pn="section-toc.1-1.6.2.5.2.1">
<?rfc needLines="7" ?> <t pn="section-toc.1-1.6.2.5.2.1.1"><xref derivedContent="6.
<section title="Requirements Language"> 5.1" format="counter" sectionFormat="of" target="section-6.5.1"/>.  <xref derive
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", dContent="" format="title" sectionFormat="of" target="name-reconfirm-message">RE
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", CONFIRM Message</xref></t>
and "OPTIONAL" in this document are to be interpreted as described </li>
in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/> </ul>
when, and only when, they appear in all capitals, as shown here. </li>
These words may also appear in this document in lower case as <li pn="section-toc.1-1.6.2.6">
plain English words, absent their normative meanings.</t> <t pn="section-toc.1-1.6.2.6.1"><xref derivedContent="6.6" forma
</section> t="counter" sectionFormat="of" target="section-6.6"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-dns-stateful-operations-tlv">DNS
<section title="Fatal Errors"> Stateful Operations TLV Context Summary</xref></t>
<t>Certain invalid situations are described in this specification, </li>
like a server sending a Push Notification subscription request to a clien <li pn="section-toc.1-1.6.2.7">
t, <t pn="section-toc.1-1.6.2.7.1"><xref derivedContent="6.7" forma
or a client sending a Push Notification response to a server. t="counter" sectionFormat="of" target="section-6.7"/>.  <xref derivedContent=""
These should never occur with a correctly implemented client and server, format="title" sectionFormat="of" target="name-client-initiated-terminatio">Clie
and if they do occur then they indicate a serious implementation error. nt-Initiated Termination</xref></t>
In these extreme cases there is no reasonable expectation of a graceful r </li>
ecovery, <li pn="section-toc.1-1.6.2.8">
and the recipient detecting the error should respond by unilaterally <t pn="section-toc.1-1.6.2.8.1"><xref derivedContent="6.8" forma
aborting the session without regard for data loss. t="counter" sectionFormat="of" target="section-6.8"/>.  <xref derivedContent=""
Such cases are addressed by having an engineer investigate the format="title" sectionFormat="of" target="name-client-fallback-to-polling">Clien
cause of the failure and fixing the problem in the software.</t> t Fallback to Polling</xref></t>
</li>
<t>Where this specification says "forcibly abort", it means </ul>
sending a TCP RST to terminate the TCP connection, </li>
<li pn="section-toc.1-1.7">
<t pn="section-toc.1-1.7.1"><xref derivedContent="7" format="counter
" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" format="titl
e" sectionFormat="of" target="name-security-considerations">Security Considerati
ons</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.7.2">
<li pn="section-toc.1-1.7.2.1">
<t pn="section-toc.1-1.7.2.1.1"><xref derivedContent="7.1" forma
t="counter" sectionFormat="of" target="section-7.1"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-security-services">Security Servi
ces</xref></t>
</li>
<li pn="section-toc.1-1.7.2.2">
<t pn="section-toc.1-1.7.2.2.1"><xref derivedContent="7.2" forma
t="counter" sectionFormat="of" target="section-7.2"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-tls-name-authentication">TLS Name
Authentication</xref></t>
</li>
<li pn="section-toc.1-1.7.2.3">
<t pn="section-toc.1-1.7.2.3.1"><xref derivedContent="7.3" forma
t="counter" sectionFormat="of" target="section-7.3"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-tls-early-data">TLS Early Data</x
ref></t>
</li>
<li pn="section-toc.1-1.7.2.4">
<t pn="section-toc.1-1.7.2.4.1"><xref derivedContent="7.4" forma
t="counter" sectionFormat="of" target="section-7.4"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-tls-session-resumption">TLS Sessi
on Resumption</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.8">
<t pn="section-toc.1-1.8.1"><xref derivedContent="8" format="counter
" sectionFormat="of" target="section-8"/>.  <xref derivedContent="" format="titl
e" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xre
f></t>
</li>
<li pn="section-toc.1-1.9">
<t pn="section-toc.1-1.9.1"><xref derivedContent="9" format="counter
" sectionFormat="of" target="section-9"/>.  <xref derivedContent="" format="titl
e" sectionFormat="of" target="name-references">References</xref></t>
<ul bare="true" empty="true" indent="2" spacing="compact" pn="sectio
n-toc.1-1.9.2">
<li pn="section-toc.1-1.9.2.1">
<t pn="section-toc.1-1.9.2.1.1"><xref derivedContent="9.1" forma
t="counter" sectionFormat="of" target="section-9.1"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-normative-references">Normative R
eferences</xref></t>
</li>
<li pn="section-toc.1-1.9.2.2">
<t pn="section-toc.1-1.9.2.2.1"><xref derivedContent="9.2" forma
t="counter" sectionFormat="of" target="section-9.2"/>.  <xref derivedContent=""
format="title" sectionFormat="of" target="name-informative-references">Informati
ve References</xref></t>
</li>
</ul>
</li>
<li pn="section-toc.1-1.10">
<t pn="section-toc.1-1.10.1"><xref derivedContent="" format="none" s
ectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="t
itle" sectionFormat="of" target="name-acknowledgments">Acknowledgments</xref></t
>
</li>
<li pn="section-toc.1-1.11">
<t pn="section-toc.1-1.11.1"><xref derivedContent="" format="none" s
ectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="t
itle" sectionFormat="of" target="name-authors-addresses">Authors' Addresses</xre
f></t>
</li>
</ul>
</section>
</toc>
</front>
<middle>
<section numbered="true" toc="include" removeInRFC="false" pn="section-1">
<name slugifiedName="name-introduction">Introduction</name>
<t pn="section-1-1">Domain Name System (DNS) records may be updated using
DNS Update
<xref target="RFC2136" format="default" sectionFormat="of" derivedContent=
"RFC2136"/>. Other mechanisms such
as a Discovery Proxy <xref target="RFC8766" format="default" sectionFormat
="of" derivedContent="RFC8766"/> can
also generate changes to a DNS zone. This document specifies a protocol
for DNS clients to subscribe to receive asynchronous notifications of
changes to RRsets of interest. It is immediately relevant in the case of
DNS-based Service Discovery <xref target="RFC6763" format="default" sectio
nFormat="of" derivedContent="RFC6763"/>
but is not limited to that use case; it provides a general DNS
mechanism for DNS record change notifications. Familiarity with the DNS
protocol and DNS packet formats is assumed <xref target="RFC1034" format="
default" sectionFormat="of" derivedContent="RFC1034"/> <xref target="RFC1035" fo
rmat="default" sectionFormat="of" derivedContent="RFC1035"/> <xref target="RFC68
95" format="default" sectionFormat="of" derivedContent="RFC6895"/>.</t>
<section numbered="true" toc="include" removeInRFC="false" pn="section-1.1
">
<name slugifiedName="name-requirements-language">Requirements Language</
name>
<t pn="section-1.1-1">
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>
", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are
to be interpreted as
described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="o
f" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFor
mat="of" derivedContent="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-1.2
">
<name slugifiedName="name-fatal-errors">Fatal Errors</name>
<t pn="section-1.2-1">Certain invalid situations are described in this s
pecification,
such
as a server sending a Push Notification subscription request to a
client, or a client sending a Push Notification response to a server.
These should never occur with a correctly implemented client and
server, and if they do occur, then they indicate a serious
implementation error. In these extreme cases, there is no reasonable
expectation of a graceful recovery, and the recipient detecting the
error should respond by unilaterally aborting the session without
regard for data loss. Such cases are addressed by having an engineer
investigate the cause of the failure and fixing the problem in the
software.</t>
<t pn="section-1.2-2">Where this specification says "forcibly abort", it
means
sending a TCP RST to terminate the TCP connection
and the TLS session running over that TCP connection. and the TLS session running over that TCP connection.
In the BSD Sockets API, this is achieved by setting the In the BSD Sockets API, this is achieved by setting the
SO_LINGER option to zero before closing the socket.</t> SO_LINGER option to zero before closing the socket.</t>
</section>
<?rfc needLines="40" ?> </section>
</section> <section numbered="true" toc="include" removeInRFC="false" pn="section-2">
</section> <name slugifiedName="name-motivation">Motivation</name>
<t pn="section-2-1">As the domain name system continues to adapt to new us
<section title="Motivation"> es and changes
<t>As the domain name system continues to adapt to new uses and changes in in deployment, polling has the potential to burden DNS servers at many
deployment, polling has the potential to burden DNS servers at many levels throu levels throughout the network. Other network protocols have successfully
ghout the network. Other network protocols have successfully deployed a publish/ deployed a publish/subscribe model following the Observer design pattern
subscribe model following the <xref target="obs">Observer design pattern</xref>. <xref target="OBS" format="default" sectionFormat="of" derivedContent="OBS
<xref target="XEP0060">XMPP Publish-Subscribe</xref> and <xref target="RFC4 "/>. Extensible Messaging and
287">Atom</xref> are examples. While DNS servers are generally highly tuned and Presence Protocol (XMPP) Publish-Subscribe
capable of a high rate of query/response traffic, adding a publish/subscribe mod <xref target="XEP0060" format="default" sectionFormat="of" derivedContent=
el for tracking changes to DNS records can deliver more timely notification of c "XEP0060"/> and Atom <xref target="RFC4287" format="default" sectionFormat="of"
hanges with reduced CPU usage and lower network traffic.</t> derivedContent="RFC4287"/> are examples. While DNS
servers are generally highly tuned and capable of a high rate of
<t><xref target="RFC6762">Multicast DNS</xref> implementations always liste query/response traffic, adding a publish/subscribe model for tracking
n on a well known link-local changes to DNS records can deliver more timely notifications of changes
IP multicast group address, and changes are sent to that multicast group ad with reduced CPU usage and lower network traffic.</t>
dress for all group members to receive. <t pn="section-2-2">The guiding design principle of DNS Push Notifications
Therefore, Multicast DNS already has asynchronous change notification capab is that clients that choose to use DNS Push Notifications,
ility. instead of repeated polling with DNS queries,
When <xref target="RFC6763">DNS Service Discovery</xref> is used across a w will receive the same results as they could
ide area network using Unicast DNS via sufficiently rapid polling, except more efficiently.
(possibly facilitated via a <xref target="DisProx">Discovery Proxy</xref>) This means that the rules for
it would be beneficial to have an equivalent which records match a given DNS Push Notification subscription are the
capability for Unicast DNS, to allow clients to learn about DNS record chan same as the already established rules used to determine
ges in a timely manner without polling.</t> which records match a given DNS query <xref target="RFC1034" format="defau
lt" sectionFormat="of" derivedContent="RFC1034"/>.
<t>The <xref target="LLQ">DNS Long-Lived Queries (LLQ) mechanism</xref> is For example, name comparisons are done in a case-insensitive manner,
an existing deployed solution to provide asynchronous change notifications, used and a record of type CNAME in a zone matches any DNS TYPE in a query or
by Apple's <xref target="RFC6281">Back to My Mac</xref> service subscription.</t>
introduced in Mac OS X 10.5 Leopard in 2007. <t pn="section-2-3">Multicast DNS <xref target="RFC6762" format="default"
Back to My Mac was designed in an era when the data center operations staff sectionFormat="of" derivedContent="RFC6762"/>
asserted that it was impossible for a server to handle large numbers of mostly- implementations always listen on a well-known link-local IP multicast
idle TCP connections, so LLQ was defined as a UDP-based protocol, effectively re group address, and changes are sent to that multicast group address for
plicating much of TCP's connection state management logic in user space, and cre all group members to receive. Therefore, Multicast DNS already has
ating its own imitation of existing TCP features like the three-way handshake, f asynchronous change notification capability. When DNS-based Service Disco
low control, and reliability.</t> very
<xref target="RFC6763" format="default" sectionFormat="of" derivedContent=
<t>This document builds on experience gained with the LLQ protocol, with an "RFC6763"/> is used across a wide
improved design. area network using Unicast DNS (possibly facilitated via a Discovery
Instead of using UDP, this specification uses Proxy <xref target="RFC8766" format="default" sectionFormat="of" derivedCo
<xref target="RFC8490">DNS Stateful Operations (DSO)</xref> ntent="RFC8766"/>), it would be
running over TLS over TCP, beneficial to have an equivalent capability for Unicast DNS in order to
and therefore doesn't need to reinvent existing TCP functionality. allow clients to learn about DNS record changes in a timely manner
Using TCP also gives long-lived low-traffic connections better longevity th without polling.</t>
rough NAT gateways <t pn="section-2-4">The DNS Long-Lived Queries (LLQ) mechanism <xref targe
without depending on the gateway to support t="RFC8764" format="default" sectionFormat="of" derivedContent="RFC8764"/> is an
<xref target="RFC6886">NAT Port Mapping Protocol (NAT-PMP)</xref> or existing deployed solution to provide
<xref target="RFC6887">Port Control Protocol (PCP)</xref>, or asynchronous change notifications; it was used by Apple's Back to
resorting to excessive keepalive traffic.</t> My Mac <xref target="RFC6281" format="default" sectionFormat="of" derivedC
ontent="RFC6281"/> service
<?rfc needLines="9" ?> introduced in Mac OS X 10.5 Leopard in 2007. Back to My Mac was
</section> designed in an era when the data center operations staff asserted that
it was impossible for a server to handle large numbers of
<section title="Overview"> TCP connections, even if those connections carried
<t>A DNS Push Notification client subscribes for Push Notifications for a p very little traffic and spent most of their time idle.
articular RRset by connecting to the appropriate Push Notification server for th Consequently, LLQ was defined as a UDP-based protocol, effectively
at RRset, and sending DSO message(s) indicating the RRset(s) of interest. When t replicating much of TCP's connection state management logic in user
he client loses interest in receiving further updates to these records, it unsub space and creating its own imitation of existing TCP features like flow
scribes.</t> control, reliability, and the three-way handshake.</t>
<t pn="section-2-5">This document builds on experience gained with the LLQ
<t>The DNS Push Notification server for a DNS zone is any server capable protocol, with
an improved design. Instead of using UDP, this specification uses DNS
Stateful Operations (DSO) <xref target="RFC8490" format="default" sectionF
ormat="of" derivedContent="RFC8490"/> running over TLS over TCP, and therefore
doesn't need to reinvent existing TCP functionality. Using TCP also
gives long-lived low-traffic connections better longevity through NAT
gateways without depending on the gateway to support NAT Port Mapping
Protocol (NAT-PMP) <xref target="RFC6886" format="default" sectionFormat="
of" derivedContent="RFC6886"/> or
Port Control Protocol (PCP) <xref target="RFC6887" format="default" sectio
nFormat="of" derivedContent="RFC6887"/>, or resorting to excessive keepalive
traffic.</t>
</section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-3">
<name slugifiedName="name-overview">Overview</name>
<t pn="section-3-1">A DNS Push Notification client subscribes for Push Not
ifications for
a particular RRset by connecting to the appropriate Push Notification
server for that RRset and sending DSO message(s) indicating the
RRset(s) of interest. When the client loses interest in receiving
further updates to these records, it unsubscribes.</t>
<t pn="section-3-2">The DNS Push Notification server for a DNS zone is any
server capable
of generating the correct change notifications for a name. of generating the correct change notifications for a name.
It may be a primary, secondary, or stealth name server <xref target="RFC771 It may be a primary, secondary, or stealth name server <xref target="RFC849
9"/>.</t> 9" format="default" sectionFormat="of" derivedContent="RFC8499"/>.</t>
<t pn="section-3-3">The <tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt> SRV recor
<t>The <spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</spanx d for
> SRV record for a a zone <bcp14>MAY</bcp14> reference the same target host and port as
zone MAY reference the same target host and port as that zone's that zone's <tt>_dns‑update‑tls._tcp.&lt;zone&gt;</tt> SRV
<spanx style="verb">_dns&nbhy;update&nbhy;tls._tcp.&lt;zone&gt;</spanx> SRV record. When the same target host and port is offered for both DNS
record. When the same target host and port is offered for both DNS Updates and Updates and DNS Push Notifications, a client <bcp14>MAY</bcp14> use a
DNS Push Notifications, a client MAY use a single DSO session to that server for single DSO session to that server for both DNS Updates and DNS Push
both DNS Updates and DNS Push Notification Subscriptions. Notification subscriptions. DNS Updates and DNS Push Notifications may
DNS Updates and DNS Push Notifications may be handled on different ports on be handled on different ports on the same target host, in which case
the same target host, in which case they are not considered to be the "same ser they are not considered to be the "same server" for the purposes of this
ver" for the purposes of this specification, and communications with these two p specification, and communications with these two ports are handled
orts are handled independently. independently. Supporting DNS Updates and DNS Push Notifications on the
Supporting DNS Updates and DNS Push Notifications on the same server is OPT same server is <bcp14>OPTIONAL</bcp14>. A DNS Push Notification server
IONAL. A DNS Push Notification server is not required to support DNS Update.</t> is not required to support DNS Update.</t>
<t pn="section-3-4">Standard DNS Queries <bcp14>MAY</bcp14> be sent over a
<t>Standard DNS Queries MAY be sent over a DNS Push Notification (i.e., DSO DNS Push
) Notification (i.e., DSO) session. For any zone for which the server is
session. For any zone for which the server is authoritative, it authoritative, it <bcp14>MUST</bcp14> respond authoritatively for
MUST respond authoritatively for queries for names falling within queries for names falling within that zone (e.g., the
that zone (e.g., the <spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zon <tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt> SRV record) both for
e&gt;</spanx> SRV normal DNS queries and for DNS Push Notification subscriptions. For
record) both for normal DNS queries and for DNS Push Notification subscriptio names for which the server is acting as a recursive resolver (e.g., when
ns. the server is the local recursive resolver) for any query for which it
For names for which the server is acting as a recursive supports DNS Push Notification subscriptions, it <bcp14>MUST</bcp14>
resolver (e.g., when the server is the local recursive resolver) for any quer also support standard queries.</t>
y <t pn="section-3-5">DNS Push Notifications impose less load on the respond
for which it supports DNS Push Notification subscriptions, it MUST also suppo ing server than
rt rapid polling would, but Push Notifications do still have a
standard queries.</t> cost. Therefore, DNS Push Notification clients <bcp14>MUST NOT</bcp14>
recklessly create an excessive number of Push Notification
<t>DNS Push Notifications impose less load on the responding server than ra subscriptions. Specifically:</t>
pid polling would, but Push Notifications do still have a cost, so DNS Push Noti <ol type="(%c)" spacing="normal" start="1" pn="section-3-6">
fication clients MUST NOT recklessly create an excessive number of Push Notifica <li pn="section-3-6.1" derivedCounter="(a)">A subscription should only b
tion subscriptions. Specifically:</t> e active when there is a valid reason to need
live data (for example, an on-screen display is currently showing the results
<t>(a) A subscription should only be active when there is a valid reason to to the user), and the subscription <bcp14>SHOULD</bcp14> be canceled as soon
need live data (for example, an on-screen display is currently showing the resu as the need for that data ends (for example, when the user dismisses that
lts to the user) and the subscription SHOULD be cancelled as soon as the need fo display). In the case of a device like a smartphone that, after some period
r that data ends (for example, when the user dismisses that display). In the cas of inactivity, goes to sleep or otherwise darkens its screen, it should cancel
e of a device like a smartphone which, after some period of inactivity, goes to its subscriptions when darkening the screen (since the user cannot see any
sleep or otherwise darkens its screen, it should cancel its subscriptions when d changes on the display anyway) and reinstate its subscriptions when
arkening the screen (since the user cannot see any changes on the display anyway reawakening from display sleep.
) and reinstate its subscriptions when re-awakening from display sleep.</t> </li>
<li pn="section-3-6.2" derivedCounter="(b)">A DNS Push Notification clie
<t>(b) A DNS Push Notification client SHOULD NOT routinely keep a DNS Push nt <bcp14>SHOULD NOT</bcp14> routinely keep a
Notification subscription active 24 hours a day, 7 days a week, just to keep a l DNS Push Notification subscription active 24 hours a day, 7 days a week, just
ist in memory up to date so that if the user does choose to bring up an on-scree to keep a list in memory up to date so that if the user does choose to bring
n display of that data, it can be displayed really fast. DNS Push Notifications up an on-screen display of that data, it can be displayed really fast. DNS
are designed to be fast enough that there is no need to pre-load a "warm" list i Push Notifications are designed to be fast enough that there is no need to
n memory just in case it might be needed later.</t> pre-load a "warm" list in memory just in case it might be needed later.
</li>
<t>Generally, as described in the <xref target="RFC8490">DNS Stateful Opera </ol>
tions specification</xref>, a client must not keep a DSO session to a server ope <t pn="section-3-7">Generally, as described in the DNS Stateful Operations
n indefinitely if it has no subscriptions (or other operations) active on that s specification
ession. A client may close a DSO session immediately it becomes idle, and then i <xref target="RFC8490" format="default" sectionFormat="of" derivedContent=
f needed in the future, open a new session when required. Alternatively, a clien "RFC8490"/>, a client
t may speculatively keep an idle DSO session open for some time, subject to the must not keep a DSO session to a server open indefinitely if it has no
constraint that it must not keep a session open that has been idle for more than subscriptions (or other operations) active on that session. A client
the session's idle timeout (15 seconds by default) <xref target="RFC8490"/>.</t should begin closing a DSO session immediately after it becomes idle,
> and then, if needed in
the future, open a new session when required. Alternatively, a client
<t>Note that a DSO session that has an active DNS Push Notification subscri may speculatively keep an idle DSO session open for some time, subject
ption is not considered idle, to the constraint that it must not keep a session open that has been
even if there is no traffic flowing for an extended period of time. idle for more than the session's idle timeout (15 seconds by default)
In this case the DSO inactivity timeout does not apply, because the session <xref target="RFC8490" format="default" sectionFormat="of" derivedContent=
is not inactive, "RFC8490"/>.</t>
but the keepalive interval does still apply, to ensure generation of <t pn="section-3-8">Note that a DSO session that has an active DNS Push No
sufficient messages to maintain state in middleboxes (such at NAT gateways tification
or firewalls) subscription is not considered idle, even if there is no traffic flowing
and for the client and server to periodically verify that they still have c for an extended period of time. In this case, the DSO inactivity
onnectivity to each other. timeout does not apply, because the session is not inactive, but the
This is described in Section 6.2 of the <xref target="RFC8490">DSO specific keepalive interval does still apply, to ensure the generation of
ation</xref>.</t> sufficient messages to maintain state in middleboxes (such at NAT
gateways or firewalls) and for the client and server to periodically
<?rfc needLines="14" ?> verify that they still have connectivity to each other. This is
</section> described in <xref target="RFC8490" sectionFormat="of" section="6.2" forma
t="default" derivedLink="https://rfc-editor.org/rfc/rfc8490#section-6.2" derived
<section title="State Considerations"> Content="RFC8490">the DSO specification</xref>.</t>
<t>Each DNS Push Notification server is capable of handling some finite </section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-4">
<name slugifiedName="name-state-considerations">State Considerations</name
>
<t pn="section-4-1">Each DNS Push Notification server is capable of handli
ng some finite
number of Push Notification subscriptions. This number will vary from number of Push Notification subscriptions. This number will vary from
server to server and is based on physical machine characteristics, server to server and is based on physical machine characteristics,
network bandwidth, and operating system resource allocation. After a network capacity, and operating system resource allocation. After a
client establishes a session to a DNS server, each subscription is client establishes a session to a DNS server, each subscription is
individually accepted or rejected. Servers may employ various techniques individually accepted or rejected. Servers may employ various techniques
to limit subscriptions to a manageable level. Correspondingly, the client to limit subscriptions to a manageable level. Correspondingly, the client
is free to establish simultaneous sessions to alternate DNS servers that is free to establish simultaneous sessions to alternate DNS servers that
support DNS Push Notifications for the zone and distribute subscriptions support DNS Push Notifications for the zone and distribute subscriptions
at the client's discretion. In this way, both clients and servers can at the client's discretion. In this way, both clients and servers can
react to resource constraints.</t> react to resource constraints.</t>
<?rfc needLines="35" ?> </section>
</section> <section numbered="true" toc="include" removeInRFC="false" pn="section-5">
<name slugifiedName="name-transport">Transport</name>
<section title="Transport"> <t pn="section-5-1">Other DNS operations like DNS Update <xref target="RFC
<t>Other DNS operations like <xref target="RFC2136">DNS Update</xref> MAY u 2136" format="default" sectionFormat="of" derivedContent="RFC2136"/> <bcp14>MAY<
se either User Datagram Protocol <xref target="RFC0768">(UDP)</xref> or Transmis /bcp14> use either DNS over User
sion Control Protocol <xref target="RFC0793">(TCP)</xref> as the transport proto Datagram
col, in keeping with the historical precedent that DNS queries must first be sen Protocol (UDP) <xref target="RFC0768" format="default" sectionFormat="of"
t over UDP <xref target="RFC1123"/>. This requirement to use UDP has subsequentl derivedContent="RFC0768"/> or
y been relaxed <xref target="RFC7766"/>.</t> DNS over Transmission Control Protocol (TCP) <xref target="RFC0793" format
="default" sectionFormat="of" derivedContent="RFC0793"/> as the transport protoc
<t>In keeping with the more recent precedent, DNS Push Notification is defi ol, provided they follow
ned only for TCP. the historical precedent that DNS queries must first be sent using DNS
DNS Push Notification clients MUST use over UDP
<xref target="RFC8490">DNS Stateful Operations</xref> and only switch to DNS over TCP if needed <xref target="RFC1123" format="d
running over TLS over TCP <xref target="RFC7858"/>.</t> efault" sectionFormat="of" derivedContent="RFC1123"/>.
This requirement to prefer UDP
<t>Connection setup over TCP ensures return reachability has subsequently been relaxed <xref target="RFC7766" format="default" sect
and alleviates concerns of state overload at the server, ionFormat="of" derivedContent="RFC7766"/>.</t>
which is a potential problem with connectionless protocols, <t pn="section-5-2">In keeping with the more recent precedent, DNS Push No
which can be more vulnerable to being exploited by attackers using spoofed tification is
source addresses. defined only for TCP.
All subscribers are guaranteed to be reachable by the server by virtue of t DNS Push Notification clients <bcp14>MUST</bcp14> use
he TCP three-way handshake. DNS Stateful Operations <xref target="RFC8490" format="default" sectionForm
Flooding attacks are possible with any protocol, and a benefit of TCP is th at="of" derivedContent="RFC8490"/>
at there are already established industry best practices to guard against SYN fl running over TLS over TCP <xref target="RFC7858" format="default" sectionFo
ooding and similar attacks <xref target="SYN"/> <xref target="RFC4953"/>.</t> rmat="of" derivedContent="RFC7858"/>.</t>
<t pn="section-5-3">
<t>Use of TCP also allows DNS Push Notifications to take advantage of curre Connection setup over TCP ensures return reachability and alleviates concerns
nt and future developments in TCP, such as of state overload at the server, a potential problem with connectionless
<xref target="RFC6824">Multipath TCP (MPTCP)</xref>, protocols, which can be more vulnerable to being exploited by attackers using
<xref target="RFC7413">TCP Fast Open (TFO)</xref>, spoofed source addresses.
<xref target="I-D.ietf-tcpm-rack">the TCP RACK fast loss detection algorith
m</xref>,
and so on.</t>
<t>Transport Layer Security <xref target="RFC8446">(TLS)</xref> is well und
erstood, and used by many application-layer protocols running over TCP. TLS is d
esigned to prevent eavesdropping, tampering, and message forgery. TLS is REQUIRE
D for every connection between a client subscriber and server in this protocol s
pecification. Additional security measures such as client authentication during
TLS negotiation may also be employed to increase the trust relationship between
client and server.</t>
<?rfc needLines="25" ?>
</section>
<section title="Protocol Operation">
<t>The DNS Push Notification protocol is a session-oriented protocol, and m
akes use of
<xref target="RFC8490">DNS Stateful Operations (DSO)</xref>.</t>
<t>For details of the DSO message format refer to the All subscribers are guaranteed to be reachable by the server by virtue of
<xref target="RFC8490">DNS Stateful Oper-ations specification</xref>. the TCP three-way handshake. Flooding attacks are possible with any
protocol, and a benefit of TCP is that there are already established
industry best practices to guard against SYN flooding and similar attacks
<xref target="SYN" format="default" sectionFormat="of" derivedContent="SYN"
/> <xref target="RFC4953" format="default" sectionFormat="of" derivedContent="RF
C4953"/>.</t>
<t pn="section-5-4">Use of TCP also allows DNS Push Notifications to take
advantage of
current and future developments in TCP such as Multipath TCP (MPTCP)
<xref target="RFC8684" format="default" sectionFormat="of" derivedContent=
"RFC8684"/>, TCP Fast Open (TFO)
<xref target="RFC7413" format="default" sectionFormat="of" derivedContent=
"RFC7413"/>, the TCP RACK fast loss
detection algorithm <xref target="I-D.ietf-tcpm-rack" format="default" sec
tionFormat="of" derivedContent="TCPRACK"/>, and so on.</t>
<t pn="section-5-5">Transport Layer Security (TLS) <xref target="RFC8446"
format="default" sectionFormat="of" derivedContent="RFC8446"/> is well understoo
d and is used by many
application-layer protocols running over TCP. TLS is designed to prevent
eavesdropping, tampering, and message forgery. TLS is
<bcp14>REQUIRED</bcp14> for every connection between a client subscriber
and server in this protocol specification. Additional security measures
such as client authentication during TLS negotiation may also be
employed to increase the trust relationship between client and
server.</t>
</section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-6">
<name slugifiedName="name-protocol-operation">Protocol Operation</name>
<t pn="section-6-1">The DNS Push Notification protocol is a session-orient
ed protocol and
makes use of
DNS Stateful Operations (DSO) <xref target="RFC8490" format="default" secti
onFormat="of" derivedContent="RFC8490"/>.</t>
<t pn="section-6-2">For details of the DSO message format, refer to the
DNS Stateful Operations specification <xref target="RFC8490" format="defaul
t" sectionFormat="of" derivedContent="RFC8490"/>.
Those details are not repeated here.</t> Those details are not repeated here.</t>
<t pn="section-6-3">DNS Push Notification clients and servers <bcp14>MUST<
<t>DNS Push Notification clients and servers MUST support DSO. /bcp14> support
DSO.
A single server can support DNS Queries, DNS Updates, and DNS Push A single server can support DNS Queries, DNS Updates, and DNS Push
Notifications (using DSO) on the same TCP port.</t> Notifications (using DSO) on the same TCP port.</t>
<t pn="section-6-4">A DNS Push Notification exchange begins with the clien
<t>A DNS Push Notification exchange begins with the client discovering the t discovering
appropriate server, the appropriate server, using the procedure described in <xref target="dis
using the procedure described in <xref target="discovery"/>, and then makin covery" format="default" sectionFormat="of" derivedContent="Section 6.1"/>, and
g a TLS/TCP connection to it.</t> then making a TLS/TCP
connection to it.</t>
<t>A typical DNS Push Notification client will immediately issue a DSO <t pn="section-6-5">After making the TLS/TCP connection to the server,
Keepalive operation to request a session timeout and/or keepalive interval a typical DNS Push Notification client will then immediately issue a DSO
Keepalive operation to establish the DSO session
and request a session timeout and/or keepalive interval
longer than the 15-second default values, but this is not required. longer than the 15-second default values, but this is not required.
A DNS Push Notification client MAY issue other requests on the A DNS Push Notification client <bcp14>MAY</bcp14> issue other requests on
the
session first, and only issue a DSO Keepalive session first, and only issue a DSO Keepalive
operation later if it determines that to be necessary. operation later if it determines that to be necessary.
Sending either a DSO Keepalive operation or a Push Notification Sending either a DSO Keepalive operation or a Push Notification
subscription request over the TLS/TCP connection to the server signals the subscription request over the TLS/TCP connection to the server signals
the
client's support of DSO and serves to establish a DSO session.</t> client's support of DSO and serves to establish a DSO session.</t>
<t pn="section-6-6">In accordance with the current set of active subscript
<t>In accordance with the current set of active subscriptions, ions,
the server sends relevant asynchronous Push Notifications to the server sends relevant asynchronous Push Notifications to
the client. Note that a client MUST be prepared to receive the client. Note that a client <bcp14>MUST</bcp14> be prepared to receive
(and silently ignore) Push Notifications for subscriptions it (and silently ignore) Push Notifications for subscriptions it
has previously removed, since there is no way to prevent the has previously removed, since there is no way to prevent the
situation where a Push Notification is in flight from server situation where a Push Notification is in flight from server
to client while the client's UNSUBSCRIBE message cancelling to client while the client's UNSUBSCRIBE message canceling
that subscription is simultaneously in flight from client to that subscription is simultaneously in flight from client to
server.</t> server.</t>
<section anchor="discovery" numbered="true" toc="include" removeInRFC="fal
<?rfc needLines="30" ?> se" pn="section-6.1">
<section title="Discovery" anchor="discovery"> <name slugifiedName="name-discovery">Discovery</name>
<t>The first step in establishing a DNS Push Notification subscription i <t pn="section-6.1-1">The first step in establishing a DNS Push Notifica
s to discover an appropriate DNS server that supports DNS Push Notifications for tion
the desired zone.</t> subscription is to discover an appropriate DNS server that
supports DNS Push Notifications for the desired zone.</t>
<t>The client begins by opening a DSO Session to its normal configured <t pn="section-6.1-2">The client begins by opening a DSO session to its
DNS recursive resolver and requesting a Push Notification subscription. normal configured
DNS recursive resolver and requesting a Push Notification
subscription.
This connection is made to TCP port 853, the default port for This connection is made to TCP port 853, the default port for
<xref target="RFC7858">DNS-over-TLS</xref>. DNS over TLS <xref target="RFC7858" format="default" sectionFormat="of" derivedContent="RFC7858"/>.
If the request for a Push Notification subscription is successful, If the request for a Push Notification subscription is successful,
and the recursive resolver doesn't already have an active subscription f and the recursive resolver doesn't already have an active subscription
or that name, type, and class, for that name, type, and class,
then the recursive resolver will make a corresponding then the recursive resolver will make a corresponding
Push Notification subscription on the client's behalf. Push Notification subscription on the client's behalf.
Results received are relayed to the client. Results received are relayed to the client.
This is closely analogous to how a client sends a normal DNS This is closely analogous to how a client sends a normal DNS
query to its configured DNS recursive resolver which, query to its configured DNS recursive resolver, which,
if it doesn't already have appropriate answer(s) in its cache, if it doesn't already have appropriate answer(s) in its cache,
issues an upstream query to satisfy the request.</t> issues an upstream query to satisfy the request.</t>
<t pn="section-6.1-3">In many contexts, the recursive resolver will be a
<t>In many contexts, the recursive resolver will be able to handle ble to handle
Push Notifications for all names that the client may need to follow. Push Notifications for all names that the client may need to follow.
Use of VPN tunnels and Private DNS <xref target="RFC8499"/> Use of VPN tunnels and Private DNS <xref target="RFC8499" format="defaul t" sectionFormat="of" derivedContent="RFC8499"/>
can create some additional complexity in the client software here; can create some additional complexity in the client software here;
the techniques to handle VPN tunnels and Private DNS for DNS Push the techniques to handle VPN tunnels and Private DNS for DNS Push
Notifications are the same as those already used to handle this for Notifications are the same as those already used to handle this for
normal DNS queries.</t> normal DNS queries.</t>
<t pn="section-6.1-4">If the recursive resolver does not support DNS ove
<t>If the recursive resolver r TLS, or
does not support DNS over TLS, or
supports DNS over TLS but is not listening on TCP port 853, or supports DNS over TLS but is not listening on TCP port 853, or
supports DNS over TLS on TCP port 853 but does not support DSO on that p supports DNS over TLS on TCP port 853 but does not support DSO on that
ort, port, then the DSO session establishment will fail <xref target="RFC8490
then the DSO Session session establishment will fail <xref target="RFC84 " format="default" sectionFormat="of" derivedContent="RFC8490"/>.</t>
90"/>.</t> <t pn="section-6.1-5">If the recursive resolver does support DSO on TCP
port 853
<t>If the recursive resolver does support DSO but not Push Notification but does not support Push Notification subscriptions,
subscriptions, then it will return the DSO error code DSOTYPENI (11).</t then when the client attempts to create a subscription,
> the server will return the DSO error code DSOTYPENI (11).</t>
<t pn="section-6.1-6">In some cases, the recursive resolver may support
<t>In some cases, the recursive resolver may support DSO and Push DSO and Push
Notification subscriptions, but may not be able Notification subscriptions but may not be able
to subscribe for Push Notifications for a particular name. to subscribe for Push Notifications for a particular name.
In this case, the recursive resolver should return In this case, the recursive resolver should return
SERVFAIL to the client. This includes being unable SERVFAIL to the client. This includes being unable
to establish a connection to establish a connection
to the zone's DNS Push Notification server or establishing to the zone's DNS Push Notification server or establishing
a connection but receiving a non success response code. a connection but receiving a non-success response code.
In some cases, where the client has a pre-established trust In some cases, where the client has a pre-established trust
relationship with the owner of the zone (that is not handled relationship with the owner of the zone (that is not handled
via the usual mechanisms for VPN software) the client may via the usual mechanisms for VPN software), the client may
handle these failures by contacting the zone's DNS Push server handle these failures by contacting the zone's DNS Push Notification
server
directly.</t> directly.</t>
<t pn="section-6.1-7">In any of the cases described above where the clie
<t>In any of the cases described above where the client nt
fails to establish a DNS Push Notification subscription via its fails to establish a DNS Push Notification subscription via its
configured recursive resolver, the client should proceed to discover configured recursive resolver, the client should proceed to discover
the appropriate server for direct communication. The client MUST the appropriate server for direct communication. The client
also determine which TCP port on the server is listening for <bcp14>MUST</bcp14>
connections, which need not be (and often is not) the typical TCP also determine on which TCP port the server is listening for
port 53 used for conventional DNS, or TCP port 853 used for DNS connections, which need not be, and often is not,
over TLS.</t> TCP port 53 (traditionally used for conventional DNS) or
TCP port 853 (traditionally used for DNS over TLS).</t>
<t>The discovery algorithm described here is an iterative algorithm, <t pn="section-6.1-8">The discovery algorithm described here is an itera
tive algorithm,
which starts with the full name of the record to which the which starts with the full name of the record to which the
client wishes to subscribe. Successive SOA queries are then client wishes to subscribe. Successive SOA queries are then
issued, trimming one label each time, until issued, trimming one label each time, until
the closest enclosing authoritative server is discovered. the closest enclosing authoritative server is discovered.
There is also an optimization to enable the client to There is also an optimization to enable the client to
take a "short cut" directly to the SOA record of take a "short cut" directly to the SOA record of
the closest enclosing authoritative server in many cases.</t> the closest enclosing authoritative server in many cases.</t>
<ol spacing="normal" type="1" start="1" pn="section-6.1-9">
<t> <li pn="section-6.1-9.1" derivedCounter="1.">The client begins the dis
<list style="numbers"> covery by sending a DNS query to its
<t>The client begins the discovery by sending a DNS query to its loc local resolver, with record type SOA <xref target="RFC1035" format="de
al resolver, with record type fault" sectionFormat="of" derivedContent="RFC1035"/> for the record name to whic
<xref target="RFC1035">SOA</xref> for the record name to which it wi h it wishes to
shes to subscribe. subscribe. As an example, suppose the client wishes to subscribe to
As an example, suppose the client wishes to subscribe to PTR records PTR records with the name <tt>_ipp._tcp.headoffice.example.com</tt>
with the name _ipp._tcp.headoffice.example.com (to
(to discover Internet Printing Protocol (IPP) printers <xref target= discover Internet Printing Protocol (IPP) printers <xref target="RFC80
"RFC8010"/> <xref target="RFC8011"/> 10" format="default" sectionFormat="of" derivedContent="RFC8010"/> <xref target=
being advertised in the head office of Example Company.). "RFC8011" format="default" sectionFormat="of" derivedContent="RFC8011"/> being a
The client begins by sending an SOA query for _ipp._tcp.headoffice.e dvertised in the head office of Example
xample.com to the local recursive resolver. Company). The client begins by sending an SOA query for
The goal is to determine the server authoritative for the name _ipp. <tt>_ipp._tcp.headoffice.example.com</tt> to the local recursive
_tcp.headoffice.example.com. resolver.
The closest enclosing DNS zone containing the name _ipp._tcp.headoff The goal is to determine the server that is authoritative for the
ice.example.com could be example.com, name
or headoffice.example.com, or _tcp.headoffice.example.com, or even _ <tt>_ipp._tcp.headoffice.example.com</tt>. The closest enclosing
ipp._tcp.headoffice.example.com. DNS zone
The client does not know in advance where the closest enclosing zone containing the name <tt>_ipp._tcp.headoffice.example.com</tt> could
cut occurs, be
which is why it uses the iterative procedure described here to disco <tt>example.com</tt>, or <tt>headoffice.example.com</tt>, or
ver this information.</t> <tt>_tcp.headoffice.example.com</tt>, or even
<tt>_ipp._tcp.headoffice.example.com</tt>. The client does not know
<t>If the requested SOA record exists, it will be returned in the An in
swer section with a NOERROR response code, and advance where the closest enclosing zone cut occurs, which is why it
the client has succeeded in discovering the information it needs. uses the iterative procedure described here to discover this
<vspace /> information.</li>
(This language is not placing any new requirements on DNS recursive <li pn="section-6.1-9.2" derivedCounter="2.">
resolvers. <t pn="section-6.1-9.2.1">If the requested SOA record exists, it wil
This text merely describes the existing operation of the DNS protoco l be returned in the
l Answer Section with a NOERROR response code, and the client has
<xref target="RFC1034"/> <xref target="RFC1035"/>.)</t> succeeded in discovering the information it needs.
</t>
<t>If the requested SOA record does not exist, the client will get b <t pn="section-6.1-9.2.2">
ack a NOERROR/NODATA response or an NXDOMAIN/Name Error response. (This language is not placing any new requirements on DNS
In either case, the local resolver would normally include the SOA re recursive resolvers.
cord for the closest enclosing zone of the requested name in the Authority Secti This text merely describes the existing operation of the DNS
on. protocol
If the SOA record is received in the Authority Section, then <xref target="RFC1034" format="default" sectionFormat="of" derivedCo
the client has succeeded in discovering the information it needs. ntent="RFC1034"/> <xref target="RFC1035" format="default" sectionFormat="of" der
<vspace /> ivedContent="RFC1035"/>.)</t>
(This language is not placing any new requirements on DNS recursive </li>
resolvers. <li pn="section-6.1-9.3" derivedCounter="3.">
This text merely describes the existing operation of the DNS protoco <t pn="section-6.1-9.3.1">If the requested SOA record does not exist
l , the client will get
regarding negative responses <xref target="RFC2308"/>.)</t> back a NOERROR/NODATA response or an NXDOMAIN/Name Error response.
In either case, the local resolver would normally include the SOA
<t>If the client receives a response containing no SOA record, record for the closest enclosing zone of the requested name in the
then it proceeds with the iterative approach. Authority Section. If the SOA record is received in the Authority
The client strips the leading label from the current query name, Section, then the client has succeeded in discovering the
and if the resulting name has at least two labels in it, information it needs.
the client sends an SOA query for that new name, </t>
and processing continues at step 2 above, <t pn="section-6.1-9.3.2">
repeating the iterative search until either an SOA is received, (This language is not placing any new requirements on DNS
or the query name consists of a single label, i.e., a Top Level Doma recursive resolvers.
in (TLD). This text merely describes the existing operation of the DNS
In the case of a single-label name (TLD), this is a network configur protocol
ation error, regarding negative responses <xref target="RFC2308" format="default"
which should not happen, and the client gives up. sectionFormat="of" derivedContent="RFC2308"/>.)</t>
The client may retry the operation at a later time, of the client's </li>
choosing, <li pn="section-6.1-9.4" derivedCounter="4.">If the client receives a
such after a change in network attachment.</t> response containing no SOA record, then
it proceeds with the iterative approach. The client strips the
<t>Once the SOA is known (either by virtue of being seen in the Answ leading label from the current query name, and if the resulting name
er Section, or in the Authority Section), the client sends a DNS query with type has at least two labels in it, then the client sends an SOA query
<xref target="RFC2782">SRV</xref> for the record name for
<spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</spanx that new name and processing continues at step 2 above, repeating
>, where &lt;zone&gt; is the owner name of the discovered SOA record.</t> the iterative search until either an SOA is received or the query
name consists of a single label, i.e., a Top-Level Domain (TLD). In
<t>If the zone in question is set up to offer DNS Push Notifications the case of a single-label name (TLD), this is a network
then this SRV record MUST exist. configuration error, which should not happen, and the client gives
(If this SRV record does not exist then the zone is not correctly up. The client may retry the operation at a later time of the
configured for DNS Push Notifications as specified in this document. client's choosing, such as after a change in network
) attachment.</li>
The SRV <spanx style="verb">target</spanx> contains the name of the <li pn="section-6.1-9.5" derivedCounter="5.">Once the SOA is known (by
server providing DNS Push Notifications for the zone. The port number on which t virtue of being seen either in the
o contact the server is in the SRV record <spanx style="verb">port</spanx> field Answer Section or in the Authority Section), the client sends a DNS
. The address(es) of the target host MAY be included in the Additional Section, query with type SRV <xref target="RFC2782" format="default" sectionFor
however, the address records SHOULD be authenticated before use as described bel mat="of" derivedContent="RFC2782"/>
ow in <xref target="tls_name_auth"/> and in for the record name
<xref target="RFC7673">the specification for using DANE TLSA Records <tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt>, where
with SRV Records</xref>, if applicable.</t> &lt;zone&gt; is the owner name of the discovered SOA record.</li>
<li pn="section-6.1-9.6" derivedCounter="6.">If the zone in question i
<t anchor="SRV">More than one SRV record may be returned. In this ca s set up to offer DNS Push
se, the <spanx style="verb">priority</spanx> and <spanx style="verb">weight</spa Notifications, then this SRV record <bcp14>MUST</bcp14> exist. (If
nx> values in the returned SRV records are used to determine the order in which this SRV record does not exist, then the zone is not correctly
to contact the servers for subscription requests. As described in <xref target=" configured for DNS Push Notifications as specified in this
RFC2782">the SRV specification</xref>, the server with the lowest <spanx style=" document.) The SRV <tt>target</tt> contains the name of the server
verb">priority</spanx> is first contacted. If more than one server has the same providing DNS Push Notifications for the zone. The port number on
<spanx style="verb">priority</spanx>, the <spanx style="verb">weight</spanx> ind which to contact the server is in the SRV record <tt>port</tt>
icates the weighted probability that the client should contact that server. High field. The address(es) of the target host <bcp14>MAY</bcp14> be
er weights have higher probabilities of being selected. included in the Additional Section, however, the address records
If a server is not willing to accept a subscription request, <bcp14>SHOULD</bcp14> be authenticated before use as described in
or is not reachable within a reasonable time, as determined by the c <xref target="tls_name_auth" format="default" sectionFormat="of" deriv
lient, edContent="Section 7.2"/> and in the
then a subsequent server is to be contacted.</t> specification for using DNS-Based Authentication of Named Entities
(DANE) TLSA Records with SRV Records <xref target="RFC7673" format="d
</list> efault" sectionFormat="of" derivedContent="RFC7673"/>, if applicable.</li>
</t> <li anchor="SRV" pn="section-6.1-9.7" derivedCounter="7.">More than on
e SRV record may be returned. In this
<t>Each time a client makes a new DNS Push Notification subscription, case, the <tt>priority</tt> and <tt>weight</tt> values in the
it SHOULD repeat the discovery process in order to determine returned SRV records are used to determine the order in which to
the preferred DNS server for that subscription at that time. contact the servers for subscription requests. As described in the
If a client already has a DSO session with that DNS server SRV specification <xref target="RFC2782" format="default" sectionForma
the client SHOULD reuse that existing DSO session for the new subscripti t="of" derivedContent="RFC2782"/>,
on, the server with the lowest <tt>priority</tt> is first contacted. If
otherwise, a new DSO session is established. more than one server has the same <tt>priority</tt>, the
The client MUST respect the DNS TTL values on records it receives while <tt>weight</tt> indicates the weighted probability that the client
performing should contact that server. Higher weights have higher probabilities
the discovery process and store them in its local cache with this lifeti of being selected. If a server is not willing to accept a
me subscription request, or is not reachable within a reasonable time,
(as it will generally be do anyway for all DNS queries it performs). as determined by the client, then a subsequent server is to be
This means that, as long as the DNS TTL values on the authoritative reco contacted.</li>
rds are set </ol>
to reasonable values, repeated application of the discovery process can <t pn="section-6.1-10">Each time a client makes a new DNS Push Notificat
be completed ion subscription,
nearly instantaneously by the client, using only locally-stored cached d it <bcp14>SHOULD</bcp14> repeat the discovery process in order to
ata.</t> determine the preferred DNS server for that subscription at that time.
If a client already has a DSO session with that DNS server, the client
<?rfc needLines="48" ?> <bcp14>SHOULD</bcp14> reuse that existing DSO session for the new
</section> subscription; otherwise, a new DSO session is established. The client
<bcp14>MUST</bcp14> respect the DNS TTL values on records it receives
<section title="DNS Push Notification SUBSCRIBE" anchor="subscribe"> while performing the discovery process and store them in its local
<t>After connecting, and requesting a longer idle timeout and/or cache with this lifetime (as it will generally do anyway for all
keepalive interval if necessary, a DNS Push Notification client<vspace /> DNS queries it performs). This means that, as long as the DNS TTL
then indicates its desire to receive DNS Push Notifications for<vspace /> values on the authoritative records are set to reasonable values,
a given domain name by sending a SUBSCRIBE request to the server.<vspace repeated application of the discovery process can be completed
/> practically
A SUBSCRIBE request is encoded in a DSO message <xref target="RFC8490"/>. instantaneously by the client, using only locally stored cached
<vspace /> data.</t>
This specification defines a primary DSO TLV for DNS Push Notification SU </section>
BSCRIBE Requests (tentatively DSO Type Code 0x40).</t> <section anchor="subscribe" numbered="true" toc="include" removeInRFC="fal
se" pn="section-6.2">
<t>DSO messages with the SUBSCRIBE TLV as the Primary TLV are permitted i <name slugifiedName="name-dns-push-notification-subsc">DNS Push Notifica
n TLS early data, tion SUBSCRIBE</name>
provided that the precautions described in <xref target="early_data"/> ar <t pn="section-6.2-1">After connecting, and requesting a longer idle tim
e followed.</t> eout and/or
keepalive interval if necessary, a DNS Push Notification client then
<t>The entity that initiates a SUBSCRIBE request is by definition the cli indicates its desire to receive DNS Push Notifications for a given
ent. domain name by sending a SUBSCRIBE request to the server. A SUBSCRIBE
A server MUST NOT send a SUBSCRIBE request over an existing session from request is encoded in a DSO message <xref target="RFC8490" format="defau
a client. lt" sectionFormat="of" derivedContent="RFC8490"/>. This specification defines a
If a server does send a SUBSCRIBE request over a DSO session initiated by DSO Primary TLV for DNS Push Notification SUBSCRIBE Requests
a client, (DSO Type Code 0x0040).</t>
this is a fatal error and the client MUST forcibly abort the connection i <t pn="section-6.2-2">DSO messages with the SUBSCRIBE TLV as the Primary
mmediately.</t> TLV are
permitted in TLS early data, provided that the precautions described
<t>Each SUBSCRIBE request generates exactly one SUBSCRIBE response from t in
he server. <xref target="early_data" format="default" sectionFormat="of" derivedCon
The entity that initiates a SUBSCRIBE response is by definition the serve tent="Section 7.3"/> are followed.</t>
r. <t pn="section-6.2-3">The entity that initiates a SUBSCRIBE request is b
A client MUST NOT send a SUBSCRIBE response. y definition the
If a client does send a SUBSCRIBE response, client. A server <bcp14>MUST NOT</bcp14> send a SUBSCRIBE request
this is a fatal error and the server MUST forcibly abort the connection i over an existing session from a client. If a server does send a
mmediately.</t> SUBSCRIBE request over a DSO session initiated by a client, this is a
fatal error and the client <bcp14>MUST</bcp14> forcibly abort the
<section title="SUBSCRIBE Request"> connection immediately.</t>
<t pn="section-6.2-4">Each SUBSCRIBE request generates exactly one SUBSC
<t>A SUBSCRIBE request begins with the standard RIBE response
<xref target="RFC8490">DSO 12-byte header</xref>, followed by the SUBSC from the server. The entity that initiates a SUBSCRIBE response is by
RIBE primary TLV. definition the server. A client <bcp14>MUST NOT</bcp14> send a
A SUBSCRIBE request is illustrated in <xref target="subscribe_req"/>.</ SUBSCRIBE response. If a client does send a SUBSCRIBE response, this
t> is a fatal error and the server <bcp14>MUST</bcp14> forcibly abort the
connection immediately.</t>
<t>The MESSAGE ID field MUST be set to a unique value, that the client <section numbered="true" toc="include" removeInRFC="false" pn="section-6
is not using for any other active operation on this DSO session. For the purpose .2.1">
s here, a MESSAGE ID is in use on this session if the client has used it in a re <name slugifiedName="name-subscribe-request">SUBSCRIBE Request</name>
quest for which it has not yet received a response, or if the client has used it <t pn="section-6.2.1-1">A SUBSCRIBE request begins with the standard D
for a subscription which it has not yet cancelled using UNSUBSCRIBE. In the SUB SO 12-byte header
SCRIBE response the server MUST echo back the MESSAGE ID value unchanged.</t> <xref target="RFC8490" format="default" sectionFormat="of" derivedCont
ent="RFC8490"/>, followed by the
<t>The other header fields MUST be set as described in the SUBSCRIBE Primary TLV. A SUBSCRIBE request is illustrated in <xref ta
<xref target="RFC8490">DSO spec-ification</xref>. rget="subscribe_req" format="default" sectionFormat="of" derivedContent="Figure
The DNS OPCODE field contains the OPCODE value for DNS Stateful Operati 1"/>.</t>
ons (6). <t pn="section-6.2.1-2">The MESSAGE ID field <bcp14>MUST</bcp14> be se
The four count fields must be zero, and the corresponding four sections t to a unique
must be empty (i.e., absent).</t> value that the client is not using for any other active operation
on this DSO session. For the purposes here, a MESSAGE ID is in use
<t>The DSO-TYPE is SUBSCRIBE (tentatively 0x40).</t> on this session if either the client has used it in a request for
which it
<t>The DSO-LENGTH is the length of the DSO-DATA that follows, which spe has not yet received a response, or if the client has used it for a
cifies subscription that it has not yet canceled using UNSUBSCRIBE. In
the SUBSCRIBE response, the server <bcp14>MUST</bcp14> echo back the
MESSAGE ID value unchanged.</t>
<t pn="section-6.2.1-3">The other header fields <bcp14>MUST</bcp14> be
set as described
in the
<xref target="RFC8490" format="default" sectionFormat="of" derivedConte
nt="RFC8490">DSO specification</xref>.
The DNS OPCODE field contains the OPCODE value for DNS Stateful
Operations (6).
The four count fields must be zero, and the corresponding four
sections must be empty (i.e., absent).</t>
<t pn="section-6.2.1-4">The DSO-TYPE is SUBSCRIBE (0x0040).</t>
<t pn="section-6.2.1-5">The DSO-LENGTH is the length of the DSO-DATA t
hat follows, which
specifies
the name, type, and class of the record(s) being sought.</t> the name, type, and class of the record(s) being sought.</t>
<figure anchor="subscribe_req" align="left" suppress-title="false" pn=
<figure align="left" anchor="subscribe_req" title="SUBSCRIBE Request">< "figure-1">
artwork align="left"><![CDATA[ <name slugifiedName="name-subscribe-request-2">SUBSCRIBE Request</na
me>
<artwork align="left" name="" type="" alt="" pn="section-6.2.1-6.1">
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = SUBSCRIBE (tentatively 0x40) | | DSO-TYPE = SUBSCRIBE (0x0040) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | > DSO-DATA | TYPE | &gt; DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| CLASS | / | CLASS | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /]]></artwork></figure> +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /</artwork>
</figure>
<t>The DSO-DATA for a SUBSCRIBE request MUST contain exactly one NAME, <t pn="section-6.2.1-7">The DSO-DATA for a SUBSCRIBE request <bcp14>MU
TYPE, and CLASS. ST</bcp14> contain
Since SUBSCRIBE requests are sent over TCP, multiple SUBSCRIBE DSO requ exactly one NAME, TYPE, and CLASS.
est messages Since SUBSCRIBE requests are sent over TCP, multiple SUBSCRIBE DSO
can be concatenated in a single TCP stream and packed efficiently into request messages
TCP segments.</t> can be concatenated in a single TCP stream and packed efficiently
into TCP segments.</t>
<t>If accepted, the subscription will stay in effect until the client c <t pn="section-6.2.1-8">If accepted, the subscription will stay in eff
ancels the subscription using UNSUBSCRIBE or until the DSO session between the c ect until the
lient and the server is closed.</t> client cancels the subscription using UNSUBSCRIBE or until the DSO
session between the client and the server is closed.</t>
<t>SUBSCRIBE requests on a given session MUST be unique. <t pn="section-6.2.1-9">SUBSCRIBE requests on a given session <bcp14>M
A client MUST NOT send a SUBSCRIBE message that duplicates the UST</bcp14> be
NAME, TYPE and CLASS of an existing active subscription on that DSO ses unique. A client <bcp14>MUST NOT</bcp14> send a SUBSCRIBE message
sion. that duplicates the name, type and class of an existing active
For the purpose of this matching, the established DNS case-insensitivit subscription on that DSO session. For the purpose of this matching,
y the established DNS case insensitivity for US-ASCII letters <xref targ
for US-ASCII letters <xref target="RFC0020" /> applies (e.g., "example. et="RFC0020" format="default" sectionFormat="of" derivedContent="RFC0020"/> appl
com" and "Example.com" are the same). ies (e.g., "example.com" and
If a server receives such a duplicate SUBSCRIBE message, "Example.com" are the same). If a server receives such a duplicate
this is a fatal error and the server MUST forcibly abort the connection SUBSCRIBE message, this is a fatal error and the server
immediately.</t> <bcp14>MUST</bcp14> forcibly abort the connection immediately.</t>
<t pn="section-6.2.1-10">DNS wildcarding is not supported.
<t>DNS wildcarding is not supported. That is, a wildcard ("*") in a SUB That is, an asterisk character ("*") in a SUBSCRIBE message matches
SCRIBE message matches only a literal wildcard character ("*") in the zone, and only a literal asterisk character ("*") in a name and nothing else.
nothing else.</t> Similarly, a CNAME in a SUBSCRIBE message matches only a CNAME
record
<t>Aliasing is not supported. That is, a CNAME in a SUBSCRIBE message m with that name in the zone and no other records with that name.</t>
atches only a literal CNAME record in the zone, and no other records with the sa <t pn="section-6.2.1-11">A client may SUBSCRIBE to records that are un
me owner name.</t> known to the server
at the time of the request (providing that the name falls within one
<t>A client may SUBSCRIBE to records that are unknown to the server at of the zone(s) the server is responsible for), and this is not an
the time of the request (providing that the name falls within one of the zone(s) error. The server <bcp14>MUST NOT</bcp14> return NXDOMAIN in this
the server is responsible for) and this is not an error. The server MUST NOT re case. The server <bcp14>MUST</bcp14> accept these requests and send
turn NXDOMAIN in this case. The server MUST accept these requests and send Push Push Notifications if and when matching records are found in the
Notifications if and when matching records are found in the future.</t> future.</t>
<t pn="section-6.2.1-12">If neither TYPE nor CLASS are ANY (255), then
<t>If neither TYPE nor CLASS are ANY (255) then this is a specific subs this is a specific
cription to changes for the given NAME, TYPE and CLASS. If one or both of TYPE o subscription to changes for the given name, type, and class. If one
r CLASS are ANY (255) then this subscription matches any type and/or any class, or both of TYPE or CLASS are ANY (255), then this subscription
as appropriate.</t> matches all types and/or all classes as appropriate.</t>
<t pn="section-6.2.1-13">NOTE: A little-known quirk of DNS is that in
<?rfc needLines="14" ?> DNS QUERY requests,
<t>NOTE: A little-known quirk of DNS is that in DNS QUERY requests, QTY QTYPE and QCLASS 255 mean "ANY", not "ALL". They indicate that the
PE and QCLASS 255 mean "ANY" not "ALL". They indicate that the server should res server should respond with ANY matching records of its choosing, not
pond with ANY matching records of its choosing, not necessarily ALL matching rec necessarily ALL matching records. This can lead to some surprising
ords. This can lead to some surprising and unexpected results, where a query ret and unexpected results, where a query returns some valid answers,
urns some valid answers but not all of them, and makes QTYPE = 255 (ANY) queries but
less useful than people sometimes imagine.</t> not all of them, and makes QTYPE = 255 (ANY) queries less useful
than people sometimes imagine.</t>
<t>When used in conjunction with SUBSCRIBE, TYPE and CLASS 255 should b <t pn="section-6.2.1-14">When used in conjunction with SUBSCRIBE, TYPE
e interpreted to mean "ALL", not "ANY". After accepting a subscription where one 255 and CLASS 255
or both of TYPE or CLASS are 255, the server MUST send Push Notification Update should be interpreted to mean "ALL", not "ANY". After accepting a
s for ALL record changes that match the subscription, not just some of them.</t> subscription where one or both of TYPE or CLASS are 255, the server
<?rfc needLines="48" ?> <bcp14>MUST</bcp14> send Push Notification Updates for ALL record
</section> changes that match the subscription, not just some of them.</t>
</section>
<section title="SUBSCRIBE Response" anchor="subresp"> <section anchor="subresp" numbered="true" toc="include" removeInRFC="fal
se" pn="section-6.2.2">
<t>A SUBSCRIBE response begins with the standard <name slugifiedName="name-subscribe-response">SUBSCRIBE Response</name
<xref target="RFC8490">DSO 12-byte header</xref>. >
<t pn="section-6.2.2-1">A SUBSCRIBE response begins with the standard
DSO 12-byte header <xref target="RFC8490" format="default" sectionForma
t="of" derivedContent="RFC8490"/>.
The QR bit in the header is set indicating it is a response. The QR bit in the header is set indicating it is a response.
The header MAY be followed by one or more optional TLVs, such as a Retr The header <bcp14>MAY</bcp14> be followed by one or more
y Delay TLV. optional Additional TLVs such as a Retry Delay Additional TLV.
A SUBSCRIBE response is illustrated in <xref target="subscribe_resp"/>. A SUBSCRIBE response is illustrated in <xref target="subscribe_resp" fo
</t> rmat="default" sectionFormat="of" derivedContent="Figure 2"/>.</t>
<t pn="section-6.2.2-2">The MESSAGE ID field <bcp14>MUST</bcp14> echo
<t>The MESSAGE ID field MUST echo the value given in the MESSAGE ID fie the value given in
ld of the SUBSCRIBE request. the MESSAGE ID field of the SUBSCRIBE request. This is how the
This is how the client knows which request is being responded to.</t> client knows which request is being responded to.</t>
<t pn="section-6.2.2-3">The other header fields <bcp14>MUST</bcp14> be
<t>The other header fields MUST be set as described in the set as described
<xref target="RFC8490">DSO spec-ification</xref>. in the <xref target="RFC8490" format="default" sectionFormat="of" deri
The DNS OPCODE field contains the OPCODE value for DNS Stateful Operati vedContent="RFC8490">DSO specification</xref>. The DNS OPCODE field
ons (6). contains the OPCODE
The four count fields must be zero, and the corresponding four sections value for DNS Stateful Operations (6). The four count fields must
must be empty (i.e., absent).</t> be zero, and the corresponding four sections must be empty (i.e.,
absent).</t>
<t>A SUBSCRIBE response message MUST NOT include a SUBSCRIBE TLV. <t pn="section-6.2.2-4">A SUBSCRIBE response message <bcp14>MUST NOT</
If a client receives a SUBSCRIBE response message containing a SUBSCRIB bcp14> include a
E TLV SUBSCRIBE TLV.
then the response message is processed but the SUBSCRIBE TLV MUST be si If a client receives a SUBSCRIBE response message containing a
lently ignored.</t> SUBSCRIBE TLV,
then the response message is processed but the SUBSCRIBE TLV
<figure align="left" anchor="subscribe_resp" title="SUBSCRIBE Response" <bcp14>MUST</bcp14> be silently ignored.</t>
><artwork align="left"><![CDATA[ <figure anchor="subscribe_resp" align="left" suppress-title="false" pn
="figure-2">
<name slugifiedName="name-subscribe-response-2">SUBSCRIBE Response</
name>
<artwork align="left" name="" type="" alt="" pn="section-6.2.2-5.1">
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID | \ | MESSAGE ID | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
]]>
</artwork></figure>
<?rfc needLines="20" ?>
<t>In the SUBSCRIBE response the RCODE indicates whether or not the sub
scription was accepted. Supported RCODEs are as follows:</t>
<texttable title="SUBSCRIBE Response codes" anchor="subscribe_rcodes">
<ttcol align="left">Mnemonic</ttcol>
<ttcol align="center">Value</ttcol>
<ttcol align="left">Description</ttcol>
<c>NOERROR</c><c>0</c><c>SUBSCRIBE successful.</c>
<c>FORMERR</c><c>1</c><c>Server failed to process request due to a malf
ormed request.</c>
<c>SERVFAIL</c><c>2</c><c>Server failed to process request due to a pro
blem with the server.</c>
<c>NOTIMP</c><c>4</c><c>Server does not implement DSO.</c>
<c>REFUSED</c><c>5</c><c>Server refuses to process request for policy o
r security reasons.</c>
<c>NOTAUTH</c><c>9</c><c>Server is not authoritative for the requested
name.</c>
<c>DSOTYPENI</c><c>11</c><c>SUBSCRIBE operation not supported.</c>
</texttable>
<t>This document specifies only these RCODE values for SUBSCRIBE Respon
ses. Servers sending SUBSCRIBE Responses SHOULD use one of these values. Note th
at NXDOMAIN is not a valid RCODE in response to a SUBSCRIBE Request. However, fu
ture circumstances may create situations where other RCODE values are appropriat
e in SUBSCRIBE Responses, so clients MUST be prepared to accept SUBSCRIBE Respon
ses with any other RCODE value.</t>
<t>If the server sends a nonzero RCODE in the SUBSCRIBE response, that
means:
<?rfc subcompact="yes" ?>
<list style="letters">
<t>the client is (at least partially) misconfigured, or</t>
<t>the server resources are exhausted, or</t>
<t>there is some other unknown failure on the server.</t>
</list>
<?rfc subcompact="no" ?>
In any case, the client shouldn't retry the subscription to this server
right away. If multiple SRV records were returned as described in <xref target=
"discovery"/>, <xref target="SRV"/>, a subsequent server MAY be tried immediatel
y.</t>
<t>If the client has other successful subscriptions to this server, the
se subscriptions remain even though additional subscriptions may be refused. Nei
ther the client nor the server are required to close the connection, although, e
ither end may choose to do so.</t>
<t>If the server sends a nonzero RCODE then it SHOULD append a Retry De
lay TLV <xref target="RFC8490"/> to the response specifying a delay before the c
lient attempts this operation again. Recommended values for the delay for differ
ent RCODE values are given below. These recommended values apply both to the def
ault values a server should place in the Retry Delay TLV, and the default values
a client should assume if the server provides no Retry Delay TLV.
<list style="bullets">
<t>For RCODE = 1 (FORMERR) the delay may be any value selected by t
he implementer. A value of five minutes is RECOMMENDED, to reduce the risk of hi
gh load from defective clients.</t>
<t>For RCODE = 2 (SERVFAIL) the delay should be chosen according to
the level of server overload and the anticipated duration of that overload. By
default, a value of one minute is RECOMMENDED. If a more serious server failure
occurs, the delay may be longer in accordance with the specific problem encounte
red.</t>
<t>For RCODE = 4 (NOTIMP), which occurs on a server that doesn't im </artwork>
plement </figure>
<xref target="RFC8490">DNS Stateful Operations</xref>, <t pn="section-6.2.2-6">In the SUBSCRIBE response, the RCODE indicates
whether or not the
subscription was accepted. Supported RCODEs are as follows:</t>
<table anchor="subscribe_rcodes" align="center" pn="table-1">
<name slugifiedName="name-subscribe-response-codes">SUBSCRIBE Respon
se Codes</name>
<thead>
<tr>
<th align="left" colspan="1" rowspan="1">Mnemonic</th>
<th align="center" colspan="1" rowspan="1">Value</th>
<th align="left" colspan="1" rowspan="1">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" colspan="1" rowspan="1">NOERROR</td>
<td align="center" colspan="1" rowspan="1">0</td>
<td align="left" colspan="1" rowspan="1">SUBSCRIBE successful.</
td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">FORMERR</td>
<td align="center" colspan="1" rowspan="1">1</td>
<td align="left" colspan="1" rowspan="1">Server failed to proces
s request due to a
malformed request.</td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">SERVFAIL</td>
<td align="center" colspan="1" rowspan="1">2</td>
<td align="left" colspan="1" rowspan="1">Server failed to proces
s request due to a
problem with the server.</td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">NOTIMP</td>
<td align="center" colspan="1" rowspan="1">4</td>
<td align="left" colspan="1" rowspan="1">Server does not impleme
nt DSO.</td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">REFUSED</td>
<td align="center" colspan="1" rowspan="1">5</td>
<td align="left" colspan="1" rowspan="1">Server refuses to proce
ss request for policy
or security reasons.</td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">NOTAUTH</td>
<td align="center" colspan="1" rowspan="1">9</td>
<td align="left" colspan="1" rowspan="1">Server is not authorita
tive for the requested
name.</td>
</tr>
<tr>
<td align="left" colspan="1" rowspan="1">DSOTYPENI</td>
<td align="center" colspan="1" rowspan="1">11</td>
<td align="left" colspan="1" rowspan="1">SUBSCRIBE operation not
supported.</td>
</tr>
</tbody>
</table>
<t pn="section-6.2.2-8">This document specifies only these RCODE value
s for SUBSCRIBE
Responses. Servers sending SUBSCRIBE Responses <bcp14>SHOULD</bcp14>
use one of these values. Note that NXDOMAIN is not a valid RCODE in
response to a SUBSCRIBE Request. However, future circumstances may
create situations where other RCODE values are appropriate in
SUBSCRIBE Responses, so clients <bcp14>MUST</bcp14> be prepared to
accept and handle SUBSCRIBE Responses with any other nonzero RCODE
error values.</t>
<t pn="section-6.2.2-9">If the server sends a nonzero RCODE in the SUB
SCRIBE response,
that means:
</t>
<ol spacing="compact" type="a" start="1" pn="section-6.2.2-10">
<li pn="section-6.2.2-10.1" derivedCounter="a.">the client is (at le
ast partially) misconfigured, or</li>
<li pn="section-6.2.2-10.2" derivedCounter="b.">the server resources
are exhausted, or</li>
<li pn="section-6.2.2-10.3" derivedCounter="c.">there is some other
unknown failure on the server.</li>
</ol>
<t pn="section-6.2.2-11">
In any case, the client shouldn't retry the subscription to this
server right away. If multiple SRV records were returned as
described in <xref target="SRV" format="default" sectionFormat="of" d
erivedContent="Section 6.1, Paragraph 9, Item 7"/>, a subsequent server
<bcp14>MAY</bcp14> be tried immediately.</t>
<t pn="section-6.2.2-12">If the client has other successful subscripti
ons to this server,
these subscriptions remain even though additional subscriptions may
be refused. Neither the client nor the server is required to close
the connection, although either end may choose to do so.</t>
<t pn="section-6.2.2-13">If the server sends a nonzero RCODE, then it
<bcp14>SHOULD</bcp14>
append a Retry Delay Additional TLV <xref target="RFC8490" format="def
ault" sectionFormat="of" derivedContent="RFC8490"/>
to the response specifying a delay before the client attempts this
operation again. Recommended values for the delay for different
RCODE values are given below. These recommended values apply both to
the default values a server should place in the Retry Delay
Additional TLV and
the default values a client should assume if the server provides no
Retry Delay Additional TLV.
</t>
<ul spacing="normal" empty="true" bare="false" pn="section-6.2.2-14">
<li pn="section-6.2.2-14.1">For RCODE = 1 (FORMERR), the delay may b
e any value selected
by
the implementer. A value of five minutes is
<bcp14>RECOMMENDED</bcp14> to reduce the risk of high load from
defective clients.</li>
<li pn="section-6.2.2-14.2">For RCODE = 2 (SERVFAIL), the delay shou
ld be chosen according
to the level of server overload and the anticipated duration of
that overload. By default, a value of one minute is
<bcp14>RECOMMENDED</bcp14>. If a more serious server failure
occurs, the delay may be longer in accordance with the specific
problem encountered.</li>
<li pn="section-6.2.2-14.3">For RCODE = 4 (NOTIMP), which occurs on
a server that doesn't
implement
DNS Stateful Operations <xref target="RFC8490" format="default" sec
tionFormat="of" derivedContent="RFC8490"/>,
it is unlikely that the server will begin supporting DSO it is unlikely that the server will begin supporting DSO
in the next few minutes, so the retry delay SHOULD be one hour. in the next few minutes, so the retry delay <bcp14>SHOULD</bcp14>
be one hour.
Note that in such a case, a server that doesn't implement DSO Note that in such a case, a server that doesn't implement DSO
is unlikely to place a Retry Delay TLV in its response, so this is unlikely to place a Retry Delay Additional TLV in its
recommended value in particular applies to what a client should ass response, so this
ume by default.</t> recommended value in particular applies to what a client should
assume by default.</li>
<t>For RCODE = 5 (REFUSED), which occurs on a server that implement <li pn="section-6.2.2-14.4">For RCODE = 5 (REFUSED), which occurs on
s DNS Push Notifications, but is currently configured to disallow DNS Push Notif a server that
ications, the retry delay may be any value selected by the implementer and/or co implements DNS Push Notifications but is currently configured to
nfigured by the operator.</t> disallow DNS Push Notifications, the retry delay may be any value
<t>If the server being queried is listed in a selected by the implementer and/or configured by the
<spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</span operator.</li>
x> <li pn="section-6.2.2-14.5">If the server being queried is listed in
a
<tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt>
SRV record for the zone, then this is a misconfiguration, SRV record for the zone, then this is a misconfiguration,
since this server is being advertised as supporting DNS Push Notifi since this server is being advertised as supporting DNS Push
cations for this zone, Notifications for this zone,
but the server itself is not currently configured to perform that t but the server itself is not currently configured to perform that
ask. task.
Since it is possible that the misconfiguration may be repaired Since it is possible that the misconfiguration may be repaired
at any time, the retry delay should not be set too high. By defaul at any time, the retry delay should not be set too high. By
t, default,
a value of 5 minutes is RECOMMENDED.</t> a value of 5 minutes is <bcp14>RECOMMENDED</bcp14>.</li>
<li pn="section-6.2.2-14.6">For RCODE = 9 (NOTAUTH), which occurs on
<t>For RCODE = 9 (NOTAUTH), which occurs on a server that implement a server that
s DNS Push Notifications, but is not configured to be authoritative for the requ implements DNS Push Notifications but is not configured to be
ested name, the retry delay may be any value selected by the implementer and/or authoritative for the requested name, the retry delay may be any
configured by the operator.</t> value selected by the implementer and/or configured by the
<t>If the server being queried is listed in a operator.</li>
<spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</span <li pn="section-6.2.2-14.7">If the server being queried is listed in
x> a
<tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt>
SRV record for the zone, then this is a misconfiguration, SRV record for the zone, then this is a misconfiguration,
since this server is being advertised as supporting DNS Push Notifi since this server is being advertised as supporting DNS Push
cations for this zone, Notifications for this zone,
but the server itself is not currently configured to perform that t but the server itself is not currently configured to perform that
ask. task.
Since it is possible that the misconfiguration may be repaired Since it is possible that the misconfiguration may be repaired
at any time, the retry delay should not be set too high. By defaul at any time, the retry delay should not be set too high. By
t, default,
a value of 5 minutes is RECOMMENDED.</t> a value of 5 minutes is <bcp14>RECOMMENDED</bcp14>.</li>
<li pn="section-6.2.2-14.8">For RCODE = 11 (DSOTYPENI),
<t>For RCODE = 11 (DSOTYPENI), which occurs on a server that implements DSO but doesn't
which occurs on a server that implements DSO but doesn't implement implement DNS Push Notifications,
DNS Push Notifications, it is unlikely that the server will begin supporting DNS Push
it is unlikely that the server will begin supporting DNS Push Notif Notifications
ications in the next few minutes, so the retry delay <bcp14>SHOULD</bcp14>
in the next few minutes, so the retry delay SHOULD be one hour.</t> be one hour.</li>
<li pn="section-6.2.2-14.9">For other RCODE values, the retry delay
<t>For other RCODE values, the retry delay should be set by the ser should be
ver as appropriate for that error condition. By default, a value of 5 minutes is set by the server as appropriate for that error condition.
RECOMMENDED.</t> By default, a value of 5 minutes is
</list> <bcp14>RECOMMENDED</bcp14>.</li>
</t> </ul>
<t>For RCODE = 9 (NOTAUTH), the time delay applies to requests for othe <t pn="section-6.2.2-15">For RCODE = 9 (NOTAUTH), the time delay appli
r names falling within the same zone. Requests for names falling within other zo es to requests for
nes are not subject to the delay. For all other RCODEs the time delay applies to other names falling within the same zone. Requests for names falling
all subsequent requests to this server.</t> within other zones are not subject to the delay. For all other
RCODEs, the time delay applies to all subsequent requests to this
<t>After sending an error response the server MAY allow the session to server.</t>
remain open, <t pn="section-6.2.2-16">After sending an error response, the server <
or MAY send a DNS Push Notification Retry Delay Operation TLV instructi bcp14>MAY</bcp14>
ng the client to close the session, allow the session to remain open, or <bcp14>MAY</bcp14> follow it
as described in the <xref target="RFC8490">DSO specification</xref>. with
Clients MUST correctly handle both cases.</t> a DSO Retry Delay operation (using the Retry Delay Primary TLV)
instructing the client to close the session as described in the
<?rfc needLines="48" ?> <xref target="RFC8490" format="default" sectionFormat="of" derivedCont
</section> ent="RFC8490">DSO specification</xref>.
</section> Clients <bcp14>MUST</bcp14> correctly handle both cases.
Note that the
<section title="DNS Push Notification Updates" anchor="push"> DSO Retry Delay operation (using the Retry Delay Primary TLV)
<t>Once a subscription has been successfully established, the server gene is different to the Retry Delay Additional TLV mentioned above.
rates PUSH messages to send to the client as appropriate. In the case that the a </t>
nswer set was already non-empty at the moment the subscription was established, </section>
an initial PUSH message will be sent immediately following the SUBSCRIBE Respons </section>
e. Subsequent changes to the answer set are then communicated to the client in s <section anchor="push" numbered="true" toc="include" removeInRFC="false" p
ubsequent PUSH messages.</t> n="section-6.3">
<name slugifiedName="name-dns-push-notification-updat">DNS Push Notifica
<t>A client MUST NOT send a PUSH message. tion Updates</name>
<t pn="section-6.3-1">Once a subscription has been successfully establis
hed,
the server generates PUSH messages to send to the client as
appropriate.
In the case that the answer set was already non-empty at the moment
the subscription was established, an initial PUSH message will be sent
immediately following the SUBSCRIBE Response. Subsequent changes to
the
answer set are then communicated to the client in subsequent PUSH
messages.</t>
<t pn="section-6.3-2">A client <bcp14>MUST NOT</bcp14> send a PUSH messa
ge.
If a client does send a PUSH message, If a client does send a PUSH message,
or a PUSH message is sent with the QR bit set indicating that it is a res or a PUSH message is sent with the QR bit set indicating that it is a
ponse, response,
this is a fatal error and the receiver MUST forcibly abort the connection this is a fatal error and the receiver <bcp14>MUST</bcp14> forcibly
immediately.</t> abort the connection immediately.</t>
<section numbered="true" toc="include" removeInRFC="false" pn="section-6
<section title="PUSH Message"> .3.1">
<name slugifiedName="name-push-message">PUSH Message</name>
<t>A PUSH unidirectional message begins with the standard <t pn="section-6.3.1-1">A PUSH unidirectional message begins with the
<xref target="RFC8490">DSO 12-byte header</xref>, followed by the PUSH standard
primary TLV. DSO 12-byte header <xref target="RFC8490" format="default" sectionForma
A PUSH message is illustrated in <xref target="push_msg"/>.</t> t="of" derivedContent="RFC8490"/>,
followed by the PUSH Primary TLV.
<t>In accordance with the definition of DSO unidirectional messages, A PUSH message is illustrated in <xref target="push_msg" format="defaul
the MESSAGE ID field MUST be zero. t" sectionFormat="of" derivedContent="Figure 3"/>.</t>
<t pn="section-6.3.1-2">In accordance with the definition of DSO unidi
rectional messages,
the MESSAGE ID field <bcp14>MUST</bcp14> be zero.
There is no client response to a PUSH message.</t> There is no client response to a PUSH message.</t>
<t pn="section-6.3.1-3">The other header fields <bcp14>MUST</bcp14> be
<t>The other header fields MUST be set as described in the set as described
<xref target="RFC8490">DSO spec-ification</xref>. in the
The DNS OPCODE field contains the OPCODE value for DNS Stateful Operati DSO specification <xref target="RFC8490" format="default" sectionFormat
ons (6). ="of" derivedContent="RFC8490"/>.
The four count fields must be zero, and the corresponding four sections The DNS OPCODE field contains the OPCODE value for DNS Stateful
must be empty (i.e., absent).</t> Operations (6).
The four count fields must be zero, and the corresponding four
<t>The DSO-TYPE is PUSH (tentatively 0x41).</t> sections must be empty (i.e., absent).</t>
<t pn="section-6.3.1-4">The DSO-TYPE is PUSH (0x0041).</t>
<t>The DSO-LENGTH is the length of the DSO-DATA that follows, which spe <t pn="section-6.3.1-5">The DSO-LENGTH is the length of the DSO-DATA t
cifies hat follows, which
specifies
the changes being communicated.</t> the changes being communicated.</t>
<t pn="section-6.3.1-6">The DSO-DATA contains one or more change notif
<t>The DSO-DATA contains one or more change notifications. ications.
A PUSH Message MUST contain at least one change notification. A PUSH Message <bcp14>MUST</bcp14> contain at least one change
notification.
If a PUSH Message is received that contains no change notifications, If a PUSH Message is received that contains no change notifications,
this is a fatal error, and the client MUST forcibly abort the connectio this is a fatal error and the client <bcp14>MUST</bcp14> forcibly
n immediately.</t> abort the connection immediately.</t>
<t pn="section-6.3.1-7">The change notification records are formatted
<t>The change notification records are formatted similarly to how similarly to how
DNS Resource Records are conventionally expressed in DNS messages, DNS Resource Records are conventionally expressed in DNS messages,
as illustrated in <xref target="push_msg"/>, as illustrated in <xref target="push_msg" format="default" sectionForma t="of" derivedContent="Figure 3"/>,
and are interpreted as described below.</t> and are interpreted as described below.</t>
<t pn="section-6.3.1-8">The TTL field holds an unsigned 32-bit integer
<?rfc needLines="6" ?> <xref target="RFC2181" format="default" sectionFormat="of" derivedContent="RFC2
<t>The TTL field holds an unsigned 32-bit integer <xref target="RFC2181 181"/>.
"/>. If the TTL is in the range 0 to 2,147,483,647 seconds (0 to
If the TTL is in the range 0 to 2,147,483,647 seconds (0 to 2^31 - 1, o 2<sup>31</sup> - 1, or 0x7FFFFFFF),
r 0x7FFFFFFF), then a new DNS Resource Record with the given name, type, class, and
then a new DNS Resource Record with the given name, type, class and RDA RDATA is added.
TA is added. Type and class <bcp14>MUST NOT</bcp14> be 255 (ANY). If either type
Type and class MUST NOT be 255 (ANY). If either type or class are 255 ( or class are 255 (ANY),
ANY) this is a fatal error and the client <bcp14>MUST</bcp14> forcibly
this is a fatal error, and the client MUST forcibly abort the connectio abort the connection immediately.
n immediately. A TTL of 0 means that this record should be retained for as long as
A TTL of 0 means that this record should be retained for as long as the the subscription is active
subscription is active, and should be discarded immediately the moment the subscription is
and should be discarded immediately the moment the subscription is canc canceled.</t>
elled.</t> <t pn="section-6.3.1-9">If the TTL has the value 0xFFFFFFFF, then the
DNS Resource Record
<t>If the TTL has the value 0xFFFFFFFF, then the with the given name, type, class, and RDATA is removed. Type and
DNS Resource Record with the given name, type, class and RDATA is remov class <bcp14>MUST NOT</bcp14> be 255 (ANY). If either type or class
ed. are 255 (ANY), this is a fatal error and the client
Type and class MUST NOT be 255 (ANY). If either type or class are 255 ( <bcp14>MUST</bcp14> forcibly abort the connection immediately.</t>
ANY) <t pn="section-6.3.1-10">If the TTL has the value 0xFFFFFFFE, then thi
this is a fatal error, and the client MUST forcibly abort the connectio s is a 'collective'
n immediately.</t> remove notification. For collective remove notifications, RDLEN
<bcp14>MUST</bcp14> be zero, and consequently, the RDATA
<t>If the TTL has the value 0xFFFFFFFE, then this is a 'collective' rem <bcp14>MUST</bcp14> be empty. If a change notification is received
ove notification. where TTL = 0xFFFFFFFE and RDLEN is not zero, this is a fatal error
For collective remove notifications RDLEN MUST be zero and consequently and the client <bcp14>MUST</bcp14> forcibly abort the connection
the RDATA MUST be empty. immediately.</t>
If a change notification is received where TTL = 0xFFFFFFFE and RDLEN i <t pn="section-6.3.1-11">There are three types of collective remove no
s not zero, tification.
this is a fatal error, and the client MUST forcibly abort the connectio For collective remove notifications:</t>
n immediately.</t> <ul bare="false" empty="false" spacing="normal" pn="section-6.3.1-12">
<li pn="section-6.3.1-12.1">If CLASS is not 255 (ANY) and TYPE is no
<t>There are three types of collective remove notification:</t> t 255 (ANY), then for the given
name, this removes all records of the specified type in the specified class.
<t>For collective remove notifications, </li>
if CLASS is not 255 (ANY) and TYPE is not 255 (ANY) <li pn="section-6.3.1-12.2">If CLASS is not 255 (ANY) and TYPE is 25
then for the given name this removes all records of the specified type 5 (ANY), then for the given name,
in the specified class.</t> this removes all records of all types in the specified class.
</li>
<t>For collective remove notifications, <li pn="section-6.3.1-12.3">If CLASS is 255 (ANY), then for the give
if CLASS is not 255 (ANY) and TYPE is 255 (ANY) n name, this removes all records
then for the given name this removes all records of all types in the sp of all types in all classes. In this case, TYPE <bcp14>MUST</bcp14> be set to
ecified class.</t> zero on
transmission and <bcp14>MUST</bcp14> be silently ignored on reception.
<t>For collective remove notifications, </li>
if CLASS is 255 (ANY), </ul>
then for the given name this removes all records of all types in all cl <t pn="section-6.3.1-13">Summary of change notification types:
asses. </t>
In this case TYPE MUST be set to zero on transmission, and MUST be sile <ul spacing="normal" bare="false" empty="false" pn="section-6.3.1-14">
ntly ignored on reception.</t> <li pn="section-6.3.1-14.1">
<t pn="section-6.3.1-14.1.1">Remove all RRsets from a name in all
<?rfc needLines="19" ?> classes:<br/>
<t>Summary of change notification types: TTL = 0xFFFFFFFE, RDLEN = 0, CLASS = 255 (ANY).</t>
<list style="bullets"> </li>
<t>Remove all RRsets from a name, in all classes<vspace /> <li pn="section-6.3.1-14.2">
TTL = 0xFFFFFFFE, RDLEN = 0, CLASS = 255 (ANY)</t> <t pn="section-6.3.1-14.2.1">Remove all RRsets from a name in give
n class:<br/>
<t>Remove all RRsets from a name, in given class:<vspace /> TTL = 0xFFFFFFFE, RDLEN = 0, CLASS gives class, TYPE = 255
TTL = 0xFFFFFFFE, RDLEN = 0, CLASS gives class, TYPE = 255 (ANY)</t (ANY).</t>
> </li>
<li pn="section-6.3.1-14.3">
<t>Remove specified RRset from a name, in given class:<vspace /> <t pn="section-6.3.1-14.3.1">Remove specified RRset from a name in
TTL = 0xFFFFFFFE, RDLEN = 0<vspace /> given class:<br/>
CLASS and TYPE specify the RRset being removed</t> TTL = 0xFFFFFFFE, RDLEN = 0,<br/>
CLASS and TYPE specify the RRset being removed.</t>
<t>Remove an individual RR from a name:<vspace /> </li>
TTL = 0xFFFFFFFF<vspace /> <li pn="section-6.3.1-14.4">
CLASS, TYPE, RDLEN and RDATA specify the RR being removed</t> <t pn="section-6.3.1-14.4.1">Remove an individual RR from a name:<
br/>
<t>Add individual RR to a name<vspace /> TTL = 0xFFFFFFFF,<br/>
TTL &gt;= 0 and TTL &lt;= 0x7FFFFFFF<vspace /> CLASS, TYPE, RDLEN, and RDATA specify the RR being removed.</t>
CLASS, TYPE, RDLEN, RDATA and TTL specify the RR being added</t> </li>
</list> <li pn="section-6.3.1-14.5">
</t> <t pn="section-6.3.1-14.5.1">Add individual RR to a name:<br/>
TTL &gt;= 0 and TTL &lt;= 0x7FFFFFFF,<br/>
<t>Note that it is valid for the RDATA of an added or removed DNS Resou CLASS, TYPE, RDLEN, RDATA, and TTL specify the RR being
rce Record to be empty (zero length). added.</t>
For example, an <xref target="RFC3123">Address Prefix List Resource Rec </li>
ord</xref> may have empty RDATA. </ul>
Therefore, a change notification with RDLEN = 0 does not automatically <t pn="section-6.3.1-15">Note that it is valid for the RDATA of an add
indicate a remove notification. ed or removed DNS
If RDLEN = 0 and TTL is the in the range 0 - 0x7FFFFFFF, this change no Resource Record to be empty (zero length). For example, an Address
tification signals the addition of a Prefix List Resource Record <xref target="RFC3123" format="default" se
record with the given name, type, class, and empty RDATA. ctionFormat="of" derivedContent="RFC3123"/> may have empty RDATA. Therefore, a
If RDLEN = 0 and TTL = 0xFFFFFFFF, this change notification signals the change
removal specifically of that single notification with RDLEN = 0 does not automatically indicate a remove
record with the given name, type, class, and empty RDATA.</t> notification. If RDLEN = 0 and TTL is in the range 0 to
0x7FFFFFFF, this change notification signals the addition of a
<t>If the TTL is any value other than 0xFFFFFFFF, 0xFFFFFFFE, or a valu record with the given name, type, class, and empty RDATA. If RDLEN
e in the range 0 - 0x7FFFFFFF, = 0 and TTL = 0xFFFFFFFF, this change notification signals the
then the receiver SHOULD silently ignore this particular change notific removal specifically of that single record with the given name,
ation record. type, class, and empty RDATA.</t>
The connection is not terminated and other valid change notification re <t pn="section-6.3.1-16">If the TTL is any value other than 0xFFFFFFFF
cords , 0xFFFFFFFE, or a
value in the range 0 to 0x7FFFFFFF,
then the receiver <bcp14>SHOULD</bcp14> silently ignore this
particular change notification record.
The connection is not terminated and other valid change notification
records
within this PUSH message are processed as usual.</t> within this PUSH message are processed as usual.</t>
<t pn="section-6.3.1-17">In the case where a single change affects mor
<t>For efficiency, when generating a PUSH message, a server SHOULD e than one active
include as many change notifications as it has immediately available to subscription, only one PUSH message is sent. For example, a PUSH
send, message adding a given record may match both a SUBSCRIBE request
rather than sending each change notification as a separate DSO message. with the same TYPE and a different SUBSCRIBE request with TYPE = 255
Once it has exhausted the list of change notifications immediately avai (ANY). It is not the case that two PUSH messages are sent because
lable to send, the new record matches two active subscriptions.</t>
a server SHOULD then send the PUSH message immediately, <t pn="section-6.3.1-18">The server <bcp14>SHOULD</bcp14> encode chang
rather than waiting to see if additional change notifications become av e notifications in
ailable.</t> the most efficient manner possible.
For example, when three AAAA records are removed from a given name,
<?rfc needLines="6" ?> and no other AAAA
<t>For efficiency, when generating a PUSH message, a server SHOULD records exist for that name, the server <bcp14>SHOULD</bcp14> send a
use standard DNS name compression, "Remove specified RRset from a name in given class" PUSH message,
with offsets relative to the beginning of the DNS message <xref target= not three separate
"RFC1035"/>. "Remove an individual RR from a name" PUSH messages.
When multiple change notifications in a single PUSH message have the sa Similarly, when both an SRV and a TXT record are removed from a
me owner name, given name, and no other
this name compression can yield significant savings. records of any kind exist for that name in that class, the server
Name compression should be performed as specified in Section 18.14 of t <bcp14>SHOULD</bcp14> send a
he "Remove all RRsets from a name in given class" PUSH message, not two
<xref target="RFC6762">Multicast DNS specification</xref>, namely, separate
owner names should always be compressed, "Remove specified RRset from a name in given class" PUSH
and names appearing within RDATA should be compressed for only the RR t messages.</t>
ypes listed below: <t pn="section-6.3.1-19">For efficiency, when generating a PUSH messag
<list style="hanging"> e, rather than
<t>NS, CNAME, PTR, DNAME, SOA, MX, AFSDB, RT, KX, RP, PX, SRV, NSEC</ sending
t> each change notification as a separate DSO message, a server
</list></t> <bcp14>SHOULD</bcp14> include as many change notifications as it has
immediately available to send to that client, even if those change
<t>Servers may generate PUSH messages up to a maximum DNS message lengt notifications apply to different subscriptions from that
h of 16,382 bytes, client. Conceptually, a PUSH
message is a session-level mechanism, not a subscription-level
mechanism.
Once it has exhausted the list of change notifications immediately
available to send to that client,
a server <bcp14>SHOULD</bcp14> then send the PUSH message
immediately
rather than waiting speculatively to see if additional change
notifications become available.</t>
<t pn="section-6.3.1-20">For efficiency, when generating a PUSH messag
e a server
<bcp14>SHOULD</bcp14> use standard DNS name compression, with
offsets
relative to the beginning of the DNS message <xref target="RFC1035" fo
rmat="default" sectionFormat="of" derivedContent="RFC1035"/>. When multiple cha
nge notifications in a single
PUSH message have the same owner name, this name compression can
yield significant savings. Name compression should be performed as
specified in <xref target="RFC6762" sectionFormat="of" section="18.14"
format="default" derivedLink="https://rfc-editor.org/rfc/rfc6762#section-18.14"
derivedContent="RFC6762">the Multicast DNS specification</xref>; namely,
owner names
should always be compressed, and names appearing within RDATA should
be compressed for only the RR types listed below:
</t>
<dl newline="false" spacing="normal" pn="section-6.3.1-21">
<dt pn="section-6.3.1-21.1"/>
<dd pn="section-6.3.1-21.2">NS, CNAME, PTR, DNAME, SOA, MX, AFSDB, R
T, KX, RP, PX, SRV,
NSEC</dd>
</dl>
<t pn="section-6.3.1-22">Servers may generate PUSH messages up to a ma
ximum DNS message
length of 16,382 bytes,
counting from the start of the DSO 12-byte header. counting from the start of the DSO 12-byte header.
Including the two-byte length prefix that is used to frame DNS over a b Including the two-byte length prefix that is used to frame DNS over a
yte stream byte stream
like TLS, this makes a total of 16,384 bytes. like TLS, this makes a total of 16,384 bytes.
Servers MUST NOT generate PUSH messages larger than this. Servers <bcp14>MUST NOT</bcp14> generate PUSH messages larger than
this.
Where the immediately available change notifications Where the immediately available change notifications
are sufficient to exceed a DNS message length of 16,382 bytes, are sufficient to exceed a DNS message length of 16,382 bytes,
the change notifications MUST be communicated in separate PUSH messages the change notifications <bcp14>MUST</bcp14> be communicated in
separate PUSH messages
of up to 16,382 bytes each. of up to 16,382 bytes each.
DNS name compression becomes less effective for messages larger than 16 DNS name compression becomes less effective for messages larger than
,384 bytes, 16,384 bytes,
so little efficiency benefit is gained by sending messages larger than so little efficiency benefit is gained by sending messages larger
this.</t> than this.</t>
<t pn="section-6.3.1-23">If a client receives a PUSH message with a DN
<t>If a client receives a PUSH message with a DNS message length larger S message length
than 16,382 bytes, larger than 16,382 bytes,
this is a fatal error, and the client MUST forcibly abort the connectio this is a fatal error and the client <bcp14>MUST</bcp14> forcibly
n immediately.</t> abort the connection immediately.</t>
<figure anchor="push_msg" align="left" suppress-title="false" pn="figu
<figure align="left" anchor="push_msg" title="PUSH Message"><artwork al re-3">
ign="left"><![CDATA[ <name slugifiedName="name-push-message-2">PUSH Message</name>
<artwork align="left" name="" type="" alt="" pn="section-6.3.1-24.1"
>
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = PUSH (tentatively 0x41) | | DSO-TYPE = PUSH (0x0041) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TTL | | | TTL | |
| (32-bit unsigned big-endian integer) | > DSO-DATA | (32-bit unsigned big-endian integer) | &gt; DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| RDLEN (16-bit unsigned big-endian integer) | | | RDLEN (16-bit unsigned big-endian integer) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ RDATA (sized as necessary) \ | \ RDATA (sized as necessary) \ |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
: NAME, TYPE, CLASS, TTL, RDLEN, RDATA : | : NAME, TYPE, CLASS, TTL, RDLEN, RDATA : |
: Repeated As Necessary : / : Repeated As Necessary : /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /]]></artwork></figure> +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /</artwork>
</figure>
<t>When processing the records received in a PUSH Message, the receivin <t pn="section-6.3.1-25">When processing the records received in a PUS
g client MUST validate H Message, the
that the records being added or removed correspond with at least one cu receiving client <bcp14>MUST</bcp14> validate
rrently active that the records being added or removed correspond with at least one
subscription on that session. Specifically, the record name MUST match currently active
the name given in the subscription on that session. Specifically, the record name
SUBSCRIBE request, subject to the usual established DNS case-insensitiv <bcp14>MUST</bcp14> match the name given in the
ity for US-ASCII letters. SUBSCRIBE request, subject to the usual established DNS
case-insensitivity for US-ASCII letters.
For individual additions and removals, For individual additions and removals,
if the TYPE in the SUBSCRIBE request was not ANY (255) if the TYPE in the SUBSCRIBE request was not ANY (255),
then the TYPE of the record must match the TYPE given in the SUBSCRIBE then the TYPE of the record must either be CNAME or match the TYPE
request, and given in the SUBSCRIBE request, and
if the CLASS in the SUBSCRIBE request was not ANY (255) if the CLASS in the SUBSCRIBE request was not ANY (255),
then the CLASS of the record must match the CLASS given in the SUBSCRIB then the CLASS of the record must match the CLASS given in the
E request. SUBSCRIBE request.
For collective removals, at least one of the records being removed must For collective removals, at least one of the records being removed
match an active subscription. must match an active subscription.
If a matching active subscription on that session is not found, then th If a matching active subscription on that session is not found, then
at particular that particular
addition/removal record is silently ignored. Processing of other additi addition/removal record is silently ignored. The processing of other
ons and removal records additions and removal records
in this message is not affected. The DSO session is not closed. This is in this message is not affected. The DSO session is not closed. This
to allow for is to allow for
the unavoidable race condition where a client sends an outbound UNSUBSC the unavoidable race condition where a client sends an outbound
RIBE while UNSUBSCRIBE while
inbound PUSH messages for that subscription from the server are still i inbound PUSH messages for that subscription from the server are still
n flight.</t> in flight.</t>
<t pn="section-6.3.1-26">The TTL of an added record is stored by the c
<t>In the case where a single change affects more than one active subsc lient. While the
ription, only one PUSH message is sent. For example, a PUSH message adding a giv subscription
en record may match both a SUBSCRIBE request with the same TYPE and a different is active the TTL is not decremented, because a change to the TTL
SUBSCRIBE request with TYPE = 255 (ANY). It is not the case that two PUSH messag would
es are sent because the new record matches two active subscriptions.</t>
<t>The server SHOULD encode change notifications in the most efficient
manner possible.
For example, when three AAAA records are removed from a given name, and
no other AAAA
records exist for that name, the server SHOULD send a "remove an RRset
from a name"
PUSH message, not three separate "remove an individual RR from a name"
PUSH messages.
Similarly, when both an SRV and a TXT record are removed from a given n
ame, and no other
records of any kind exist for that name, the server SHOULD send a "remo
ve all RRsets
from a name" PUSH message, not two separate "remove an RRset from a nam
e" PUSH messages.</t>
<t>A server SHOULD combine multiple change notifications in a single PU
SH message when possible, even if those change notifications apply to different
subscriptions. Conceptually, a PUSH message is a session-level mechanism, not a
subscription-level mechanism.</t>
<t>The TTL of an added record is stored by the client. While the subsc
ription
is active, the TTL is not decremented, because a change to the TTL wo
uld
produce a new update. produce a new update.
For as long as a relevant subscription remains active, the client For as long as a relevant subscription remains active, the client
SHOULD assume that when a record goes away the server will notify it <bcp14>SHOULD</bcp14> assume that when a record goes away, the
of that fact. Consequently, a client does not have to poll to verify server will notify it
that the record is still there. Once a subscription is cancelled of that fact. Consequently, a client does not have to poll to
(individually, or as a result of the DSO session being closed) record verify
aging for records covered by the subscription resumes and records are that the record is still there. Once a subscription is canceled
(individually, or as a result of the DSO session being closed),
record
aging for records covered by the subscription resumes and records
are
removed from the local cache when their TTL reaches zero.</t> removed from the local cache when their TTL reaches zero.</t>
<?rfc needLines="48" ?> </section>
</section> </section>
</section> <section anchor="unsubscribe" numbered="true" toc="include" removeInRFC="f
alse" pn="section-6.4">
<section title="DNS Push Notification UNSUBSCRIBE" anchor="unsubscribe"> <name slugifiedName="name-dns-push-notification-unsub">DNS Push Notifica
<t>To cancel an individual subscription without closing the entire DSO se tion UNSUBSCRIBE</name>
ssion, the client sends an UNSUBSCRIBE message over the established DSO session <t pn="section-6.4-1">To cancel an individual subscription without closi
to the server.</t> ng the entire DSO
session, the client sends an UNSUBSCRIBE message over the established
<t>The entity that initiates an UNSUBSCRIBE message is by definition the DSO session to the server.</t>
client. <t pn="section-6.4-2">The entity that initiates an UNSUBSCRIBE message i
A server MUST NOT send an UNSUBSCRIBE message over an existing session fr s by definition
om a client. the client.
If a server does send an UNSUBSCRIBE message over a DSO session initiated A server <bcp14>MUST NOT</bcp14> send an UNSUBSCRIBE message over an
by a client, existing session from a client.
or an UNSUBSCRIBE message is sent with the QR bit set indicating that it If a server does send an UNSUBSCRIBE message over a DSO session
is a response, initiated by a client,
this is a fatal error and the receiver MUST forcibly abort the connection or an UNSUBSCRIBE message is sent with the QR bit set indicating that
immediately.</t> it is a response,
this is a fatal error and the receiver <bcp14>MUST</bcp14> forcibly
<section title="UNSUBSCRIBE Message"> abort the connection immediately.</t>
<section numbered="true" toc="include" removeInRFC="false" pn="section-6
<t>An UNSUBSCRIBE unidirectional message begins with the standard .4.1">
<xref target="RFC8490">DSO 12-byte header</xref>, followed by the UNSUB <name slugifiedName="name-unsubscribe-message">UNSUBSCRIBE Message</na
SCRIBE primary TLV. me>
An UNSUBSCRIBE message is illustrated in <xref target="unsubscribe_msg" <t pn="section-6.4.1-1">An UNSUBSCRIBE unidirectional message begins w
/>.</t> ith the standard
DSO 12-byte header <xref target="RFC8490" format="default" sectionForma
<t>In accordance with the definition of DSO unidirectional messages, t="of" derivedContent="RFC8490"/>,
the MESSAGE ID field MUST be zero. followed by the UNSUBSCRIBE Primary TLV.
An UNSUBSCRIBE message is illustrated in <xref target="unsubscribe_msg"
format="default" sectionFormat="of" derivedContent="Figure 4"/>.</t>
<t pn="section-6.4.1-2">In accordance with the definition of DSO unidi
rectional messages,
the MESSAGE ID field <bcp14>MUST</bcp14> be zero.
There is no server response to an UNSUBSCRIBE message.</t> There is no server response to an UNSUBSCRIBE message.</t>
<t pn="section-6.4.1-3">The other header fields <bcp14>MUST</bcp14> be
<t>The other header fields MUST be set as described in the set as described
<xref target="RFC8490">DSO spec-ification</xref>. in the
The DNS OPCODE field contains the OPCODE value for DNS Stateful Operati <xref target="RFC8490" format="default" sectionFormat="of" derivedConte
ons (6). nt="RFC8490">DSO specification</xref>.
The four count fields must be zero, and the corresponding four sections The DNS OPCODE field contains the OPCODE value for DNS Stateful
must be empty (i.e., absent).</t> Operations (6).
The four count fields must be zero, and the corresponding four
<t>The DSO-TYPE is UNSUBSCRIBE (tentatively 0x42).</t> sections must be empty (i.e., absent).</t>
<t pn="section-6.4.1-4">The DSO-TYPE is UNSUBSCRIBE (0x0042).</t>
<t>The DSO-LENGTH field contains the value 2, the length of the 2-octet <t pn="section-6.4.1-5">The DSO-LENGTH field contains the value 2, the
MESSAGE ID contained in the DSO-DATA.</t> length of the
2-octet MESSAGE ID contained in the DSO-DATA.</t>
<t>The DSO-DATA contains the value previously given in the MESSAGE ID f <t pn="section-6.4.1-6">The DSO-DATA contains the value previously giv
ield of an active SUBSCRIBE request. en in the MESSAGE
This is how the server knows which SUBSCRIBE request is being cancelled ID field of an active SUBSCRIBE request.
. This is how the server knows which SUBSCRIBE request is being
After receipt of the UNSUBSCRIBE message, the SUBSCRIBE request is no l canceled.
onger active.</t> After receipt of the UNSUBSCRIBE message, the SUBSCRIBE request is no
longer active.</t>
<t>It is allowable for the client to issue an UNSUBSCRIBE message for a <t pn="section-6.4.1-7">It is allowable for the client to issue an UNS
previous SUBSCRIBE request UBSCRIBE message
for a previous SUBSCRIBE request
for which the client has not yet received a SUBSCRIBE response. for which the client has not yet received a SUBSCRIBE response.
This is to allow for the case where a client starts and stops a subscri This is to allow for the case where a client starts and stops a
ption in less than the subscription in less than the
round-trip time to the server. round-trip time to the server.
The client is NOT required to wait for the SUBSCRIBE response before is The client is NOT required to wait for the SUBSCRIBE response before
suing the UNSUBSCRIBE message.</t> issuing the UNSUBSCRIBE message.</t>
<t pn="section-6.4.1-8">Consequently, it is possible for a server to r
<?rfc needLines="6" ?> eceive an
<t>Consequently, it is possible for a server to receive an UNSUBSCRIBE UNSUBSCRIBE message
message
that does not match any currently active subscription. that does not match any currently active subscription.
This can occur when a client sends a SUBSCRIBE request, This can occur when a client sends a SUBSCRIBE request,
which subsequently fails and returns an error code, which subsequently fails and returns an error code,
but the client sent an UNSUBSCRIBE message before it but the client sent an UNSUBSCRIBE message before it
became aware that the SUBSCRIBE request had failed. became aware that the SUBSCRIBE request had failed.
Because of this, servers MUST silently ignore Because of this, servers <bcp14>MUST</bcp14> silently ignore
UNSUBSCRIBE messages that do not match any currently active subscriptio UNSUBSCRIBE messages that do not match any currently active
n.</t> subscription.</t>
<figure anchor="unsubscribe_msg" align="left" suppress-title="false" p
<figure align="left" anchor="unsubscribe_msg" title="UNSUBSCRIBE Messag n="figure-4">
e"><artwork align="left"><![CDATA[ <name slugifiedName="name-unsubscribe-message-2">UNSUBSCRIBE Message
</name>
<artwork align="left" name="" type="" alt="" pn="section-6.4.1-9.1">
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = UNSUBSCRIBE (tentatively 0x42) | | DSO-TYPE = UNSUBSCRIBE (0x0042) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (2) | | DSO-LENGTH (2) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| SUBSCRIBE MESSAGE ID | > DSO-DATA | SUBSCRIBE MESSAGE ID | &gt; DSO-DATA
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /]]></artwork></figure> +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /</artwork>
</figure>
<?rfc needLines="48" ?> </section>
</section> </section>
</section> <section anchor="reconfirm" numbered="true" toc="include" removeInRFC="fal
se" pn="section-6.5">
<section title="DNS Push Notification RECONFIRM" anchor="reconfirm"> <name slugifiedName="name-dns-push-notification-recon">DNS Push Notifica
<t>Sometimes, particularly when used with a <xref target="DisProx">Discov tion RECONFIRM</name>
ery Proxy</xref>, a DNS Zone may contain stale data. When a client encounters da <t pn="section-6.5-1">Sometimes, particularly when used with a Discovery
ta that it believes may be stale (e.g., an SRV record referencing a target host+ Proxy <xref target="RFC8766" format="default" sectionFormat="of" derivedContent
port that is not responding to connection requests) the client can send a RECONF ="RFC8766"/>, a DNS Zone may contain
IRM message to ask the server to re-verify that the data is still valid. For a D stale data. When a client encounters data that it believes may be
iscovery Proxy, this causes it to issue new Multicast DNS queries to ascertain w stale (e.g., an SRV record referencing a target host+port that is not
hether the target device is still present. How the Discovery Proxy causes these responding to connection requests), the client can send a RECONFIRM
new Multicast DNS queries to be issued depends on the details of the underlying message to ask the server to re-verify that the data is still
Multicast DNS implementation being used. valid. For a Discovery Proxy, this causes it to issue new Multicast
For example, a Discovery Proxy built on Apple's dns_sd.h API <xref target DNS queries to ascertain whether the target device is still
="SD-API"/> present. How the Discovery Proxy causes these new Multicast DNS
responds to a DNS Push Notification RECONFIRM message by calling queries to be issued depends on the details of the underlying
the underlying API's DNSServiceReconfirmRecord() routine.</t> Multicast DNS implementation being used. For example, a Discovery
Proxy built on Apple's dns_sd.h API <xref target="SD-API" format="defaul
<t>For other types of DNS server, the RECONFIRM operation is currently un t" sectionFormat="of" derivedContent="SD-API"/> responds to a DNS Push Notificat
defined, and SHOULD result in a NOERROR response, but otherwise need not cause a ion RECONFIRM
ny action to occur.</t> message by calling the underlying API's DNSServiceReconfirmRecord()
routine.</t>
<t>Frequent use of RECONFIRM operations may be a sign of network unreliab <t pn="section-6.5-2">For other types of DNS server, the RECONFIRM opera
ility, or some kind of misconfiguration, so RECONFIRM operations MAY be logged o tion is currently
r otherwise communicated to a human administrator to assist in detecting and rem undefined and <bcp14>SHOULD</bcp14> result in a NOERROR response, but
edying such network problems.</t> it need not cause any other action to occur.</t>
<t pn="section-6.5-3">Frequent use of RECONFIRM operations may be a sign
<t>If, after receiving a valid RECONFIRM message, the server determines t of network
hat the disputed records are in fact no longer valid, then subsequent DNS PUSH M unreliability, or some kind of misconfiguration, so RECONFIRM
essages will be generated to inform interested clients. Thus, one client discove operations <bcp14>MAY</bcp14> be logged or otherwise communicated to a
ring that a previously-advertised device (like a network printer) is no longer p human administrator to assist in detecting and remedying such network
resent has the side effect of informing all other interested clients that the de problems.</t>
vice in question is now gone.</t> <t pn="section-6.5-4">If, after receiving a valid RECONFIRM message, the
server
<t>The entity that initiates a RECONFIRM message is by definition the cli determines that the disputed records are in fact no longer valid, then
ent. subsequent DNS PUSH Messages will be generated to inform interested
A server MUST NOT send a RECONFIRM message over an existing session from clients. Thus, one client discovering that a previously advertised
a client. device (like a network printer) is no longer present has the side
If a server does send a RECONFIRM message over a DSO session initiated by effect of informing all other interested clients that the device in
a client, question is now gone.</t>
or a RECONFIRM message is sent with the QR bit set indicating that it is <t pn="section-6.5-5">The entity that initiates a RECONFIRM message is b
a response, y definition the
this is a fatal error and the receiver MUST forcibly abort the connection client.
immediately.</t> A server <bcp14>MUST NOT</bcp14> send a RECONFIRM message over an
existing session from a client.
<?rfc needLines="20" ?> If a server does send a RECONFIRM message over a DSO session initiated
<section title="RECONFIRM Message"> by a client,
or a RECONFIRM message is sent with the QR bit set indicating that it
<t>A RECONFIRM unidirectional message begins with the standard is a response,
<xref target="RFC8490">DSO 12-byte header</xref>, followed by the RECON this is a fatal error and the receiver <bcp14>MUST</bcp14> forcibly
FIRM primary TLV.<vspace /> abort the connection immediately.</t>
A RECONFIRM message is illustrated in <xref target="reconfirm_msg"/>.</ <section numbered="true" toc="include" removeInRFC="false" pn="section-6
t> .5.1">
<name slugifiedName="name-reconfirm-message">RECONFIRM Message</name>
<t>In accordance with the definition of DSO unidirectional messages, <t pn="section-6.5.1-1">A RECONFIRM unidirectional message begins with
the MESSAGE ID field MUST be zero. the standard DSO
12-byte header <xref target="RFC8490" format="default" sectionFormat="
of" derivedContent="RFC8490"/>,
followed by the RECONFIRM Primary TLV.
A RECONFIRM message is illustrated in <xref target="reconfirm_msg" for
mat="default" sectionFormat="of" derivedContent="Figure 5"/>.</t>
<t pn="section-6.5.1-2">In accordance with the definition of DSO unidi
rectional messages,
the MESSAGE ID field <bcp14>MUST</bcp14> be zero.
There is no server response to a RECONFIRM message.</t> There is no server response to a RECONFIRM message.</t>
<t pn="section-6.5.1-3">The other header fields <bcp14>MUST</bcp14> be
<t>The other header fields MUST be set as described in the set as described
<xref target="RFC8490">DSO spec-ification</xref>. in the
The DNS OPCODE field contains the OPCODE value for DNS Stateful Operati <xref target="RFC8490" format="default" sectionFormat="of" derivedConte
ons (6). nt="RFC8490">DSO specification</xref>.
The four count fields must be zero, and the corresponding four sections The DNS OPCODE field contains the OPCODE value for DNS Stateful
must be empty (i.e., absent).</t> Operations (6).
The four count fields must be zero, and the corresponding four
<t>The DSO-TYPE is RECONFIRM (tentatively 0x43).</t> sections must be empty (i.e., absent).</t>
<t pn="section-6.5.1-4">The DSO-TYPE is RECONFIRM (0x0043).</t>
<t>The DSO-LENGTH is the length of the data that follows, which specifi <t pn="section-6.5.1-5">The DSO-LENGTH is the length of the data that
es follows, which
specifies
the name, type, class, and content of the record being disputed.</t> the name, type, class, and content of the record being disputed.</t>
<t pn="section-6.5.1-6">A DNS Push Notifications RECONFIRM message con
<t>The DSO-DATA for a RECONFIRM message MUST contain exactly one record tains exactly one
. RECONFIRM Primary TLV.
The DSO-DATA for a RECONFIRM message has no count field to specify more The DSO-DATA in a RECONFIRM Primary TLV <bcp14>MUST</bcp14> contain
than one record. exactly one record.
Since RECONFIRM messages are sent over TCP, multiple RECONFIRM messages The DSO-DATA in a RECONFIRM Primary TLV has no count field to
can be concatenated in a single TCP stream and packed efficiently into specify more than one record.
TCP segments.</t> Since RECONFIRM messages are sent over TCP, multiple RECONFIRM
messages
<t>TYPE MUST NOT be the value ANY (255) and CLASS MUST NOT be the value can be concatenated in a single TCP stream and packed efficiently
ANY (255).</t> into TCP segments.
Note that this means that DNS name compression cannot be used
<t>DNS wildcarding is not supported. That is, a wildcard ("*") in a REC between different RECONFIRM messages.
ONFIRM message matches only a literal wildcard character ("*") in the zone, and However, when a client is sending multiple RECONFIRM messages this
nothing else.</t> indicates
a situation with serious network problems, and this is not expected
<t>Aliasing is not supported. That is, a CNAME in a RECONFIRM message m to occur
atches only a literal CNAME record in the zone, and no other records with the sa frequently enough that optimizing efficiency in this case is
me owner name.</t> important.
</t>
<t>Note that there is no RDLEN field, since the length of the RDATA can <t pn="section-6.5.1-7">TYPE <bcp14>MUST NOT</bcp14> be the value ANY
be inferred from DSO-LENGTH, so an additional RDLEN field would be redundant.</ (255) and CLASS
t> <bcp14>MUST NOT</bcp14> be the value ANY (255).</t>
<t pn="section-6.5.1-8">DNS wildcarding is not supported.
<figure align="left" anchor="reconfirm_msg" title="RECONFIRM Message">< That is, an asterisk character ("*") in a RECONFIRM message matches
artwork align="left"><![CDATA[ only a literal asterisk character ("*") in a name and nothing else.
Similarly, a CNAME in a RECONFIRM message matches only a CNAME
record
with that name in the zone and no other records with that name.</t>
<t pn="section-6.5.1-9">Note that there is no RDLEN field,
since the length of the RDATA can be inferred from DSO-LENGTH,
so an additional RDLEN field would be redundant.</t>
<t pn="section-6.5.1-10">Following the same rules as for PUSH messages
, DNS name
compression SHOULD
be used within the RDATA of the RECONFIRM message, with offsets
relative to the
beginning of the DNS message <xref target="RFC1035" format="default" s
ectionFormat="of" derivedContent="RFC1035"/>.</t>
<figure anchor="reconfirm_msg" align="left" suppress-title="false" pn=
"figure-5">
<name slugifiedName="name-reconfirm-message-2">RECONFIRM Message</na
me>
<artwork align="left" name="" type="" alt="" pn="section-6.5.1-11.1"
>
1 1 1 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
| MESSAGE ID (MUST BE ZERO) | \ | MESSAGE ID (MUST BE ZERO) | \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
|QR| OPCODE(6) | Z | RCODE | | |QR| OPCODE(6) | Z | RCODE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| QDCOUNT (MUST BE ZERO) | | | QDCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > HEADER +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; HEADER
| ANCOUNT (MUST BE ZERO) | | | ANCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| NSCOUNT (MUST BE ZERO) | | | NSCOUNT (MUST BE ZERO) | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| ARCOUNT (MUST BE ZERO) | / | ARCOUNT (MUST BE ZERO) | /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ / +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /
| DSO-TYPE = RECONFIRM (tentatively 0x43) | | DSO-TYPE = RECONFIRM (0x0043) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| DSO-LENGTH (number of octets in DSO-DATA) | | DSO-LENGTH (number of octets in DSO-DATA) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ \
\ NAME \ \ \ NAME \ \
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
| TYPE | | | TYPE | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ > DSO-DATA +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ &gt; DSO-DATA
| CLASS | | | CLASS | |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |
\ RDATA \ / \ RDATA \ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /]]></artwork></figure> +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ /</artwork>
</figure>
<?rfc needLines="48" ?> </section>
</section> </section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-6.6
</section> ">
<section title="DNS Stateful Operations TLV Context Summary"> <name slugifiedName="name-dns-stateful-operations-tlv">DNS Stateful Oper
<t>This document defines four new DSO TLVs. As recommended in Section 8.2 ations TLV Context Summary</name>
of the <xref target="RFC8490">DNS Stateful Operations specification</xref>, the <t pn="section-6.6-1">This document defines four new DSO TLVs. As recomm
valid contexts of these new TLV types are summarized below.</t> ended in <xref target="RFC8490" sectionFormat="of" section="8.2" format="default
<t>The client TLV contexts are: " derivedLink="https://rfc-editor.org/rfc/rfc8490#section-8.2" derivedContent="R
<?rfc subcompact="yes" ?> FC8490">the DNS Stateful
<list style="hanging"> Operations specification</xref>, the valid contexts of these
<t hangText="C-P:">Client request message, primary TLV</t> new TLV types are summarized below.</t>
<t hangText="C-U:">Client unidirectional message, primary TLV</t> <t pn="section-6.6-2">The client TLV contexts are:
<t hangText="C-A:">Client request or unidirectional message, addition
al TLV</t>
<t hangText="CRP:">Response back to client, primary TLV</t>
<t hangText="CRA:">Response back to client, additional TLV</t>
</list>
<?rfc subcompact="no" ?>
</t>
<texttable title="DSO TLV Client Context Summary" anchor="tlv_client_cont
exts">
<ttcol align="right">TLV Type</ttcol>
<ttcol align="center">C-P</ttcol>
<ttcol align="center">C-U</ttcol>
<ttcol align="center">C-A</ttcol>
<ttcol align="center">CRP</ttcol>
<ttcol align="center">CRA</ttcol>
<c>SUBSCRIBE</c><c>X</c><c></c><c></c><c></c><c></c>
<c>PUSH</c><c></c><c></c><c></c><c></c><c></c>
<c>UNSUBSCRIBE</c><c></c><c>X</c><c></c><c></c><c></c>
<c>RECONFIRM</c><c></c><c>X</c><c></c><c></c><c></c>
</texttable>
<t>The server TLV contexts are:
<?rfc subcompact="yes" ?>
<list style="hanging">
<t hangText="S-P:">Server request message, primary TLV</t>
<t hangText="S-U:">Server unidirectional message, primary TLV</t>
<t hangText="S-A:">Server request or unidirectional message, additional
TLV</t>
<t hangText="SRP:">Response back to server, primary TLV</t>
<t hangText="SRA:">Response back to server, additional TLV</t>
</list>
<?rfc subcompact="no" ?>
</t>
<texttable title="DSO TLV Server Context Summary" anchor="tlv_server_contex
ts">
<ttcol align="right">TLV Type</ttcol>
<ttcol align="center">S-P</ttcol>
<ttcol align="center">S-U</ttcol>
<ttcol align="center">S-A</ttcol>
<ttcol align="center">SRP</ttcol>
<ttcol align="center">SRA</ttcol>
<c>SUBSCRIBE</c><c></c><c></c><c></c><c></c><c></c>
<c>PUSH</c><c></c><c>X</c><c></c><c></c><c></c>
<c>UNSUBSCRIBE</c><c></c><c></c><c></c><c></c><c></c>
<c>RECONFIRM</c><c></c><c></c><c></c><c></c><c></c>
</texttable>
</section>
<section title="Client-Initiated Termination">
<t>An individual subscription is terminated by sending an UNSUBSCRIBE TLV
for that specific subscription, or all subscriptions can be cancelled at once b
y the client closing the DSO session. When a client terminates an individual sub
scription (via UNSUBSCRIBE) or all subscriptions on that DSO session (by ending
the session) it is signaling to the server that it is no longer interested in re
ceiving those particular updates. It is informing the server that the server may
release any state information it has been keeping with regards to these particu
lar subscriptions.</t>
<t>After terminating its last subscription on a session via UNSUBSCRIBE,
a client MAY close the session immediately, or it may keep it open if it anticip
ates performing further operations on that session in the future. If a client wi
shes to keep an idle session open, it MUST respect the maximum idle time require
d by the server <xref target="RFC8490"/>.</t>
<t>If a client plans to terminate one or more subscriptions on a session
and doesn't intend to keep that session open, then as an efficiency optimization
it MAY instead choose to simply close the session, which implicitly terminates
all subscriptions on that session. This may occur because the client computer is
being shut down, is going to sleep, the application requiring the subscriptions
has terminated, or simply because the last active subscription on that session
has been cancelled.</t>
<t>When closing a session, a client should perform an orderly close of </t>
the TLS session. <dl newline="false" spacing="compact" pn="section-6.6-3">
Typical APIs will provide a session <dt pn="section-6.6-3.1">C-P:</dt>
close method that will send a TLS close_notify alert <dd pn="section-6.6-3.2">Client request message, Primary TLV</dd>
(see Section 6.1 of the TLS 1.3 specification <xref target="RFC8446"/>). <dt pn="section-6.6-3.3">C-U:</dt>
This instructs the recipient that the sender will not send any more data <dd pn="section-6.6-3.4">Client Unidirectional message, primary TLV</d
over the session. d>
After sending the TLS close_notify alert <dt pn="section-6.6-3.5">C-A:</dt>
the client MUST gracefully close the underlying connection using a TCP FI <dd pn="section-6.6-3.6">Client request or unidirectional message, Add
N, itional TLV</dd>
so that the TLS close_notify is reliably delivered. <dt pn="section-6.6-3.7">CRP:</dt>
The mechanisms for gracefully closing a TCP connection with a TCP FIN var <dd pn="section-6.6-3.8">Response back to client, Primary TLV</dd>
y depending on the networking API. <dt pn="section-6.6-3.9">CRA:</dt>
For example, in the BSD Sockets API, sending a TCP FIN is achieved by cal <dd pn="section-6.6-3.10">Response back to client, Additional TLV</dd>
ling "shutdown(s,SHUT_WR)" </dl>
and keeping the socket open until all remaining data has been read from i <table anchor="tlv_client_contexts" align="center" pn="table-2">
t.</t> <name slugifiedName="name-dso-tlv-client-context-summ">DSO TLV Client
Context Summary</name>
<thead>
<tr>
<th align="right" colspan="1" rowspan="1">TLV Type</th>
<th align="center" colspan="1" rowspan="1">C-P</th>
<th align="center" colspan="1" rowspan="1">C-U</th>
<th align="center" colspan="1" rowspan="1">C-A</th>
<th align="center" colspan="1" rowspan="1">CRP</th>
<th align="center" colspan="1" rowspan="1">CRA</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right" colspan="1" rowspan="1">SUBSCRIBE</td>
<td align="center" colspan="1" rowspan="1">X</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">PUSH</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">UNSUBSCRIBE</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1">X</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">RECONFIRM</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1">X</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
</tbody>
</table>
<t pn="section-6.6-5">The server TLV contexts are:
<t>If the session is forcibly closed at the TCP level by sending a </t>
<dl newline="false" spacing="compact" pn="section-6.6-6">
<dt pn="section-6.6-6.1">S-P:</dt>
<dd pn="section-6.6-6.2">Server request message, Primary TLV</dd>
<dt pn="section-6.6-6.3">S-U:</dt>
<dd pn="section-6.6-6.4">Server Unidirectional message, primary TLV</d
d>
<dt pn="section-6.6-6.5">S-A:</dt>
<dd pn="section-6.6-6.6">Server request or unidirectional message, Add
itional TLV</dd>
<dt pn="section-6.6-6.7">SRP:</dt>
<dd pn="section-6.6-6.8">Response back to server, Primary TLV</dd>
<dt pn="section-6.6-6.9">SRA:</dt>
<dd pn="section-6.6-6.10">Response back to server, Additional TLV</dd>
</dl>
<table anchor="tlv_server_contexts" align="center" pn="table-3">
<name slugifiedName="name-dso-tlv-server-context-summ">DSO TLV Server
Context Summary</name>
<thead>
<tr>
<th align="right" colspan="1" rowspan="1">TLV Type</th>
<th align="center" colspan="1" rowspan="1">S-P</th>
<th align="center" colspan="1" rowspan="1">S-U</th>
<th align="center" colspan="1" rowspan="1">S-A</th>
<th align="center" colspan="1" rowspan="1">SRP</th>
<th align="center" colspan="1" rowspan="1">SRA</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right" colspan="1" rowspan="1">SUBSCRIBE</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">PUSH</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1">X</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">UNSUBSCRIBE</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
<tr>
<td align="right" colspan="1" rowspan="1">RECONFIRM</td>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
<td align="center" colspan="1" rowspan="1"/>
</tr>
</tbody>
</table>
</section>
<section numbered="true" toc="include" removeInRFC="false" pn="section-6.7
">
<name slugifiedName="name-client-initiated-terminatio">Client-Initiated
Termination</name>
<t pn="section-6.7-1">An individual subscription is terminated by sendin
g an UNSUBSCRIBE
TLV for that specific subscription, or all subscriptions can be
canceled at once by the client closing the DSO session. When a client
terminates an individual subscription (via UNSUBSCRIBE) or all
subscriptions on that DSO session (by ending the session), it is
signaling to the server that it is no longer interested in receiving
those particular updates. It is informing the server that the server
may release any state information it has been keeping with regards to
these particular subscriptions.</t>
<t pn="section-6.7-2">After terminating its last subscription on a sessi
on via
UNSUBSCRIBE, a client <bcp14>MAY</bcp14> close the session immediately
or it may keep it open if it anticipates performing further operations
on that session in the future. If a client wishes to keep an idle
session open, it <bcp14>MUST</bcp14> respect the maximum idle time
required by the server <xref target="RFC8490" format="default" sectionFo
rmat="of" derivedContent="RFC8490"/>.</t>
<t pn="section-6.7-3">If a client plans to terminate one or more subscri
ptions on a
session and doesn't intend to keep that session open, then as an
efficiency optimization, it <bcp14>MAY</bcp14> instead choose to
simply
close the session, which implicitly terminates all subscriptions on
that session. This may occur because the client computer is being shut
down, is going to sleep, the application requiring the subscriptions
has terminated, or simply because the last active subscription on that
session has been canceled.</t>
<t pn="section-6.7-4">When closing a session, a client should perform an
orderly close of
the TLS session. Typical APIs will provide a session close method
that will send a TLS close_notify alert as described in <xref target="RF
C8446" sectionFormat="of" section="6.1" format="default" derivedLink="https://rf
c-editor.org/rfc/rfc8446#section-6.1" derivedContent="RFC8446">the TLS 1.3 speci
fication</xref>.
This instructs the
recipient that the sender will not send any more data over the
session. After sending the TLS close_notify alert, the client
<bcp14>MUST</bcp14> gracefully close the underlying connection using a
TCP FIN so that the TLS close_notify is reliably delivered. The
mechanisms for gracefully closing a TCP connection with a TCP FIN vary
depending on the networking API. For example, in the BSD Sockets API,
sending a TCP FIN is achieved by calling "shutdown(s,SHUT_WR)" and
keeping the socket open until all remaining data has been read from
it.</t>
<t pn="section-6.7-5">If the session is forcibly closed at the TCP level
by sending a
RST from either end of the connection, data may be lost.</t> RST from either end of the connection, data may be lost.</t>
<?rfc needLines="10" ?> </section>
</section> <section anchor="polling" numbered="true" toc="include" removeInRFC="false
" pn="section-6.8">
<section title="Client Fallback to Polling" anchor="polling"> <name slugifiedName="name-client-fallback-to-polling">Client Fallback to
<t>There are cases where a client may exhaust all avenues for Polling</name>
<t pn="section-6.8-1">There are cases where a client may exhaust all ave
nues for
establishing a DNS Push Notification subscription without success. establishing a DNS Push Notification subscription without success.
This can happen if the client's configured recursive resolver This can happen if the client's configured recursive resolver does not
does not support DNS over TLS, or support DNS over TLS, or supports DNS over TLS but is not listening on
supports DNS over TLS but is not listening on TCP port 853, or TCP port 853, or supports DNS over TLS on TCP port 853 but does not
supports DNS over TLS on TCP port 853 but does not support DSO on that p support DSO on that port, or for some other reason is unable to
ort, provide a DNS Push Notification subscription. In this case, the
or for some other reason is unable to provide a DNS Push Notification su client
bscription. will attempt to communicate directly with an appropriate server, and
In this case the client will attempt to communicate directly with an app it may be that the zone apex discovery fails, or there is no
ropriate server, <tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt> SRV record, or
and it may be that the zone apex discovery fails, or there is no the server indicated in the SRV record is misconfigured, overloaded,
<spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</spanx> SR or is
V record, unresponsive for some other reason.</t>
or server indicated in the SRV record is misconfigured, <t pn="section-6.8-2">Regardless of the reason for the failure, after be
or is unresponsive for some other reason.</t> ing unable to
establish the desired DNS Push Notification subscription, it is likely
<t>Regardless of the reason for the failure, that the client will still wish to know the answer it seeks, even if
after being unable to establish the desired DNS Push Notification subscr that answer cannot be obtained with the timely change notifications
iption, provided by DNS Push Notifications. In such cases, it is likely that
it is likely that the client will still wish to know the answer it seeks the client will obtain the answer it seeks via a conventional DNS
, query instead, repeated at some interval to detect when the answer
even if that answer cannot be obtained with the timely RRset changes.</t>
change notifications provided by DNS Push Notifications. <t pn="section-6.8-3">In the case where a client responds to its failure
In such cases it is likely that the client will obtain to establish a
the answer it seeks via a conventional DNS query instead, DNS Push Notification subscription by falling back to polling with
repeated at some interval to detect when the answer RRset changes.</t> conventional DNS queries instead, the polling rate should be
controlled to avoid placing excessive burden on the server. The
<t>In the case where a client responds to its interval between successive DNS queries for the same name, type, and
failure to establish a DNS Push Notification subscription class <bcp14>SHOULD</bcp14> be at least the minimum of 900 seconds (15
by falling back to polling with conventional DNS queries instead, minutes) or two seconds more than the TTL of the answer RRset.</t>
the polling rate should be controlled to avoid placing excessive burden <t pn="section-6.8-4">The reason that for TTLs up to 898 seconds the que
on the server. ry should
The interval between successive DNS queries for the same name, type and not be reissued until two seconds <em>after</em> the answer RRset has
class expired, is to ensure that the answer RRset has also expired from the
SHOULD be at least the minimum of: 900 seconds (15 minutes), cache on the client's configured recursive resolver. Otherwise
or two seconds more than the TTL of the answer RRset.</t> (particularly if the clocks on the client and the recursive resolver
do not run at precisely the same rate), there's a risk of a race
<t>The reason that for TTLs shorter than 898 seconds the query should condition where the client queries its configured recursive resolver
not be reissued until two seconds *after* the answer RRset has expired i just as the answer RRset has one second remaining in the recursive
s resolver's cache. The client would receive a reply telling it
to ensure that the answer RRset has also expired from that the answer RRset has one second remaining; the client
the cache on the client's configured recursive resolver. would then requery the recursive resolver again one second later.
Otherwise If by this time the answer RRset has actually expired from the
(particularly if the clocks on the client and the recursive resolver's cache, the recursive resolver would then
recursive resolver do not run at precisely the same rate) issue a new query to fetch fresh data from the
there's a risk of a race condition where authoritative server. Waiting until the answer RRset has definitely
the client queries its configured recursive resolver just as the answer expired from the cache on the client's configured recursive resolver
RRset has avoids this race condition and any unnecessary additional queries it
one second remaining in the recursive resolver's cache. causes.</t>
The client would then receive a reply telling it that the answer RRset <t pn="section-6.8-5">Each time a client is about to reissue its query t
has one second remaining, and then the client would then re-query the o discover
recursive resolver again one second later when the answer RRset
actually expires, and only then would the
recursive resolver issue a new query to fetch new fresh
data from the authoritative server.
Waiting until the answer RRset has definitely expired from the
the cache on the client's configured recursive resolver
avoids this race condition and unnecessary additional queries it causes.
</t>
<t>Each time a client is about to reissue its query to discover
changes to the answer RRset, it should first make a new attempt to changes to the answer RRset, it should first make a new attempt to
establish a DNS Push Notification subscription, using previously establish a DNS Push Notification subscription using previously
cached DNS answers as appropriate. cached DNS answers as appropriate. After a temporary misconfiguration
After a temporary misconfiguration has been remedied, has been remedied, this allows a client that is polling to return to
this allows a client that is polling to return to using using DNS Push Notifications for asynchronous notification of
DNS Push Notifications for asynchronous notification of changes.</t> changes.</t>
</section> </section>
</section> </section>
<section anchor="Security" numbered="true" toc="include" removeInRFC="false"
<section title="Security Considerations" anchor="Security"> pn="section-7">
<t>The Strict Privacy Usage Profile for DNS over TLS is REQUIRED for DNS Pu <name slugifiedName="name-security-considerations">Security Considerations
sh Notifications <xref target="RFC8310"/>. Cleartext connections for DNS Push No </name>
tifications are not permissible. Since this is a new protocol, transition mechan <t pn="section-7-1">The Strict Privacy profile for DNS over TLS is
isms from the Opportunistic Privacy profile are unnecessary.</t> <bcp14>REQUIRED</bcp14> for DNS Push Notifications <xref target="RFC8310"
format="default" sectionFormat="of" derivedContent="RFC8310"/>. Cleartext connec
<t>Also, see Section 9 of the DNS over (D)TLS Usage Profiles document <xref tions for DNS Push
target="RFC8310"/> for additional recommendations for various versions of TLS u Notifications are not permissible. Since this is a new protocol,
sage.</t> transition mechanisms from the Opportunistic Privacy profile are
unnecessary.</t>
<t>As a consequence of requiring TLS, client certificate authentication and <t pn="section-7-2">Also, see
verification may also be enforced by the server for stronger client-server secu <xref target="RFC8310" sectionFormat="of" section="9" format="default" der
rity or end-to-end security. However, recommendations for security in particular ivedLink="https://rfc-editor.org/rfc/rfc8310#section-9" derivedContent="RFC8310"
deployment scenarios are outside the scope of this document.</t> >the document Usage
Profiles for DNS over (D)TLS</xref>
<t>DNSSEC is RECOMMENDED for the authentication of DNS Push Notification se for additional
rvers. recommendations for various versions of TLS usage.</t>
TLS alone does not provide complete security. <t pn="section-7-3">As a consequence of requiring TLS, client certificate
TLS certificate verification can provide reasonable assurance that the clie authentication
nt is really talking to the and verification may also be enforced by the server for stronger
server associated with the desired host name, but since the desired host na client-server security or end-to-end security. However, recommendations
me is learned via a DNS SRV query, for security in particular deployment scenarios are outside the scope of
if the SRV query is subverted then the client may have a secure connection this document.</t>
to a rogue server. <t pn="section-7-4">DNSSEC is <bcp14>RECOMMENDED</bcp14> for the authentic
DNSSEC can provide added confidence that the SRV query has not been subvert ation of DNS
ed.</t> Push Notification servers. TLS alone does not provide complete
security. TLS certificate verification can provide reasonable assurance
<?rfc needLines="14" ?> that the client is really talking to the server associated with the
<section title="Security Services"> desired host name, but since the desired host name is learned via a DNS
<t>It is the goal of using TLS to provide the following security services SRV query, if the SRV query is subverted, then the client may have a
: secure connection to a rogue server. DNSSEC can provide added
<list style="hanging"> confidence that the SRV query has not been subverted.</t>
<t hangText="Confidentiality:">All application-layer communication is <section numbered="true" toc="include" removeInRFC="false" pn="section-7.1
encrypted with the goal that no party should be able to decrypt it except the i ">
ntended receiver.</t> <name slugifiedName="name-security-services">Security Services</name>
<t hangText="Data integrity protection:">Any changes made to the comm <t pn="section-7.1-1">It is the goal of using TLS to provide the followi
unication in transit are detectable by the receiver.</t> ng security
<t hangText="Authentication:">An end-point of the TLS communication i services:
s authenticated as the intended entity to communicate with.</t> </t>
<t hangText="Anti-replay protection:">TLS provides for the detection <dl newline="false" spacing="normal" pn="section-7.1-2">
of and prevention <dt pn="section-7.1-2.1">Confidentiality:</dt>
against messages sent previously over a TLS connection (such as DNS P <dd pn="section-7.1-2.2">All application-layer communication is encryp
ush Notifications). ted with the goal
If prior messages are re-sent at a later time as a form of a man-in-t that no party should be able to decrypt it except the intended
he-middle attack receiver.</dd>
then the receiver will detect this and reject the replayed messages.< <dt pn="section-7.1-2.3">Data integrity protection:</dt>
/t> <dd pn="section-7.1-2.4">Any changes made to the communication in tran
</list> sit are detectable
</t> by the receiver.</dd>
<t>Deployment recommendations on the appropriate key lengths and cypher s <dt pn="section-7.1-2.5">Authentication:</dt>
uites are beyond the scope of this document. Please refer to <xref target="BCP19 <dd pn="section-7.1-2.6">An endpoint of the TLS communication is authe
5">TLS Recommendations</xref> for the best current practices. Keep in mind that nticated as the
best practices only exist for a snapshot in time and recommendations will contin intended entity to communicate with.</dd>
ue to change. Updated versions or errata may exist for these recommendations.</t <dt pn="section-7.1-2.7">Anti-replay protection:</dt>
> <dd pn="section-7.1-2.8">TLS provides for the detection of and prevent
</section> ion
against messages sent previously over a TLS connection (such as DNS
<section title="TLS Name Authentication" anchor="tls_name_auth"> Push Notifications).
<t>As described in <xref target="discovery"/>, the client discovers the D If prior messages are re-sent at a later time as a form of a
NS Push Notification server using an SRV lookup for the record name <spanx style man-in-the-middle attack,
="verb">_dns&nbhy;push&nbhy;tls._tcp.&lt;zone&gt;</spanx>. The server connection then the receiver will detect this and reject the replayed
endpoint SHOULD then be authenticated using DANE TLSA records for the associate messages.</dd>
d SRV record. This associates the target's name and port number with a trusted T </dl>
LS certificate <xref target="RFC7673"/>. This procedure uses the TLS Server Name <t pn="section-7.1-3">Deployment recommendations on the appropriate key
Indication (SNI) extension <xref target="RFC6066"/> to inform the server of the lengths and
name the client has authenticated through the use of TLSA records. Therefore, i cipher suites are beyond the scope of this document. Please refer to
f the SRV record passes DNSSEC validation and a TLSA record matching the target the current
name is useable, an SNI extension must be used for the target name to ensure the TLS Recommendations <xref target="BCP195" format="default" sectionFormat=
client is connecting to the server it has authenticated. If the target name doe "of" derivedContent="BCP195"/>
s not have a usable TLSA record, then the use of the SNI extension is optional. for the best current practices.
See <xref target="RFC8310">Usage Profiles for DNS over TLS and DNS over DTLS</xr Keep in mind that best practices only exist for a snapshot in time,
ef> for more information on authenticating domain names.</t> and recommendations will continue to change.
</section> Updated versions or errata may exist for these recommendations.</t>
</section>
<section title="TLS Early Data" anchor="early_data"> <section anchor="tls_name_auth" numbered="true" toc="include" removeInRFC=
<t>DSO messages with the SUBSCRIBE TLV as the Primary TLV are permitted i "false" pn="section-7.2">
n TLS early data. <name slugifiedName="name-tls-name-authentication">TLS Name Authenticati
Using TLS early data can save one network round trip, and can result in t on</name>
he client obtaining results faster.</t> <t pn="section-7.2-1">As described in <xref target="discovery" format="d
efault" sectionFormat="of" derivedContent="Section 6.1"/>, the
<t>However, there are some factors to consider before using TLS early dat client discovers the DNS Push Notification server using an SRV lookup
a.</t> for the record name
<tt>_dns‑push‑tls._tcp.&lt;zone&gt;</tt>. The server
<t>TLS Early Data is not forward secret. connection endpoint <bcp14>SHOULD</bcp14> then be authenticated using
In cases where forward secrecy of DNS Push Notification subscriptions is DANE TLSA records for the associated SRV record. This associates the
required, target's name and port number with a trusted TLS certificate <xref targe
the client should not use TLS Early Data.</t> t="RFC7673" format="default" sectionFormat="of" derivedContent="RFC7673"/>. This
procedure uses the TLS
<t>With TLS early data there are no guarantees of non-replay between conn Server Name Indication (SNI) extension <xref target="RFC6066" format="de
ections. fault" sectionFormat="of" derivedContent="RFC6066"/> to inform the server of the
name the client has
authenticated through the use of TLSA records. Therefore, if the SRV
record passes DNSSEC validation and a TLSA record matching the target
name is usable, an SNI extension must be used for the target name to
ensure the client is connecting to the server it has authenticated. If
the target name does not have a usable TLSA record, then the use of
the SNI extension is optional. See Usage Profiles for DNS over TLS and
DNS over DTLS <xref target="RFC8310" format="default" sectionFormat="of"
derivedContent="RFC8310"/> for more
information on authenticating domain names.</t>
</section>
<section anchor="early_data" numbered="true" toc="include" removeInRFC="fa
lse" pn="section-7.3">
<name slugifiedName="name-tls-early-data">TLS Early Data</name>
<t pn="section-7.3-1">DSO messages with the SUBSCRIBE TLV as the Primary
TLV are
permitted in TLS early data.
Using TLS early data can save one network round trip and can result in
the client obtaining results faster.</t>
<t pn="section-7.3-2">However, there are some factors to consider before
using TLS early
data.</t>
<t pn="section-7.3-3">TLS early data is not forward secret.
In cases where forward secrecy of DNS Push Notification subscriptions
is required,
the client should not use TLS early data.</t>
<t pn="section-7.3-4">With TLS early data, there are no guarantees of no
n-replay between
connections.
If packets are duplicated and delayed in the network, If packets are duplicated and delayed in the network,
the later arrivals could be mistaken for new subscription requests. the later arrivals could be mistaken for new subscription requests.
Generally this is not a major concern, Generally, this is not a major concern
since the amount of state generated on the server for since the amount of state generated on the server for
these spurious subscriptions is small and short-lived, these spurious subscriptions is small and short lived
since the TCP connection will not complete the three-way handshake. since the TCP connection will not complete the three-way handshake.
Servers MAY choose to implement rate-limiting measures that are activated Servers <bcp14>MAY</bcp14> choose to implement rate-limiting measures
when that are activated when
the server detects an excessive number of spurious subscription requests. the server detects an excessive number of spurious subscription
</t> requests.</t>
<t pn="section-7.3-5">For further guidance on use of TLS early data, ple
<t>For further guidance please see discussion of zero round-trip data ase see
(Section 2.3, Section 8, and Appendix E.5) discussion of zero round-trip data
in the TLS 1.3 specification, <xref target="RFC8446"/>.</t> in Sections <xref target="RFC8446" sectionFormat="bare" section="2.3" for
</section> mat="default" derivedLink="https://rfc-editor.org/rfc/rfc8446#section-2.3" deriv
edContent="RFC8446"/>
<section title="TLS Session Resumption" anchor="resumption"> and
<t>TLS Session Resumption <xref target="RFC8446"/> <xref target="RFC8446" sectionFormat="bare" section="8" format="default"
derivedLink="https://rfc-editor.org/rfc/rfc8446#section-8" derivedContent="RFC84
46"/>, and Appendix
<xref target="RFC8446" sectionFormat="bare" section="E.5" format="default
" derivedLink="https://rfc-editor.org/rfc/rfc8446#appendix-E.5" derivedContent="
RFC8446"/>, of <xref target="RFC8446" format="default" sectionFormat="of" derive
dContent="RFC8446">the TLS 1.3 specification</xref>.</t>
</section>
<section anchor="resumption" numbered="true" toc="include" removeInRFC="fa
lse" pn="section-7.4">
<name slugifiedName="name-tls-session-resumption">TLS Session Resumption
</name>
<t pn="section-7.4-1">TLS session resumption <xref target="RFC8446" form
at="default" sectionFormat="of" derivedContent="RFC8446"/>
is permissible on DNS Push Notification servers. is permissible on DNS Push Notification servers.
However, closing the TLS connection terminates the DSO session. However, closing the TLS connection terminates the DSO session.
When the TLS session is resumed, the DNS Push Notification server will no When the TLS session is resumed, the DNS Push Notification server will
t not
have any subscription state and will proceed as with any other new DSO se have any subscription state and will proceed as with any other new DSO
ssion. session.
Use of TLS Session Resumption may allow a TLS connection to be set up mor Use of TLS session resumption may allow a TLS connection to be set up
e quickly, more quickly,
but the client will still have to recreate any desired subscriptions.</t> but the client will still have to recreate any desired
<?rfc needLines="30" ?> subscriptions.</t>
</section> </section>
</section> </section>
<section anchor="IANA" numbered="true" toc="include" removeInRFC="false" pn=
<section title="IANA Considerations" anchor="IANA"> "section-8">
<name slugifiedName="name-iana-considerations">IANA Considerations</name>
<t>This document defines a new service name, only applicable for the TCP pr <t pn="section-8-1">This document defines a new service name, only applica
otocol, ble for the TCP
to be recorded in the IANA Service Type Registry <xref target="RFC6335"/><x protocol,
ref target="SRVTYPE"/>.</t> which has been recorded in the IANA "Service Name and Transport Protocol
<texttable title="IANA Service Type Assignments" anchor="iana_service_table Port Number Registry" <xref target="RFC6335" format="default" sectionForma
"> t="of" derivedContent="RFC6335"/> <xref target="SRVTYPE" format="default" sectio
<ttcol width="25%" align="left">Name</ttcol> nFormat="of" derivedContent="SRVTYPE"/>.</t>
<ttcol align="center">Port</ttcol> <table anchor="iana_service_table" align="center" pn="table-4">
<ttcol align="center">Value</ttcol> <name slugifiedName="name-iana-service-type-assignmen">IANA Service Type
<ttcol align="left">Definition</ttcol> Assignments</name>
<c>DNS Push Notification Service Type</c> <thead>
<c>None</c> <tr>
<c><spanx style="verb">_dns&nbhy;push&nbhy;tls._tcp</spanx></c> <th align="left" colspan="1" rowspan="1">Name</th>
<c><xref target="discovery"/></c> <th align="center" colspan="1" rowspan="1">Port</th>
</texttable> <th align="center" colspan="1" rowspan="1">Value</th>
<th align="center" colspan="1" rowspan="1">Section</th>
<t>This document defines four new DNS Stateful Operation TLV types </tr>
to be recorded in the IANA DSO Type Code Registry <xref target="RFC8490"/>< </thead>
xref target="DSOTYPE"/>.</t> <tbody>
<texttable title="IANA DSO TLV Type Code Assignments" anchor="iana_tlv_tabl <tr>
e"> <td align="left" colspan="1" rowspan="1">DNS Push Notification Servi
<ttcol align="left" >Name</ttcol> ce Type</td>
<ttcol align="center" width="18%">Value</ttcol> <td align="center" colspan="1" rowspan="1">None</td>
<ttcol align="center" >Early Data</ttcol> <td align="center" colspan="1" rowspan="1">
<ttcol align="center" width="28%">Status</ttcol> <tt>_dns‑push‑tls._tcp</tt></td>
<ttcol align="left" width="20%">Definition</ttcol> <td align="center" colspan="1" rowspan="1">
<c>SUBSCRIBE</c> <xref target="discovery" format="counter" sectionFormat="of" deriv
<c>TBA (0x40)</c> edContent="6.1"/></td>
<c>OK</c> </tr>
<c>Standards Track</c> </tbody>
<c><xref target="subscribe"/></c> </table>
<c>PUSH</c> <t pn="section-8-3">This document defines four new DNS Stateful Operation
<c>TBA (0x41)</c> TLV types,
<c>NO</c> which have been recorded in the IANA "DSO Type Codes" registry <xref target
<c>Standards Track</c> ="RFC8490" format="default" sectionFormat="of" derivedContent="RFC8490"/> <xref
<c><xref target="push"/></c> target="DSOTYPE" format="default" sectionFormat="of" derivedContent="DSOTYPE"/>.
<c>UNSUBSCRIBE</c> </t>
<c>TBA (0x42)</c> <table anchor="iana_tlv_table" align="center" pn="table-5">
<c>NO</c> <name slugifiedName="name-iana-dso-tlv-type-code-assi">IANA DSO TLV Type
<c>Standards Track</c> Code Assignments</name>
<c><xref target="unsubscribe"/></c> <thead>
<c>RECONFIRM</c> <tr>
<c>TBA (0x43)</c> <th align="left" colspan="1" rowspan="1">Name</th>
<c>NO</c> <th align="center" colspan="1" rowspan="1">Value</th>
<c>Standards Track</c> <th align="center" colspan="1" rowspan="1">Early Data</th>
<c><xref target="reconfirm"/></c> <th align="center" colspan="1" rowspan="1">Status</th>
</texttable> <th align="center" colspan="1" rowspan="1">Section</th>
</tr>
<t>This document defines no new DNS OPCODEs or RCODEs.</t> </thead>
<tbody>
<?rfc needLines="12" ?> <tr>
</section> <td align="left" colspan="1" rowspan="1">SUBSCRIBE</td>
<td align="center" colspan="1" rowspan="1">0x0040</td>
<section title="Acknowledgements" anchor="Acknowledgements"> <td align="center" colspan="1" rowspan="1">OK</td>
<t>The authors would like to thank Kiren Sekar and Marc Krochmal for previo <td align="center" colspan="1" rowspan="1">Standards Track</td>
us work completed in this field.</t> <td align="center" colspan="1" rowspan="1">
<xref target="subscribe" format="counter" sectionFormat="of" deriv
<t>This draft has been improved due to comments from edContent="6.2"/></td>
Ran Atkinson, </tr>
Tim Chown, <tr>
Sara Dickinson, <td align="left" colspan="1" rowspan="1">PUSH</td>
Mark Delany, <td align="center" colspan="1" rowspan="1">0x0041</td>
Ralph Droms, <td align="center" colspan="1" rowspan="1">NO</td>
Jan Komissar, <td align="center" colspan="1" rowspan="1">Standards Track</td>
Eric Rescorla, <td align="center" colspan="1" rowspan="1">
Michael Richardson, <xref target="push" format="counter" sectionFormat="of" derivedCon
David Schinazi, tent="6.3"/></td>
Manju Shankar Rao, </tr>
Robert Sparks, <tr>
Markus Stenberg, <td align="left" colspan="1" rowspan="1">UNSUBSCRIBE</td>
Andrew Sullivan, <td align="center" colspan="1" rowspan="1">0x0042</td>
Michael Sweet, <td align="center" colspan="1" rowspan="1">NO</td>
Dave Thaler, <td align="center" colspan="1" rowspan="1">Standards Track</td>
Brian Trammell, <td align="center" colspan="1" rowspan="1">
Bernie Volz, <xref target="unsubscribe" format="counter" sectionFormat="of" der
Eric Vyncke, ivedContent="6.4"/></td>
Christopher Wood, </tr>
Liang Xia, <tr>
<td align="left" colspan="1" rowspan="1">RECONFIRM</td>
<td align="center" colspan="1" rowspan="1">0x0043</td>
<td align="center" colspan="1" rowspan="1">NO</td>
<td align="center" colspan="1" rowspan="1">Standards Track</td>
<td align="center" colspan="1" rowspan="1">
<xref target="reconfirm" format="counter" sectionFormat="of" deriv
edContent="6.5"/></td>
</tr>
</tbody>
</table>
<t pn="section-8-5">This document defines no new DNS OPCODEs or RCODEs.</t
>
</section>
</middle>
<back>
<displayreference target="I-D.ietf-tcpm-rack" to="TCPRACK"/>
<references pn="section-9">
<name slugifiedName="name-references">References</name>
<references pn="section-9.1">
<name slugifiedName="name-normative-references">Normative References</na
me>
<reference anchor="DSOTYPE" target="https://www.iana.org/assignments/dns
-parameters/" quoteTitle="true" derivedAnchor="DSOTYPE">
<front>
<title>Domain Name System (DNS) Parameters</title>
<author>
<organization showOnFrontPage="true">IANA</organization>
</author>
</front>
</reference>
<reference anchor="RFC0020" target="https://www.rfc-editor.org/info/rfc2
0" quoteTitle="true" derivedAnchor="RFC0020">
<front>
<title>ASCII format for network interchange</title>
<author initials="V.G." surname="Cerf" fullname="V.G. Cerf">
<organization showOnFrontPage="true"/>
</author>
<date year="1969" month="October"/>
</front>
<seriesInfo name="STD" value="80"/>
<seriesInfo name="RFC" value="20"/>
<seriesInfo name="DOI" value="10.17487/RFC0020"/>
</reference>
<reference anchor="RFC0768" target="https://www.rfc-editor.org/info/rfc7
68" quoteTitle="true" derivedAnchor="RFC0768">
<front>
<title>User Datagram Protocol</title>
<author initials="J." surname="Postel" fullname="J. Postel">
<organization showOnFrontPage="true"/>
</author>
<date year="1980" month="August"/>
</front>
<seriesInfo name="STD" value="6"/>
<seriesInfo name="RFC" value="768"/>
<seriesInfo name="DOI" value="10.17487/RFC0768"/>
</reference>
<reference anchor="RFC0793" target="https://www.rfc-editor.org/info/rfc7
93" quoteTitle="true" derivedAnchor="RFC0793">
<front>
<title>Transmission Control Protocol</title>
<author initials="J." surname="Postel" fullname="J. Postel">
<organization showOnFrontPage="true"/>
</author>
<date year="1981" month="September"/>
</front>
<seriesInfo name="STD" value="7"/>
<seriesInfo name="RFC" value="793"/>
<seriesInfo name="DOI" value="10.17487/RFC0793"/>
</reference>
<reference anchor="RFC1034" target="https://www.rfc-editor.org/info/rfc1
034" quoteTitle="true" derivedAnchor="RFC1034">
<front>
<title>Domain names - concepts and facilities</title>
<author initials="P.V." surname="Mockapetris" fullname="P.V. Mockape
tris">
<organization showOnFrontPage="true"/>
</author>
<date year="1987" month="November"/>
<abstract>
<t>This RFC is the revised basic definition of The Domain Name Sys
tem. It obsoletes RFC-882. This memo describes the domain style names and thei
r used for host address look up and electronic mail forwarding. It discusses th
e clients and servers in the domain name system and the protocol used between th
em.</t>
</abstract>
</front>
<seriesInfo name="STD" value="13"/>
<seriesInfo name="RFC" value="1034"/>
<seriesInfo name="DOI" value="10.17487/RFC1034"/>
</reference>
<reference anchor="RFC1035" target="https://www.rfc-editor.org/info/rfc1
035" quoteTitle="true" derivedAnchor="RFC1035">
<front>
<title>Domain names - implementation and specification</title>
<author initials="P.V." surname="Mockapetris" fullname="P.V. Mockape
tris">
<organization showOnFrontPage="true"/>
</author>
<date year="1987" month="November"/>
<abstract>
<t>This RFC is the revised specification of the protocol and forma
t used in the implementation of the Domain Name System. It obsoletes RFC-883. T
his memo documents the details of the domain name client - server communication.
</t>
</abstract>
</front>
<seriesInfo name="STD" value="13"/>
<seriesInfo name="RFC" value="1035"/>
<seriesInfo name="DOI" value="10.17487/RFC1035"/>
</reference>
<reference anchor="RFC1123" target="https://www.rfc-editor.org/info/rfc1
123" quoteTitle="true" derivedAnchor="RFC1123">
<front>
<title>Requirements for Internet Hosts - Application and Support</ti
tle>
<author initials="R." surname="Braden" fullname="R. Braden" role="ed
itor">
<organization showOnFrontPage="true"/>
</author>
<date year="1989" month="October"/>
<abstract>
<t>This RFC is an official specification for the Internet communit
y. It incorporates by reference, amends, corrects, and supplements the primary
protocol standards documents relating to hosts. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="STD" value="3"/>
<seriesInfo name="RFC" value="1123"/>
<seriesInfo name="DOI" value="10.17487/RFC1123"/>
</reference>
<reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2
119" quoteTitle="true" derivedAnchor="RFC2119">
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</tit
le>
<author initials="S." surname="Bradner" fullname="S. Bradner">
<organization showOnFrontPage="true"/>
</author>
<date year="1997" month="March"/>
<abstract>
<t>In many standards track documents several words are used to sig
nify the requirements in the specification. These words are often capitalized.
This document defines these words as they should be interpreted in IETF document
s. This document specifies an Internet Best Current Practices for the Internet
Community, and requests discussion and suggestions for improvements.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/>
<seriesInfo name="DOI" value="10.17487/RFC2119"/>
</reference>
<reference anchor="RFC2136" target="https://www.rfc-editor.org/info/rfc2
136" quoteTitle="true" derivedAnchor="RFC2136">
<front>
<title>Dynamic Updates in the Domain Name System (DNS UPDATE)</title
>
<author initials="P." surname="Vixie" fullname="P. Vixie" role="edit
or">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Thomson" fullname="S. Thomson">
<organization showOnFrontPage="true"/>
</author>
<author initials="Y." surname="Rekhter" fullname="Y. Rekhter">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Bound" fullname="J. Bound">
<organization showOnFrontPage="true"/>
</author>
<date year="1997" month="April"/>
<abstract>
<t>Using this specification of the UPDATE opcode, it is possible t
o add or delete RRs or RRsets from a specified zone. Prerequisites are specifie
d separately from update operations, and can specify a dependency upon either th
e previous existence or nonexistence of an RRset, or the existence of a single R
R. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2136"/>
<seriesInfo name="DOI" value="10.17487/RFC2136"/>
</reference>
<reference anchor="RFC2181" target="https://www.rfc-editor.org/info/rfc2
181" quoteTitle="true" derivedAnchor="RFC2181">
<front>
<title>Clarifications to the DNS Specification</title>
<author initials="R." surname="Elz" fullname="R. Elz">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Bush" fullname="R. Bush">
<organization showOnFrontPage="true"/>
</author>
<date year="1997" month="July"/>
<abstract>
<t>This document considers some areas that have been identified as
problems with the specification of the Domain Name System, and proposes remedie
s for the defects identified. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2181"/>
<seriesInfo name="DOI" value="10.17487/RFC2181"/>
</reference>
<reference anchor="RFC2782" target="https://www.rfc-editor.org/info/rfc2
782" quoteTitle="true" derivedAnchor="RFC2782">
<front>
<title>A DNS RR for specifying the location of services (DNS SRV)</t
itle>
<author initials="A." surname="Gulbrandsen" fullname="A. Gulbrandsen
">
<organization showOnFrontPage="true"/>
</author>
<author initials="P." surname="Vixie" fullname="P. Vixie">
<organization showOnFrontPage="true"/>
</author>
<author initials="L." surname="Esibov" fullname="L. Esibov">
<organization showOnFrontPage="true"/>
</author>
<date year="2000" month="February"/>
<abstract>
<t>This document describes a DNS RR which specifies the location o
f the server(s) for a specific protocol and domain. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2782"/>
<seriesInfo name="DOI" value="10.17487/RFC2782"/>
</reference>
<reference anchor="RFC6066" target="https://www.rfc-editor.org/info/rfc6
066" quoteTitle="true" derivedAnchor="RFC6066">
<front>
<title>Transport Layer Security (TLS) Extensions: Extension Definiti
ons</title>
<author initials="D." surname="Eastlake 3rd" fullname="D. Eastlake 3
rd">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="January"/>
<abstract>
<t>This document provides specifications for existing TLS extensio
ns. It is a companion document for RFC 5246, "The Transport Layer Security (TLS
) Protocol Version 1.2". The extensions specified are server_name, max_fragment
_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_req
uest. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6066"/>
<seriesInfo name="DOI" value="10.17487/RFC6066"/>
</reference>
<reference anchor="RFC6335" target="https://www.rfc-editor.org/info/rfc6
335" quoteTitle="true" derivedAnchor="RFC6335">
<front>
<title>Internet Assigned Numbers Authority (IANA) Procedures for the
Management of the Service Name and Transport Protocol Port Number Registry</tit
le>
<author initials="M." surname="Cotton" fullname="M. Cotton">
<organization showOnFrontPage="true"/>
</author>
<author initials="L." surname="Eggert" fullname="L. Eggert">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Touch" fullname="J. Touch">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Westerlund" fullname="M. Westerlund">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="August"/>
<abstract>
<t>This document defines the procedures that the Internet Assigned
Numbers Authority (IANA) uses when handling assignment and other requests relat
ed to the Service Name and Transport Protocol Port Number registry. It also dis
cusses the rationale and principles behind these procedures and how they facilit
ate the long-term sustainability of the registry.</t>
<t>This document updates IANA's procedures by obsoleting the previ
ous UDP and TCP port assignment procedures defined in Sections 8 and 9.1 of the
IANA Allocation Guidelines, and it updates the IANA service name and port assign
ment procedures for UDP-Lite, the Datagram Congestion Control Protocol (DCCP), a
nd the Stream Control Transmission Protocol (SCTP). It also updates the DNS SRV
specification to clarify what a service name is and how it is registered. This
memo documents an Internet Best Current Practice.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="165"/>
<seriesInfo name="RFC" value="6335"/>
<seriesInfo name="DOI" value="10.17487/RFC6335"/>
</reference>
<reference anchor="RFC6895" target="https://www.rfc-editor.org/info/rfc6
895" quoteTitle="true" derivedAnchor="RFC6895">
<front>
<title>Domain Name System (DNS) IANA Considerations</title>
<author initials="D." surname="Eastlake 3rd" fullname="D. Eastlake 3
rd">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="April"/>
<abstract>
<t>This document specifies Internet Assigned Numbers Authority (IA
NA) parameter assignment considerations for the allocation of Domain Name System
(DNS) resource record types, CLASSes, operation codes, error codes, DNS protoco
l message header bits, and AFSDB resource record subtypes. It obsoletes RFC 619
5 and updates RFCs 1183, 2845, 2930, and 3597.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="42"/>
<seriesInfo name="RFC" value="6895"/>
<seriesInfo name="DOI" value="10.17487/RFC6895"/>
</reference>
<reference anchor="RFC7673" target="https://www.rfc-editor.org/info/rfc7
673" quoteTitle="true" derivedAnchor="RFC7673">
<front>
<title>Using DNS-Based Authentication of Named Entities (DANE) TLSA
Records with SRV Records</title>
<author initials="T." surname="Finch" fullname="T. Finch">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Miller" fullname="M. Miller">
<organization showOnFrontPage="true"/>
</author>
<author initials="P." surname="Saint-Andre" fullname="P. Saint-Andre
">
<organization showOnFrontPage="true"/>
</author>
<date year="2015" month="October"/>
<abstract>
<t>The DNS-Based Authentication of Named Entities (DANE) specifica
tion (RFC 6698) describes how to use TLSA resource records secured by DNSSEC (RF
C 4033) to associate a server's connection endpoint with its Transport Layer Sec
urity (TLS) certificate (thus enabling administrators of domain names to specify
the keys used in that domain's TLS servers). However, application protocols th
at use SRV records (RFC 2782) to indirectly name the target server connection en
dpoints for a service domain name cannot apply the rules from RFC 6698. Therefo
re, this document provides guidelines that enable such protocols to locate and u
se TLSA records.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7673"/>
<seriesInfo name="DOI" value="10.17487/RFC7673"/>
</reference>
<reference anchor="RFC7766" target="https://www.rfc-editor.org/info/rfc7
766" quoteTitle="true" derivedAnchor="RFC7766">
<front>
<title>DNS Transport over TCP - Implementation Requirements</title>
<author initials="J." surname="Dickinson" fullname="J. Dickinson">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Dickinson" fullname="S. Dickinson">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Bellis" fullname="R. Bellis">
<organization showOnFrontPage="true"/>
</author>
<author initials="A." surname="Mankin" fullname="A. Mankin">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="Wessels" fullname="D. Wessels">
<organization showOnFrontPage="true"/>
</author>
<date year="2016" month="March"/>
<abstract>
<t>This document specifies the requirement for support of TCP as a
transport protocol for DNS implementations and provides guidelines towards DNS-
over-TCP performance on par with that of DNS-over-UDP. This document obsoletes R
FC 5966 and therefore updates RFC 1035 and RFC 1123.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7766"/>
<seriesInfo name="DOI" value="10.17487/RFC7766"/>
</reference>
<reference anchor="RFC7858" target="https://www.rfc-editor.org/info/rfc7
858" quoteTitle="true" derivedAnchor="RFC7858">
<front>
<title>Specification for DNS over Transport Layer Security (TLS)</ti
tle>
<author initials="Z." surname="Hu" fullname="Z. Hu">
<organization showOnFrontPage="true"/>
</author>
<author initials="L." surname="Zhu" fullname="L. Zhu">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Heidemann" fullname="J. Heidemann">
<organization showOnFrontPage="true"/>
</author>
<author initials="A." surname="Mankin" fullname="A. Mankin">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="Wessels" fullname="D. Wessels">
<organization showOnFrontPage="true"/>
</author>
<author initials="P." surname="Hoffman" fullname="P. Hoffman">
<organization showOnFrontPage="true"/>
</author>
<date year="2016" month="May"/>
<abstract>
<t>This document describes the use of Transport Layer Security (TL
S) to provide privacy for DNS. Encryption provided by TLS eliminates opportunit
ies for eavesdropping and on-path tampering with DNS queries in the network, suc
h as discussed in RFC 7626. In addition, this document specifies two usage prof
iles for DNS over TLS and provides advice on performance considerations to minim
ize overhead from using TCP and TLS with DNS.</t>
<t>This document focuses on securing stub-to-recursive traffic, as
per the charter of the DPRIVE Working Group. It does not prevent future applic
ations of the protocol to recursive-to-authoritative traffic.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7858"/>
<seriesInfo name="DOI" value="10.17487/RFC7858"/>
</reference>
<reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8
174" quoteTitle="true" derivedAnchor="RFC8174">
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</ti
tle>
<author initials="B." surname="Leiba" fullname="B. Leiba">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="May"/>
<abstract>
<t>RFC 2119 specifies common key words that may be used in protoco
l specifications. This document aims to reduce the ambiguity by clarifying tha
t only UPPERCASE usage of the key words have the defined special meanings.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="8174"/>
<seriesInfo name="DOI" value="10.17487/RFC8174"/>
</reference>
<reference anchor="RFC8310" target="https://www.rfc-editor.org/info/rfc8
310" quoteTitle="true" derivedAnchor="RFC8310">
<front>
<title>Usage Profiles for DNS over TLS and DNS over DTLS</title>
<author initials="S." surname="Dickinson" fullname="S. Dickinson">
<organization showOnFrontPage="true"/>
</author>
<author initials="D." surname="Gillmor" fullname="D. Gillmor">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Reddy" fullname="T. Reddy">
<organization showOnFrontPage="true"/>
</author>
<date year="2018" month="March"/>
<abstract>
<t>This document discusses usage profiles, based on one or more au
thentication mechanisms, which can be used for DNS over Transport Layer Security
(TLS) or Datagram TLS (DTLS). These profiles can increase the privacy of DNS t
ransactions compared to using only cleartext DNS. This document also specifies
new authentication mechanisms -- it describes several ways that a DNS client can
use an authentication domain name to authenticate a (D)TLS connection to a DNS
server. Additionally, it defines (D)TLS protocol profiles for DNS clients and s
ervers implementing DNS over (D)TLS. This document updates RFC 7858.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8310"/>
<seriesInfo name="DOI" value="10.17487/RFC8310"/>
</reference>
<reference anchor="RFC8446" target="https://www.rfc-editor.org/info/rfc8
446" quoteTitle="true" derivedAnchor="RFC8446">
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.3</titl
e>
<author initials="E." surname="Rescorla" fullname="E. Rescorla">
<organization showOnFrontPage="true"/>
</author>
<date year="2018" month="August"/>
<abstract>
<t>This document specifies version 1.3 of the Transport Layer Secu
rity (TLS) protocol. TLS allows client/server applications to communicate over
the Internet in a way that is designed to prevent eavesdropping, tampering, and
message forgery.</t>
<t>This document updates RFCs 5705 and 6066, and obsoletes RFCs 50
77, 5246, and 6961. This document also specifies new requirements for TLS 1.2 i
mplementations.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8446"/>
<seriesInfo name="DOI" value="10.17487/RFC8446"/>
</reference>
<reference anchor="RFC8490" target="https://www.rfc-editor.org/info/rfc8
490" quoteTitle="true" derivedAnchor="RFC8490">
<front>
<title>DNS Stateful Operations</title>
<author initials="R." surname="Bellis" fullname="R. Bellis">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Dickinson" fullname="J. Dickinson">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Dickinson" fullname="S. Dickinson">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Lemon" fullname="T. Lemon">
<organization showOnFrontPage="true"/>
</author>
<author initials="T." surname="Pusateri" fullname="T. Pusateri">
<organization showOnFrontPage="true"/>
</author>
<date year="2019" month="March"/>
<abstract>
<t>This document defines a new DNS OPCODE for DNS Stateful Operati
ons (DSO). DSO messages communicate operations within persistent stateful sessi
ons using Type Length Value (TLV) syntax. Three TLVs are defined that manage se
ssion timeouts, termination, and encryption padding, and a framework is defined
for extensions to enable new stateful operations. This document updates RFC 103
5 by adding a new DNS header OPCODE that has both different message semantics an
d a new result code. This document updates RFC 7766 by redefining a session, pr
oviding new guidance on connection reuse, and providing a new mechanism for hand
ling session idle timeouts.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8490"/>
<seriesInfo name="DOI" value="10.17487/RFC8490"/>
</reference>
<reference anchor="SRVTYPE" target="https://www.iana.org/assignments/ser
vice-names-port-numbers/" quoteTitle="true" derivedAnchor="SRVTYPE">
<front>
<title>Service Name and Transport Protocol Port Number Registry</tit
le>
<author>
<organization showOnFrontPage="true">IANA</organization>
</author>
</front>
</reference>
</references>
<references pn="section-9.2">
<name slugifiedName="name-informative-references">Informative References
</name>
<reference anchor="BCP195" target="https://www.rfc-editor.org/info/bcp19
5" quoteTitle="true" derivedAnchor="BCP195">
<front>
<title>Recommendations for Secure Use of Transport Layer Security (T
LS) and Datagram Transport Layer Security (DTLS)</title>
<author initials="Y." surname="Sheffer" fullname="Y. Sheffer">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Holz" fullname="R. Holz">
<organization showOnFrontPage="true"/>
</author>
<author initials="P." surname="Saint-Andre" fullname="P. Saint-Andre
">
<organization showOnFrontPage="true"/>
</author>
<date year="2015" month="May"/>
</front>
<seriesInfo name="BCP" value="195"/>
<seriesInfo name="RFC" value="7525"/>
</reference>
<reference anchor="OBS" target="https://en.wikipedia.org/w/index.php?tit
le=Observer_pattern&amp;oldid=939702131" quoteTitle="true" derivedAnchor="OBS">
<front>
<title>Observer pattern</title>
<author>
<organization showOnFrontPage="true">Wikipedia</organization>
</author>
<date month="February" year="2020"/>
</front>
</reference>
<reference anchor="RFC2308" target="https://www.rfc-editor.org/info/rfc2
308" quoteTitle="true" derivedAnchor="RFC2308">
<front>
<title>Negative Caching of DNS Queries (DNS NCACHE)</title>
<author initials="M." surname="Andrews" fullname="M. Andrews">
<organization showOnFrontPage="true"/>
</author>
<date year="1998" month="March"/>
<abstract>
<t>RFC1034 provided a description of how to cache negative respons
es. It however had a fundamental flaw in that it did not allow a name server to
hand out those cached responses to other resolvers, thereby greatly reducing th
e effect of the caching. This document addresses issues raise in the light of e
xperience and replaces RFC1034 Section 4.3.4. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2308"/>
<seriesInfo name="DOI" value="10.17487/RFC2308"/>
</reference>
<reference anchor="RFC3123" target="https://www.rfc-editor.org/info/rfc3
123" quoteTitle="true" derivedAnchor="RFC3123">
<front>
<title>A DNS RR Type for Lists of Address Prefixes (APL RR)</title>
<author initials="P." surname="Koch" fullname="P. Koch">
<organization showOnFrontPage="true"/>
</author>
<date year="2001" month="June"/>
<abstract>
<t>The Domain Name System (DNS) is primarily used to translate dom
ain names into IPv4 addresses using A RRs (Resource Records). Several approache
s exist to describe networks or address ranges. This document specifies a new D
NS RR type "APL" for address prefix lists. This memo defines an Experimental Pr
otocol for the Internet community.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3123"/>
<seriesInfo name="DOI" value="10.17487/RFC3123"/>
</reference>
<reference anchor="RFC4287" target="https://www.rfc-editor.org/info/rfc4
287" quoteTitle="true" derivedAnchor="RFC4287">
<front>
<title>The Atom Syndication Format</title>
<author initials="M." surname="Nottingham" fullname="M. Nottingham"
role="editor">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Sayre" fullname="R. Sayre" role="edit
or">
<organization showOnFrontPage="true"/>
</author>
<date year="2005" month="December"/>
<abstract>
<t>This document specifies Atom, an XML-based Web content and meta
data syndication format. [STANDARDS-TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4287"/>
<seriesInfo name="DOI" value="10.17487/RFC4287"/>
</reference>
<reference anchor="RFC4953" target="https://www.rfc-editor.org/info/rfc4
953" quoteTitle="true" derivedAnchor="RFC4953">
<front>
<title>Defending TCP Against Spoofing Attacks</title>
<author initials="J." surname="Touch" fullname="J. Touch">
<organization showOnFrontPage="true"/>
</author>
<date year="2007" month="July"/>
<abstract>
<t>Recent analysis of potential attacks on core Internet infrastru
cture indicates an increased vulnerability of TCP connections to spurious resets
(RSTs), sent with forged IP source addresses (spoofing). TCP has always been s
usceptible to such RST spoofing attacks, which were indirectly protected by chec
king that the RST sequence number was inside the current receive window, as well
as via the obfuscation of TCP endpoint and port numbers. For pairs of well-kno
wn endpoints often over predictable port pairs, such as BGP or between web serve
rs and well-known large-scale caches, increases in the path bandwidth-delay prod
uct of a connection have sufficiently increased the receive window space that of
f-path third parties can brute-force generate a viable RST sequence number. The
susceptibility to attack increases with the square of the bandwidth, and thus p
resents a significant vulnerability for recent high-speed networks. This docume
nt addresses this vulnerability, discussing proposed solutions at the transport
level and their inherent challenges, as well as existing network level solutions
and the feasibility of their deployment. This document focuses on vulnerabilit
ies due to spoofed TCP segments, and includes a discussion of related ICMP spoof
ing attacks on TCP connections. This memo provides information for the Internet
community.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4953"/>
<seriesInfo name="DOI" value="10.17487/RFC4953"/>
</reference>
<reference anchor="RFC6281" target="https://www.rfc-editor.org/info/rfc6
281" quoteTitle="true" derivedAnchor="RFC6281">
<front>
<title>Understanding Apple's Back to My Mac (BTMM) Service</title>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="Z." surname="Zhu" fullname="Z. Zhu">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Wakikawa" fullname="R. Wakikawa">
<organization showOnFrontPage="true"/>
</author>
<author initials="L." surname="Zhang" fullname="L. Zhang">
<organization showOnFrontPage="true"/>
</author>
<date year="2011" month="June"/>
<abstract>
<t>This document describes the implementation of Apple Inc.'s Back
to My Mac (BTMM) service. BTMM provides network connectivity between devices s
o that a user can perform file sharing and screen sharing among multiple compute
rs at home, at work, or on the road. The implementation of BTMM addresses the i
ssues of single sign-on authentication, secure data communication, service disco
very, and end-to-end connectivity in the face of Network Address Translators (NA
Ts) and mobility of devices. This document is not an Internet Standards Track
specification; it is published for informational purposes.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6281"/>
<seriesInfo name="DOI" value="10.17487/RFC6281"/>
</reference>
<reference anchor="RFC6762" target="https://www.rfc-editor.org/info/rfc6
762" quoteTitle="true" derivedAnchor="RFC6762">
<front>
<title>Multicast DNS</title>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Krochmal" fullname="M. Krochmal">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="February"/>
<abstract>
<t>As networked devices become smaller, more portable, and more ub
iquitous, the ability to operate with less configured infrastructure is increasi
ngly important. In particular, the ability to look up DNS resource record data
types (including, but not limited to, host names) in the absence of a convention
al managed DNS server is useful.</t>
<t>Multicast DNS (mDNS) provides the ability to perform DNS-like o
perations on the local link in the absence of any conventional Unicast DNS serve
r. In addition, Multicast DNS designates a portion of the DNS namespace to be f
ree for local use, without the need to pay any annual fee, and without the need
to set up delegations or otherwise configure a conventional DNS server to answer
for those names.</t>
<t>The primary benefits of Multicast DNS names are that (i) they r
equire little or no administration or configuration to set them up, (ii) they wo
rk when no infrastructure is present, and (iii) they work during infrastructure
failures.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6762"/>
<seriesInfo name="DOI" value="10.17487/RFC6762"/>
</reference>
<reference anchor="RFC6763" target="https://www.rfc-editor.org/info/rfc6
763" quoteTitle="true" derivedAnchor="RFC6763">
<front>
<title>DNS-Based Service Discovery</title>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Krochmal" fullname="M. Krochmal">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="February"/>
<abstract>
<t>This document specifies how DNS resource records are named and
structured to facilitate service discovery. Given a type of service that a clie
nt is looking for, and a domain in which the client is looking for that service,
this mechanism allows clients to discover a list of named instances of that des
ired service, using standard DNS queries. This mechanism is referred to as DNS-b
ased Service Discovery, or DNS-SD.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6763"/>
<seriesInfo name="DOI" value="10.17487/RFC6763"/>
</reference>
<reference anchor="RFC6886" target="https://www.rfc-editor.org/info/rfc6
886" quoteTitle="true" derivedAnchor="RFC6886">
<front>
<title>NAT Port Mapping Protocol (NAT-PMP)</title>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Krochmal" fullname="M. Krochmal">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="April"/>
<abstract>
<t>This document describes a protocol for automating the process o
f creating Network Address Translation (NAT) port mappings. Included in the pro
tocol is a method for retrieving the external IPv4 address of a NAT gateway, thu
s allowing a client to make its external IPv4 address and port known to peers th
at may wish to communicate with it. From 2005 onwards, this protocol was impleme
nted in Apple products including Mac OS X, Bonjour for Windows, and AirPort wire
less base stations. In 2013, NAT Port Mapping Protocol (NAT-PMP) was superseded
by the IETF Standards Track RFC "Port Control Protocol (PCP)", which builds on
NAT-PMP and uses a compatible packet format, but adds a number of significant en
hancements.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6886"/>
<seriesInfo name="DOI" value="10.17487/RFC6886"/>
</reference>
<reference anchor="RFC6887" target="https://www.rfc-editor.org/info/rfc6
887" quoteTitle="true" derivedAnchor="RFC6887">
<front>
<title>Port Control Protocol (PCP)</title>
<author initials="D." surname="Wing" fullname="D. Wing" role="editor
">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Cheshire" fullname="S. Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Boucadair" fullname="M. Boucadair">
<organization showOnFrontPage="true"/>
</author>
<author initials="R." surname="Penno" fullname="R. Penno">
<organization showOnFrontPage="true"/>
</author>
<author initials="P." surname="Selkirk" fullname="P. Selkirk">
<organization showOnFrontPage="true"/>
</author>
<date year="2013" month="April"/>
<abstract>
<t>The Port Control Protocol allows an IPv6 or IPv4 host to contro
l how incoming IPv6 or IPv4 packets are translated and forwarded by a Network Ad
dress Translator (NAT) or simple firewall, and also allows a host to optimize it
s outgoing NAT keepalive messages.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="6887"/>
<seriesInfo name="DOI" value="10.17487/RFC6887"/>
</reference>
<reference anchor="RFC7413" target="https://www.rfc-editor.org/info/rfc7
413" quoteTitle="true" derivedAnchor="RFC7413">
<front>
<title>TCP Fast Open</title>
<author initials="Y." surname="Cheng" fullname="Y. Cheng">
<organization showOnFrontPage="true"/>
</author>
<author initials="J." surname="Chu" fullname="J. Chu">
<organization showOnFrontPage="true"/>
</author>
<author initials="S." surname="Radhakrishnan" fullname="S. Radhakris
hnan">
<organization showOnFrontPage="true"/>
</author>
<author initials="A." surname="Jain" fullname="A. Jain">
<organization showOnFrontPage="true"/>
</author>
<date year="2014" month="December"/>
<abstract>
<t>This document describes an experimental TCP mechanism called TC
P Fast Open (TFO). TFO allows data to be carried in the SYN and SYN-ACK packets
and consumed by the receiving end during the initial connection handshake, and
saves up to one full round-trip time (RTT) compared to the standard TCP, which r
equires a three-way handshake (3WHS) to complete before data can be exchanged.
However, TFO deviates from the standard TCP semantics, since the data in the SYN
could be replayed to an application in some rare circumstances. Applications s
hould not use TFO unless they can tolerate this issue, as detailed in the Applic
ability section.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="7413"/>
<seriesInfo name="DOI" value="10.17487/RFC7413"/>
</reference>
<reference anchor="RFC8010" target="https://www.rfc-editor.org/info/rfc8
010" quoteTitle="true" derivedAnchor="RFC8010">
<front>
<title>Internet Printing Protocol/1.1: Encoding and Transport</title
>
<author initials="M." surname="Sweet" fullname="M. Sweet">
<organization showOnFrontPage="true"/>
</author>
<author initials="I." surname="McDonald" fullname="I. McDonald">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="January"/>
<abstract>
<t>The Internet Printing Protocol (IPP) is an application-level pr
otocol for distributed printing using Internet tools and technologies. This doc
ument defines the rules for encoding IPP operations, attributes, and values into
the Internet MIME media type called "application/ipp". It also defines the rul
es for transporting a message body whose Content-Type is "application/ipp" over
HTTP and/or HTTPS. The IPP data model and operation semantics are described in
"Internet Printing Protocol/1.1: Model and
Semantics" (RFC 8011).</t>
</abstract>
</front>
<seriesInfo name="STD" value="92"/>
<seriesInfo name="RFC" value="8010"/>
<seriesInfo name="DOI" value="10.17487/RFC8010"/>
</reference>
<reference anchor="RFC8011" target="https://www.rfc-editor.org/info/rfc8
011" quoteTitle="true" derivedAnchor="RFC8011">
<front>
<title>Internet Printing Protocol/1.1: Model and Semantics</title>
<author initials="M." surname="Sweet" fullname="M. Sweet">
<organization showOnFrontPage="true"/>
</author>
<author initials="I." surname="McDonald" fullname="I. McDonald">
<organization showOnFrontPage="true"/>
</author>
<date year="2017" month="January"/>
<abstract>
<t>The Internet Printing Protocol (IPP) is an application-level pr
otocol for distributed printing using Internet tools and technologies. This doc
ument describes a simplified model consisting of abstract objects, attributes, a
nd operations that is independent of encoding and transport. The model consists
of several objects, including Printers and Jobs. Jobs optionally support multi
ple Documents.</t>
<t>IPP semantics allow End Users and Operators to query Printer ca
pabilities; submit Print Jobs; inquire about the status of Print Jobs and Printe
rs; and cancel, hold, and release Print Jobs. IPP semantics also allow Operator
s to pause and resume Jobs and Printers.</t>
<t>Security, internationalization, and directory issues are also a
ddressed by the model and semantics. The IPP message encoding and transport are
described in "Internet Printing Protocol/1.1: Encoding
and Transport" (RFC 8010).</t>
<t>This document obsoletes RFCs 2911, 3381, and 3382.</t>
</abstract>
</front>
<seriesInfo name="STD" value="92"/>
<seriesInfo name="RFC" value="8011"/>
<seriesInfo name="DOI" value="10.17487/RFC8011"/>
</reference>
<reference anchor="RFC8499" target="https://www.rfc-editor.org/info/rfc8
499" quoteTitle="true" derivedAnchor="RFC8499">
<front>
<title>DNS Terminology</title>
<author initials="P." surname="Hoffman" fullname="P. Hoffman">
<organization showOnFrontPage="true"/>
</author>
<author initials="A." surname="Sullivan" fullname="A. Sullivan">
<organization showOnFrontPage="true"/>
</author>
<author initials="K." surname="Fujiwara" fullname="K. Fujiwara">
<organization showOnFrontPage="true"/>
</author>
<date year="2019" month="January"/>
<abstract>
<t>The Domain Name System (DNS) is defined in literally dozens of
different RFCs. The terminology used by implementers and developers of DNS prot
ocols, and by operators of DNS systems, has sometimes changed in the decades sin
ce the DNS was first defined. This document gives current definitions for many
of the terms used in the DNS in a single document.</t>
<t>This document obsoletes RFC 7719 and updates RFC 2308.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="219"/>
<seriesInfo name="RFC" value="8499"/>
<seriesInfo name="DOI" value="10.17487/RFC8499"/>
</reference>
<reference anchor="RFC8684" target="https://www.rfc-editor.org/info/rfc8
684" quoteTitle="true" derivedAnchor="RFC8684">
<front>
<title>TCP Extensions for Multipath Operation with Multiple Addresse
s</title>
<author initials="A." surname="Ford" fullname="A. Ford">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Raiciu" fullname="C. Raiciu">
<organization showOnFrontPage="true"/>
</author>
<author initials="M." surname="Handley" fullname="M. Handley">
<organization showOnFrontPage="true"/>
</author>
<author initials="O." surname="Bonaventure" fullname="O. Bonaventure
">
<organization showOnFrontPage="true"/>
</author>
<author initials="C." surname="Paasch" fullname="C. Paasch">
<organization showOnFrontPage="true"/>
</author>
<date year="2020" month="March"/>
<abstract>
<t>TCP/IP communication is currently restricted to a single path p
er connection, yet multiple paths often exist between peers. The simultaneous us
e of these multiple paths for a TCP/IP session would improve resource usage with
in the network and thus improve user experience through higher throughput and im
proved resilience to network failure.</t>
<t>Multipath TCP provides the ability to simultaneously use multip
le paths between peers. This document presents a set of extensions to traditiona
l TCP to support multipath operation. The protocol offers the same type of servi
ce to applications as TCP (i.e., a reliable bytestream), and it provides the com
ponents necessary to establish and use multiple TCP flows across potentially dis
joint paths.</t>
<t>This document specifies v1 of Multipath TCP, obsoleting v0 as s
pecified in RFC 6824, through clarifications and modifications primarily driven
by deployment experience.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="8684"/>
<seriesInfo name="DOI" value="10.17487/RFC8684"/>
</reference>
<reference anchor="RFC8764" target="https://www.rfc-editor.org/info/rfc8
764" quoteTitle="true" derivedAnchor="RFC8764">
<front>
<title>Apple's DNS Long-Lived Queries Protocol</title>
<author initials="S" surname="Cheshire" fullname="Stuart Cheshire">
<organization showOnFrontPage="true"/>
</author>
<author initials="M" surname="Krochmal" fullname="Marc Krochmal">
<organization showOnFrontPage="true"/>
</author>
<date month="June" year="2020"/>
</front>
<seriesInfo name="RFC" value="8764"/>
<seriesInfo name="DOI" value="10.17487/RFC8764"/>
</reference>
<reference anchor="RFC8766" target="https://www.rfc-editor.org/info/rfc8
766" quoteTitle="true" derivedAnchor="RFC8766">
<front>
<title>Discovery Proxy for Multicast DNS-Based Service Discovery</ti
tle>
<author initials="S" surname="Cheshire" fullname="Stuart Cheshire">
<organization showOnFrontPage="true"/>
</author>
<date month="June" year="2020"/>
</front>
<seriesInfo name="RFC" value="8766"/>
<seriesInfo name="DOI" value="10.17487/RFC8766"/>
</reference>
<reference anchor="SD-API" target="https://opensource.apple.com/source/m
DNSResponder/mDNSResponder-878.70.2/mDNSShared/dns_sd.h.auto.html" quoteTitle="t
rue" derivedAnchor="SD-API">
<front>
<title>dns_sd.h</title>
<author>
<organization showOnFrontPage="true">Apple Inc.</organization>
</author>
</front>
</reference>
<reference anchor="SYN" target="https://www.cisco.com/web/about/ac123/ac
147/archived_issues/ipj_9-4/ipj_9-4.pdf" quoteTitle="true" derivedAnchor="SYN">
<front>
<title>Defenses Against TCP SYN Flooding Attacks</title>
<author initials="W." surname="Eddy" fullname="Wesley Eddy">
<organization showOnFrontPage="true">Verizon Federal Network Syste
ms</organization>
<address>
<email>weddy@grc.nasa.gov</email>
</address>
</author>
<date year="2006" month="December"/>
<keyword>TCP</keyword>
</front>
<refcontent>The Internet Protocol Journal</refcontent>
<refcontent>Cisco Systems</refcontent>
<refcontent>Volume 9</refcontent>
<refcontent>Number 4</refcontent>
</reference>
<reference anchor="I-D.ietf-tcpm-rack" quoteTitle="true" target="https:/
/tools.ietf.org/html/draft-ietf-tcpm-rack-08" derivedAnchor="TCPRACK">
<front>
<title>RACK: a time-based fast loss detection algorithm for TCP</tit
le>
<author initials="Y" surname="Cheng" fullname="Yuchung Cheng">
<organization showOnFrontPage="true"/>
</author>
<author initials="N" surname="Cardwell" fullname="Neal Cardwell">
<organization showOnFrontPage="true"/>
</author>
<author initials="N" surname="Dukkipati" fullname="Nandita Dukkipati
">
<organization showOnFrontPage="true"/>
</author>
<author initials="P" surname="Jha" fullname="Priyaranjan Jha">
<organization showOnFrontPage="true"/>
</author>
<date month="March" day="9" year="2020"/>
<abstract>
<t>This document presents a new TCP loss detection algorithm calle
d RACK ("Recent ACKnowledgment"). RACK uses the notion of time, instead of pack
et or sequence counts, to detect losses, for modern TCP implementations that can
support per-packet timestamps and the selective acknowledgment (SACK) option.
It is intended to be an alternative to the DUPACK threshold approach [RFC6675],
as well as other nonstandard approaches such as FACK [FACK].</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-tcpm-rack-08"/>
<format type="TXT" target="http://www.ietf.org/internet-drafts/draft-i
etf-tcpm-rack-08.txt"/>
<refcontent>Work in Progress</refcontent>
</reference>
<reference anchor="XEP0060" target="https://xmpp.org/extensions/xep-0060
.html" quoteTitle="true" derivedAnchor="XEP0060">
<front>
<title>Publish-Subscribe</title>
<author initials="P." surname="Millard" fullname="Peter Millard">
<organization showOnFrontPage="true"/>
<address>
<email/>
</address>
</author>
<author initials="P." surname="Saint-Andre" fullname="Peter
Saint-Andre">
<organization showOnFrontPage="true"/>
<address>
<email>peter@andyet.net</email>
</address>
</author>
<author initials="R." surname="Meijer" fullname="Ralph Meijer">
<organization showOnFrontPage="true"/>
<address>
<email>ralphm@ik.nu</email>
</address>
</author>
<date month="October" year="2019"/>
</front>
<refcontent>XSF XEP 0060
</refcontent>
</reference>
</references>
</references>
<section anchor="Acknowledgments" numbered="false" toc="include" removeInRFC
="false" pn="section-appendix.a">
<name slugifiedName="name-acknowledgments">Acknowledgments</name>
<t pn="section-appendix.a-1">The authors would like to thank <contact full
name="Kiren Sekar"/> and
<contact fullname="Marc Krochmal"/> for previous work completed in this
field.</t>
<t pn="section-appendix.a-2">This document has been improved due to commen
ts from
<contact fullname="Ran Atkinson"/>,
<contact fullname="Tim Chown"/>,
<contact fullname="Sara Dickinson"/>,
<contact fullname="Mark Delany"/>,
<contact fullname="Ralph Droms"/>,
<contact fullname="Jan Komissar"/>,
<contact fullname="Eric Rescorla"/>,
<contact fullname="Michael Richardson"/>,
<contact fullname="David Schinazi"/>,
<contact fullname="Manju Shankar Rao"/>,
<contact fullname="Robert Sparks"/>,
<contact fullname="Markus Stenberg"/>,
<contact fullname="Andrew Sullivan"/>,
<contact fullname="Michael Sweet"/>,
<contact fullname="Dave Thaler"/>,
<contact fullname="Brian Trammell"/>,
<contact fullname="Bernie Volz"/>,
<contact fullname="Éric Vyncke"/>,
<contact fullname="Christopher Wood"/>,
<contact fullname="Liang Xia"/>,
and and
Soraia Zlatkovic. <contact fullname="Soraia Zlatkovic"/>.
Ted Lemon provided clarifying text that was greatly appreciated.</t> <contact fullname="Ted Lemon"/> provided clarifying text that was greatly
<?rfc needLines="15" ?> appreciated.</t>
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<author fullname="Tom Pusateri" initials="T." surname="Pusateri">
<back> <organization showOnFrontPage="true">Unaffiliated</organization>
<!-- References split into informative and normative --> <address>
<postal>
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1. define an ENTITY at the top, and use "ampersand character"RFC2629; here ( <region>NC</region>
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2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xml <country>United States of America</country>
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</address>
Both are cited textually in the same manner: by using xref elements. </author>
If you use the PI option, xml2rfc will, by default, try to find included fil <author fullname="Stuart Cheshire" initials="S." surname="Cheshire">
es in the same <organization showOnFrontPage="true">Apple Inc.</organization>
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filing system or remote ones accessed by http (http://domain/dir/... ).--> <region>CA</region>
<code>95014</code>
<references title="Normative References"> <country>United States of America</country>
&RFC0020; </postal>
&RFC0768; <phone>+1 (408) 996-1010</phone>
&RFC0793; <email>cheshire@apple.com</email>
&RFC1034; </address>
&RFC1035; </author>
&RFC1123; </section>
&RFC2119; </back>
&RFC2136;
&RFC2181;
&RFC2782;
&RFC6066;
<?rfc include="reference.RFC.6335" ?>
&RFC6895;
&RFC7673;
&RFC7766;
&RFC7858;
&RFC8174;
&RFC8310;
&RFC8446;
&RFC8490;
<reference anchor="SRVTYPE"
target="http://www.iana.org/assignments/service-names-port-numbers/">
<front>
<title>Service Name and Transport Protocol Port Number Registry</title>
<author/>
<date/>
</front>
</reference>
<reference anchor="DSOTYPE"
target="https://www.iana.org/assignments/dns-parameters/">
<front>
<title>DSO Type Code Registry</title>
<author/>
<date/>
</front>
</reference>
</references>
<!-- Use needLines to make sure "Authors' Addresses" line doesn't appear as the
last line on the page -->
<?rfc needLines="9" ?>
<references title="Informative References">
<reference anchor="BCP195" target="http://www.rfc-editor.org/info/bcp195"><
front>
<title>Recommendations for Secure Use of Transport Layer Security (TL
S) and Datagram Transport Layer Security (DTLS)</title>
<author initials="Y." surname="Sheffer" fullname="Yaron Sheffer"/>
<author initials="R." surname="Holz" fullname="Ralph Holz"/>
<author initials="P." surname="Saint-Andre" fullname="Peter Saint-And
re"/>
<date year="2015" month="May"/>
</front><seriesInfo name="BCP" value="195"/><seriesInfo name="RFC" valu
e="7525"/></reference>
&RFC2308;
&RFC3123;
&RFC4287;
&RFC4953;
&RFC6281;
&RFC6762;
&RFC6763;
&RFC6824;
&RFC6886;
&RFC6887;
&RFC7413;
&RFC7719;
&RFC8010;
&RFC8011;
&RFC8499;
&I-D.ietf-tcpm-rack;
<reference anchor='LLQ'>
<front>
<title>DNS Long-Lived Queries</title>
<author initials='S' surname='Cheshire' fullname='Stuart Cheshire'>
<organization />
</author>
<author initials='M' surname='Krochmal' fullname='Marc Krochmal'>
<organization />
</author>
<date month='March' day='4' year='2019' />
<abstract><t>DNS Long-Lived Queries (LLQ) is a protocol for extending the DNS pr
otocol to support change notification, thus allowing clients to learn about chan
ges to DNS data without polling the server. From 2007 onwards, LLQ was implemen
ted in Apple products including Mac OS X, Bonjour for Windows, and AirPort wirel
ess base stations. In 2019, the LLQ protocol was superseded by the IETF Standar
ds Track RFC "DNS Push Notifications", which builds on experience gained with th
e LLQ protocol to create a superior replacement.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-sekar-dns-llq-03' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-sekar-dns-llq-03.txt'
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</reference>
<reference anchor='DisProx'>
<front>
<title>Discovery Proxy for Multicast DNS-Based Service Discovery</title>
<author initials='S' surname='Cheshire' fullname='Stuart Cheshire'>
<organization />
</author>
<date month='March' day='24' year='2019' />
<abstract><t>This document specifies a network proxy that uses Multicast DNS to
automatically populate the wide-area unicast Domain Name System namespace with r
ecords describing devices and services found on the local link.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-dnssd-hybrid-10' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-dnssd-hybrid-10.t
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</reference>
<reference anchor='SYN'>
<front>
<title>Defenses Against TCP SYN Flooding Attacks</title>
<author initials='W.' surname='Eddy' fullname='Wesley Eddy'>
<organization>Verizon Federal Network Systems</organization>
<address>
<email>weddy@grc.nasa.gov</email>
</address>
</author>
<date year='2006' month='December' />
<keyword>TCP</keyword>
</front>
<seriesInfo name="The Internet Protocol Journal," value='Cisco Systems' /
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<seriesInfo name='Volume' value='9' />
<seriesInfo name='Number' value='4' />
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<reference anchor='obs' target="https://en.wikipedia.org/wiki/Observer_patt
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<front>
<title>Observer Pattern</title>
<author/>
<date/>
</front>
</reference>
<reference anchor='SD-API' target="https://opensource.apple.com/source/mDNS
Responder/mDNSResponder-878.70.2/mDNSShared/dns_sd.h.auto.html">
<front>
<title>dns_sd.h API</title>
<author/>
<date/>
</front>
</reference>
<reference anchor="XEP0060">
<front>
<title>Publish-Subscribe</title>
<author initials="P." surname="Millard" fullname="Peter Millard">
<organization/>
<address>
<email/>
</address>
</author>
<author initials="P." surname="Saint-Andre" fullname="Peter Saint-Andre
">
<organization/>
<address>
<email>peter@andyet.net</email>
</address>
</author>
<author initials="R." surname="Meijer" fullname="Ralph Meijer">
<organization/>
<address>
<email>ralphm@ik.nu</email>
</address>
</author>
<date day="01" month="July" year="2010"/>
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<seriesInfo name="XSF XEP" value="0060"/>
<format type="HTML" target="http://xmpp.org/extensions/xep-0060.html"/>
</reference>
</references>
</back>
</rfc> </rfc>
 End of changes. 82 change blocks. 
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This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/