draft.xml.in

<?xml version='1.0' encoding='UTF-8'?>


<!DOCTYPE rfc [
  <!ENTITY nbsp    "&#160;">
  <!ENTITY zwsp   "&#8203;">
  <!ENTITY nbhy   "&#8209;">
  <!ENTITY wj     "&#8288;">
]>

<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-regext-epp-ttl-18" number="9803" ipr="trust200902" submissionType="IETF" consensus="true" tocInclude="true" tocDepth="4" symRefs="true" sortRefs="true" updates="" obsoletes="" version="3" xml:lang="en">

  <front>
    <title abbrev="TTL Mapping for EPP">Extensible Provisioning Protocol (EPP) Mapping for DNS Time-to-Live (TTL) Values</title>
    <seriesInfo name="RFC" value="9803"/>
    <author fullname="Gavin Brown">
      <organization>ICANN</organization>
      <address>
        <postal>
          <street>12025 Waterfront Drive, Suite 300</street>
          <city>Los Angeles</city>
          <region>CA</region>
          <code>90292</code>
          <country>United States of America</country>
        </postal>
        <email>gavin.brown@icann.org</email>
        <uri>https://www.icann.org/</uri>
      </address>
    </author>
    <date month="June" year="2025"/>
    <area>ART</area>
    <workgroup>regext</workgroup>

<!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on https://www.rfc-editor.org/search. -->

<!-- GB: done. -->

    <keyword>EPP</keyword>
    <keyword>DNS</keyword>
    <keyword>TTL</keyword>
    <keyword>time-to-live</keyword>

    <abstract>
      <t>This document describes an extension to the Extensible Provisioning
      Protocol (EPP) that allows EPP clients to manage the Time-to-Live (TTL)
      value for domain name delegation records.
      </t>
    </abstract>
  </front>

  <middle>
    <section>
      <name>Introduction</name>
      <t>
	The principal output of any domain name registry system is a DNS zone
	file, which contains the delegation record(s) for names registered
	within a zone (such as a top-level domain).  These records typically
	include one or more <tt>NS</tt> records, but may also include
	<tt>DS</tt> records for domains secured with DNSSEC <xref
	target="RFC9364"/>, and <tt>DNAME</tt> records for Internationalized Domain Name (IDN) variants <xref
	target="RFC6927"/>.  <tt>A</tt> and/or <tt>AAAA</tt> records may also
	be published for nameservers where they are required by DNS resolvers
	to avoid an infinite loop.</t>
      <t>
	Typically, the Time-to-Live (TTL) value (see <xref section="5"
	sectionFormat="of" target="RFC9499"/>) of these records is determined
	by the registry operator.  However, in some circumstances it may be
	desirable to allow the sponsoring client of a domain name to change
	the TTL values used for that domain's delegation: for example, to
	reduce the amount of time required to complete a change of DNS
	servers, DNSSEC deployment or key rollover, or to allow for fast
	rollback of such changes.</t>
      <t>
	This document describes an EPP extension to the domain name and host
	object mappings (described in <xref target="RFC5731"/> and <xref
	target="RFC5732"/>, respectively) that allows the sponsor of a domain
	name or host object to change the TTL values of the resource record(s)
	associated with that object.  It also describes how EPP servers should
	handle TTLs specified by EPP clients and how both parties coordinate
	to manage TTL values in response to changes in operational or security
	requirements.</t>

      <section>
        <name>Conventions Used in This Document</name>
        <t>
    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&nbsp;14 <xref target="RFC2119"/> <xref
    target="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
        </t>

        <t>
	  In this document's examples, "C:" represents lines sent by a protocol client and
	  "S:" represents lines returned by a protocol server.  Indentation
	  and white space in these examples are provided only to illustrate element
	  relationships and are not required features of this protocol.</t>
        <t>
	  A protocol client that is authorized to manage an existing object is
	  described as a "sponsoring" client throughout this document.</t>
        <t>
	  XML is case sensitive.  Unless stated otherwise, the XML specifications
	  and examples provided in this document <bcp14>MUST</bcp14> be
	  interpreted in the character case presented in order to develop a
	  conforming implementation.</t>
        <t>
	  EPP uses XML namespaces to provide an extensible object management
	  framework and to identify schemas required for XML instance parsing
	  and validation.  These namespaces and schema definitions are used to
	  identify both the base protocol schema and the schemas for managed
	  objects.</t>
        <t>
	  The XML namespace prefixes used in these examples (such as the string
	  <tt>ttl</tt> in <tt>ttl:create</tt>) are solely for illustrative
	  purposes.  A conforming implementation <bcp14>MUST NOT</bcp14>
	  require the use of these or any other specific namespace prefixes.</t>
        <t>
	  In accordance with Section 3.2.2.1 of XML Schema Part 2: Datatypes
	  <xref target="XSD-DATATYPES"/>, the allowable lexical
	  representations for the <tt>xs:boolean</tt> datatype are the strings
	  "<tt>0</tt>" and "<tt>false</tt>" for the concept 'false' and the
	  strings "<tt>1</tt>" and "<tt>true</tt>" for the concept 'true'.
	  Implementations <bcp14>MUST</bcp14> support both styles of lexical
	  representation.</t>
      </section>

      <section anchor="extension-elements">
        <name>Extension Elements</name>
        <t>This extension adds additional elements to the EPP domain and host mappings.</t>
        <section anchor="ttl_element">
          <name>The &lt;ttl:ttl&gt; Element</name>
          <t>
	    The <tt>&lt;ttl:ttl&gt;</tt> element is used to define TTL values
	    for the DNS resource records associated with domain and host
	    objects.
	  </t>
          <t>
	    <tt>&lt;ttl:ttl&gt;</tt> elements have the optional following
	    attributes, depending on whether they appear in an EPP command or
	    response:
	  </t>

<!-- [rfced] We have reformatted the list below for readability; please review
and let us know if you prefer otherwise.

Original:
   <ttl:ttl> elements have the optional following attributes, depending
   on whether they appear in an EPP command or response:

   1.  "for", which is REQUIRED in both commands and responses, and
       which specifies the DNS record type to which the TTL value
       pertains.  This attribute MUST have one of the following values:
       "NS", "DS", "DNAME", "A", "AAAA" or "custom";

   2.  If the value of the "for" attribute is "custom", then the
       <ttl:ttl> element MUST also have a "custom" attribute containing
       a DNS record type conforming with the regular expression in
       Section 3.1 of [RFC6895].  Additionally, the record type MUST be
       registered with IANA in [IANA-RRTYPES].

   3.  "min", which MUST NOT be present in EPP commands but MAY be
       present in EPP responses (see Section 2.1.1), and which is used
       by the server to indicate the lowest value that may be set;

   4.  "default", which MUST NOT be present in EPP commands but MAY be
       present in EPP responses (see Section 2.1.1), and which is used
       by the server to indicate the default value;

   5.  "max", which MUST NOT be present in EPP commands but MAY be
       present in EPP responses (see Section 2.1.1), and which is used
       by the server to indicate the highest value that may be set;

Current:
   "for"
      REQUIRED in both commands and responses, and specifies the DNS
      record type to which the TTL value pertains.  This attribute MUST
      have one of the following values: "NS", "DS", "DNAME", "A", "AAAA"
      or "custom".

   "custom"
      If the value of the "for" attribute is "custom", then the
      <ttl:ttl> element MUST also have a "custom" attribute containing a
      DNS record type conforming with the regular expression in
      Section 3.1 of [RFC6895].  Additionally, the record type MUST be
      registered with IANA in [IANA-RRTYPES].

   "min"
      MUST NOT be present in EPP commands but MAY be present in EPP
      responses (see Section 2.1.1).  It is also used by the server to
      indicate the lowest value that may be set.

   "default"
      MUST NOT be present in EPP commands but MAY be present in EPP
      responses (see Section 2.1.1).  It is also used by the server to
      indicate the default value.

   "max"
      MUST NOT be present in EPP commands but MAY be present in EPP
      responses (see Section 2.1.1).  It is also used by the server to
      indicate the highest value that may be set.
-->

          <dl newline="true">
            <dt>"<tt>for</tt>"</dt>
	    <dd>
	      <bcp14>REQUIRED</bcp14> in both commands and responses, and
	      specifies the DNS record type to which the TTL value pertains.
	      This attribute <bcp14>MUST</bcp14> have one of the following
	      values: "<tt>NS</tt>", "<tt>DS</tt>", "<tt>DNAME</tt>",
	      "<tt>A</tt>", "<tt>AAAA</tt>" or "<tt>custom</tt>".
	    </dd>
	    <dt>"<tt>custom</tt>"</dt>
	      <dd>If the value of the "<tt>for</tt>" attribute is
	      "<tt>custom</tt>", then the <tt>&lt;ttl:ttl&gt;</tt> element
	      <bcp14>MUST</bcp14> also have a "<tt>custom</tt>" attribute
	      containing a DNS record type conforming with the regular
	      expression in <xref sectionFormat="of" section="3.1"
	      target="RFC6895"/>.  Additionally, the record type
	      <bcp14>MUST</bcp14> be registered with IANA in <xref
	      target="IANA-RRTYPES"/>.
	      </dd>

            <dt>"<tt>min</tt>"</dt>
	    <dd>
	      <bcp14>MUST NOT</bcp14> be present in EPP commands but
	      <bcp14>MAY</bcp14> be present in EPP responses (see <xref
	      target="info-command"/>). It is used by the server to
	      indicate the lowest value that may be set.
	    </dd>

            <dt>"<tt>default</tt>"</dt>
	    <dd>
	      <bcp14>MUST NOT</bcp14> be present in EPP commands but
	      <bcp14>MAY</bcp14> be present in EPP responses (see <xref
	      target="info-command"/>). It is used by the server to
	      indicate the default value.
	    </dd>

            <dt>"<tt>max</tt>"</dt>
	    <dd>
	      <bcp14>MUST NOT</bcp14> be present in EPP commands but
	      <bcp14>MAY</bcp14> be present in EPP responses (see <xref
	      target="info-command"/>). It is used by the server to
	      indicate the highest value that may be set.
	    </dd>
          </dl>

          <t>
	    When present, the value of the "<tt>min</tt>" attribute
	    <bcp14>MUST</bcp14> be lower than the value of the "<tt>max</tt>"
	    attribute. The "<tt>default</tt>" attribute <bcp14>MUST</bcp14> be
	    between the "<tt>min</tt>" and "<tt>max</tt>" values, inclusively.</t>

          <section anchor="element-content">
            <name>Element Content</name>
            <t>
	      The XML schema found in <xref target="formal-syntax"/> of this
	      document restricts the content of <tt>&lt;ttl:ttl&gt;</tt>
	      elements to be either:</t>
            <ol>
              <li>a non-negative integer, indicating the value of the TTL in seconds, or</li>
              <li>empty, in which case the server's default TTL for the given record type is to be applied.</li>
            </ol>
          </section>

          <section anchor="supported-dns-record-types">
            <name>Supported DNS Record Types</name>
            <t>
	      To facilitate forward compatibility with future changes to the
	      DNS protocol, this document does not enumerate or restrict the
	      DNS record types that can be included in the "<tt>custom</tt>"
	      attribute of the <tt>&lt;ttl:ttl&gt;</tt> element.</t>
            <t>
	      The regular expression that is used to validate the values of
	      the "<tt>custom</tt>" attribute is based on the expression found
	      in <xref sectionFormat="of" section="3.1" target="RFC6895"/>,
	      and it is intended to match both existing and future RRTYPE
	      mnemonics.  This eliminates the need to update this document in
	      the event that new DNS records that exist above a zone cut
	      (<xref sectionFormat="of" section="7" target="RFC9499"/>) are
	      specified.</t>
            <t>
	      Nevertheless, EPP servers that implement this extension
	      <bcp14>MUST</bcp14> restrict the DNS record types that are
	      accepted in <tt>&lt;create&gt;</tt> and <tt>&lt;update&gt;</tt>
	      commands, and included in <tt>&lt;info&gt;</tt> responses,
	      allowing only those types that are (a) registered in <xref
	      target="IANA-RRTYPES"/> and (b) appropriate for use above a zone
	      cut.</t>
            <t>
	      A server that receives a <tt>&lt;create&gt;</tt> or
	      <tt>&lt;update&gt;</tt> command that attempts to set TTL values
	      for inapplicable DNS record types <bcp14>MUST</bcp14> respond
	      with a 2306 "Parameter value policy" error.</t>
            <t>
	      As an illustrative example, a server <bcp14>MAY</bcp14> allow
	      clients to specify TTL values for the following record types for
	      domain objects:
	    </t>

            <ol>
              <li>
                <tt>NS</tt>;
	      </li>
              <li>
                <tt>DS</tt> (if the server also implements <xref target="RFC5910"/>);
	      </li>
              <li>
                <tt>DNAME</tt> (if the server implements IDN variants using
                <tt>DNAME</tt> records).
	      </li>
            </ol>

            <section>
              <name>Glue Records</name>
              <t>
		Glue records are described in <xref section="7"
		sectionFormat="of" target="RFC9499"/>.</t>
              <t>
		Servers that implement host objects <xref target="RFC5732"/>
		<bcp14>MAY</bcp14> allow clients to specify TTL values for
		<tt>A</tt> and <tt>AAAA</tt> records for host objects.</t>
              <t>
		A server supporting host objects that receives a command that
		attempts to set TTL values for <tt>A</tt> and <tt>AAAA</tt>
		records on a domain object <bcp14>MUST</bcp14> respond with a
		2306 "Parameter value policy" error.</t>
              <t>
		EPP servers that use the host attribute model (described in
		<xref sectionFormat="of" section="1.1" target="RFC5731"/>)
		<bcp14>MAY</bcp14> allow clients to specify TTL values for
		<tt>A</tt> and <tt>AAAA</tt> records for domain objects.</t>
            </section>
          </section>

          <section anchor="info-element">
            <name>The &lt;ttl:info&gt; Element</name>
            <t>
	      The <tt>&lt;ttl:info&gt;</tt> element is used by clients to
	      request that the server include additional information in
	      <tt>&lt;info&gt;</tt> responses for domain and host objects.</t>
            <t>
	      It has a single <bcp14>OPTIONAL</bcp14> "<tt>policy</tt>"
	      attribute, which takes a boolean value with a default value of
	      "<tt>false</tt>".</t>
            <t>
	      The semantics of this element are described in <xref
	      target="info-command"/>.</t>

        <t>Below is an example of a <tt>&lt;ttl:info&gt;</tt>
        element with an explicit "<tt>policy</tt>" attribute:</t>

        <sourcecode type="xml"><![CDATA[
<ttl:info policy="true"/>
]]></sourcecode>

<!-- [rfced] The section titles for 1.2.1.3.1 and 1.2.2. are similar.
For clarity, which of these options do you prefer? Or, please feel
free to suggest otherwise.
a) Make the title of Section 1.2.1.3.1 more specific, or
b) Include the example in 1.2.1.3 and remove section 1.2.1.3.1, or
c) Move the example in 1.2.1.3.1 to a subsection of Section 1.2.2 ("Examples").

Original:
1.2.1.3.  The <ttl:info> element

   [...]

1.2.1.3.1.  Example

   <ttl:info policy="true"/>

1.2.2.  Examples


Perhaps (if option b):

1.2.1.3.  The <ttl:info> element

   The <ttl:info> element is used by clients to request that the server
   include additional information in <info> responses for domain and
   host objects.

   It has a single OPTIONAL policy attribute, which takes a boolean
   value with a default value of false.

   The semantics of this element are described in Section 2.1.1.
   Here's an example: <ttl:info policy="true"/>

1.2.2. Examples
-->

<!-- GB: I chose Option B and made the appropriate edits. -->

          </section>
        </section>

        <section>
          <name>Examples</name>
          <section>
            <name>Explicit TTL Value (&lt;create&gt; or &lt;update&gt; Command)</name>
           <sourcecode type="xml"><![CDATA[
<ttl:ttl for="NS">3600</ttl:ttl>
]]></sourcecode>
          </section>

          <section>
            <name>Explicit TTL Value (&lt;info&gt; Policy Mode)</name>
            <sourcecode type="xml"><![CDATA[
<ttl:ttl
  for="NS"
  min="60"
  default="86400"
  max="172800">3600</ttl:ttl>
]]></sourcecode>
          </section>
          <section>
            <name>Empty Value Indicating Default TTL (&lt;create&gt; or &lt;update&gt; Command, &lt;info&gt; Default Mode)</name>

            <sourcecode type="xml"><![CDATA[
<ttl:ttl for="NS"/>
]]></sourcecode>
          </section>

          <section>
            <name>Custom Record Type (&lt;create&gt; or &lt;update&gt; Command, &lt;info&gt; Default Mode)</name>
            <sourcecode type="xml"><![CDATA[
<ttl:ttl
  for="custom"
  custom="NEWRRTYPE">3600</ttl:ttl>
]]></sourcecode>
          </section>
        </section>
      </section>
    </section>
    <section>
      <name>EPP Command Mapping</name>
      <section>
        <name>EPP Query Commands</name>
        <section anchor="info-command">
          <name>EPP &lt;info&gt; Command</name>
          <t>
	    This extension defines an additional element for EPP
	    <tt>&lt;info&gt;</tt> commands and responses for domain and host
	    objects.</t>
          <t>
	    The EPP <tt>&lt;info&gt;</tt> command is extended to support two
	    different modes:</t>
          <ol>
            <li>The Default Mode (<xref target="default-mode"/>), which
            requests the inclusion of all non-default TTL values in the
            response; and</li>
            <li>The Policy Mode (<xref target="policy-mode"/>), which requests
            the inclusion of TTL information for all supported DNS record
            types in the response, along with the minimum, default, and maximum
            values for those records.</li>
          </ol>

          <section anchor="default-mode">
            <name>Default Mode</name>
            <t>
	      If a server receives an <tt>&lt;info&gt;</tt> command for a
	      domain or host object that includes a <tt>&lt;ttl:info&gt;</tt>
	      element with a "<tt>policy</tt>" attribute that is "<tt>0</tt>"
	      or "<tt>false</tt>", then the EPP response <bcp14>MUST</bcp14>
	      contain <tt>&lt;ttl:ttl&gt;</tt> records for all DNS record
	      types that have non-default TTL values.  These elements
	      <bcp14>MUST NOT</bcp14> have the "<tt>min</tt>",
	      "<tt>default</tt>", and "<tt>max</tt>" attributes.</t>
            <t>
	      Below is an example domain <tt>&lt;info&gt;</tt> command with a
	      <tt>&lt;ttl:info&gt;</tt> element with a "<tt>policy</tt>"
	      attribute that is "<tt>false</tt>":</t>

            <sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <info>
C:       <domain:info
C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:       </domain:info>
C:     </info>
C:     <extension>
C:       <ttl:info
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
C:         policy="false"/>
C:     </extension>
C:   </command>
C: </epp>
]]></sourcecode>

            <t>
	      Below is an example domain <tt>&lt;info&gt;</tt> response to a command with
	      a <tt>&lt;ttl:info&gt;</tt> element with a "<tt>policy</tt>"
	      attribute that is "<tt>false</tt>":</t>

            <sourcecode type="xml" markers="false"><![CDATA[
S: <?xml version="1.0" encoding="utf-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <domain:infData
S:         xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
S:         <domain:name>example.com</domain:name>
S:         <domain:roid>EXAMPLE1-REP</domain:roid>
S:         <domain:status s="ok"/>
S:         <domain:ns>
S:           <domain:hostObj>ns1.example.com</domain:hostObj>
S:           <domain:hostObj>ns1.example.net</domain:hostObj>
S:         </domain:ns>
S:         <domain:clID>ClientX</domain:clID>
S:         <domain:crID>ClientX</domain:crID>
S:         <domain:crDate>2023-11-08T10:14:55.0Z</domain:crDate>
S:         <domain:exDate>2024-11-08T10:14:55.0Z</domain:exDate>
S:       </domain:infData>
S:     </resData>
S:     <extension>
S:       <ttl:infData
S:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:         <ttl:ttl for="NS">172800</ttl:ttl>
S:         <ttl:ttl for="DS">300</ttl:ttl>
S:       </ttl:infData>
S:       <secDNS:infData
S:         xmlns:secDNS="urn:ietf:params:xml:ns:secDNS-1.1">
S:         <secDNS:dsData>
S:           <secDNS:keyTag>12345</secDNS:keyTag>
S:           <secDNS:alg>13</secDNS:alg>
S:           <secDNS:digestType>2</secDNS:digestType>
S:           <secDNS:digest>49FD46E6C4B45C55D4AC</secDNS:digest>
S:         </secDNS:dsData>
S:       </secDNS:infData>
S:     </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>
]]></sourcecode>

            <t>
	      Below is an example host <tt>&lt;info&gt;</tt> command with a
	      &lt;ttl:info&gt; element with a "<tt>policy</tt>" attribute that
	      is "<tt>false</tt>":</t>

            <sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <info>
C:       <host:info
C:        xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:       </host:info>
C:     </info>
C:     <extension>
C:       <ttl:info
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
C:         policy="false"/>
C:     </extension>
C:   </command>
C: </epp>
]]></sourcecode>

            <t>Below is an example host <tt>&lt;info&gt;</tt> response to a command with a
            &lt;ttl:info&gt; element with a "<tt>policy</tt>" attribute that is
            "<tt>false</tt>":</t>

            <sourcecode type="xml" markers="false"><![CDATA[
S: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <host:infData
S:         xmlns:host="urn:ietf:params:xml:ns:host-1.0">
S:         <host:name>ns1.example.com</host:name>
S:         <host:roid>NS1_EXAMPLE1-REP</host:roid>
S:         <host:status s="ok"/>
S:         <host:addr ip="v4">192.0.2.2</host:addr>
S:         <host:addr ip="v6">2001:db8::8:800:200c:417a</host:addr>
S:         <host:clID>ClientX</host:clID>
S:         <host:crID>ClientX</host:crID>
S:         <host:crDate>2023-11-08T10:14:55.0Z</host:crDate>
S:       </host:infData>
S:     </resData>
S:     <extension>
S:       <ttl:infData
S:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:         <ttl:ttl for="A">172800</ttl:ttl>
S:         <ttl:ttl for="AAAA">86400</ttl:ttl>
S:       </ttl:infData>
S:     </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>
]]></sourcecode>

          </section>
          <section anchor="policy-mode">
            <name>Policy Mode</name>
            <t>
	      If a server receives an <tt>&lt;info&gt;</tt> command for a
	      domain or host object that includes a <tt>&lt;ttl:info&gt;</tt>
	      element with a "<tt>policy</tt>" attribute that is "<tt>1</tt>" or
	      "<tt>true</tt>", then the EPP response <bcp14>MUST</bcp14>
	      contain <tt>&lt;ttl:ttl&gt;</tt> records for all supported DNS
	      record types, irrespective of whether those record types are
	      actually in use by the object in question.  These elements
	      <bcp14>MUST</bcp14> have the "<tt>min</tt>", "<tt>default</tt>",
	      and "<tt>max</tt>" attributes.</t>
            <t>
	      Below is an example domain <tt>&lt;info&gt;</tt> command requesting the
	      server policies:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <info>
C:       <domain:info
C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:       </domain:info>
C:     </info>
C:     <extension>
C:       <ttl:info
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
C:         policy="true"/>
C:     </extension>
C:   </command>
C: </epp>
]]></sourcecode>

            <t>Below is an example domain <tt>&lt;info&gt;</tt> response providing the server policies:</t>

<sourcecode type="xml" markers="false"><![CDATA[
S: <?xml version="1.0" encoding="utf-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <domain:infData
S:         xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
S:         <domain:name>example.com</domain:name>
S:         <domain:roid>EXAMPLE1-REP</domain:roid>
S:         <domain:status s="ok"/>
S:         <domain:ns>
S:           <domain:hostObj>ns1.example.com</domain:hostObj>
S:           <domain:hostObj>ns1.example.net</domain:hostObj>
S:         </domain:ns>
S:         <domain:clID>ClientX</domain:clID>
S:         <domain:crID>ClientX</domain:crID>
S:         <domain:crDate>2023-11-08T10:14:55.0Z</domain:crDate>
S:         <domain:exDate>2024-11-08T10:14:55.0Z</domain:exDate>
S:       </domain:infData>
S:     </resData>
S:     <extension>
S:       <ttl:infData
S:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:         <ttl:ttl for="NS"
S:           min="3600"
S:           default="86400"
S:           max="172800">172800</ttl:ttl>
S:         <ttl:ttl for="DS"
S:           min="60"
S:           default="86400"
S:           max="172800">300</ttl:ttl>
S:       </ttl:infData>
S:       <secDNS:infData
S:         xmlns:secDNS="urn:ietf:params:xml:ns:secDNS-1.1">
S:         <secDNS:dsData>
S:           <secDNS:keyTag>12345</secDNS:keyTag>
S:           <secDNS:alg>13</secDNS:alg>
S:           <secDNS:digestType>2</secDNS:digestType>
S:           <secDNS:digest>49FD46E6C4B45C55D4AC</secDNS:digest>
S:         </secDNS:dsData>
S:       </secDNS:infData>
S:     </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>
]]></sourcecode>

            <t>Below is an example host <tt>&lt;info&gt;</tt> command requesting the server policies:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <info>
C:       <host:info
C:        xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:       </host:info>
C:     </info>
C:     <extension>
C:       <ttl:info
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
C:         policy="true"/>
C:     </extension>
C:   </command>
C: </epp>
]]></sourcecode>

            <t>Below is an example host <tt>&lt;info&gt;</tt> response providing the server policies:</t>

<sourcecode type="xml" markers="false"><![CDATA[
S: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
S: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
S:   <response>
S:     <result code="1000">
S:       <msg>Command completed successfully</msg>
S:     </result>
S:     <resData>
S:       <host:infData
S:         xmlns:host="urn:ietf:params:xml:ns:host-1.0">
S:         <host:name>ns1.example.com</host:name>
S:         <host:roid>NS1_EXAMPLE1-REP</host:roid>
S:         <host:status s="ok"/>
S:         <host:addr ip="v4">192.0.2.2</host:addr>
S:         <host:addr ip="v6">2001:db8::8:800:200c:417a</host:addr>
S:         <host:clID>ClientX</host:clID>
S:         <host:crID>ClientX</host:crID>
S:         <host:crDate>2023-11-08T10:14:55.0Z</host:crDate>
S:       </host:infData>
S:     </resData>
S:     <extension>
S:       <ttl:infData
S:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
S:         <ttl:ttl for="A"
S:           min="3600"
S:           default="86400"
S:           max="172800">172800</ttl:ttl>
S:         <ttl:ttl for="AAAA"
S:           min="3600"
S:           default="86400"
S:           max="172800">86400</ttl:ttl>
S:       </ttl:infData>
S:     </extension>
S:     <trID>
S:       <clTRID>ABC-12345</clTRID>
S:       <svTRID>54322-XYZ</svTRID>
S:     </trID>
S:   </response>
S: </epp>
]]></sourcecode>

          </section>
        </section>
      </section>

      <section>
        <name>EPP Transform Commands</name>
        <section>
          <name>EPP &lt;create&gt; Command</name>
          <t>
	    This extension defines an additional element for EPP
	    <tt>&lt;create&gt;</tt> commands for domain and host objects.</t>
          <t>
	    The <tt>&lt;command&gt;</tt> element of the
	    <tt>&lt;create&gt;</tt> command <bcp14>MAY</bcp14> contain an
	    <tt>&lt;extension&gt;</tt> element that <bcp14>MAY</bcp14>
	    contain a <tt>&lt;ttl:create&gt;</tt> element.  This element
	    <bcp14>MUST</bcp14> contain one or more <tt>&lt;ttl:ttl&gt;</tt>
	    records as described in <xref target="extension-elements"/>.</t>

      <t>If an EPP server receives a <tt>&lt;create&gt;</tt> command
      containing a TTL value that is outside the server's permitted range,
      it <bcp14>MUST</bcp14> reject the command with a 2004
      "Parameter value range error" response.</t>

          <t>
	    Below is an example domain <tt>&lt;create&gt;</tt> command:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <create>
C:       <domain:create
C:         xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:         <domain:period unit="y">1</domain:period>
C:         <domain:ns>
C:           <domain:hostObj>ns1.example.com</domain:hostObj>
C:           <domain:hostObj>ns1.example.net</domain:hostObj>
C:         </domain:ns>
C:         <domain:authInfo>
C:           <domain:pw/>
C:         </domain:authInfo>
C:       </domain:create>
C:     </create>
C:     <extension>
C:       <ttl:create
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:ttl for="NS">172800</ttl:ttl>
C:         <ttl:ttl for="DS">300</ttl:ttl>
C:       </ttl:create>
C:       <secDNS:create
C:         xmlns:secDNS="urn:ietf:params:xml:ns:secDNS-1.1">
C:         <secDNS:dsData>
C:           <secDNS:keyTag>12345</secDNS:keyTag>
C:           <secDNS:alg>13</secDNS:alg>
C:           <secDNS:digestType>2</secDNS:digestType>
C:           <secDNS:digest>49FD46E6C4B45C55D4AC</secDNS:digest>
C:         </secDNS:dsData>
C:       </secDNS:create>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>
]]></sourcecode>


          <t>Below is an example host <tt>&lt;create&gt;</tt> command:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <create>
C:       <host:create
C:         xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:         <host:addr ip="v4">192.0.2.2</host:addr>
C:         <host:addr ip="v6">2001:db8::8:800:200c:417a</host:addr>
C:       </host:create>
C:     </create>
C:     <extension>
C:       <ttl:create
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:ttl for="A"/>
C:         <ttl:ttl for="AAAA">86400</ttl:ttl>
C:       </ttl:create>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>
]]></sourcecode>
        </section>
        <section>
          <name>EPP &lt;update&gt; Command</name>
          <t>
	    This extension defines an additional element for EPP
	    <tt>&lt;update&gt;</tt> commands for domain and host objects.</t>
          <t>
	    The <tt>&lt;command&gt;</tt> element of the
	    <tt>&lt;update&gt;</tt> command <bcp14>MAY</bcp14> contain an
	    <tt>&lt;extension&gt;</tt> element that <bcp14>MAY</bcp14>
	    contain a <tt>&lt;ttl:update&gt;</tt> element.  This element
	    <bcp14>MUST</bcp14> contain one or more <tt>&lt;ttl:ttl&gt;</tt>
	    records as described in <xref target="extension-elements"/>.</t>

      <t>
  If an EPP server receives an <tt>&lt;update&gt;</tt> command
  containing a TTL value that is outside the server's permitted
  range, it <bcp14>MUST</bcp14> reject the command with a
  2004 "Parameter value range error" response.</t>

          <t>
	    Below is an example domain <tt>&lt;update&gt;</tt> command:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <update>
C:       <domain:update
C:         xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
C:         <domain:name>example.com</domain:name>
C:       </domain:update>
C:     </update>
C:     <extension>
C:       <ttl:update
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:ttl for="NS"/>
C:         <ttl:ttl for="custom"
C:           custom="DELEG"/>
C:         <ttl:ttl for="DS">86400</ttl:ttl>
C:       </ttl:update>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>
]]></sourcecode>

          <t>Below is an example host <tt>&lt;update&gt;</tt> command:</t>

<sourcecode type="xml" markers="false"><![CDATA[
C: <?xml version="1.0" encoding="UTF-8" standalone="no"?>
C: <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
C:   <command>
C:     <update>
C:       <host:update
C:         xmlns:host="urn:ietf:params:xml:ns:host-1.0">
C:         <host:name>ns1.example.com</host:name>
C:       </host:update>
C:     </update>
C:     <extension>
C:       <ttl:update
C:         xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
C:         <ttl:ttl for="A">86400</ttl:ttl>
C:         <ttl:ttl for="AAAA">3600</ttl:ttl>
C:       </ttl:update>
C:     </extension>
C:     <clTRID>ABC-12345</clTRID>
C:   </command>
C: </epp>
]]></sourcecode>
        </section>
      </section>
    </section>

    <section anchor="server-processing">
      <name>Server Processing of TTL Values</name>
      <section anchor="permitted-types">
        <name>Permitted Record Types</name>
        <t>
	  EPP servers <bcp14>MAY</bcp14> restrict the supported DNS record
	  types.  For example, a server <bcp14>MAY</bcp14> allow clients to
	  specify TTL values for <tt>DS</tt> records only.</t>
        <t>
	  A server that receives a <tt>&lt;create&gt;</tt> or
	  <tt>&lt;update&gt;</tt> command that includes a restricted record
	  type <bcp14>MUST</bcp14> respond with a 2306 "Parameter value
	  policy" error.</t>
        <t>
	  Clients can discover the DNS record types for which an EPP server
	  permits TTL values to be changed by performing a Policy Mode
	  <tt>&lt;info&gt;</tt> command, as outlined in <xref
	  target="policy-mode"/>.</t>
      </section>

      <section anchor="using_ttl_values">
        <name>Use of TTL Values in Delegation Records</name>
        <t>
	  EPP servers that implement this extension <bcp14>SHOULD</bcp14> use
	  the values provided by EPP clients for the TTL values of records
	  published in the DNS for domain and (if supported) host objects.
	  Server operators <bcp14>MAY</bcp14> disregard these values in order
	  to address security and stability issues, as described in <xref
	  target="operational-considerations"/> and <xref
	  target="security-considerations"/>.</t>
        <t>
	  EPP servers that use the host attribute model
	  <bcp14>SHOULD</bcp14> use any <tt>NS</tt>, <tt>A</tt>, and/or
	  <tt>AAAA</tt> TTL values specified for the domain object when
	  publishing <tt>NS</tt>, <tt>A</tt>, and/or <tt>AAAA</tt> records
	  derived from host attributes.</t>
      </section>
    </section>

    <section anchor="oob-changes">
      <name>Out-of-Band Changes to TTL Values</name>
      <t>In order to address operational or security issues, EPP server
      operators <bcp14>MAY</bcp14> make changes to TTL values out-of-band
      (that is, not in response to an <tt>&lt;update&gt;</tt> command received
      from the sponsoring client).
      </t>
      <t>
	Server operators <bcp14>MAY</bcp14> also implement automatic reset of
	TTL values, so that they revert to the default value a certain amount
	of time after an update has been made.
      </t>
      <t>
	If a TTL value is changed out-of-band, EPP server operators
	<bcp14>MAY</bcp14> notify the sponsoring client using the EPP Change
	Poll Extension <xref target="RFC8590"/>, which provides a
	generalized method for EPP servers to notify clients of changes to
	objects under their sponsorship.
      </t>
    </section>

    <section anchor="operational-considerations">
      <name>Operational Considerations</name>
      <section>
        <name>Operational Impact of TTL Values</name>
        <t>
	  Registry operators must consider the balance between registrants'
	  desire for changes to domains to be visible in the DNS quickly, and
	  the increased DNS query traffic that short TTLs can bring.</t>
        <t>
	  Registry operators <bcp14>SHOULD</bcp14> implement limits on the
	  maximum and minimum accepted TTL values that are narrower than the
	  values permitted in the XML schema in <xref target="formal-syntax"/>
	  (which were chosen to allow any TTL permitted in DNS records). This
	  is in order to prevent scenarios where an excessively high or low
	  TTL causes operational issues on either side of the zone cut.</t>
        <t><xref target="oob-changes"/> describes how server operators
        <bcp14>MAY</bcp14> unilaterally change TTL values in order to address
        operational or security issues, or only permit changes for limited
        time periods (after which TTLs revert to the default).</t>
      </section>
      <section>
        <name>When TTL Values Should Be Changed</name>
        <t>
	  A common operational mistake is changing the DNS record TTLs during
	  or after the planned change to the records themselves.  This arises
	  due to a misunderstanding about how TTLs work.</t>
        <t>
	  It is <bcp14>RECOMMENDED</bcp14> that guidance be provided to users
	  so they are aware that changes to a TTL are only effective in
	  shortening transition periods if implemented a period of time (at
	  least equal to the current TTL) <em>before</em> the planned change.
	  The latency between receipt of the <tt>&lt;update&gt;</tt> command
	  and the actual publication of the changes in the DNS should also be
	  taken into consideration in this calculation.</t>
      </section>
      <section>
        <name>Changes to Server Policy</name>
        <t>
	  Registry operators may change their policies relating to TTL values
	  from time to time.  Previously configured TTL values may
	  consequently fall outside a newly applied policy.  This document
	  places no obligation on EPP server operators in respect of these
	  values, and server operators may, as part of a policy change, change
	  the TTL values specified by clients for domain and host objects.
	  <xref target="oob-changes"/> describes how such out-of-band changes
	  should be carried out.</t>
      </section>
    </section>
    <section anchor="security-considerations">
      <name>Security Considerations</name>
      <section>
        <name>Fast Flux DNS</name>
        <t>
	  Some malicious actors use a technique called "fast flux DNS" <xref
	  target="SAC-025"/> to rapidly change the DNS configuration for a
	  zone in order to evade takedown and law enforcement activity.
	  Server operators should take this into consideration when setting
	  the lower limit on TTL values, since a short TTL on delegations may
	  enhance the effectiveness of fast flux techniques on evasion.</t>
        <t>
	  Client implementations that provide an interface for customers to
	  configure TTL values for domain names should consider implementing
	  controls to deter and mitigate abusive behavior, such as those
	  outlined in the "Current and Possible Mitigation Alternatives"
	  section of <xref target="SAC-025"/>.</t>
      </section>
      <section>
        <name>Compromised User Accounts</name>
        <t>
	  An attacker who obtains access to a customer account at a domain
	  registrar that supports this extension could make unauthorized
	  changes to the <tt>NS</tt> and/or glue records for a domain, and
	  then increase the associated TTLs so that the changes persist in
	  caches for a long time after the attack has been detected.</t>
        <t>
	  Client implementations that provide an interface for customers to
	  configure TTL values for domain names should consider implementing
	  upper limits in order to reduce the impact of account compromise, in
	  addition to best practices relating to credential management,
	  multi-factor authentication, risk-based access control, and so on.</t>
      </section>
    </section>
    <section anchor="IANA">
      <name>IANA Considerations</name>
      <section>
        <name>XML Namespace</name>
        <t>This document uses URNs to describe XML namespaces and XML schemas
        conforming to a registry mechanism described in <xref
        target="RFC3688"/>.  The following URI assignments have been made by
        IANA:</t>

        <t>Registration for the TTL namespace:</t>
	<dl spacing="compact" newline="false">
          <dt>URI:</dt><dd><tt>urn:ietf:params:xml:ns:epp:ttl-1.0</tt></dd>
          <dt>Registrant Contact:</dt><dd>IESG</dd>
          <dt>XML:</dt><dd>None. Namespace URIs do not represent an XML specification.</dd>
        </dl>

        <t>Registration for the TTL XML schema:</t>
	<dl spacing="compact" newline="false">
          <dt>URI:</dt><dd><tt>urn:ietf:params:xml:schema:epp:ttl-1.0</tt></dd>
          <dt>Registrant Contact:</dt><dd>IESG</dd>
          <dt>XML:</dt><dd>See <xref target="formal-syntax"/> of this
          document.</dd>
        </dl>
      </section>
      <section>
        <name>EPP Extension Registry</name>

<!-- [rfced] Section 7.2: May we update the name of the extension as
shown below? If so, we will ask IANA to update the registry accordingly (https://www.iana.org/assignments/epp-extensions/epp-extensions.xhtml).

This would match the edited title of this document as well as the
value's name as it appears in RFC 9499.

CURRENT:
Extensible Provisioning Protocol (EPP) Mapping for DNS Time-To-Live (TTL) values

SUGGESTED (lowercase 't' and capital 'V'):
Extensible Provisioning Protocol (EPP) Mapping for DNS Time-to-Live (TTL) Values

In that registry, we note that "Name of Extension" for this one also
matches the title of the RFC:
Extensible Provisioning Protocol (EPP) Secure Authorization
Information for Transfer (RFC 9167)
-->

<!-- GB: agreed on the name change. -->

        <t>The EPP extension described in this document has been registered by
        IANA in the "Extensions for the Extensible Provisioning Protocol
        (EPP)" registry described in <xref target="RFC7451"/>.  The details of
        the registration are as follows:</t>

	<dl spacing="compact" newline="false">
          <dt>Name of Extension:</dt>
	  <dd>Extensible Provisioning Protocol (EPP) Mapping for DNS Time-To-Live (TTL) values</dd>

          <dt>Document Status:</dt>
	  <dd>Standards Track</dd>

          <dt>Reference:</dt>
	  <dd>RFC 9803</dd>

          <dt>Registrant:</dt>
	  <dd>IESG</dd>

          <dt>TLDs:</dt>
	  <dd>Any</dd>

          <dt>IPR Disclosure:</dt>
	  <dd>None</dd>

          <dt>Status:</dt>
	  <dd>Active</dd>

          <dt>Notes:</dt>
	  <dd>None</dd>
        </dl>
      </section>
    </section>
    <section anchor="formal-syntax">
      <name>Formal Syntax</name>
      <t>
	The formal syntax presented here is a complete schema representation
	of the extension suitable for automated validation of EPP XML
	instances.</t>

<sourcecode type="xml" markers="false"><![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<schema
  xmlns="http://www.w3.org/2001/XMLSchema"
  targetNamespace="urn:ietf:params:xml:ns:epp:ttl-1.0"
  xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"
  elementFormDefault="qualified">
  <annotation>
    <documentation>
      Extensible Provisioning Protocol v1.0 extension
      schema for Time-To-Live (TTL) values for domain
      and host objects.
    </documentation>
  </annotation>

  <element name="info">
    <complexType>
      <attribute name="policy" type="boolean" default="false"/>
    </complexType>
  </element>

  <!--
    <ttl> elements can appear in <create> and
    <update> commands, and <info> responses
  -->

  <element name="create" type="ttl:commandContainer">
    <unique name="uniqueRRTypeForCreate">
      <selector xpath="ttl:ttl"/>
      <field xpath="@for"/>
    </unique>
  </element>

  <element name="update" type="ttl:commandContainer">
    <unique name="uniqueRRTypeForUpdate">
      <selector xpath="ttl:ttl"/>
      <field xpath="@for"/>
    </unique>
  </element>

  <element name="infData" type="ttl:responseContainer">
    <unique name="uniqueRRTypeForInfo">
      <selector xpath="ttl:ttl"/>
      <field xpath="@for"/>
    </unique>
  </element>

  <complexType name="commandContainer">
    <sequence>
      <element
        name="ttl"
        type="ttl:commandTTLType"
        minOccurs="1"
        maxOccurs="unbounded"/>
    </sequence>
  </complexType>

  <complexType name="responseContainer">
    <sequence>
      <element
        name="ttl"
        type="ttl:responseTTLType"
        minOccurs="1"
        maxOccurs="unbounded"/>
    </sequence>
  </complexType>

  <complexType name="commandTTLType">
    <simpleContent>
      <extension base="ttl:ttlOrNull">
        <attribute
          name="for"
          type="ttl:rrType"
          use="required"/>

        <attribute
          name="custom"
          type="ttl:customRRType"/>
      </extension>
    </simpleContent>
  </complexType>

  <complexType name="responseTTLType">
    <simpleContent>
      <extension base="ttl:ttlOrNull">
        <attribute
          name="for"
          type="ttl:rrType"
          use="required"/>

        <attribute
          name="custom"
          type="ttl:customRRType"/>

        <attribute
          name="min"
          type="ttl:ttlValue"/>

        <attribute
          name="default"
          type="ttl:ttlValue"/>

        <attribute
          name="max"
          type="ttl:ttlValue"/>
      </extension>
    </simpleContent>
  </complexType>

  <!--
    union type allowing the element to either contain
    nothing or a TTL value
  -->
  <simpleType name="ttlOrNull">
    <union
      memberTypes="ttl:emptyValue ttl:ttlValue"/>
  </simpleType>

  <!-- empty value type -->
  <simpleType name="emptyValue">
    <restriction base="token">
      <length value="0"/>
    </restriction>
  </simpleType>

  <!-- TTL value type -->
  <simpleType name="ttlValue">
    <restriction base="nonNegativeInteger">
      <minInclusive value="0"/>
      <maxInclusive value="2147483647"/>
    </restriction>
  </simpleType>

  <!-- resource record mnemonic type -->
  <simpleType name="rrType">
    <restriction base="token">
      <enumeration value="NS" />
      <enumeration value="DS" />
      <enumeration value="DNAME" />
      <enumeration value="A" />
      <enumeration value="AAAA" />
      <enumeration value="custom" />
    </restriction>
  </simpleType>

  <!-- custom resource record type -->
  <simpleType name="customRRType">
    <restriction base="token">
      <pattern value="A|[A-Z][A-Z0-9\-]*[A-Z0-9]"/>
    </restriction>
  </simpleType>
</schema>
]]></sourcecode>

    </section>
  </middle>
  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3688.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5731.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5732.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5910.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6895.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>

<!-- [XSD-DATATYPES] Updated to match internal guidance for W3C references. -->
        <reference anchor="XSD-DATATYPES" target="https://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">
          <front>
            <title>XML Schema Part 2: Datatypes Second Edition</title>
            <author initials="P." surname="Biron" fullname="Paul V. Biron" role="editor"/>
            <author initials="A." surname="Malhotra" fullname="Ashok Malhotra" role="editor"/>
            <date month="October" year="2004"/>
          </front>
          <refcontent>W3C Recommendation</refcontent>
          <annotation>Latest version available at <eref target="https://www.w3.org/TR/xmlschema-2/" brackets="angle"/>.</annotation>
        </reference>
        <reference anchor="IANA-RRTYPES" target="https://www.iana.org/assignments/dns-parameters">
          <front>
            <title>Resource Record (RR) TYPEs</title>
            <author>
              <organization>IANA</organization>
            </author>
          </front>
        </reference>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6927.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7451.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8590.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9364.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9499.xml"/>
        <reference anchor="SAC-025" target="https://www.icann.org/en/system/files/files/sac-025-en.pdf">
          <front>
            <title>SSAC Advisory on Fast Flux Hosting and DNS</title>
            <author>
              <organization>ICANN Security and Stability Advisory Committee (SSAC)</organization>
            </author>
            <date month="January" year="2008"/>
          </front>
          <seriesInfo name="SAC" value="025"/>
        </reference>
      </references>
    </references>

    <section numbered="false">
      <name>Acknowledgments</name>
      <t>The author wishes to thank the following people for their advice and
      feedback during the development of this document:</t>
      <ul>
        <li><t><contact fullname="James Gould"/></t></li>
        <li><t><contact fullname="Hugo Salgado"/></t></li>
        <li><t><contact fullname="Patrick Mevzek"/></t></li>
        <li><t><contact fullname="Rick Wilhelm"/></t></li>
        <li><t><contact fullname="Marc Groeneweg"/></t></li>
        <li><t><contact fullname="Ties de Kock"/></t></li>
        <li><t><contact fullname="Tim Wicinski"/></t></li>
        <li><t><contact fullname="Jasdip Singh"/></t></li>
      </ul>
    </section>
  </back>

<!-- [rfced] FYI, we have added expansions for abbreviations upon first use
per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please review each
expansion in the document carefully to ensure correctness.
-->

<!-- GB: they all look fine. -->

<!-- [rfced] Regarding usage of  <tt>, <em>, and <strong> elements,
please review the occurrences and let us know if any updates are
needed for consistency. Details below.

In the HTML and PDF outputs, <tt> yields fixed-width font.
In the text output, there is no change.
 - In this document: seemingly used for RR names, attribute names,
and some examples.

In the HTML and PDF outputs, <em> yields italics.
In the text output, <em> yields an underscore before and after.
 - In this document: used for one instance of emphasis.

In the HTML and PDF outputs, <strong> yields bold.
In the text output, <strong> yields an asterisk before and after.
 - In this document: used for field names in the IANA Considerations.
 - We recommend removing these, as the asterisks seem unnecessary in the
text file, and this font styling is not typically used in
IANA Considerations sections. Please let us know if you agree.
-->

<!-- GB: agreed. all <strong> tags have been removed. -->

<!-- [rfced] Please review the "type" attribute of each sourcecode element
in the XML file to ensure correctness. If the current list of preferred
values for "type"
(https://www.rfc-editor.org/rpc/wiki/doku.php?id=sourcecode-types)
does not contain an applicable type, then feel free to let us know.
Also, it is acceptable to leave the "type" attribute not set. -->

<!-- GB: I have set the "type" attribute of all <sourcecode> elements. -->

<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.  Updates of this nature typically
result in more precise language, which is helpful for readers.

For example, please consider whether "white space" should be updated in the
text below:

   Indentation and white space in examples are provided only to illustrate
   element relationships and are not required features of this protocol.
-->

<!-- GB: I don't see any suggested alternative to "white space" in the NIST
  guidance. I did some googling and the only suggested alternative is "empty
  space", but I think the context it was suggested in was graphic design. In this
  context I think that phrase would be ambiguous. -->

</rfc>