Registration Protocols Extensions (regext)                      G. Brown
Internet-Draft                                                     ICANN
Intended status: Standards Track                         14 October 2024
Expires: 17 April 2025


  Extensible Provisioning Protocol (EPP) mapping for DNS Time-To-Live
                              (TTL) values
                      draft-ietf-regext-epp-ttl-17

Abstract

   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.

About this draft

   This note is to be removed before publishing as an RFC.

   The source for this draft, and an issue tracker, may can be found at
   https://github.com/gbxyz/epp-ttl-extension.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 17 April 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.



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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Conventions used in this document . . . . . . . . . . . .   4
     1.2.  Extension elements  . . . . . . . . . . . . . . . . . . .   4
       1.2.1.  The <ttl:ttl> element . . . . . . . . . . . . . . . .   5
         1.2.1.1.  Element content . . . . . . . . . . . . . . . . .   5
         1.2.1.2.  Supported DNS record types  . . . . . . . . . . .   6
         1.2.1.3.  The <ttl:info> element  . . . . . . . . . . . . .   7
       1.2.2.  Examples  . . . . . . . . . . . . . . . . . . . . . .   7
         1.2.2.1.  Explicit TTL value (<create> or <update>
                 command)  . . . . . . . . . . . . . . . . . . . . .   7
         1.2.2.2.  Explicit TTL value (<info> policy mode) . . . . .   7
         1.2.2.3.  Empty value indicating default TTL (<create> or
                 <update> command, <info> default mode)  . . . . . .   7
         1.2.2.4.  Custom record type (<create> or <update> command,
                 <info> default mode)  . . . . . . . . . . . . . . .   7
   2.  EPP command mapping . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  EPP query commands  . . . . . . . . . . . . . . . . . . .   7
       2.1.1.  EPP <info> command  . . . . . . . . . . . . . . . . .   8
         2.1.1.1.  Default Mode  . . . . . . . . . . . . . . . . . .   8
         2.1.1.2.  Policy Mode . . . . . . . . . . . . . . . . . . .  11
     2.2.  EPP transform commands  . . . . . . . . . . . . . . . . .  14
       2.2.1.  EPP <create> command  . . . . . . . . . . . . . . . .  14
       2.2.2.  EPP <update> command  . . . . . . . . . . . . . . . .  16
   3.  Server processing of TTL values . . . . . . . . . . . . . . .  18
     3.1.  Permitted record types  . . . . . . . . . . . . . . . . .  18
     3.2.  Use of TTL values in delegation records . . . . . . . . .  18
   4.  Out-of-band changes to TTL values . . . . . . . . . . . . . .  18
   5.  Operational considerations  . . . . . . . . . . . . . . . . .  18
     5.1.  Operational impact of TTL values  . . . . . . . . . . . .  18
     5.2.  When TTL values should be changed . . . . . . . . . . . .  19
     5.3.  Changes to server policy  . . . . . . . . . . . . . . . .  19
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  19
     6.1.  Fast-flux DNS . . . . . . . . . . . . . . . . . . . . . .  19
     6.2.  Compromised user accounts . . . . . . . . . . . . . . . .  20
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  20
     7.1.  XML namespace . . . . . . . . . . . . . . . . . . . . . .  20
     7.2.  EPP extension registry  . . . . . . . . . . . . . . . . .  21
   8.  Formal syntax . . . . . . . . . . . . . . . . . . . . . . . .  21
   9.  Implementation status . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Verisign EPP SDK  . . . . . . . . . . . . . . . . . . . .  24



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     9.2.  Pepper EPP Client . . . . . . . . . . . . . . . . . . . .  25
   10. Change log  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     10.1.  Changes from 16 to 17  . . . . . . . . . . . . . . . . .  25
     10.2.  Changes from 15 to 16  . . . . . . . . . . . . . . . . .  25
     10.3.  Changes from 14 to 15  . . . . . . . . . . . . . . . . .  26
     10.4.  Changes from 13 to 14  . . . . . . . . . . . . . . . . .  26
     10.5.  Changes from 12 to 13  . . . . . . . . . . . . . . . . .  26
     10.6.  Changes from 11 to 12  . . . . . . . . . . . . . . . . .  26
     10.7.  Changes from 10 to 11  . . . . . . . . . . . . . . . . .  26
     10.8.  Changes from 09 to 10  . . . . . . . . . . . . . . . . .  26
     10.9.  Changes from 08 to 09  . . . . . . . . . . . . . . . . .  26
     10.10. Changes from 07 to 08  . . . . . . . . . . . . . . . . .  27
     10.11. Changes from 06 to 07  . . . . . . . . . . . . . . . . .  27
     10.12. Changes from 05 to 06  . . . . . . . . . . . . . . . . .  27
     10.13. Changes from 04 to 05  . . . . . . . . . . . . . . . . .  27
     10.14. Changes from 04 to 05  . . . . . . . . . . . . . . . . .  27
     10.15. Changes from 03 to 04  . . . . . . . . . . . . . . . . .  27
     10.16. Changes from 02 to 03  . . . . . . . . . . . . . . . . .  27
     10.17. Changes from 01 to 02  . . . . . . . . . . . . . . . . .  28
     10.18. Changes from 00 to 01  . . . . . . . . . . . . . . . . .  28
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     12.1.  Normative references . . . . . . . . . . . . . . . . . .  29
     12.2.  Informative references . . . . . . . . . . . . . . . . .  30
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   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 NS records, but may also include DS records for
   domains secured with DNSSEC ([RFC9364]), and DNAME records for IDN
   variants ([RFC6927]).  A and/or AAAA records may also be published
   for nameservers where required by DNS resolvers to avoid an infinite
   loop.

   Typically, the Time-To-Live value (TTL, see Section 5 of [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.

   This document describes an EPP extension to the domain name and host
   object mappings (described in [RFC5731] and [RFC5732], respectively)
   which allows the sponsor of a domain name or host object to change



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   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 co-ordinate to manage TTL values in
   response to changes in operational or security requirements.

1.1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   In examples, "C:" represents lines sent by a protocol client and "S:"
   represents lines returned by a protocol server.  Indentation and
   white space in examples are provided only to illustrate element
   relationships and are not required features of this protocol.

   A protocol client that is authorized to manage an existing object is
   described as a "sponsoring" client throughout this document.

   XML is case sensitive.  Unless stated otherwise, XML specifications
   and examples provided in this document MUST be interpreted in the
   character case presented in order to develop a conforming
   implementation.

   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.

   The XML namespace prefixes used in examples (such as the string ttl
   in ttl:create) are solely for illustrative purposes.  A conforming
   implementation MUST NOT require the use of these or any other
   specific namespace prefixes.

   In accordance with Section 3.2.2.1 of XML Schema Part 2: Datatypes
   [XSD-DATATYPES], the allowable lexical representations for the
   xs:boolean datatype are the strings "0" and "false" for the concept
   'false' and the strings "1" and "true" for the concept 'true'.
   Implementations MUST support both styles of lexical representation.

1.2.  Extension elements

   This extension adds additional elements to the EPP domain and host
   mappings.




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1.2.1.  The <ttl:ttl> element

   The <ttl:ttl> element is used to define TTL values for the DNS
   resource records associated with domain and host objects.

   <ttl:ttl> elements may have the following attributes, depending on
   whether it appears in a command or response frame:

   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.

   3.  "min", which MUST NOT be present in command frames but MAY be
       present in response frames (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 command frames but MAY be
       present in response frames (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 command frames but MAY be
       present in response frames (see Section 2.1.1), and which is used
       by the server to indicate the highest value that may be set;

   When present, the value of the "min" attribute MUST be lower than the
   value of the "max" attribute.  The "default" attribute MUST be
   between the "min" and "max" values, inclusively.

1.2.1.1.  Element content

   The XML schema found in Section 8 of this document restricts the
   content of <ttl:ttl> elements to be either:

   1.  a non-negative integer, indicating the value of the TTL in
       seconds, or

   2.  empty, in which case the server's default TTL for the given
       record type is to be applied.






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1.2.1.2.  Supported DNS record types

   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 "custom" attribute of the <ttl:ttl>
   element.

   The regular expression which is used to validate the values of the
   "custom" attribute is based on the expression found in Section 3.1 of
   [RFC6895], and 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 (Section 7 of
   [RFC9499]) are specified.

   Nevertheless, EPP servers which implement this extension MUST
   restrict the DNS record types that are accepted in <create> and
   <update> commands, and included in <info> responses, allowing only
   those types that are actually published in the DNS for domain and
   host objects.

   A server that receives a <create> or <update> command that attempts
   to set TTL values for inapplicable DNS record types MUST respond with
   a 2306 "Parameter value policy" error.

   As an illustrative example, a server MAY allow clients to specify TTL
   values for the following record types for domain objects:

   1.  NS;

   2.  DS (if the server also implements [RFC5910]);

   3.  DNAME (if the server implements IDN variants using DNAME
       records).

1.2.1.2.1.  Glue records

   Glue records are described in Section 7 of [RFC9499].

   Servers which implement host objects ([RFC5732]) MAY allow clients to
   specify TTL values for A and AAAA records for host objects.

   A server supporting host objects which receives a command that
   attempts to set TTL values for A and AAAA records on a domain object
   MUST respond with a 2306 "Parameter value policy" error.

   EPP servers which use the "host attribute" model (described in
   Section 1.1 of [RFC5731]) MAY allow clients to specify TTL values for
   A and AAAA records for domain objects.



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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.

1.2.1.3.1.  Example

   <ttl:info policy="true"/>

1.2.2.  Examples

1.2.2.1.  Explicit TTL value (<create> or <update> command)

   <ttl:ttl for="NS">3600<ttl:ttl>

1.2.2.2.  Explicit TTL value (<info> policy mode)

   <ttl:ttl
     for="NS"
     min="60"
     default="86400"
     max="172800">3600<ttl:ttl>

1.2.2.3.  Empty value indicating default TTL (<create> or <update>
          command, <info> default mode)

   <ttl:ttl for="NS"/>

1.2.2.4.  Custom record type (<create> or <update> command, <info>
          default mode)

   <ttl:ttl
     for="custom"
     custom="NEWRRTYPE">3600<ttl:ttl>

2.  EPP command mapping

2.1.  EPP query commands







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2.1.1.  EPP <info> command

   This extension defines an additional element for EPP <info> commands
   and responses for domain and host objects.

   The EPP <info> command is extended to support two different modes:

   1.  The Default Mode (Section 2.1.1.1), which requests the inclusion
       of all non-default TTL values in the response; and

   2.  The Policy Mode (Section 2.1.1.2), 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.

2.1.1.1.  Default Mode

   If a server receives an <info> command for a domain or host object
   which includes a <ttl:info> element with a "policy" attribute that is
   "0" or "false", then the EPP response MUST contain <ttl:ttl> records
   for all DNS record types that have non-default TTL values.  These
   elements MUST NOT have the "min", "default" and "max" attributes.

   Example domain <info> command with a <ttl:info> element with a policy
   attribute that is false:

   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>

   Example domain <info> response to a command with a <ttl:info> element
   with a policy attribute that is false:






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   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>

   Example host <info> command with a <ttl:info> element with a policy
   attribute that is false:




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   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>

   Example host <info> response to a command with a <ttl:info> element
   with a policy attribute that is false:
































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   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>

2.1.1.2.  Policy Mode

   If a server receives an <info> command for a domain or host object
   which includes a <ttl:info> element with a "policy" attribute is "1"
   or "true", then the EPP response MUST contain <ttl:ttl> records for
   all supported DNS record types, irrespective of whether those record
   types are actually in use by the object in question.  These elements
   MUST have the "min", "default" and "max" attributes.

   Example domain <info> command requesting the server policies:








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   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>

   Example domain <info> response providing the server policies:

   <?xml version="1.0" encoding="utf-8" standalone="no"?>
   <epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
     <response>
       <result code="1000">
         <msg>Command completed successfully</msg>
       </result>
       <resData>
         <domain:infData
           xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
           <domain:name>example.com</domain:name>
           <domain:roid>EXAMPLE1-REP</domain:roid>
           <domain:status s="ok"/>
           <domain:ns>
             <domain:hostObj>ns1.example.com</domain:hostObj>
             <domain:hostObj>ns1.example.net</domain:hostObj>
           </domain:ns>
           <domain:clID>ClientX</domain:clID>
           <domain:crID>ClientX</domain:crID>
           <domain:crDate>2023-11-08T10:14:55.0Z</domain:crDate>
           <domain:exDate>2024-11-08T10:14:55.0Z</domain:exDate>
         </domain:infData>
       </resData>
       <extension>
         <ttl:infData
           xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0">
           <ttl:ttl for="NS"
             min="3600"
             default="86400"
             max="172800">172800</ttl:ttl>



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           <ttl:ttl for="DS"
             min="60"
             default="86400"
             max="172800">300</ttl:ttl>
         </ttl:infData>
         <secDNS:infData
           xmlns:secDNS="urn:ietf:params:xml:ns:secDNS-1.1">
           <secDNS:dsData>
             <secDNS:keyTag>12345</secDNS:keyTag>
             <secDNS:alg>13</secDNS:alg>
             <secDNS:digestType>2</secDNS:digestType>
             <secDNS:digest>49FD46E6C4B45C55D4AC</secDNS:digest>
           </secDNS:dsData>
         </secDNS:infData>
       </extension>
       <trID>
         <clTRID>ABC-12345</clTRID>
         <svTRID>54322-XYZ</svTRID>
       </trID>
     </response>
   </epp>

   Example host <info> command requesting the server policies:

   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>

   Example host <info> response providing the server policies:









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   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>

2.2.  EPP transform commands

2.2.1.  EPP <create> command

   This extension defines an additional element for EPP <create>
   commands for domain and host objects.






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   The <command> element of the <create> command frame MAY contain an
   <extension> element which MAY contain a <ttl:create> element.  This
   element MUST contain one or more <ttl:ttl> records as described in
   Section 1.2.

   Example domain <create> command:

   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>

   Example host <create> command:






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   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>

   If an EPP server receives a <create> command containing a TTL value
   that is outside the server's permitted range, it MUST reject the
   command with a 2004 "Parameter value range error" response.

2.2.2.  EPP <update> command

   This extension defines an additional element for EPP <update>
   commands for domain and host objects.

   The <command> element of the <update> command frame MAY contain an
   <extension> element which MAY contain a <ttl:update> element.  This
   element MUST contain one or more <ttl:ttl> records as described in
   Section 1.2.

   Example domain <update> command:














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   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>

   Example host <update> command:

   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>

   If an EPP server receives an <update> command containing a TTL value
   that is outside the server's permitted range, it MUST reject the
   command with a 2004 "Parameter value range error" response.




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3.  Server processing of TTL values

3.1.  Permitted record types

   Servers SHOULD restrict the supported DNS record types in accordance
   with their own policy.  For example, a server MAY allow clients to
   specify TTL values for DS records only.

   A server which receives a <create> or <update> command which includes
   a restricted record type MUST respond with a 2306 "Parameter value
   policy" error.

   Clients can discover the DNS record types for which an EPP server
   permits TTL values to be changed by performing a "Policy Mode" <info>
   command, as outlined in Section 2.1.1.2.

3.2.  Use of TTL values in delegation records

   EPP servers which implement this extension SHOULD use the values
   provided by EPP clients for the TTL values of records published in
   the DNS for domain and (if supported) host objects.

   EPP servers that use the "host attribute" model SHOULD use any NS, A
   and/or AAAA TTL values specified for the domain object when
   publishing NS, A and/or AAAA records derived from host attributes.

4.  Out-of-band changes to TTL values

   EPP server operators MAY, in order to address operational or security
   issues, make changes to TTL values out-of-band (that is, not in
   response to an <update> command received from the sponsoring client).

   Server operators MAY 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.

   If a TTL value is changed out-of-band, EPP server operators MAY
   notify the sponsoring client using the EPP Change Poll extension
   ([RFC8590]), which provides a generalised method for EPP servers to
   notify clients of changes to objects under their sponsorship.

5.  Operational considerations

5.1.  Operational impact of TTL values

   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.



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   Registry operators SHOULD implement limits on the maximum and minimum
   accepted TTL values that are narrower than the values permitted in
   the XML schema in the Formal syntax (which were chosen to allow any
   TTL permitted in DNS records), in order to prevent scenarios where an
   excessively high or low TTL causes operational issues on either side
   of the zone cut.

   Section 4 describes how server operators MAY 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).

5.2.  When TTL values should be changed

   A common operational mistake is changing of DNS record TTLs during or
   after the planned change to the records themselves.  This arises due
   to a misunderstanding about how TTLs work.

   It is RECOMMENDED 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 — _before_ the planned change.  The latency
   between receipt of the <update> command and the actual publication of
   the changes in the DNS should also be taken into consideration in
   this calculation.

5.3.  Changes to server policy

   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.  Section 4
   describes how such out-of-band changes should be carried out.

6.  Security considerations

6.1.  Fast-flux DNS

   Some malicious actors use a technique called "fast flux DNS"
   ([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.





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   Client implementations which provide an interface for customers to
   configure TTL values for domain names should consider implementing
   controls to deter and mitigate abusive behaviour, such as those
   outlined in the "Current and Possible Mitigation Alternatives"
   section of [SAC-025].

6.2.  Compromised user accounts

   An attacker who obtains access to a customer account at a domain
   registrar which supports this extension could make unauthorised
   changes to the NS 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.

   Client implementations which 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.

7.  IANA considerations

7.1.  XML namespace

   This document uses URNs to describe XML namespaces and XML schemas
   conforming to a registry mechanism described in [RFC3688].  The
   following URI assignment is requested of IANA:

   Registration for the TTL namespace:

      *URI:* urn:ietf:params:xml:ns:epp:ttl-1.0

      *Registrant Contact:* IESG

      *XML:* None.  Namespace URIs do not represent an XML specification

   Registration for the TTL XML schema:

      *URI:* urn:ietf:params:xml:schema:epp:ttl-1.0

      *Registrant Contact:* IESG

      *XML:* See the "Formal syntax" section of this document








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7.2.  EPP extension registry

   The EPP extension described in this document is to be registered by
   IANA in the Extensions for the "Extensible Provisioning Protocol
   (EPP)" registry described in [RFC7451].  The details of the
   registration are as follows:

      *Name of Extension:* Extensible Provisioning Protocol (EPP)
      Mapping for DNS Time-To-Live (TTL) values

      *Document Status:* Standards Track

      *Reference:* URL of this document

      *Registrant Name and Email Address:* IESG

      *TLDs:* Any

      *IPR Disclosure:* None

      *Status:* Active

      *Notes:* None

8.  Formal syntax

   The formal syntax presented here is a complete schema representation
   of the extension suitable for automated validation of EPP XML
   instances.

   <?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>



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     </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>




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     <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



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         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>

9.  Implementation status

   This section is to be removed before publishing as an RFC.

9.1.  Verisign EPP SDK

   *Organization:* Verisign Inc.

   *Name:* Verisign EPP SDK




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   *Description:* The Verisign EPP SDK includes both a full client
   implementation and a full server stub implementation of this
   specification.

   *Level of maturity:* Development

   *Coverage:* All aspects of the protocol are implemented.

   *Licensing:* GNU Lesser General Public License

   *Contact:* jgould@verisign.com

   *URL:* https://www.verisign.com/en_US/channel-resources/domain-
   registry-products/epp-sdks

9.2.  Pepper EPP Client

   *Name:* Pepper EPP Client

   *Description:* The Pepper EPP client fully implements this
   specification.  The underlying Net::EPP:: Perl module also implements
   this specification.

   *Level of maturity:* Development

   *Coverage:* All aspects of the protocol will be implemented.

   *Licensing:* Perl Artistic License

   *Contact:* The author of this document.

   *URL:* https://github.com/gbxyz/pepper

10.  Change log

   This section is to be removed before publishing as an RFC.

10.1.  Changes from 16 to 17

   1.  Further updates as suggested during IESG review.

10.2.  Changes from 15 to 16

   1.  Updates as suggested during IESG review.







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10.3.  Changes from 14 to 15

   1.  Updates as suggested during AD review.

   2.  In the last paragraph of Section 3.2, make both lists of RR types
       be the same.

   3.  Update error codes to be consistent: 2004 (range error) when the
       TTL value is outside the permitted range, and 2306 (policy error)
       for an invalid record type.

   4.  Correct section in reference to RFC 6895 (thanks Jasdip Singh).

   5.  Minor typographic fixes (thanks Jasdip Singh).

10.4.  Changes from 13 to 14

   1.  Resolve remaining nit before IESG submission.

10.5.  Changes from 12 to 13

   1.  Updates as per the document shepherd's suggestions.

10.6.  Changes from 11 to 12

   1.  Updates as per the document shepherd's email to the list of
       2024-06-10.

10.7.  Changes from 10 to 11

   1.  Fix double word in Section 3.2.

10.8.  Changes from 09 to 10

   Changes resulting from the Dnsdir review:

   1.  Fixed example IPv6 addresses to use the preferred prefix
       2001:DB8::.

   2.  Added paragraph to Section 3.1 describing how clients can use the
       Policy Mode <info> command (Section 2.1.1.2) to discover the DNS
       record types supported by the server.

10.9.  Changes from 08 to 09

   1.  Some wording changes suggested by James Gould and Tim Wicinski.





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10.10.  Changes from 07 to 08

   1.  Some wording changes suggested by Rick Wilhelm.

10.11.  Changes from 06 to 07

   1.  Minor wording changes and nits reported by JG.

10.12.  Changes from 05 to 06

   1.  Changed how <info> commands work so that a <ttl:info> element is
       required in order for <ttl:ttl> elements to be included in the
       response.  Thanks to JG for this feedback.

10.13.  Changes from 04 to 05

   1.  removed the erroneous required="true" attribute from the min,
       default and max attributes of the responseTTLType type (thanks
       JG).

   2.  fixed the reference to RFC 6895 (thanks HS).

10.14.  Changes from 04 to 05

   1.  Add the Verisign EPP SDK to Section 9.

   2.  Add the <ttl:info> element and document how it affects server
       <info> responses.

   3.  Updated examples to exercise more of the schema.

   4.  Minor schema issue fixed.

10.15.  Changes from 03 to 04

   1.  Changed the for attribute to be an enumeration and added the
       custom attribute.

   2.  Added the min, default and max attributes.

   3.  Apply feedback from Jim Gould.

10.16.  Changes from 02 to 03

   1.  Rolled back the "straw man" syntax from 02. ttl:ttl now has a for
       attribute which can be any DNS record type.  Section 1.2.1.2
       describes how the set of supported record types may be limited.




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   2.  Removed the global/explicit models and just use the explicit
       model.

   3.  Removed the cascading effect where a TTL set on a domain affects
       subordinate hosts.

10.17.  Changes from 01 to 02

   1.  Renamed the ttl:seconds XSD type to ttl:container, and the
       ttl:nonNegativeInteger type to ttl:ttlType, to permit multiple
       TTL values.

   2.  Converted XML instances from artwork to source code.

10.18.  Changes from 00 to 01

   1.  Incorporate feedback from Jim Gould.

   2.  Add wording to describe how TTL values are jointly managed by
       both clients and servers.

   3.  Fix minimum/maximum TTL value and schema namespace (thanks
       Patrick Mevzek).

   4.  Moved text on how the server should handle impermissible TTL
       values from the top of Section 4 to Sections 3.2.1 and 3.2.2
       (thanks Rick Wilhelm).

   5.  Namespace changed from urn:ietf:params:xml:ns:ttl-1.0 to
       urn:ietf:params:xml:ns:epp:ttl-1.0.

   6.  Added discussion on EPP servers which use the host attribute
       model in Section 3.2 (thanks Hugo Salgado).

   7.  Added a Change Log (Section 10).

11.  Acknowledgements

   The author wishes to thank the following people for their advice and
   feedback during the development of this document:

   1.  James Gould

   2.  Hugo Salgado

   3.  Patrick Mevzek

   4.  Rick Wilhelm



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   5.  Marc Groeneweg

   6.  Ties de Kock

   7.  Tim Wicinski

   8.  Jasdip Singh

12.  References

12.1.  Normative references

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC5731]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Domain Name Mapping", STD 69, RFC 5731,
              DOI 10.17487/RFC5731, August 2009,
              <https://www.rfc-editor.org/info/rfc5731>.

   [RFC5732]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Host Mapping", STD 69, RFC 5732, DOI 10.17487/RFC5732,
              August 2009, <https://www.rfc-editor.org/info/rfc5732>.

   [RFC5910]  Gould, J. and S. Hollenbeck, "Domain Name System (DNS)
              Security Extensions Mapping for the Extensible
              Provisioning Protocol (EPP)", RFC 5910,
              DOI 10.17487/RFC5910, May 2010,
              <https://www.rfc-editor.org/info/rfc5910>.

   [RFC6895]  Eastlake 3rd, D., "Domain Name System (DNS) IANA
              Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
              April 2013, <https://www.rfc-editor.org/info/rfc6895>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [XSD-DATATYPES]
              World Wide Web Consortium (W3C), "XML Schema Part 2:
              Datatypes Second Edition", October 2004,
              <https://www.w3.org/TR/xmlschema-2/>.



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12.2.  Informative references

   [RFC6927]  Levine, J. and P. Hoffman, "Variants in Second-Level Names
              Registered in Top-Level Domains", RFC 6927,
              DOI 10.17487/RFC6927, May 2013,
              <https://www.rfc-editor.org/info/rfc6927>.

   [RFC7451]  Hollenbeck, S., "Extension Registry for the Extensible
              Provisioning Protocol", RFC 7451, DOI 10.17487/RFC7451,
              February 2015, <https://www.rfc-editor.org/info/rfc7451>.

   [RFC8590]  Gould, J. and K. Feher, "Change Poll Extension for the
              Extensible Provisioning Protocol (EPP)", RFC 8590,
              DOI 10.17487/RFC8590, May 2019,
              <https://www.rfc-editor.org/info/rfc8590>.

   [RFC9364]  Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
              RFC 9364, DOI 10.17487/RFC9364, February 2023,
              <https://www.rfc-editor.org/info/rfc9364>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/info/rfc9499>.

   [SAC-025]  ICANN Security and Stability Advisory Committee (SSAC),
              "SSAC Advisory on Fast Flux Hosting and DNS", SAC 25,
              January 2008,
              <https://www.icann.org/en/system/files/files/sac-
              025-en.pdf>.

Author's Address

   Gavin Brown
   ICANN
   12025 Waterfront Drive, Suite 300
   Los Angeles, CA 90292
   United States of America
   Email: gavin.brown@icann.org
   URI:   https://www.icann.org/












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