Internet-Draft | TTL mapping for EPP | September 2024
Brown | Expires 6 March 2025 | [Page]

Workgroup:
  Registration Protocols Extensions (regext)
Internet-Draft:
  draft-ietf-regext-epp-ttl-16
Published:
  2 September 2024
Intended Status:
  Standards Track
Expires:
  6 March 2025
Author:
  G. Brown
  ICANN

# Extensible Provisioning Protocol (EPP) mapping for DNS Time-To-Live (TTL) values

## 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶

This Internet-Draft will expire on 6 March 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. 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.¶

## 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 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.¶

#### 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.¶

##### 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.¶

##### 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

#### 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`:¶

    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`:¶

    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`:¶

    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:¶

    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>
            <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:¶

    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.¶

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:¶

    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:¶

    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.¶

## 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.¶

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.¶

## 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.¶

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¶

### 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>
      </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>

¶

## 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¶

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 15 to 16

1. Updates as suggested during IESG review.¶

### 10.2. 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).¶

### 10.3. Changes from 13 to 14

1. Resolve remaining nit before IESG submission.¶

### 10.4. Changes from 12 to 13

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

### 10.5. Changes from 11 to 12

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

### 10.6. Changes from 10 to 11

1. Fix double word in Section 3.2.¶

### 10.7. 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.¶

### 10.8. Changes from 08 to 09

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

### 10.9. Changes from 07 to 08

1. Some wording changes suggested by Rick Wilhelm.¶

### 10.10. Changes from 06 to 07

1. Minor wording changes and nits reported by JG.¶

### 10.11. 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.¶

### 10.12. 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).¶

### 10.13. 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.¶

### 10.14. 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.¶

### 10.15. 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.¶
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.¶

### 10.16. 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.¶

### 10.17. 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¶
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/>.

### 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