| Internet-Draft | TTL mapping for EPP | September 2023 |
| Brown | Expires 8 March 2024 | [Page] |
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.¶
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.¶
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This Internet-Draft will expire on 8 March 2024.¶
Copyright (c) 2023 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.¶
The principal output of any domain name provisioning 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 include, at minimum, one or more NS records, but may also include A and/or AAAA glue records, DS records, and DNAME records for IDN variants ([RFC6927]).¶
Typically, the Time-To-Live value (TTL, see Section 5 of [RFC8499]) 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 used for that domain: 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 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.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶
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:secs) are solely for illustrative purposes.
A conforming implementation MUST NOT require the use of these or any other specific namespace prefixes.¶
This extension adds additional elements to the EPP domain and host mappings. Two modes are supported: a global TTL mode, where a single value is specified for all DNS records associated with the object, and an explicit mode, where specific TTL values are provided for each DNS record type. These modes are described further below.¶
EPP servers MUST support at least one of these modes.
If an EPP server received a command which uses an unsupported mode, it MUST respond with a 2102 "unimplemented option" error.¶
A global TTL value is represented using the <ttl:ttl> element. EPP clients and servers use this element in EPP commands and responses to indicate the TTL value for all DNS records associated with an object.¶
The <ttl:ttl> element MAY contain an unsigned integer value indicating the TTL in seconds, or MAY be empty, in which case the server's default value will be applied.¶
Example global TTL value:¶
<ttl:ttl>3600</ttl:ttl>¶
Example global TTL default value:¶
<ttl:ttl/>¶
The explicit model allows distinct TTL values to be defined for each DNS record type associated with an object.¶
Explicit TTL values are represented using the <ttl:ttls> element. Depending on the object type, this element will have different child elements.¶
For domain objects, the <ttl:ttls> element contains the following child elements:¶
<ttl:NS> element, which contains the TTL values for the NS records associated with the domain name;¶
<ttl:DS> element, which contains the TTL values for the DS record(s) associated with the domain name;¶
<ttl:DNAME> element, which contains the TTL values for the DNAME record associated with the domain name;¶
<ttl:A> element, which contains the TTL values for the A records associated with the domain name;¶
<ttl:AAAA> element, which contains the TTL values for the AAAAA records associated with the domain name.¶
The <ttl:NS>, <ttl:DS>, <ttl:DNAME>, <ttl:A> and <ttl:AAAA> elements all have the same content model as the <ttl:ttl> element; that is, they may contain an unsigned integer, or may be empty, signifying the default value.¶
Example explicit TTL values for a normal domain object:¶
<ttl:ttls> <ttl:NS/> <ttl:DS>3600</ttl:DS> </ttl:ttls>¶
Example explicit TTL values for a domain object with IDN variants:¶
<ttl:ttls> <ttl:NS/> <ttl:DNAME/> </ttl:ttls>¶
For host objects, the <ttl:ttls> element MUST contain at least one of the following child elements:¶
<ttl:A> element, which contains the TTL values for the A records associated with the domain name, OR¶
<ttl:AAAA> element, which contains the TTL values for the AAAAA records associated with the domain name.¶
The <ttl:A> and <ttl:AAAA> elements all have the same content model as the <ttl:ttl> element; that is, they may contain an unsigned integer, or may be empty, signifying the default value.¶
Example explicit TTL values for a host object:¶
<ttl:ttls> <ttl:A>86400</ttl:A> <ttl:AAAA>86400</ttl:AAAA> </ttl:ttls>¶
This explicit TTL model permits the specifying of TTL values for NS, DS, DNAME, for domain objects, and A and AAAA records for domain and host objects.
However, conformant implementations SHOULD NOT specify TTL values for record types that are not in active use.
For example, if a domain has no associated DS records, then setting a value for the <ttl:DS> element makes little sense.
Similarly, if a host object has no IPv6 addresses, then the value of the <ttl:AAAA> element SHOULD NOT be specified.¶
This extension defines an additional element for EPP <info> responses for domain and host objects.¶
When a server receives a domain or host <info> command from a client which included the extension namespace in the <svcExtension> element of the <login> command, the response MUST contain an <extension> element, which MUST contain a <ttl:infData> element.
This element MUST contain either a <ttl:ttl> element or a <ttl:ttls> element.¶
Example domain <info> response:¶
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:registrant>jd1234</domain:registrant> S: <domain:contact type="admin">sh8013</domain:contact> S: <domain:contact type="tech">sh8013</domain:contact> 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>ClientY</domain:crID> S: <domain:crDate>1999-04-03T22:00:00.0Z</domain:crDate> S: <domain:upID>ClientX</domain:upID> S: <domain:upDate>1999-12-03T09:00:00.0Z</domain:upDate> S: <domain:exDate>2005-04-03T22:00:00.0Z</domain:exDate> S: <domain:trDate>2000-04-08T09:00:00.0Z</domain:trDate> S: <domain:authInfo> S: <domain:pw>2fooBAR</domain:pw> S: </domain:authInfo> S: </domain:infData> S: </resData> S: <extension> S: <ttl:infData S: xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"> S: <ttl:ttls> S: <ttl:NS/> S: <ttl:DS>3600</ttl:DS> S: <ttl:A>86400</ttl:A> S: <ttl:AAAA>86400</ttl:AAAA> S: </ttl:ttls> S: </ttl:infData> S: </extension> S: <trID> S: <clTRID>ABC-12345</clTRID> S: <svTRID>54322-XYZ</svTRID> S: </trID> S: </response> S:</epp>¶
Example host <info> response:¶
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="linked"/> S: <host:status s="clientUpdateProhibited"/> S: <host:addr ip="v4">192.0.2.2</host:addr> S: <host:addr ip="v4">192.0.2.29</host:addr> S: <host:addr ip="v6">1080::8:800:200C:417A</host:addr> S: <host:clID>ClientY</host:clID> S: <host:crID>ClientX</host:crID> S: <host:crDate>1999-04-03T22:00:00.0Z</host:crDate> S: <host:upID>ClientX</host:upID> S: <host:upDate>1999-12-03T09:00:00.0Z</host:upDate> S: <host:trDate>2000-04-08T09:00:00.0Z</host:trDate> S: </host:infData> S: </resData> S: <extension> S: <ttl:infData S: xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"> S: <ttl:ttls> S: <ttl:A>86400</ttl:A> S: <ttl:AAAA>86400</ttl:AAAA> S: </ttl:ttls> S: </ttl:infData> S: </extension> S: <trID> S: <clTRID>ABC-12345</clTRID> S: <svTRID>54322-XYZ</svTRID> S: </trID> S: </response> S:</epp>¶
This extension defines an additional element for EPP <create> commands for domain and host objects.¶
The <create> command MAY contain an <extension> element which MAY contain a <ttl:create> element.
This element MUST contain either a <ttl:ttl> element or a <ttl:ttls> element.¶
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">2</domain:period> C: <domain:ns> C: <domain:hostObj>ns1.example.net</domain:hostObj> C: <domain:hostObj>ns2.example.net</domain:hostObj> C: </domain:ns> C: <domain:registrant>jd1234</domain:registrant> C: <domain:contact type="admin">sh8013</domain:contact> C: <domain:contact type="tech">sh8013</domain:contact> C: <domain:authInfo> C: <domain:pw>2fooBAR</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>3600</ttl:ttl> C: </ttl: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="v4">192.0.2.29</host:addr> C: <host:addr ip="v6">1080::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>3600</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 that is outside the server's permitted range, it MUST reject the command with a 2306 "Parameter value policy error" response.¶
This extension defines an additional element for EPP <update> commands for domain and host objects.¶
The <update> command MAY contain an <extension> element which MAY contain a <ttl:update> element.
This element MUST contain either a <ttl:ttl> element or a <ttl:ttls> element.¶
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/> 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:add> C: <host:addr ip="v4">192.0.2.22</host:addr> C: <host:status s="clientUpdateProhibited"/> C: </host:add> C: <host:rem> C: <host:addr ip="v6">1080::8:800:200C:417A</host:addr> C: </host:rem> C: <host:chg> C: <host:name>ns2.example.com</host:name> C: </host:chg> C: </host:update> C: </update> C: <extension> C: <ttl:update C: xmlns:ttl="urn:ietf:params:xml:ns:epp:ttl-1.0"> C: <ttl:ttls> C: <ttl:A>3600</ttl:A> C: <ttl:AAAA>3600</ttl:AAAA> C: </ttl:ttls> 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 that is outside the server's permitted range, it MUST reject the command with a 2306 "Parameter value policy error" response.¶
EPP servers which implement this extension SHOULD use the values provided by EPP clients for the TTL values of NS and DS records published in the DNS for domain objects, and A and AAAA records published in the DNS for host objects.¶
EPP servers that use the "host attribute" model (described in section 1.1 of [RFC5731]) SHOULD use the TTL of the domain object when publishing NS, A and AAAA records derived from host attributes.¶
The extension in this document allows TTL values to be configured for both domain and host objects.
In domain name registries, these object types have a hierarchical relationship, in that a host object may be subordinate to a domain object: for example, the host object ns1.example.com is subordinate to the domain object example.com.¶
When publishing A and AAAA for host objects, TTL values for host objects SHOULD take precedence over the TTL of the superordinate domain object.
However, if no TTL value is specified for a subordinate host object, but a TTL value is specified for the superordinate domain object, then the domain object's TTL value MAY be used for the host object instead of the default TTL value.¶
If a domain name has variants ([RFC6927]) that are linked to that domain, then any NS or DNAME records published for those variants MAY use the same TTL as that used for the primary domain.¶
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).¶
Additionally, server operators MAY implement an automatic reset of TTL values, so that they may be changed for a finite period before and after a planned change, and then revert to a standard value.¶
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 servrers to notify clients of changes to objects under their sponsorship.¶
Domain registry operators must strike a balance between, on the one hand, the desire of registrants for changes to their domains to be visible in the DNS quickly, and on the other, the increased DNS query traffic that short TTLs can bring. Historically, registry operators have used a global TTL value which was applied to all delegations within their zones, which could then be tuned to an optimum value.¶
Domain 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 5 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).¶
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.¶
Client implementations of this specification SHOULD ensure that the user understands 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.¶
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.¶
Registry operators SHOULD take this into consideration when setting the lower limit on TTL values, since a short TTL on delegations has the potential to enhance the effectiveness of fast flux techniques on evasion.¶
This document uses URNs to describe XML namespaces and XML schemas conforming to a registry mechanism described in [RFC3688]. The following URI assignment has been made by IANA:¶
Registration for the TTL namespace:¶
urn:ietf:params:xml:ns:epp:ttl-1.0¶
Registration for the TTL XML schema:¶
urn:ietf:params:xml:schema:epp:ttl-1.0¶
The EPP extension described in this document has been registered by the IANA in the Extensions for the "Extensible Provisioning Protocol (EPP)" registry described in [RFC7451]. The details of the registration are as follows:¶
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="create" type="ttl:container"/>
<element name="update" type="ttl:container"/>
<element name="infData" type="ttl:container"/>
<complexType name="container">
<choice>
<element name="ttls" type="ttl:ttlSetType"/>
<element name="ttl" type="ttl:ttlOrNull"/>
</choice>
</complexType>
<complexType name="ttlSetType">
<sequence>
<element name="NS" type="ttl:ttlOrNull" minOccurs="0"/>
<element name="DS" type="ttl:ttlOrNull" minOccurs="0"/>
<element name="DNAME" type="ttl:ttlOrNull" minOccurs="0"/>
<element name="A" type="ttl:ttlOrNull" minOccurs="0"/>
<element name="AAAA" type="ttl:ttlOrNull" minOccurs="0"/>
</sequence>
</complexType>
<simpleType name="ttlOrNull">
<union memberTypes="token ttl:ttlValue" />
</simpleType>
<simpleType name="ttlValue">
<restriction base="nonNegativeInteger">
<minInclusive value="0"/>
<maxInclusive value="2147483647"/>
</restriction>
</simpleType>
</schema>
¶
This section is to be removed before publishing as an RFC.¶
urn:ietf:params:xml:ns:ttl-1.0 to urn:ietf:params:xml:ns:epp:ttl-1.0.¶