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

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 (). Typically, the Time-To-Live (TTL, see Section 5 of ) 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 a that domain: for example, to reduce the amount of time required to complete a change of DNS servers or DNSSEC deployment of 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 and , respectively) which allows the sponsor of a domain name or host object to change the TTL associated with that object.

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 . 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 xmlns:ttl) are solely for illustrative purposes. A conforming implementation MUST NOT require the use of these or any other specific namespace prefixes.

This specification defines a two new elements that are included in <info>, <create> and <update> commands: <ttl:secs>, which contains a 32-bit unsigned integer indicating the TTL (expressed in seconds) which will be applied to the delegation records for the associated domain name or host object; and <ttl:until>, which contains a date and time after which a TTL (specified using the <ttl:secs> element) should revert to the server's default value. Examples:

<secs xmlns="urn:ietf:params:xml:ns:ttl-1.0">3600</secs> <until xmlns="urn:ietf:params:xml:ns:ttl-1.0">2022-12-01T08:00:00.0Z</until> The <ttl:until> element is OPTIONAL in <create>, <update> and <info> commands. EPP servers which do not support this element MUST reject commands which contain it with a 2012 "Unimplemented option" response. Conversely, EPP servers whose policies require the use of the <ttl:until> element MUST reject commands which do not contain it with a 2003 "Required parameter missing" response.

This extension defines additional elements for EPP <info> responses for domain and host objects. The <info> response MAY contain an <extension> element, which MAY contain a <ttl:infData> element, which contains the following child elements: A <ttl:secs> element showing the current TTL for the object; and An OPTIONAL <ttl:until> element containing the date and time after which the TTL will revert to the server's default value. The <ttl:until> MUST NOT appear in <info> responses if: (1) the server does not support this element, (2) the object already has the server's default TTL value, or (3) the server does not implement automatic reversion of custom TTL values. 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:ttl-1.0"> S: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> 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:ttl-1.0"> S: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> 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 additional elements for EPP <create> commands for domain and host objects. The <create> command MAY contain an <extension> element which MAY contain a <ttl:create> element, which contains the following child elements: A <ttl:secs> element showing the desired TTL for the object; and An OPTIONAL <ttl:until> element containing the date and time after which the TTL should revert to the server's default value. 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:ttl-1.0"> C: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> 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:ttl-1.0"> C: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> C: </ttl:create> C: </extension> C: <clTRID>ABC-12345</clTRID> C: </command> C: </epp> EPP servers which do not support the <ttl:until> element MUST reject commands which contain it with a 2012 "Unimplemented option" response.

This extension defines additional elements for EPP <update> commands for domain and host objects. The <update> command MAY contain an <extension> element which MAY contain a <ttl:create> element, which contains the following child elements: A <ttl:secs> element showing the desired TTL for the object; and An OPTIONAL <ttl:until> element containing the date and time after which the TTL should revert to the server's default value. 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: xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> 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:ttl-1.0"> C: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> 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:ttl-1.0"> C: <ttl:secs>3600</ttl:secs> S: <ttl:until>2022-12-01T08:30:00.0Z</ttl:until> C: </ttl:update> C: </extension> C: <clTRID>ABC-12345</clTRID> C: </command> C: </epp> EPP servers which do not support the <ttl:until> element MUST reject commands which contain it with a 2012 "Unimplemented option" response.

If an EPP server receives a command containing a TTL that is outside the server's permitted range (see and below), it MUST reject the command with a 2004 "Parameter value range error" response.

EPP servers which implement this extension SHOULD use the values provided by EPP clients for the TTL values of NS, A, AAAA and DS records published in the DNS for the corresponding delegation.

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 configured for a subordinate host object, but a TTL value is configured for the superordinate domain object, then the domain object's TTL value SHOULD be used for the host object instead of the default TTL value.

If a domain name has variants () that are linked to that domain, then any NS or DNAME records published for those variants MUST 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. In the event of changes to TTL values taking place out-of-band, EPP server operators SHOULD notify the sponsoring client using the EPP Change Poll extension ().

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 (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. Similarly, EPP servers which support the <ttl:until> element MUST reject commands (with a 2004 "parameter value range error" response) if the specified date and time is in the past, or is otherwise outside a server-defined range of acceptable values. EPP servers MAY vary the range of acceptable values for the <ttl:until> element based on the value of the <ttl:secs> element: for example, to allow the setting of a very short TTL for a short period of time, while permitting longer TTLs to be used for longer periods, as the following table illustrates: TTL value range Maximum duration 0-60s - 61-299s 3600s 300-1099s 43200s 1200-3599s 86400s ≥ 3600s any In the above policy, the default TTL is one hour, and the server will reject any TTL below 60 seconds. Clients can set TTLs of between one and five minutes for a maximum of one hour, or between five minutes and thirty minutes for up to twelve hours, or between 30 minutes and one hour for up to one day.

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.

Many malicious actors use a technique called "fast flux DNS" 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 . The following URI assignment has been made by IANA: Registration for the TTL namespace: URI: urn:ietf:params:xml:ns:ttl-1.0 Registrant Contact: See the author of this document XML: None. Namespace URIs do not represent an XML specification Registration for the TTL XML schema: URI: urn:ietf:params:xml:ns:ttl-1.0 Registrant Contact: See the author of this document XML: See the "" section of this document

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 . 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: Experimental Reference: URL of this document Registrant Name and Email Address: See the author of this document TLDs: Any IPR Disclosure: None Status: Active Notes: None

<?xml version="1.0" encoding="UTF-8"?> <schema xmlns:ttl="urn:ietf:params:xml:ns:ttl-1.0"> <annotation> <documentation> Extensible Provisioning Protocol v1.0 domain name extension schema for Time-To-Live (TTL) modification in all DNS responses for a domain name including delegation (NS) records and any address (A) records. </documentation> </annotation>  <element name="create" type="ttl:ttlType"/> <element name="update" type="ttl:ttlType"/>  <element name="infData" type="ttl:ttlType"/> <complexType name="ttlType"> <sequence> <element name="secs" type="ttl:nonNegativeInteger"/> <element name="until" type="dateTime" minoccurs="0"/> </sequence> </complexType> <simpleType name="nonNegativeInteger"> <restriction base="nonNegativeInteger"> <minInclusive value="1"/> <maxInclusive value="4294967295"/> </restriction> </simpleType> </schema>