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 value (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 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 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 ttl:secs) 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 new element, <ttl:secs>, that is included in <info> responses, and <create> and <update> commands. The <ttl:secs> element takes two forms: the first contains a 32-bit unsigned integer indicating the TTL (expressed in seconds) which will be applied to the DNS records for the associated domain name or host object. Example:

<ttl:secs>3600</secs> The second form, which contains no content, indicates that (a) in <info> responses, no specific value has been set for the object, or (b) in <create> and <update> commands, that the client wishes to remove a previously set value, in favour of the default value. Note that this does no mean that no TTL is published in DNS records (since this is not possible), rather, that the server-determined default TTL is (or should be) used for that object. Example:

<ttl:secs/>

This extension defines an additional element for EPP <info> responses for domain and host objects. The <info> response MAY contain an <extension> element, which MAY contain a <ttl:infData> element. This element contains a single <ttl:secs> 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:ttl-1.0"> S: <ttl:secs>3600</ttl:secs> 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: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 contains a single <ttl:secs> 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:ttl-1.0"> C: <ttl:secs>3600</ttl:secs> 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> C: </ttl:create> C: </extension> C: <clTRID>ABC-12345</clTRID> C: </command> C: </epp>

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 contains a single <ttl:secs> 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: 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> 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> C: </ttl:update> C: </extension> C: <clTRID>ABC-12345</clTRID> C: </command> C: </epp>

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 and DS records published in the DNS for domain objects, and A and AAAA records published in the DNS for host objects.

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 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 SHOULD 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 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.

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 targetNamespace="urn:ietf:params:xml:ns:ttl-1.0" xmlns:ttl="urn:ietf:params:xml:ns:ttl-1.0" xmlns="http://www.w3.org/2001/XMLSchema" 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:seconds"/> <element name="update" type="ttl:seconds"/> <element name="infData" type="ttl:seconds"/> <complexType name="seconds"> <choice> <element name="secs" type="ttl:nonNegativeInteger"/> <element name="secs"/> </choice> </complexType> <simpleType name="nonNegativeInteger"> <restriction base="nonNegativeInteger"> <minInclusive value="1"/> <maxInclusive value="4294967295"/> </restriction> </simpleType> <complexType name="null"> <sequence/> </complexType> </schema>