Internet Engineering Task Force (IETF)                          J. Gould
Request for Comments: 9038                                VeriSign, Inc.
Category: Standards Track                                    M. Casanova
ISSN: 2070-1721                                                   SWITCH
                                                                May 2021


      Extensible Provisioning Protocol (EPP) Unhandled Namespaces

Abstract

   The Extensible Provisioning Protocol (EPP), as defined in RFC 5730,
   includes a method for the client and server to determine the objects
   to be managed during a session and the object extensions to be used
   during a session.  The services are identified using namespace URIs,
   and an "unhandled namespace" is one that is associated with a service
   not supported by the client.  This document defines an operational
   practice that enables the server to return information associated
   with unhandled namespace URIs and that maintains compliance with the
   negotiated services defined in RFC 5730.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9038.

Copyright Notice

   Copyright (c) 2021 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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Conventions Used in This Document
   2.  Unhandled Namespaces
   3.  Use of EPP <extValue> for Unhandled Namespace Data
     3.1.  Unhandled Object-Level Extension
     3.2.  Unhandled Command-Response Extension
   4.  Signaling Client and Server Support
   5.  Usage with General EPP Responses
   6.  Usage with Poll-Message EPP Responses
   7.  Implementation Considerations
     7.1.  Client Implementation Considerations
     7.2.  Server Implementation Considerations
   8.  IANA Considerations
     8.1.  XML Namespace
     8.2.  EPP Extension Registry
   9.  Security Considerations
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   The Extensible Provisioning Protocol (EPP), as defined in [RFC5730],
   includes a method for the client and server to determine the objects
   to be managed during a session and the object extensions to be used
   during a session.  The services are identified using namespace URIs.
   How should the server handle service data that needs to be returned
   in the response when the client does not support the required service
   namespace URI, which is referred to as an "unhandled namespace"?  An
   unhandled namespace is a significant issue for the processing of the
   poll messages described in [RFC5730], since poll messages are
   inserted by the server prior to knowing the supported client
   services, and the client needs to be capable of processing all poll
   messages.  Returning an unhandled namespace poll message is not
   compliant with the negotiated services defined in [RFC5730], and
   returning an error makes the unhandled namespace poll message a
   poison message by halting the processing of the poll queue.  An
   unhandled namespace is also an issue for general EPP responses when
   the server has information that it cannot return to the client due to
   the client's supported services.  The server should be able to return
   unhandled namespace information that the client can process later.
   This document defines an operational practice that enables the server
   to return information associated with unhandled namespace URIs and
   that maintains compliance with the negotiated services defined in
   [RFC5730].

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.

   XML [W3C.REC-xml11-20060816] 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.

   In examples, "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.

   The examples reference XML namespace prefixes that are used for the
   associated XML namespaces.  Implementations MUST NOT depend on the
   example XML namespaces and instead employ a proper namespace-aware
   XML parser and serializer to interpret and output the XML documents.
   The example namespace prefixes used and their associated XML
   namespaces include:

   changePoll:  urn:ietf:params:xml:ns:changePoll-1.0

   domain:  urn:ietf:params:xml:ns:domain-1.0

   secDNS:  urn:ietf:params:xml:ns:secDNS-1.1

   In the template example XML, placeholder content is represented by
   the following variables:

   [NAMESPACE-XML]:  XML content associated with a login service
       namespace URI.  An example is the <domain:infData> element
       content in [RFC5731].

   [NAMESPACE-URI]:  XML namespace URI associated with the [NAMESPACE-
       XML] XML content.  An example is "urn:ietf:params:xml:ns:domain-
       1.0" in [RFC5731].

2.  Unhandled Namespaces

   An unhandled namespace is an XML namespace that is associated with a
   response extension that is not included in the client-specified EPP
   login services of [RFC5730].  The EPP login services consist of the
   set of XML namespace URIs included in the <objURI> or <extURI>
   elements of the EPP <login> command [RFC5730].  The services
   supported by the server are included in the <objURI> and <extURI>
   elements of the EPP <greeting> [RFC5730], which should be a superset
   of the login services included in the EPP <login> command.  A server
   may have information associated with a specific namespace that it
   needs to return in the response to a client.  The unhandled
   namespaces problem exists when the server has information that it
   needs to return to the client, but the namespace of the information
   is not supported by the client based on the negotiated EPP <login>
   command services.

3.  Use of EPP <extValue> for Unhandled Namespace Data

   In [RFC5730], the <extValue> element is used to provide additional
   error diagnostic information, including the <value> element that
   identifies the client-provided element that caused a server error
   condition and the <reason> element containing the human-readable
   message that describes the reason for the error.  This operational
   practice extends the use of the <extValue> element for the purpose of
   returning unhandled namespace information in a successful response.

   When a server has data to return to the client that the client does
   not support based on the login services, the server MAY return a
   successful response with the data for each unsupported namespace
   moved into an <extValue> element [RFC5730].  The unhandled namespace
   will not cause an error response, but the unhandled namespace data
   will instead be moved to an <extValue> element, along with a reason
   why the unhandled namespace data could not be included in the
   appropriate location of the response.  The <extValue> element will
   not be processed by the XML processor.  The <extValue> element
   contains the following child elements:

   <value>:  Contains a child element with the unhandled namespace XML.
       The unhandled namespace MUST be declared in the child element or
       any containing element, including the root element.  XML
       processing of the <value> element is disabled by the XML schema
       in [RFC5730], so the information can safely be returned in the
       <value> element.

   <reason>:  A formatted, human-readable message that indicates the
       reason the unhandled namespace data was not returned in the
       appropriate location of the response.  The formatted reason
       SHOULD follow the Augmented Backus-Naur Form (ABNF) grammar
       [RFC5234] format: NAMESPACE-URI " not in login services", where
       NAMESPACE-URI is the unhandled XML namespace like
       "urn:ietf:params:xml:ns:domain-1.0" in [RFC5731].

   This document applies to the handling of unsupported namespaces for
   object-level extensions and command-response extensions [RFC3735].
   This document does not apply to the handling of unsupported
   namespaces for protocol-level extensions or authentication-
   information extensions [RFC3735].  Refer to the following sections on
   how to handle an unsupported object-level extension namespace or an
   unsupported command-response extension namespace.

3.1.  Unhandled Object-Level Extension

   An object-level extension in [RFC5730] is a child element of the
   <resData> element.  If the client does not handle the namespace of
   the object-level extension, then the <resData> element is removed and
   its object-level extension child element is moved into an <extValue>
   <value> element [RFC5730], with the namespace URI included in the
   corresponding <extValue> <reason> element.  The response becomes a
   general EPP response without the <resData> element.

   Below is a template response for a supported object-level extension.
   The [NAMESPACE-XML] variable represents the object-level extension
   XML.

   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:      [NAMESPACE-XML]
   S:    </resData>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

   Below is a template for an unhandled namespace response for an
   unsupported object-level extension.  The [NAMESPACE-XML] variable
   represents the object-level extension XML, and the [NAMESPACE-URI]
   variable represents the object-level extension XML namespace URI.

   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:      <extValue>
   S:        <value>
   S:          [NAMESPACE-XML]
   S:        </value>
   S:        <reason>
   S:          [NAMESPACE-URI] not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

   The EPP response is converted from an object response to a general
   EPP response by the server when the client does not support the
   object-level extension namespace URI.

   Below is an example of a <transfer> query response (see Section 3.1.3
   of [RFC5731]) converted into an unhandled namespace 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:      <extValue>
   S:        <value>
   S:          <domain:trnData
   S:            xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   S:            <domain:name>example.com</domain:name>
   S:            <domain:trStatus>pending</domain:trStatus>
   S:            <domain:reID>ClientX</domain:reID>
   S:            <domain:reDate>2000-06-06T22:00:00.0Z</domain:reDate>
   S:            <domain:acID>ClientY</domain:acID>
   S:            <domain:acDate>2000-06-11T22:00:00.0Z</domain:acDate>
   S:            <domain:exDate>2002-09-08T22:00:00.0Z</domain:exDate>
   S:          </domain:trnData>
   S:        </value>
   S:        <reason>
   S:          urn:ietf:params:xml:ns:domain-1.0 not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

3.2.  Unhandled Command-Response Extension

   A command-response extension in [RFC5730] is a child element of the
   <extension> element.  If the client does not handle the namespace of
   the command-response extension, the command-response child element is
   moved into an <extValue> <value> element [RFC5730], with the
   namespace URI included in the corresponding <extValue> <reason>
   element.  Afterwards, if there are no additional command-response
   child elements, the <extension> element MUST be removed.

   Below is a template response for a supported command-response
   extension.  The [NAMESPACE-XML] variable represents the command-
   response extension XML.

   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:    <extension>
   S:      [NAMESPACE-XML]
   S:    </extension>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

   Below is a template of an unhandled namespace response for an
   unsupported command-response extension.  The [NAMESPACE-XML] variable
   represents the command-response extension XML, and the [NAMESPACE-
   URI] variable represents the command-response extension XML namespace
   URI.

   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:      <extValue>
   S:        <value>
   S:         [NAMESPACE-XML]
   S:        </value>
   S:        <reason>
   S:          [NAMESPACE-URI] not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

   The EPP response is converted to an unhandled namespace response by
   moving the unhandled command-response extension from under the
   <extension> to an <extValue> element.

   Below is example of the Delegation Signer (DS) Data Interface <info>
   response (see Section 5.1.2 of [RFC5910]) converted to an unhandled
   namespace response.

   S:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   S:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0"
   S:     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   S:  <response>
   S:    <result code="1000">
   S:      <msg>Command completed successfully</msg>
   S:      <extValue>
   S:        <value>
   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>3</secDNS:alg>
   S:              <secDNS:digestType>1</secDNS:digestType>
   S:              <secDNS:digest>49FD46E6C4B45C55D4AC</secDNS:digest>
   S:            </secDNS:dsData>
   S:          </secDNS:infData>
   S:        </value>
   S:        <reason>
   S:          urn:ietf:params:xml:ns:secDNS-1.1 not in login services
   S:        </reason>
   S:      </extValue>
   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>ns2.example.com</domain:hostObj>
   S:        </domain:ns>
   S:        <domain:host>ns1.example.com</domain:host>
   S:        <domain:host>ns2.example.com</domain:host>
   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:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

4.  Signaling Client and Server Support

   This document does not define new EPP protocol elements but rather
   specifies an operational practice using the existing EPP protocol,
   where the client and the server can signal support for the
   operational practice using a namespace URI in the login and greeting
   extension services.  The namespace URI
   "urn:ietf:params:xml:ns:epp:unhandled-namespaces-1.0" is used to
   signal support for the operational practice.  The client includes the
   namespace URI in an <svcExtension> <extURI> element of the <login>
   command [RFC5730].  The server includes the namespace URI in an
   <svcExtension> <extURI> element of the greeting [RFC5730].

   A client that receives the namespace URI in the server's greeting
   extension services can expect the following supported behavior by the
   server:

   *  support unhandled namespace object-level extensions and command-
      response extensions in EPP poll messages, per Section 6

   *  support the option of unhandled namespace command-response
      extensions in general EPP responses, per Section 5

   A server that receives the namespace URI in the client's <login>
   command extension services can expect the following supported
   behavior by the client:

   *  support monitoring the EPP poll messages and general EPP responses
      for unhandled namespaces

5.  Usage with General EPP Responses

   The unhandled namespace approach defined in Section 3 MAY be used for
   a general EPP response to an EPP command.  A general EPP response
   includes any EPP response that is not a poll message.  The use of the
   unhandled namespace approach for poll-message EPP responses is
   defined in Section 6.  The server MAY exclude the unhandled namespace
   information in the general EPP response or MAY include it using the
   unhandled namespace approach.

   The unhandled namespace approach for general EPP responses SHOULD
   only be applicable to command-response extensions, defined in
   Section 3.2, since the server SHOULD NOT accept an object-level EPP
   command if the client did not include the object-level namespace URI
   in the login services.  An object-level EPP response extension is
   returned when the server successfully executes an object-level EPP
   command extension.  The server MAY return an unhandled object-level
   extension to the client, as defined in Section 3.1.

   Returning domain name Redemption Grace Period (RGP) data, based on
   [RFC3915], provides an example of applying the unhandled namespace
   approach for a general EPP response.  If the client does not include
   the "urn:ietf:params:xml:ns:rgp-1.0" namespace URI in the login
   services and the domain <info> response of a domain name does have
   RGP information, the server MAY exclude the <rgp:infData> element
   from the EPP response or MAY include it under the <extValue> element,
   per Section 3.2.

   Below is an example of a domain name <info> response [RFC5731]
   converted to an unhandled <rgp:infData> element (see Section 4.1.1 of
   [RFC3915]) included under an <extValue> element:

   S:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   S:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0"
   S:     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   S:     xsi:schemaLocation="urn:ietf:params:xml:ns:epp-1.0
   S:     epp-1.0.xsd">
   S:  <response>
   S:    <result code="1000">
   S:      <msg>Command completed successfully</msg>
   S:      <extValue>
   S:        <value>
   S:          <rgp:infData xmlns:rgp="urn:ietf:params:xml:ns:rgp-1.0"
   S:           xsi:schemaLocation="urn:ietf:params:xml:ns:rgp-1.0
   S:           rgp-1.0.xsd">
   S:            <rgp:rgpStatus s="redemptionPeriod"/>
   S:          </rgp:infData>
   S:        </value>
   S:        <reason>
   S:          urn:ietf:params:xml:ns:rgp-1.0 not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <resData>
   S:      <domain:infData
   S:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0"
   S:        xsi:schemaLocation="urn:ietf:params:xml:ns:domain-1.0
   S:        domain-1.0.xsd">
   S:        <domain:name>example.com</domain:name>
   S:        <domain:roid>EXAMPLE1-REP</domain:roid>
   S:        <domain:status s="pendingDelete"/>
   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:host>ns1.example.com</domain:host>
   S:        <domain:host>ns2.example.com</domain:host>
   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:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

6.  Usage with Poll-Message EPP Responses

   The unhandled namespace approach, defined in Section 3, MUST be used
   if there is unhandled namespace information included in a <poll>
   response.  The server inserts poll messages into the client's poll
   queue independent of knowing the supported client login services;
   therefore, there may be unhandled object-level extensions and
   command-response extensions included in a client's poll queue.  In
   [RFC5730], the <poll> command is used by the client to retrieve and
   acknowledge poll messages that have been inserted by the server.  The
   <poll> response is an EPP response that includes the <msgQ> element
   that provides poll queue metadata about the message.  The unhandled
   namespace approach, defined in Section 3, is used for an unhandled
   object-level extension and for each of the unhandled command-response
   extensions attached to the <poll> response.  The resulting <poll>
   response MAY have either or both the object-level extension or
   command-response extensions moved to <extValue> elements, as defined
   in Section 3.

   The change poll message, as defined in Section 3.1.2 of [RFC8590],
   which is an extension of any EPP object, is an example of applying
   the unhandled namespace approach for <poll> responses.  Below are
   examples of converting the domain name <info> response example in
   Section 3.1.2 of [RFC8590] to an unhandled namespace response.  The
   object that will be used in the examples is a domain name object
   [RFC5731].

   Below is a domain name <info> <poll> response [RFC5731] with the
   unhandled <changePoll:changeData> element [RFC8590] included under an
   <extValue> element.

   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="1301">
   S:      <msg lang="en-US">
   S:        Command completed successfully; ack to dequeue</msg>
   S:      <extValue>
   S:        <value>
   S:          <changePoll:changeData
   S:           xmlns:changePoll="urn:ietf:params:xml:ns:changePoll-1.0"
   S:           state="after">
   S:            <changePoll:operation>update</changePoll:operation>
   S:            <changePoll:date>
   S:              2013-10-22T14:25:57.0Z</changePoll:date>
   S:            <changePoll:svTRID>12345-XYZ</changePoll:svTRID>
   S:            <changePoll:who>URS Admin</changePoll:who>
   S:            <changePoll:caseId type="urs">urs123
   S:            </changePoll:caseId>
   S:            <changePoll:reason>URS Lock</changePoll:reason>
   S:          </changePoll:changeData>
   S:        </value>
   S:        <reason>
   S:        urn:ietf:params:xml:ns:changePoll-1.0 not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <msgQ count="201" id="1">
   S:      <qDate>2013-10-22T14:25:57.0Z</qDate>
   S:      <msg>Registry initiated update of domain.</msg>
   S:    </msgQ>
   S:    <resData>
   S:      <domain:infData
   S:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   S:        <domain:name>domain.example</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:clID>ClientX</domain:clID>
   S:        <domain:crID>ClientY</domain:crID>
   S:        <domain:crDate>2012-04-03T22:00:00.0Z</domain:crDate>
   S:        <domain:exDate>2014-04-03T22:00:00.0Z</domain:exDate>
   S:      </domain:infData>
   S:    </resData>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

   Below is an unhandled domain name <info> <poll> response [RFC5731]
   and the unhandled <changePoll:changeData> element [RFC8590] included
   under an <extValue> element.

   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="1301">
   S:      <msg>Command completed successfully; ack to dequeue</msg>
   S:      <extValue>
   S:        <value>
   S:          <domain:infData
   S:            xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   S:            <domain:name>domain.example</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:clID>ClientX</domain:clID>
   S:            <domain:crID>ClientY</domain:crID>
   S:            <domain:crDate>2012-04-03T22:00:00.0Z</domain:crDate>
   S:            <domain:exDate>2014-04-03T22:00:00.0Z</domain:exDate>
   S:          </domain:infData>
   S:        </value>
   S:        <reason>
   S:          urn:ietf:params:xml:ns:domain-1.0 not in login services
   S:        </reason>
   S:      </extValue>
   S:      <extValue>
   S:        <value>
   S:          <changePoll:changeData
   S:            xmlns:changePoll=
   S:              "urn:ietf:params:xml:ns:changePoll-1.0"
   S:            state="after">
   S:            <changePoll:operation>update</changePoll:operation>
   S:            <changePoll:date>
   S:              2013-10-22T14:25:57.0Z</changePoll:date>
   S:            <changePoll:svTRID>12345-XYZ</changePoll:svTRID>
   S:            <changePoll:who>URS Admin</changePoll:who>
   S:            <changePoll:caseId type="urs">urs123
   S:            </changePoll:caseId>
   S:            <changePoll:reason>URS Lock</changePoll:reason>
   S:          </changePoll:changeData>
   S:        </value>
   S:        <reason>
   S:        urn:ietf:params:xml:ns:changePoll-1.0 not in login services
   S:        </reason>
   S:      </extValue>
   S:    </result>
   S:    <msgQ count="201" id="1">
   S:      <qDate>2013-10-22T14:25:57.0Z</qDate>
   S:      <msg>Registry initiated update of domain.</msg>
   S:    </msgQ>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

7.  Implementation Considerations

   There are implementation considerations for the client and the server
   to help address the risk of the client ignoring unhandled namespace
   information included in an EPP response that is needed to meet
   technical, policy, or legal requirements.

7.1.  Client Implementation Considerations

   To reduce the likelihood of a client receiving unhandled namespace
   information, the client should consider implementing the following:

   1.  Ensure that the client presents the complete set of what it
       supports when presenting its login services.  If there are gaps
       between the services supported by the client and the login
       services included in the login command, the client may receive
       unhandled namespace information that the client could have
       supported.

   2.  Support all of the services included in the server greeting
       services that may be included in an EPP response, including the
       <poll> responses.  The client should evaluate the gaps between
       the greeting services and the login services provided in the
       login command to identify extensions that need to be supported.

   3.  Proactively monitor for unhandled namespace information in the
       EPP responses by looking for the inclusion of the <extValue>
       element in successful responses, record the unsupported namespace
       included in the <reason> element, and record the unhandled
       namespace information included in the <value> element for later
       processing.  The unhandled namespace should be implemented by the
       client to ensure that information is processed fully in future
       EPP responses.

7.2.  Server Implementation Considerations

   To assist the clients in recognizing unhandled namespaces, the server
   should consider implementing the following:

   1.  Monitor for returning unhandled namespace information to clients
       and report it to the clients out of band to EPP, so the clients
       can add support for the unhandled namespaces.

   2.  Look for the unhandled namespace support in the login services
       when returning optional unhandled namespace information in
       general EPP responses.

8.  IANA Considerations

8.1.  XML Namespace

   This document uses URNs to describe XML namespaces conforming to a
   registry mechanism described in [RFC3688].  The following URI
   assignment has been made by IANA.

   URI:  urn:ietf:params:xml:ns:epp:unhandled-namespaces-1.0
   Registrant Contact:  IESG
   XML:  None.  Namespace URIs do not represent an XML specification.

8.2.  EPP Extension Registry

   The EPP operational practice described in this document has been
   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) Unhandled
      Namespaces"
   Document Status:  Standards Track
   Reference:  RFC 9038
   Registrant:  IETF, <iesg@ietf.org>
   TLDs:  Any
   IPR Disclosure:  None
   Status:  Active
   Notes:  None

9.  Security Considerations

   This document does not provide any security services beyond those
   described by EPP [RFC5730] and protocol layers used by EPP.  The
   security considerations described in these other specifications apply
   to this specification as well.  Since the unhandled namespace content
   is XML that is not processed in the first pass by the XML parser, the
   client SHOULD validate the XML when the content is processed to
   protect against the inclusion of malicious content.

10.  References

10.1.  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>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
              <https://www.rfc-editor.org/info/rfc5730>.

   [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>.

   [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>.

   [W3C.REC-xml11-20060816]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E.,
              Yergeau, F., and J. Cowan, "Extensible Markup Language
              (XML) 1.1 (Second Edition)", World Wide Web Consortium
              Recommendation REC-xml11-20060816, 16 August 2006,
              <https://www.w3.org/TR/2006/REC-xml11-20060816>.

10.2.  Informative References

   [RFC3735]  Hollenbeck, S., "Guidelines for Extending the Extensible
              Provisioning Protocol (EPP)", RFC 3735,
              DOI 10.17487/RFC3735, March 2004,
              <https://www.rfc-editor.org/info/rfc3735>.

   [RFC3915]  Hollenbeck, S., "Domain Registry Grace Period Mapping for
              the Extensible Provisioning Protocol (EPP)", RFC 3915,
              DOI 10.17487/RFC3915, September 2004,
              <https://www.rfc-editor.org/info/rfc3915>.

   [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>.

   [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>.

Acknowledgements

   The authors wish to thank the following people for their feedback and
   suggestions: Thomas Corte, Scott Hollenbeck, Patrick Mevzek, and
   Marcel Parodi.

Authors' Addresses

   James Gould
   VeriSign, Inc.
   12061 Bluemont Way
   Reston, VA 20190
   United States of America

   Email: jgould@verisign.com
   URI:   http://www.verisign.com


   Martin Casanova
   SWITCH
   P.O. Box
   CH-8021 Zurich
   Switzerland

   Email: martin.casanova@switch.ch
   URI:   http://www.switch.ch