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    From: draft-ietf-regext-unhandled-namespaces-08        Proposed Standard

    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