<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="std" consensus="true" docName="draft-ietf-sipcore-multiple-reasons-01" indexInclude="true" ipr="trust200902" number="9366" prepTime="2023-03-07T20:11:59" scripts="Common,Latin" sortRefs="true" submissionType="IETF" symRefs="true" tocDepth="3" tocInclude="true" updates="3326" xml:lang="en">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-sipcore-multiple-reasons-01" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9366" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title abbrev="Multiple SIP Reason Header Field Values">Multiple SIP Reason Header Field Values</title>
    <seriesInfo name="RFC" value="9366" stream="IETF"/>
    <author initials="R." surname="Sparks" fullname="Robert Sparks">
      <organization showOnFrontPage="true"/>
      <address>
        <email>rjsparks@nostrum.com</email>
      </address>
    </author>
    <date month="03" year="2023"/>
    <area>ART</area>
    <workgroup>SIPCORE</workgroup>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">The SIP Reason header field as defined in RFC 3326 allows only one Reason value per protocol value. Experience with more recently defined protocols shows it is useful to allow multiple values with the same protocol value. This document updates RFC 3326 to allow multiple values for an indicated registered protocol when that protocol defines what the presence of multiple values means.</t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This is an Internet Standards Track document.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            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.
        </t>
        <t indent="0" pn="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <eref target="https://www.rfc-editor.org/info/rfc9366" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2023 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-conventions">Conventions</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-update-to-rfc-3326">Update to RFC 3326</xref></t>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.6.2">
              <li pn="section-toc.1-1.6.2.1">
                <t indent="0" pn="section-toc.1-1.6.2.1.1"><xref derivedContent="6.1" format="counter" sectionFormat="of" target="section-6.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.2">
                <t indent="0" pn="section-toc.1-1.6.2.2.1"><xref derivedContent="6.2" format="counter" sectionFormat="of" target="section-6.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgments">Acknowledgments</xref></t>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-address">Author's Address</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section anchor="introduction" numbered="true" removeInRFC="false" toc="include" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">The SIP Reason header field as defined in RFC 3326 allows only one Reason value per protocol value. Experience with more recently defined protocols shows it is useful to allow multiple values with the same protocol value <xref target="I-D.ietf-stir-identity-header-errors-handling" format="default" sectionFormat="of" derivedContent="STIRREASONS"/>. This document updates RFC 3326 to allow multiple values for an indicated registered protocol when that protocol defines what the presence of multiple values means. It does not change the requirement in RFC 3326 restricting the header field contents to one value per protocol for those protocols that do not define what multiple values mean.</t>
    </section>
    <section anchor="conventions" numbered="true" removeInRFC="false" toc="include" pn="section-2">
      <name slugifiedName="name-conventions">Conventions</name>
      <t indent="0" pn="section-2-1">
    The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
    "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
      </t>
    </section>
    <section anchor="update-to-rfc-3326" numbered="true" removeInRFC="false" toc="include" pn="section-3">
      <name slugifiedName="name-update-to-rfc-3326">Update to RFC 3326</name>
      <t indent="0" pn="section-3-1">The last paragraph of <xref section="2" sectionFormat="of" target="RFC3326" format="default" derivedLink="https://rfc-editor.org/rfc/rfc3326#section-2" derivedContent="RFC3326"/> is replaced as follows:</t>
      <t indent="0" pn="section-3-2">OLD:</t>
      <blockquote pn="section-3-3">
        <t indent="0" pn="section-3-3.1">A SIP message <bcp14>MAY</bcp14> contain more than one Reason value (i.e., multiple
   Reason lines), but all of them <bcp14>MUST</bcp14> have different protocol values
   (e.g., one SIP and another Q.850).  An implementation is free to
      ignore Reason values that it does not understand.</t>
      </blockquote>
      <t indent="0" pn="section-3-4">NEW:</t>
      <blockquote pn="section-3-5">
        <t indent="0" pn="section-3-5.1">A SIP message <bcp14>MAY</bcp14> contain more than one Reason value (i.e., multiple
   Reason lines). If the registered protocol for the Reason value specifies
   what it means for multiple values to occur in one message, more than one
   value for that protocol <bcp14>MAY</bcp14> be present. Otherwise, there <bcp14>MUST</bcp14> be only
   one value per protocol provided (e.g., one SIP and another Q.850).  An
   implementation is free to ignore Reason values that it does not understand.</t>
      </blockquote>
    </section>
    <section anchor="security-considerations" numbered="true" removeInRFC="false" toc="include" pn="section-4">
      <name slugifiedName="name-security-considerations">Security Considerations</name>
      <t indent="0" pn="section-4-1">This document adds no security considerations to the use of SIP. The security considerations in <xref target="RFC3326" format="default" sectionFormat="of" derivedContent="RFC3326"/> and those in any registered protocols used in Reason header field values should be considered.</t>
    </section>
    <section anchor="iana-considerations" numbered="true" removeInRFC="false" toc="include" pn="section-5">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <t indent="0" pn="section-5-1">This document has no IANA actions.</t>
    </section>
  </middle>
  <back>
    <displayreference target="I-D.ietf-stir-identity-header-errors-handling" to="STIRREASONS"/>
    <references pn="section-6">
      <name slugifiedName="name-references">References</name>
      <references pn="section-6.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized.  This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC3326" target="https://www.rfc-editor.org/info/rfc3326" quoteTitle="true" derivedAnchor="RFC3326">
          <front>
            <title>The Reason Header Field for the Session Initiation Protocol (SIP)</title>
            <author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>
            <author fullname="D. Oran" initials="D." surname="Oran"/>
            <author fullname="G. Camarillo" initials="G." surname="Camarillo"/>
            <date month="December" year="2002"/>
            <abstract>
              <t indent="0">The REGISTER function is used in a Session Initiation Protocol (SIP) system primarily to associate a temporary contact address with an address-of-record.  This contact is generally in the form of a Uniform Resource Identifier (URI), such as Contact:   and is generally dynamic and associated with the IP address or hostname of the SIP User Agent (UA).  The problem is that network topology may have one or more SIP proxies between the UA and the registrar, such that any request traveling from the user's home network to the registered UA must traverse these proxies.  The REGISTER method does not give us a mechanism to discover and record this sequence of proxies in the registrar for future use.  This document defines an extension header field, "Path" which provides such a mechanism. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="3326"/>
          <seriesInfo name="DOI" value="10.17487/RFC3326"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications.  This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
      </references>
      <references pn="section-6.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="I-D.ietf-stir-identity-header-errors-handling" target="https://datatracker.ietf.org/doc/html/draft-ietf-stir-identity-header-errors-handling-08" quoteTitle="true" derivedAnchor="STIRREASONS">
          <front>
            <title>Identity Header Errors Handling for STIR</title>
            <author initials="C." surname="Wendt" fullname="Chris Wendt">
              <organization showOnFrontPage="true">Somos Inc.</organization>
            </author>
            <date month="February" day="25" year="2023"/>
            <abstract>
              <t indent="0">   This document extends STIR and the Authenticated Identity Management
   in the Session Initiation Protocol (SIP) error handling procedures to
   include the mapping of verification failure reasons to STIR defined
   4xx codes so the failure reason of an Identity header field can be
   conveyed to the upstream authentication service when local policy
   dictates that the call should continue in the presence of a
   verification failure.  This document also defines procedures that
   enable a failure reason to be mapped to a specific Identity header
   field for scenarios that use multiple Identity header fields where
   some may have errors and others may not and the handling of those
   situations is defined.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-stir-identity-header-errors-handling-08"/>
          <refcontent>Work in Progress</refcontent>
        </reference>
      </references>
    </references>
    <section anchor="acknowledgments" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgments">Acknowledgments</name>
      <t indent="0" pn="section-appendix.a-1">This text is based on discussions at a STIR Working Group interim meeting. <contact fullname="Jean Mahoney"/> and <contact fullname="Russ Housley"/> provided suggestions that vastly improved the first attempts at assembling these words. <contact fullname="Christer Holmberg"/>, <contact fullname="Dale Worley"/>, <contact fullname="Brian Rosen"/>, <contact fullname="Chris Wendt"/>, and <contact fullname="Paul Kyzivat"/> provided constructive discussion during SIPCORE Working Group adoption.</t>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.b">
      <name slugifiedName="name-authors-address">Author's Address</name>
      <author initials="R." surname="Sparks" fullname="Robert Sparks">
        <organization showOnFrontPage="true"/>
        <address>
          <email>rjsparks@nostrum.com</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
