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Internet Engineering Task Force (IETF) R. Sparks Request for Comments: 9366 March 2023 Updates: 3326 Category: Standards Track ISSN: 2070-1721

              Multiple SIP Reason Header Field Values

Abstract

 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.

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/rfc9366.

Copyright Notice

 Copyright (c) 2023 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 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.

Table of Contents

 1.  Introduction
 2.  Conventions
 3.  Update to RFC 3326
 4.  Security Considerations
 5.  IANA Considerations
 6.  References
   6.1.  Normative References
   6.2.  Informative References
 Acknowledgments
 Author's Address

1. Introduction

 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 [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.

2. Conventions

 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.

3. Update to RFC 3326

 The last paragraph of Section 2 of [RFC3326] is replaced as follows:

 OLD:

 |  A SIP message MAY contain more than one Reason value (i.e.,
 |  multiple Reason lines), but all of them MUST 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.

 NEW:

 |  A SIP message MAY 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 MAY be present.
 |  Otherwise, there MUST 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.

4. Security Considerations

 This document adds no security considerations to the use of SIP.  The
 security considerations in [RFC3326] and those in any registered
 protocols used in Reason header field values should be considered.

5. IANA Considerations

 This document has no IANA actions.

6. References

6.1. 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>.

 [RFC3326]  Schulzrinne, H., Oran, D., and G. Camarillo, "The Reason
            Header Field for the Session Initiation Protocol (SIP)",
            RFC 3326, DOI 10.17487/RFC3326, December 2002,
            <https://www.rfc-editor.org/info/rfc3326>.

 [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>.

6.2. Informative References

 [STIRREASONS]
            Wendt, C., "Identity Header Errors Handling for STIR",
            Work in Progress, Internet-Draft, draft-ietf-stir-
            identity-header-errors-handling-08, 25 February 2023,
            <https://datatracker.ietf.org/doc/html/draft-ietf-stir-
            identity-header-errors-handling-08>.

Acknowledgments

 This text is based on discussions at a STIR Working Group interim
 meeting.  Jean Mahoney and Russ Housley provided suggestions that
 vastly improved the first attempts at assembling these words.
 Christer Holmberg, Dale Worley, Brian Rosen, Chris Wendt, and Paul
 Kyzivat provided constructive discussion during SIPCORE Working Group
 adoption.

Author's Address

 Robert Sparks
 Email: rjsparks@nostrum.com