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
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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