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Internet Engineering Task Force (IETF) R. SparksRequest for Comments: 8217 OracleUpdates:3261,3325,3515,3892,4508, August 20175002,5318,5360,5502Category: Standards TrackISSN: 2070-1721Clarifications for When to Use the name-addr Production in SIP MessagesAbstractRFC 3261 constrained several SIP header fields whose grammar contains the "name-addr / addr-spec" alternative to use name-addr when certain characters appear. Unfortunately, it expressed the constraints with prose copied into each header field definition, and at least one header field was missed. Further, the constraint has not been copied into documents defining extension headers whose grammar contains the alternative. This document updatesRFC 3261 to state the constraint generically and clarifies that the constraint applies to all SIP header fields where there is a choice between using name-addr or addr-spec. It also updates the RFCs that define extension SIP header fields using the alternative to clarify that the constraint applies (RFCs 3325, 3515, 3892, 4508, 5002, 5318, 5360, and 5502).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 inSection 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8217.Sparks Standards Track [Page 1]

RFC 8217                name-addr Clarifications             August 2017Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .33.  Updates toRFC 3261 . . . . . . . . . . . . . . . . . . . . .44.  Updates to RFCs Defining SIP Extension Header Fields  . . . .45.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .56.  Security Considerations . . . . . . . . . . . . . . . . . . .57.  Normative References  . . . . . . . . . . . . . . . . . . . .5   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .6   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .61.  Introduction   [RFC3261] defines several header fields that contain URIs to allow   both a form that contains the bare URI (addr-spec) and one that   provides a name and the URI (name-addr).  This subset, taken from the   ABNF [RFC5234] specified in [RFC3261], shows the relevant part of the   definition of the syntax of the "From" header field:     From        =  ( "From" / "f" ) HCOLON from-spec     from-spec   =  ( name-addr / addr-spec )                    *( SEMI from-param )     name-addr      =  [ display-name ] LAQUOT addr-spec RAQUOT     addr-spec      =  SIP-URI / SIPS-URI / absoluteURI   The prose inSection 20.20 of [RFC3261], which discusses the "From"   header field, constrains how the production may be used by saying:      Even if the "display-name" is empty, the "name-addr" form      MUST be used if the "addr-spec" contains a comma, question      mark, or semicolon.Sparks                       Standards Track                    [Page 2]

RFC 8217 name-addr Clarifications August 2017Section 20.39 of [RFC3261], which discusses the "To" header field, contains no such constraining text. This constraint is specified slightly differently, but with the same intent, in the introduction toSection 20 of [RFC3261]: The Contact, From, and To header fields contain a URI. If the URI contains a comma, question mark or semicolon, the URI MUST be enclosed in angle brackets (< and >). Unfortunately, this can be read to only apply to the Contact, From, and To header fields, making it necessary to provide the constraint explicitly in the prose discussing any other header field using the name-addr or addr-spec alternative. As extension header fields were standardized, the specifications sometimes failed to include the constraint. Many errata have been entered to correct this omission. When the constraint has been included, the requirement to use the name-addr form has not been consistently stated. This memo updates the specifications of SIP and its extensions to clarify that the constraint to use the name-addr form applies anywhere there is a choice between the name-addr and addr-spec production rules in the grammar for SIP header fields. It is important to note that a message formed without honoring the constraint will still be syntactically valid, but it would very likely be interpreted differently. The characters after the comma, question mark, or semicolon will, in most cases, be interpreted as header field parameters or additional header field values as discussed inSection 7.3.1 of [RFC3261]. (An exception is the degenerate case of a URL like sip:10.0.0.1,@10.0.0.0 where it is possible to parse the comma via the 'user' production).2. Terminology 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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.Sparks Standards Track [Page 3]

RFC 8217                name-addr Clarifications             August 20173.  Updates toRFC 3261   This text from introduction toSection 20 of [RFC3261]:     The Contact, From, and To header fields contain a URI.  If the URI     contains a comma, question mark or semicolon, the URI MUST be     enclosed in angle brackets (< and >).  Any URI parameters are     contained within these brackets.  If the URI is not enclosed in     angle brackets, any semicolon-delimited parameters are     header-parameters, not URI parameters.   is replaced with:     When constructing the value of any SIP header field whose grammar     allows choosing between name-addr and addr-spec, such as those     that use the form '(name-addr / addr-spec)', the addr-spec form     MUST NOT be used if its value would contain a comma, semicolon,     or question mark.     When a URI appears in such a header field, any URI parameters MUST     be contained within angle brackets (< and >).  If the URI is not     enclosed in angle brackets, any semicolon-delimited parameters are     header-parameters, not URI parameters.     The header fields defined in this specification that allow this     choice are "To", "From", "Contact", and "Reply-To".4.  Updates to RFCs Defining SIP Extension Header Fields   The following Standards Track RFCs: [RFC3515], [RFC3892], [RFC4508],   and [RFC5360]   and the following Informational RFCs: [RFC3325], [RFC5002],   [RFC5318], and [RFC5502]   are updated to include:      This RFC contains the definition of one or more SIP header fields      that allow choosing between addr-spec and name-addr when      constructing header field values. As specified inRFC 8217,      the "addr-spec" form MUST NOT be used if its value would contain      a comma, semicolon, or question mark.   The status of these RFCs remains unchanged.  In particular the status   of the Informational RFCs remains Informational.Sparks                       Standards Track                    [Page 4]

RFC 8217                name-addr Clarifications             August 20175.  IANA Considerations   This document does not require any IANA actions.6.  Security Considerations   The updates specified in this memo clarify a constraint on the   grammar for producing SIP messages.  It introduces no new security   considerations.  One pre-existing consideration is worth reiterating:   messages produced without honoring the constraint will very likely be   misinterpreted by the receiving element.7.  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,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,              A., Peterson, J., Sparks, R., Handley, M., and E.              Schooler, "SIP: Session Initiation Protocol",RFC 3261,              DOI 10.17487/RFC3261, June 2002,              <http://www.rfc-editor.org/info/rfc3261>.   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private              Extensions to the Session Initiation Protocol (SIP) for              Asserted Identity within Trusted Networks",RFC 3325,              DOI 10.17487/RFC3325, November 2002,              <http://www.rfc-editor.org/info/rfc3325>.   [RFC3515]  Sparks, R., "The Session Initiation Protocol (SIP) Refer              Method",RFC 3515, DOI 10.17487/RFC3515, April 2003,              <http://www.rfc-editor.org/info/rfc3515>.   [RFC3892]  Sparks, R., "The Session Initiation Protocol (SIP)              Referred-By Mechanism",RFC 3892, DOI 10.17487/RFC3892,              September 2004, <http://www.rfc-editor.org/info/rfc3892>.   [RFC4508]  Levin, O. and A. Johnston, "Conveying Feature Tags with              the Session Initiation Protocol (SIP) REFER Method",RFC 4508, DOI 10.17487/RFC4508, May 2006,              <http://www.rfc-editor.org/info/rfc4508>.   [RFC5002]  Camarillo, G. and G. Blanco, "The Session Initiation              Protocol (SIP) P-Profile-Key Private Header (P-Header)",RFC 5002, DOI 10.17487/RFC5002, August 2007,              <http://www.rfc-editor.org/info/rfc5002>.Sparks                       Standards Track                    [Page 5]

RFC 8217                name-addr Clarifications             August 2017   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234,              DOI 10.17487/RFC5234, January 2008,              <http://www.rfc-editor.org/info/rfc5234>.   [RFC5318]  Hautakorpi, J. and G. Camarillo, "The Session Initiation              Protocol (SIP) P-Refused-URI-List Private-Header              (P-Header)",RFC 5318, DOI 10.17487/RFC5318, December              2008, <http://www.rfc-editor.org/info/rfc5318>.   [RFC5360]  Rosenberg, J., Camarillo, G., Ed., and D. Willis, "A              Framework for Consent-Based Communications in the Session              Initiation Protocol (SIP)",RFC 5360,              DOI 10.17487/RFC5360, October 2008,              <http://www.rfc-editor.org/info/rfc5360>.   [RFC5502]  van Elburg, J., "The SIP P-Served-User Private-Header              (P-Header) for the 3GPP IP Multimedia (IM) Core Network              (CN) Subsystem",RFC 5502, DOI 10.17487/RFC5502, April              2009, <http://www.rfc-editor.org/info/rfc5502>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <http://www.rfc-editor.org/info/rfc8174>.Acknowledgments   Brett Tate identified this issue in several extension documents,   submitted several corresponding errata, and drove the discussion that   led to this memo.  Substantive comments leading to this text were   provided by Paul Kyzivat, Gonzalo Camarillo, Dale Worley, and   Yehoshua Gev.Author's Address   Robert Sparks   Oracle   Email: rjsparks@nostrum.comSparks                       Standards Track                    [Page 6]

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