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Internet Engineering Task Force (IETF)                        A.B. RoachRequest for Comments: 7621                                       MozillaUpdates:6665                                                August 2015Category: Standards TrackISSN: 2070-1721A Clarification on the Use of Globally Routable User Agent URIs (GRUUs)                in the SIP Event Notification FrameworkAbstract   Experience since the publication of the most recent SIP Events   framework (in July 2012) has shown that there is room for   interpretation around the use of Globally Routable User Agent URIs in   that specification.  This document clarifies the intended behavior.   This document updatesRFC 6665.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 5741.   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/rfc7621.Copyright Notice   Copyright (c) 2015 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.Roach                        Standards Track                    [Page 1]

RFC 7621              SIP Events GRUU Clarification          August 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Clarification of GRUU Handling  . . . . . . . . . . . . . . .23.  Security Considerations . . . . . . . . . . . . . . . . . . .34.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .35.  Normative References  . . . . . . . . . . . . . . . . . . . .3   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .41.  Introduction   This document is intended to clarify a point of implementor confusion   arising from lack of clarity in [RFC6665].2.  Clarification of GRUU Handling   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].Section 4.5.1 of [RFC6665] contains the following normative   requirement on implementations:      Notifiers MUST implement the Globally Routable User Agent URI      (GRUU) extension defined in [RFC5627], and MUST use a GRUU as      their local target.  This allows subscribers to explicitly target      desired devices.   The second sentence of this paragraph attempted to set context for   the normative statement: the reason GRUUs are required in this   context is to allow you to send SUBSCRIBE or REFER requests to a   specific user agent, with the target of the subscription request   being something like an INVITE dialog on that device.  Consequently,   the requirement to include a GRUU as a local target was intended to   apply not just to the local target for SUBSCRIBE-created dialogs, but   to *all* dialogs, even those created by INVITE.  This requirement has   been interpreted in a variety of ways by implementors, so a   clarification is in order.   Discussion subsequent to the publication of [RFC6665] has highlighted   obscure cases in which implementations might be notifiers in some   contexts, but may not wish to act as notifiers in others.  Under   these narrow circumstances, the restriction described above is not   necessary for dialogs about which the notifier will never accept   subscriptions (although the use of GRUUs in such a context causes no   harm, either).Roach                        Standards Track                    [Page 2]

RFC 7621              SIP Events GRUU Clarification          August 2015   This document updates [RFC6665] to clarify the actual requirements.   The replacement text is as follows:      Notifiers MUST implement the Globally Routable User Agent URI      (GRUU) extension defined in [RFC5627].  Notifiers MUST use a GRUU      as their local target for all dialog-forming methods and all      target-refresh methods, except for those dialogs for which they      will reject all subscription requests (implicit or explicit).  For      clarity: an implementation that uses a non-GRUU local contact      under the exception described above MUST reject a request that      might create a subscription to the associated dialog, regardless      of whether such subscription would be created by a SUBSCRIBE or a      REFER message.  The rejection code under such conditions SHOULD be      403 (Forbidden) unless some other code is more appropriate to the      circumstances.  The foregoing requirements to implement and use      GRUUs specifically include dialogs created by the INVITE method.3.  Security Considerations   This mechanism does not introduce any security issues beyond those   discussed in [RFC6665].4.  IANA Considerations   This document requests no actions of IANA.5.  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>.   [RFC5627]  Rosenberg, J., "Obtaining and Using Globally Routable User              Agent URIs (GRUUs) in the Session Initiation Protocol              (SIP)",RFC 5627, DOI 10.17487/RFC5627, October 2009,              <http://www.rfc-editor.org/info/rfc5627>.   [RFC6665]  Roach, A.B., "SIP-Specific Event Notification",RFC 6665,              DOI 10.17487/RFC6665, July 2012,              <http://www.rfc-editor.org/info/rfc6665>.Roach                        Standards Track                    [Page 3]

RFC 7621              SIP Events GRUU Clarification          August 2015Author's Address   Adam Roach   Mozilla   Dallas, TX   United States   Phone: +1 650 903 0800 x863   Email: adam@nostrum.comRoach                        Standards Track                    [Page 4]