CoRE Working group C. Bormann Internet-Draft Universität Bremen TZI Updates: 9176 (if approved) 23 July 2023 Intended status: Informational Expires: 24 January 2024 CoRE Target Attributes Registry draft-ietf-core-target-attr-05 Abstract The Constrained RESTful Environments (CoRE) specifications apply Web technologies to constrained environments. One important such technology is Web Linking (RFC 8288), which CoRE specifications use as the basis for a number of discovery protocols, such as the Link Format (RFC 6690) in CoAP's Resource Discovery Protocol (Section 7.2 of RFC7252) and the Resource Directory (RD, RFC 9176). Web Links can have target attributes, the names of which are not generally coordinated by the Web Linking specification (Section 2.2 of RFC 8288). This document introduces an IANA registry for coordinating names of target attributes when used in CoRE. It updates the RD Parameters IANA Registry created by RFC 9176 to coordinate with this registry. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-core-target-attr/. Discussion of this document takes place on the core Working Group mailing list (mailto:core@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/core/. Subscribe at https://www.ietf.org/mailman/listinfo/core/. Source for this draft and an issue tracker can be found at https://github.com/core-wg/core-target-attr. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Bormann Expires 24 January 2024 [Page 1] Internet-Draft CoRE Target Attributes Registry July 2023 Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 24 January 2024. 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 2.1. Instructions for the Designated Expert . . . . . . . . . 4 2.2. Structure of Entries . . . . . . . . . . . . . . . . . . 4 2.3. Initial Entries . . . . . . . . . . . . . . . . . . . . . 5 3. Security considerations . . . . . . . . . . . . . . . . . . . 6 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Normative References . . . . . . . . . . . . . . . . . . 6 4.2. Informative References . . . . . . . . . . . . . . . . . 7 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 Bormann Expires 24 January 2024 [Page 2] Internet-Draft CoRE Target Attributes Registry July 2023 1. Introduction The Constrained RESTful Environments (CoRE) specifications apply Web technologies to constrained environments. One important such technology is Web Linking [RFC8288], which CoRE specifications use as the basis for a number of discovery protocols, such as the Link Format [RFC6690] in CoAP's Resource Discovery Protocol (Section 7.2 of [RFC7252]) and the Resource Directory [RFC9176]. Web Links can have target attributes. The original Web Linking specification (Section 3 of [RFC5988]) did not attempt to coordinate names of target attributes except for providing common target attributes for use in the Link HTTP header. The current revision of that specification clarifies (Section 2.2 of [RFC8288]): | This specification does not attempt to coordinate the name of | target attributes, their cardinality, or use. Those creating and | maintaining serialisations SHOULD coordinate their target | attributes to avoid conflicts in semantics or syntax and MAY | define their own registries of target attributes. This document introduces an IANA registry for coordinating names of target attributes when used in CoRE, with specific instructions for the Designated Expert for this registry (Section 2.1). It updates the RD Parameters IANA Registry created by [RFC9176] to coordinate with this registry. With a registry now available, registration of target attributes is strongly encouraged. The incentive is that an unregistered attribute name might be registered with a different meaning at any time. 1.1. 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 in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. IANA Considerations This specification creates a new Target Attributes registry in the "Constrained RESTful Environments (CoRE) Parameters" registry group [IANA.core-parameters], with the policy "Expert Review" (Section 4.5 of [BCP26]). Bormann Expires 24 January 2024 [Page 3] Internet-Draft CoRE Target Attributes Registry July 2023 2.1. Instructions for the Designated Expert The expert is requested to guide the registrant towards reasonably short target attribute names where the shortness will help conserve resources in constrained systems, but also to be frugal in the allocation of very short names, keeping them in reserve for applications that are likely to enjoy wide use and can make good use of their shortness. The expert is also instructed to direct the registrant to provide a specification (Section 4.6 of [BCP26]), but can make exceptions, for instance when a specification is not available at the time of registration but is likely forthcoming. Any questions or issues that might interest a wider audience might be raised by the expert on the core-parameters@ietf.org mailing list for a time-limited discussion. This might include security considerations, or opportunities for orchestration, e.g., when different names with similar intent are being or could be registered. If the expert becomes aware of target attributes that are deployed and in use, they may also initiate a registration on their own if they deem such a registration can avert potential future collisions. 2.2. Structure of Entries Each entry in the registry must include: Attribute Name: a lower case ASCII [STD80] string that starts with a letter and can contain digits and hyphen-minus characters afterward ([a-z][-a-z0-9]*). (Note that [RFC8288] requires target attribute names to be interpreted in a case-insensitive way; the restriction to lower case here ensures that they are registered in a predictable form). Brief description: a brief description Change Controller: see Section 2.3 of [BCP26] Reference: a reference document that provides a description of the target attribute, including the semantics for when the target attribute appears more than once in a link. Bormann Expires 24 January 2024 [Page 4] Internet-Draft CoRE Target Attributes Registry July 2023 2.3. Initial Entries Initial entries in this registry are listed in Table 1. +===========+=========================+============+===============+ | Attribute | Brief description | Change | Reference | | Name | | Controller | | +===========+=========================+============+===============+ | href | reserved (not useful as | IESG | [RFC6690] | | | target attribute name) | | | +-----------+-------------------------+------------+---------------+ | anchor | reserved (not useful as | IESG | [RFC6690] | | | target attribute name) | | | +-----------+-------------------------+------------+---------------+ | rel | reserved (not useful as | IESG | [RFC6690] | | | target attribute name) | | | +-----------+-------------------------+------------+---------------+ | rev | reserved (not useful as | IESG | [RFC6690] | | | target attribute name) | | | +-----------+-------------------------+------------+---------------+ | hreflang | (Web Linking) | IESG | [RFC8288] | +-----------+-------------------------+------------+---------------+ | media | (Web Linking) | IESG | [RFC8288] | +-----------+-------------------------+------------+---------------+ | title | (Web Linking) | IESG | [RFC8288] | +-----------+-------------------------+------------+---------------+ | type | (Web Linking) | IESG | [RFC8288] | +-----------+-------------------------+------------+---------------+ | rt | resource type | IESG | Section 3.1 | | | | | of [RFC6690] | +-----------+-------------------------+------------+---------------+ | if | interface description | IESG | Section 3.2 | | | | | of [RFC6690] | +-----------+-------------------------+------------+---------------+ | sz | maximum size estimate | IESG | Section 3.3 | | | | | of [RFC6690] | +-----------+-------------------------+------------+---------------+ | ct | Content-Format hint | IESG | Section 7.2.1 | | | | | of [RFC7252] | +-----------+-------------------------+------------+---------------+ | obs | observable resource | IESG | Section 6 of | | | | | [RFC7641] | +-----------+-------------------------+------------+---------------+ | hct | HTTP-CoAP URI mapping | IESG | Section 5.5 | | | template | | of [RFC8075] | +-----------+-------------------------+------------+---------------+ | osc | hint: resource only | IESG | Section 9 of | | | accessible using OSCORE | | [RFC8613] | Bormann Expires 24 January 2024 [Page 5] Internet-Draft CoRE Target Attributes Registry July 2023 +-----------+-------------------------+------------+---------------+ | ep | Endpoint Name (with | IESG | Section 9.3 | | | rt="core.rd-ep") | | of [RFC9176] | +-----------+-------------------------+------------+---------------+ | d | Sector (with | IESG | Section 9.3 | | | rt="core.rd-ep") | | of [RFC9176] | +-----------+-------------------------+------------+---------------+ | base | Registration Base URI | IESG | Section 9.3 | | | (with rt="core.rd-ep") | | of [RFC9176] | +-----------+-------------------------+------------+---------------+ | et | Endpoint Type (with | IESG | Section 9.3 | | | rt="core.rd-ep") | | of [RFC9176] | +-----------+-------------------------+------------+---------------+ Table 1: Initial Entries in the Target Attributes Registry A number of names are reserved as they are used for parameters in links other than target attributes. A further set of target attributes is predefined in [RFC8288] and is imported into this registry. Section 9.3 of [RFC9176] created the "RD Parameters" IANA registry. This document requests IANA to add the following note to that registry: Note: All entries with the "A" flag set, including new ones, MUST also be registered in the "Target Attributes" registry [IANA.core-parameters]. 3. Security considerations The security considerations of [RFC8288] apply, as do those of the discovery specifications [RFC6690], [RFC7252], and [RFC9176]. 4. References 4.1. Normative References [BCP26] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [IANA.core-parameters] IANA, "Constrained RESTful Environments (CoRE) Parameters", . Bormann Expires 24 January 2024 [Page 6] Internet-Draft CoRE Target Attributes Registry July 2023 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017, . [STD80] Cerf, V., "ASCII format for network interchange", STD 80, RFC 20, DOI 10.17487/RFC0020, October 1969, . 4.2. Informative References [RFC5988] Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/RFC5988, October 2010, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, . [RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and E. Dijk, "Guidelines for Mapping Implementations: HTTP to the Constrained Application Protocol (CoAP)", RFC 8075, DOI 10.17487/RFC8075, February 2017, . [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, . Bormann Expires 24 January 2024 [Page 7] Internet-Draft CoRE Target Attributes Registry July 2023 [RFC9176] Amsüss, C., Ed., Shelby, Z., Koster, M., Bormann, C., and P. van der Stok, "Constrained RESTful Environments (CoRE) Resource Directory", RFC 9176, DOI 10.17487/RFC9176, April 2022, . Acknowledgements The CoRE WG had been discussing setting up a registry for target attributes since the final touches were made on [RFC6690]. The update of the Web Linking specification to [RFC8288] provided the formal setting, but it took until Jaime Jiménez provided the set of initial registrations to generate a first version of this specification. The current version addresses additional input and working group last call comments by Esko Dijk, Marco Tiloca, Thomas Fossati, and Mohamed Boucadair, as well as area director review comments from Rob Wilton. Contributors Jaime Jiménez Ericsson Email: jaime@iki.fi Jaime provided the list of initial registrations. Author's Address Carsten Bormann Universität Bremen TZI Postfach 330440 D-28359 Bremen Germany Phone: +49-421-218-63921 Email: cabo@tzi.org Bormann Expires 24 January 2024 [Page 8]