Network Working Group C. Bormann Internet-Draft Universitaet Bremen TZI Updates: 6690, 7252, 7641, 7959, 8132, October 24, 2018 8323 (if approved) Intended status: Standards Track Expires: April 27, 2019 Constrained Application Protocol (CoAP): Corrections and Clarifications draft-bormann-core-corr-clar-00 Abstract RFC 7252 defines the Constrained Application Protocol (CoAP), along with a number of additional specifications, including RFC 7641, RFC 7959, RFC 8132, and RFC 8323. RFC 6690 defines the link format that is used in CoAP self-description documents. Some parts of the specification may be unclear or even contain errors that may lead to misinterpretations that may impair interoperability between different implementations. The present document provides corrections, additions, and clarifications to the RFCs cited; this document thus updates these RFCs. In addition, other clarifications related to the use of CoAP in other specifications, including RFC 7390 and RFC 8075, are also provided. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 April 27, 2019. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. Bormann Expires April 27, 2019 [Page 1] Internet-Draft Corrections and Clarifications to CoAP October 2018 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 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 Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Process . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. RFC 7252 . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. RFC7252-5.10.5: Max-Age . . . . . . . . . . . . . . . . . 4 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 5.2. Informative References . . . . . . . . . . . . . . . . . 5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction [RFC7252] defines the Constrained Application Protocol (CoAP), along with a number of additional specifications, including [RFC7641], [RFC7959], [RFC8132], and [RFC8323]. [RFC6690] defines the link format that is used in CoAP self-description documents. During implementation and interoperability testing of these RFCs, and in their practical use, some ambiguities and common misinterpretations have been identified, as well as a few errors. The present document summarizes identified issues and provides corrections needed for implementations of CoAP to interoperate, i.e., it constitutes an update to the RFCs referenced. This document also provides other clarifications related to common misinterpretations of the specification. References to CoAP should, therefore, also include this document. In addition, some clarifications and corrections are also provided for documents that are related to CoAP, including RFC 7390 and RFC 8075. Bormann Expires April 27, 2019 [Page 2] Internet-Draft Corrections and Clarifications to CoAP October 2018 1.1. Process The present document is an Internet-Draft, which is not intended to be published as an RFC quickly. Instead, it will be maintained as a running document of the CoRE WG, probably for a number of years, until the need for new entries tails off and the document can finally be published as an RFC. (This paragraph to be rephrased when that happens.) The status of this document as a running document of the WG implies a consensus process that is applied in making updates to it. The rest of this subsection provides more details about this consensus process. (This is the intended status; currently, the document is an individual submission only.) (Consensus process TBD, but it will likely be based on an editor's version in a publicly accessible git repository, as well as periodic calls for consensus that lead to a new published Internet-Draft;.) 1.2. 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 in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. When a section of this document makes formal corrections, additions or invalidations to text in a referenced RFC, this is clearly summarized. The text from the RFC that is being addressed is given and labeled "INCOMPLETE", "INCORRECT", or "INCORRECT AND INVALIDATED", followed by the correct text labeled "CORRECTED", where applicable. When text is added that does not simply correct text in previous specifications, it is given with the label "FORMAL ADDITION". Where a resolution has not yet been agreed, the resolution is marked PENDING. In this document, a reference to a section in RFC nnnn is written as RFC nnnn-, where is the section number. 2. RFC 7252 Bormann Expires April 27, 2019 [Page 3] Internet-Draft Corrections and Clarifications to CoAP October 2018 2.1. RFC7252-5.10.5: Max-Age In the discussion of [I-D.ietf-core-too-many-reqs], a comment was made that it would be needed to define the point in time relative to which Max-Age is defined. A sender might reference it to the time it actually sends the message containing the option (and paragraph 3 of RFC7252-5.10.5 indeed requests that Max-Age be updated each time a message is retransmitted). The receiver of the message does not have reliable information about the time of sending, though. It may instead reference the Max-Age to the time of reception. This in effect extends the time of Max-Age by the latency of the packet. This extension was deemed acceptable for the purposes of [I-D.ietf-core-too-many-reqs], but may be suboptimal when Max-Age is about the lifetime of a response object. INCOMPLETE: The value is intended to be current at the time of transmission. PENDING. 3. IANA Considerations None yet. (Individual clarifications may contain IANA considerations; these will then be referenced here.) 4. Security Considerations This document provides a number of corrections and clarifications to existing RFCs, but it does not make any changes with regard to the security aspects of the protocol. As a consequence, the security considerations of the referenced RFCs apply without additions. (To be changed when that is no longer true; probably the security considerations will then be on the individual clarifications.) 5. References 5.1. 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, . Bormann Expires April 27, 2019 [Page 4] Internet-Draft Corrections and Clarifications to CoAP October 2018 [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, . [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, . [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K., Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets", RFC 8323, DOI 10.17487/RFC8323, February 2018, . 5.2. Informative References [I-D.ietf-core-too-many-reqs] Keranen, A., "Too Many Requests Response Code for the Constrained Application Protocol", draft-ietf-core-too- many-reqs-05 (work in progress), October 2018. Acknowledgements The present document is modeled after RFC 4815 and the Internet- Drafts of the ROHC WG that led to it. Many thanks to the co-chairs of the ROHC WG and WG members that made this a worthwhile and successful experiment at the time. Bormann Expires April 27, 2019 [Page 5] Internet-Draft Corrections and Clarifications to CoAP October 2018 Author's Address Carsten Bormann Universitaet Bremen TZI Postfach 330440 Bremen D-28359 Germany Phone: +49-421-218-63921 Email: cabo@tzi.org Bormann Expires April 27, 2019 [Page 6]