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Versions: 00

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.




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   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.





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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-<number>, where <number> is the section number.

2.  RFC 7252








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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,
              <https://www.rfc-editor.org/info/rfc2119>.






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   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <https://www.rfc-editor.org/info/rfc6690>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>.

   [RFC7959]  Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
              the Constrained Application Protocol (CoAP)", RFC 7959,
              DOI 10.17487/RFC7959, August 2016,
              <https://www.rfc-editor.org/info/rfc7959>.

   [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,
              <https://www.rfc-editor.org/info/rfc8132>.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc8323>.

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.




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Author's Address

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org









































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