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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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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