Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track July 2, 2018
Expires: January 3, 2019
Too Many Requests Response Code for the Constrained Application Protocol
draft-ietf-core-too-many-reqs-02
Abstract
A Constrained Application Protocol (CoAP) server can experience
temporary overload because one or more clients are sending requests
to the server at a higher rate than the server is capable or willing
to handle. This document defines a new CoAP Response Code for a
server to indicate that a client should reduce the rate of requests.
Status of This Memo
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This Internet-Draft will expire on January 3, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CoAP Server Behavior . . . . . . . . . . . . . . . . . . . . 3
4. CoAP Client Behavior . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] Response Codes
are used by a CoAP server to indicate the result of the attempt to
understand and satisfy a request sent by a client.
CoAP Response Codes are similar to the HTTP [RFC7230] Status Codes
and many codes are shared with similar semantics by both CoAP and
HTTP. HTTP has the code "429" registered for "Too Many Requests"
[RFC6585]. This document registers a CoAP Response Code "4.29" for
similar purpose and also defines use of the Max-Age option to
indicate a back-off period after which a client can try the request
again.
While a server may not be able to response to a one kind of request,
it may be able to respond to a different request, even from the same
client. Therefore the back-off period applies only to similar
requests. For the purpose of this response code, a request is
similar if it has the same method, Request-URI, and payload. Also if
a client is sending a sequence of requests that are part of the same
series (e.g., a set of measurements to be processed by the server)
they can be considered similar even if request payloads or URIs may
be different. Because request similarity is context-dependent, it is
up to the application logic to decide how similar requests should be
suppressed.
The 4.29 code is similar to the 5.03 "Service Unavailable" [RFC7252]
code in a way that the 5.03 code can also be used by a server to
signal an overload situation. However the 4.29 code indicates that
the too frequent requests from the requesting client are the reason
for the overload.
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2. Terminology
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
specification are to be interpreted as described in [RFC2119].
Readers should also be familiar with the terms and concepts discussed
in [RFC7252].
3. CoAP Server Behavior
If a CoAP server is unable to serve a client that is sending CoAP
request messages more often than the server is capable or willing to
handle, the server SHOULD respond to the request(s) with the Response
Code 4.29, "Too Many Requests". The Max-Age option is used to
indicate the number of seconds after which the server assumes it is
OK for the client to retry the request.
An action result payload (see Section 5.5.1 in [RFC7252]) can be sent
by the server to give more guidance to the client, e.g., about the
details of the overload situation.
4. CoAP Client Behavior
If a client receives the 4.29 Response Code from a CoAP server to a
request, it SHOULD NOT send a similar request to the server before
the time indicated in the Max-Age option has passed.
A client MUST NOT rely on a server being able to send the 4.29
Response Code in an overload situation because an overloaded server
may not be able to reply to all requests at all.
5. Security Considerations
Replying to CoAP requests with a Response Code consumes resources
from a server. For a server under attack it may be more appropriate
to simply drop requests without responding.
If a CoAP reply with the Too Many Requests Response Code is not
authenticated and integrity protected, an attacker can attempt to
spoof a reply and make the client wait for an extended period of time
before trying again.
6. IANA Considerations
IANA is requested to register the following Response Code in the
"CoRE Parameters Registry", "CoAP Response Codes" sub-registry:
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o Response Code: 4.29
o Description: Too Many Requests
o Reference: [[This document]]
7. Acknowledgements
This Response Code definition was originally part of the "Publish-
Subscribe Broker for CoAP" document [I-D.ietf-core-coap-pubsub].
Author would like to thank Abhijan Bhattacharyya, Carsten Bormann,
Gyorgy Rethy, Klaus Hartke, and Sandor Katona for their contributions
and reviews.
8. References
8.1. 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>.
[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>.
8.2. Informative References
[I-D.ietf-core-coap-pubsub]
Koster, M., Keranen, A., and J. Jimenez, "Publish-
Subscribe Broker for the Constrained Application Protocol
(CoAP)", draft-ietf-core-coap-pubsub-04 (work in
progress), March 2018.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/info/rfc6585>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", RFC
7230, DOI 10.17487/RFC7230, June 2014, <https://www.rfc-
editor.org/info/rfc7230>.
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Author's Address
Ari Keranen
Ericsson
Email: ari.keranen@ericsson.com
Keranen Expires January 3, 2019 [Page 5]
