"Too Many Requests" Response Code for the Constrained Application Protocol
RFC 8516
Internet Engineering Task Force (IETF) A. Keranen
Request for Comments: 8516 Ericsson
Category: Standards Track January 2019
ISSN: 2070-1721
"Too Many Requests" Response Code for
the Constrained Application Protocol
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
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8516.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Keranen Standards Track [Page 1]
RFC 8516 "Too Many Requests" Response Code for CoAP January 2019
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CoAP Server Behavior . . . . . . . . . . . . . . . . . . . . 3
4. CoAP Client Behavior . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] response codes
are used by a CoAP server to indicate the result of an 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 purposes and uses the Max-Age option (see Section 5.10.5 of
[RFC7252]) to indicate a back-off period after which a client can try
the request again.
While a server may not be able to respond to one kind of request, it
may be able to respond to a request of a different kind, 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 and Request-URI. 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 URIs are different.
Because request similarity is context-dependent, it is up to the
application logic to decide how the similarity of the requests should
be evaluated.
The 4.29 code is similar to the 5.03 "Service Unavailable" [RFC7252]
code in that the 5.03 code can also be used by a server to signal an
overload situation. The 5.03 code also uses the Max-Age option to
indicate the time after which a client can retry. However, the 4.29
code indicates that the too-frequent requests from the requesting
client are the reason for the overload.
Keranen Standards Track [Page 2]
RFC 8516 "Too Many Requests" Response Code for CoAP January 2019
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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