Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track November 7, 2018
Expires: May 11, 2019
Too Many Requests Response Code for the Constrained Application Protocol
draft-ietf-core-too-many-reqs-06
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 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 May 11, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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.
Keranen Expires May 11, 2019 [Page 1]
Internet-Draft Too Many Requests Response Code for CoAP November 2018
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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
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 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 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 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 may be 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 a way 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 Expires May 11, 2019 [Page 2]
Internet-Draft Too Many Requests Response Code for CoAP November 2018
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.
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 of [RFC7252]) can be sent
by the server to give more guidance to the client, e.g., about the
details of the overload situation.
The 4.29 Response Code is only returned to the client(s) sending
requests too frequently; if other clients are sending requests that
cannot be served due to server overload, the 5.03 Response Code is
more appropriate.
If a client repeats a request that was answered with 4.29 before Max-
Age time has passed, it is possible that the client sent multiple
requests before receiving the first answer or that the client did not
recognize the Response Code. To slow down clients that do not
recognize the 4.29 code, the server MAY respond with a more generic
error code (e.g., 5.03). The server SHOULD rate-limit 4.29 replies
taking into account its usual load shedding policies. However, any
such method that adds per-client state to the server may be
counterproductive to reducing load.
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. If the 4.29
response does not contain a Max-Age option, the default value (60
seconds, as defined in Section 5.10.5 of [RFC7252]) is assumed.
Keranen Expires May 11, 2019 [Page 3]
Internet-Draft Too Many Requests Response Code for CoAP November 2018
Note that a client may receive a 4.29 Response Code already on a
first request to a server. This can happen, for example, if there is
a proxy on the path and the server replies based on the load from
multiple clients aggregated by the proxy, or if a client has
restarted recently and does not remember its recent requests.
A client should 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 at all to some requests.
5. Security Considerations
Security considerations of [RFC7252] apply also to this Response
Code.
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 at all. However, dropping
requests is likely to cause also well-behaving clients to simply
retry the requests.
As with any other CoAP reply, a client should trust this Response
Code only to extent it trusts the underlying security mechanisms
(e.g., DTLS [RFC6347]) for authentication and freshness. 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.
If the Response Code is sent without encryption, it may leak
information about the server overload situation and client traffic
patterns.
6. IANA Considerations
IANA is requested to register the following Response Code in the
"CoRE Parameters Registry", "CoAP Response Codes" sub-registry:
o Response Code: 4.29
o Description: Too Many Requests
o Reference: [[This document]]
IANA is requested to add this document as an additional reference for
the Max-Age option in the "CoAP Option Numbers" sub-registry.
Keranen Expires May 11, 2019 [Page 4]
Internet-Draft Too Many Requests Response Code for CoAP November 2018
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,
Daniel Migault, Gyorgy Rethy, Jana Iyengar, Jim Schaad, Klaus Hartke,
Mohit Sethi, 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>.
[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>.
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-05 (work in
progress), July 2018.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[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>.
Keranen Expires May 11, 2019 [Page 5]
Internet-Draft Too Many Requests Response Code for CoAP November 2018
Author's Address
Ari Keranen
Ericsson
Email: ari.keranen@ericsson.com
Keranen Expires May 11, 2019 [Page 6]
