draft-ietf-core-too-many-reqs-06.txt   rfc8516.txt 
Network Working Group A. Keranen Internet Engineering Task Force (IETF) A. Keranen
Internet-Draft Ericsson Request for Comments: 8516 Ericsson
Intended status: Standards Track November 7, 2018 Category: Standards Track January 2019
Expires: May 11, 2019 ISSN: 2070-1721
Too Many Requests Response Code for the Constrained Application Protocol "Too Many Requests" Response Code for
draft-ietf-core-too-many-reqs-06 the Constrained Application Protocol
Abstract Abstract
A Constrained Application Protocol (CoAP) server can experience A Constrained Application Protocol (CoAP) server can experience
temporary overload because one or more clients are sending requests 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 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 to handle. This document defines a new CoAP response code for a
server to indicate that a client should reduce the rate of requests. server to indicate that a client should reduce the rate of requests.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on May 11, 2019. 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 Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CoAP Server Behavior . . . . . . . . . . . . . . . . . . . . 3 3. CoAP Server Behavior . . . . . . . . . . . . . . . . . . . . 3
4. CoAP Client Behavior . . . . . . . . . . . . . . . . . . . . 3 4. CoAP Client Behavior . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] Response Codes The Constrained Application Protocol (CoAP) [RFC7252] response codes
are used by a CoAP server to indicate the result of the attempt to are used by a CoAP server to indicate the result of an attempt to
understand and satisfy a request sent by a client. understand and satisfy a request sent by a client.
CoAP Response Codes are similar to the HTTP [RFC7230] Status Codes CoAP response codes are similar to the HTTP [RFC7230] status codes,
and many codes are shared with similar semantics by both CoAP and and many codes are shared with similar semantics by both CoAP and
HTTP. HTTP has the code "429" registered for "Too Many Requests" HTTP. HTTP has the code "429" registered for "Too Many Requests"
[RFC6585]. This document registers a CoAP Response Code "4.29" for [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 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 [RFC7252]) to indicate a back-off period after which a client can try
the request again. the request again.
While a server may not be able to respond to one kind of request, it 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 may be able to respond to a request of a different kind, even from
same client. Therefore the back-off period applies only to similar the same client. Therefore, the back-off period applies only to
requests. For the purpose of this response code, a request is similar requests. For the purpose of this response code, a request
similar if it has the same method and Request-URI. Also if a client is similar if it has the same method and Request-URI. Also, if a
is sending a sequence of requests that are part of the same series client is sending a sequence of requests that are part of the same
(e.g., a set of measurements to be processed by the server) they can series (e.g., a set of measurements to be processed by the server),
be considered similar even if request URIs may be different. Because they can be considered similar even if request URIs are different.
request similarity is context-dependent, it is up to the application Because request similarity is context-dependent, it is up to the
logic to decide how the similarity of the requests should be application logic to decide how the similarity of the requests should
evaluated. be evaluated.
The 4.29 code is similar to the 5.03 "Service Unavailable" [RFC7252] 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 code in that the 5.03 code can also be used by a server to signal an
signal an overload situation. The 5.03 code also uses the Max-Age overload situation. The 5.03 code also uses the Max-Age option to
option to indicate the time after which a client can retry. However indicate the time after which a client can retry. However, the 4.29
the 4.29 code indicates that the too-frequent requests from the code indicates that the too-frequent requests from the requesting
requesting client are the reason for the overload. client are the reason for the overload.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Readers should also be familiar with the terms and concepts discussed Readers should also be familiar with the terms and concepts discussed
in [RFC7252]. in [RFC7252].
3. CoAP Server Behavior 3. CoAP Server Behavior
If a CoAP server is unable to serve a client that is sending CoAP 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 request messages more often than the server is capable or willing to
handle, the server SHOULD respond to the request(s) with the Response 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 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 indicate the number of seconds after which the server assumes it is
OK for the client to retry the request. OK for the client to retry the request.
An action result payload (see Section 5.5.1 of [RFC7252]) can be sent 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 by the server to give more guidance to the client, e.g., details of
details of the overload situation. the overload situation.
The 4.29 Response Code is only returned to the client(s) sending The 4.29 response code is only returned to the client(s) sending
requests too frequently; if other clients are sending requests that requests too frequently; if other clients are sending requests that
cannot be served due to server overload, the 5.03 Response Code is cannot be served due to server overload, the 5.03 response code is
more appropriate. more appropriate.
If a client repeats a request that was answered with 4.29 before Max- If a client repeats a request that was answered with 4.29 before
Age time has passed, it is possible that the client sent multiple 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 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 response code. To slow down clients that do not
recognize the 4.29 code, the server MAY respond with a more generic 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 error code (e.g., 5.03). The server SHOULD rate-limit 4.29 replies
taking into account its usual load shedding policies. However, any taking into account its usual load-shedding policies. However, any
such method that adds per-client state to the server may be such method that adds per-client state to the server may be
counterproductive to reducing load. counterproductive to reducing the load.
4. CoAP Client Behavior 4. CoAP Client Behavior
If a client receives the 4.29 Response Code from a CoAP server to a 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 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 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 response does not contain a Max-Age option, the default value (60
seconds, as defined in Section 5.10.5 of [RFC7252]) is assumed. seconds, as defined in Section 5.10.5 of [RFC7252]) is assumed.
Note that a client may receive a 4.29 Response Code already on a Note that a client may receive a 4.29 response code on a first
first request to a server. This can happen, for example, if there is request to a server. This can happen, for example, if there is a
a proxy on the path and the server replies based on the load from proxy on the path and the server replies based on the load from
multiple clients aggregated by the proxy, or if a client has multiple clients aggregated by the proxy, or if a client has
restarted recently and does not remember its recent requests. restarted recently and does not remember its recent requests.
A client should not rely on a server being able to send the 4.29 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 response code in an overload situation because an overloaded server
may not be able to reply at all to some requests. may not be able to reply at all to some requests.
5. Security Considerations 5. Security Considerations
Security considerations of [RFC7252] apply also to this Response Security considerations of [RFC7252] apply to this response code
Code. also.
Replying to CoAP requests with a Response Code consumes resources Replying to CoAP requests with a response code consumes resources
from a server. For a server under attack it may be more appropriate from a server. For a server under attack, it may be more appropriate
to simply drop requests without responding at all. However, dropping to simply drop requests without responding at all. However, dropping
requests is likely to cause also well-behaving clients to simply requests is also likely to cause well-behaving clients to simply
retry the requests. retry the requests.
As with any other CoAP reply, a client should trust this Response As with any other CoAP reply, a client should trust this response
Code only to extent it trusts the underlying security mechanisms code only to the extent that it trusts the underlying security
(e.g., DTLS [RFC6347]) for authentication and freshness. If a CoAP mechanisms (e.g., DTLS [RFC6347]) for authentication and freshness.
reply with the Too Many Requests Response Code is not authenticated If a CoAP reply with the "Too Many Requests" response code is not
and integrity protected, an attacker can attempt to spoof a reply and authenticated and integrity protected, an attacker can attempt to
make the client wait for an extended period of time before trying spoof a reply and make the client wait for an extended period of time
again. before trying again.
If the Response Code is sent without encryption, it may leak If the response code is sent without encryption, it may leak
information about the server overload situation and client traffic information about the server overload situation and client traffic
patterns. patterns.
6. IANA Considerations 6. IANA Considerations
IANA is requested to register the following Response Code in the IANA has registered the following response code in the "CoAP Response
"CoRE Parameters Registry", "CoAP Response Codes" sub-registry: Codes" subregistry within the "Constrained RESTful Environments
(CoRE) Parameters" registry:
o Response Code: 4.29 o Response Code: 4.29
o Description: Too Many Requests o Description: Too Many Requests
o Reference: [[This document]] o Reference: RFC 8516
IANA is requested to add this document as an additional reference for
the Max-Age option in the "CoAP Option Numbers" sub-registry.
7. Acknowledgements
This Response Code definition was originally part of the "Publish- IANA has added this document as an additional reference for the
Subscribe Broker for CoAP" document [I-D.ietf-core-coap-pubsub]. Max-Age option in the "CoAP Option Numbers" subregistry.
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 7. References
8.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References 7.2. Informative References
[I-D.ietf-core-coap-pubsub] [CoAP-BROKER]
Koster, M., Keranen, A., and J. Jimenez, "Publish- Koster, M., Keranen, A., and J. Jimenez, "Publish-
Subscribe Broker for the Constrained Application Protocol Subscribe Broker for the Constrained Application Protocol
(CoAP)", draft-ietf-core-coap-pubsub-05 (work in (CoAP)", Work in Progress, draft-ietf-core-coap-pubsub-06,
progress), July 2018. January 2019.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/info/rfc6585>. <https://www.rfc-editor.org/info/rfc6585>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
Acknowledgements
This response code definition was originally part of the "Publish-
Subscribe Broker for CoAP" document [CoAP-BROKER]. The 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.
Author's Address Author's Address
Ari Keranen Ari Keranen
Ericsson Ericsson
Hirsalantie 11
02420 Jorvas
Finland
Email: ari.keranen@ericsson.com Email: ari.keranen@ericsson.com
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