draft-ietf-core-hop-limit-04.txt   draft-ietf-core-hop-limit-05.txt 
CORE M. Boucadair CORE M. Boucadair
Internet-Draft Orange Internet-Draft Orange
Intended status: Standards Track T. Reddy Intended status: Standards Track T. Reddy
Expires: January 4, 2020 McAfee Expires: March 12, 2020 McAfee
J. Shallow J. Shallow
July 3, 2019 September 9, 2019
Constrained Application Protocol (CoAP) Hop-Limit Option Constrained Application Protocol (CoAP) Hop-Limit Option
draft-ietf-core-hop-limit-04 draft-ietf-core-hop-limit-05
Abstract Abstract
The presence of Constrained Application Protocol (CoAP) proxies may The presence of Constrained Application Protocol (CoAP) proxies may
lead to infinite forwarding loops, which is undesirable. To prevent lead to infinite forwarding loops, which is undesirable. To prevent
and detect such loops, this document specifies the Hop-Limit CoAP and detect such loops, this document specifies the Hop-Limit CoAP
option. option.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 4, 2020. This Internet-Draft will expire on March 12, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Intended Usage . . . . . . . . . . . . . . . . . . . . . 2 1.1. Intended Usage . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Hop-Limit Option . . . . . . . . . . . . . . . . . . . . . . 3 3. Hop-Limit Option . . . . . . . . . . . . . . . . . . . . . . 3
4. HTTP-Mapping Considerations . . . . . . . . . . . . . . . . . 5 4. Debugging & Troubleshooting . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. HTTP-Mapping Considerations . . . . . . . . . . . . . . . . . 5
5.1. CoAP Response Code . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.2. CoAP Option Number . . . . . . . . . . . . . . . . . . . 6 6.1. CoAP Response Code . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6.2. CoAP Option Number . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
More and more applications are using the Constrained Application More and more applications are using the Constrained Application
Protocol (CoAP) [RFC7252] as a communication protocol between Protocol (CoAP) [RFC7252] as a communication protocol between
involved application agents. For example, involved application agents. For example,
[I-D.ietf-dots-signal-channel] specifies how CoAP is used as a [I-D.ietf-dots-signal-channel] specifies how CoAP is used as a
distributed denial-of-service (DDoS) attack signaling protocol for signaling protocol between domains under distributed denial-of-
seeking for help from DDoS mitigation providers. In such contexts, a service (DDoS) attacks and DDoS mitigation providers. In such
CoAP client can communicate directly with a server or indirectly via contexts, a CoAP client can communicate directly with a server or
proxies. indirectly via proxies.
When multiple proxies are involved, infinite forwarding loops may be When multiple proxies are involved, infinite forwarding loops may be
experienced (e.g., routing misconfiguration, policy conflicts). To experienced (e.g., routing misconfiguration, policy conflicts). To
prevent such loops, this document defines a new CoAP option, called prevent such loops, this document defines a new CoAP option, called
Hop-Limit (Section 3). Also, the document defines a new CoAP Hop-Limit (Section 3). Also, the document defines a new CoAP
Response Code (Section 5.1) to report loops together with relevant Response Code (Section 6.1) to report loops together with relevant
diagnostic information to ease troubleshooting. diagnostic information to ease troubleshooting (Section 4).
1.1. Intended Usage 1.1. Intended Usage
The Hop-Limit option has originally been designed for a specific use The Hop-Limit option has originally been designed for a specific use
case [I-D.ietf-dots-signal-channel]. However, its intended usage is case [I-D.ietf-dots-signal-channel]. However, its intended usage is
general: CoAP proxies that do not have specific knowledge that proxy general: CoAP proxies that do not have specific knowledge that proxy
forwarding loops are avoided in some other way, are expected to forwarding loops are avoided in some other way, are expected to
implement this option and have it enabled by default. implement this option and have it enabled by default.
Note that this means that a server that receives requests both via Note that this means that a server that receives requests both via
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"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 BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all 14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Readers should be familiar with the terms and concepts defined in Readers should be familiar with the terms and concepts defined in
[RFC7252]. [RFC7252].
3. Hop-Limit Option 3. Hop-Limit Option
The Hop-Limit option (see Section 5.2) is an elective option used to The Hop-Limit option (see Section 6.2) is an elective option used to
detect and prevent infinite loops when proxies are involved. The detect and prevent infinite loops when proxies are involved. The
option is not repeatable. Therefore, any message carrying multiple option is not repeatable. Therefore, any message carrying multiple
Hop-Limit options MUST be handled following the procedure specified Hop-Limit options MUST be handled following the procedure specified
in Section 5.4.5 of [RFC7252]. in Section 5.4.5 of [RFC7252].
The value of the Hop-Limit option is encoded as an unsigned integer The value of the Hop-Limit option is encoded as an unsigned integer
(see Section 3.2 of [RFC7252]). This value MUST be between 1 and 255 (see Section 3.2 of [RFC7252]). This value MUST be between 1 and 255
inclusive. CoAP messages received with a Hop-Limit option set to '0' inclusive. CoAP messages received with a Hop-Limit option set to '0'
or greater than '255' MUST be rejected by a CoAP server/proxy using or greater than '255' MUST be rejected by a CoAP server/proxy using
4.00 (Bad Request). 4.00 (Bad Request).
The Hop-Limit option is safe to forward. That is, a CoAP proxy which The Hop-Limit option is safe to forward. That is, a CoAP proxy which
does not understand the Hop-Limit option should forward it on. The does not understand the Hop-Limit option should forward it on. The
option is also part of the cache key. As such, a CoAP proxy which option is also part of the cache key. As such, a CoAP proxy which
does not understand the Hop-Limit option must follow the does not understand the Hop-Limit option must follow the
recommendations in Section 5.7.1 of [RFC7252] for caching. Note that recommendations in Section 5.7.1 of [RFC7252] for caching. Note that
loops which involve only such proxies won't be detected. loops which involve only such proxies will not be detected.
Nevertheless, the presence of such proxies won't prevent infinite Nevertheless, the presence of such proxies will not prevent infinite
loop detection if at least one CoAP proxy which support the Hop-Limit loop detection if at least one CoAP proxy which support the Hop-Limit
option is involved in the loop. option is involved in the loop.
A CoAP proxy which understands the Hop-Limit option MAY be A CoAP proxy which understands the Hop-Limit option MAY be
instructed, using a configuration parameter, to insert a Hop-Limit instructed, using a configuration parameter, to insert a Hop-Limit
option when relaying a request which do not include the Hop-Limit option when relaying a request which do not include the Hop-Limit
option. option.
The initial Hop-Limit value should be configurable. If no initial The initial Hop-Limit value should be configurable. If no initial
value is explicitly provided, the default initial Hop-Limit value of value is explicitly provided, the default initial Hop-Limit value of
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will be observed if a less value of the Hop-Limit option is used will be observed if a less value of the Hop-Limit option is used
instead. instead.
CoAP messages MUST NOT be forwarded if the Hop-Limit option is set to CoAP messages MUST NOT be forwarded if the Hop-Limit option is set to
'0' after decrement. Messages that cannot be forwarded because of '0' after decrement. Messages that cannot be forwarded because of
exhausted Hop-Limit SHOULD be logged with a TBA1 (Hop Limit Reached) exhausted Hop-Limit SHOULD be logged with a TBA1 (Hop Limit Reached)
error response sent back to the CoAP peer. It is RECOMMENDED that error response sent back to the CoAP peer. It is RECOMMENDED that
CoAP implementations support means to alert administrators about loop CoAP implementations support means to alert administrators about loop
errors so that appropriate actions are undertaken. errors so that appropriate actions are undertaken.
4. Debugging & Troubleshooting
To ease debugging and troubleshooting, the CoAP proxy which detects a To ease debugging and troubleshooting, the CoAP proxy which detects a
loop includes its information in the diagnostic payload under the loop includes its information in the diagnostic payload under the
conditions detailed in Section 5.5.2 of [RFC7252]. That information conditions detailed in Section 5.5.2 of [RFC7252]. That information
MUST NOT include any space character. The information inserted by a MUST NOT include any space character. The information inserted by a
CoAP proxy can be, for example, a proxy name (e.g., p11.example.net), CoAP proxy can be, for example, a proxy name (e.g., p11.example.net),
proxy alias (e.g., myproxyalias), or IP address (e.g., 2001:db8::1). proxy alias (e.g., myproxyalias), or IP address (e.g., 2001:db8::1).
Each intermediate proxy involved in relaying a TBA1 (Hop Limit Each intermediate proxy involved in relaying a TBA1 (Hop Limit
Reached) error message prepends its own information in the diagnostic Reached) error message prepends its own information in the diagnostic
payload with a space character used as separator. Only one payload with a space character used as separator. Only one
information per proxy should appear in the diagnostic payload. Doing information per proxy should appear in the diagnostic payload. Doing
so allows to limit the size of the TBA1 (Hop Limit Reached) error so allows to limit the size of the TBA1 (Hop Limit Reached) error
message, and to ease correlation with hops count. Note that an message, and to ease correlation with hops count. Note that an
intermediate proxy prepends its information only if there is enough intermediate proxy prepends its information only if there is enough
space as determined by the Path MTU (Section 4.6 of [RFC7252]). If space as determined by the Path MTU (Section 4.6 of [RFC7252]). If
not, an intermediate proxy forwards the TBA1 (Hop Limit Reached) not, an intermediate proxy forwards the TBA1 (Hop Limit Reached)
error message to the next hop without updating the diagnostic error message to the next hop without updating the diagnostic
payload. payload.
4. HTTP-Mapping Considerations 5. HTTP-Mapping Considerations
This section focuses on the HTTP mappings specific to the CoAP This section focuses on the HTTP mappings specific to the CoAP
extension specified in this document. As a reminder, the basic extension specified in this document. As a reminder, the basic
normative requirements on HTTP/CoAP mappings are defined in normative requirements on HTTP/CoAP mappings are defined in
Section 10 of [RFC7252]. The implementation guidelines for HTTP/CoAP Section 10 of [RFC7252]. The implementation guidelines for HTTP/CoAP
mappings are elaborated in [RFC8075]. mappings are elaborated in [RFC8075].
By default, the HTTP-to-CoAP Proxy inserts a Hop-Limit option By default, the HTTP-to-CoAP Proxy inserts a Hop-Limit option
following the guidelines in Section 3. The HTTP-to-CoAP Proxy MAY be following the guidelines in Section 3. The HTTP-to-CoAP Proxy MAY be
instructed by policy to insert a Hop-Limit option only if a Via instructed by policy to insert a Hop-Limit option only if a Via
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the diagnostic payload of TBA1 (Hop Limit Reached) as per Section 6.6 the diagnostic payload of TBA1 (Hop Limit Reached) as per Section 6.6
of [RFC8075]. of [RFC8075].
By default, the CoAP-to-HTTP Proxy inserts a Via header field in the By default, the CoAP-to-HTTP Proxy inserts a Via header field in the
HTTP request if the CoAP request includes a Hop-Limit option. The HTTP request if the CoAP request includes a Hop-Limit option. The
CoAP-to-HTTP Proxy MAY be instructed by policy to insert a CDN-Loop CoAP-to-HTTP Proxy MAY be instructed by policy to insert a CDN-Loop
header field instead of the Via header field. header field instead of the Via header field.
The CoAP-to-HTTP Proxy maps the 508 (Loop Detected) HTTP response The CoAP-to-HTTP Proxy maps the 508 (Loop Detected) HTTP response
status code to TBA1 (Hop Limit Reached). Moreover, the CoAP-to-HTTP status code to TBA1 (Hop Limit Reached). Moreover, the CoAP-to-HTTP
Proxy inserts its information following the guidelines in Section 3. Proxy inserts its information following the guidelines in Section 4.
When both HTTP-to-CoAP and CoAP-to-HTTP proxies are involved, the When both HTTP-to-CoAP and CoAP-to-HTTP proxies are involved, the
loop detection may get broken if the proxy-forwarded traffic loop detection may get broken if the proxy-forwarded traffic
repeatedly crosses the HTTP-to-CoAP and CoAP-to-HTTP proxies. repeatedly crosses the HTTP-to-CoAP and CoAP-to-HTTP proxies.
Nevertheless, if the loop is within the CoAP or HTTP legs, the loop Nevertheless, if the loop is within the CoAP or HTTP legs, the loop
detection is still functional. detection is still functional.
5. IANA Considerations 6. IANA Considerations
6.1. CoAP Response Code
5.1. CoAP Response Code
IANA is requested to add the following entry to the "CoAP Response IANA is requested to add the following entry to the "CoAP Response
Codes" sub-registry available at https://www.iana.org/assignments/ Codes" sub-registry available at https://www.iana.org/assignments/
core-parameters/core-parameters.xhtml#response-codes: core-parameters/core-parameters.xhtml#response-codes:
+------+------------------+-----------+ +------+------------------+-----------+
| Code | Description | Reference | | Code | Description | Reference |
+------+------------------+-----------+ +------+------------------+-----------+
| TBA1 | Hop Limit Reached| [RFCXXXX] | | TBA1 | Hop Limit Reached| [RFCXXXX] |
+------+------------------+-----------+ +------+------------------+-----------+
Table 1: CoAP Response Codes Table 1: CoAP Response Codes
This document suggests 5.08 as a code to be assigned for the new This document suggests 5.08 as a code to be assigned for the new
response code. response code.
Editorial Note: Please update TBA1 statements within the document Editorial Note: Please update TBA1 statements within the document
with the assigned code. with the assigned code.
5.2. CoAP Option Number 6.2. CoAP Option Number
IANA is requested to add the following entry to the "CoAP Option IANA is requested to add the following entry to the "CoAP Option
Numbers" sub-registry available at https://www.iana.org/assignments/ Numbers" sub-registry available at https://www.iana.org/assignments/
core-parameters/core-parameters.xhtml#option-numbers: core-parameters/core-parameters.xhtml#option-numbers:
+--------+---+---+---+---+------------------+-----------+ +--------+---+---+---+---+------------------+-----------+
| Number | C | U | N | R | Name | Reference | | Number | C | U | N | R | Name | Reference |
+--------+---+---+---+---+------------------+-----------+ +--------+---+---+---+---+------------------+-----------+
| TBA2 | | | | | Hop-Limit | [RFCXXXX] | | TBA2 | | | | | Hop-Limit | [RFCXXXX] |
+--------+---+---+---+---+------------------+-----------+ +--------+---+---+---+---+------------------+-----------+
C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
Table 2: CoAP Option Number Table 2: CoAP Option Number
6. Security Considerations 7. Security Considerations
Security considerations related to CoAP proxying are discussed in Security considerations related to CoAP proxying are discussed in
Section 11.2 of [RFC7252]. Section 11.2 of [RFC7252].
The diagnostic payload of a TBA1 (Hop Limit Reached) error message The diagnostic payload of a TBA1 (Hop Limit Reached) error message
may leak sensitive information revealing the topology of an may leak sensitive information revealing the topology of an
administrative domain. To prevent that, a CoAP proxy which is administrative domain. To prevent that, a CoAP proxy which is
located at the boundary of an administrative domain MAY be instructed located at the boundary of an administrative domain MAY be instructed
to strip the diagnostic payload or part of it before forwarding on to strip the diagnostic payload or part of it before forwarding on
the TBA1 (Hop Limit Reached) response. the TBA1 (Hop Limit Reached) response.
7. Acknowledgements 8. Acknowledgements
This specification was part of [I-D.ietf-dots-signal-channel]. Many This specification was part of [I-D.ietf-dots-signal-channel]. Many
thanks to those who reviewed DOTS specifications. thanks to those who reviewed DOTS specifications.
Thanks to Klaus Hartke, Carsten Bormann, Peter van der Stok, and Jim Thanks to Klaus Hartke, Carsten Bormann, Peter van der Stok, Jim
Schaad for the reviews. Schaad, and Jaime Jimenez for the reviews.
Carsten Bormann provided the "Intended Usage" text. Carsten Bormann provided the "Intended Usage" text.
8. References 9. References
8.1. Normative References 9.1. 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>.
[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>.
skipping to change at page 7, line 36 skipping to change at page 7, line 44
[RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and [RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
E. Dijk, "Guidelines for Mapping Implementations: HTTP to E. Dijk, "Guidelines for Mapping Implementations: HTTP to
the Constrained Application Protocol (CoAP)", RFC 8075, the Constrained Application Protocol (CoAP)", RFC 8075,
DOI 10.17487/RFC8075, February 2017, DOI 10.17487/RFC8075, February 2017,
<https://www.rfc-editor.org/info/rfc8075>. <https://www.rfc-editor.org/info/rfc8075>.
[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 9.2. Informative References
[I-D.ietf-dots-signal-channel] [I-D.ietf-dots-signal-channel]
K, R., Boucadair, M., Patil, P., Mortensen, A., and N. K, R., Boucadair, M., Patil, P., Mortensen, A., and N.
Teague, "Distributed Denial-of-Service Open Threat Teague, "Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification", draft- Signaling (DOTS) Signal Channel Specification", draft-
ietf-dots-signal-channel-34 (work in progress), May 2019. ietf-dots-signal-channel-37 (work in progress), July 2019.
[RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop [RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop
Detection in Content Delivery Networks (CDNs)", RFC 8586, Detection in Content Delivery Networks (CDNs)", RFC 8586,
DOI 10.17487/RFC8586, April 2019, DOI 10.17487/RFC8586, April 2019,
<https://www.rfc-editor.org/info/rfc8586>. <https://www.rfc-editor.org/info/rfc8586>.
Authors' Addresses Authors' Addresses
Mohamed Boucadair Mohamed Boucadair
Orange Orange
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