< draft-ietf-core-hop-limit-03.txt   draft-ietf-core-hop-limit-04.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: August 30, 2019 McAfee Expires: January 4, 2020 McAfee
J. Shallow J. Shallow
NCC Group July 3, 2019
February 26, 2019
Constrained Application Protocol (CoAP) Hop Limit Option Constrained Application Protocol (CoAP) Hop-Limit Option
draft-ietf-core-hop-limit-03 draft-ietf-core-hop-limit-04
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
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This Internet-Draft will expire on August 30, 2019. This Internet-Draft will expire on January 4, 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
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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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Intended Usage . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Hop-Limit Option . . . . . . . . . . . . . . . . . . . . . . 3 3. Hop-Limit Option . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. HTTP-Mapping Considerations . . . . . . . . . . . . . . . . . 5
4.1. CoAP Response Code . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.2. CoAP Option Number . . . . . . . . . . . . . . . . . . . 5 5.1. CoAP Response Code . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5.2. CoAP Option Number . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
More and more applications are using Constrained Application Protocol More and more applications are using the Constrained Application
(CoAP) [RFC7252] as a communication protocol between involved Protocol (CoAP) [RFC7252] as a communication protocol between
application agents. For example, [I-D.ietf-dots-signal-channel] involved application agents. For example,
specifies how CoAP is used as a distributed denial-of-service (DDoS) [I-D.ietf-dots-signal-channel] specifies how CoAP is used as a
attack signaling protocol seeking for help from DDoS mitigation distributed denial-of-service (DDoS) attack signaling protocol for
providers. In such contexts, a CoAP client can communicate directly seeking for help from DDoS mitigation providers. In such contexts, a
with a server or indirectly via proxies. CoAP client can communicate directly with a server or indirectly via
proxies.
When multiple proxies are involved, infinite forwarding loops may be When multiple proxies are involved, infinite forwarding loops may be
experienced. To prevent such loops, this document defines a new CoAP experienced (e.g., routing misconfiguration, policy conflicts). To
option, called Hop-Limit (Section 3), which is inserted in particular prevent such loops, this document defines a new CoAP option, called
by on-path proxies. Also, the document defines a new CoAP Response Hop-Limit (Section 3). Also, the document defines a new CoAP
Code (Section 4.1) to report loops together with relevant diagnostic Response Code (Section 5.1) to report loops together with relevant
information to ease troubleshooting. diagnostic information to ease troubleshooting.
1.1. Intended Usage
The Hop-Limit option has originally been designed for a specific use
case [I-D.ietf-dots-signal-channel]. However, its intended usage is
general: CoAP proxies that do not have specific knowledge that proxy
forwarding loops are avoided in some other way, are expected to
implement this option and have it enabled by default.
Note that this means that a server that receives requests both via
proxies and directly from clients may see otherwise identical
requests with and without the Hop-Limit option included; servers with
internal caching will therefore also want to implement this option.
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 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 4.2) is an elective option used to The Hop-Limit option (see Section 5.2) 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 rejected using 4.00 (Bad Request) error Hop-Limit options MUST be handled following the procedure specified
message. in Section 5.4.5 of [RFC7252].
The value of the Hop-Limit option is encoded as an 8-bit unsigned The value of the Hop-Limit option is encoded as an unsigned integer
integer (see Section 3.2 of [RFC7252]). This value MUST be between 1 (see Section 3.2 of [RFC7252]). This value MUST be between 1 and 255
and 255 inclusive. CoAP messages received with a Hop-Limit option inclusive. CoAP messages received with a Hop-Limit option set to '0'
set to '0' or greater than '255' MUST be rejected by a CoAP server/ or greater than '255' MUST be rejected by a CoAP server/proxy using
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 won't be detected.
Nevertheless, the presence of such proxies won't prevent infinite Nevertheless, the presence of such proxies won't 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
16 MUST be used. This value is chosen to be sufficiently large to 16 MUST be used. This value is chosen to be sufficiently large to
guarantee that a CoAP request would not be dropped in networks when guarantee that a CoAP request would not be dropped in networks when
there were no loops, but not so large as to consume CoAP proxy there were no loops, but not so large as to consume CoAP proxy
resources when a loop does occur. Lower values should be used with resources when a loop does occur. Lower values should be used with
caution and only in networks where topologies are known by the CoAP caution and only in networks where topologies are known by the CoAP
client (or proxy) inserting the Hop-Limit option. client (or proxy) inserting the Hop-Limit option.
Because forwarding errors may occur if inadequate Hop-Limit values Because forwarding errors may occur if inadequate Hop-Limit values
are used, proxies at the boundaries of an administrative domain MAY are used, proxies at the boundaries of an administrative domain MAY
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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.
To ease debugging and troubleshooting, the CoAP proxy which detects a To ease debugging and troubleshooting, the CoAP proxy which detects a
loop SHOULD include its information (e.g., proxy name, proxy alias, loop includes its information in the diagnostic payload under the
IP address) in the diagnostic payload under the conditions detailed conditions detailed in Section 5.5.2 of [RFC7252]. That information
in Section 5.5.2 of [RFC7252]. That information MUST NOT include any MUST NOT include any space character. The information inserted by a
space character. 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).
Each intermediate proxy involved in relaying a TBA1 (Hop Limit Each intermediate proxy involved in relaying a TBA1 (Hop Limit
Reached) error message SHOULD prepend its own information in the Reached) error message prepends its own information in the diagnostic
diagnostic payload with a space character used as separator. Only payload with a space character used as separator. Only one
one information per proxy SHOULD appear in the diagnostic payload. information per proxy should appear in the diagnostic payload. Doing
Doing so allows to limit the size of the TBA1 (Hop Limit Reached) so allows to limit the size of the TBA1 (Hop Limit Reached) error
error message, and to ease correlation with hops count. message, and to ease correlation with hops count. Note that an
intermediate proxy prepends its information only if there is enough
space as determined by the Path MTU (Section 4.6 of [RFC7252]). If
not, an intermediate proxy forwards the TBA1 (Hop Limit Reached)
error message to the next hop without updating the diagnostic
payload.
4. IANA Considerations 4. HTTP-Mapping Considerations
4.1. CoAP Response Code This section focuses on the HTTP mappings specific to the CoAP
extension specified in this document. As a reminder, the basic
normative requirements on HTTP/CoAP mappings are defined in
Section 10 of [RFC7252]. The implementation guidelines for HTTP/CoAP
mappings are elaborated in [RFC8075].
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
instructed by policy to insert a Hop-Limit option only if a Via
(Section 5.7.1 of [RFC7230]) or CDN-Loop header field [RFC8586] is
present in the HTTP request.
The HTTP-to-CoAP Proxy uses 508 (Loop Detected) as the HTTP response
status code to map TBA1 (Hop Limit Reached). Furthermore, it maps
the diagnostic payload of TBA1 (Hop Limit Reached) as per Section 6.6
of [RFC8075].
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
CoAP-to-HTTP Proxy MAY be instructed by policy to insert a CDN-Loop
header field instead of the Via header field.
The CoAP-to-HTTP Proxy maps the 508 (Loop Detected) HTTP response
status code to TBA1 (Hop Limit Reached). Moreover, the CoAP-to-HTTP
Proxy inserts its information following the guidelines in Section 3.
When both HTTP-to-CoAP and CoAP-to-HTTP proxies are involved, the
loop detection may get broken if the proxy-forwarded traffic
repeatedly crosses the HTTP-to-CoAP and CoAP-to-HTTP proxies.
Nevertheless, if the loop is within the CoAP or HTTP legs, the loop
detection is still functional.
5. IANA Considerations
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 5.06 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.
4.2. CoAP Option Number 5.2. 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
5. Security Considerations 6. 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 response. the TBA1 (Hop Limit Reached) response.
6. Acknowledgements 7. 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, and Jim
Schaad for the reviews. Schaad for the reviews.
7. References Carsten Bormann provided the "Intended Usage" text.
7.1. Normative References 8. References
8.1. 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
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[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>.
[RFC8075] Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
E. Dijk, "Guidelines for Mapping Implementations: HTTP to
the Constrained Application Protocol (CoAP)", RFC 8075,
DOI 10.17487/RFC8075, February 2017,
<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>.
7.2. Informative References 8.2. 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-28 (work in progress), January ietf-dots-signal-channel-34 (work in progress), May 2019.
2019.
[RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop
Detection in Content Delivery Networks (CDNs)", RFC 8586,
DOI 10.17487/RFC8586, April 2019,
<https://www.rfc-editor.org/info/rfc8586>.
Authors' Addresses Authors' Addresses
Mohamed Boucadair Mohamed Boucadair
Orange Orange
Rennes 35000 Rennes 35000
France France
Email: mohamed.boucadair@orange.com Email: mohamed.boucadair@orange.com
Tirumaleswar Reddy Tirumaleswar Reddy
McAfee, Inc. McAfee, Inc.
Embassy Golf Link Business Park Embassy Golf Link Business Park
Bangalore, Karnataka 560071 Bangalore, Karnataka 560071
India India
Email: kondtir@gmail.com Email: kondtir@gmail.com
Jon Shallow Jon Shallow
NCC Group
United Kingdom United Kingdom
Email: jon.shallow@nccgroup.com Email: supjps-ietf@jpshallow.com
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