CORE M. Boucadair
Internet-Draft Orange
Intended status: Standards Track T. Reddy
Expires: February 17, 2019 McAfee
J. Shallow
NCC Group
August 16, 2018
Constrained Application Protocol (CoAP) Hop Limit Option
draft-boucadair-core-hop-limit-00
Abstract
The presence of Constrained Application Protocol (CoAP) proxies may
lead to infinite forwarding loops, which is undesirable. To prevent
and detect such loops, this document specifies the Hop-Limit CoAP
option.
Status of This Memo
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This Internet-Draft will expire on February 17, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Hop-Limit Option . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4.1. CoAP Response Code . . . . . . . . . . . . . . . . . . . 3
4.2. CoAP Option Number . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
More and more applications are using Constrained Application Protocol
(CoAP) [RFC7252] as a communication protocol between involved
application agents. For example, [I-D.ietf-dots-signal-channel]
specifies how CoAP is used as a distributed denial-of-service (DDoS)
attack signaling protocol seeking for help from DDoS mitigation
providers. In such contexts, a CoAP client can communicate directly
with a server or indirectly via a proxy.
When multiple proxies are involved, infinite forwarding loops may be
experienced. To prevent such loops, this document defines a new CoAP
option, called Hop-Limit, which is inserted by on-path proxies.
Also, the document defines a new CoAP Response Code to report loops
together with relevant diagnostic information to ease
troubleshooting.
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
[RFC2119].
Readers should be familiar with the terms and concepts defined in
[RFC7252].
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3. Hop-Limit Option
Hop-Limit option (see Section 4.2) is used to detect and prevent
infinite loops when proxies are involved. Only one single instance
of the option is allowed in a message.
The length of the Hop-Limit option is 1 byte. The value of the Hop-
Limit option is encoded as an unsigned integer (see Section 3.2 of
[RFC7252]).
Each intermediate proxy involved in the handling of a CoAP message
MUST decrement the Hop-Limit option value by 1 prior to forwarding
upstream if this parameter exists.
CoAP messages MUST NOT be forwarded if the Hop-Limit option is set to
'0' after decrement. Messages that cannot be forwarded because of
exhausted Hop-Limit SHOULD be logged with a 5.06 (Hop Limit Reached)
error message sent back to the CoAP peer. It is RECOMMENDED that
CoAP agents support means to alert administrators about loop errors
so that appropriate actions are undertaken.
To ease debugging and troubleshooting, the CoAP proxy which detects a
loop SHOULD include its information (e.g., server name, server alias,
IP address) in the diagnostic payload under the conditions detailed
in Section 5.5.2 of [RFC7252].
Each intermediate proxy involved in relaying a 5.06 (Hop Limit
Reached) error message SHOULD prepend its own information in the
diagnostic payload with a space character used as separator. Only
one information per proxy MUST appear in the diagnostic payload.
The initial Hop-Limit value SHOULD be configurable. If no initial
value is explicitly provided, the default initial Hop-Limit value of
16 MUST be used. Because forwarding errors may occur if inadequate
Hop-Limit values are used, proxies at the boundaries of an
administrative domain MAY be instructed to rewrite the value of Hop-
Limit carried in received messages (that is, ignore the value of Hop-
Limit received in a message).
4. IANA Considerations
4.1. CoAP Response Code
IANA is requested to add the following entries to the "CoAP Response
Codes" sub-registry available at https://www.iana.org/assignments/
core-parameters/core-parameters.xhtml#response-codes:
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+------+------------------+-----------+
| Code | Description | Reference |
+------+------------------+-----------+
| 5.06 | Hop Limit Reached| [RFCXXXX] |
+------+------------------+-----------+
Table 1: CoAP Response Codes
4.2. CoAP Option Number
IANA is requested to add the following entry to the "CoAP Option
Numbers" sub-registry available at https://www.iana.org/assignments/
core-parameters/core-parameters.xhtml#option-numbers:
+--------+---+---+---+---+------------------+-----------+
| Number | C | U | N | R | Name | Reference |
+--------+---+---+---+---+------------------+-----------+
| 2 | | x | - | | Hop-Limit | [RFCXXXX] |
+--------+---+---+---+---+------------------+-----------+
C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
Table 2: CoAP Option Number
5. Security Considerations
Security considerations related to CoAP proxying are discussed in
Section 11.2 of [RFC7252].
6. References
6.1. 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>.
6.2. Informative References
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[I-D.ietf-dots-signal-channel]
Reddy, T., Boucadair, M., Patil, P., Mortensen, A., and N.
Teague, "Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification", draft-
ietf-dots-signal-channel-22 (work in progress), August
2018.
Authors' Addresses
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
Jon Shallow
NCC Group
United Kingdom
Email: jon.shallow@nccgroup.trust
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