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Versions: 00 draft-ietf-core-hop-limit

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

   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 February 17, 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
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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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