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Versions: 00 draft-barthel-oam-schc

lpwan Working Group                                           D. Barthel
Internet-Draft                                                 Orange SA
Intended status: Informational                                L. Toutain
Expires: May 1, 2018              Institut MINES TELECOM; IMT Atlantique
                                                            A. Kandasamy
                                                                  Acklio
                                                        October 28, 2017


       LPWAN Static Context Header Compression (SCHC) for ICMPv6
                      draft-barthel-icmpv6-schc-00

Abstract

   ICMPv6 is a companion protocol to IPv6.  It defines messages that
   inform the source of IPv6 packets of errors during packet delivery.
   It also defines the Echo Request/Reply messages that are used for
   basic network troubleshooting (ping command).  ICMPv6 messages are
   transported on IPv6.

   This document describes how to adapt ICMPv6 to Low Power Wide Area
   Networks (LPWANs) by compressing ICMPv6/IPv6 headers and by
   protecting the LPWAN network and the Device from undesirable ICMPv6
   traffic.

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 http://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 May 1, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Use cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Detailed behavior . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Device is the source of an ICMPv6 error message . . . . .   4
     4.2.  Device is the destination of an ICMPv6 error message  . .   4
       4.2.1.  ICMPv6 error message compression. . . . . . . . . . .   5
     4.3.  Device does a ping  . . . . . . . . . . . . . . . . . . .   6
     4.4.  Device is ping'ed . . . . . . . . . . . . . . . . . . . .   8
   5.  Traceroute  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   ICMPv6 [RFC4443] is a companion protocol to IPv6 [RFC8200].

   [RFC4443] defines a generic message format.  This format is used for
   messages to be sent back to the source of an IPv6 packet to inform it
   about errors during packet delivery.

   More specifically, [RFC4443] defines 4 error messages: Destination
   Unreachable, Packet Too Big, Time Exceeded and Parameter Problem.

   [RFC4443] also defines the Echo Request and Echo Reply messages,
   which provide support for the ping application.

   Other ICMPv6 messages are defined in other RFCs, such as an extended
   format of the same messages [RFC4884] and other messages used by the
   Neighbor Discovery Protocol [RFC4861].





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   This document focuses on using Static Context Header Compression
   (SCHC) to compress [RFC4443] messages that need to be transmitted
   over the LPWAN network, and on having the LPWAN gateway proxying the
   Device to save it the unwanted traffic.

   LPWANs' salient characteristics are described in
   [I-D.ietf-lpwan-overview]

2.  Terminology

   This draft re-uses the Terminology defined in
   [I-D.ietf-lpwan-ipv6-static-context-hc].

   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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Use cases

   In the LPWAN architecture, we can distinguish the following cases:

   o  the Device is the (purported) source of an ICMP error message,
      mainly in response to an incorrect incoming IPv6 message, or in
      response to a ping request.  In this case, as much as possible,
      the core SCHC C/D should act as a proxy and originate the ICMP
      message, so that the Device and the LPWAN network are protected
      from this unwanted traffic.

   o  the Device is the destination of the ICMP message, mainly in
      response to a packet sent by the Device to the network that
      generates an error.  In this case, we want the ICMP message to
      reach the Device, and this document describes in section
      Section 4.2.1 what SCHC compression should be applied.

   o  the Device is the originator of an Echo Request message, and
      therefore the destination of the Echo Reply message.

   o  the Device is the destination of an Echo Request message, and
      therefore the purported source of an Echo Reply message.

   These cases are further described in Section 4.








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4.  Detailed behavior

4.1.  Device is the source of an ICMPv6 error message

   As stated in [RFC4443], a node should generate an ICMPv6 message in
   response to an IPv6 packet that is malformed or which cannot be
   processed due to some incorrect field value.

   The general intent of this document is to spare both the Device and
   the LPWAN network this un-necessary traffic.  The incorrect packets
   should be caught at the core SCHC C/D and the ICMPv6 notification
   should be sent back from there.

        Device       NGW     core SCHC C/D                 Internet Host

          |           |            |    Destination Port=XXX    |
          |           |            |<---------------------------|
          |           |            |                            |
          |           |            |--------------------------->|
          |           |            | ICMPv6 Port Unreachable    |
          |           |            |                            |
          |           |            |                            |



    Figure 1: Example of ICMPv6 error message sent back to the Internet

   Figure 1 shows an example of an IPv6 packet trying to reach a Device.
   Let's assume that the port number used as destination port is not
   "known" (needs better definition) from the core SCHC C/D.  Instead of
   sending the packet over the LPWAN and having this packet rejected by
   the Device, the core SCHC C/D issues an ICMPv6 error message
   "Destination Unreachable" (Type 1) with Code 1 ("Port Unreachable")
   on behalf of the Device.

   TODO: This assumes that all ports that the Device listens to will be
   matched by a SCHC rule.  Is this the basic assumption of SCHC that
   all packets that do not match a rule are rejected?  If yes, why do
   have fragmentation also for uncompressed packets?

   TODO: discuss the various Type/Code that are expected to be generated
   in response to various errors.

4.2.  Device is the destination of an ICMPv6 error message

   In this situation, we assume that a Device has been configured to
   send information to a server on the Internet.  If this server becomes
   no longer accessible, an ICMPv6 message will be generated back



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   towards the Device by an intermediate router.  This information can
   be useful to the Device, for example for reducing the reporting rate
   in case of periodic reporting of data.  Therefore, we compress the
   ICMPv6 message using SCHC and forward it to the Device over the
   LPWAN.

       Device       NGW     core SCHC C/D                Internet Server

         |           |            |                            |
         | SCHC compressed IPv6   |                            |
         |~~~~~~~~~~~|----------->|----------------------X     |
         |           |            | <---------------------     |
         |<~~~~~~~~~~|------------| ICMPv6 Host unreachable    |
         |SCHC compressed ICMPv6  |                            |
         |           |            |                            |
         |           |            |                            |



     Figure 2: Example of ICMPv6 error message sent back to the Device

   Figure 2 illustrates this behavior.  The ICMPv6 error message is
   compressed as described in Section 4.2.1 and forwarded over the LPWAN
   to the Device.

4.2.1.  ICMPv6 error message compression.

   The ICMPv6 error messages defined in [RFC4443] contain the fields
   shown in Figure 3.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Value                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    As much of invoking packet                 |
       +                as possible without the ICMPv6 packet          +
       |                exceeding the minimum IPv6 MTU                 |


                   Figure 3: ICMPv6 Error Message format

   [RFC4443] states that Type can take the values 1 to 4, and Code can
   be set to values between 0 and 6.  Value is unused for the
   Destination Unreachable and Time Exceeded messages.  It contains the
   MTU for the Packet Too Big message and a pointer to the byte causing



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   the error for the Parameter Error message.  Therefore, Value is never
   expected to be greater than 1280 in LPWAN networks.

   The following generic rule can therefore be used to compress all
   ICMPv6 error messages as defined today.  More specific rules can also
   be defined to achieve better compression of some error messages.

   The Type field can be associated to a matching list [1, 2, 3, 4] and
   is therefore compressed down to 2 bits.  Code can be reduced to 3
   bits using the LSB CDA.  Value can be sent on 11 bits using the LSB
   CDA, but if the Device is known to send smaller packets, then the
   size of this field can be further reduced.

   By [RFC4443], the rest of the ICMPv6 message must contain as much as
   possible of the IPv6 offending (invoking) packet that triggered this
   ICMPv6 error message.  This information is used to try and identify
   the SCHC rule that was used to decompress the offending IPv6 packet.
   If the rule can be found then the Rule Id is added at the end of the
   compressed ICMPv6 message.  Otherwise the compressed packet ends with
   the compressed Value field.

   [RFC4443] states that the "ICMPv6 error message MUST include as much
   of the IPv6 offending (invoking) packet ... as possible".  In order
   to comply with this requirement, if there is enough information in
   the incoming ICMPv6 message for the core SCHC C/D to identify the
   rule that has been used to decompress the erroneous IPv6 packet, this
   Rule Id must be sent in the compressed ICMPv6 message to the Device.
   TODO: the erroneous IPv6 packet header (not just the Rule Id) should
   be sent back.  This includes the Rule Id and the compression residue.
   This means the SCHC C/D uses the context backwards (in the reverse
   direction).  How does the Device know it must also use the context
   backwards?

   TODO: how does one know that the "payload" of a compressed-header
   packet is in fact another compressed header?

4.3.  Device does a ping

   If a ping request is generated by a Device, then SCHC compression
   applies.

   The format of an ICMPv6 Echo Request message is described in
   Figure 4, with Type=128 and Code=0.








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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Identifier          |        Sequence Number        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Data ...
       +-+-+-+-+-


               Figure 4: ICMPv6 Echo Request message format

   If we assume that one rule will be devoted to compressing Echo
   Request messages, then Type and Code are known in the rule to be 128
   and 0 and can therefore be elided with the not-sent CDA.

   Checksum can be reconstructed with the compute-checksum CDA and
   therefore is not transmitted.

   [RFC4443] states that Identifier and Sequence Number are meant to
   "aid in matching Echo Replies to this Echo Request" and that they
   "may be zero".  Data is "zero or more bytes of arbitrary data".

   We recommend that Identifier be zero, Sequence Number be a counter on
   3 bits, and Data be zero bytes (absent).  Therefore, Identifier is
   elided with the not-sent CDA, Sequence Number is transmitted on 3
   bits with the LSB CDA and no Data is transmitted.

   The transmission cost of the Echo Request message is therefore the
   size of the Rule Id + 3 bits.

   When the destination receives the Echo Request message, it will
   respond back with a Echo Reply message.  This message bears the same
   format as the Echo Request message but with Type = 129 (see
   Figure 4).

   [RFC4443] states that the Identifier, Sequence Number and Data fields
   of the Echo Reply message shall contain the same values as the
   invoking Echo Request message.  Therefore, a rule shall be used
   similar to that used for compressing the Echo Request message.

   TODO: how about a shared rule for Echo Request and Echo Reply with an
   LSB(1) CDA on the Type field?  Or exploiting the Up/Down direction
   field in the rule?






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4.4.  Device is ping'ed

   If the Device is ping'ed (i.e., is the destination of an Echo Request
   message), the default behavior is to avoid propagating the Echo
   Request message over the LPWAN.

   This is the recommended behavior with the Code 0 (default value) of
   the Echo Request message.  In addition, this document defines two
   other Code values to achieve two other behaviors.

   The resulting three behaviors are shown on Figure 5 and described
   below:

        Device       NGW     core SCHC C/D                 Internet Host

          |           |            |    Echo Request, Code=0    |
          |           |            |<---------------------------|
          |           |            |                            |
          |           |            |--------------------------->|
          |           |            |    Echo Reply,   Code=0    |
          |           |            |                            |
          |           |            |    Echo Request, Code=1    |
          |           |<==========>|<---------------------------|
          |           |            |                            |
          |           |            |--------------------------->|
          |           |            |    Echo Reply,   Code=1    |
          |           |            |    last seen               |
          |           |            |                            |
          |           |            |    Echo Request, Code=2    |
          |<~~~~~~~~~~|------------|<---------------------------|
          |           |            |                            |
          |~~~~~~~~~~~|----------->|--------------------------->|
          |           |            |    Echo Reply,   Code=2    |
          |           |            |    last seen               |
          |           |            |                            |


              Figure 5: Examples of ICMPv6 Echo Request/Reply

   o  Code = 0: The Echo Request message is not propagated on the LPWAN
      to the Device.  If the SCHC C/D finds a rule in the context with
      the IPv6 address of the Device, it responds with an Echo Reply on
      behalf of the Device.  If no rule is found with that IPv6 address,
      the SCHC C/D does not respond.

   TODO: again, we are assuming that no compression rule is equivalent
   to the device not providing the service.




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   o  Code = 1: the SCHC C/D queries the NGW (or maintains a local
      database) and answers with the number of seconds since the Device
      last transmission.

   TODO: what does it mean to answer "with the number of seconds ..."?
   There is no such field in an Echo Reply message.  Do we overwrite one
   of the fields (Identifier, Sequencer Number, Data)?  They are all
   supposed to be copied from the Echo Request.  Do we change their
   definition with Code==1 or Code==2?

   o  Code = 2: the SCHC C/D compresses the ICMPv6 message and forwards
      it to the Device.  The Echo Reply message sent by the Device is
      also compressed.  Since the Echo Request message comes from the
      Internet, the values of the Identifier, Sequence Number and Data
      fields cannot be known in advance, and therefore must be
      transmitted.  However, it is likely that the Echo Request with
      Code 2 will be firewalled from the Internet and restricted to
      authorized users.  Therefore, the Echo Request message can be
      assumed to have the same content as recommended in Section 4.3,
      and the same compression rules apply.

5.  Traceroute

   The traceroute6 program sends successive probe packets destined to a
   chosen target but with the Hop Limit value successively incremented
   from the initial value 1.

   It expects to receive a "Time Exceeded" (Type = 3) "Hop Limit" (Code
   = 0) ICMPv6 error message back from the successive routers along the
   path to the destination.

   The probe packet is usually a UDP datagram, but can also be a TCP
   datagram or even an ICMPv6 message.  The destination port is chosen
   in the unassigned range in hope that the destination, when eventually
   reached, will respond with a "Destination Unreachable" (Type = 1)
   "Port Unreachable" (Code = 4) ICMPv6 error message.

   It is not anticipated that a Device will want to traceroute a
   destination on the Internet.

   By contrast, a host on the Internet may attempt to traceroute an IPv6
   address that is assigned to an LPWAN device.  This is described in
   Figure 6.








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        Device       NGW     core SCHC C/D                 Internet

          |           |            | Hop Limit=1, Dest Port=XXX |
          |           |            |<---------------------------|
          |           |            |                            |
          |           |            |--------------------------->|
          |           |            |   ICMPv6 Hop Limit error   |
          |           |            |                            |
          |           |            |                            |
          |           |            | Hop Limit=2, Dest Port=XXX |
          |           |            |<---------------------------|
          |           |            |                            |
          |           |            |--------------------------->|
          |           |            |  ICMPv6 Port Unreachable   |



            Figure 6: Example of traceroute to the LPWAN Device

   When the probe packet first reaches the core SCHC C/D, its remaining
   Hop Limit is 1.  The core SCHC C/D will respond back with a "Time
   Exceeded" (Type = 3) "Hop Limit" (Code = 0) ICMPv6 error message.
   Later on, when the probe packet reaches the code SCHC C/D with a Hop
   Limit value of 2, the core SCHC C/D will, as explained in
   Section 4.1, answer back with a "Destination Unreachable" (Type = 1)
   "Port Unreachable" (Code = 4) ICMPv6 error message.  This is what the
   traceroute6 command expects.  Therefore, the traceroute6 command will
   work with LPWAN IPv6 destinations, except for the time displayed for
   the destination, which is actually the time to its proxy.

   However, if the probe packet happens to hit a port that matches a
   SCHC rule for that Device, the packet will be compressed with this
   rule and sent over the LPWAN, which is unfortunate.  Forwarding of
   packets to the Device over the LPWAN should only be done from
   authenticated/trusted sources anyway.  Rate-limitation on top of
   authentication will mitigate this nuisance.

6.  Security considerations

   TODO

7.  IANA Considerations

   TODO







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8.  References

8.1.  Normative References

   [I-D.ietf-lpwan-ipv6-static-context-hc]
              Minaburo, A., Toutain, L., and C. Gomez, "LPWAN Static
              Context Header Compression (SCHC) and fragmentation for
              IPv6 and UDP", draft-ietf-lpwan-ipv6-static-context-hc-07
              (work in progress), October 2017.

   [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>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007, <https://www.rfc-
              editor.org/info/rfc4861>.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              DOI 10.17487/RFC4884, April 2007, <https://www.rfc-
              editor.org/info/rfc4884>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017, <https://www.rfc-
              editor.org/info/rfc8200>.

8.2.  Informative References

   [I-D.ietf-lpwan-overview]
              Farrell, S., "LPWAN Overview", draft-ietf-lpwan-
              overview-07 (work in progress), October 2017.






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Authors' Addresses

   Dominique Barthel
   Orange SA
   28 chemin du Vieux Chene
   BP 98
   38243 Meylan Cedex
   France

   Email: dominique.barthel@orange.com


   Laurent Toutain
   Institut MINES TELECOM; IMT Atlantique
   2 rue de la Chataigneraie
   CS 17607
   35576 Cesson-Sevigne Cedex
   France

   Email: laurent.toutain@imt-atlantique.fr


   Arunprabhu Kandasamy
   Acklio
   2bis rue de la Chataigneraie
   35510 Cesson-Sevigne Cedex
   France

   Email: arun@ackl.io






















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