6lo Working Group                                             D. Dujovne
Internet-Draft                                Universidad Diego Portales
Intended status: Standards Track                           M. Richardson
Expires: March 12, 2020                         Sandelman Software Works
                                                      September 09, 2019

  IEEE802.15.4 Informational Element encapsulation of 6tisch Join and
                         Enrollment Information


   In TSCH mode of IEEE802.15.4, as described by [RFC8180],
   opportunities for broadcasts are limited to specific times and
   specific channels.  Nodes in a TSCH network typically frequently send
   Enhanced Beacon (EB) frames to announce the presence of the network.
   This document provides a mechanism by which small details critical
   for new nodes (pledges) and long sleeping nodes may be carried within
   the Enhanced Beacon.

Status of This Memo

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   This Internet-Draft will expire on March 12, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Use of BCP 14 Terminology . . . . . . . . . . . . . . . .   2
     1.2.  Layer-2 Synchronization . . . . . . . . . . . . . . . . .   2
     1.3.  Layer-3 synchronization IPv6 Router solicitations and
           advertisements  . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Definition . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Change history . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   [RFC7554] describes the use of the time-slotted channel hopping
   (TSCH) mode of [ieee802154].  As further details in [RFC8180], an
   Enhanced Beacon is transmitted during a slot designated a broadcast

1.1.  Use of BCP 14 Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   [BCP14] [RFC2119] when, and only when, they appear in all capitals,
   as shown here.

   Other terminology can be found in [I-D.ietf-6tisch-architecture] in
   section 2.1.

1.2.  Layer-2 Synchronization

   As explained in section 6 of [RFC8180], the Enhanced Beacon has a
   number of purposes: synchronization of ASN and Join Metric, timeslot
   template identifier, the channel hopping sequence identifier, TSCH
   SlotFrame and Link IE.

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   The Enhanced Beacon (EB) is used by nodes already part of a TSCH
   network to annouce its existance.  Receiving an EB allows a Joining
   Node (pledge) to learn about the network and synchronize to it.  The
   EB may also be used as a means for a node already part of the network
   to re-synchronize [RFC7554].

   There are a limited number of timeslots designated as a broadcast
   slot by each router.  These slots are rare, and with 10ms slots, with
   a slot-frame length of 100, there may be only 1 slot/s for the

1.3.  Layer-3 synchronization IPv6 Router solicitations and

   At layer 3, [RFC4861] defines a mechanism by which nodes learn about
   routers by listening for multicasted Router Advertisements (RA).  If
   no RA is heard within a set time, then a Router Solicitation (RS) may
   be multicast, to which an RA will be received, usually unicast.

   Although [RFC6775] reduces the amount of multicast necessary to do
   address resolution via Neighbor Solicitation messages, it still
   requires multicast of either RAs or RS.  This is an expensive
   operation for two reasons: there are few multicast timeslots for
   unsolicited RAs; if a pledge node does not hear an RA, and decides to
   send a RS (consuming a broadcast aloha slot with unencrypted
   traffic), unicast RS may be sent in response.

   This is a particularly acute issue for the join process for the
   following reasons:

   1.  use of a multicast slot by even a non-malicious unauthenticated
       node for a Router Solicitation may overwhelm that time slot.

   2.  it may require many seconds of on-time before a new pledge hears
       a Router Soliciation that it can use.

   3.  a new pledge may listen to many Enhanced Beacons before it can
       pick an appropriate network and/or closest Join Assistant to
       attach to.  If it must listen for a RS as well as find the
       Enhanced Beacon, then the process may take a very long time.

2.  Protocol Definition

   [RFC8137] creates a registry for new IETF IE subtypes.  This document
   allocates a new subtype.

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   The new IE subtype structure is as follows.  As explained in
   [RFC8137] the length of the Sub-Type Content can be calculated from
   the container, so no length information is necessary.

                        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
   |   TBD-XXX     |R|P| res |  proxy prio |    rank priority      |
   | pan priority  |                                               |
   +---------------+                                               +
   |                           Join Proxy lower-64                 |
   +                        (present if P=1)                       +
   |                                                               |
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |                                               |
   +-+-+-+-+-+-+-+-+                                               +
   |                           network ID                          |
   +                   variable length, up to 16 bytes             +
   ~                                                               ~
   +                                                               +
   |                                                               |
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |

   proxy priority  this field indicates the willingness to act as join
      proxy.  Lower value indicates willing to act as a Join Proxy as
      described in [I-D.ietf-6tisch-minimal-security].  Values range 0
      (most willing) to 0x7e (least willing).  A priority of 0x7f
      indicates that the announcer should never be considered as a
      viable enrollment proxy.  Only unenrolled pledges look at this

   pan priority  the pan priority is a value set by the DODAG root to
      indicate the relative priority of this LLN compared to those with
      different PANIDs.  This value may be used as part of the
      enrollment priority, but typically is used by devices which have
      already enrolled, and need to determine which PAN to pick.
      Unenrolled pledges MAY consider this value when selecting a PAN to
      join.  Enrolled devices MAY consider this value when looking for
      an eligible parent device.

   rank priority  the rank "priority" is set by the 6LR which sent the
      beacon and is an indication of how willing this 6LR is to serve as
      an RPL parent within a particular network ID.  This is a local
      value to be determined in other work.  It might be calculated from
      RPL rank, and it may include some modifications based upon current

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      number of children, or number of neighbor cache entries available.
      This value MUST be ignored by pledges, it is for enrolled devices

   R  the Router Advertisement R-flag is set if the sending node will
      act as a Router for host-only nodes that need addressing via
      unicast Router Solicitation messages.

   P  if the Proxy Address P-flag is set, then the lower 64-bits of the
      Join Proxy's Link Layer address follows the network ID.  If the
      Proxy Address bit is not set, then the Link Layer address of the
      Join Proxy is identical to the Layer-2 8-byte address used to
      originate this enhanced beacon.  In either case, the layer-2
      address of any IPv6 traffic to the originator of this beacon may
      use the layer-2 address which was used to originate the beacon.

   join-proxy interface ID  if the P bit is set, then 64 bits (8 bytes)
      of address are present.  This field provides the suffix of the
      Link-Local address of the Join Proxy.  The associated prefix is
      well-known as fe80::/64.

   network ID  this is an variable length field, up to 16-bytes in size
      that uniquely identifies this network, potentially among many
      networks that are operating in the same frequencies in overlapping
      physical space.  The length of this field can be calculated as
      being whatever is left in the Information Element.

   In a 6tisch network, where RPL [RFC6550] is used as the mesh routing
   protocol, the network ID can be constructed from a SHA256 hash of the
   prefix (/64) of the network.  That is just a suggestion for a default
   value.  In some LLNs where multiple PANIDs may lead to the same
   management device (the JRC), then a common value that is the same
   across all PANs MUST be configured.

3.  Security Considerations

   All of the contents of this Information Element are sent in the
   clear.  The containing Enhanced Beacon is not encrypted.

   The Enhanced Beagon is authenticated at the layer-2 level using
   802.15.4 mechanisms using the network-wide keying material.  Nodes
   which are enrolled will have the network-wide keying material and can
   validate the beacon.

   Pledges which have not yet enrolled are unable to authenticate the

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4.  Privacy Considerations

   The use of a network ID may reveal information about the network.
   The use of a SHA256 hash of the DODAGID, rather than using the
   DODAGID directly provides some cover the addresses used within the
   network.  The DODAGID is usually the IPv6 address of the root of the
   RPL mesh.

   An interloper with a radio sniffer would be able to use the network
   ID to map out the extend of the mesh network.

5.  IANA Considerations

   Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID.
   This entry should be called 6tisch-Join-Info, and should refer to
   this document.

6.  Acknowledgements

   Thomas Watteyne provided extensive editorial comments on the

7.  References

7.1.  Normative References

   [BCP14]    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>.

              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work
              in progress), August 2019.

              Vucinic, M., Simon, J., Pister, K., and M. Richardson,
              "Minimal Security Framework for 6TiSCH", draft-ietf-
              6tisch-minimal-security-12 (work in progress), July 2019.

              IEEE Standard, ., "802.15.4-2015 - IEEE Standard for Low-
              Rate Wireless Personal Area Networks (WPANs)", 2015,

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,

   [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
              IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
              Internet of Things (IoT): Problem Statement", RFC 7554,
              DOI 10.17487/RFC7554, May 2015,

   [RFC8137]  Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information
              Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May
              2017, <https://www.rfc-editor.org/info/rfc8137>.

7.2.  Informative References

              Richardson, M., "6tisch Secure Join protocol", draft-ietf-
              6tisch-dtsecurity-secure-join-01 (work in progress),
              February 2017.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,

   [RFC8180]  Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
              IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
              Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180,
              May 2017, <https://www.rfc-editor.org/info/rfc8180>.

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Appendix A.  Change history

   The rank priority was expanded to 2 bytes.

   00: The extension was originally for the use of Pledges only during
   the enrollment/join process.  Additional information was desired for
   nodes which have already enrolled in order to aid in the joining
   (selecting of a parent) of an RPL DAG.  The term "join" was realized
   to be ambiguous, meaning different things to different groups, and so
   the activity where the pledge finds a "Join Proxy" has been named

   -1: This is an evolution of an earlier proposal which provided for
   storing an entire IPv6 Router Adverisement in an Informational
   Element.  It was deemed too general a solution, possibly subject to
   mis-use.  This proposal restricts the use to just the key pieces of
   information required.

Authors' Addresses

   Diego Dujovne (editor)
   Universidad Diego Portales
   Escuela de Informatica y Telecomunicaciones, Av. Ejercito 441
   Santiago, Region Metropolitana

   Phone: +56 (2) 676-8121
   Email: diego.dujovne@mail.udp.cl

   Michael Richardson
   Sandelman Software Works

   Email: mcr+ietf@sandelman.ca

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