802.15.4 Informational Element encapsulation of 6tisch Join Information
draft-richardson-6tisch-join-enhanced-beacon-00

6lo Working Group                                          M. Richardson
Internet-Draft                                  Sandelman Software Works
Intended status: Informational                         February 08, 2017
Expires: August 12, 2017

802.15.4 Informational Element encapsulation of 6tisch Join Information
            draft-richardson-6tisch-join-enhanced-beacon-00

Abstract

   In TSCH mode of 802.15.4, as described by [I-D.ietf-6tisch-minimal],
   opportunities for broadcasts are limited to specific times and
   specific channels.  An enhanced beacon must be broadcast periodically
   by every router to keep all nodes in sync.  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 August 12, 2017.

Copyright Notice

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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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Layer-2 Synchronization . . . . . . . . . . . . . . . . .   2
     1.3.  Layer-3 synchronization IPv6 Router solicitations and
           advertisements  . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Definition . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Protocol Example  . . . . . . . . . . . . . . . . . . . .   4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Change history . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [I-D.ietf-6tisch-architecture] describes the use of the time-slotted
   channel hopping (TSCH) mode of [ieee802154].  As further details in
   [I-D.ietf-6tisch-minimal], an Enhanced Beacon is transmitted during a
   slot designated a broadcast slot.

   EDNOTE: Explain why broadcasts are rare, and why we need them.  What
   the Enhanced Beacon is, and what Information Elements are, and how
   the IETF has a subtype for that area.  Explain what kind of things
   could be placed in Information Elements, how big they could be, and
   how they could be compressed.

1.1.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119] and indicate requirement levels for compliant STuPiD
   implementations.

1.2.  Layer-2 Synchronization

   As explained in section 6 of [I-D.ietf-6tisch-minimal], 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 is used by operating nodes to correct drift in
   their clock, by nodes on medium length sleeps to resynchronize their
   ASN, by nodes that have slept through a network rekey to rediscover
   the network, and by new Joining Nodes (pledges) to learn about the
   existance of the network.

   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
   beacon.

1.3.  Layer-3 synchronization IPv6 Router solicitations and
      advertisements

   At layer 3, [RFC2461] 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), many 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

   [I-D.kivinen-802-15-ie] creates a registry for new IETF IE subtypes.
   This document allocates a new subtype TBD-XXX.

   This document documents a new IE subtype structure is as follows.  As
   explained in [I-D.kivinen-802-15-ie] the length of the Sub-Type

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   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     |J|I|R| R E S V |         network ID            |
   +-+-+-+-+-+-+-+-+-+-+-+---------+                               |
   |                           network ID                          |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      network ID               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   J  the Join Proxy flag is set if the sending node will operate as a
      Join Proxy according to [I-D.ietf-6tisch-minimal-security].

   I  the Initiate Join flag is set if this network supports pledges
      initiating the join process themselves according to
      [I-D.ietf-6tisch-minimal-security].  If not set, then the pledge
      should do an NS DAD operation ([RFC6775] section 4.3, explained in
      [I-D.ietf-6tisch-dtsecurity-secure-join]) and then remain silent,
      to wait to be contacted.

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

   network ID  this is an opaque 16-byte identifier that uniquely
      identifies this network, potentially among many networks that are
      operating in the same frequencies in overlapping physical space.

   In a 6tisch network, where RPL is used as the mesh routing protocol,
   the network ID SHOULD be constructed from a SHA256 hash of the
   DODAGID of the network.  The result will be a 32-byte hash, and the
   lower 16-bytes should be used.

2.1.  Protocol Example

   Here are three examples of processing.

3.  Security Considerations

   All of the contents of this Information Element are sent in the
   clear.  The containing Enhanced Beacon is not encrypted, but may be
   authenticated to nodes which have already received network-wide
   keying material.

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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.

5.  IANA Considerations

   Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID.
   This entry should be called 6LoRH-in-IE.

   Allocate a new number TBD-YYY from Neighbor Discovery Option Types
   (RFC2461) with the name "Constrained Network Identification".

6.  References

6.1.  Normative References

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work
              in progress), January 2017.

   [I-D.ietf-6tisch-minimal]
              Vilajosana, X., Pister, K., and T. Watteyne, "Minimal
              6TiSCH Configuration", draft-ietf-6tisch-minimal-19 (work
              in progress), January 2017.

   [I-D.kivinen-802-15-ie]
              Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information
              Element for IETF", draft-kivinen-802-15-ie-04 (work in
              progress), October 2016.

   [ieee802154]
              IEEE Standard, ., "802.15.4-2015 - IEEE Standard for Low-
              Rate Wireless Personal Area Networks (WPANs)", 2015,
              <http://standards.ieee.org/findstds/
              standard/802.15.4-2015.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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   [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461,
              DOI 10.17487/RFC2461, December 1998,
              <http://www.rfc-editor.org/info/rfc2461>.

   [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,
              <http://www.rfc-editor.org/info/rfc6775>.

6.2.  Informative References

   [I-D.ietf-6tisch-dtsecurity-secure-join]
              Richardson, M., "6tisch Secure Join protocol", draft-ietf-
              6tisch-dtsecurity-secure-join-00 (work in progress),
              December 2016.

   [I-D.ietf-6tisch-minimal-security]
              Vucinic, M., Simon, J., and K. Pister, "Minimal Security
              Framework for 6TiSCH", draft-ietf-6tisch-minimal-
              security-01 (work in progress), February 2017.

Appendix A.  Change history

   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.

Author's Address

   Michael Richardson
   Sandelman Software Works

   Email: mcr+ietf@sandelman.ca

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