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6tisch Working Group                     D. Dujovne
Internet-Draft                Universidad Diego Portales
Intended status: Standards Track              M. Richardson
Expires: 21 July 2020 Â Â Â Â Â Â Â Â Â Â Â Â Â Sandelman Software Works
                             18 January 2020
  IEEE 802.15.4 Information Element encapsulation of 6TiSCH Join and
             Enrollment Information
      draft-ietf-6tisch-enrollment-enhanced-beacon-08
Abstract
  In TSCH mode of IEEE STD 802.15.4, opportunities for broadcasts are
  limited to specific times and specific channels. Nodes in a TSCH
  network typically frequently send transmit Enhanced Beacon (EB) frames to
  announce the presence of the network. This document provides a
  mechanism by which small details information critical for new nodes (pledges) and
  long sleeping nodes may be carried within the Enhanced Beacon.
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 21 July 2020.
Copyright Notice
  Copyright (c) 2020 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 to this document. Code Components
  extracted from this document must include Simplified BSD License text
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  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
   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 . . . . . . . . . . . . . . . . . . . . .  4
  3. Security Considerations . . . . . . . . . . . . . . . . . . .  6
  4. Privacy Considerations . . . . . . . . . . . . . . . . . . .  6
  5. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  6
  6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  7
  7. References . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.1. Normative References . . . . . . . . . . . . . . . . . .  7
   7.2. Informative References . . . . . . . . . . . . . . . . .  8
  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .  8
1. Introduction
  [RFC7554] describes the use of the time-slotted channel hopping
  (TSCH) mode of [ieee802154]. As further detailed in [RFC8180], an
  Enhanced Beacon (EB) is transmitted during a slot designated a
  broadcast slot.
1.1. Use of BCP 14 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
  BCP 14 [RFC2119] [RFC8174] 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 (EB) has
  a number of purposes: synchronization of ASN and Join Metric,
  carrying timeslot template identifier, carrying the channel hopping
  sequence identifier, and indicating the TSCH SlotFrame.
  The EB is used by nodes already part of a TSCH network to annouce announce its
  their existence. Receiving an EB allows a Joining Node (pledge) to learn
  about the network and how to synchronize to it. The EB may also be used as
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  a means for a node already part of the network to re-synchronize
  [RFC7554].
  There is are a limited number of timeslots designated as a broadcast slot
  slots by each router in the network. Considering 10ms slots and a slot-
  frame length of 100, these slots are rare and could result in only 1
  slot/s for a broadcast, which needs to be used for the beacon.
  Additional broadcasts for Router Advertisements, or Neighbor
  Discovery could even more scarce.
1.3. Layer-3 synchronization: IPv6 Router Solicitations and
   Advertisements
  At layer 3, [RFC4861] defines a mechanism by which nodes learn about
  routers by receiving multicast Router Advertisements (RA). If no RA
  is heard received within a set time, then a Router Solicitation (RS) may be
  sent transmitted as a 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 (NS) messages, it still
  requires multicast of either RAs or RS. This is an expensive
  operation for two reasons: First, there are few multicast timeslots
  for unsolicited RAs; and second, if a pledge node does not hear receive an
  RA, and decides to send a transmit an RS, a broadcast aloha slot is consumed with
  unencrypted traffic. In this case, a unicast RS may be sent transmitted 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 (RS) may overwhelm that time slot.
  2. it may require many seconds of on-time before a new pledge hears
    receives a Router Advertisement (RA) that it can use.
  3. a new pledge may listen have to receive for to many Enhanced Beacons (EB) before it
    can pick an appropriate network and/or closest Join Assistant to
    attach to. If it must remain in the receive state listen for a an RA as well as find the
    Enhanced Beacon (EB), then the process may take a very long time.
  This document defines a new IETF IE subtype to provide join and
  enrollment information to prospective pledges in a more efficient
  way.
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2. Protocol Definition
  [RFC8137] creates a registry for new IETF IE subtypes. This document
  allocates a new subtype.
  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       +
  ~                                ~
  +                                +
  |                                |
  +        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |        |
  +-+-+-+-+-+-+-+-+
            Figure 1: IE subtype structure
  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-local 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 destination
   layer-2 address of this beacon may use the layer-2 address which
   was used to originate the beacon.
  proxy priority (proxy prio) this field indicates the willingness of
   the sender to act as join proxy. Lower value indicates greater
   willingness to act as a Join Proxy as described in
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   [I-D.ietf-6tisch-minimal-security]. Values range 0x00 (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 value.
  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
   number of children, or number of neighbor cache entries available.
   This value MUST be ignored by pledges, it is for enrolled devices
   only.
  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.
  Join Proxy lower-64 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 a 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.
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3. Security Considerations
  All of the contents of this Information Element are sent transmitted in the
  clear. The content of the containing Enhanced Beacon is not encrypted. This is a
  restriction in the cryptographic architecture of the 802.15.4 TSCH mechanism.
  In order to decrypt or do integrity checking of layer-2 frames in
  TSCH, the TSCH Absolute Slot Number (ASN) is needed. The Enhanced
  Beacon provides the ASN to new (and long-sleeping) nodes.
  The Enhanced Beagon Beacon 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, providing them with a trusted
  Pledges which have not yet enrolled are unable to authenticate the
  beacons, and will be forced to temporarily take the contents on
  faith. After enrollment, a newly enrolled node will be able to
  return to the beacon and validate it.
  In addition to the enrollment and join information described in this
  document, the Enhanced Beacon contains a description of the TSCH
  schedule to be used by the transmitter of this packet. The schedule
  can provide an attacker with a list of channels and frequencies on
  which communication will occur. Knowledge of this can help an
  attacker to more efficiently jam communications, although there is
  future work being considered to make some of the schedule less
  visible.
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 extent of the mesh network.
5. IANA Considerations
  Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID, as
  defined by [RFC8137]. This entry should be called 6tisch-Join-Info,
  and should refer to this document.
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6. Acknowledgements
  Thomas Watteyne provided extensive editorial comments on the
  document. Carles Gomez Montenegro generated a detailed review of the
  document at WGLC. Tim Evens provided a number of useful editorial
  suggestions.
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>.
  [I-D.ietf-6tisch-minimal-security]
       Vucinic, M., Simon, J., Pister, K., and M. Richardson,
       "Constrained Join Protocol (CoJP) for 6TiSCH", Work in
       Progress, Internet-Draft, draft-ietf-6tisch-minimal-
       security-15, 10 December 2019, <http://www.ietf.org/
       internet-drafts/draft-ietf-6tisch-minimal-security-
       15.txt>.
  [ieee802154]
       IEEE standard for Information Technology, ., "IEEE Std.
       802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
       and Physical Layer (PHY) Specifications for Low-Rate
       Wireless Personal Area Networks", 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,
       <https://www.rfc-editor.org/info/rfc2119>.
  [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>.
  [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,
       <https://www.rfc-editor.org/info/rfc6775>.
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  [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>.
  [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>.
7.2. Informative References
  [I-D.ietf-6tisch-architecture]
       Thubert, P., "An Architecture for IPv6 over the TSCH mode
       of IEEE 802.15.4", Work in Progress, Internet-Draft,
       draft-ietf-6tisch-architecture-28, 29 October 2019,
       <http://www.ietf.org/internet-drafts/draft-ietf-6tisch-
       architecture-28.txt>.
  [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,
       <https://www.rfc-editor.org/info/rfc6550>.
  [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,
       <https://www.rfc-editor.org/info/rfc7554>.
  [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>.
Authors' Addresses
  Diego Dujovne (editor)
  Universidad Diego Portales
  Escuela de Informatica y Telecomunicaciones, Av. Ejercito 441
  Santiago, Region Metropolitana
  Chile
  Phone: +56 (2) 676-8121
  Email: diego.dujovne@mail.udp.cl
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  Michael Richardson
  Sandelman Software Works
  Email: mcr+ietf@sandelman.ca
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