IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP
draft-ietf-6lo-blemesh-05

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6Lo Working Group                                               C. Gomez
Internet-Draft                                               S. Darroudi
Intended status: Standards Track    Universitat Politecnica de Catalunya
Expires: September 10, 2019                                T. Savolainen
                                                              DarkMatter
                                                               M. Spoerk
                                           Graz University of Technology
                                                           March 9, 2019

           IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP
                       draft-ietf-6lo-blemesh-05

Abstract

   RFC 7668 describes the adaptation of 6LoWPAN techniques to enable
   IPv6 over Bluetooth low energy networks that follow the star
   topology.  However, recent Bluetooth specifications allow the
   formation of extended topologies as well.  This document specifies
   mechanisms that are needed to enable IPv6 mesh over Bluetooth Low
   Energy links established by using the Bluetooth Internet Protocol
   Support Profile.  This document does not specify the routing protocol
   to be used in an IPv6 mesh over Bluetooth LE links.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 10, 2019.

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
   Provisions Relating to IETF Documents

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   (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 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.  Terminology and Requirements Language . . . . . . . . . .   3
   2.  Bluetooth LE Networks and the IPSP  . . . . . . . . . . . . .   3
   3.  Specification of IPv6 mesh over Bluetooth LE links  . . . . .   4
     3.1.  Protocol stack  . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Subnet model  . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Link model  . . . . . . . . . . . . . . . . . . . . . . .   6
       3.3.1.  Stateless address autoconfiguration . . . . . . . . .   6
       3.3.2.  Neighbor Discovery  . . . . . . . . . . . . . . . . .   6
       3.3.3.  Header compression  . . . . . . . . . . . . . . . . .   7
       3.3.4.  Unicast and multicast mapping . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Appendix  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Bluetooth Low Energy (hereinafter, Bluetooth LE) was first introduced
   in the Bluetooth 4.0 specification.  Bluetooth LE (which has been
   marketed as Bluetooth Smart) is a low-power wireless technology
   designed for short-range control and monitoring applications.
   Bluetooth LE is currently implemented in a wide range of consumer
   electronics devices, such as smartphones and wearable devices.  Given
   the high potential of this technology for the Internet of Things, the
   Bluetooth Special Interest Group (Bluetooth SIG) and the IETF have
   produced specifications in order to enable IPv6 over Bluetooth LE,
   such as the Internet Protocol Support Profile (IPSP) [IPSP], and RFC
   7668, respectively.  Bluetooth 4.0 only supports Bluetooth LE
   networks that follow the star topology.  In consequence, RFC 7668 was
   specifically developed and optimized for that type of network
   topology.  However, the functionality described in RFC 7668 is not
   sufficient and would fail to enable an IPv6 mesh over Bluetooth LE

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   links.  This document specifies mechanisms that are needed to enable
   IPv6 mesh over Bluetooth LE links.  This document does not specify
   the routing protocol to be used in an IPv6 mesh over Bluetooth LE
   links.

1.1.  Terminology and Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The terms 6LoWPAN Node (6LN), 6LoWPAN Router (6LR) and 6LoWPAN Border
   Router (6LBR) are defined as in [RFC6775], with an addition that
   Bluetooth LE central and Bluetooth LE peripheral (see Section 2) can
   both be adopted by a 6LN, a 6LR or a 6LBR.

2.  Bluetooth LE Networks and the IPSP

   Bluetooth LE defines two Generic Access Profile (GAP) roles of
   relevance herein: the Bluetooth LE central role and the Bluetooth LE
   peripheral role.  A device in the central role, which is called
   central from now on, has traditionally been able to manage multiple
   simultaneous connections with a number of devices in the peripheral
   role, called peripherals hereinafter.  Bluetooth 4.1 (now deprecated)
   introduced the possibility for a peripheral to be connected to more
   than one central simultaneously, therefore allowing extended
   topologies beyond the star topology for a Bluetooth LE network.  In
   addition, a device may simultaneously be a central in a set of link
   layer connections, as well as a peripheral in others.  On the other
   hand, the IPSP enables discovery of IP-enabled devices and the
   establishment of a link layer connection for transporting IPv6
   packets.  The IPSP defines the Node and Router roles for devices that
   consume/originate IPv6 packets and for devices that can route IPv6
   packets, respectively.  Consistently with Bluetooth 4.1 and
   subsequent Bluetooth versions (e.g.  Bluetooth 4.2 [BTCorev4.2] or
   subsequent), a device may implement both roles simultaneously.

   This document assumes a mesh network composed of Bluetooth LE links,
   where link layer connections are established between neighboring
   IPv6-enabled devices (see Section 3.3.2, item 3.b)).  The IPv6
   forwarding devices of the mesh have to implement both Node and Router
   roles, while simpler leaf-only nodes can implement only the Node
   role.  In an IPv6 mesh over Bluetooth LE links, a node is a neighbor
   of another node, and vice versa, if a link layer connection has been
   established between both by using the IPSP functionality for
   discovery and link layer connection establishment for IPv6 packet
   transport.

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3.  Specification of IPv6 mesh over Bluetooth LE links

3.1.  Protocol stack

   Figure 1 illustrates the protocol stack for IPv6 mesh over Bluetooth
   LE links.  There are two main differences with the IPv6 over
   Bluetooth LE stack in RFC 7668: a) the adaptation layer below IPv6
   (labelled as "6Lo for IPv6 mesh over Bluetooth LE") is now adapted
   for IPv6 mesh over Bluetooth LE links, and b) the protocol stack for
   IPv6 mesh over Bluetooth LE links includes IPv6 routing
   functionality.

                         +------------------------------------+
                         |             Application            |
            +---------+  +------------------------------------+
            |  IPSS   |  |            UDP/TCP/other           |
            +---------+  +------------------------------------+
            |  GATT   |  |             IPv6  |routing|        |
            +---------+  +------------------------------------+
            |  ATT    |  | 6Lo for IPv6 mesh over Bluetooh LE |
            +---------+--+------------------------------------+
            |                 Bluetooth LE L2CAP              |
       -  - +-------------------------------------------------+- - - HCI
            |               Bluetooth LE Link Layer           |
            +-------------------------------------------------+
            |                Bluetooth LE Physical            |
            +-------------------------------------------------+

      Figure 1: Protocol stack for IPv6 mesh over Bluetooth LE links.

   Bluetooth 4.2 defines a default MTU for Bluetooth LE of 251 bytes.
   Excluding the L2CAP header of 4 bytes, a protocol data unit (PDU)
   size of 247 bytes is available for the layer above L2CAP.  (Note:
   earlier Bluetooth LE versions offered a maximum amount of 23 bytes
   for the layer atop L2CAP.)  The L2CAP provides a fragmentation and
   reassembly solution for transmitting or receiving larger PDUs.  At
   each link, the IPSP defines means for negotiating a link-layer
   connection that provides an MTU of 1280 octets or higher for the IPv6
   layer [IPSP].  The link-layer MTU is negotiated separately for each
   direction.  Implementations that require an equal link-layer MTU for
   the two directions SHALL use the smallest of the possibly different
   MTU values.

   Note that this specification allows using different MTUs in different
   links.  If an implementation requires use of the same MTU on every
   one of its links, and a new node with a smaller MTU is added to the
   network, a renegotiation of one or more links can occur.  In the

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   worst case, the renegotiations could cascade network-wide.  In that
   case, implementers need to assess the impact of such phenomenon.

   Similarly to RFC 7668, fragmentation functionality from 6LoWPAN
   standards is not used for IPv6 mesh over Bluetooth LE links.
   Bluetooth LE's fragmentation support provided by L2CAP is used when
   necessary.

3.2.  Subnet model

   For IPv6 mesh over Bluetooth LE links, a multilink model has been
   chosen, as further illustrated in Figure 2.  As IPv6 over Bluetooth
   LE is intended for constrained nodes, and for Internet of Things use
   cases and environments, the complexity of implementing a separate
   subnet on each peripheral-central link and routing between the
   subnets appears to be excessive.  In this specification, the benefits
   of treating the collection of point-to-point links between a central
   and its connected peripherals as a single multilink subnet rather
   than a multiplicity of separate subnets are considered to outweigh
   the multilink model's drawbacks as described in [RFC4903].

                                                          /
       .--------------------------------.                /
      /     6LR           6LN        6LN \              /
     /         \             \          \ \            /
    |           \             \          \ |          /
    |  6LN ----- 6LR --------- 6LR ------ 6LBR ----- |  Internet
    |   <--Link--> <---Link--->/<--Link->/ |         |
     \                        /         / /           \
      \           6LN ---- 6LR ----- 6LR /             \
       '--------------------------------'               \
                                                         \

     <------------ Subnet -----------------><---- IPv6 connection -->
                                                  to the Internet

       Figure 2: Example of an IPv6 mesh over a Bluetooth LE network
                         connected to the Internet

   One or more 6LBRs are connected to the Internet. 6LNs are connected
   to the network through a 6LR or a 6LBR.  A prefix is used on the
   whole subnet.

   IPv6 mesh over Bluetooth LE links MUST follow a route-over approach.
   This document does not specify the routing protocol to be used in an
   IPv6 mesh over Bluetooth LE links.

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3.3.  Link model

3.3.1.  Stateless address autoconfiguration

   6LN, 6LR and 6LBR IPv6 addresses in an IPv6 mesh over Bluetooth LE
   links are configured as per section 3.2.2 of RFC 7668.

   Multihop DAD functionality as defined in section 8.2 of RFC 6775 and
   updated by RFC 8505, or some substitute mechanism (see section
   3.3.2), MUST be supported.

3.3.2.  Neighbor Discovery

   'Neighbor Discovery Optimization for IPv6 over Low-Power Wireless
   Personal Area Networks (6LoWPANs)' [RFC6775], subsequently updated by
   'Registration Extensions for IPv6 over Low-Power Wireless Personal
   Area Network (6LoWPAN) Neighbor Discovery' [RFC8505], describes the
   neighbor discovery functionality adapted for use in several 6LoWPAN
   topologies, including the mesh topology.  The route-over
   functionality of RFC 6775 and RFC 8505 MUST be supported.

   The following aspects of the Neighbor Discovery optimizations for
   6LoWPAN [RFC6775],[RFC8505] are applicable to Bluetooth LE 6LNs:

   1.  A Bluetooth LE host MUST register its non-link-local addresses
   with its routers by sending a Neighbor Solicitation (NS) message with
   the Extended Address Registration Option (EARO) and process the
   Neighbor Advertisement (NA) accordingly.  The NS with the EARO option
   MUST be sent irrespective of the method used to generate the IID.
   The EARO option includes a Registration Ownership Verifier (ROVR)
   field [RFC8505].  In the case of Bluetooth LE, by default the ROVR
   field is filled with the 48-bit device address used by the Bluetooth
   LE node converted into 64-bit Modified EUI-64 format [RFC4291].
   Optionally, a cryptographic ID (see [I-D.ietf-6lo-ap-nd] MAY be
   placed in the ROVR field.  If a cryptographic ID is used, address
   registration and multihop DAD formats and procedures defined in
   [I-D.ietf-6lo-ap-nd] MUST be used, unless an alternative mechanism
   offering equivalent protection is used.  As per RFC 8505, a 6LN MUST
   NOT register its link-local address.

   If the 6LN registers for a same compression context multiple
   addresses that are not based on Bluetooth device address, the header
   compression efficiency will decrease.

   2.  For sending Router Solicitations and processing Router
   Advertisements the Bluetooth LE hosts MUST, respectively, follow
   Sections 5.3 and 5.4 of [RFC6775], and Section 5.6 of [RFC8505].

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   3.  The router behavior for 6LRs and 6LBRs is described in Section 6
   of RFC 6775, and updated by RFC 8505.  However, as per this
   specification: a) Routers SHALL NOT use multicast NSs to discover
   other routers' link layer addresses.  b) As per section 6.2 of RFC
   6775, in a dynamic configuration scenario, a 6LR comes up as a non-
   router and waits to receive a Router Advertisement for configuring
   its own interface address first, before setting its interfaces to be
   advertising interfaces and turning into a router.  In order to
   support such operation in an IPv6 mesh over Bluetooth LE links, a 6LR
   first uses the IPSP Node role only.  Once the 6LR has established a
   connection with another node previously running as a router, and
   receives a Router Advertisement from that router, the 6LR configures
   its own interface address, it turns into a router, and it runs as an
   IPSP Router.  A 6LBR uses the IPSP Router role since the 6LBR is
   initialized.  See an example in the Appendix.

   4.  Border router behavior is described in Section 7 of RFC 6775, and
   updated by RFC 8505.

   RFC 6775 defines substitutable mechanisms for distributing prefixes
   and context information (section 8.1 of RFC 6775), as well as for
   Duplicate Address Detection across a route-over 6LoWPAN (section 8.2
   of RFC 6775).  RFC 8505 updates those mechanisms and the related
   message formats.  Implementations of this specification MUST support
   the features described in sections 8.1 and 8.2 of RFC 6775, as
   updated by RFC 8505, unless some alternative ("substitute") from some
   other specification is supported by the implementation.

3.3.3.  Header compression

   Header compression as defined in RFC 6282 [RFC6282], which specifies
   the compression format for IPv6 datagrams on top of IEEE 802.15.4, is
   REQUIRED as the basis for IPv6 header compression on top of Bluetooth
   LE.  All headers MUST be compressed according to RFC 6282 [RFC6282]
   encoding formats.

   To enable efficient header compression, when the 6LBR sends a Router
   Advertisement it MUST include a 6LoWPAN Context Option (6CO)
   [RFC6775] matching each address prefix advertised via a Prefix
   Information Option (PIO) [RFC4861] for use in stateless address
   autoconfiguration.

   The specific optimizations of RFC 7668 for header compression, which
   exploit the star topology and ARO, cannot be generalized in an IPv6
   mesh over Bluetooth LE links.  Still, a subset of those optimizations
   can be applied in some cases in such a network.  In particular, the
   latter comprise link-local interactions, non-link- local packet
   transmissions originated and performed by a 6LN, and non-link-local

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   packets transmitted (but not necessarily originated) by the neighbor
   of a 6LN to that 6LN.  For the rest of packet transmissions, context-
   based compression MAY be used.

   When a device transmits a packet to a neighbor, the sender MUST fully
   elide the source IID if the source IPv6 address is the link-local
   address based on the sender's Bluetooth device address (SAC=0,
   SAM=11).  The sender also MUST fully elide the destination IPv6
   address if it is the link-local address based on the neighbor's
   Bluetooth device address (DAC=0, DAM=11).

   A 6LN SHOULD register its non-link-local address with ARO in the
   next-hop router.  Note that in some cases (e.g. very short-lived
   connections) it may not be worthwhile for a 6LN to send an NS with
   ARO for registering its address.  When a 6LN transmits a packet, with
   a non-link-local source address that the 6LN has registered with ARO
   in the next-hop router for the indicated prefix, the source address
   MUST be fully elided if it is the latest address that the 6LN has
   registered for the indicated prefix (SAC=1, SAM=11).  If the source
   non-link-local address is not the latest registered by the 6LN, then
   the 64 bits of the IID SHALL be fully carried in-line (SAC=1, SAM=01)
   or if the first 48 bits of the IID match with the latest address
   registered by the 6LN, then the last 16 bits of the IID SHALL be
   carried in-line (SAC=1, SAM=10).

   When a router transmits a packet to a neighboring 6LN, with a non-
   link-local destination address, the router MUST fully elide the
   destination IPv6 address if the destination address is the latest
   registered by the 6LN with ARO for the indicated context (DAC=1,
   DAM=11).  If the destination address is a non-link-local address and
   not the latest registered, then the 6LN MUST either include the IID
   part fully in-line (DAM=01) or, if the first 48 bits of the IID match
   to the latest registered address, then elide those 48 bits (DAM=10).

3.3.4.  Unicast and multicast mapping

   The Bluetooth LE Link Layer does not support multicast.  Hence,
   traffic is always unicast between two Bluetooth LE neighboring nodes.
   If a node needs to send a multicast packet to several neighbors, it
   has to replicate the packet and unicast it on each link.  However,
   this may not be energy efficient, and particular care must be taken
   if the node is battery powered.  A router (i.e. a 6LR or a 6LBR) MUST
   keep track of neighboring multicast listeners, and it MUST NOT
   forward multicast packets to neighbors that have not registered as
   listeners for multicast groups the packets belong to.

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4.  IANA Considerations

   There are no IANA considerations related to this document.

5.  Security Considerations

   The security considerations in RFC 7668 apply.

   IPv6 mesh over Bluetooth LE links requires a routing protocol to find
   end-to-end paths.  Unfortunately, the routing protocol may generate
   additional opportunities for threats and attacks to the network.

   RFC 7416 [RFC 7416] provides a systematic overview of threats and
   attacks on the IPv6 Routing Protocol for Low-Power and Lossy Networks
   (RPL), as well as countermeasures.  In that document, described
   threats and attacks comprise threats due to failures to authenticate,
   threats due to failure to keep routing information, threats and
   attacks on integrity, and threats and attacks on availability.
   Reported countermeasures comprise confidentiality attack, integrity
   attack, and availability attack countermeasures.

   While this specification does not state the routing protocol to be
   used in IPv6 mesh over Bluetooth LE links, the guidance of RFC 7416
   is useful when RPL is used in such scenarios.  Furthermore, such
   guidance may partly apply for other routing protocols as well.

   The ROVR can be derived from the Bluetooth device address.  However,
   such a ROVR can be spoofed, and therefore, any node connected to the
   subnet and aware of a registered-address-to-ROVR mapping could
   perform address theft and impersonation attacks.  Use of Address
   Protected Neighbor Discovery [I-D.ietf-6lo-ap-nd] provides protection
   against such attacks.

6.  Contributors

   Carlo Alberto Boano (Graz University of Technology) contributed to
   the design and validation of this document.

7.  Acknowledgements

   The Bluetooth, Bluetooth Smart and Bluetooth Smart Ready marks are
   registered trademarks owned by Bluetooth SIG, Inc.

   The authors of this document are grateful to all RFC 7668 authors,
   since this document borrows many concepts (albeit, with necessary
   extensions) from RFC 7668.

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   The authors also thank Alain Michaud, Mark Powell, Martin Turon,
   Bilhanan Silverajan, Rahul Jadhav and Pascal Thubert for their
   comments, which helped improve the document.

   Carles Gomez has been supported in part by the Spanish Government
   Ministerio de Economia y Competitividad through projects
   TEC2012-32531, TEC2016-79988-P and FEDER.

8.  Appendix

   This appendix provides an example of Bluetooth LE connection
   establishment and use of IPSP roles in an IPv6 mesh over Bluetooth LE
   links that uses dynamic configuration.  The example follows text in
   Section 3.3.2, item 3.b).

   The example assumes a network with one 6LBR, two 6LRs and three 6LNs,
   as shown in Figure 3.  Connectivity between the 6LNs and the 6LBR is
   only possible via the 6LRs.

   The following text describes the different steps as time evolves, in
   the example.  Note that other sequences of events that may lead to
   the same final scenario are also possible.

   At the beginning, the 6LBR starts running as an IPSP Router, whereas
   the rest of devices are not yet initialized (Step 1).  Next, the 6LRs
   start running as IPSP Nodes, i.e., they use Bluetooth LE
   advertisement packets to announce their presence and support of IPv6
   capabilities (Step 2).  The 6LBR (already running as an IPSP Router)
   discovers the presence of the 6LRs and establishes one Bluetooth LE
   connection with each 6LR (Step 3).  After establishment of those link
   layer connections (and after reception of Router Advertisements from
   the 6LBR), Step 4, the 6LRs start operating as routers, and also
   initiate the IPSP Router role (note: whether the IPSP Node role is
   kept running simultaneously is an implementation decision).  Then,
   6LNs start running the IPSP Node role (Step 5).  Finally, the 6LRs
   discover presence of the 6LNs and establish connections with the
   latter (Step 6).

   Step 1
   ******
                                        6LBR
                                   (IPSP: Router)

                              6LR                 6LR
                      (not initialized)     (not initialized)

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                6LN                 6LN                  6LN
       (not initialized)      (not initialized)     (not initialized)

   Step 2
   ******
                                        6LBR
                                   (IPSP: Router)

                              6LR                 6LR
                         (IPSP: Node)         (IPSP: Node)

                6LN                 6LN                  6LN
       (not initialized)      (not initialized)     (not initialized)

   Step 3
   ******

                                        6LBR
                                   (IPSP: Router)
     Bluetooth LE connection -->   /            \
                                  /              \
                              6LR                 6LR
                         (IPSP: Node)         (IPSP: Node)

                6LN                 6LN                  6LN
       (not initialized)      (not initialized)     (not initialized)

   Step 4
   ******

                                        6LBR
                                   (IPSP: Router)
                                   /            \

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                                  /              \
                              6LR                 6LR
                         (IPSP: Router)      (IPSP: Router)

                6LN                 6LN                  6LN
       (not initialized)      (not initialized)     (not initialized)

   Step 5
   ******

                                        6LBR
                                   (IPSP: Router)
                                   /            \
                                  /              \
                              6LR                 6LR
                         (IPSP: Router)      (IPSP: Router)

                6LN                   6LN                6LN
            (IPSP: Node)         (IPSP: Node)        (IPSP: Node)

   Step 6
   ******

                                        6LBR
                                   (IPSP: Router)
                                   /            \
                                  /              \
                              6LR                 6LR
                        (IPSP: Router)       (IPSP: Router)
                         /           \       /            \
                        /             \     /              \
                       /               \   /                \
                    6LN                 6LN                  6LN
               (IPSP: Node)         (IPSP: Node)         (IPSP: Node)

     Figure 3: An example of connection establishment and use of IPSP
              roles in an IPv6 mesh over Bluetooth LE links.

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9.  References

9.1.  Normative References

   [BTCorev4.2]
              Bluetooth Special Interest Group, "Bluetooth Core
              Specification Version 4.2", December 2014,
              <https://www.bluetooth.com/specifications/
              archived-specifications>.

   [IPSP]     Bluetooth Special Interest Group, "Bluetooth Internet
              Protocol Support Profile Specification Version 1.0.0",
              December 2014, <https://www.bluetooth.org/en-
              us/specification/adopted-specifications>.

   [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>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [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>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <https://www.rfc-editor.org/info/rfc6282>.

   [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>.

   [RFC7668]  Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
              Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
              <https://www.rfc-editor.org/info/rfc7668>.

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   [RFC8505]  Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
              <https://www.rfc-editor.org/info/rfc8505>.

9.2.  Informative References

   [BTCorev4.1]
              Bluetooth Special Interest Group, "Bluetooth Core
              Specification Version 4.1", December 2013,
              <https://www.bluetooth.org/en-us/specification/
              adopted-specifications>.

   [I-D.ietf-6lo-ap-nd]
              Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
              "Address Protected Neighbor Discovery for Low-power and
              Lossy Networks", draft-ietf-6lo-ap-nd-11 (work in
              progress), February 2019.

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
              DOI 10.17487/RFC4903, June 2007,
              <https://www.rfc-editor.org/info/rfc4903>.

   [RFC7416]  Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
              and M. Richardson, Ed., "A Security Threat Analysis for
              the Routing Protocol for Low-Power and Lossy Networks
              (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
              <https://www.rfc-editor.org/info/rfc7416>.

Authors' Addresses

   Carles Gomez
   Universitat Politecnica de Catalunya
   C/Esteve Terradas, 7
   Castelldefels  08860
   Spain

   Email: carlesgo@entel.upc.edu

   Seyed Mahdi Darroudi
   Universitat Politecnica de Catalunya
   C/Esteve Terradas, 7
   Castelldefels  08860
   Spain

   Email: sm.darroudi@entel.upc.edu

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   Teemu Savolainen
   DarkMatter LLC

   Email: teemu.savolainen@darkmatter.ae

   Michael Spoerk
   Graz University of Technology
   Inffeldgasse 16/I
   Graz  8010
   Austria

   Email: michael.spoerk@tugraz.at

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