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Versions: 00 01 02 03                                                   
6LoWPAN                                                       P. Thubert
Internet-Draft                                                     Cisco
Intended status: Standards Track                          March 18, 2008
Expires: September 19, 2008


                         LoWPAN Backbone Router
                draft-thubert-6lowpan-backbone-router-00

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on September 19, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   ISA100.11a is a Working Group at the ISA SP100 standard committee
   that covers Wireless Systems for Industrial Automation and Process
   Control.  The WG is mandated to design a scalable, industrial grade
   LowPAN for devices such as sensors, valves, and actuators.  The
   upcoming standard uses the 6LoWPAN format for the network header.  It
   also introduces the concept of a Backbone Router to merge small
   LoWPANs via a high speed transit and scale the ISA100.11a network.
   This paper proposes an IPv6 version of the Backbone Router concept.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  New Neighbor Discovery options . . . . . . . . . . . . . . . .  6
     4.1.  Binding Update Option  . . . . . . . . . . . . . . . . . .  6
     4.2.  Binding Acknowledgement Option . . . . . . . . . . . . . .  7
   5.  LowPAN device operations . . . . . . . . . . . . . . . . . . .  8
     5.1.  Forming addresses  . . . . . . . . . . . . . . . . . . . .  8
     5.2.  Binding process  . . . . . . . . . . . . . . . . . . . . .  9
     5.3.  Looking up neighbor addresses  . . . . . . . . . . . . . .  9
     5.4.  Answering address look up  . . . . . . . . . . . . . . . . 10
   6.  Backbone router operations . . . . . . . . . . . . . . . . . . 10
     6.1.  Exposing the Backbone Router . . . . . . . . . . . . . . . 10
     6.2.  Binding process  . . . . . . . . . . . . . . . . . . . . . 11
     6.3.  Looking up neighbor addresses  . . . . . . . . . . . . . . 11
     6.4.  Answering address look up  . . . . . . . . . . . . . . . . 12
     6.5.  Forwarding packets . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15
























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1.  Introduction

   ISA100.11a is a Working Group at the ISA SP100 standard committee
   that covers Wireless Systems for Industrial Automation and Process
   Control.  The ISA100.11a is mandated to design a scalable, industrial
   grade wireless network and application layer suite of protocols for
   low power devices such as sensors and actuators, with a response time
   on the order of 100ms.

   In order to meet industrial requirements for non-critical monitoring,
   alerting, supervisory control, open loop control and some closed loop
   control applications, the Working Group is leveraging advanced
   technology at every layer, including a mix of DSSS and FHSS at the
   MAC/PHY layer, path diversity at Data Link Layer, and endorsed the
   6LoWPAN format for the network header, making it possible to utilize
   IP based protocols such as BACnet IP, Profibus IP and Modbus TCP
   without significant changes to those protocols.

   The ISA100.11a WG has also introduced the concept of a Backbone
   Router that would interconnect small LoWPANs over a high speed
   transit network and scale a single ISA100.11a network up to the
   thousands of nodes.

   This paper specifies IP layer functionalities that are required to
   implement a such Backbone Router with IPv6, in particular the
   application of the "IP Version 6 Addressing Architecture" [RFC4291],
   "Neighbor Discovery for IP version 6" [RFC4861] and "IPv6 Stateless
   Address Autoconfiguration" [RFC4862].  The use of EUI-64 based link
   local addresses, Neighbor Discovery Proxying and Optimistic Duplicate
   Address Detection are discussed.  Also, the concept of Transit Link
   is introduced to implement the transit network that is envisioned by
   ISA100.11a.

   This draft solves the problem of finding the other Backbone Router or
   gateway on the transit link from a 64 bits address that is used as
   interface ID for building a link local address.  The Backbone Router
   acts as proxy for all nodes attached to it through a process of
   registration.  The Backbone Router also acts as a server for all
   Neighbor Discovery flows from and to its nodes, avoiding the burden
   of multicast over the LoWPAN.

   The way the PAN IDs and 16-bit short addresses are allocated and
   distributed in the case of an 802.15.4 network is not covered by this
   specification.  This specification is compatible with a deployment
   where each Backbone Router is connected to a different PAN-ID that is
   managed locally, as well as a deployment where the whole transit link
   and all nodes attached are a single PAN-ID.  Similarly, the aspects
   of joining and securing the network are out of scope.



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2.  Terminology

   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 [RFC2119].

   Readers are expected to be familiar with all the terms and concepts
   that are discussed in "Neighbor Discovery for IP version 6"
   [RFC4861], "IPv6 Stateless Address Autoconfiguration" [RFC4862],
   "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
   Overview, Assumptions, Problem Statement, and Goals" [RFC4919] and
   "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944].

   Readers would benefit from reading "Mobility Support in IPv6"
   [RFC3775], "Neighbor Discovery Proxies (ND Proxy)" [RFC4389] and
   "Optimistic Duplicate Address Detection" [RFC4429] prior to this
   specification for a clear understanding of the art in ND-proxying and
   binding.  This document defines additional terms:

   Transit Link

      This is an IPv6 link that interconnects 2 or more backbone
      routers.  It is expected to be deployed as a high speed backbone
      in order to federate a potentially large set of LoWPANS.  Also
      referred to as a LoWPAN backbone or transit network.

   Backbone Router

      An IPv6 router that interconnects the LoWPAN with a Transit Link.

   Extended LoWPAN

      This is the aggregation of multiple LoWPANs as defined in
      [RFC4919] interconnected by a Transit Link via Backbone Routers
      and forming a single IPv6 link.

   Binding

      The association of the LoWPAN node IPv6 address and Interface ID
      with associated proxying states including the remaining lifetime
      of that association.

   Registration

      The process during which a LoWPAN node sends a Binding ND message
      to a Backbone Router causing a binding for the LoWPAN node to be
      registered.




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3.  Overview

   A Transit Link federates multiple LoWPANs as a single IP link, the
   extended LoWPAN.  Each LoWPAN is anchored at a Backbone Router.  The
   Backbone Routers interconnect the LoWPANs over the Transit Link.  A
   node can move freely from a LoWPAN anchored at a Backbone Router to a
   LoWPAN anchored at another Backbone Router on the same Transit Link
   and conserve its link local and any other IPv6 address it has formed.


               ---+------------------------
                  |          Plant Network
                  |
               +-----+
               |     | Gateway
               |     |
               +-----+
                  |
                  |      Transit Link
            +--------------------+------------------+
            |                    |                  |
         +-----+             +-----+             +-----+
         |     | Backbone    |     | Backbone    |     | Backbone
         |     | router      |     | router      |     | router
         +-----+             +-----+             +-----+
            o                o   o  o              o o
        o o   o  o       o o   o  o  o         o  o  o  o o
       o  o o  o o       o   o  o  o  o        o  o  o o o
       o   o  o  o          o    o  o           o  o   o
         o   o o               o  o                 o o

         LoWPAN              LoWPAN              LoWPAN


                Figure 1: Transit Link and Backbone Routers

   In order to achieve this, the Transit link is used as reference for
   Neighbor Discovery operations, by extending the concept of a Home
   Link as defined in [RFC3775] for Mobile IPv6.  In particular,
   Backbone Routers perform ND proxying for the LoWPAN nodes in the
   LoWPANs they own.

   The backbone router operation is compatible with that of a Home
   Agent.  This enables mobility support for sensor devices that would
   move outside of the network delimited by the transit link.  This also
   enables collocation of Home Agent functionality within Backbone
   Router functionality on the same interface of the router.




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   The Backbone Router is centric for ND operation inside the LoWPAN.
   Part of the reason is the cost of the support for multicasting over
   the LoWPAN that this specification avoids for the Neighbor
   Solicitation flows.  As a result, a LoWPAN node performs unicast
   exchanges to its Backbone Router to claim and lookup addresses, and
   the Backbone Router proxies the ND requests over the Transit Link
   when necessary.

   This specification documents the extensions to IPv6 Neighbor
   Discovery that enables a LoWPAN Node to claim and lookup addresses
   using a Backbone Router as an intermediate proxy.  The draft also
   documents the use of EUI-64 based link-local addresses and the way
   they are claimed by the Backbone Routers over the transit link.

   For the purpose of Neighbor Discovery proxying, this specification
   documents the LoWPAN binding cache, a conceptual data structure that
   is similar to the MIP6 binding cache.

   Another function of the Backbone Router is to perform 6LowPAN
   compression and uncompression between the LoWPAN and the Transit Link
   and ensure MTU compatibility.  Packets flow uncompressed over the
   Transit Link and are routed normally towards a Gateway or an
   Application sitting on the transit link or on a different link that
   is reachable via IP.


4.  New Neighbor Discovery options

4.1.  Binding Update Option

   The binding Update Option echoes the BU in [RFC3775] for Mobile IPv6.
   At this stage of the specification, there is no control bit or
   suboption.  The BU option is used in Neighbor Solicitation messages
   sent by the LoWPAN node to its Backbone Router for registration.

      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      |    Length     |        Sequence #             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Reserved                    |       Lifetime                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   sub-option(s)...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 2: NS BU option





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   Type:  8-bit unsigned integer.  Value is "to be assigned by IANA".

   Length:  8-bit unsigned integer set to 1 when there is no suboption.
      The length of the option (including the type and length fields and
      the suboptions) in units of 8 octets.

   Sequence #:  A 16-bit unsigned integer used by the receiving node to
      sequence Binding Updates and by the sending node to match a
      returned Binding Acknowledgement option with this Binding Update
      option.

   Lifetime:  16-bit unsigned integer.  The number of time units
      remaining before the binding MUST be considered expired.  A value
      of zero indicates that the Binding Cache entry for the mobile node
      MUST be deleted.  (In this case the specified care-of address MUST
      also be set equal to the home address.)  One time unit is 4
      seconds.

4.2.  Binding Acknowledgement Option

   The Binding Ack Option echoes the Binding Ack in [RFC3775] for Mobile
   IPv6.  At this stage of the specification, there is no control bit or
   suboption.  The Binding Ack option is used in Neighbor Advertisement
   messages sent by the Backbone Router to a LoWPAN node to acknowledge
   its registration.  A status indicates the completion.

      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      |    Length     |    Status     |    Reserved   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Sequence #              |       Lifetime                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   sub-option(s)...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 3: NA Binding Ack option

   Type:  8-bit unsigned integer.  Value is "to be assigned by IANA".

   Length:  8-bit unsigned integer set to 1 when there is no suboption.
      The length of the option (including the type and length fields and
      the suboptions) in units of 8 octets.

   Status:  8-bit unsigned integer indicating the disposition of the
      Binding Update.  Values of the Status field less than 128 indicate
      that the Binding Update Option was accepted by the Backbone
      Router.  Values greater than or equal to 128 indicate that the



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      Binding Update was rejected by the Backbone Router.  The following
      Status values are currently defined:

      0  Binding Update accepted (primary)

      2  Binding Update accepted (secondary)

      128  Reason unspecified

      129  Administratively prohibited

      130  Insufficient resources

      134  Duplicate Address Detection failed

      135  Duplicate Address Detection failed

   Sequence #:  16-bit unsigned integer.  The Sequence Number in the
      Binding Acknowledgement is copied from the Sequence Number field
      in the Binding Update.  It is used by the LoWPAN node in matching
      this Binding Acknowledgement with an outstanding Binding Update.

   Lifetime:  16-bit unsigned integer.  The granted lifetime, in time
      units of 4 seconds, for which the Backbone Router SHOULD retain
      the entry for this LoWPAN node in its Binding Cache.  The value of
      this field is undefined if the Status field indicates that the
      Binding Update was rejected.


5.  LowPAN device operations

5.1.  Forming addresses

   All nodes are required to autoconfigure at least one address, a link-
   local address that is derived from the IEEE 64-bit extended media
   access control address that is globally unique to the device.  Link-
   local address are described in section 2.5.6 of [RFC4291].  Appendix
   A of that specification explains how the node builds an interface-ID
   based on the IEEE 64-bit extended MAC address by inverting the "u"
   (universal/local) bit.

   As a result, knowledge of the 64-bit address of another node on the
   same extended LoWPAN is enough to derive its link-local address and
   reach it over IP.  Another consequence is that the link local address
   is presumably unique on the Extended LoWPAN, which enables the use of
   Optimistic Duplicate Address Detection (oDAD) [RFC4429] over the
   Transit Link and the LoWPAN.  The address is created as optimistic to
   enable its use in the binding process with the Backbone Router.



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   The node might also form Unique Local and Global Unicast addresses,
   for instance if it needs to be reachable from the outside of the
   Extended LoWPAN, or if it can manage its own mobility as prescribed
   by Mobile IPv6 [RFC3775].  In that case, the node needs to bind each
   individual address individually.

5.2.  Binding process

   The binding process is very similar to that of a MIP6 mobile node,
   though the messages used are Neighbor Discovery messages with new
   extensions to specify a binding relationship associated to the
   advertisements.  A LoWPAN Address is tentative as long as the binding
   is not confirmed by the Backbone Router.

   The LoWPAN node uses unicast Neighbor Solicitations to perform the
   binding.  The destination Address is that of the Backbone Router.
   The source address the unspecified address as long as the address is
   still optimistic or tentative, and it is the link local address of
   the node after DAD is completed.  The target address is the address
   being bound.  A new binding-update option specifies parameters such
   as the binding lifetime.

   The acknowledgment to an NS is a unicast Neighbor Advertisement with
   a new Binding Acknowledgement option that contains the status of the
   binding.  The source of the packet is the link-local address of the
   Backbone Router.  The destination address is the link-local address
   of the LoWPAN node, and the Target Address field contains the address
   being bound.  That unicast NA is not to be confused with the response
   to a DAD and does not mean that the address is duplicated.

   A bit in the Binding Acknowledgement option indicates whether the
   Backbone Router has completed DAD and now owns the bound address over
   the Transit Link.  If the bit is set, the LoWPAN node set the address
   from optimistic to preferred.

   This specification also introduces the concept of secondary binding.
   For redundancy, a node might place a secondary binding with one or
   more other Backbone Routers over a same or different LoWPANs.  A flag
   in the binding option indicates whether the binding is secondary.

   The Backbone Router might learn the PAN-ID and the 16-bit short
   address from the NS message if it was not already known by another
   means that is not within the scope of this specification.

5.3.  Looking up neighbor addresses

   A LoWPAN node does not use multicast for its Neighbor Solicitation.
   Whether for DAD or lookup purposes, all NS messages are sent in



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   unicast to the Backbone Router, that answers in unicast as well.

   The Target link-layer address in the response is either that of the
   destination if a short cut is possible over the LoWPAN, or that of
   the Backbone Router if the destination is reachable over the Transit
   Link, in which case the Backbone Router will terminate 6LoWPAN and
   relay the packet.

5.4.  Answering address look up

   A LoWPAN node does not need to join the solicited-node multicast
   address for its own addresses and should not have to answer a
   multicast Neighbor Solicitation.  It may be programmed to answer a
   unicast NS but that is not required by this specification.


6.  Backbone router operations

6.1.  Exposing the Backbone Router

   The Backbone Router forms a link-local address in exactly the same
   way as any other node on the LoWPAN.  It uses the same link local
   address for the Transit Link and for all the associated LoWPAN(s)
   connected to that Backbone Router.

   The Backbone Router announces itself using Router Advertisements (RA)
   messages that are broadcasted periodically over the LOWPAN. (note:
   can we merge RA with some other maintenance packet or distribute the
   info from the manager in some specific cases like ISA100.11a where
   such a thing exists?). (also, when the node moves to another LoWPAN,
   is there a way to let it know faster which is the Backbone Router so
   that it can stimulate a RA using RS?).

   A new option in the RA indicates the Backbone Router capability.  In
   this way a node can learn the PAN-ID and the 16-bit short address for
   the Backbone Router if it was not already acquired from another
   process that is not covered by this specification.

   The Backbone Router MAY also announce any prefix that is configured
   on the transit link, and serve as the default gateway for any node on
   the Transit Link or on the attached LoWPANs.

   The transit link Maximum Transmission Unit serves as base for Path
   MTU discovery and Transport layer Maximum Segment Size negotiation
   (see section 8.3 of [RFC2460]) for all nodes in the LoWPANs.  To
   achieve this, the Backbone Router announces the MTU of the transit
   link over the LoWPAN using the MTU option in the RA message as
   prescribed in section "4.6.4.  MTU" of IPv6 Neighbor Discovery



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   [RFC4861].

   LoWPAN nodes SHOULD form IPv6 packets that are smaller than that MTU.
   As a result, those packets should not require any fragmentation over
   the transit link though they might be intranet-fragmented over the
   LoWPAN itself as prescribed by [RFC4944]).

   More information on the MTU issue with regard to ND-proxying can be
   found in Neighbor Discovery Proxies [RFC4389] and
   [I-D.van-beijnum-multi-mtu].

6.2.  Binding process

   Upon a new binding for a link-local address based on a IEEE 64-bit
   extended MAC address, the Backbone Router uses Optimistic DAD on the
   Transit Link.  Any other Backbone Router that would happen to have a
   binding for that same address SHOULD yield and deprecate its binding
   to secondary if it was primary.  A positive acknowledgement can be
   sent to the LoWPAN node right away if oDAD is used on the Transit
   Link.

   The Backbone Router operation on the transit link is similar to that
   of a Home Agent as specified in Mobility Support for IPv6 [RFC3775].
   In particular, the Neighbor Advertisement message is used as
   specified in section "10.4.1.  Intercepting Packets for a Mobile
   Node" with one exception that the override (O) bit is not set,
   indicating that this Backbone Router acts as a proxy for the LoWPAN
   and will yield should another Backbone Router claim that address on
   the Transit Link.  This enables the LoWPAN node to join a different
   Backbone Router at any time without the complexities of terminating a
   current binding.

   This specification also introduces the concept of secondary binding.
   Upon a secondary binding, the Backbone Router will not announce or
   defend the address on the transit link, but will be able to forward
   packets to the node over its LoWPAN interface.  For other addresses,
   the rules in [RFC3775] apply for compatibility.

6.3.  Looking up neighbor addresses

   A Backbone Router knows and proxies for all the IPv6 addresses that
   are registered to it.  When resolving a target address, the Backbone
   Router first considers its binding cache.  If this address is in the
   cache, then the target is reachable over the LoWPAN as indicated in
   the cache.  Else, the Backbone Router locates the target over the
   transit link using standard "Neighbor Discovery" [RFC4861] over that
   link.




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   If the target is located over a LoWPAN owned by another Backbone
   Router, then that other Backbone Router is in charge of answering the
   Neighbor Solicitation on behalf of the target node.

6.4.  Answering address look up

   To enable proxying over the Transit Link, a Backbone Router must join
   the solicited-node multicast address on that link for all the
   registered addresses of the nodes in its LoWPANs.  The Backbone
   Router answers the Neighbor Solicitation with a Neighbor
   Advertisement that indicates its own link-layer address in the Target
   link-layer address option.

   A Backbone Router expects and answers unicast Neighbor Solicitations
   for all nodes in its LoWPANs.  It answers as a proxy for the real
   target.  The target link-layer address in the response is either that
   of the destination if a short cut is possible over the LoWPAN, or
   that of the Backbone Router if the destination is reachable over the
   Transit Link, in which case the Backbone Router will terminate
   6LoWPAN and relay the packet.

6.5.  Forwarding packets

   Upon receiving packets on one of its LoWPAN interfaces, the Backbone
   Router checks whether it has a binding for the source address.  If it
   does, then the Backbone Router can forward the packet to another
   LoWPAN node or over the Transit link.  Otherwise, the Backbone Router
   MUST discard the packet.  If the packet is to be transmitted over the
   Transit link, then the 6LoWPAN sublayer is terminated and the full
   IPv6 packet is uncompressed and reassembled.

   When forwarding a packet from the Transit Link towards a LOwPAN
   interface, the Backbone Router performs the 6LoWPAN sublayer
   operations of compression and fragmentation and passes the packet to
   the lower layer for transmission.


7.  Security Considerations

   This specification expects that the link layer is sufficiently
   protected, either by means of physical or IP security for the Transit
   Link or MAC sublayer cryptography.  In particular, it is expected
   that the LoWPAN MAC provides secure unicast to/from the Backbone
   Router and secure broadcast from the Backbone Router in a way that
   prevents tempering with or replaying the RA messages.

   The use of EUI-64 for forming the Interface ID in the link local
   address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and



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   address privacy techniques.  Considering the envisioned deployments
   and the MAC layer security applied, this is not considered an issue
   at this time.


8.  IANA Considerations

   Need new NS/NA option numbers for the binding flow.


9.  Acknowledgments

   The author wishes to thank Geoff Mulligan for his help and in-depth
   review.


10.  References

10.1.  Normative References

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, April 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.






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10.2.  Informative References

   [I-D.van-beijnum-multi-mtu]
              Beijnum, I., "Extensions for Multi-MTU Subnets",
              draft-van-beijnum-multi-mtu-02 (work in progress),
              February 2008.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, August 2007.


Author's Address

   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410
   FRANCE

   Phone: +33 4 97 23 26 34
   Email: pthubert@cisco.com

















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