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Versions: (draft-shelby-6lowpan-nd) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 RFC 6775

6lowpan Working Group                                     Z. Shelby, Ed.
Internet-Draft                                                 Sensinode
Updates: 4944 (if approved)                                   P. Thubert
Intended status: Standards Track                                   Cisco
Expires: August 5, 2010                                           J. Hui
                                                               Arch Rock
                                                          S. Chakrabarti
                                                             IP Infusion
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                             E. Nordmark
                                                                     Sun
                                                        February 1, 2010


                       6LoWPAN Neighbor Discovery
                        draft-ietf-6lowpan-nd-08

Abstract

   This document specifies a new Neighbor Discovery mechanism suitable
   for LoWPANs.  The 6LoWPAN format allows IPv6 to be used over energy
   and bandwidth constrained wireless networks often making use of
   multihop topologies.  However, the use of classic IPv6 Neighbor
   Discovery with 6LoWPAN has several problems.  Classic Neighbor
   Discovery was not designed for non-transitive wireless links, and the
   traditional IPv6 link concept and heavy use of multicast makes it
   unpractical.  This document specifies a simple Neighbor Discovery
   mechanism both sufficient yet minimal for LoWPAN operation.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.




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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 5, 2010.

Copyright Notice

   Copyright (c) 2010 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
   (http://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 BSD License.
































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Goals, Assumptions, and Guesses  . . . . . . . . . . . . .  5
     1.2.  Why not classic IPv6 ND? . . . . . . . . . . . . . . . . .  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.1.  6LoWPAN Terminology  . . . . . . . . . . . . . . . . . . .  7
     2.2.  ND Terminology . . . . . . . . . . . . . . . . . . . . . .  9
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  Topology . . . . . . . . . . . . . . . . . . . . . . . . . 11
     3.2.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 12
     3.3.  Operation  . . . . . . . . . . . . . . . . . . . . . . . . 13
   4.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Node Registration/Confirmation Message . . . . . . . . . . 14
     4.2.  Router Solicitation Message  . . . . . . . . . . . . . . . 16
     4.3.  Router Advertisement Message . . . . . . . . . . . . . . . 17
     4.4.  Message Options  . . . . . . . . . . . . . . . . . . . . . 18
       4.4.1.  6LoWPAN Address Option . . . . . . . . . . . . . . . . 18
       4.4.2.  6LoWPAN Information Option . . . . . . . . . . . . . . 19
       4.4.3.  6LoWPAN Summary Option . . . . . . . . . . . . . . . . 21
       4.4.4.  Owner Interface Identifier Option  . . . . . . . . . . 22
   5.  Protocol Specification . . . . . . . . . . . . . . . . . . . . 23
     5.1.  Interface initialization . . . . . . . . . . . . . . . . . 23
     5.2.  Node Registration  . . . . . . . . . . . . . . . . . . . . 24
       5.2.1.  Processing a Node Registration Message . . . . . . . . 25
       5.2.2.  Processing a Node Confirmation Message . . . . . . . . 25
     5.3.  Duplicate Address Detection  . . . . . . . . . . . . . . . 26
     5.4.  Next-hop Determination . . . . . . . . . . . . . . . . . . 27
     5.5.  Address Resolution . . . . . . . . . . . . . . . . . . . . 27
     5.6.  Unreachability Detection . . . . . . . . . . . . . . . . . 28
     5.7.  Context Dissemination  . . . . . . . . . . . . . . . . . . 28
   6.  LoWPAN Node Specification  . . . . . . . . . . . . . . . . . . 29
     6.1.  Conceptual structures  . . . . . . . . . . . . . . . . . . 29
     6.2.  Conceptual variables . . . . . . . . . . . . . . . . . . . 30
   7.  LoWPAN Router Specification  . . . . . . . . . . . . . . . . . 30
     7.1.  Router Configuration Variables . . . . . . . . . . . . . . 30
     7.2.  Becoming an Advertising Interface  . . . . . . . . . . . . 30
     7.3.  Router Advertisement Message Content . . . . . . . . . . . 31
     7.4.  Sending Unsolicited Router Advertisements  . . . . . . . . 32
     7.5.  Ceasing To Be an Advertising Interface . . . . . . . . . . 32
     7.6.  Processing Router Solicitations  . . . . . . . . . . . . . 32
     7.7.  Binding Table  . . . . . . . . . . . . . . . . . . . . . . 32
   8.  Ad-hoc LoWPAN  . . . . . . . . . . . . . . . . . . . . . . . . 32
   9.  Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 33
   10. Use of 6LoWPAN-ND under RFC4861-only stacks  . . . . . . . . . 34
   11. Message Examples . . . . . . . . . . . . . . . . . . . . . . . 34
     11.1. NR/NC message exchange . . . . . . . . . . . . . . . . . . 34
     11.2. Router advertisement . . . . . . . . . . . . . . . . . . . 36



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   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 37
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 38
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 38
   15. Changelog  . . . . . . . . . . . . . . . . . . . . . . . . . . 38
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 42
     16.2. Informative References . . . . . . . . . . . . . . . . . . 43
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44











































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1.  Introduction

   The IPv6 over IEEE 802.15.4 [RFC4944] document has specified how to
   carry IPv6 packets over IEEE 802.15.4 and similar networks (6LoWPANs
   or LoWPANs for short) with the help of an adaptation header which
   comes before the IP header.  A link in such a 6LoWPAN is
   characterized as lossy, low-power, low bit-rate, short range, with
   many nodes saving energy with long deep sleep periods.  Multicast as
   used in classic IPv6 Neighbor Discovery [RFC4861] is not desirable in
   such a wireless low-power, lossy network.

   Moreover, LoWPAN links are asymmetric and non-transient in nature;
   they are not always considered to be in a fixed network nor are they
   bounded by our traditional definition of a wired-link.  A LoWPAN is
   potentially composed of a large amount of overlapping radio ranges,
   eventually federated by a backbone or a backhaul link.  Although a
   given radio range has broadcast capabilities, the aggregation of
   these is a complex Non-Broadcast MultiAccess (NBMA, [RFC2491])
   structure with (generally) no LoWPAN-wide multicast capabilities.
   link-local scope is in reality defined by reachability and radio
   strength.  Thus we can consider a LoWPAN to be made up of links with
   undetermined connectivity properties as defined in
   [I-D.ietf-autoconf-adhoc-addr-model], along with the corresponding
   assumptions defined therein.  The classic IPv6 Neighbor Discovery
   [RFC4861] control messages, the use of multicast and their default
   frequency also attribute to unnecessary waste of energy in LoWPANs.

   This specification introduces a new mechanism called Node
   Registration, used to optimize the interface between hosts and
   routers in a LoWPAN.  That registration mechanism provides a service
   somewhat similar to the Multicast Address Resolution Server (MARS)
   [RFC2022] for a limited purpose, and in a much simpler and less
   generic fashion.  The use of Router Advertisements to disseminate
   prefix and header compression context throughout the LoWPAN is also
   specified.  The solution supports the use of both link-layer- or
   LoWPAN-level mesh (Mesh Under) and IP routing (Route Over) solutions
   for multihop forwarding.  This specification is both sufficient and
   required for LoWPAN operation.  The 6LoWPAN-ND mechanism could also
   coexist with [RFC4861], [RFC3122] or other future ND mechanisms
   (although the motivation or detailed specification of such
   coexistence is out of scope for the present document).

   The document defines two new ICMPv6 messages: Node Registration and
   Node Confirmation.







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1.1.  Goals, Assumptions, and Guesses

   This document has the following main goals and assumptions, as well
   as two guesses that may or may not be true in a specific LoWPAN but
   still have shaped the optimizations.

   Goals:

   o  Optimize ND with a mechanism that is minimal yet sufficient for
      LoWPAN operation in both mesh-under and route-over configurations.

   o  Minimize signalling by avoiding the use of multicast flooding and
      reducing the frequency of link scope multicast messages inside the
      LoWPANs.

   o  Disseminate context information throughout the LoWPAN used by
      [I-D.ietf-6lowpan-hc].

   o  Minimize the complexity of LoWPAN Nodes.

   o  Optimize the interfaces between nodes and their default routers.

   Assumptions:

   o  A subnet includes all the LoWPAN Nodes sharing the same IPv6
      prefix.

   o  A single LoWPAN is configured in a homogeneous way, i.e., IIDs are
      formed by nodes in a uniform matter and DAD is performed by
      routers in a uniform way.

   o  Link layer technology is e.g.  IEEE 802.15.4 as in [RFC4944], or
      any other link-layer exhibiting non-transitivity or a similar
      topology.

1.2.  Why not classic IPv6 ND?

   IPv6 Neighbor Discovery [RFC4861] provides several important
   functions such as Router Discovery, Address Resolution, Duplicate
   Address Detection, Redirect, Prefix and Parameter Discovery.

   Following power-on and initialization of the network in IPv6 Ethernet
   networks, a node joins the solicited-node multicast address on the
   interface and then performs duplicate address detection (DAD) for the
   acquired link-local address by sending a solicited-node multicast
   message to the link.  After that it sends multicast messages to the
   all-router address to solicit router advertisements.  Once the host
   receives a valid router advertisement with the "A" flag, it



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   autoconfigures the IPv6 address with the advertised prefix in the
   router advertisement (RA).  Besides this, the IPv6 routers usually
   send router advertisements periodically on the network.  RAs are sent
   to the all-node multicast address.  Nodes send Neighbor Solicitation/
   Neighbor Advertisement messages to resolve the IPv6 address of the
   destination on the link.  These NS/NA messages are also often
   multicast messages and it is assumed that the node is on the same
   link and relies on the fact that the destination node is always
   powered and generally reliable.

   A LoWPAN network typically uses two types of L2 addresses -- for
   example 16-bit short addresses and 64-bit unique addresses as defined
   in [RFC4944].  Moreover, the available L2 payload size on the order
   of less than 100 bytes where we often might need to use header
   compression and use a minimum payload.  The network is lossy and low-
   powered, and it does not provide multicast capability at the link-
   layer, thus simulating multicast behavior by both using broadcast or
   sending a number of unicast messages, both expensive for the low-
   powered network and the low-processing capable nodes.  Often these
   low-powered nodes conserve energy by using sleep schedules; waking
   them up to receive IPv6 signaling messages such as multicast messages
   for NS or periodic RAs is not practical.  Also they are not capable
   of processing address-resolution for their neighbors effectively.
   Due to the radio strength of its neighboring router or its own
   strength, a node may often move from one router to another without
   physically moving from one place to another.  Considering the above
   characteristics in a LoWPAN, and the IPv6 Neighbor Discovery
   [RFC4861] base protocol requirements, it was concluded that classic
   Neighbor Discovery is not suitable as it is and a 6LoWPAN-specific ND
   definition would be useful and efficient for the wide deployment of
   IPv6 over low-powered wireless networks of embedded devices.


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].

   This specification requires readers to be familiar with all the terms
   and concepts that are discussed in "IPv6 Stateless Address
   Autoconfiguration" [RFC4862], "IPv6 over Low-Power Wireless Personal
   Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement,
   and Goals" [RFC4919], "Transmission of IPv6 Packets over IEEE
   802.15.4 Networks" [RFC4944] and "IP Addressing Model in Ad Hoc
   Networks" [I-D.ietf-autoconf-adhoc-addr-model].

   Readers would benefit from reading "Optimistic Duplicate Address



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   Detection" [RFC4429] ("oDAD") prior to this specification.

   This specification makes extensive use of the same terminology
   defined in [RFC4861] unless otherwise redefined below.

2.1.  6LoWPAN Terminology

   This section defines additional general terms related to the 6LoWPAN
   architecture used in this specification:

   IP Routing

      The forwarding of datagrams at the IP layer between arbitrary
      source-destination pairs, during which the IPv6 hop limit is
      decremented.  In the LoWPAN context, IP routing is performed by
      LoWPAN Routers on a single interface within the same subnet.
      Exact match search is performed on the destination address of the
      IP packet to find the next-hop to the destination.  Referred to as
      routing in this document.

   Link

      The link is a communication facility or medium over which nodes
      can communicate at the link-layer, i.e., the layer directly below
      IP ([RFC4861]). 6LoWPAN assumes the use of low-power and lossy
      wireless links such as IEEE 802.15.4, which is a special type of
      link as described in [RFC4861] exhibiting severe asymmetric
      reachability with both asymmetric (A can reach B, but B can't
      reach A) and non-transitive (A can reach B, and B can reach C, but
      A can't reach C) qualities.  The use of link-layer mesh technology
      (see Mesh Under) emulates transitivity across the link but still
      has problems with asymmetricity.  Multicast on a link-layer mesh,
      if available, is often implemented as an expensive broadcast
      flood.  Due to their nature, these are considered links with
      undetermined connectivity properties as defined in
      [I-D.ietf-autoconf-adhoc-addr-model].

   Link-local

      Standard IPv6 link-local scope is defined in [RFC4291] and
      [RFC4861].  Link-local scope is achieved by setting the hop limit
      to 1, using a link-local prefix (FE80::) or link-local multicast
      scope (FFx2::).  If a link is non-transitive then link-local scope
      may include only a subset of nodes on the link (the set of nodes
      within symmetric radio range of a node).  Nodes in the link-local
      scope of a node are its neighbors, and this link-local scope may
      differ from the perspective of each node.  Therefore, link-local
      addresses are of limited value as discussed in



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      [I-D.ietf-autoconf-adhoc-addr-model].

   LoWPAN Host

      A node that only sources or sinks IPv6 datagrams.  Referred to as
      a host in this document.

   LoWPAN Node

      A node that composes a LoWPAN, referring to both hosts and
      routers.  Simply called a node in this document.

   LoWPAN Router

      A LoWPAN node that forwards datagrams between arbitrary source-
      destination pairs using a single 6LoWPAN interface performing IP
      routing on that interface.

   LoWPAN Mesh node

      A LoWPAN node that forwards data between arbitrary source-
      destination pairs using link addresses (and thus only exists in
      Mesh Under LoWPANs).

   Mesh Under

      A term referring to a configuration where the link-local scope is
      defined by the boundaries of the LoWPAN (or a sizable part of it,
      if Mesh Under is combined with Route Over) and includes all the
      6LoWPAN interfaces within it.  There are forwarding and multihop
      routing functions at L2 to achieve transitivity on the link.  In
      this configuration the link may still exhibit lossy, asymmetric,
      NBMA (non-availability of mesh-wide multicast) behavior.

   Route Over

      A term referring to a configuration where the LoWPAN is made up of
      several partially overlapping links and link-local scope reaches
      only a subset of the LoWPAN nodes.  IP routing is performed by
      LoWPAN Routers to provide connectivity across the LoWPAN.  A
      LoWPAN with this configuration may consist of both routers and
      hosts.  Route Over and Mesh Under are not mutually exclusive, and
      IP routing may be used between links that perform Mesh Under.

   Subnet






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      A subnet is the collection of interfaces having the same IPv6
      subnet prefix on a link, as defined in [RFC4291].  A LoWPAN is
      made up of the interfaces of LoWPAN Nodes and Edge Routers sharing
      the same subnet prefix.  This Route Over configuration exhibits a
      multi-hop subnet feature with regard to hop limit as discussed in
      [RFC4903], and thus 6LoWPAN applications should be careful when
      making assumptions about the hop limit as it may be decremented in
      a LoWPAN.

2.2.  ND Terminology

   This section defines Neighbor Discovery specific terminology used in
   this specification:

   Simple LoWPAN

      A Simple LoWPAN consists of a single Edge Router and the set of
      LoWPAN nodes on the same LoWPAN Subnet, shown in Figure 1.

   Ad-hoc LoWPAN

      An isolated LoWPAN, not connected to any other IP networks.  Ad-
      Hoc LoWPANs make use of Unique on-link IPv6 Unicast Addresses
      (ULAs) [RFC4193].

   Backbone Link

      This is an IPv6 link that interconnects two or more edge routers
      in an Extended LoWPAN topology.  It is expected to be deployed as
      a high speed backbone in order to federate a potentially large set
      of LoWPANs.

   LoWPAN Edge Router

      An IPv6 router that interconnects the LoWPAN to another IP
      network.  Referred to as an Edge Router in this document.

   Registration

      The process during which a LoWPAN node sends a Node Registration
      message to a Router creating a binding for the LoWPAN node.










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          Infrastructure Cloud
                   |
                   |
                   |
                +-----+
                |     | Edge
                |     | router
                +-----+
                  o  o
               o   o    o
             o  o   o  o o        o: LoWPAN Node
              o   o  o  o
                o   o o

             Simple LoWPAN


                    Figure 1: A simple LoWPAN topology


3.  Protocol Overview

   6LoWPAN Neighbor Discovery (6LoWPAN-ND) optimizes IPv6 ND with a
   mechanism which is on its own minimal yet sufficient for LoWPAN IPv6
   operation. 6LoWPAN-ND defines a node registration mechanism
   optimizing the node-router interface.  This mechanism requires no
   flooding and reduces link-local multicast frequency. 6LoWPAN-ND
   supports non-transitive links, the use of both mesh-under and route-
   over techniques and makes no assumptions about synchronization
   between hosts using the same router.  This specification is REQUIRED
   for LoWPAN operation, but MAY also coexist with [RFC4861], [RFC3122]
   or other future ND mechanisms.  Any use of [RFC4944] without this
   specification is NOT RECOMMENDED.

   The following features are defined by 6LoWPAN-ND (see Section
   Section 5 for details):

   Node Registration:  Method in which nodes in the LoWPAN register with
      Routers, creating state about nodes attached to that router
      (binding table).

   Next-hop Determination:  The specification defines a simple next-hop
      determination rule.

   Address Resolution:  The Node Registration mechanism provides
      sufficient a priori state in nodes and routers to resolve an IPv6
      address to its associated link-layer address on the node-router
      interface.  Host-host resolution is out of scope of this



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      specification.

   Unreachability Detection:  Unreachability between a node and router
      is determined based on link-layer acknowledgements to node
      registration and unicast data messages.  Host-host unreachability
      detection is out of scope.  Destination unreachability detection
      is performed using ICMPv6 destination unreachable messages.

   Context Dissemination:  The dissemination of LoWPAN context as used
      by [I-D.ietf-6lowpan-hc] is defined as an ICMPv6 option, along
      with an associated summary option to reduce message size when many
      contexts are advertised.

   This specification makes use of RS/RA message exchanges similar to
   classic ND, which in 6LoWPAN-ND may also carry additional options for
   context dissemination (6LoWPAN Information Option, 6IO) and reducing
   RA message size (6LoWPAN Summary Option, 6SO).  In addition
   6LoWPAN-ND defines two new ICMP packet types:

   Node Registration (NR):  Sent by a node to a Router to register a
      binding.

   Node Confirmation (NC):  The response sent by a Router back to the
      registering node.

3.1.  Topology

   6LoWPAN-ND makes little assumption about synchronization between
   nodes in a LoWPAN except between a node and the routers it has
   registered with. 6LoWPAN-ND is designed to work also with Ad-hoc
   topologies.  The case of Ad-hoc LoWPAN operation is described in
   Section 8.

   6LoWPAN-ND is compatible with the use of link-layer mesh or [RFC4944]
   mesh techniques, which alleviate the otherwise non-transitive nature
   of wireless links.  If used throughout the LoWPAN, this so-called
   Mesh Under topology thus makes the entire link appear to the IP layer
   as having a link-local scope covering all the 6LoWPAN interfaces in
   the LoWPAN.  This kind of LoWPAN is made up of hosts and Edge
   Routers.  This link still exhibits lossy, low-rate, asymmetric
   behavior along with sleep cycles.  The non-transitive nature of the
   link can also be overcome using IP routing within the LoWPAN, also
   called a Route Over topology.  LoWPAN Routers are used in the LoWPAN
   to provide routing between all nodes in the LoWPAN.  LoWPAN Router
   operations are specified in Section 7. link-local scope includes the
   neighbors of each node within symmetric wireless range.  Mesh Under
   and Route Over techniques are not mutually exclusive, and it may be
   possible to combine IP routing and mesh link-layers within a LoWPAN.



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3.2.  Bootstrapping

   1.  A node (host or router) first forms an Interface Identifier (IID)
   from its EUI-64 or other appropriate MAC address, and goes on to form
   a link-local unicast address as in [RFC4944].  When a LoWPAN Node
   wants to join a LoWPAN, it does so by listening for Router
   Advertisements, or by broadcasting a Router Solicitation (RS) and
   receiving RA responses from on-link routers (see Figure 2).  If a
   valid prefix is advertised in the RA, the host may also autoconfigure
   a global address.  At this point the node has also chosen one or more
   default routers based on RAs.

   2.  Next the node will attempt to perform initial Node Registration.
   Registration is always performed with a link-local Router by sending
   a unicast Node Registration (NR) message to it.  This message
   exchange is illustrated in Figure 3.  The NR includes the addresses
   the node wants to register, and it is possible to request the router
   to assign an address.

   3.  After processing the addresses and performing DAD if necessary,
   the Router replies with a Node Confirmation (NC).  This confirmation
   includes the set of addresses now confirmed by this router.  The Host
   is now capable of using the LoWPAN.


   Node                                                     Router
    |                                                          |
    |       ---------- Router Solicitation -------->           |
    |                                                          |
    |       <-------- Router Advertisement ---------           |
    |                                                          |


   Figure 2: Basic RS/RA exchange between a node and any on-link router
                      (LoWPAN Router or Edge Router)



   Node                                                      Router
    |                                                          |
    |       ---------- Node Registration -------->             |
    |                                                          |
    |       <--------- Node Confirmation ---------             |
    |                                                          |


                 Figure 3: Basic ND registration exchange




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3.3.  Operation

   The node may now send packets to any IPv6 address inside or outside
   the LoWPAN.  Next-hop determination assumes destinations are off-link
   (and thus forwarded to a default router) except for link-local scope
   addresses which are always on-link.  The information needed for
   resolving the link-layer address of default routers or registered
   nodes is known a priori as a result of node registration.

   The LoWPAN Router binding table is soft, and thus must be renewed
   periodically as indicated by the lifetime of the binding.  This is
   achieved by periodically sending a new NR message.  If a host moves,
   or the network topology changes, and the current routers are no
   longer available, the host then starts the registration process with
   another router.  If the host is still in the same LoWPAN (same subnet
   prefix), its IPv6 addresses remain the same.  If the host moves to a
   different LoWPAN (thus with a different subnet prefix), the
   bootstrapping process is initiated again.  See Section 6 for details
   on node operation.

   LoWPAN Routers periodically send RAs to their neighbors.  The Edge
   Router initiates the first RAs, and information from these RAs is
   included in the RAs of each further router, causing the information
   to be disseminated throughout the LoWPAN.  RA periods should be
   optimized to reduce signalling.  See Section 7 for detailed router
   operation.


4.  Message Formats

   This section defines the message and option formats used in this
   document.  The new messages are all ICMPv6 messages.  In addition,
   new options for ICMPv6 messages are defined.

   The following new ICMPv6 message types are defined:

   o  Node Registration (NR)

   o  Node Confirmation (NC)

   In addition, the following new ICMPv6 options are defined:

   o  6LoWPAN Address Option (6AO)

   o  6LoWPAN Information Option (6IO)

   o  6LoWPAN Summary Option (6SO)




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   o  Owner Interface Identifier Option (OIIO)

   The following [RFC4861] messages are used as specified in this
   section:

   o  Router Solicitation (RS)

   o  Router Advertisement (RA)

4.1.  Node Registration/Confirmation Message

   The Node Registration (NR) and Node Confirmation (NC) messages are
   used by a node to register with a Router.  Any option that is not
   recognized MUST be skipped silently.  The Node Registration message
   is sent by the LoWPAN Node to the link-local unicast IPv6 address of
   a on-link Router.

   When registering the first time the (which then still has optimistic
   addresses) source address of the Node Registration must be the IPv6
   unspecified address to comply with oDAD.  In subsequent
   registrations, the IPv6 source address is then the link-local IPv6
   address of the sender.  A registration is periodically refreshed by
   sending a new NR message more frequently than the Binding Lifetime
   indicated by the node during registraion.

   Address Options are included in the NR message for each IPv6 address
   to be registered, and included in the corresponding NC to indicate
   success.

    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      |Status | Code  |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      TID      |P|R|                Reserved                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Binding Lifetime       |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Owner Nonce                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Owner Interface Identifier                   +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Registration option(s)...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 4: Node Registration/Confirmation message format



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   IP Fields:

      Source Address:  The IPv6 address of the source.  This address
         MUST be the IPv6 unspecified address for initial registration.

      Destination Address:  The link-local unicast IPv6 address of a on-
         link router when sent by a node.

      Hop Limit:  255

   ICMP Fields:

      Type:  TBD1 for Node Registration, TBD2 for Node Confirmation.

      Status:  4-bit unsigned integer.  Sent only in NC messages,
         ignored in NR messages.  Values 0-7 are reserved for success
         codes:

            0 is unqualified success.

         Values 8-15 are reserved for error codes:

            8 is send to indicate that the router is saturated and an
            alternative router should be used.

      Code:  4-bit unsigned integer.

            0 indicates this NR is a request sent directly from the
            originating host, or this NC is a corresponding response.

            1 indicates that the NR message has been relayed by a
            router, or that the NC is to be relayed by the router
            indicated as the destination.  (For future use)

            2 indicates this NC is a request for the node to re-
            register.

            4-15 are reserved for future use.

      Checksum:  The ICMP checksum.

      TID:  8-bit unsigned integer.  A unique Transaction ID assigned by
         the host and used to match replies.  A lollipop mechanism is
         used to increment the TID upon each new registration.  The TID
         is not incremented upon a on-link refresh.  In a Node
         Confirmation TID is that of the corresponding NR.  TID is set
         to 0 upon booting, and is incremented with each NR message.
         After reaching 0xFF, the value loops to 16 (0x10) and is



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         incremented from there.  Thus the values between 0-15 MUST only
         used after a boot or reboot.

      P: 1-bit Primary flag.  Not yet used by this specification, always
         set to 1.

      R: 1-bit Router flag.  Used to indicate the role of node sending
         the NR message.  Set to 0 by hosts and to 1 by routers.

      Binding Lifetime:  16-bit unsigned integer.  The amount of time in
         10 second intervals remaining before the binding of this owner
         interface identifier, and all associated address options and
         configuration options, MUST be considered expired.  A value of
         zero indicates that the Binding Cache entries for the
         registered owner interface identifier MUST be deleted.  A value
         of 0xFFFF indicates an idefinite lifetime.  (The 16-bit field
         covers up to slightly more than a week of Binding Lifetime.)

      Reserved:  This field is unused.  It MUST be initialized to zero
         by the sender and MUST be ignored by the receiver.

      Owner Interface Identifier (OII):  A globally unique identifier
         for the requesting host's interface.  Typically the EUI-64
         derived IID.

      Owner Nonce:  A 32-bit Nonce generated randomly by the node upon
         booting, and generated again each time the node re-boots.  This
         Nonce may be used to detect duplicate OIIs.

   Possible Options:

      6LoWPAN Address Option(s):  An Address Option is included for each
         address the host wants to bind for this interface.

      6LoWPAN Information Option:  This option includes information
         about the prefixes of the LoWPAN along with other context
         information.  Although normally carried in RA messages, a 6IO
         option MAY also be carried in NC messages.

      Future versions of this protocol may define new option types.
      Receivers MUST silently ignore any options they do not recognize
      and continue processing the message.

4.2.  Router Solicitation Message

   The RS message format for 6LoWPAN is identical to the classic
   [RFC4861] RS message.  The following clarifications are made
   regarding the use of RS in LoWPANs.



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   If a node has only optimistic addresses, not yet confirmed by a
   Router, then the IPv6 source address in the RS MUST be the IPv6
   unspecified address.  The Source Link-Layer Address Option MUST NOT
   be included in the RS at any time.  Instead the Owner Interface
   Identifier specified in this document MUST be included in the RS.

   The Code field of the Router Solicitation message is used to
   inidicate whether a node wants to receive the full set of 6IOs in the
   RA response, or just the 6SO.  An RS with Code = 0 is used to request
   just the 6LoWPAN Summary Option, and Code = 1 is used to request the
   full set of 6IOs.

4.3.  Router Advertisement Message

   The RA message format for 6LoWPAN is identical to the classic
   [RFC4861] RA message.  The use of flags is however defined in the
   6LoWPAN context, and additional new options are identified.  RA
   messages are sent either to link-local all-nodes multicast, or to a
   link-local unicast address as a response to an RS.

   Updated Flag Definitions:

      Prf:  2-bit signed integer.  Default Router Preference as defined
         in [RFC4191].  Indicates whether to prefer this router over
         other default routers.  LoWPAN Routers with no ER available
         MUST set Prf to (11) for low preference, LoWPAN Routers with ER
         availability MUST set Prf to (00) for normal preference, and
         LoWPAN Edge Routers MUST set Prf to (01) for high preference.

   Options:

      6LoWPAN Information Option:  This option includes information
         about the prefixes of the LoWPAN along with other context
         information.

      6LoWPAN Summary Option:  This option provides a sequence number
         associated with the current prefix options.  It allows the
         prefix options themselves to be sent only when a change has
         occured, or when requested with an RS Code = 1.

      Prefix Information Option:  If needed for backward compatibility,
         an RA may also be sent using the classic [RFC4861] Prefix
         Information Option which all LoWPAN nodes MUST be able to
         parse.  If possible, routers in the LoWPAN SHOULD make use of
         6IO and 6SO options instead of PIO.

      The MTU and SLLAO options defined in [RFC4861] are not used by
      this specification.



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      Future versions of this protocol may define new option types.
      Receivers MUST silently ignore any options they do not recognize
      and continue processing the message.

4.4.  Message Options

   This section defines the new 6LoWPAN-ND message options.

4.4.1.  6LoWPAN Address Option

   The 6LoWPAN Address Option (6AO) is used to indicate the address
   which a node wants to register, and to indicate the success or
   failure of that binding in an NC.  Multiple Address Options can be
   included in a message.  In order to be as compact as possible, fields
   are used to indicate the compression of the IPv6 address.  The 6AO
   also allows for duplicate addresses (e.g. anycasts), the request of a
   generated address for claim and defend use, or for an address to be
   removed.

    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     |  S  |    P    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |D|A|R|O|      Reserved         |         IPv6 Address        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                  Figure 5: 6LoWPAN Address Option format

   Type:  TBD3

   Length:  8-bit unsigned integer.  The length of the option (including
      the type and length fields) in units of 8 octets.

   Status:  8-bit unsigned integer. 0 means unqualified success.  Any
      value below 128 is a positive status that means that the binding
      for this address was created or is being created optimistically.
      Only used in a confirmation.

   D: 1-bit Duplicate flag.  When set, indicates that duplicates are
      allowed for this address (to support anycast) in a request.

   A: 1-bit Address Generation flag.  Set to indicate that the host is
      requesting a generated address for claim and defend addressing.
      In a request when A is set the IPv6 address length is 0.  Set to
      indicate that an address has been assigned in a confirmation.  P
      and S are set to indicate the type of address requested and



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      assigned when A is set.  Otherwise must be 0.

   R: 1-bit Removal flag.  When set, indicates that this particular
      address binding MUST be removed from a whiteboard (in a request)
      or MUST not be used any longer (in a confirmation).

   O: 1-bit Optimistic flag.  When set, indicates that this particular
      address is optimistic and has not yet been checked for duplicates.

   P: 5-bit unsigned integer.  Identifies prefix compression or type, if
      any.

      0-15:  Prefix compressed; upon decompression, the prefix given by
         the compression context with the same numerical CID as the P
         field given is inserted.

      16:  Prefix is carried inline.

      17:  Prefix compressed; upon decompression, the link-local prefix
         (fe80::) is inserted.

      18-31:  Reserved.

   S: 3-bit unsigned integer.  Identifies suffix compression or type, if
      any.

      0: Suffix carried inline.

      1: Suffix compressed and assumes the same value as the Owner
         Interface Identifier field in the NR/NC message header.

      2: Suffix compressed for an IID formed from an IEEE 802.15.4 16-
         bit short addresses.  Only the 16-bit short-address is carried
         in-line.  The IID is formed from this address as specified in
         [RFC4944].

      3-7:  Reserved.

   IPv6 Address:  The IPv6 address to be registered with the ER, or
      confirmed by the ER.  Parts of the address may be elided as per
      the P and S fields.

4.4.2.  6LoWPAN Information Option

   This option carries prefix information for LoWPANs, and is similar in
   use to the Prefix Information Option of [RFC4861].  However this
   option allows for the dissemination of multiple contexts identified
   by a Context Identifier (CID) for use in 6LoWPAN address compression.



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    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    |  Info Length  |L|A|C|V|  CID  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Valid Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                 Prefix or Address Information                 .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 6: 6LoWPAN Information Option format

   Type:  TBD4

   Length:  8-bit unsigned integer.  The length of the option (including
      the type and length fields) in units of 8 octets.  May be 1, 2 or
      3 depending on the length of the Information field.

   Info Length:  8-bit unsigned integer.  The number of leading bits in
      the Information field that are valid.  The value ranges from 0 to
      128.  The info length field provides necessary information for on-
      link determination (when combined with the L flag in the prefix
      information option).  It also assists with address
      autoconfiguration as specified in [RFC4862], for which there may
      be more restrictions on the info length.

   L: 1-bit on-link flag, similar to the L flag in [RFC4861].  This flag
      MUST be unset for Route Over LoWPANs and Extended LoWPANs, and MAY
      be set for Mesh Under Simple LoWPANs.

   A: 1-bit autonomous address-configuration flag.  When set indicates
      that this prefix can be used for stateless address configuration
      as specified in [RFC4861].

   C: 1-bit context flag.  This flag indicates that this information
      option also serves as a context on the LoWPAN, which is identified
      by the CID field.

   V: 1-bit context validity flag.  This flag indicates if the context
      is valid, and is used only in combination with the C flag.  A
      context that is not valid MUST not be used for compression, but
      MAY be used in decompression in case another compressor still
      considers the context as valid.






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   CID:  4-bit Context Identifier for this prefix information.  CID is
      used by context based header compression specified in
      [I-D.ietf-6lowpan-hc].  The list of CIDs for a LoWPAN is
      configured on Edge Routers, who distribute the prefix list to all
      nodes in the LoWPAN.

   Valid Lifetime:  32-bit unsigned integer.  The length of time in
      seconds (relative to the time the packet is sent) that the prefix
      is valid for the purpose of on-link determination.  A value of all
      one bits (0xffffffff) represents infinity.

   Information:  The IPv6 prefix or context information indicated.  This
      may be a partial prefix, a partial context or even an entire IPv6
      address for use as a context for compression.

4.4.3.  6LoWPAN Summary Option

   This option identifies the set of prefix information options by a
   sequence number.  This allows for the full set of prefix information
   options to be sent only periodically in unsolicited RAs.  If a host
   detects a difference in the sequence number of this option, then the
   prefix information has likely changed, and is then requested with an
   RS.  An RA sent in response to a unicast RS always includes the full
   set of prefix information.

    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 Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V|          Reserved           |           ER Metric           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 7: 6LoWPAN Summary Option

   Type:  TBD5

   Length:  1

   Sequence Number:  16-bit signed integer.  Indicates the freshness of
      the information advertised by the RA.

   ER Metric:  16-bit unsigned integer.  The ER Metric gives an
      indication of the cost (in routing metric terms) of reaching nodes
      outside the LoWPAN via an ER through this router.  The metric
      SHOULD be derived in a well-defined way from the routing protocol
      used in the LoWPAN (possibly by structuring the 16 bits available
      e.g. into a major and a minor metric), and has a mid-range default



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      value of 0x8000.  Edge Routers most likely set this field to 0.  A
      host SHOULD take this metric into account when choosing default
      routers by making a scalar comparison, preferring routers with
      numerically lower ER Metric values.

   V: 1-bit flag.  Indicates if the sequence number is valid and the
      router is advertising information obtained from another router.

   Reserved:  This field is unused.  It MUST be initialized to zero by
      the sender and MUST be ignored by the receiver.

4.4.4.  Owner Interface Identifier Option

   This option is used together with Router Solicitation messages when a
   node has only optimistic addresses before initial 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    |      TID      |    Reserved   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Owner Nonce                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                  Owner Interface Identifier                   +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 8: Owner Interface Identifier Option

   Type:  TBD6

   Length:  2

   TID:  8-bit unsigned integer.  This field is set to the last TID
      value used for sending an NR message.

   Reserved:  This field is unused.  It MUST be initialized to zero by
      the sender and MUST be ignored by the receiver.

   Owner Nonce:  A 32-bit Owner Nonce generated randomly by the node
      upon booting, and generated again each time the node re-boots.
      This Owner Nonce is used to detect duplicate OIIs.

   Owner Interface Identifier:  A globally unique identifier for the
      host's interface.  This is typically the EUI-64 derived IID of the
      interface.




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5.  Protocol Specification

   This section specifies the functions defined by this specification,
   along with pointers to needed procedures from other specifications.
   These basic procedures are sufficient and required for LoWPAN
   operation.

5.1.  Interface initialization

   A LoWPAN node forms a 64-bit Interface Identifier (IID) as specified
   in Section 6 of [RFC4944].  This may be based on the EUI-64
   identifier, an assigned 16-bit short address, or any other
   appropriate MAC address.  All nodes MUST configure at least one
   address, a link-local address, by concatenating its IID with the
   prefix FE80::/64 as specified in Section 7 of [RFC4944].  As a
   result, knowledge of the IID of another LoWPAN Node is enough to
   derive its link-local address and reach it on the same link.  If
   derived from an EUI-64 or an equivalent the link-local address is
   presumably unique on the LoWPAN, which enables the use of Optimistic
   Duplicate Address Detection (oDAD) [RFC4429].  The address SHOULD be
   created as optimistic before it has been confirmed by Node
   Registration (Section Section 5.2).  This document assumes that
   addresses are formed in a uniform manner in a LoWPAN.  Appropriate
   steps SHOULD be taken to ensure that only correctly configured
   devices participate in the LoWPAN, e.g. using L2 security mechanisms.

   A node MUST join the all-nodes multicast address, which is used for
   receiving RAs from routers.  A router MUST also join the all-routers
   multicast address.  A node MAY join other multicast addresses such as
   the solicited-node multicast address if its link-layer includes
   multicast support, but that is not required by this specification.

   Nodes MAY learn the address of routers using traditional means such
   as L2 configuration or Router Advertisement messages as in [RFC4861].
   When sending a Router Solicitation it MUST not have the SLLAO Option,
   but instead MUST include the OII Option.  If the sender of the RS has
   only optimistic addresses, it MUST not use them as the IPv6 source
   address for the RS, but instead uses the IPv6 unspecified address.
   This procedure is to comply with the use of optimistic addresses as
   per oDAD [RFC4429].

   The node SHOULD also form a global unicast address for routing inside
   the LoWPAN and reachability from outside the LoWPAN.  If a valid
   prefix is available from an RA ('A' flag is set), then a global
   unicast address MAY be derived following the general description in
   Section 5.5 of [RFC4862].  This address is marked optimistic until
   confirmed by the Node Registration process.  If the LoWPAN is
   operating in ad-hoc mode, then the prefix is a Unique on-link IPv6



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   Address (ULA) prefix [RFC4193] as specified in Section 8 (use of a
   ULA prefix requires no changes to node operation).  A node MAY
   alternatively acquire a global unicast address using other suitable
   means, e.g.  DHCPv6, L2 assignment or manual configuration.

5.2.  Node Registration

   The node registration process is very similar to that of a MIPv6
   mobile node, though the messages used are new Neighbor Discovery ICMP
   messages.  A LoWPAN Node address optimistic as long as the binding is
   not confirmed a router.  The LoWPAN Node sends a unicast Node
   Registration to an on-link Router to perform the binding.  While a
   nodes addresses are still optimistic (first registration in a
   LoWPAN), the IPv6 unspecified address must be used as the source.
   Registration SHOULD be preferred with on-link Edge Routers rather
   than LoWPAN Routers if available.  The Preference Flag of the RA is
   used to differentiate between ERs (Prf=01) and LoWPAN Routers
   (Prf=00).  LoWPAN Routers with Prf=11 SHOULD NOT be used for
   registration.  Furthermore the ER Metric in the 6LoWPAN Summary
   Option SHOULD be used to rank routers.

   A unique Owner Interface Identifier (OII) is included in the Node
   Registration so the binding can be identified throughout the LoWPAN.
   The OII SHOULD be formed from the EUI-64 of the interface in the same
   way as the node's link-local address IID as defined in [RFC4944].  A
   randomly generated 32-bit Owner Nonce is formed each time a node
   boots or reboots.  This is included in the NR and may be used to
   detect duplicate OIIs.  While cryptographic randomness [RFC4086] is
   not strictly required, the randomness SHOULD be derived using a
   mechanism of similar quality.

   The NR message includes an Address Option for each address to be
   registered.  Thus the message is structured as follows:

   ICMPv6 (Node Registration (Address Option[0], Address Option[1],
   Address Option[n]))

   This registration method includes a way of requesting a unique
   address by setting the 'A' flag in an Address Option during
   registration.  This is useful for receiving a unique short link-layer
   address.  How a router assigns such an address is out of scope for
   this document.

   A unique Transaction ID (TID) is included by the host in the NR
   message and used to match replies.  A lollipop mechanism is used.
   TID is set to 0 upon booting, and is incremented with each Request NR
   message.  The TID MUST NOT be incremented when sending a Refresh NR
   message.  After reaching 0xFF, the value loops to 16 (0x10) and is



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   incremented from there.  Thus the values between 0-15 MUST only used
   after a boot or reboot while not yet registered.  A node that has not
   heard a valid Node Confirmation for 16 Node Registration messages in
   a row restarts with a on-link next TID of zero (the node MAY, but
   need not, generate a new Owner Nonce).

   The acknowledgment to a Node Registration is a unicast Node
   Confirmation message that contains the status of the bindings.  The
   source of the packet is the link-local address of the on-link router.
   The destination address is the link-local address of the node.  An
   Address Option for each confirmed or assigned address is included.
   Upon successful completion in the Node Confirmation message, the
   LoWPAN Node sets the address from optimistic to preferred.  See
   Section 11 for message examples.

   Node bindings have timeouts associated with them, therefore nodes
   must periodically send a new Node Registration message to renew the
   binding.  The period between Request NR messages SHOULD be less than
   BindingLifetime.  If a node no longer receives Node Confirmation
   messages from any router in the current subnet, the registration
   process starts over.

5.2.1.  Processing a Node Registration Message

   When a router receives a Node Registration message from a node, it
   first checks for correctness of the message fields and options.  In
   the case of an existing node, the message is used to refresh the
   corresponding entries in the router's binding table.

   In the case of a new node, then a binding table entry is made for
   each 6AO in the message.  The router SHOULD perform Duplicate Address
   Detection on each optimistic address (O flag set), see Section 5.3
   for further information on the DAD procedure.  If a 6AO option with
   an A flag is received, then the router should aquire a suitable
   address for the node.  How this is done is out of scope.  Depending
   on the link-layer and network it may be possible to generate a random
   address (DAD MUST be performed in this case), aquire an address from
   a link-layer coordinator, or perform DHCPv6 in a managed network to
   name a few.

   After processing all 6AO options, a unicast Node Confirmation message
   is sent back to the node with an appropriate NC Status code and
   success codes for each 6AO option in the same order as received.

5.2.2.  Processing a Node Confirmation Message

   When a router receives a Node Registration message from a node, it
   first checks for correctness of the message fields and options.



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   If a NC is recieved with a success status (0-7), then the node goes
   on to process 6LoWPAN Address Options.  If a successful NC is
   received with a code of 2, this indicates that the node should re-
   register with that router.

   6LoWPAN Address Options are processed one at a time.  A success
   status (0-127) indicates that the address was successfully bound with
   the router.  If the address is marked optimistic, it is now updated
   to preferred.  A failure code (128-) indicates that the binding
   failed.  See Section 4.4.1 for an explanation of 6AO codes.  A
   binding failure may indicate that a duplicate address (and thus a
   duplicate IID) already exists.  In this case the node SHOULD attempt
   to form a new IID and restart the registration process.  If this is
   not possible, the node MUST not participate in the LoWPAN.

   If a NC is received with an error status (8 or greater), then the
   registration has failed.  See Section 4.1 for an explanation of NR/NC
   codes.  If no successful Node Confirmation is received within the
   timeout (RegistrationTimeout) and number of retries
   (RegistrationRetries), then registration should be performed with
   another router in the default router list.

5.3.  Duplicate Address Detection

   It is important for proper network operation that duplicate addresses
   are not used in a LoWPAN as described in "IPv6 Stateless Address
   Autoconfiguration" [RFC4862].  Furthermore, as LoWPANs are made up of
   links with undetermined connectivity, it is important that address
   uniqueness is ensured thoughout the routing domain as discussed in
   [I-D.ietf-autoconf-adhoc-addr-model].  LoWPAN Hosts may be very
   simple, and thus are not expected to have the capability of
   performing a duplicate address detection (DAD) algorithm themselves.
   Therefore the handling of DAD is considered a function of LoWPAN
   Routers.  This document does not perform DAD as defined in [RFC4862],
   but instead makes use of alternative techniques appropriate for
   LoWPANs.  It is assumed that all routers in a LoWPAN are configured
   to perform DAD in a uniform way.  If there is only a single router in
   the LoWPAN, as occurs in mesh-under or star topologies, then a router
   automatically detects duplicates by checking its own binding table
   during registration, thus no additional mechanism is needed.

   If a router receives a Node Registration 6AO with the Optimistic Flag
   (O) set, it SHOULD perform DAD on this address.  If the router
   generates or assigns an address for a node in response to a 6AO with
   the A flag set, it SHOULD perform DAD on that address.  DAD MAY be
   disabled if the address has been generated or assigned in such a way
   that there is high confidence of no duplicates (WARNING IN LARGE
   PRINT).  Examples include the use of an EUI-64 to form an IID or



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   DHCPv6 performed through a single server uniformly by all nodes in
   the LoWPAN (as per the homogeneous LoWPAN assumption).

   A router can be configured to perform DAD using one of the following
   techniques, the details of which are out of the scope of this
   document:

   Extended LoWPAN:  The Extended LoWPAN technique defined in (draft
      tbd) provides DAD during its ER registration.

   Routing protocol:  If supported, a routing protocol mechanism could
      be used to check for the existance of an address in the LoWPAN,
      assuming that it is covered by a single routing domain.

5.4.  Next-hop Determination

   The IP address of the next-hop for a destination is determined as
   follows.  Destinations to the link-local prefix (FE80::) are always
   sent on the link to that destination.  All other prefixes are assumed
   to be off-link as recommended in
   [I-D.ietf-autoconf-adhoc-addr-model].  They are therefore sent to the
   IP address of a router chosen from the Default Router List.

   Multicast addresses are considered to be on-link and are resolved as
   specified in [RFC4944] or relative future documents.  A LoWPAN Node
   is not required to maintain a minimum of one buffer per neighbor as
   specified in [RFC4861], as address lookup is not performed as part of
   next-hop determination.  Anycast addresses are always considered to
   be off-link.

5.5.  Address Resolution

   The node registration mechanism provides sufficient a priori state in
   nodes and routers to resolve an IPv6 address to its associated link-
   layer address on the node-router interface.  As prefixes are always
   assumed to be off-link, resolution between hosts is not needed.

   Information about link-layer addresses is stored by nodes about
   routers in its default router list, and by routers about nodes in its
   binding table.  This information is stored during the node
   registration process.  In order to achieve LoWPAN compression, most
   global addresses are also formed using a link-layer address.  A node
   can minimize memory usage by making use of an educated guess and
   storing link-layer address information only if it differs from the
   link-layer address corresponding to the IID of the IPv6 address
   (i.e., differs in more than the on-link/global bit being inverted).





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5.6.  Unreachability Detection

   Unreachability between a node and router is determined based on NR/NC
   and RS/RA exchanges and other unicast L3 data messages.  Host-host
   unreachability detection is out of scope.

   In order to detect unreachable destinations, nodes SHOULD support
   type 1 ICMPv6 destination unreachable messages [RFC4443].  LoWPAN
   Routers or Edge Routers make use of ICMPv6 destination unreachable to
   indicate that delivery to that destination is not possible.

5.7.  Context Dissemination

   Network configuration parameters carried in Router Advertisements
   originate at edge routers and must disseminate to all routers and
   hosts within the LoWPAN.  RAs include either 6LoWPAN Information
   Options (one for each context) and a 6LoWPAN Summary Option, or just
   a 6LoWPAN Summary Option.

   For the dissemination of context information using the 6IO, a strict
   lifecycle SHOULD be used in order to ensure the context information
   stays synchronized throughout the LoWPAN.  New context information
   SHOULD be introduced into the LoWPAN with C=1 and V=0, to ensure it
   is known by all nodes that may have to decompress based on this
   context information.  Only when it is reasonable to assume that this
   information was successfully disseminated SHOULD an option with C=1
   and V=1 be sent, enabling the actual use of the context information
   for compression.

   Conversely, to avoid that nodes send packets making use of previous
   values of contexts, resulting in ambiguity when receiving a packet
   that uses a recently changed context, old values of a context SHOULD
   be taken out of use for a while before new values are assigned to
   this specific context.  That is, in preparation for a change of
   context information, its dissemination SHOULD continue for at least
   MIN_CONTEXT_CHANGE_DELAY with C=1 and V=0.  Only when it is
   reasonable to assume that the fact that the context is now invalid
   was successfully disseminated, should the context ID be taken out of
   dissemination or reused with a different Information field.  In the
   latter case, dissemination of the new value again SHOULD start with
   C=1 and V=0, as above.

   The 6LoWPAN Summary Option is used to support information
   dissemination from one or more edge routers to all other nodes in the
   LoWPAN.  The option includes a "V" flag which indicates that the
   information contained in the Router Advertisement is valid.  The
   option also includes a sequence number to ensure that all nodes
   converge on the same settings.  The sequence number is incremented by



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   the originating Edge Router each time the set of prefix information
   changes.

   As the number of prefixes or addresses included for context
   compression in an RA may be large (up to 16), it is beneficial to
   avoid the need to always include all options in every RA.  Therefore
   routers SHOULD only include the 6LoWPAN Summary Option in unsolicited
   RAs, unless a set of prefix information with a new sequence number is
   being disseminated.  In the case of a new sequence number, the router
   SHOULD include all 6LoWPAN Information Options in the RA.  A node may
   use an RS with Code set to 1 in order to get the whole prefix
   information set in case it misses the RA sent when the sequence
   number changes.  An RS with Code set to 0 is responded to with an RA
   with the 6SO.


6.  LoWPAN Node Specification

   This section specifies the conceptual data structures and variables
   of a LoWPAN Node.

6.1.  Conceptual structures

   LoWPAN Nodes make use of the following conceptual data structures:

   Prefix List  - The list of prefixes which are advertised in Router
      Advertisements, along with an associated invalidation timer.  Each
      entry is associated with the sequence number last advertised in
      the 6LoWPAN Summary Option.  Unlike in [RFC4861], these prefixes
      are always assumed to be off-link.

   Context List  - The list of context and their associated CID which
      are advertised in Router Advertisements, along with an associated
      invalidation timer.  Each entry is associated with the sequence
      number last advertised in the 6LoWPAN Summary Option.  This list
      may be realized together with the Prefix List.

   Default Router List  - As in [RFC4861].  For networks where address
      resolution needs to be performed, this list also contains link-
      layer information about each router.

   These conceptual data structures may be realized in many ways.  As
   LoWPAN Nodes have very limited memory the number of cache entries
   should be limited, duplicate entries between caches referenced, and
   full IPv6 addresses represented in a compressed format where
   possible.





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6.2.  Conceptual variables

   The following variables are kept for each interface on a node, and
   default values are overridden by information in Router
   Advertisements:

   CurHopLimit         The default hop limit to be used when sending IP
                       packets.

   CurTID              The current Transaction ID (TID) value for use in
                       NR messages.

   BindingLifetime     The binding lifetime sent in Node Registration
                       messages.

   RegistrationTimeout The time to wait for a Node Confirmation after
                       sending a Node Registration.  SHOULD be at least
                       MIN_NR_TIMEOUT.

   RegistrationRetries The number of times to try to send a Node
                       Registration, which SHOULD be less than
                       MAX_NR_RETRIES.


7.  LoWPAN Router Specification

   LoWPAN Routers are used in a route over configuration where the
   network is composed of overlapping link-local scopes.  LoWPAN Edge
   Routers are implement LoWPAN Router functionality.  As a result, we
   extend classic ND as specified in [RFC4861] to operate over such non-
   transitive LoWPAN links.  This section describes ND for 6LoWPAN
   router operations.  Note that this section does not entirely apply to
   pure Mesh Under LoWPANs where the are no LoWPAN Routers, although
   they do have LoWPAN Edge Routers.

7.1.  Router Configuration Variables

   A router MUST allow the configuration of conceptual variables as
   defined in Section 6.2.1 of [RFC4861].  AdvReachableTime and
   AdvRetransTimer are not used.

7.2.  Becoming an Advertising Interface

   An interface may become an advertising interface as specified in
   Section 6.2.2 of [RFC4861].

   A LoWPAN Router's interface MAY become an advertising interface
   before all of its router variables have been initialized.  The router



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   MUST learn these variables (e.g.  AdvCurHopLimit, prefix and context
   information, etc.) from neighboring routers.  While the variables are
   not initialized, the router MAY send Router Advertisement with the
   "Solicit" flag set to solicit Router Advertisements from neighboring
   routers.  However, the router MUST set the Router Lifetime field to
   zero while one or more of its variables are uninitialized.

7.3.  Router Advertisement Message Content

   A router sends periodic as well as solicited Router Advertisements
   out its advertising interface.  Outgoing Router Advertisements are
   filled with the following values consistent with the message format
   given in this document.

      - In the Router Lifetime field: if the router has a default route,
      the interface's configured AdvDefaultLifetime.  If the router does
      not have a default route, zero.

      - In the M and O flags: the current value of AdvManagedFlag and
      AdvOtherConfigFlag, respectively.

      - In the Preference flag: this flag is set to 00 to indicate that
      the sender is a LoWPAN Router.

      - In the Cur Hop Limit field: the current value of CurHopLimit.

      - In the Reachable Time field: not used, set to zero.

      - In the Retrans Timer field: not used, set to zero.

      - In the options:

         - 6LoWPAN Summary Option: to indicate if the information
         contained in the Router Advertisement is valid and, if so, the
         freshness of the information contained in the Router
         Advertisement message.  The option fields are set as follows:

            - In the "valid" flag: the current value of
            AdvInformationValid.

            - In the Sequence Number field: the current value of
            AdvInformationSequence.

            - The ER Metric field is used by a routing algorithm to
            indicate the cost of reaching an ER through this router.






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         - 6LoWPAN Information options: one 6LoWPAN Information option
         for each prefix listed in AdvPrefixList with the option fields
         set from the information in the AdvPrefxList entry as follows:

            - In the "on-link" flag: the entry's AdvOnLinkFlag.

            - In the "Autonomous address configuration" flag: the
            entry's AdvAutonomousFlag.

            - In the Valid Lifetime field: the entry's AdvValidLifetime.

7.4.  Sending Unsolicited Router Advertisements

   As specified in Section 6.2.4 of [RFC4861].

7.5.  Ceasing To Be an Advertising Interface

   As specified in Section 6.2.5 of [RFC4861].

7.6.  Processing Router Solicitations

   As specified in Section 6.2.6 of [RFC4861].

7.7.  Binding Table

   Routers maintain an set of information about nodes that are currently
   registered through it called the binding table.

   The binding table contains an entry with information such as the
   registered node's OII, link-local IPv6 address and the binding
   lifetime from the last NR.  If address resolution is required, the
   table will also include corresponding link-layer address information.


8.  Ad-hoc LoWPAN

   LoWPAN networks by nature may often work in an ad-hoc fashion,
   without an infrastructure or connectivity to the global Internet.
   6LoWPAN-ND may still be applied in such networks.

   A LoWPAN Router in the Ad-hoc LoWPAN is configured to implement basic
   Edge Router functionality (initiating RA dissemination) and generates
   a prefix based on Unique on-link IPv6 Unicast Addresses (ULAs) as
   defined in [RFC4193].  A ULA is made up of the prefix fc00::/7, a
   global ID and a subnet ID.  The global ID is randomly generated, and
   the subnet ID is not used.  The Edge Router is responsible for the
   generation of the ULA prefix to be advertised to the LoWPAN and used
   by all nodes.  ULA generation may use the algorithm suggested Section



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   3.2.2 of [RFC4193] or something appropriate to the Edge Router's
   capabilities.  There SHOULD be only one Edge Router in an Ad-hoc
   LoWPAN (just as in a Simple LoWPAN) to keep prefix consistency.

   In the case that an Edge Router on a Simple LoWPAN does not have a
   prefix available from its IPv6 address, it SHOULD advertise a ULA
   prefix in a similar manner.


9.  Protocol Constants

   This section defines the protocol constants used in this document
   based on a subset of [RFC4861] constants. (*) indicates constants
   modified from [RFC4861] and (+) indicates new constants.

   Additional protocol constants are defined in Section Section 4.

   Edge Router Constants:

   MIN_CONTEXT_CHANGE_DELAY+               60 seconds

   Router Constants:

   MAX_INITIAL_RTR_ADVERT_INTERVAL*        60 seconds

   MAX_INITIAL_RTR_ADVERTISEMENTS          3 transmissions

   MAX_FINAL_RTR_ADVERTISEMENTS            3 transmissions

   MIN_DELAY_BETWEEN_RAS*                  10 seconds

   MAX_RA_DELAY_TIME*                      2 seconds

   Host Constants:

   MAX_RTR_SOLICITATION_DELAY*             2 second

   RTR_SOLICITATION_INTERVAL*              10 seconds

   MAX_RTR_SOLICITATIONS                   3 transmissions

   Node Constants:

   MAX_NR_RETRIES+                         3 transmissions







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   MIN_NR_TIMEOUT+                         5 seconds


10.  Use of 6LoWPAN-ND under RFC4861-only stacks

   Some IPv6 stacks (e.g. on PCs) and tools (e.g. radvd) hard-wire the
   mechanisms of RFC4861 for all links.  This section explains the
   adaptation needed in order to use a 6LoWPAN interface under such an
   RFC4861-only implementation.

   There are several ways to implement 6LoWPAN-ND in combination with an
   IPv6 stack:

   o  6LoWPAN-ND is integrated with the IPv6 stack and its tools.  This
      is common for LoWPAN nodes.

   o  6LoWPAN-ND is implemented as part of the interface, configuration
      is used to turn off RFC4861 mechanisms in the IPv6 stack.  For
      example, Proxy-ND interfaces can be used in Linux to disable most
      built-in ND mechanisms.  This model is common for Edge Routers
      running on a standard operating system.

   o  6LoWPAN-ND is implemented as part of the interface, and it
      performs adaptation for RFC4861 mechanisms running on the IPv6
      stack.  The binding table is used to answer RFC4861 messages, and
      appropriate options added to RA messages.

   Classic RS/RA messages can be used with a LoWPAN, thus allowing e.g.
   for an unmodified radvd (with appropriate configuration) to be run on
   an Edge Router as long as context dissemination is not needed.  It is
   however recommended that 6IO and 6SO options be used if possible,
   which is easily achieved by patching existing RA tools or performing
   adaptation.


11.  Message Examples

   This section provides basic examples of messages and options from
   this document.

11.1.  NR/NC message exchange

   When a host wanting to register to a router, a simple NR/NC request
   message exchange occurs.  In this example a host wants to register
   its address generated with Stateless Address Autoconfiguration (SAA),
   and in addition requests a generated short address.

   First the Host sends an NR message to the link-local address of the



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   router.  In this example the host includes a 600 second binding
   lifetime and its modified EUI-64 as the Owner Interface Identifier.
   The message has two Address Options.  The host has just booted,
   therefore the TID starts with 0.  This example assumes that the
   LoWPAN prefix has been assigned CID 0.

   IPv6 Source: Unspecified address
   IPv6 Destination: Router's link-local address

    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 = TBD   |   0   |   0   |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TID = 0     |1|0|                 Reserved                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Binding Lifetime = 60      |            Reserved           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Owner Nonce                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Owner Interface Identifier =                 +
   |                Modified EUI-64 of the interface               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                        Figure 9: Basic NR request.


    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 = TBD   |   Length = 1  |  Status = 0   | S=1 |  P=0    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|0|0|1|      Reserved         |         Padding  = 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 10: NR Address Option 1, for the SAA address.












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    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 = TBD   |   Length = 1  |  Status = 0   | S=2 |  P=0    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|1|0|0|      Reserved         |         Padding = 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        Figure 11: NR Address Option 2, for the requested address.


   IPv6 Source: Router's link-local address
   IPv6 Destination: Host's link-local address

   The base NC message is identical to the base NR message above.


                   Figure 12: Corresponding NC message.



   Address Option 1 is identical to Address Option 1 in the NR.


           Figure 13: NC Address Option 1, for the SAA address.


   Address Option 2 now includes the generated address.

    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 = TBD   |   Length = 1  |  Status = 0   | S=2 |  P=0    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|1|0|0|      Reserved         |   Generated 16-bit address    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        Figure 14: NC Address Option 2, for the requested address.

11.2.  Router advertisement

   Routers and Edge Routers in LoWPAN networks periodically send RA
   messages.  In the following example is of an RA message sent by a
   router.  The only difference if an Edge Router would send the message
   is that the Preference flag would be 10.




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   In the example the Preference flag is 01 (router), and a 1200s Router
   Lifetime is advertised.  A 6LoWPAN Prefix Information Option is
   included.


     IPv6 Source: Router's link-local address
     IPv6 Destination: All-nodes multicast address

      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 = 134   |   Code = 0    |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Cur Hop Limit |0|0|0|0 0|Rsrvd|    Router Lifetime = 1200     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Reachable Time = 0                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Retrans Timer = 0                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 15: RA message example.


    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 = TBD   |  Length = 2   |     PL = 64   |0|1|1|1| CID=0 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Valid Lifetime = 3000                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                    Prefix = 2001:DB8::/64                     .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 16: 6LoWPAN Information Option example.


12.  Security Considerations

   The security considerations of IPv6 Neighbor Discovery [RFC4861]
   apply.  Additional considerations can be found in [RFC3756].

   This specification expects that the link layer is sufficiently
   protected, either by means of physical or IP security for the
   backbone link or MAC sublayer cryptography.  In other words, model 1
   from [RFC3756] applies.  In particular, it is expected that the



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   LoWPAN MAC provides secure unicast to/from Routers and secure
   broadcast from the Routers in a way that prevents tampering with or
   replaying the RA messages.  However, any future 6LoWPAN security
   protocol that applies to Neighbor Discovery for 6LoWPAN protocol, is
   out of scope of this document.

   The use of EUI-64 for forming the Interface ID in the link on-link
   address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
   address privacy techniques.  Considering the envisioned deployments
   and the MAC layer security applied, this is not considered an issue
   at this time.


13.  IANA Considerations

   This document requires two new ICMPv6 message types:

   o  Node Registration (TBD1)

   o  Node Confirmation (TBD2)

   The document also requires four new ND option types under the
   subregistry "IPv6 Neighbor Discovery Option Formats":

   o  6LoWPAN Address Option (TBD3)

   o  6LoWPAN Information Option (TBD4)

   o  6LoWPAN Summary Option (TBD5)

   o  Owner Interface Identifier Option (TBD6)

   [TO BE REMOVED: This registration should take place at the following
   location: http://www.iana.org/assignments/icmpv6-parameters]


14.  Acknowledgments

   The authors thank Richard Kelsey, Geoff Mulligan, Julien Abeille,
   Alexandru Petrescu, Peter Siklosi, Pieter De Mil, Fred Baker, Anthony
   Schoofs, Phil Roberts and Joakim Eriksson for useful discussions and
   comments that have helped shaped and improve this document.


15.  Changelog

   Changes from -07 to -08:




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      o Removed Extended LoWPAN and Whiteboard related sections.

      o Included reference to the autoconf addressing model.

      o Added Optimistic Flag to 6AO.

      o Added guidelines on routers performing DAD.

      o Removed the NR/NC Advertising Interval.

      o Added assumption of uniform IID formation and DAD throughout a
      LoWPAN.

   Changes from -06 to -07:

      o Updated addressing and address resolution (#60).

      o Changed the Address Option to 6LoWPAN Address Option, fixed S
      values (#61).

      o Added support for classic RFC4861 RA Prefix Information messages
      to be processed (#62).

      o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861
      stack (#63).

      o Updated the NR/NC message with a new Router flag, combined the
      Code and Status fields into one byte, and added the capability to
      carry 6IOs (#64).

      o Made co-existence with other ND mechanisms clear (#59).

      o Added a new Protocol Specification section with all mechanisms
      specified there (#59).

      o Removed dependencies and conflicts with RFC4861 wherever
      possible (#59).

      o Some editorial cleanup.

   Changes from -05 to -06:

      o Fixed the Prf codes (#52).

      o Corrected the OIIO TID field to 8-bits.  Changed the Nonce/OII
      order in both the OIIO and the NR/NC. (#53)





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      o Corrected an error in Table 1 (#54).

      o Fixed asymmetric and a misplaced transient in the 6LoWPAN
      terminology section.

      o Added Updates RFC4861 to header

   Changes from -04 to -05:

      o Meaning of the RA's M-bit changed to original [RFC4861] meaning
      (#46).

      o Terms "on-link" and "off-link" used in place of "on-link" and
      "off-link".

      o Next-hop determination text simplified (#49).

      o Neighbor cache and destination cache removed.

      o IID to link-layer address requirement relaxed.

      o NR/NC changes to enable on-link refresh with routers (#48).

      o Modified 6LoWPAN Information Option (#47).

      o Added a Protocol Constants section (#24)

      o Added the NR processing table (#51)

      o Considered the use of SeND on backbone NS/NA messages (#50)

   Changes from -03 to -04:

      o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix
      generation a features useful also in Simple and Extended LoWPANs.
      (#41)

      o Added a 32-bit Owner Nonce to the NR/NC messages and the
      Whiteboard, removed the TID history. (#39)

      o Improved the duplicate OII detection algorithm using the Owner
      Nonce. (#39)

      o Clarified the use of Source and Target link-layer options in
      NR/NC. (#43)

      o Included text on the use of alternative methods to acquire
      addresses. (#38)



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      o Removed S=2 from Address Option (not needed). (#36)

      o Added a section on router dissemination consistency. (#44)

      o Small improvements and extensive editing. (#42, #37, #35)

   Changes from -02 to -03:

      o Updated terminology, with RFC4861 non-transitive link model.

      o 6LoWPAN and ND terminology separated.

      o Protocol overview explains RFC4861 diff in detail.

      o RR/RC is now Node Registration/Confirmation (NR/NC).

      o Added NR failure codes.

      o ER Metric now included in 6LoWPAN Summary Option for use in
      default router determination by hosts.

      o Examples of host data structures, and the Whiteboard given.

      o Whiteboard is supported by all Edge Routers for option
      simplicity.

      o Edge Router Specification chapter re-structured, clarifying
      optional Extended LoWPAN operation.

      o NS/NA now completely optional for nodes.  No address resolution
      or NS/NA NUD required.

      o link-local operation now compatible with oDAD (was broken).

      o Exception to hop limit = 255 for NR/NC messages.

      o Security considerations improved.

      o ICMPv6 destination unreachable supported.

   Changes from -01 to -02:

      o Fixed 16 != 0xff bug (ticket closed).

      o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket
      closed).





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      o Terminology cleanup based on Alex's comments.

      o General editing improvements.

   Changes from -00 to -01:

      o Specified the duplicate owner interface identifier procedures.
      A TID lollipop algorithm was sufficient (nonce unnecessary).

      o Defined fault tolerance using secondary bindings.

      o Defined ad-hoc network operation.

      o Removed the E flag from RA and the X flag from RR/RC.

      o Completed message examples.

      o Lots of improvements in text quality and consistency were made.


16.  References

16.1.  Normative References

   [I-D.ietf-autoconf-adhoc-addr-model]
              Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
              Hoc Networks", draft-ietf-autoconf-adhoc-addr-model-02
              (work in progress), January 2010.

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

   [RFC2491]  Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
              over Non-Broadcast Multiple Access (NBMA) networks",
              RFC 2491, January 1999.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [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.




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   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 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.

16.2.  Informative References

   [I-D.ietf-6lowpan-hc]
              Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams in 6LoWPAN Networks", draft-ietf-6lowpan-hc-06
              (work in progress), October 2009.

   [RFC2022]  Armitage, G., "Support for Multicast over UNI 3.0/3.1
              based ATM Networks", RFC 2022, November 1996.

   [RFC3122]  Conta, A., "Extensions to IPv6 Neighbor Discovery for
              Inverse Discovery Specification", RFC 3122, June 2001.

   [RFC3756]  Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
              Discovery (ND) Trust Models and Threats", RFC 3756,
              May 2004.

   [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.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", BCP 106, RFC 4086, June 2005.

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
              June 2007.

   [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.



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Authors' Addresses

   Zach Shelby (editor)
   Sensinode
   Hallituskatu 13-17D
   Oulu  90100
   FINLAND

   Phone: +358407796297
   Email: zach@sensinode.com


   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


   Jonathan W. Hui
   Arch Rock Corporation
   501 2nd St. Ste. 410
   San Francisco, California  94107
   USA

   Phone: +415 692 0828
   Email: jhui@archrock.com


   Samita Chakrabarti
   IP Infusion
   1188 Arquest Street
   Sunnyvale, California
   USA

   Phone:
   Email: samitac@ipinfusion.com









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   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   Fax:   +49-421-218-7000
   Email: cabo@tzi.org


   Erik Nordmark
   Sun Microsystems
   17 Network Circle
   Menlo Park, California  94025
   USA

   Phone:
   Email: Erik.Nordmark@Sun.COM
































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