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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: 4861 (if approved)                                   P. Thubert
Intended status: Standards Track                                   Cisco
Expires: March 26, 2010                                           J. Hui
                                                               Arch Rock
                                                          S. Chakrabarti
                                                             IP Infusion
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                             E. Nordmark
                                                                     Sun
                                                      September 22, 2009


                       6LoWPAN Neighbor Discovery
                        draft-ietf-6lowpan-nd-06

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
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   This Internet-Draft will expire on March 26, 2010.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of



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   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document specifies Neighbor Discovery optimized for 6LoWPAN.
   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 standard IPv6 Neighbor Discovery
   with 6LoWPAN has several problems.  Standard Neighbor Discovery was
   not designed for non-transitive wireless links, and the standard IPv6
   link concept and heavy use of multicast makes it unpractical.  This
   document specifies a new ND mechanism allowing for the efficient
   detection of duplicate addresses over entire LoWPANs, which also
   optimizes other ND operations.  In addition, context dissemination,
   claim and defend address generation, and the support of Extended
   LoWPANs over Backbone Links are specified.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Goals & Assumptions  . . . . . . . . . . . . . . . . . . .  6
     1.2.  Why not standard IPv6 ND?  . . . . . . . . . . . . . . . .  7
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.1.  6LoWPAN Terminology  . . . . . . . . . . . . . . . . . . .  8
     2.2.  ND Terminology . . . . . . . . . . . . . . . . . . . . . . 11
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . . 13
     3.1.  Topology . . . . . . . . . . . . . . . . . . . . . . . . . 15
     3.2.  Links  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     3.3.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 15
     3.4.  Basic operation  . . . . . . . . . . . . . . . . . . . . . 17
     3.5.  Optional features  . . . . . . . . . . . . . . . . . . . . 17
   4.  6LoWPAN-ND Messages  . . . . . . . . . . . . . . . . . . . . . 18
     4.1.  Node Registration/Confirmation Message . . . . . . . . . . 18
     4.2.  Router Solicitation Message  . . . . . . . . . . . . . . . 22
     4.3.  Router Advertisement Message . . . . . . . . . . . . . . . 22
     4.4.  NS/NA Messages . . . . . . . . . . . . . . . . . . . . . . 23
     4.5.  6LoWPAN-ND Message Options . . . . . . . . . . . . . . . . 23
       4.5.1.  Address Option . . . . . . . . . . . . . . . . . . . . 23
       4.5.2.  6LoWPAN Information Option . . . . . . . . . . . . . . 25
       4.5.3.  6LoWPAN Summary Option . . . . . . . . . . . . . . . . 27
       4.5.4.  Owner Interface Identifier Option  . . . . . . . . . . 28
   5.  LoWPAN Node Specification  . . . . . . . . . . . . . . . . . . 29
     5.1.  Conceptual structures and variables  . . . . . . . . . . . 29
     5.2.  Interface initialization . . . . . . . . . . . . . . . . . 30
     5.3.  Registration process . . . . . . . . . . . . . . . . . . . 31
     5.4.  Next-hop determination . . . . . . . . . . . . . . . . . . 34
     5.5.  Destination unreachability detection . . . . . . . . . . . 34
   6.  LoWPAN Router Specification  . . . . . . . . . . . . . . . . . 34
     6.1.  Router Configuration Variables . . . . . . . . . . . . . . 35
     6.2.  Becoming an Advertising Interface  . . . . . . . . . . . . 35
     6.3.  Router Advertisement Message Content . . . . . . . . . . . 35
     6.4.  Sending Unsolicited Router Advertisements  . . . . . . . . 36
     6.5.  Ceasing To Be an Advertising Interface . . . . . . . . . . 36
     6.6.  Processing Router Solicitations  . . . . . . . . . . . . . 37
     6.7.  Router Advertisement Consistency . . . . . . . . . . . . . 37
     6.8.  Binding Table  . . . . . . . . . . . . . . . . . . . . . . 37
     6.9.  Processing a Node Registration Message . . . . . . . . . . 37
     6.10. Relaying a Node Confirmation Message . . . . . . . . . . . 38
   7.  LoWPAN Edge Router Specification . . . . . . . . . . . . . . . 38
     7.1.  The Whiteboard . . . . . . . . . . . . . . . . . . . . . . 39
     7.2.  Simple LoWPAN  . . . . . . . . . . . . . . . . . . . . . . 40
     7.3.  Extended LoWPAN  . . . . . . . . . . . . . . . . . . . . . 41
     7.4.  Ad-hoc LoWPAN  . . . . . . . . . . . . . . . . . . . . . . 41
     7.5.  Registration process . . . . . . . . . . . . . . . . . . . 42
     7.6.  Forwarding packets between a LoWPAN and an IPv6



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           infrastructure . . . . . . . . . . . . . . . . . . . . . . 43
     7.7.  Address collision detection and resolution . . . . . . . . 44
     7.8.  Duplicate OII detection  . . . . . . . . . . . . . . . . . 46
     7.9.  Fault tolerance  . . . . . . . . . . . . . . . . . . . . . 48
   8.  Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 49
   9.  Message Examples . . . . . . . . . . . . . . . . . . . . . . . 50
     9.1.  Basic NR/NC message exchange . . . . . . . . . . . . . . . 50
     9.2.  Relaying an NR message . . . . . . . . . . . . . . . . . . 52
     9.3.  Router advertisement . . . . . . . . . . . . . . . . . . . 53
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 54
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 54
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 55
   13. Changelog  . . . . . . . . . . . . . . . . . . . . . . . . . . 55
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 58
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 58
     14.2. Informative References . . . . . . . . . . . . . . . . . . 59
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 59


































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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 with the
   help of an adaptation header which comes before the IP header.  A
   link in 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 IPv6 Neighbor Discovery [RFC4861] is
   not desirable in such a wireless low-power, lossy network.

   Moreover, LoWPAN links are non-symmetric and transient in nature;
   they are not always considered to be in a fixed network nor are they
   bounded by our standard definition of a wired-link.  A LoWPAN is
   potentially composed of a potentially 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 no multicast capabilities.  Link-local
   scope is in reality defined by reachability and radio strength.  The
   standard IPv6 Neighbor Discovery [RFC4861] control messages, the use
   of multicast and their default frequency also attribute to
   unnecessary waste of energy in LoWPANs.

   6LoWPAN Neighbor discovery provides for basic bootstrapping and
   network operation, along with advanced features such as claim and
   defend address generation and Extended LoWPANs over backbone links,
   while avoiding the use of multicast flooding.  The solution supports
   the use of both link-layer or LoWPAN mesh (Mesh Under) and IP routing
   (Route Over) multihop solutions.  Unlike standard IPv6 ND [RFC4861],
   this document specifically takes the characteristics of low-power,
   lossy wireless links into account.

   This specification introduces a registration mechanism over the radio
   edge of the NBMA network and proxy operation over the federating
   backbone or backhaul.  That registration mechanism provides a service
   somewhat similar to the Multicast Address Resolution Server (MARS)
   [RFC2022] for a limited purpose, and in a lot simpler and less
   generic fashion.  For those link scope multicasts that could not be
   avoided, such as for Router Advertisements, optimizations may be used
   to optimize the dissemination of the information in the Low Power
   network.

   The concept of a LoWPAN Whiteboard located at Edge Routers (ERs) is
   introduced, which allows for Duplicate Address Detection and claim
   and defend addressing for the entire LoWPAN.  Address resolution is
   not required, and thus makes LoWPAN operation power efficient and to
   reduces LoWPAN Node complexity.  A new registration/confirmation
   message sequence is specified, allowing nodes to register their IPv6



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   addresses with an Edge Router.

   The Whiteboard makes use of soft bindings, thus nodes send periodic
   registration messages in order to maintain their bindings.  Changes
   in network topology, and mobility between ERs and LoWPANs are
   supported.  The dissemination of RA information between LoWPAN
   Routers in multihop IP LoWPANs is also discussed.

   This document also specifies the seamless integration of an Extended
   LoWPAN with multiple edge routers on a shared backbone link (e.g.
   Ethernet) to form a single IPv6 subnet.  This allows nodes to keep
   the same IPv6 address throughout a large network, and allows for easy
   communications with nodes over the backbone link and with other IPv6
   hosts.

   The document defines two new ICMPv6 messages: Node Registration and
   Node Confirmation.  In addition a new 6LOWPAN_ER anycast address is
   introduced, used by LoWPAN Routers in order to relay a registration
   message to any Edge Router.

1.1.  Goals & Assumptions

   This document has the following main goals and makes several
   assumptions.

   Goals:

   o  Enable ND operations over an entire LoWPAN, even with non-
      transitive links and over multihop IP hops.

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

   o  Disseminate context information throughout the LoWPAN.

   o  Minimize the complexity of LoWPAN Nodes.

   o  Interconnect LoWPANs with backbone links seamlessly.

   o  Provide a mechanism for claim and defend addressing.

   Assumptions:

   o  Link layer technology may be e.g.  IEEE 802.15.4 as in [RFC4944],
      or any other suitable link-layer.





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   o  Link-local IPv6 addresses are derived from a unique identifier
      (e.g.  EUI-64).

   o  There is typically a direct mapping between the IPv6 address IID
      and the link-layer address (this is already an assumption by
      [RFC4944] used for header compression), thus address resolution is
      not normally required.

   o  A subnet includes all the LoWPAN Nodes, Edge Router(s) and
      optionally their backbone link sharing the same IPv6 prefix.

1.2.  Why not standard 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
   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



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   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 standard
   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] and "Transmission of IPv6 Packets over IEEE
   802.15.4 Networks" [RFC4944].

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

   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 hop limit is
      decremented.  In the LoWPAN context, IP routing is performed by
      LoWPAN Routers on a single interface within the same link to
      overcome the non-transitive nature of the link.  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.





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   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.  Furthermore complex Non-broadcast
      Multi-Access (NBMA) behaviour is exhibited as these links do not
      support native multicast, and broadcast reaches only a subset of
      nodes on the link.  Such a wireless link may consist of multiple
      overlapping link-local scopes.  Link-local scope multicast on such
      a link is realized as a broadcast.

      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 is usually
      implemented as a broadcast flood.

   Link-local

      Standard IPv6 link-local scope as defined in [RFC4291] and
      [RFC4861] is supported by the 6LoWPAN link and subnet model.
      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.

      The terms on-link and off-link no longer have clear meaning on
      non-transitive links.  Instead a node within link-local scope is
      said to be local, and a node outside of link-local scope is said
      to be non-local.

   LoWPAN Host

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

   LoWPAN Node







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      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 exist 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 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
      behaviour.

   Route Over

      A term referring to a configuration where the link is non-
      transitive and the link-local scope reaches only a subset of the
      LoWPAN nodes.  IP routing is performed by LoWPAN Routers to
      overcome the nature of the link.  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

      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.  Due to the non-transitive nature of
      LoWPAN links, IP routing may be used on the link to provide
      transitivity.  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.





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2.2.  ND Terminology

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

   Ad-hoc LoWPAN

      An isolated LoWPAN, not connected to any other IP networks.  Ad-
      Hoc LoWPANs make use of Unique Local 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.

   Binding

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

   Extended LoWPAN

      This is the aggregation of multiple LoWPANs as defined in
      [RFC4919] interconnected by a backbone link via Edge Routers and
      forming a single subnet, shown in Figure 2.

   LoWPAN Edge Router

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

   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.  If the
      Edge Router has a Whiteboard, all nodes belonging to its LoWPAN
      have a whiteboard entry.

   Registration

      The process during which a LoWPAN node sends a Node Registration
      ND message to an Edge Router causing a binding for the LoWPAN node
      to be registered.




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   Whiteboard

      A conceptual data structure similar to a MIPv6 binding cache which
      may be supported by Edge Routers.  The Whiteboard is used for
      performing DAD and NUD across the entire LoWPAN.  The Whiteboard
      contains bindings for LoWPAN nodes that contain, among others, an
      Owner Interface Identifier, Owner Nonce, IPv6 address, TID and a
      remaining lifetime of the binding.



          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






















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         Infrastructure Cloud
                  |
                  |
               +-----+                 +-----+
               |     | Router          |     | Host
               |     |                 |     |
               +-----+                 +-----+
                  |                       |
                  |     Backbone link     |
            +--------------------+------------------+
            |                    |                  |
         +-----+             +-----+             +-----+
         |     | Edge        |     | Edge        |     | Edge
         |     | Router      |     | Router      |     | Router
         +-----+             +-----+             +-----+
            o         o       o   o  o      o        o o
        o o   o  o  o  o  o o   o  o  o  o  o   o  o  o  o
       o  o o  o o   o    o   o  o  o  o     o   o  o  o o
       o   o  o  o     o    o    o  o     o      o  o   o
         o   o o     o          o  o      o    o       o

                         Extended LoWPAN

      Figure 2: Extended LoWPAN with a backbone link and edge routers


3.  Protocol Overview

   6LoWPAN Neighbor discovery (6LoWPAN-ND) provides additions and
   optimizations to IPv6 ND [RFC4861] specifically supporting 6LoWPAN.
   Basic Neighbor Discovery mechanisms are optimized, avoiding the use
   of multicast flooding and minimizing link-local multicast (broadcast)
   frequency.  The detection of duplicate addresses is performed across
   the entire LoWPAN.  This is achieved using a Whiteboard located on
   the Edge Routers of the LoWPAN network.  An Extended LoWPAN topology
   over a shared backbone link is optionally supported.

   The following list summarizes 6LoWPAN-ND operations and the
   differences with [RFC4861]:

   Router Discovery:  As in [RFC4861] with the addition of new 6LoWPAN
      specific options to Router Advertisements.

   Prefix Discovery:  The discovery of 6LoWPAN prefixes with context
      identifiers.  Destinations are assumed to be non-local unless
      explicitly known to be a neighbor.





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   Address Autoconfiguration:  Stateless address autoconfiguration is
      supported as in [RFC4861].  Additionally a claim and defend
      address generation method is supported using the Whiteboard.

   Address Resolution:  Not typically performed, as IIDs are normally
      formed from link-layer addresses.  Mechanism is however included
      enabling routers to perform address resolution for local
      destinations.

   Next-hop Determination:  Next-hop determination is greatly simplified
      compared to [RFC4861].

   Neighbor Unreachability Detection:  Not performed using NS/NA,
      however ICMP destination unreachable messages are supported.

   Duplicate Address Detection:  The detection of duplicate addresses is
      performed across the entire LoWPAN using a lookup on the
      Whiteboard using a new registration method.  Edge routers in an
      Extended LoWPAN formation perform standard [RFC4861] DAD on the
      backbone link.

   Redirect:  Redirect messages are not used.

   Node Registration (new):  Method in which nodes in the LoWPAN
      register with Edge Routers, creating Whiteboard state about all
      IPv6 addresses in the LoWPAN.

   Whiteboard Resolution (new):  This method is used in the Extended
      LoWPAN topology, using the backbone link to resolve conflicts
      between the Whiteboards of Edge Routers.

   This specification makes use of RS/RA message exchanges along with
   standard NS/NA on the Backbone Link.  The use of NS/NA message
   exchanges in the LoWPAN are not required by this document.  In
   addition 6LoWPAN-ND defines two new ICMP packet types:

   Node Registration:  Sent by a node to an Edge Router to register a
      binding for an IPv6 address in the Whiteboard.  Is relayed by an
      intermediate router if there is no local Edge Router.

   Node Confirmation:  The response sent by an Edge Router or router
      back to the registering node.  May be relayed by an intermediate
      router.








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3.1.  Topology

   ND for 6LoWPAN is designed to work with a wide variety of 6LoWPAN
   topologies, including isolated Ad-hoc LoWPANs, Simple LoWPANs and
   Extended LoWPANs.  A Simple LoWPAN topology is assumed by default in
   the text.  The case of Ad-hoc LoWPAN operation is described in
   Section 7.4.  Edge Router operation and Extended LoWPAN functionality
   are described in Section 7.  Edge Routers which will operate only in
   Simple LoWPANs do not need to support Extended LoWPAN functionality,
   such as Edge Routers which do not have a Backbone Link (but instead
   e.g. an ADSL interface).

3.2.  Links

   The use of IEEE 802.15.4 or any other similar link-layer technology
   which exhibits the characteristics defined for a 6LoWPAN link such as
   low data-rates, packet loss, limited range, asymmetricity and long
   sleep-cycles.  This specification is able to deal with the non-
   symmetric, non-transitive nature of these links.

   6LoWPAN-ND is agnostic to the use of link-layer mesh or [RFC4944]
   mesh techniques, which alleviate the otherwise non-transitive nature
   of wireless links.  This so-called Mesh Under topology thus makes the
   entire link to 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 6.
   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 is possible to combine IP routing and mesh
   link-layers within a LoWPAN.

3.3.  Bootstrapping

   1.  A Host first performs stateless address autoconfiguration of its
   link-local unicast address for each LoWPAN interface from its EUI-64
   as in [RFC4944].  When a LoWPAN Node wants to join a LoWPAN, it does
   so by listening for Route Advertisements from Edge Routers or LoWPAN
   Routers, or by broadcasting a Router Solicitation (RS) and receiving
   RA responses from local routers (see Figure 3).  If a valid prefix is
   advertised in the RA, the host will also form an optimistic global
   unique address with stateless address autoconfiguration (or any other



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   suitable method).  At this point the node has also chosen one or more
   default routers.

   2.  Next the node will attempt to perform initial registration with
   an Edge Router.  Registration is always performed with a link-local
   Edge Router or router by sending a unicast Node Registration (NR)
   message to it.  Registering directly with an Edge Router is of course
   preferred as shown in Figure 4 (the ER is differentiated by the Prf
   flag in its RA), although all LoWPAN Routers have the ability to
   relay NR/NC messages on behalf of a node as shown in Figure 5.

   These message exchanges are illustrated below.  The NR contains the
   addresses the node wants to register.  A node may request a short
   address to be generated on its behalf by including an Address Option
   with the A flag and an address of length 0 in the NR.

   3.  The Edge Router replies either directly with a Node Confirmation
   (NC), or through the relaying router.  Note that routers only exist
   in Route Over configurations, and in pure Mesh Under configurations
   nodes are always within link-local scope of an Edge Router.  This NC
   includes the set of addresses now confirmed to be bound to the
   Whiteboard of the ER.  The Host is now capable of using the LoWPAN
   fully, and the ER forwards on its behalf.


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


    Figure 3: Basic RS/RA exchange between a node and any local router
                      (LoWPAN Router or Edge Router)



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


     Figure 4: Basic ND registration exchange when the Edge Router is
                                   local



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   Node                 Router (ICMP relay)               Edge Router
    |                            |                             |
    |       ---- NR --->         |        ---- NR --->         |
    |                            |                             |
    |      <---- NC ----         |       <---- NC  ----        |
    |                            |                             |


    Figure 5: Registration exchange relayed by a router (no local ER),
                       the messages are ICMP relayed

3.4.  Basic operation

   The node may now send packets to any IPv6 address inside or outside
   the LoWPAN.  Destinations are assumed to be non-local unless known to
   be within link-local scope (valid entry in the neighbor cache).
   Address resolution is not required to be performed with neighbors as
   in [RFC4861], but instead the IID part of the IPv6 address directly
   corresponds to a MAC address.  NS/NA messages are not used.

   The Whiteboard address bindings and assignments are soft, and thus
   must be renewed periodically as indicated by the lifetime of the
   binding.  This is achieved by periodically sending a new NR to the
   ER.  If a host moves, or the network topology changes, and the
   current ER is no longer available, the host then starts the
   registration process with another ER.  If the host is still in the
   same Extended LoWPAN (same subnet prefix), its IPv6 addresses remain
   the same.  Claim and defend addresses generated by the Whiteboard
   must be remembered by the host and refreshed in order to keep the
   address.  If the host moves to a different LoWPAN (thus with a
   different subnet prefix), the bootstrapping process is initiated
   again.  See Section 5 for details on node operation.

   LoWPAN Routers periodically send RAs to their neighbors.  The Edge
   Router initiates the first RAs, and this information is included in
   the RAs of each router.  RA periods can be optimized to reduce
   signalling.  See Section 6 for detailed router operation.

3.5.  Optional features

   This documents specifies a method for forming Extended LoWPAN
   networks with multiple ERs on a backbone link.  This optional Edge
   Router feature allows for the detection of duplicate addresses across
   the entire Extended LoWPAN and backbone links, seen as a single
   subnet.  The method uniquely identifies the LoWPAN Host on the
   backbone, and overrides the claim on an address on behalf of a LoWPAN
   Host.  Thus a Host can keep the same address, and appears the same to
   other hosts on the backbone link, regardless of moving its binding



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   from one ER to another.  See Section 7 for a description of Extended
   LoWPAN operation.  Extended LoWPAN operation does not require changes
   to node operation.


4.  6LoWPAN-ND Messages

   This section introduces message formats for all messages used in this
   document.  The new messages are all ICMPv6 messages and extend the
   capabilities of "The IPv6 Neighbor Discovery Protocol" [RFC4861].  In
   addition, new options for the ICMPv6 Router Advertisement message are
   defined.

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

   o  Router Solicitation

   o  Router Advertisement

   o  Neighbor Solicitation (Extended LoWPAN only)

   o  Neighbor Advertisement (Extended LoWPAN only)

   The following new ICMPv6 message types are defined:

   o  Node Registration

   o  Node Confirmation

   In addition, the following new ICMPv6 options are defined:

   o  Address Option

   o  6LoWPAN Information Option

   o  6LoWPAN Summary Option

   o  Owner Interface Identifier Option

4.1.  Node Registration/Confirmation Message

   The Node Registration (NR) and Node Confirmation (NC) messages are
   used by a node to register with an ER, and for the ER to confirm the
   binding.  The NR is also used to refresh its registration with a
   local router at a faster interval.  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 an local



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   Edge Router or LoWPAN Router.  NR/NC messages may be sent over
   multiple IP hops within the LoWPAN by relaying routers, thus received
   messages with a hop limit less than 255 MUST be accepted by LoWPAN
   Routers from senders with a source address in the same LoWPAN.
   Relaying routers may also use the 6LOWPAN_ER anycast address as the
   destination.

   When registering the first time (the node still has optimistic
   addresses) it sends an NR message to the link-local unicast address
   of an local ER or LoWPAN Router.  The source address must be the IPv6
   unspecified address to comply with oDAD.

   Nodes send subsequent NR messages to a local ER or router, however
   the IPv6 source address is then the link-local IPv6 address of the
   sender.  NR local refresh messages SHOULD be sent more often to a
   local router, thus reducing the amount of traffic sent to ERs over
   multiple hops.  The timings of registrations and local refresh
   messages are indicated by the Binding Lifetime and Advertising
   Interval fields, respectively.

   This same message format is also used for relayed NR/NC messages,
   with an alternative code that is set when the message has been
   relayed.  When relaying, a new message is created with an updated
   checksum, and a code is used to indicate relaying.  The hop limit is
   not decremented when relaying.

   Address Options are included in the NR message for each IPv6 address
   to be registered, and included in the corresponding NC to indicate
   success.  When NR/NC messages are sent through a relaying router
   Target link-layer and Source link-layer address options are used to
   indicate the ER with which registration occured (in an NC) or which
   ER should preferably be used (in an NR).



















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

          Figure 6: Node Registration/Confirmation message format

   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 an
         local Edge Router or router when sent by a node.  The
         destination IPv6 address of an Edge Router or the 6LOWPAN_ER
         anycast address when sent by a relaying router.

      Hop Limit:  255

   ICMP Fields:

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

      Code:  0 indicates this NR is a request sent directly from the
         originating host, or this NC is a corresponding response. 1
         indicates that the message has been relayed by a router. 2
         indicates this NC is a request for the node to re-register. 3
         indicates this NR is a local refresh to the router, or this NC
         is the reply to a refresh.  Values 128-255 are reserved for
         error codes. 128 is sent in an NC response by a router to
         indicate that no ER is available. 129 is sent by a router or
         Edge Router to indicate that Whiteboard registration is not
         supported.





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

      P: 1-bit Primary flag.  Set to indicate that the Edge Router is
         primary and MAY represent the node if used in a Extended
         LoWPAN.  If the flag is not set then the router MUST not
         represent the node on the backbone.  The flag is echoed in a
         confirmation.

      Status:  8-bit unsigned integer.  Values TBD. 0 means unqualified
         success.  Any value below 128 is a positive status that means
         that the binding was created or is being created
         optimistically.

      Binding Lifetime:  16-bit unsigned integer.  The amount of time in
         units of minutes (up to 45 days) 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.

      Advertising Lifetime:  16-bit unsigned integer.  The amount of
         time in units of 10 seconds (up to a week) the node will
         advertise itself to its local router using a NR local refresh.
         This field is ignored if the Binding Lifetime is set to 0.

      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 is used by ERs to detect duplicate OIIs Section 7.8.






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   Possible Options:

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

      Configuration options:  Other configuration information requests
         and configuration settings may be carried in options of NR/NC
         messages.  Such options are not defined in this document.

      Source link-layer address:  This option SHOULD be added to the NC
         by the relaying router to indicate the identity of the ER for
         use by a host.  Format as defined in [RFC4861] and [RFC4944].

      Target link-layer address:  This option MAY be included by a node
         in an NR to indicate the preferred ER to be used by a relaying
         router.  Format as defined in [RFC4861] and [RFC4944].

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

4.2.  Router Solicitation Message

   The RS message format for 6LoWPAN is identical to the [RFC4861] RS
   message.  The following changes are made regarding the use of RS in
   LoWPANs.  If a node has only optimistic addresses, not yet confirmed
   by an Edge 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, as the MAC address is
   implicitly known.  Instead the Owner Interface Identifier specified
   in this document MUST be included in the RS.

4.3.  Router Advertisement Message

   The RA message format for 6LoWPAN is identical to the [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.



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   Possible 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 periodically in
         unsolicited RAs.

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

4.4.  NS/NA Messages

   NS/NA messages are also employed between ERs on the backbone link.
   For this use a unique identifier is required in the message as an
   option to uniquely identify a host's interface.  The standard NS/NA
   message is used in this document is as per [RFC4861] with the an
   additional Owner Interface Identifier Option defined in this
   document.  The Owner Interface Identifier is the same as that carried
   in NR/NC messages and associated with bindings.

   If NS/NA messages are sent on the LoWPAN link (which is not required
   by this specification), they do not carry link-layer address options,
   because of link non-transitivity and the Extended LoWPAN topologies
   do not preserve the MAC address.  For the same reason redirect is not
   supported.  Instead they MUST include the Owner Interface Identifier
   option to help resolve conflict.

4.5.  6LoWPAN-ND Message Options

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

4.5.1.  Address Option

   The Address Option is used to indicate the address which a node wants
   to register with an ER in an NR, 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
   Address Option also allows for duplicate addresses (e.g. anycasts),
   the request of a generated address for claim and defend, or for an
   address to be removed.





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


                      Figure 7: 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.  Values TBD. 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
      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).

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

      16:  Prefix is carried inline.

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

      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.





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      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 is a 6LoWPAN 16-bit short address as defined in RFC 4944
         or as appropriate for the link-layer of the LoWPAN.

      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.

4.5.2.  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.

    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 8: 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.






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   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 local flag.  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 and 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.

   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 local 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.

   For the dissemination of context information, 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



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   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.

4.5.3.  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 9: 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



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      e.g. into a major and a minor metric), and has a mid-range default
      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.

4.5.4.  Owner Interface Identifier Option

   This option is for use with standard NS and NA messages between ERs
   over a backbone link.  By using this option, the binding in question
   can be uniquely identified and matched with the whiteboard entries of
   each ER.

     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 10: Owner Interface Identifier Option

   Type:  TBD6

   Length:  2

   TID:  8-bit unsigned integer.  A unique Transaction ID assigned by
      the host in the associated NR and used to match NC replies.

   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 by ERs to detect duplicate OIIs.





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   Owner Interface Identifier:  A globally unique identifier for the
      host's interface associated with the binding for the NS/NA message
      in question.  This is typically the EUI-64 derived IID of the
      interface.


5.  LoWPAN Node Specification

   This section specifies LoWPAN node operations, and explains the
   differences to [RFC4861] node operation, while specifying the new
   Node Registration operation.  Instead of relying on multicast ND
   messages for DAD and neighbor unreachability detection, LoWPAN Nodes
   send unicast messages to an Edge Router in the LoWPAN which keeps a
   Whiteboard of all bound addresses from nodes attached to that ER.
   Thus these functions are performed across the entire LoWPAN using the
   Whiteboard, which allows 6LoWPAN-ND to operate over asymmetric, non-
   transitive links and with sleeping nodes.  Node complexity and energy
   consumption are reduced as address resolution and the support of
   redirect are not required, ND traffic is reduced and nodes do not
   exchange NS/NA messages.  In an Extended LoWPAN topology, ND
   functions are performed across the entire Extended LoWPAN, and a node
   may change its point of attachment within the LoWPAN without changing
   its IPv6 addresses.  Extended LoWPAN operation is transparent for
   nodes.

5.1.  Conceptual structures and variables

   LoWPAN Nodes make use of the same conceptual data structures as
   defined in [RFC4861] Section 5.1, with the following differences:

   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 non-local.

   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.






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   Edge Router List  - This new structure contains the list of Edge
      Routers the node is registered with an associated timeout and
      primary flag.  This list may be combined with the Default Router
      List.  Non-local ERs can be included in this list but this is not
      required.

   These conceptual data structure 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.

   The following Neighbor Discovery variables are kept for each
   interface, and default values are overridden by information in Router
   Advertisements:

   LinkMTU             The LinkMTU variable is by default 1280 octets
                       for 6LoWPAN.

   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.

   AdvertiseInterval   The advertisement interval sent in Node
                       Registration messages.  Should be less than
                       BindingLifetime.

   RegistrationTimeout The time to wait for a Node Confirmation after
                       sendinf 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.

5.2.  Interface initialization

   All nodes are required to autoconfigure at least one address, a link-
   local address, which is derived from the IEEE 64-bit extended MAC
   address that is globally unique to the interface as in [RFC4944].  As
   a result, knowledge of the 64-bit address of another LoWPAN Node is
   enough to derive its link-local address and reach it if on the same
   link.  Another consequence is that the link-local address is



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   presumably unique on the Extended LoWPAN, which enables the use of
   Optimistic Duplicate Address Detection (oDAD) [RFC4429] over the
   backbone link and the LoWPAN.  The address SHOULD be created as
   optimistic before it has been confirmed by an Edge Router.  Due to
   the way 6LoWPAN networks perform address compression [RFC4944] nodes
   within a LoWPAN use addresses in a homogeneous way and the unicast
   IPv6 address IID resolves directly to a corresponding link-layer
   address.  As a result, address resolution within the LoWPAN is not
   normally required.

   A node MUST join the all-nodes multicast address, which is used for
   receiving RAs from routers.  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 Edge Routers or 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 SLLA 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 using Stateless Address
   Autoconfiguration [RFC4862].  This address is marked optimistic until
   confirmed by the ER.  If the LoWPAN is operating in ad-hoc mode, then
   the prefix is a Unique Local IPv6 Address (ULA) prefix [RFC4193] as
   specified in Section 7.4 (use of a ULA prefix requires no changes to
   node operation).  A node MAY alternatively aquire a global unicast
   address using other suitable means, e.g.  DHCPv6, L2 assignment or
   manual configuration.

5.3.  Registration process

   The binding 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 is tentative or optimistic as long as the binding
   is not confirmed by the ER.  There are two kinds of Node
   Registrations.  Requests NRs (Code = 0) are used for initial
   registration with an ER, ans subsequent ER binding updates.  Requests
   are sent infrequently to minimize overhead (as they may be sent over
   multiple hops).  Refresh NRs (Code = 3) are only sent to the local
   LoWPAN Router in order to refresh its binding table.  Refresh



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   messages are sent more often than Request messages.  If an ER is
   local, then refresh messages are not sent.

   The LoWPAN Node uses unicast Node Registrations with local ERs or
   LoWPAN Routers to perform the binding.  The destination address is
   the link-local unicast address of an local ER or LoWPAN Router.
   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 local ERs 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 choose a router to use for registration.

   When performing Node Registration through a LoWPAN Router, the actual
   ER is transparent to the node by default (the router chooses the best
   ER).  In order to provide nodes the possibility to control which ER
   they register with, Target link-layer and Source link-layer address
   options are used with NR/NC messages.  LoWPAN Routers include a
   Source link-layer address option when relaying an NC to a node, this
   indicates the IID of the ER.  When sending an NR to a LoWPAN Router,
   a node may choose to include a Target link-layer address option with
   the IID of the ER the node wants to register with.  The router then
   attempts to make use of that ER if available.

   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 is used by ERs 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 from the ER by setting the 'A' flag in an Address Option
   during registration.  This is useful for receiving a unique short
   link-layer address, and works in a claim and defend fashion.
   Although the address is generated by the ER and checked for
   uniqueness across the LoWPAN, it is just like any other address



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   binding in the whiteboard of the ER after assignment.  Thus in order
   to keep using this address the host must keep refreshing the address
   binding, including when moving to another ER in the same LoWPAN.

   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
   incremented from there.  Thus the values between 0-15 MUST only used
   after a boot or reboot while not yet registered with an ER.  A node
   that has not heard a valid Node Confirmation for 16 Node Registration
   messages in a row restarts with a local 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 binding.  The
   source of the packet is the link-local address of the local ER or
   LoWPAN 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 or
   tentative to preferred.  See Section 9 for detailed message examples.

   If a Node Confirmation is received with an error code (128 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 there may be no Edge Routers in
   the LoWPAN.  See Section 7.4 for more information on ad-hoc network
   operation.

   This specification also introduces the concept of a secondary
   binding.  For redundancy, a node might place a secondary binding with
   one or more other Edge Routers on the same or different LoWPANs.  The
   'P' flag in the Node Registration Identity Request Option indicates
   whether the binding is primary.  A primary binding MUST be maintained
   with exactly one Edge Router in each LoWPAN at any time.  The use of
   this mechanism for fault tolerance is explained in Section 7.9.

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




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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 sent on
   the link to that destination.  All other prefixes are assumed to be
   non-local as the subnet with that prefix may be larger than link-
   local scope (non-transitive property).  They are therefore sent to
   the IP address of a router chosen from the Default Router List.
   Address resolution is not normally performed as IIDs are derived from
   link-layer addresses.  If it must be performed, then hosts look up
   link-layer information about routers from their Default Router List,
   and routers about hosts using their Binding Table.  Hosts
   communication directly using link-local addresses (always derived
   from a link-layer address), and thus don't perform address resolution
   on each-other.

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

   Care must be used with anycast addresses, as anycast address
   resolution is normally performed with a multicast NS/NA exchange in
   [RFC4861].  As LoWPAN Nodes are not required to perform address
   resolution, and do no use NS/NA messages, anycast addresses MUST be
   considered to be non-local.

5.5.  Destination unreachability detection

   LoWPAN Nodes do not perform [RFC4861] address resolution, DAD or NUD.
   Therefore NS/NA messages are not supported.

   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.


6.  LoWPAN Router Specification

   LoWPAN Routers are used in a route over configuration where the
   network is composed of overlapping link-local scopes.  As a result,
   we extend 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 apply to pure
   Mesh Under LoWPANs where the are no LoWPAN Routers.  In addition to
   the operations described in this section, LoWPAN Routers also need to



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   implement the basic LoWPAN Node operations in Section 5.

   Network configuration parameters carried in Router Advertisements
   originate at edge routers and must disseminate to all routers and
   hosts within the LoWPAN.  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.

   Because Node Registration/Confirmation exchanges between LoWPAN Nodes
   and LoWPAN Routers only occur over link-local scope, such messages
   must be relayed between nodes and ERs when separated by multiple IP
   hops.  Every LoWPAN Router MUST also serve as a relay to ensure that
   any neighboring node can successfully participate in the LoWPAN.

6.1.  Router Configuration Variables

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

6.2.  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
   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.

6.3.  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.





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

      - In the Preference flag: this flag is set to 01 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.

         - 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 "local" flag: the entry's AdvOnLinkFlag.

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

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

6.4.  Sending Unsolicited Router Advertisements

   As specified in Section 6.2.4 of [RFC4861].

6.5.  Ceasing To Be an Advertising Interface

   As specified in Section 6.2.5 of [RFC4861].





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6.6.  Processing Router Solicitations

   As specified in Section 6.2.6 of [RFC4861].

6.7.  Router Advertisement Consistency

   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.

   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
   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 Prefix 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, or when answering an RS, the router SHOULD include all
   6LoWPAN Information Options in the RA.  Therefore a node may use an
   RS in order to get the whole prefix information set in case it misses
   the RA sent when the sequence number changes.

6.8.  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 advertisement
   interval from the last NR.  If address resolution is required, the
   table will also include corresponding link-layer address information.

6.9.  Processing a Node Registration Message

   When a router receives a Node Registration refresh message (Code = 3)
   from a node, it immediately reponds to the sender with a Node
   Confirmation message (Code = 3).  The information in the NR is used
   to update its binding table.



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   When a router receives a Node Registration request message (Code = 0)
   from a node, it sets the Code field to 1 indicating that the message
   has been relayed.  The IPv6 source address is set to that of the
   router.  Furthermore the checksum is re-calculated and the hop limit
   is set to 255.

   By default, the router relays Node Registration messages to the
   6LOWPAN_ER anycast address.  However, the router MAY be configured to
   use a list of destination addresses, which MAY include unicast
   addresses, the 6LOWPAN_ER anycast address, or other addresses
   selected by the network administrator.  If a target link-layer
   address option is included, the router SHOULD take this into account
   as the preferred ER of the node.

6.10.  Relaying a Node Confirmation Message

   When the router receives a Relay Node Confirmation message from an
   Edge Router, the Code field is set to 1.  The Owner Interface
   Identifier and Address Option are used to form the link-local IPv6
   Destination Address for the Node Confirmation message.  The IPv6
   source address is set to the link-local address of the Router.  The
   Hop Limit of the Node Confirmation message is set to 255.

   Upon relaying a successful NC message back to a node, the router
   SHOULD use the information in the NC to update its Binding Table.


7.  LoWPAN Edge Router Specification

   Edge Routers are the routers that connect LoWPANs to an IPv6
   infrastructure via backhaul or backbone links when such an
   infrastructure is available.  To achieve that role:

      Edge Routers MUST implement LoWPAN Router features on their LoWPAN
      interfaces,

      Edge Routers MUST support Whiteboard registration for LoWPAN Nodes
      within their subnets.

      Edge Routers MAY support the Extended LoWPAN modality where a
      LoWPAN subnet is aggregated over a higher speed backbone link.

      Edge Routers supporting the extended LoWPAN modality MUST perform
      ND proxy over the backbone on behalf of their registered LoWPAN
      Nodes.

   This specification documents the LoWPAN Whiteboard, a conceptual data
   structure that is used by the Edge Routers to maintain LoWPAN Node



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   registrations.  This specification documents extensions to the IPv6
   Neighbor Discovery Protocol [RFC4861] that enables a LoWPAN Node to
   locate an Edge Router and then claim and register addresses using
   unicast exchanges with that Edge Router.

   Another function of the Edge Router is to perform 6LoWPAN compression
   and decompression between the LoWPAN and the rest of the IP network
   and ensure MTU compatibility.  Packets flow uncompressed over the
   Backbone or Backhaul Links and are routed normally towards a Gateway
   or an Application sitting outside of the LoWPAN.

   In the Extended LoWPAN case, the Edge Router also performs proxy ND
   operations over the Backbone Link on behalf of the LoWPAN Nodes that
   are registered to it.  This section also documents the proxy ND
   operation used by the Edge Routers over the Backbone link and the
   conflict resolution process that enables transparent micro-mobility
   for the LoWPAN Nodes.

7.1.  The Whiteboard

   The Whiteboard is a conceptual data structure that is maintained by
   the Edge Routers to store their knowledge of the registered LoWPAN
   Nodes.  Information maintained for each registered node includes:

   IPv6 address:  The IPv6 address being registered.  This is an IPv6
      unicast address of any scope.

   Owner Interface Identifier:  The 64-bit OII of the LoWPAN Node's
      interface (usually formed from an EUI-64) is used for Address
      collision detection and resolution (Section 7.7).

   Owner Nonce:  The 32-bit nonce generated by a node upon booting is
      used for Duplicate OII detection (Section 7.8).

   Primary flag:  Influences the proxy ND operation in the Extended
      LoWPAN case.

   Registration Age and Lifetime:  The registration age indicates how
      long ago the last registration flow took place.  When the age
      reaches the registration lifetime, the whiteboard entry is
      removed.

   It can be noted that no link-layer information is stored in the
   Whiteboard.  If the Edge Router is also used as the default gateway
   for a LoWPAN Node then it would possess LLA information in its
   Neighbor Cache.  Otherwise, it will route packets towards the LoWPAN
   Nodes and thus will not need or use the LLA of the LoWPAN Node.




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   It can also be noted that in the Extended LoWPAN case, an Edge Router
   only maintains the information on the LoWPAN Nodes that are
   registered to it.  So the full registry of all the LoWPAN Nodes in a
   subnet is actually distributed between the Edge Routers.

   The Whiteboard conceptually requires 177 bits of storage per LoWPAN
   Node entry, plus 128 bits per IPv6 address.  Considerable
   optimization when realizing a Whiteboard can be made with regard to
   IPv6 addresses using default prefix, OII and other known information
   along with lifetimes and TIDs.  In practice IPv6 address information
   can mostly be elided.

7.2.  Simple LoWPAN

   The support of the Simple LoWPAN modality is REQUIRED.  In that
   configuration, a single Edge Router serves a subnet that is formed by
   the LoWPAN Nodes that are registered to that Edge Router, as
   represented in Figure 1.  The ER may be connected to an IP
   infrastructure and may inject the prefixes for its subnet in the
   routed infrastructure.

   In a Simple LoWPAN, the Edge Router is the repository of all
   registrations and can detect a registration collision by simply using
   its Whiteboard, so the Whiteboard is the reference for Duplicate
   Address Detection operations.

   The prefix for the LoWPAN is configured on the Edge Router or
   acquired using prefix delegation.  In the absence of a global IPv6
   prefix, an ER may generate a prefix based on Unique Local 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 3.2.2 of [RFC4193] or something
   appropriate to the Edge Router's capabilities.

   The Edge Router forms a link-local address in exactly the same way as
   any other node on the LoWPAN, for instance based on its link layer
   addresses to enable 6LoWPAN Header Compression.  If the resulting
   address is not present in the Whiteboard then the Edge Router owns
   the address right away.  The Edge Router announces itself using
   Router Advertisement (RA) messages that are broadcasted periodically
   over the LOWPAN.







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7.3.  Extended LoWPAN

   The support of the Extended LoWPAN modality is OPTIONAL.  In that
   modality, a high speed Backbone Link interconnects multiple devices
   and Edge Routers to form a single subnet that encompasses IPv6 nodes
   attached to the Backbone Link and LoWPAN Nodes registered to the Edge
   Routers as represented in Figure 2.  As a result, all further
   reference to the Backbone Link and ND proxy operation over that link
   is OPTIONAL but come as a whole.

   In the Extended LoWPAN modality, the Backbone Link is used as a
   reference for address ownership and registration collision detection.
   Addresses that are not found in the Whiteboard are queried over the
   backbone using the ND operation in place for that type of link,
   typically [RFC4861]; Edge Routers represent themselves and the LoWPAN
   Nodes that are proactively registered to them.  An ND lookup over the
   backbone is not propagated over the LoWPANs, but answered by the Edge
   Router that has the registration for the target, if any.

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

   As all ERs in an Extended LoWPAN advertise the same subnet prefix on
   their LoWPAN interfaces, ERs acquire their LoWPAN subnet prefix from
   the backbone link as in [RFC4861].  In the absence of a global IPv6
   address, an IPv6 router can alternatively advertise a ULA prefix as
   defined in Section 7.2.

7.4.  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.

   If a LoWPAN Router in the Ad-hoc LoWPAN is configured to implement
   basic Edge Router Whiteboard functionality and generates a ULA prefix
   [RFC4193] (as described in Section 7.2), then 6LoWPAN-ND can be
   applied throughout the LoWPAN.  There SHOULD be only one Edge Router
   in an Ad-hoc LoWPAN (just as in a Simple LoWPAN) to keep consistency
   in the Whiteboard and ULA prefix.  However if Edge Routers in an Ad-
   hoc LoWPAN are able to emulate backbone link functionality between
   each other, and to coordinate the ULA prefix then there MAY be
   multiple Edge Routers if they implement Extended LoWPAN ER
   functionality.



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7.5.  Registration process

   An Edge Router configures the well-known 6LOWPAN_ER anycast address
   on the LoWPAN interfaces where it serves as Edge Router.  Note that
   the Edge Router will accept Node Registration messages with a hop
   limit that is lower than 255 but it MUST drop a Node Registration
   that does not come from a LoWPAN interface that is associated to the
   same subnet.

   The new Owner Interface Identifier Option in Backbone Link ND
   messages that carries the node OII, Owner Nonce and TID help
   differentiate an address collision from a new registration from the
   same node.  Details on collision detection and resolution are
   provided in Section 7.7.

   The Edge Router responds to a Node Registration with a Node
   Confirmation.  If the source address of the NR was not the
   Unspecified Address, then the destination address in the confirmation
   is the source in the NR.  If the source address of the NR was the
   Unspecified Address, then the ER acts as the LoWPAN Router for the
   source, and the destination address is the optimistic address being
   registered.  The destination link-layer address is not taken from the
   ND cache but from the source link-layer address in the NR.  The
   source address is a unicast address of the ER that matches the scope
   of the destination, preferably the destination in the NR if it is not
   anycast.

   The remainder of this section deals with the case of an Extended
   LoWPAN configuration.  In that case:

   When it inserts an address in its Whiteboard, an Edge Router SHOULD
   perform Duplicate Address Detection (DAD) over the Backbone Link to
   detect a collision.  Upon a new registration for a link-local, unique
   local or global unicast address based on an IEEE 64-bit extended MAC
   address, the Edge Router MAY use Optimistic DAD [RFC4429] on the
   Backbone Link.  A positive acknowledgement can be sent to the 6LoWPAN
   node right away if oDAD is used on the Backbone Link.

   A LoWPAN Node should be able to join a different Edge Router at any
   time without the complexities of terminating a current registration
   and renumbering.  To enable this, the ND operation on the Backbone
   Link upon a Node Registration/Confirmation flow wins the address
   ownership over an ND operation that is done asynchronously, on behalf
   of the same LoWPAN Node, upon a prior registration.  So an Edge
   Router that would happen to have a binding for that same address for
   the same LoWPAN Node will yield and depreciate its binding.

   The override (O) bit is used to differentiate a registration flow



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   from the asynchronous defense of an address by an Edge Router acting
   as a proxy.  Upon a registration flow, an Edge Router doing DAD or
   accepting a reregistration SHOULD set the override (O) bit in its NA
   messages.  Asynchronously to the registration, the Edge Router SHOULD
   NOT set the override (O) bit in its NA messages and should yield to
   an NA message with the override (O) bit set.

   So the Edge Router operation on the Backbone Link is similar to that
   of a Home Agent as specified in "Mobility Support for IPv6" [RFC3775]
   yet different.  In particular, the Neighbor Advertisement message is
   used as specified in section "10.4.1.  Intercepting Packets for a
   Mobile Node" with the exception that the override (O) bit is not set,
   indicating that this Edge Router acts as a proxy for the LoWPAN and
   will yield should another Edge Router claim that address on the
   Backbone Link.

   This specification also introduces the concept of a secondary
   binding.  Upon a secondary binding, the Edge Router will not announce
   or defend the address on the backbone link, but will be able to
   forward packets to the node over its LoWPAN interface.  This feature
   is used for fault tolerance, explained in Section 7.9.

   If the Edge Router is primary for a registration as indicated by the
   'P' flag and it is connected to a Backbone, then it SHOULD perform ND
   operations on the backbone.  In particular the Edge Router SHOULD
   reject the registration if DAD fails on the backbone.  When oDAD is
   used over the backbone the Edge Router MAY issue the Node
   Confirmation right away with a positive code, but if a collision is
   finally detected, it cancels the registration with an asynchronous
   Node Confirmation and a negative completion code on the same TID.

   If the NR message includes an Address Option with the 'A' flag set,
   this indicated the request of short address generation.  The ER
   acquires an appropriate, unique link-layer address for the network
   either by generating it and performing DAD, or with some other
   method.  If successful, this address is returned in an Address Option
   of the NC with the 'A' flag set.  The IPv6 address is formed from the
   generated link-layer address with the default prefix inline.

7.6.  Forwarding packets between a LoWPAN and an IPv6 infrastructure

   Upon receiving packets on one of its LoWPAN interfaces, the Edge
   Router checks whether it has a binding for the source address.  If it
   does, then the Edge Router can forward the packet; otherwise, the
   Edge Router MUST discard the packet.

   If the packet is to be transmitted over a Backbone or Backhaul Link,
   then the 6LoWPAN sublayer is terminated and the full IPv6 packet is



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

   From the standpoint of an Edge Router, the view of the subnet in the
   Extended LoWPAN modality is that all nodes in the subnet are either
   LoWPAN nodes registered to this ER or local on the Backbone Link,
   though in fact they might be proxied for by other ERs.  If the
   destination is a LoWPAN node registered to this ER, the ER will
   forward the packet over the LoWPAN interface either as a local
   delivery if the node is local or via intermediate LoWPAN routers
   using the routing in place in the LoWPAN.  If the destination is not
   a registered LoWPAN node, then the ER acts as if the subnet was local
   on the Backbone and looks up the node there using ND.  If the node is
   not found there either, it is assumed unreachable and an "Destination
   Unreachable" ICMP message is sent to the source as prescribed by
   [RFC4443].

7.7.  Address collision detection and resolution

   The assumption in this section is that the OII that is carried in the
   registration messages and in the NS/NA messages is globally unique.
   When this assumption fails, this is detected by an additional
   collision resolution mechanism, as detailed in Section 7.8.

   The address collision can be detected within the Edge Router if the
   Edge Router already has a registration for a given address, or over
   the Backbone Link using Duplicate Address Detection.  In the latter
   case, a new ND option, the Owner Interface Identifier Option is used
   in NS/NA messages to carry the additional information required for
   the resolution of conflicts: Transaction ID, Owner Interface
   Identifier, and Owner Nonce.  In any case, the Edge Router in charge
   of the resolution is the Edge Router that handles the registration.

   A registration is identified by the (OII, IPv6 address) pair.  A
   conflict occurs when a Node Registration is received for an IPv6
   address that is already registered with a different OII at the same
   or another Edge Router.  The resolution of such conflict is explained
   below.

   Additionally, the following principles apply to the resolution in the
   Extended LoWPAN modality:

      Mobility within a subnet is supported and welcome.  In an Extended
      LoWPAN, a LoWPAN Node may migrate its registration to a new Edge
      Router transparently and at any time.  The protocol is designed to
      recognize the mobility and silently cleanup the registration



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      states.

      A synchronous operation wins against a delayed proxy operation.
      An Edge Router that processes a Node Registration normally takes
      over an existing registration maintained by a defendant Edge
      Router.

      The decision to migrate the registration from an Edge Router to
      another is made by the Edge Router that processes a Node
      Registration message based on its own states for that registration
      and ND exchanges over the Backbone Link.

      A conflict may also occur with a node that is already present on
      the Backbone Link when the registration occurs, or with a node
      that appears on the Backbone Link while a registration already
      exists for its claimed address.  The resolution of such conflict
      is done using standard Duplicate Address Detection as prescribed
      by [RFC4862].

      A claim for an address with a better proof of ownership wins.  For
      instance a node on the backbone that proves ownership of an
      address by means of Secure ND [RFC3971] wins over a node that does
      not.  The concept of "better" is a policy and is not specified
      hereafter, though it is REQUIRED for an implementation to enable
      the enforcement of such a policy.

   Upon receiving a Node Registration message, an Edge Router looks up
   an existing registration for that IPv6 address in its LoWPAN
   whiteboard.  If the entry does not exist then the Edge Router looks
   up the address over the Backbone Link using the NS (DAD) mechanism.
   The Edge Router SHOULD include an Owner Interface Identifier Option
   in the NS message.  An Edge Router that defends that address for an
   existing registration MUST include an Owner Interface Identifier
   Option in the NA message and SHOULD NOT set the Override (O) bit.

   If no entry is found for that address and DAD times out, the Edge
   Router accepts the registration: it creates an entry on the
   whiteboard, sends a positive Node Confirmation Message to the node,
   and advertises the address on the Backbone Link.  Since this happens
   asynchronously to the Node Registration, the Edge Router SHOULD NOT
   set Override (O) bit in the NA message.

   If an entry is found in the whiteboard for the same (OII, IPv6
   address) pair, additional checking is performed for duplicate OII
   detection as detailed in Section 7.8.  If no duplication is detected,
   then the Edge Router accepts the update of the reservation: it
   updates the entry on the whiteboard, sends a positive Node
   Confirmation Message to the node, and advertises the address on the



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   Backbone Link.  Since this happens synchronously to the Node
   Registration, the Edge Router SHOULD set the Override (O) bit in the
   NA message.

   If the address is already present on the Backbone Link and defended
   by a remote Edge Router, then that Edge Router defends the address
   with the Override (O) bit reset and the Owner Interface Identifier
   Option in the NA message.

   If the Edge Router receives an NA message during the DAD period, it
   checks for an Owner Interface Identifier Option in the NA message.
   If there is no OII or the (O) bit is set then this is a duplicate
   address, DAD fails and the registration is rejected.  If there is an
   Owner Interface Identifier Option in the NA message and the OII is
   different, then DAD fails and the registration is rejected.  If the
   OII is the same, additional checking is performed for duplicate OII
   detection as detailed in Section 7.8.  If there is no duplication
   then the NA is ignored and the DAD timer keeps going.

   If the Edge Router receives an NS (DAD) message from another node
   during the DAD period, it checks for a Owner Interface Identifier
   Option in the NS message.  If there is no OII then DAD fails and the
   registration is rejected.  If there is an Owner Interface Identifier
   Option in the NA message and the OII is different, then DAD fails and
   the registration is rejected.  If the OII is the same, then the
   greatest TID wins.  In other words, if the TID in the registration is
   smaller than or equal to the TID in the OII Option then DAD fails and
   the registration is rejected.  Otherwise the NS is ignored and the
   DAD timer keeps going.

   Other Edge Routers are informed of a take over decision by an NA with
   the Override (O) bit set and silently set their own state to non-
   operational.  An Edge Router that loses ownership should attempt to
   keep the registration entry in the whiteboard till the end of the
   registration lifetime for the purpose of duplicate OII detection if
   memory capacity allows.  The TID in the whiteboard entry is updated
   with that in the OII option in the NA.

7.8.  Duplicate OII detection

   The address collision detection mechanism described in the previous
   section only works if OII values are unique to each node.  The
   purpose of the duplicate OII detection mechanism specified in this
   section is to find out where this is not the case.  Note that such an
   OII collision is a "cannot happen", as the EUI-64 assignment
   mechanisms are supposed to ensure its uniqueness.  Still, accidents
   (as well as deliberate rogue behavior, e.g. by counterfeiters) do
   happen.  The objective here is to reliably detect, not to remedy,



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   such a situation.

   In conjunction with the OII, two values are sent in each Node
   Registration (and in the OII option sent with NS/NA) to help with
   duplicate OII detection: The transaction ID (TID) and the Owner
   Nonce.  The TID is a sequence number that is also used to control the
   normal operation of a registration exchange, relating a node
   confirmation to its node registration.  The TID is set by a node in
   its Node Registration message and echoed by the Edge Router in the
   Node Confirmation message.

   The TID is maintained using the lollipop mechanism.  When a node
   starts or restarts, it sets its local next TID to zero and its local
   Owner Nonce to a random value.  (While cryptographic randomness
   [RFC4086] is not strictly required, the randomness SHOULD be derived
   using a mechanism of similar quality.)  After that, the node
   increments the local next TID after sending each Request Node
   Registration, but keeps the Owner Nonce constant.  When the TID needs
   to be incremented beyond its maximum value (0xFF), it wraps directly
   to its looping value at the base of the lollipop that is 16 (0x10).
   So a value in the straight part of the lollipop (between 0 and 0xF)
   is only used after a reboot and before the circular part of the
   lollipop is entered.

   Upon a positive Node Confirmation, if the current local next TID is
   less than 16, then the node sets it to 16.  Regardless of its current
   local next TID, a node that has not heard a valid Node Confirmation
   for 16 Node Registration messages in a row restarts with a local next
   TID of zero (the node MAY, but need not, generate a new Owner Nonce).
   In summary, this means a TID less than 16 (in the straight part of
   the lollipop) denotes a node that just started/restarted and did not
   get registered yet (or did not hear the acknowledgement), so we call
   such a TID an unacknowledged TID; conversely, TIDs of 16 or larger
   are acknowledged TIDs.

   To compare TID1 and TID2, the following rules apply:

      If at least one of TID1 and TID2 is unacknowledged (smaller than
      16) then they compare directly.

      If both TID1 and TID2 are acknowledged, then TID2 is greater than
      TID1 if (TID2 - TID1) is smaller than (TID1 - TID2).

   A TID value is consistent with the preceding one if it is the same or
   a small increment or decrement (more by or less by 0 to 16) from the
   preceding one.  If the TID arriving in a Node Registration message at
   an Edge Router is the same or a small decrement as a preceding one,
   then a registration message was duplicated or two of them crossed and



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   the most recent message should be ignored; this is not necessarily an
   indication of an OII collision.

   A Node Registration message is consistent with the Whiteboard entry
   if the TIDs are consistent and the Owner Nonce values are the same.
   As long a new Node Registration message is consistent with the
   current whiteboard entry, it appears that the new message is coming
   from the same source as the previous one and there is no OII
   collision.

   If the TID in a new Node Registration message jumps back to an
   unacknowledged value, this can be interpreted as either a new node
   competing for the OII and a reboot by the node owning the
   registration.  With this specification, this situation is
   optimistically interpreted as a reboot and not detected as a
   collision, but an actual collision will be detected and filtered out
   next.  For now, TID and OII from the new Node Registration message
   are copied into the Whiteboard entry.

   Otherwise, i.e., the TID in a new Node Registration is an
   acknowledged TID, if that is inconsistent with the most recently
   accepted TID value, or if the Owner Nonce values do not match, then
   the Node Registration message is rejected as an OII collision.

   +--------------+-----------+-----------+---------+---------+--------+
   | Case         | OII       | Nonce     | TID     | Address | Action |
   +--------------+-----------+-----------+---------+---------+--------+
   | Initial      | Unique    | *         | *       | Unique  | Accept |
   | Registration |           |           |         |         |        |
   | New Address  | Duplicate | Same      | >       | *       | Accept |
   | or Movement  |           |           |         |         |        |
   | Duplicate    | Duplicate | Same      | <=      | *       | Ignore |
   | Message      |           |           |         |         |        |
   | Node Reboot  | Duplicate | Different | < 0x10  | *       | Accept |
   | OII          | Duplicate | Different | >= 0x10 | *       | Reject |
   | Collision    |           |           |         |         |        |
   +--------------+-----------+-----------+---------+---------+--------+

      Table 1: The processing options for NR messages (* = wildcard)

7.9.  Fault tolerance

   This specification allows for a secondary registration.  The
   secondary registration enables the node to prepare states within the
   network and make the move quicker between primary and secondary.

   If an external keep alive mechanism is in place between the primary
   and the secondary Edge Routers, then the secondary registration



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   enables the secondary Edge Router to start intercepting packets on
   the backbone and forwarding them to the node before the node even
   knows that the primary is no longer operational.

   The secondary registration also enables the node to bicast a packet
   for extra reliability, that is send a copy of a packet to both Edge
   Routers without being subject to ingress filtering.  The mechanism
   that enables this filtering is not specified here.


8.  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


9.  Message Examples

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

9.1.  Basic NR/NC message exchange

   In the basic case, when a host wanting to register to the whiteboard
   is on the same link with an ER, 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
   ER.  In this example the host wants to use the Edge Router as
   primary, a 10 minute binding lifetime, a 60 second advertisement
   interval , 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: ER'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   |    Code = 0   |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TID = 0     |  Status = 0   |1|         Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Binding Lifetime = 10      |   Advertising Interval = 6    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Owner Nonce                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Owner Interface Identifier =                 +
   |                Modified EUI-64 of the interface               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 11: Basic NR request.






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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=1 |  P=0    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|0|0|        Reserved         |         Padding  = 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           Figure 12: NR Address Option 1, for the SAA 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|        Reserved         |         Padding = 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        Figure 13: NR Address Option 2, for the requested address.


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

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


                   Figure 14: Corresponding NC message.



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


           Figure 15: NC Address Option 1, for the SAA address.













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   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|        Reserved         |   Generated 16-bit address    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        Figure 16: NC Address Option 2, for the requested address.

9.2.  Relaying an NR message

   In case an ER is non-local for initial node registration, then the NR
   message from the previous example is sent to any local router in
   exactly the same format.  This router in turn relays the message to
   an ER.  As the OII of the Host is the same as its IID, the Router
   simply sets Code = 1 to indicate that the message was relayed.  The
   destination IPv6 address is that of an Edge Router and the source
   IPv6 address that of the relaying router.  The Address Options are
   not modified.

   IPv6 Source: Router's global address
   IPv6 Destination: ER's global 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   |    Code = 1   |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TID = 0     |  Status = 0   |1|         Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Binding Lifetime = 10      |   Advertising Interval = 6    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Owner Nonce                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Owner Interface Identifier =                 +
   |                Modified EUI-64 of the interface               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 17: Relayed NR message.






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9.3.  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.

   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 18: 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 19: 6LoWPAN Information Option example.







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10.  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
   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 local
   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.

   The use of Secure ND has been considered for securing NS/NA messages
   exchanged between Edge Routers on the backbone link.

   The use of IP-level forwarding of NR/NC ND messages requires relaxed
   checking of Hop Limit values in ND packets received, compared to the
   validation required by [RFC4861].  This may make ND vulnerable to
   off-LoWPAN senders that accidentally or intentionally send ND
   messages.  This specification states that Edge Routers MUST implement
   measures to filter out such off-LoWPAN ND messages.


11.  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  Address Option (TBD3)

   o  6LoWPAN Information Option (TBD4)





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   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]

   There is also the need for a new link local anycast address,
   6LOWPAN_ER for 6LoWPAN edge routers and Routers; used as a functional
   address.

   [TO BE REMOVED: This registration should take place at the following
   location: http://www.iana.org/assignments/ipv6-anycast-addresses]


12.  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.


13.  Changelog

   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)

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

      o Fixed assymetric 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 "local" and "non-local" used in place of "on-link" and
      "off-link".





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      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 local 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 aquire
      addresses. (#38)

      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.




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      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).

      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 lollypop 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.




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      o Completed message examples.

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


14.  References

14.1.  Normative References

   [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.

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

   [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.

   [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.






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14.2.  Informative References

   [I-D.ietf-6lowpan-hc]
              Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams in 6LoWPAN Networks", draft-ietf-6lowpan-hc-04
              (work in progress), December 2008.

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

   [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.

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

   [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.


Authors' Addresses

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

   Phone: +358407796297
   Email: zach@sensinode.com






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   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


   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










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

   Phone:
   Email: Erik.Nordmark@Sun.COM











































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