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An Update to 6LoWPAN ND
draft-ietf-6lo-rfc6775-update-12

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8505.
Authors Pascal Thubert , Erik Nordmark , Samita Chakrabarti , Charles E. Perkins
Last updated 2018-02-21
Replaces draft-thubert-6lo-rfc6775-update
RFC stream Internet Engineering Task Force (IETF)
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Reviews
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Gabriel Montenegro
Shepherd write-up Show Last changed 2018-01-16
IESG IESG state Became RFC 8505 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Suresh Krishnan
Send notices to "Gabriel Montenegro" <Gabriel.Montenegro@microsoft.com>
IANA IANA review state IANA - Review Needed
draft-ietf-6lo-rfc6775-update-12
6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     cisco
Updates: 6775 (if approved)                                  E. Nordmark
Intended status: Standards Track                                  Zededa
Expires: August 24, 2018                                  S. Chakrabarti
                                                                 Verizon
                                                              C. Perkins
                                                               Futurewei
                                                       February 20, 2018

                        An Update to 6LoWPAN ND
                    draft-ietf-6lo-rfc6775-update-12

Abstract

   This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to
   clarify the role of the protocol as a registration technique,
   simplify the registration operation in 6LoWPAN routers, as well as to
   provide enhancements to the registration capabilities and mobility
   detection for different network topologies including the backbone
   routers performing proxy Neighbor Discovery in a low power network.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 24, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.
   
   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Applicability of Address Registration Options . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Extended Address Registration Option (EARO) . . . . . . .   7
     4.2.  Transaction ID  . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Comparing TID values  . . . . . . . . . . . . . . . .   8
     4.3.  Registration Unique ID  . . . . . . . . . . . . . . . . .   9
     4.4.  Extended Duplicate Address Messages . . . . . . . . . . .  10
     4.5.  Registering the Target Address  . . . . . . . . . . . . .  10
     4.6.  Link-Local Addresses and Registration . . . . . . . . . .  11
     4.7.  Maintaining the Registration States . . . . . . . . . . .  12
   5.  Detecting Enhanced ARO Capability Support . . . . . . . . . .  14
   6.  Extended ND Options And Messages  . . . . . . . . . . . . . .  14
     6.1.  Enhanced Address Registration Option (EARO) . . . . . . .  14
     6.2.  Extended Duplicate Address Message Formats  . . . . . . .  17
     6.3.  New 6LoWPAN Capability Bits in the Capability Indication
           Option  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   7.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  19
     7.1.  Discovering the capabilities of an ND peer  . . . . . . .  19
       7.1.1.  Using the "E" Flag in the 6CIO  . . . . . . . . . . .  19
       7.1.2.  Using the "T" Flag in the EARO  . . . . . . . . . . .  19
     7.2.  Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . .  20
     7.3.  Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . .  20
     7.4.  Legacy 6LoWPAN Border Router  . . . . . . . . . . . . . .  21
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  23
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     10.1.  ARO Flags  . . . . . . . . . . . . . . . . . . . . . . .  24
     10.2.  ICMP Codes . . . . . . . . . . . . . . . . . . . . . . .  24
     10.3.  New ARO Status values  . . . . . . . . . . . . . . . . .  25
     10.4.  New 6LoWPAN capability Bits  . . . . . . . . . . . . . .  26
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  27
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     12.2.  Informative References . . . . . . . . . . . . . . . . .  28
     12.3.  External Informative References  . . . . . . . . . . . .  31
   Appendix A.  Applicability and Requirements Served  . . . . . . .  32
   Appendix B.  Requirements . . . . . . . . . . . . . . . . . . . .  33

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     B.1.  Requirements Related to Mobility  . . . . . . . . . . . .  33
     B.2.  Requirements Related to Routing Protocols . . . . . . . .  33
     B.3.  Requirements Related to the Variety of Low-Power Link
           types . . . . . . . . . . . . . . . . . . . . . . . . . .  34
     B.4.  Requirements Related to Proxy Operations  . . . . . . . .  35
     B.5.  Requirements Related to Security  . . . . . . . . . . . .  35
     B.6.  Requirements Related to Scalability . . . . . . . . . . .  37
     B.7.  Matching Requirements with Specifications . . . . . . . .  37
   Appendix C.  Subset of a 6LoWPAN Glossary . . . . . . . . . . . .  38
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   The scope of this draft is an IPv6 Low Power Networks including star
   and mesh topologies.  This specification modifies and extends the
   behavior and protocol elements of "Neighbor Discovery Optimization
   for IPv6 over Low-Power Wireless Personal Area Networks" (6LoWPAN ND)
   [RFC6775] to enable additional capabilities and enhancements such as:

   o  Support for indicating mobility vs retry (T-bit)

   o  Simplify the registration flow for link-local addresses

   o  Enhancement to Address Registration Option (ARO)

   o  Permitting registration of a target address

   o  Clarification of support of privacy and temporary addresses

   The applicability of 6LoWPAN ND registration is discussed in
   Section 2, and new extensions and updates to [RFC6775] are presented
   in Section 4.  Considerations on Backward Compatibility, Security and
   Privacy are also elaborated upon in Section 7, Section 8 and in
   Section 9, respectively.

2.  Applicability of Address Registration Options

   The purpose of the Address Registration Option (ARO) in the legacy
   6LoWPAN ND specification is to facilitate duplicate address detection
   (DAD) for hosts as well as populate Neighbor Cache Entries (NCE)
   [RFC4861] in the routers.  This reduces the reliance on multicast
   operations, which are often as intrusive as broadcast, in IPv6 ND
   operations.

   With this specification, a failed or useless registration can be
   detected for reasons other than address duplication.  Examples
   include: the router having run out of space; a registration bearing a
   stale sequence number perhaps denoting a movement of the host after

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   the registration was placed; a host misbehaving and attempting to
   register an invalid address such as the unspecified address
   [RFC4291]; or a host using an address which is not topologically
   correct on that link.

   In such cases the host will receive an error to help diagnose the
   issue and may retry, possibly with a different address, and possibly
   registering to a different router, depending on the returned error.
   The ability to return errors to address registrations is not intended
   to be used to restrict the ability of hosts to form and use multiple
   addresses, as recommended in "Host Address Availability
   Recommendations" [RFC7934].

   In particular, the freedom to form and register addresses is needed
   for enhanced privacy; each host may register a number of addresses
   using mechanisms such as "Privacy Extensions for Stateless Address
   Autoconfiguration (SLAAC) in IPv6" [RFC4941].

   In IPv6 ND [RFC4861], a router must have enough storage to hold
   neighbor cache entries for all the addresses to which it may forward.
   A router using the Address Registration mechanism also needs enough
   storage to hold NCEs for all the addresses that may be registered to
   it, regardless of whether or not they are actively communicating.
   The number of registrations supported by a 6LoWPAN Router (6LR) or
   6LoWPAN Border Router (6LBR) must be clearly documented.

   A network administrator should deploy updated 6LR/6LBRs to support
   the number and type of devices in their network, based on the number
   of IPv6 addresses that those devices require and their address
   renewal rate and behavior.

3.  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].

   The Terminology used in this document is consistent with and
   incorporates that described in Terms Used in Routing for Low-Power
   and Lossy Networks (LLNs).  [RFC7102].

   Other terms in use in LLNs are found in Terminology for Constrained-
   Node Networks [RFC7228].

   Readers are expected to be familiar with all the terms and concepts
   that are discussed in

   o  "Neighbor Discovery for IP version 6" [RFC4861],

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   o  "IPv6 Stateless Address Autoconfiguration" [RFC4862],

   o  "Problem Statement and Requirements for IPv6 over Low-Power
      Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606],

   o  "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
      Overview, Assumptions, Problem Statement, and Goals" [RFC4919],

   o  "Neighbor Discovery Optimization for Low-power and Lossy Networks"
      [RFC6775] and

   o  "Multi-link Subnet Support in IPv6"
      [I-D.ietf-ipv6-multilink-subnets],

   as well as the following terminology:

   Backbone Link:  An IPv6 transit link that interconnects two or more
         Backbone Routers.  It is expected to be a higher speed device
         speed compared to the LLN in order to carry the traffic that is
         required to federate multiple segments of the potentially large
         LLN into a single IPv6 subnet.

   Backbone Router:  A logical network function in an IPv6 router that
         federates a LLN over a Backbone Link.  In order to do so, the
         Backbone Router (6BBR) proxies the 6LoWPAN ND operations
         detailed in the document onto the matching operations that run
         over the backbone, typically IPv6 ND.  Note that 6BBR is a
         logical function, just like 6LR and 6LBR, and that a same
         physical router may operate all three.

   Extended LLN:  The aggregation of multiple LLNs as defined in
         [RFC4919], interconnected by a Backbone Link via Backbone
         Routers, and forming a single IPv6 MultiLink Subnet.

   Registration:  The process during which a 6LN registers its
         address(es) with the Border Router so the 6BBR can serve as
         proxy for ND operations over the Backbone.

   Binding:  The association between an IP address with a MAC address, a
         port and/or other information about the node that owns the IP
         address.

   Registered Node:  The node for which the registration is performed,
         and which owns the fields in the EARO option.

   Registering Node:  The node that performs the registration to the
         6BBR, which may proxy for the registered node.

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   Registered Address:  An address owned by the Registered Node node
         that was or is being registered.

   legacy:  a 6LN, a 6LR or a 6LBR that supports [RFC6775] but not this
         specification.

   updated:  a 6LN, a 6LR or a 6LBR that supports this specification.

4.  Updating RFC 6775

   This specification introduces the Extended Address Registration
   Option (EARO) based on the ARO as defined [RFC6775]; in particular a
   "T" flag is added that MUST be set in NS messages when this
   specification is used, and echoed in NA messages to confirm that the
   protocol is supported.

   The extensions to the ARO option are used in the Duplicate Address
   Request (DAR) and Duplicate Address Confirmation (DAC) messages, so
   as to convey the additional information all the way to the 6LBR.  In
   turn the 6LBR may proxy the registration using IPv6 ND over a
   backbone as illustrated in Figure 1.  Note that this specification
   avoids the extended DAR flow for Link Local Addresses in a Route-Over
   [RFC6606] mesh.

        6LN              6LR             6LBR            6BBR
         |                |               |                |
         |   NS(EARO)     |               |                |
         |--------------->|               |                |
         |                | Extended DAR  |                |
         |                |-------------->|                |
         |                |               |                |
         |                |               | proxy NS(EARO) |
         |                |               |--------------->|
         |                |               |                | NS(DAD)
         |                |               |                | ------>
         |                |               |                | <wait>
         |                |               |                |
         |                |               | proxy NA(EARO) |
         |                |               |<---------------|
         |                | Extended DAC  |                |
         |                |<--------------|                |
         |   NA(EARO)     |               |                |
         |<---------------|               |                |
         |                |               |                |

                     Figure 1: (Re-)Registration Flow

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   In order to support various types of link layers, it is RECOMMENDED
   to allow multiple registrations, including for privacy / temporary
   addresses, and provide new mechanisms to help clean up stale
   registration states as soon as possible.

   Section 5 of [RFC6775] specifies how a 6LN bootstraps an interface
   and locates available 6LRs; a Registering Node SHOULD prefer
   registering to a 6LR that is found to support this specification, as
   discussed in Section 7.1, over a legacy one.

4.1.  Extended Address Registration Option (EARO)

   The Extended ARO (EARO) deprecates the ARO and is backward compatible
   with it.  More details on backward compatibility can be found in
   Section 7.

   The semantics of the ARO are modified as follows:

   o  The address that is being registered with a Neighbor Solicitation
      (NS) with an EARO is now the Target Address, as opposed to the
      Source Address as specified in [RFC6775] (see Section 4.5).  This
      change enables a 6LBR to use one of its addresses as source to the
      proxy-registration of an address that belongs to a LLN Node to a
      6BBR.  This also limits the use of an address as source address
      before it is registered and the associated DAD process is
      complete.

   o  The Unique ID in the EARO Option is not required to be a MAC
      address (see Section 4.3).

   o  The specification introduces a Transaction ID (TID) field in the
      EARO (see Section 4.2).  The TID MUST be provided by a node that
      supports this specification and a new "T" flag MUST be set to
      indicate so.

   o  Finally, this specification introduces new status codes to help
      diagnose the cause of a registration failure (see Table 1).

4.2.  Transaction ID

   The Transaction ID (TID) is a sequence number that is incremented
   with each re-registration.  The TID is used to detect the freshness
   of the registration request and useful to detect one single
   registration by multiple 6LoWPAN border routers (e.g., 6LBRs and
   6BBRs) supporting the same 6LoWPAN.  The TID may also be used by the
   network to track the sequence of movements of a node in order to
   route to the current (freshest known) location of a moving node.

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   When a Registered Node is registered with multiple 6BBRs in parallel,
   the same TID SHOULD be used, to enable the 6BBRs to determine that
   the registrations are the same, and distinguish that situation from a
   movement.

4.2.1.  Comparing TID values

   The TID is a sequence counter and its operation is the exact match of
   the path sequence specified in RPL, the IPv6 Routing Protocol for
   Low-Power and Lossy Networks [RFC6550] specification.

   In order to keep this document self-contained and yet compatible, the
   text below is an exact copy from section 7.2.  "Sequence Counter
   Operation" of [RFC6550].

   A TID is deemed to be fresher than another when its value is greater
   per the operations detailed in this section.

   The TID range is subdivided in a 'lollipop' fashion ([Perlman83]),
   where the values from 128 and greater are used as a linear sequence
   to indicate a restart and bootstrap the counter, and the values less
   than or equal to 127 used as a circular sequence number space of size
   128 as in [RFC1982].  Consideration is given to the mode of operation
   when transitioning from the linear region to the circular region.
   Finally, when operating in the circular region, if sequence numbers
   are detected to be too far apart then they are not comparable, as
   detailed below.

   A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
   a value of 2^N, where N is defined to be 4 in this specification.

   For a given sequence counter,

   1.  The sequence counter SHOULD be initialized to an implementation
       defined value which is 128 or greater prior to use.  A
       recommended value is 240 (256 - SEQUENCE_WINDOW).

   2.  When a sequence counter increment would cause the sequence
       counter to increment beyond its maximum value, the sequence
       counter MUST wrap back to zero.  When incrementing a sequence
       counter greater than or equal to 128, the maximum value is 255.
       When incrementing a sequence counter less than 128, the maximum
       value is 127.

   3.  When comparing two sequence counters, the following rules MUST be
       applied:

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       1.  When a first sequence counter A is in the interval [128..255]
           and a second sequence counter B is in [0..127]:

           1.  If (256 + B - A) is less than or equal to
               SEQUENCE_WINDOW, then B is greater than A, A is less than
               B, and the two are not equal.

           2.  If (256 + B - A) is greater than SEQUENCE_WINDOW, then A
               is greater than B, B is less than A, and the two are not
               equal.

           For example, if A is 240, and B is 5, then (256 + 5 - 240) is
           21.  21 is greater than SEQUENCE_WINDOW (16), thus 240 is
           greater than 5.  As another example, if A is 250 and B is 5,
           then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW
           (16), thus 250 is less than 5.

       2.  In the case where both sequence counters to be compared are
           less than or equal to 127, and in the case where both
           sequence counters to be compared are greater than or equal to
           128:

           1.  If the absolute magnitude of difference between the two
               sequence counters is less than or equal to
               SEQUENCE_WINDOW, then a comparison as described in
               [RFC1982] is used to determine the relationships greater
               than, less than, and equal.

           2.  If the absolute magnitude of difference of the two
               sequence counters is greater than SEQUENCE_WINDOW, then a
               desynchronization has occurred and the two sequence
               numbers are not comparable.

   4.  If two sequence numbers are determined to be not comparable, i.e.
       the results of the comparison are not defined, then a node should
       give precedence to the sequence number that was most recently
       incremented.  Failing this, the node should select the sequence
       number in order to minimize the resulting changes to its own
       state.

4.3.  Registration Unique ID

   The Registration Unique ID (RUID) enables a duplicate address
   registration to be distinguished from a double registration or a
   movement.  An ND message from the 6BBR over the Backbone that is
   proxied on behalf of a Registered Node must carry the most recent
   EARO option seen for that node.  A NS/NA with an EARO and a NS/NA

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   without a EARO thus represent different nodes; if they relate to a
   same target then an address duplication is likely.

   The Registration Unique ID in [RFC6775] is a EUI-64 globally unique
   address configured at a Lower Layer, under the assumption that
   duplicate EUI-64 addresses are avoided.

   With this specification, the Registration Unique ID is allowed to be
   extended to different types of identifier, as long as the type is
   clearly indicated.  For instance, the type can be a cryptographic
   string and used to prove the ownership of the registration as
   discussed in "Address Protected Neighbor Discovery for Low-power and
   Lossy Networks" [I-D.ietf-6lo-ap-nd].  In order to support the flows
   related to the proof of ownership, this specification introduces new
   status codes "Validation Requested" and "Validation Failed" in the
   EARO.

   The Registering Node SHOULD store the unique ID, or a way to generate
   that ID, in persistent memory.  Otherwise, if a reboot causes a loss
   of memory, re-registering the same address could be impossible until
   the 6LBR times out the previous registration.

4.4.  Extended Duplicate Address Messages

   In order to map the new EARO content in the DAR/DAC messages, a new
   TID field is added to the Extended DAR (EDAR) and the Extended DAC
   (EDAC) messages as a replacement to a Reserved field, and an odd
   value of the ICMP Code indicates support for the TID, to transport
   the "T" flag.

   In order to prepare for future extensions, and though no option has
   been defined for the Duplicate Address messages, implementations
   SHOULD expect ND options after the main body, and SHOULD ignore them.

   As for the EARO, the Extended Duplicate Address messages are backward
   compatible with the legacy versions, and remarks concerning backwards
   compatibility for the protocol between the 6LN and the 6LR apply
   similarly between a 6LR and a 6LBR.

4.5.  Registering the Target Address

   The Registering Node is the node that performs the registration to
   the 6BBR.  As in [RFC6775], it may be the Registered Node as well, in
   which case it registers one of its own addresses, and indicates its
   own MAC Address as Source Link Layer Address (SLLA) in the NS(EARO).

   This specification adds the capability to proxy the registration
   operation on behalf of a Registered Node that is reachable over a LLN

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   mesh.  In that case, if the Registered Node is reachable from the
   6BBR over a Mesh-Under mesh, the Registering Node indicates the MAC
   Address of the Registered Node as SLLA in the NS(EARO).  If the
   Registered Node is reachable over a Route-Over mesh from the
   Registering Node, the SLLA in the NS(ARO) is that of the Registering
   Node.  This enables the Registering Node to attract the packets from
   the 6BBR and route them over the LLN to the Registered Node.

   In order to enable the latter operation, this specification changes
   the behavior of the 6LN and the 6LR so that the Registered Address is
   found in the Target Address field of the NS and NA messages as
   opposed to the Source Address.  With this convention, a TLLA option
   indicates the link-layer address of the 6LN that owns the address,
   whereas the SLLA Option in a NS message indicates that of the
   Registering Node, which can be the owner device, or a proxy.

   The Registering Node is reachable from the 6LR, and is also the one
   expecting packets for the 6LN.  Therefore, it MUST place its own Link
   Layer Address in the SLLA Option that MUST always be placed in a
   registration NS(EARO) message.  This maintains compatibility with
   legacy 6LoWPAN ND [RFC6775].

4.6.  Link-Local Addresses and Registration

   Considering that LLN nodes are often not wired and may move, there is
   no guarantee that a Link-Local address stays unique between a
   potentially variable and unbounded set of neighboring nodes.

   Compared to [RFC6775], this specification only requires that a Link-
   Local address is unique from the perspective of the two nodes that
   use it to communicate (e.g. the 6LN and the 6LR in an NS/NA
   exchange).  This simplifies the DAD process in Route-Over Mode for
   Link-Local addresses, and there is no exchange of Duplicate Address
   messages between the 6LR and a 6LBR for Link-Local addresses.

   In more details:

   An exchange between two nodes using Link-Local addresses implies that
   they are reachable over one hop and that at least one of the 2 nodes
   acts as a 6LR.  A node MUST register a Link-Local address to a 6LR in
   order to obtain reachability from that 6LR beyond the current
   exchange, and in particular to use the Link-Local address as source
   address to register other addresses, e.g. global addresses.

   If there is no collision with an address previously registered to
   this 6LR by another 6LN, then the Link-Local address is unique from
   the standpoint of this 6LR and the registration is acceptable.
   Alternatively, two different 6LRs might expose the same Link-Local

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   address but different link-layer addresses.  In that case, a 6LN MUST
   only interact with at most one of the 6LRs.

   The DAD process between the 6LR and a 6LBR, which is based on an
   exchange of Duplicate Address messages, does not need to take place
   for Link-Local addresses.

   When registering to a 6LR that conforms this specification, a node
   MUST use a Link-Local address as the source address of the
   registration, whatever the type of IPv6 address that is being
   registered.  That Link-Local Address MUST be either an address that
   is already registered to the 6LR, or the address that is being
   registered.

   When a Registering Node does not have an already-Registered Address,
   it MUST register a Link-Local address, using it as both the Source
   and the Target Address of an NS(EARO) message.  In that case, it is
   RECOMMENDED to use a Link-Local address that is (expected to be)
   globally unique, e.g., derived from a globally unique hardware MAC
   address.  An EARO option in the response NA indicates that the 6LR
   supports this specification.

   Since there is no Duplicate Address exchange for Link-Local
   addresses, the 6LR may answer immediately to the registration of a
   Link-Local address, based solely on its existing state and the Source
   Link-Layer Option that MUST be placed in the NS(EARO) message as
   required in [RFC6775].

   A node needs to register its IPv6 Global Unicast IPv6 Addresses
   (GUAs) to a 6LR in order to establish global reachability for these
   addresses via that 6LR.  When registering with an updated 6LR, a
   Registering Node does not use its GUA as Source Address, in contrast
   to a node that complies to [RFC6775].  For non-Link-Local addresses,
   the Duplicate Address exchange MUST conform to [RFC6775], but the
   extended formats described in this specification for the DAR and the
   DAC are used to relay the extended information in the case of an
   EARO.

4.7.  Maintaining the Registration States

   This section discusses protocol actions that involve the Registering
   Node, the 6LR and the 6LBR.  It must be noted that the portion that
   deals with a 6LBR only applies to those addresses that are registered
   to it; as discussed in Section 4.6, this is not the case for Link-
   Local addresses.  The registration state includes all data that is
   stored in the router relative to that registration, in particular,
   but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store
   additional registration information in more complex data structures

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   and use protocols that are out of scope of this document to keep them
   synchronized when they are distributed.

   When its Neighbor Cache is full, a 6LR cannot accept a new
   registration.  In that situation, the EARO is returned in a NA
   message with a Status of 2, and the Registering Node may attempt to
   register to another 6LR.

   If the registry in the 6LBR is saturated, the LBR cannot guarantee
   that a new address is effectively not a duplicate.  In that case, the
   6LBR replies to a EDAR message with a EDAC message that carries a new
   Status Code indicating "6LBR Registry saturated" Table 1.  Note: this
   code is used by 6LBRs instead of Status 2 when responding to a
   Duplicate Address message exchange and passed on to the Registering
   Node by the 6LR.  There is no point for the node to retry this
   registration immediately via another 6LR, since the problem is global
   to the network.  The node may either abandon that address, de-
   register other addresses first to make room, or keep the address in
   TENTATIVE state and retry later.

   A node renews an existing registration by sending a new NS(EARO)
   message for the Registered Address.  In order to refresh the
   registration state in the 6LBR, the registration MUST be reported to
   the 6LBR.

   A node that ceases to use an address SHOULD attempt to de-register
   that address from all the 6LRs to which it has registered the
   address, which is achieved using an NS(EARO) message with a
   Registration Lifetime of 0.

   A node that moves away from a particular 6LR SHOULD attempt to de-
   register all of its addresses registered to that 6LR and register to
   a new 6LR with an incremented TID.  When/if the node shows up
   elsewhere, an asynchronous NA(EARO) or EDAC message with a status of
   3 "Moved" SHOULD be used to clean up the state in the previous
   location.  For instance, as described in
   [I-D.ietf-6lo-backbone-router], the "Moved" status can be used by a
   6BBR in a NA(EARO) message to indicate that the ownership of the
   proxy state on the Backbone was transferred to another 6BBR, as the
   consequence of a movement of the device.  The receiver of the message
   SHOULD propagate the status down the chain towards the Registered
   node (e.g. reversing an existing RPL [RFC6550] path) and then clean
   up its state.

   Upon receiving a NS(EARO) message with a Registration Lifetime of 0
   and determining that this EARO is the freshest for a given NCE (see
   Section 4.2), a 6LR cleans up its NCE.  If the address was registered
   to the 6LBR, then the 6LR MUST report to the 6LBR, through a

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   Duplicate Address exchange with the 6LBR, indicating the null
   Registration Lifetime and the latest TID that this 6LR is aware of.

   Upon receiving the Extended DAR message, the 6LBR evaluates if this
   is the most recent TID it has received for that particular registry
   entry.  If so, then the entry is scheduled to be removed, and the
   EDAR is answered with a EDAC message bearing a Status of 0
   ("Success").  Otherwise, a Status 3 ("Moved") is returned instead,
   and the existing entry is maintained.

   When an address is scheduled to be removed, the 6LBR SHOULD keep its
   entry in a DELAY state for a configurable period of time, so as to
   protect a mobile node that de-registered from one 6LR and did not
   register yet to a new one, or the new registration did not reach yet
   the 6LBR due to propagation delays in the network.  Once the DELAY
   time is passed, the 6LBR silently removes its entry.

5.  Detecting Enhanced ARO Capability Support

   The "Generic Header Compression for IPv6 over 6LoWPANs" [RFC7400]
   introduces the 6LoWPAN Capability Indication Option (6CIO) to
   indicate a node's capabilities to its peers.

   Section 6.3 defines new flags for the 6CIO to signal support for
   EARO, as well as the node's capability to act as a 6LR, 6LBR and
   6BBR.  Section 7.1.1 specifies how the "E" flag can be used to
   provide backward compatibility.

   The 6CIO is typically sent in a Router Solicitation (RS) message.
   When used to signal capabilities per this specification, the 6CIO is
   typically present in Router Advertisement (RA) messages but can also
   be present in RS, Neighbor Solicitation (NS) and Neighbor
   Advertisement (NA) messages.

6.  Extended ND Options And Messages

   This specification does not introduce new options, but it modifies
   existing ones and updates the associated behaviors as specified in
   the following subsections.

6.1.  Enhanced Address Registration Option (EARO)

   The Address Registration Option (ARO) is defined in section 4.1. of
   [RFC6775].

   The Enhanced Address Registration Option (EARO) updates the ARO
   option within Neighbor Discovery NS and NA messages between a 6LN and
   its 6LR.  On the other hand, the Extended Duplicate Address messages,

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   EDAR and EDAC, replace the DAR and DAC messages so as to transport
   the new information between 6LRs and 6LBRs across LLN meshes such as
   6TiSCH networks.

   An NS message with an EARO option is a registration if and only if it
   also carries an SLLAO option.  The EARO option also used in NS and NA
   messages between Backbone Routers [I-D.ietf-6lo-backbone-router] over
   the Backbone link to sort out the distributed registration state; in
   that case, it does not carry the SLLAO option and is not confused
   with a registration.

   When using the EARO option, the address being registered is found in
   the Target Address field of the NS and NA messages.

   The EARO extends the ARO and is indicated by the "T" flag set.  The
   format of the EARO option is as follows:

      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 = 2  |    Status     |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Reserved  |T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +       Registration Unique ID   (EUI-64 or equivalent)         +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                              Figure 2: EARO

   Option Fields

   Type:           33

   Length:         8-bit unsigned integer.  The length of the option in
                   units of 8 bytes.  Always 2.

   Status:         8-bit unsigned integer.  Indicates the status of a
                   registration in the NA response.  MUST be set to 0 in
                   NS messages.  See Table 1 below.

   +-------+-----------------------------------------------------------+
   | Value | Description                                               |
   +-------+-----------------------------------------------------------+
   |  0..2 | See [RFC6775].  Note: a Status of 1 "Duplicate Address"   |
   |       | applies to the Registered Address. If the Source Address  |
   |       | conflicts with an existing registration, "Duplicate       |

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   |       | Source Address" should be used.                           |
   |       |                                                           |
   |   3   | Moved: The registration failed because it is not the      |
   |       | freshest.  This Status indicates that the registration is |
   |       | rejected because another more recent registration was     |
   |       | done, as indicated by a same OUI and a more recent TID.   |
   |       | One possible cause is a stale registration that has       |
   |       | progressed slowly in the network and was passed by a more |
   |       | recent one.  It could also indicate a OUI collision.      |
   |       |                                                           |
   |   4   | Removed: The binding state was removed. This may be       |
   |       | placed in an asynchronous NS(ARO) message, or as the      |
   |       | rejection of a proxy registration to a Backbone Router    |
   |       |                                                           |
   |   5   | Validation Requested: The Registering Node is challenged  |
   |       | for owning the Registered Address or for being an         |
   |       | acceptable proxy for the registration.  This Status is    |
   |       | expected in asynchronous messages from a registrar (6LR,  |
   |       | 6LBR, 6BBR) to indicate that the registration state is    |
   |       | removed, for instance due to a movement of the device.    |
   |       |                                                           |
   |   6   | Duplicate Source Address: The address used as source of   |
   |       | the NS(ARO) conflicts with an existing registration.      |
   |       |                                                           |
   |   7   | Invalid Source Address: The address used as source of the |
   |       | NS(ARO) is not a Link-Local address as prescribed by this |
   |       | document.                                                 |
   |       |                                                           |
   |   8   | Registered Address topologically incorrect: The address   |
   |       | being registered is not usable on this link, e.g. it is   |
   |       | not topologically correct                                 |
   |       |                                                           |
   |   9   | 6LBR Registry saturated: A new registration cannot be     |
   |       | accepted because the 6LBR Registry is saturated.  Note:   |
   |       | this code is used by 6LBRs instead of Status 2 when       |
   |       | responding to a Duplicate Address message exchange and    |
   |       | passed on to the Registering Node by the 6LR.             |
   |       |                                                           |
   |   10  | Validation Failed: The proof of ownership of the          |
   |       | registered address is not correct.                        |
   +-------+-----------------------------------------------------------+

                           Table 1: EARO Status

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

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   T:              One bit flag.  Set if the next octet is a used as a
                   TID.

   TID:            1-byte integer; a transaction id that is maintained
                   by the node and incremented with each transaction.
                   The node SHOULD maintain the TID in a persistent
                   storage.

   Registration Lifetime:  16-bit integer; expressed in minutes.  0
                   means that the registration has ended and the
                   associated state should be removed.

   Registration Unique IDentifier (OUI):  A globally unique identifier
                   for the node associated.  This can be the EUI-64
                   derived IID of an interface, or some provable ID
                   obtained cryptographically.

6.2.  Extended Duplicate Address Message Formats

   The Duplicate Address Request (DAR) and the Duplicate Address
   Confirmation (DAC) messages are defined in section 4.4 of [RFC6775].
   Those messages follow a common base format, which enables information
   from the ARO to be transported over multiple hops.

   The Duplicate Address Messages are extended to adapt to the Extended
   ARO format, as follows:

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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             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Status     |     TID       |     Registration Lifetime     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +          Registration Unique ID   (EUI-64 or equivalent)             +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Registered Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: Duplicate Address Messages Format

   Modified Message Fields

   Code:           The ICMP Code as defined in [RFC4443].  The ICMP Code
                   MUST be set to 1 with this specification.  An odd
                   value of the ICMP Code indicates that the TID field
                   is present and obeys this specification.

   TID:            1-byte integer; same definition and processing as the
                   TID in the EARO option as defined in Section 6.1.

   Registration Unique IDentifier (OUI):  8 bytes; same definition and
                   processing as the OUI in the EARO option as defined
                   in Section 6.1.

6.3.  New 6LoWPAN Capability Bits in the Capability Indication Option

   This specification defines new capability bits for use in the 6CIO,
   which was introduced by [RFC7400] for use in IPv6 ND RA messages.

   Routers that support this specification MUST set the "E" flag and 6LN
   SHOULD favor 6LR routers that support this specification over those
   that do not.  Routers that are capable of acting as 6LR, 6LBR and
   6BBR SHOULD set the "L", "B" and "P" flags, respectively.  In
   particular, the function 6LR is often collocated with that of 6LBR.

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   Those flags are not mutually exclusive and if a router is capable of
   performing multiple functions, it SHOULD set all the related flags.

       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 = 1  |     Reserved        |L|B|P|E|G|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Reserved                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 4: New capability Bits L, B, P, E in the 6CIO

   Option Fields

   Type:  36

   L: Node is a 6LR, it can take registrations.

   B: Node is a 6LBR.

   P: Node is a 6BBR, proxying for nodes on this link.

   E: This specification is supported and applied.

7.  Backward Compatibility

7.1.  Discovering the capabilities of an ND peer

7.1.1.  Using the "E" Flag in the 6CIO

   If the 6CIO is used in an ND message and the sending node supports
   this specification, then the "E" Flag MUST be set.

   A router that supports this specification SHOULD indicate that with a
   6CIO.

   If the Registering Node receives a 6CIO in a Router Advertisement
   message, then the setting of the "E" Flag indicates whether or not
   this specification is supported.

7.1.2.  Using the "T" Flag in the EARO

   One alternate way for a 6LN to discover the router's capabilities is
   to first register a Link Local address, placing the same address in
   the Source and Target Address fields of the NS message, and setting
   the "T" Flag.  The node may for instance register an address that is

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   based on EUI-64.  For such an address, DAD is not required and using
   the SLLAO option in the NS is actually more consistent with existing
   ND specifications such as the "Optimistic Duplicate Address Detection
   (ODAD) for IPv6" [RFC4429].

   Once its first registration is complete, the node knows from the
   setting of the "T" Flag in the response whether the router supports
   this specification.  If support is verified, the node may register
   other addresses that it owns, or proxy-register addresses on behalf
   some another node, indicating those addresses being registered in the
   Target Address field of the NS messages, while using one of its own
   previously registered addresses as source.

   A node that supports this specification MUST always use an EARO as a
   replacement to an ARO in its registration to a router.  This is
   harmless since the "T" flag and TID field are reserved in [RFC6775],
   and are ignored by a legacy router.  A router that supports this
   specification answers an ARO with an ARO and answers an EARO with an
   EARO.

   This specification changes the behavior of the peers in a
   registration flow.  To enable backward compatibility, a 6LN that
   registers to a 6LR that is not known to support this specification
   MUST behave in a manner that is compatible with [RFC6775].  A 6LN can
   achieve that by sending a NS(EARO) message with a Link-Local Address
   used as both Source and Target Address, as described in Section 4.6.
   Once the 6LR is known to support this specification, the 6LN MUST
   obey this specification.

7.2.  Legacy 6LoWPAN Node

   A legacy 6LN will use the Registered Address as source and will not
   use an EARO option.  An updated 6LR MUST accept that registration if
   it is valid per [RFC6775], and it MUST manage the binding cache
   accordingly.  The updated 6LR MUST then use the legacy Duplicate
   Address messages as specified in [RFC6775] to indicate to the 6LBR
   that the TID is not present in the messages.

   The main difference with [RFC6775] is that Duplicate Address exchange
   for DAD is avoided for Link-Local addresses.  In any case, the 6LR
   SHOULD use an EARO in the reply, and may use any of the Status codes
   defined in this specification.

7.3.  Legacy 6LoWPAN Router

   The first registration by an updated 6LN MUST be for a Link-Local
   address, using that Link-Local address as source.  A legacy 6LR will

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   not make a difference and treat that registration as if the 6LN was a
   legacy node.

   An updated 6LN will always use an EARO option in the registration NS
   message, whereas a legacy 6LR will always reply with an ARO option in
   the NA message.  From that first registration, the updated 6LN can
   determine whether or not the 6LR supports this specification.

   After detecting a legacy 6LR, an updated 6LN SHOULD attempt to find
   an alternate 6LR that is updated for a reasonable time that depends
   on the type of device and the expected deployment.

   An updated 6LN SHOULD use an EARO in the request regardless of the
   type of 6LR, legacy or updated, which implies that the "T" flag is
   set.

   If an updated 6LN moves from an updated 6LR to a legacy 6LR, the
   legacy 6LR will send a legacy DAR message, which can not be compared
   with an updated one for freshness.

   Allowing legacy DAR messages to replace a state established by the
   updated protocol in the 6LBR would be an attack vector and that
   cannot be the default behavior.

   But if legacy and updated 6LRs coexist temporarily in a network, then
   it makes sense for an administrator to install a policy that allows
   so, and the capability to install such a policy should be
   configurable in a 6LBR though it is out of scope for this document.

7.4.  Legacy 6LoWPAN Border Router

   With this specification, the Duplicate Address messages are extended
   to transport the EARO information.  Similarly to the NS/NA exchange,
   updated 6LBR devices always use the Extended Duplicate Address
   messages and all the associated behavior so they can always be
   differentiated from legacy ones.

   Note that a legacy 6LBR will accept and process an EDAR message as if
   it was a legacy DAR, so legacy support of DAD is preserved.

8.  Security Considerations

   This specification extends [RFC6775], and the security section of
   that draft also applies to this as well.  In particular, it is
   expected that the link layer is sufficiently protected to prevent a
   rogue access, either by means of physical or IP security on the
   Backbone Link and link layer cryptography on the LLN.

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   This specification also expects that the LLN MAC provides secure
   unicast to/from the Backbone Router and secure Broadcast from the
   Backbone Router in a way that prevents tampering with or replaying
   the RA messages.

   This specification recommends using privacy techniques (see
   Section 9), and protection against address theft such as provided by
   "Address Protected Neighbor Discovery for Low-power and Lossy
   Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the
   Registered Address using a cryptographic RUID.

   The registration mechanism may be used by a rogue node to attack the
   6LR or the 6LBR with a Denial-of-Service attack against the registry.
   It may also happen that the registry of a 6LR or a 6LBR is saturated
   and cannot take any more registration, which effectively denies the
   requesting a node the capability to use a new address.  In order to
   alleviate those concerns, Section 4.7 provides a number of
   recommendations that ensure that a stale registration is removed as
   soon as possible from the 6LR and 6LBR.  In particular, this
   specification recommends that:

   o  A node that ceases to use an address SHOULD attempt to de-register
      that address from all the 6LRs to which it is registered.  See
      Section 4.2 for the mechanism to avoid replay attacks and avoiding
      the use of stale registration information.

   o  The Registration lifetimes SHOULD be individually configurable for
      each address or group of addresses.  The nodes SHOULD be
      configured with a Registration Lifetime that reflects their
      expectation of how long they will use the address with the 6LR to
      which it is registered.  In particular, use cases that involve
      mobility or rapid address changes SHOULD use lifetimes that are
      larger yet of a same order as the duration of the expectation of
      presence.

   o  The router (6LR or 6LBR) SHOULD be configurable so as to limit the
      number of addresses that can be registered by a single node, as
      identified at least by MAC address and preferably by security
      credentials.  When that maximum is reached, the router should use
      a Least-Recently-Used (LRU) algorithm to clean up the addresses,
      keeping at least one Link-Local address.  The router SHOULD
      attempt to keep one or more stable addresses if stability can be
      determined, e.g. from the way the IID is formed or because they
      are used over a much longer time span than other (privacy,
      shorter-lived) addresses.  Address lifetimes SHOULD be
      individually configurable.

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   o  In order to avoid denial of registration for the lack of
      resources, administrators should take great care to deploy
      adequate numbers of 6LRs to cover the needs of the nodes in their
      range, so as to avoid a situation of starving nodes.  It is
      expected that the 6LBR that serves a LLN is a more capable node
      then the average 6LR, but in a network condition where it may
      become saturated, a particular deployment should distribute the
      6LBR functionality, for instance by leveraging a high speed
      Backbone and Backbone Routers to aggregate multiple LLNs into a
      larger subnet.

   The LLN nodes depend on the 6LBR and the 6BBR for their operation.  A
   trust model must be put in place to ensure that the right devices are
   acting in these roles, so as to avoid threats such as black-holing,
   or bombing attack whereby an impersonated 6LBR would destroy state in
   the network by using the "Removed" Status code.  This trust model
   could be at a minimum based on a Layer-2 access control, or could
   provide role validation as well (see Req5.1 in Appendix B.5).

9.  Privacy Considerations

   As indicated in section Section 2, this protocol does not aim at
   limiting the number of IPv6 addresses that a device can form.  A host
   should be able to form and register any address that is topologically
   correct in the subnet(s) advertised by the 6LR/6LBR.

   This specification does not mandate any particular way for forming
   IPv6 addresses, but it discourages using EUI-64 for forming the
   Interface ID in the Link-Local address because this method prevents
   the usage of "SEcure Neighbor Discovery (SEND)" [RFC3971] and
   "Cryptographically Generated Addresses (CGA)" [RFC3972], and that of
   address privacy techniques.

   "Privacy Considerations for IPv6 Adaptation-Layer Mechanisms"
   [RFC8065] explains why privacy is important and how to form privacy-
   aware addresses.  All implementations and deployment must consider
   the option of privacy addresses in their own environment.

   The IPv6 address of the 6LN in the IPv6 header can be compressed
   statelessly when the Interface Identifier in the IPv6 address can be
   derived from the Lower Layer address.  When it is not critical to
   benefit from that compression, e.g. the address can be compressed
   statefully, or it is rarely used and/or it is used only over one hop,
   then privacy concerns should be considered.  In particular, new
   implementations should follow the IETF "Recommendation on Stable IPv6
   Interface Identifiers" [RFC8064] This RFC recommends the use of "A
   Method for Generating Semantically Opaque Interface Identifiers with

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   IPv6 Stateless Address Autoconfiguration (SLAAC)" [RFC7217] for
   generating Interface Identifiers to be used in SLAAC.

10.  IANA Considerations

   Note to RFC Editor: please replace "This RFC" throughout this
   document by the RFC number for this specification once it is
   attributed.

   IANA is requested to make a number of changes under the "Internet
   Control Message Protocol version 6 (ICMPv6) Parameters" registry, as
   follows.

10.1.  ARO Flags

   IANA is requested to create a new subregistry for "ARO Flags".  This
   specification defines 8 positions, bit 0 to bit 7, and assigns bit 7
   for the "T" flag in Section 6.1.  The policy is "IETF Review" or
   "IESG Approval" [RFC8126].  The initial content of the registry is as
   shown in Table 2.

     New subregistry for ARO Flags under the "Internet Control Message
             Protocol version 6 (ICMPv6) [RFC4443] Parameters"

                +-------------+--------------+-----------+
                |  ARO Status | Description  | Document  |
                +-------------+--------------+-----------+
                |     0..6    | Unassigned   |           |
                |             |              |           |
                |      7      | "T" Flag     | This RFC  |
                +-------------+--------------+-----------+

                          Table 2: new ARO Flags

10.2.  ICMP Codes

   IANA is requested to create a new entry in the ICMPv6 "Code" Fields
   subregistry of the Internet Control Message Protocol version 6
   (ICMPv6) Parameters for the ICMP codes related to the ICMP type 157
   and 158 Duplicate Address Request (shown in Table 3) and Confirmation
   (shown in Table 4), respectively, as follows:

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                New entries for ICMP types 157 DAR message

               +-------+----------------------+------------+
               | Code  | Name                 | Reference  |
               +-------+----------------------+------------+
               | 0     | Original DAR message | RFC 6775   |
               |       |                      |            |
               | 1     | Extended DAR message | This RFC   |
               +-------+----------------------+------------+

                      Table 3: new ICMPv6 Code Fields

                New entries for ICMP types 158 DAC message

               +-------+----------------------+------------+
               | Code  | Name                 | Reference  |
               +-------+----------------------+------------+
               | 0     | Original DAC message | RFC 6775   |
               |       |                      |            |
               | 1     | Extended DAC message | This RFC   |
               +-------+----------------------+------------+

                      Table 4: new ICMPv6 Code Fields

10.3.  New ARO Status values

   IANA is requested to make additions to the Address Registration
   Option Status Values Registry as follows:

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            Address Registration Option Status Values Registry

   +-------------+-----------------------------------------+-----------+
   |  ARO Status | Description                             | Document  |
   +-------------+-----------------------------------------+-----------+
   |      3      | Moved                                   | This RFC  |
   |             |                                         |           |
   |      4      | Removed                                 | This RFC  |
   |             |                                         |           |
   |      5      | Validation Requested                    | This RFC  |
   |             |                                         |           |
   |      6      | Duplicate Source Address                | This RFC  |
   |             |                                         |           |
   |      7      | Invalid Source Address                  | This RFC  |
   |             |                                         |           |
   |      8      | Registered Address topologically        | This RFC  |
   |             | incorrect                               |           |
   |             |                                         |           |
   |      9      | 6LBR registry saturated                 | This RFC  |
   |             |                                         |           |
   |      10     | Validation Failed                       | This RFC  |
   +-------------+-----------------------------------------+-----------+

                      Table 5: New ARO Status values

10.4.  New 6LoWPAN capability Bits

   IANA is requested to make additions to the Subregistry for "6LoWPAN
   capability Bits" as follows:

   Subregistry for "6LoWPAN capability Bits" under the "Internet Control
              Message Protocol version 6 (ICMPv6) Parameters"

          +-----------------+----------------------+-----------+
          |  Capability Bit | Description          | Document  |
          +-----------------+----------------------+-----------+
          |        11       | 6LR  capable (L bit) | This RFC  |
          |                 |                      |           |
          |        12       | 6LBR capable (B bit) | This RFC  |
          |                 |                      |           |
          |        13       | 6BBR capable (P bit) | This RFC  |
          |                 |                      |           |
          |        14       | EARO support (E bit) | This RFC  |
          +-----------------+----------------------+-----------+

                   Table 6: New 6LoWPAN capability Bits

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11.  Acknowledgments

   Kudos to Eric Levy-Abegnoli who designed the First Hop Security
   infrastructure upon which the first backbone router was implemented.
   Many thanks to Sedat Gormus, Rahul Jadhav and Lorenzo Colitti for
   their various contributions and reviews.  Also many thanks to Thomas
   Watteyne for his early implementation of a 6LN that was instrumental
   to the early tests of the 6LR, 6LBR and Backbone Router.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

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

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <https://www.rfc-editor.org/info/rfc6775>.

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   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

12.2.  Informative References

   [I-D.chakrabarti-nordmark-6man-efficient-nd]
              Chakrabarti, S., Nordmark, E., Thubert, P., and M.
              Wasserman, "IPv6 Neighbor Discovery Optimizations for
              Wired and Wireless Networks", draft-chakrabarti-nordmark-
              6man-efficient-nd-07 (work in progress), February 2015.

   [I-D.delcarpio-6lo-wlanah]
              Vega, L., Robles, I., and R. Morabito, "IPv6 over
              802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
              progress), October 2015.

   [I-D.ietf-6lo-ap-nd]
              Thubert, P., Sarikaya, B., and M. Sethi, "Address
              Protected Neighbor Discovery for Low-power and Lossy
              Networks", draft-ietf-6lo-ap-nd-05 (work in progress),
              January 2018.

   [I-D.ietf-6lo-backbone-router]
              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-05 (work in progress), January 2018.

   [I-D.ietf-6lo-nfc]
              Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
              "Transmission of IPv6 Packets over Near Field
              Communication", draft-ietf-6lo-nfc-09 (work in progress),
              January 2018.

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work
              in progress), November 2017.

   [I-D.ietf-ipv6-multilink-subnets]
              Thaler, D. and C. Huitema, "Multi-link Subnet Support in
              IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
              progress), July 2002.

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   [I-D.ietf-mboned-ieee802-mcast-problems]
              Perkins, C., McBride, M., Stanley, D., Kumari, W., and J.
              Zuniga, "Multicast Considerations over IEEE 802 Wireless
              Media", draft-ietf-mboned-ieee802-mcast-problems-01 (work
              in progress), February 2018.

   [I-D.perkins-intarea-multicast-ieee802]
              Perkins, C., Stanley, D., Kumari, W., and J. Zuniga,
              "Multicast Considerations over IEEE 802 Wireless Media",
              draft-perkins-intarea-multicast-ieee802-03 (work in
              progress), July 2017.

   [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks]
              Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets
              over IEEE 1901.2 Narrowband Powerline Communication
              Networks", draft-popa-6lo-6loplc-ipv6-over-
              ieee19012-networks-00 (work in progress), March 2014.

   [I-D.struik-lwip-curve-representations]
              Struik, R., "Alternative Elliptic Curve Representations",
              draft-struik-lwip-curve-representations-00 (work in
              progress), October 2017.

   [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
              DOI 10.17487/RFC1982, August 1996,
              <https://www.rfc-editor.org/info/rfc1982>.

   [RFC3610]  Whiting, D., Housley, R., and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
              2003, <https://www.rfc-editor.org/info/rfc3610>.

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,
              <https://www.rfc-editor.org/info/rfc3810>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,
              <https://www.rfc-editor.org/info/rfc3972>.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
              <https://www.rfc-editor.org/info/rfc4429>.

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   [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, DOI 10.17487/RFC4919, August 2007,
              <https://www.rfc-editor.org/info/rfc4919>.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
              <https://www.rfc-editor.org/info/rfc4941>.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.

   [RFC6606]  Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
              Statement and Requirements for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Routing",
              RFC 6606, DOI 10.17487/RFC6606, May 2012,
              <https://www.rfc-editor.org/info/rfc6606>.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <https://www.rfc-editor.org/info/rfc7102>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <https://www.rfc-editor.org/info/rfc7217>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.

   [RFC7428]  Brandt, A. and J. Buron, "Transmission of IPv6 Packets
              over ITU-T G.9959 Networks", RFC 7428,
              DOI 10.17487/RFC7428, February 2015,
              <https://www.rfc-editor.org/info/rfc7428>.

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

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   [RFC7934]  Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
              "Host Address Availability Recommendations", BCP 204,
              RFC 7934, DOI 10.17487/RFC7934, July 2016,
              <https://www.rfc-editor.org/info/rfc7934>.

   [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
              "Recommendation on Stable IPv6 Interface Identifiers",
              RFC 8064, DOI 10.17487/RFC8064, February 2017,
              <https://www.rfc-editor.org/info/rfc8064>.

   [RFC8065]  Thaler, D., "Privacy Considerations for IPv6 Adaptation-
              Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
              February 2017, <https://www.rfc-editor.org/info/rfc8065>.

   [RFC8105]  Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
              M., and D. Barthel, "Transmission of IPv6 Packets over
              Digital Enhanced Cordless Telecommunications (DECT) Ultra
              Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
              2017, <https://www.rfc-editor.org/info/rfc8105>.

   [RFC8163]  Lynn, K., Ed., Martocci, J., Neilson, C., and S.
              Donaldson, "Transmission of IPv6 over Master-Slave/Token-
              Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
              May 2017, <https://www.rfc-editor.org/info/rfc8163>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

12.3.  External Informative References

   [IEEEstd802154]
              IEEE, "IEEE Standard for Low-Rate Wireless Networks",
              IEEE Standard 802.15.4, DOI 10.1109/IEEE
              P802.15.4-REVd/D01, June 2017,
              <http://ieeexplore.ieee.org/document/7460875/>.

   [Perlman83]
              Perlman, R., "Fault-Tolerant Broadcast of Routing
              Information", North-Holland Computer Networks 7: 395-405,
              1983, <http://www.cs.illinois.edu/~pbg/courses/cs598fa09/
              readings/p83.pdf>.

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Appendix A.  Applicability and Requirements Served

   This specification extends 6LoWPAN ND to provide a sequence number to
   the registration and serves the requirements expressed Appendix B.1
   by enabling the mobility of devices from one LLN to the next based on
   the complementary work in the "IPv6 Backbone Router"
   [I-D.ietf-6lo-backbone-router] specification.

   In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
   IEEE Std. 802.15.4 [IEEEstd802154], the "6TiSCH architecture"
   [I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could
   connect to the Internet via a RPL mesh Network, but this requires
   additions to the 6LoWPAN ND protocol to support mobility and
   reachability in a secured and manageable environment.  This
   specification details the new operations that are required to
   implement the 6TiSCH architecture and serves the requirements listed
   in Appendix B.2.

   The term LLN is used loosely in this specification to cover multiple
   types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low
   Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so
   as to address the requirements discussed in Appendix B.3.

   This specification can be used by any wireless node to associate at
   Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
   services including proxy-ND operations over the Backbone, effectively
   providing a solution to the requirements expressed in Appendix B.4.

   This specification is extended by "Address Protected Neighbor
   Discovery for Low-power and Lossy Networks" [I-D.ietf-6lo-ap-nd] to
   providing a solution to some of the security-related requirements
   expressed in Appendix B.5.

   "Efficiency aware IPv6 Neighbor Discovery Optimizations"
   [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND
   [RFC6775] can be extended to other types of links beyond IEEE Std.
   802.15.4 for which it was defined.  The registration technique is
   beneficial when the Link-Layer technique used to carry IPv6 multicast
   packets is not sufficiently efficient in terms of delivery ratio or
   energy consumption in the end devices, in particular to enable
   energy-constrained sleeping nodes.  The value of such extension is
   especially apparent in the case of mobile wireless nodes, to reduce
   the multicast operations that are related to IPv6 ND ([RFC4861],
   [RFC4862]) and affect the operation of the wireless medium
   [I-D.ietf-mboned-ieee802-mcast-problems]
   [I-D.perkins-intarea-multicast-ieee802].  This serves the scalability
   requirements listed in Appendix B.6.

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   Finally Appendix B.7 provides a matching of requirements with the
   specifications that serves them.

Appendix B.  Requirements

   This section lists requirements that were discussed at 6lo for an
   update to 6LoWPAN ND.  This specification meets most of them, but
   those listed in Appendix B.5 which are deferred to a different
   specification such as [I-D.ietf-6lo-ap-nd], and those related to
   multicast.

B.1.  Requirements Related to Mobility

   Due to the unstable nature of LLN links, even in a LLN of immobile
   nodes a 6LN may change its point of attachment to a 6LR, say 6LR-a,
   and may not be able to notify 6LR-a.  Consequently, 6LR-a may still
   attract traffic that it cannot deliver any more.  When links to a 6LR
   change state, there is thus a need to identify stale states in a 6LR
   and restore reachability in a timely fashion.

   Req1.1: Upon a change of point of attachment, connectivity via a new
   6LR MUST be restored in a timely fashion without the need to de-
   register from the previous 6LR.

   Req1.2: For that purpose, the protocol MUST enable to differentiate
   between multiple registrations from one 6LoWPAN Node and
   registrations from different 6LoWPAN Nodes claiming the same address.

   Req1.3: Stale states MUST be cleaned up in 6LRs.

   Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address
   concurrently to multiple 6LRs.

B.2.  Requirements Related to Routing Protocols

   The point of attachment of a 6LN may be a 6LR in an LLN mesh.  IPv6
   routing in a LLN can be based on RPL, which is the routing protocol
   that was defined at the IETF for this particular purpose.  Other
   routing protocols than RPL are also considered by Standard Defining
   Organizations (SDO) on the basis of the expected network
   characteristics.  It is required that a 6LoWPAN Node attached via ND
   to a 6LR would need to participate in the selected routing protocol
   to obtain reachability via the 6LR.

   Next to the 6LBR unicast address registered by ND, other addresses
   including multicast addresses are needed as well.  For example a
   routing protocol often uses a multicast address to register changes

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   to established paths.  ND needs to register such a multicast address
   to enable routing concurrently with discovery.

   Multicast is needed for groups.  Groups may be formed by device type
   (e.g. routers, street lamps), location (Geography, RPL sub-tree), or
   both.

   The Bit Index Explicit Replication (BIER) Architecture [RFC8279]
   proposes an optimized technique to enable multicast in a LLN with a
   very limited requirement for routing state in the nodes.

   Related requirements are:

   Req2.1: The ND registration method SHOULD be extended so that the 6LR
   is able to advertise the Address of a 6LoWPAN Node over the selected
   routing protocol and obtain reachability to that Address using the
   selected routing protocol.

   Req2.2: Considering RPL, the Address Registration Option that is used
   in the ND registration SHOULD be extended to carry enough information
   to generate a DAO message as specified in [RFC6550] section 6.4, in
   particular the capability to compute a Path Sequence and, as an
   option, a RPLInstanceID.

   Req2.3: Multicast operations SHOULD be supported and optimized, for
   instance using BIER or MPL.  Whether ND is appropriate for the
   registration to the 6BBR is to be defined, considering the additional
   burden of supporting the Multicast Listener Discovery Version 2
   [RFC3810] (MLDv2) for IPv6.

B.3.  Requirements Related to the Variety of Low-Power Link types

   6LoWPAN ND [RFC6775] was defined with a focus on IEEE Std.802.15.4
   and in particular the capability to derive a unique Identifier from a
   globally unique MAC-64 address.  At this point, the 6lo Working Group
   is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique
   to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token-
   Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field
   Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah
   [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband
   Powerline Communication Networks
   [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R)
   Low Energy [RFC7668].

   Related requirements are:

   Req3.1: The support of the registration mechanism SHOULD be extended
   to more LLN links than IEEE Std.802.15.4, matching at least the LLN

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   links for which an "IPv6 over foo" specification exists, as well as
   Low-Power Wi-Fi.

   Req3.2: As part of this extension, a mechanism to compute a unique
   Identifier should be provided, with the capability to form a Link-
   Local Address that SHOULD be unique at least within the LLN connected
   to a 6LBR discovered by ND in each node within the LLN.

   Req3.3: The Address Registration Option used in the ND registration
   SHOULD be extended to carry the relevant forms of unique Identifier.

   Req3.4: The Neighbour Discovery should specify the formation of a
   site-local address that follows the security recommendations from
   [RFC7217].

B.4.  Requirements Related to Proxy Operations

   Duty-cycled devices may not be able to answer themselves to a lookup
   from a node that uses IPv6 ND on a Backbone and may need a proxy.
   Additionally, the duty-cycled device may need to rely on the 6LBR to
   perform registration to the 6BBR.

   The ND registration method SHOULD defend the addresses of duty-cycled
   devices that are sleeping most of the time and not capable to defend
   their own Addresses.

   Related requirements are:

   Req4.1: The registration mechanism SHOULD enable a third party to
   proxy register an Address on behalf of a 6LoWPAN node that may be
   sleeping or located deeper in an LLN mesh.

   Req4.2: The registration mechanism SHOULD be applicable to a duty-
   cycled device regardless of the link type, and enable a 6BBR to
   operate as a proxy to defend the Registered Addresses on its behalf.

   Req4.3: The registration mechanism SHOULD enable long sleep
   durations, in the order of multiple days to a month.

B.5.  Requirements Related to Security

   In order to guarantee the operations of the 6LoWPAN ND flows, the
   spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided.  Once a
   node successfully registers an address, 6LoWPAN ND should provide
   energy-efficient means for the 6LBR to protect that ownership even
   when the node that registered the address is sleeping.

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   In particular, the 6LR and the 6LBR then should be able to verify
   whether a subsequent registration for a given address comes from the
   original node.

   In a LLN it makes sense to base security on layer-2 security.  During
   bootstrap of the LLN, nodes join the network after authorization by a
   Joining Assistant (JA) or a Commissioning Tool (CT).  After joining
   nodes communicate with each other via secured links.  The keys for
   the layer-2 security are distributed by the JA/CT.  The JA/CT can be
   part of the LLN or be outside the LLN.  In both cases it is needed
   that packets are routed between JA/CT and the joining node.

   Related requirements are:

   Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR, 6LBR and 6BBR to authenticate and authorize one another for
   their respective roles, as well as with the 6LoWPAN Node for the role
   of 6LR.

   Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR and the 6LBR to validate new registration of authorized
   nodes.  Joining of unauthorized nodes MUST be prevented.

   Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet
   sizes.  In particular, the NS, NA, DAR and DAC messages for a re-
   registration flow SHOULD NOT exceed 80 octets so as to fit in a
   secured IEEE Std.802.15.4 [IEEEstd802154] frame.

   Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be
   computationally intensive on the LoWPAN Node CPU.  When a Key hash
   calculation is employed, a mechanism lighter than SHA-1 SHOULD be
   preferred.

   Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate
   SHOULD be minimized.

   Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the
   variation of CCM [RFC3610] called CCM* for use at both Layer 2 and
   Layer 3, and SHOULD enable the reuse of security code that has to be
   present on the device for upper layer security such as TLS.

   Req5.7: Public key and signature sizes SHOULD be minimized while
   maintaining adequate confidentiality and data origin authentication
   for multiple types of applications with various degrees of
   criticality.

   Req5.8: Routing of packets should continue when links pass from the
   unsecured to the secured state.

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   Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR and the 6LBR to validate whether a new registration for a
   given address corresponds to the same 6LoWPAN Node that registered it
   initially, and, if not, determine the rightful owner, and deny or
   clean-up the registration that is duplicate.

B.6.  Requirements Related to Scalability

   Use cases from Automatic Meter Reading (AMR, collection tree
   operations) and Advanced Metering Infrastructure (AMI, bi-directional
   communication to the meters) indicate the needs for a large number of
   LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected
   to the 6LBR over a large number of LLN hops (e.g. 15).

   Related requirements are:

   Req6.1: The registration mechanism SHOULD enable a single 6LBR to
   register multiple thousands of devices.

   Req6.2: The timing of the registration operation should allow for a
   large latency such as found in LLNs with ten and more hops.

B.7.  Matching Requirements with Specifications

                   I-drafts/RFCs addressing requirements

         +-------------+-----------------------------------------+
         | Requirement | Document                                |
         +-------------+-----------------------------------------+
         | Req1.1      | [I-D.ietf-6lo-backbone-router]          |
         |             |                                         |
         | Req1.2      | [RFC6775]                               |
         |             |                                         |
         | Req1.3      | [RFC6775]                               |
         |             |                                         |
         | Req1.4      | This RFC                                |
         |             |                                         |
         | Req2.1      | This RFC                                |
         |             |                                         |
         | Req2.2      | This RFC                                |
         |             |                                         |
         | Req2.3      |                                         |
         |             |                                         |
         | Req3.1      | Technology Dependant                    |
         |             |                                         |
         | Req3.2      | Technology Dependant                    |
         |             |                                         |
         | Req3.3      | Technology Dependant                    |

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         |             |                                         |
         | Req3.4      | Technology Dependant                    |
         |             |                                         |
         | Req4.1      | This RFC                                |
         |             |                                         |
         | Req4.2      | This RFC                                |
         |             |                                         |
         | Req4.3      | [RFC6775]                               |
         |             |                                         |
         | Req5.1      |                                         |
         |             |                                         |
         | Req5.2      | [I-D.ietf-6lo-ap-nd]                    |
         |             |                                         |
         | Req5.3      |                                         |
         |             |                                         |
         | Req5.4      |                                         |
         |             |                                         |
         | Req5.5      | [I-D.ietf-6lo-ap-nd]                    |
         |             |                                         |
         | Req5.6      | [I-D.struik-lwip-curve-representations] |
         |             |                                         |
         | Req5.7      | [I-D.ietf-6lo-ap-nd]                    |
         |             |                                         |
         | Req5.8      |                                         |
         |             |                                         |
         | Req5.9      | [I-D.ietf-6lo-ap-nd]                    |
         |             |                                         |
         | Req6.1      | This RFC                                |
         |             |                                         |
         | Req6.2      | This RFC                                |
         +-------------+-----------------------------------------+

                     Table 7: Addressing requirements

Appendix C.  Subset of a 6LoWPAN Glossary

   This document often uses the followng acronyms:

   6BBR: 6LoWPAN Backbone Router (proxy for the registration)

   6LBR: 6LoWPAN Border Router (authoritative on DAD)

   6LN:  6LoWPAN Node

   6LR:  6LoWPAN Router (relay to the registration process)

   6CIO: Capability Indication Option

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   (E)ARO:  (Extended) Address Registration Option

   DAD:  Duplicate Address Detection

   LLN:  Low Power Lossy Network (a typical IoT network)

   NCE:  Neighbor Cache Entry

   TSCH: TimeSlotted Channel Hopping

   TID:  Transaction ID (a sequence counter in the EARO)

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D (Regus) 45 Allee des Ormes
   Mougins - Sophia Antipolis
   France

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

   Erik Nordmark
   Zededa
   Santa Clara, CA
   United States of America

   Email: nordmark@sonic.net

   Samita Chakrabarti
   Verizon
   San Jose, CA
   United States of America

   Email: samitac.ietf@gmail.com

   Charles E. Perkins
   Futurewei
   2330 Central Expressway
   Santa Clara  95050
   United States of America

   Email: charliep@computer.org

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