6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     cisco                                             Cisco Systems
Updates: 4861, 8505 (if approved)                             C. Perkins
Intended status: Standards Track                              C. Perkins                               Futurewei
Expires: April 25, June 8, 2019                                        Futurewei
                                                        October 22,                                   E. Levy-Abegnoli
                                                           Cisco Systems
                                                        December 5, 2018

                          IPv6 Backbone Router
                   draft-ietf-6lo-backbone-router-08
                   draft-ietf-6lo-backbone-router-09

Abstract

   Backbone Routers running are RFC8505 Routing Registrars that provide proxy
   services for IPv6 Neighbor Discovery can manage Discovery.  Backbone Routers federate
   multiple wireless links Links over a Backbone Link to form a large MultiLink Subnet, but it is more
   efficient if IPv6 Neighbor Discovery packets are not broadcast over
   the wireless links.  This specification specifies proxy operations
   for IPv6 Neighbor Discovery on behalf of devices located on
   broadcast-inefficient wireless networks.
   Subnet.  Backbone Routers placed along the wireless edge of the backbone
   Backbone handle IPv6 Neighbor Discovery, and route packets on behalf
   of registered nodes.  Wireless
   nodes register, or are registered by proxy, to a Backbone Router to
   establish proxy services in a fashion similar to layer-2 association.

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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 April 25, June 8, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability and Requirements Served . . . .  Terminology . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . .   4
     2.1.  BCP 14  . . . . . . . .   5
   4.  Overview . . . . . . . . . . . . . . . . .   4
     2.2.  References  . . . . . . . . .   6
   5.  Backbone Router Routing Operations . . . . . . . . . . . . .   8
     5.1.  Over the Backbone Link .   5
     2.3.  New Terms . . . . . . . . . . . . . . . .   8
     5.2.  Proxy Operations Over the LLN Interface . . . . . . . .   5
     2.4.  Acronym Definitions .   9
       5.2.1.  Routing Proxy Operations . . . . . . . . . . . . . .  10
       5.2.2.  Bridging Proxy Operations . . . .   6
   3.  Overview  . . . . . . . . . .  10
   6.  Backbone Router Proxy Operations . . . . . . . . . . . . . .  11
     6.1.  Primary and Secondary BBRs . .   7
     3.1.  Access Link . . . . . . . . . . . . .  12
     6.2.  Binding Table . . . . . . . . . .   9
     3.2.  Route-Over Mesh . . . . . . . . . . . .  12
     6.3.  Registration and Binding Table Entry Creation . . . . . .  13
     6.4.  Defending Addresses . . .  10
     3.3.  MultiLink Subnet Consistency  . . . . . . . . . . . . . .  11
     3.4.  Registering Node  . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . .  11
     3.5.  Using IPv6 ND Over the Backbone Link  .  15
   8.  Protocol Constants . . . . . . . . .  12
     3.6.  Routing Proxy Operations  . . . . . . . . . . . .  16
   9.  IANA Considerations . . . .  13
     3.7.  Bridging Proxy Operations . . . . . . . . . . . . . . . .  14
     3.8.  Leveraging Optimistic DAD .  16
   10. Future Work . . . . . . . . . . . . . . .  14
   4.  Updating RFC 4861 . . . . . . . . . .  16
   11. Acknowledgments . . . . . . . . . . . .  15
   5.  Updating RFC 8505 . . . . . . . . . . .  16
   12. References . . . . . . . . . . .  15
   6.  6BBR detailed Operations  . . . . . . . . . . . . . .  16
     12.1.  Normative References . . . .  15
     6.1.  Primary and Secondary  6BBRs  . . . . . . . . . . . . . .  16
     12.2.  Informative References .
     6.2.  Binding Table . . . . . . . . . . . . . . . .  17
     12.3.  External Informative References . . . . . .  16
     6.3.  Registration and Binding Table Entry Creation . . . . . .  19  17
     6.4.  Defending Addresses . . . . . . . . . . . . . . . . . . .  18
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  Protocol Constants  . . . . . . . . . . . . . . . . . . . . .  20
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   10. Future Work . . . . . . . . . . . . . . . . . . . . . . . . .  20
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     12.2.  Informative References . . . . . . . . . . . . . . . . .  22
     12.3.  External Informative References  . . . . . . . . . . . .  24
   Appendix A.  Changes from revision 07 to revision 08  Applicability and Requirements Served  . . . . . .  20 .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20  26

1.  Introduction

   IEEE STD. 802.1 [IEEEstd8021] Ethernet Bridging provides an efficient
   and reliable broadcast service; applications and protocols have been
   built that heavily depend on that feature for their core operation.
   Unfortunately, many Low-Power Lossy Networks (LLNs) and local wireless
   networks generally do not economically provide the broadcast capabilities of
   Ethernet Bridging; Bridging in an economical fashion; protocols designed for
   bridged networks that rely on broadcast multicast and broadcast often exhibit
   disappointing behaviours when applied employed unmodified to on a local wireless
   medium (see [I-D.ietf-mboned-ieee802-mcast-problems]).

   WiFi

   Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended
   Service Set (ESS) act as bridges.  In order to ensure Ethernet Bridges [IEEEstd8021], with the
   interesting caveat that the bridging state is populated proactively
   at the association time.  This ensures a solid connectivity to the devices
   node (STA) and protect protects the wireless medium against harmful
   broadcasts, they refrain from relying on broadcast-intensive
   protocols such as the broadcast-
   intensive Transparent Bridging on reactive lookups.  In other words, the wireless side.
   Instead, an
   association process is used to register the MAC addresses Address of the wireless device (STA) STA to
   the AP.  The APs subsequently proxy proxies the bridging operation and eliminate does
   not need to forward the broadcast lookups over the radio.

   Like Transparent Bridging, the operations of the broadcasts.

   The IPv6 [RFC8200]
   Neighbor Discovery [RFC4861] [RFC4862] Protocol (IPv6 ND) operations are
   reactive and rely heavily on multicast transmissions to locate an on-link on-
   link correspondent and ensure address
   uniqueness. the uniqueness of an Address.  The
   mechanism for Duplicate Address Detection [RFC4862] (DAD) mechanism [RFC4862] was also
   designed as a natural match with the efficient broadcast operation of
   Ethernet Bridging.  However, since broadcast can be unreliable over
   wireless media, DAD often fails to discover duplications
   [I-D.yourtchenko-6man-dad-issues].  DAD usually appears
   to work on wireless media,  A conflict of IPv6 Address is
   still a very rare event, not because address duplication is Address duplications are
   detected and solved as designed, but because of the use sheer entropy of
   the 64-bit Interface IDs makes duplication into a very rare event. IDs.

   IPv6 multicast messages are typically broadcast over the wireless
   medium.  They
   medium; they are processed by most if not all the wireless nodes over
   the subnet - e.g., the ESS fabric - even when very few if any of them are the
   nodes is subscribed to the multicast address.  A simple flow.  The IPv6 ND Neighbor
   Solicitation (NS)
   [RFC4861], that [RFC4861] is such a message; NS messages are used
   for DAD and Address lookup, and are frequently observed in a
   situation of mobility and when a node wakes up and reconnects to the
   wireless network.  The NS message is supposedly targeted to a Sollicitated-Node
   Multicast Address (SNMA) [RFC4291] and should in theory only reach a
   very small group of nodes, nodes; but since Layer-3 multicast messages are
   effectively broadcasted at Layer-2, the volume of Address lookups and
   DADs over a large fabric can
   congest effectively consume bandwidth to the
   point that it becomes detrimental to unicast traffic (see
   [I-D.ietf-mboned-ieee802-mcast-problems]).

   Additionally, wireless bandwidth
   [I-D.ietf-mboned-ieee802-mcast-problems].  The IPv6 ND operation
   leads nodes that do not belong to undesirable the SNMA group
   still have to keep their radio awake and listen to broadcasted NS
   messages, which is a total waste of energy for them.  In order to
   control their power consumption in consumption, battery-operated devices. nodes such as IOT
   sensors and smartphones may then elect to blindly ignore a portion of
   the broadcasts, which tends to make the Layer-3 protocol operations
   even less reliable.

   These problems suggest restricting can be alleviated by a reduction of IPv6 ND broadcasts
   over wireless access links, which can be done by dividing up links.  One classical way to achieve this to
   split the subnet. broadcast domains and route between subnets, possibly by
   assigning a /64 prefix to each wireless node (see [RFC8273]).

   Another way is to take over (proxy) proxy the Layer-3 protocols that rely on broadcast operation
   operations at the boundary of the wired and wireless domains, emulating in a
   fashion similar to the Layer-2 association but at layer-3.  For instance,  To that
   effect, IEEE 802.11 [IEEEstd80211] specifies requires ARP and ND proxy proxy-ND
   [RFC4389] services at the Access Points (APs).

   Current devices rely on (APs), and this specification
   is a possible response to that requirement.

   IPv6 proxy-ND services can be obtained automatically by snooping the
   IPV6 ND protocol (see [I-D.bi-savi-wlan]).  Proprietary techniques
   for detecting association state,
   which is failure-prone in lossy IPv6 ND and mobile conditions.  With
   snooping, a state (e.g. a new DHCP snooping are effectively deployed, and though
   snooping is really useful to cancel undesirable broadcast
   transmissions, it has also proven to be unreliable; An IPv6 address) Address
   may not be discovered, discovered immediately due to a packet loss, or a silent
   node that does not use the Address for a while; a change of state
   (e.g. due a movement) may be missed, missed or misordered, leading to
   unreliable connectivity.

   WPAN devices (i.e., those implementing IEEE STD. 802.15.4
   [IEEEstd802154]) can make use connectivity and a partial knowledge of the state of Neighbor Discovery Optimization for
   IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
   [RFC6775] which treats the
   network.

   With this specification, a wireless medium node proactively registers its
   IPv6 Addresses using a NS(EARO) as different from
   Ethernet.  RFC 6775 specified in [RFC8505] to an IPv6
   Backbone Router (6BBR).  The 6BBR is updated as [I-D.ietf-6lo-rfc6775-update]; a Routing Registrar per
   [RFC8505].  It is also a Border Router that performs the
   update includes changes IPv6 proxy
   Neighbor Discovery operations on its Backbone interface on behalf of
   the 6LNs that are required by this document.

2.  Applicability and Requirements Served registered on its LLN interfaces.  This specification updates and generalizes 6LoWPAN ND to a broader
   range effectively
   recreates at Layer-3 the equivalent of Low power and Lossy Networks (LLNs) with support an association such as found
   in IEEE STD. 802.11 for
   Duplicate Address Detection (DAD) and address the purpose of providing reachability to the
   registered Addresses without the need of a broadcast lookup that does not
   require broadcasts over the LLNs.  The term LLN is used loosely in
   wireless medium.  Additional benefits are discussed in Appendix A.

2.  Terminology

2.1.  BCP 14

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this specification document are to cover multiple types of WLANs and WPANs,
   including Low-Power Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD.
   802.11AH be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and IEEE STD. 802.15.4 wireless meshes, so only when, they appear in all
   capitals, as to address shown here.

2.2.  References

   In this document, readers will encounter terms and concepts that are
   discussed in the
   requirements listed following documents:

   o  "Neighbor Discovery Proxies (proxy-ND)" [RFC4389]

   o  "Optimistic Duplicate Address Detection" [RFC4429], and

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

   o  "IPv6 Stateless Address Autoconfiguration" [RFC4862],

   o  "MultiLink Subnet Issues" [RFC4903],

   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],

   o  ,"Mobility Support in Appendix B.3 of [I-D.ietf-6lo-rfc6775-update]
   "Requirements Related IPv6" [RFC6275],

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

   o  "Registration Extensions for 6LoWPAN Neighbor Discovery"
      [RFC8505].

2.3.  New Terms

   This document also introduces the following terminology:

   Federated

         A subnet that is partitionned over a Backbone and one or more
         (wireless) access links, is said to be federated into one
         MultiLink Subnet by the Variety proxy-ND operation of Low-Power Link types".

   For 6BBRs located at
         the TimeSlotted Channel Hopping (TSCH) mode edge of [IEEEstd802154], the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how Backbone and the access links and providing a 6LoWPAN
         semblance of a non-partitionned subnet for IPv6 ND host could connect to over the Internet via
         Backbone.

   Sleeping Proxy

         A 6BBR acts as a RPL mesh
   Network, but doing so requires extensions to the 6LOWPAN Sleeping Proxy if it answers ND protocol
   to support mobility and reachability in a secure and manageable
   environment.  The extensions detailed in this document also work for
   the 6TiSCH architecture, serving Neighbor
         Solicitation over the requirements listed in
   Appendix B.2 Backbone on behalf of [I-D.ietf-6lo-rfc6775-update] "Requirements Related the Registered
         Node.

   Unicasting  Proxy

         A Unicasting Proxy forwards NS messages to the Registering
         Node, transforming Layer-2 multicast into unicast.

   Routing Protocols".

   This specification also applies to wireless links such Proxy

         A Routing Proxy advertises its own MAC Address as Low-Power
   IEEE STD. 802.11 (Wi-Fi) and IEEE STD. 802.15.1 (Bluetooth)
   [IEEEstd802151].  It makes use of extensions to [RFC6775] to enable
   proxy operation by the 6BBR, as specified TLLA in
   [I-D.ietf-6lo-rfc6775-update].  The BBR proxy operations eliminate
         the need for wireless nodes to respond synchronously when a lookup is
   performed for their addresses.  This provides proxied NAs over the function Backbone, as opposed to that of a Sleep the
         node that performs the registration.

   Bridging Proxy for ND [I-D.nordmark-6man-dad-approaches].

   This draft establishes a Backbone

         A Bridging Proxy advertises the MAC Address of the node that treats multiple LLNs
         performs the registration as a
   single IPv6 MultiLink Subnet.  Each LLN the TLLA in the subnet is anchored at
   an IPv6 Backbone Router (6BBR).  The Backbone Routers interconnect proxied NAs over
         the LLNs Backbone.  In that case, the MAC Address and advertise the addresses mobility
         of 6LN is still visible across the 6LNs using proxy-ND
   operations.  This specification extends IPv6 ND bridged Backbone fabric.

   Primary  6BBR

         The 6BBR that will defend a Registered Address for the purpose
         of DAD over the backbone to
   distinguish address movement from duplication and eliminate stale
   state in Backbone.

   Secondary  6BBR

         A 6BBR other than the backbone routers and backbone nodes once a 6LN has
   roamed.  In this way, mobile nodes may roam rapidly from one Primary 6BBR to which an Address is
         registered.  A Secondary Router MAY advertise the next Address over
         the Backbone and requirements in Appendix B.1 of
   [I-D.ietf-6lo-rfc6775-update] "Requirements Related to Mobility" are
   met. proxy for it.

2.4.  Acronym Definitions

   This specification enables any 6LN to register its IPv6 addresses document uses the following acronyms:

   6BBR: 6LoWPAN Backbone Router

   6LBR: 6LoWPAN Border Router

   6LN:  6LoWPAN Node

   6LR:  6LoWPAN Router

   6CIO: Capability Indication Option

   EARO: (Extended) Address Registration Option -- (E)ARO

   EDAR: (Extended) Duplicate Address Request -- (E)DAR

   EDAC: (Extended) Duplicate Address Confirmation -- (E)DAC
   DAD:  Duplicate Address Detection

   DODAG:  Destination-Oriented Directed Acyclic Graph

   LLN:  Low-Power and
   thereby obtain routing services including proxy-ND operations over Lossy Network

   NA:   Neighbor Advertisement

   NCE:  Neighbor Cache Entry

   ND:   Neighbor Discovery

   NDP:  Neighbor Discovery Protocol

   NS:   Neighbor Solicitation

   ROVR: Registration Ownership Verifier (pronounced rover)

   RPL:  IPv6 Routing Protocol for LLNs (pronounced ripple) [RFC6550]

   RA:   Router Advertisement

   RS:   Router Solicitation

   TID:  Transaction ID (a sequence counter in the backbone, providing a solution EARO)

3.  Overview

   A 6BBR provides proxy-ND services to the requirements expressed in
   Appendix B.4 of [I-D.ietf-6lo-rfc6775-update] "Requirements Related 6LNs attached to Proxy Operations".

   The Link Layer Address (LLA) an LLN that is returned as Target LLA (TLLA) in
   Neighbor Advertisements (NA) messages by
   anchored at the 6BBR 6BBR; this way, a subnet that is located on behalf of the
   Registered Node over a
   Backbone can be extended in the backbone LLN as a MultiLink Subnet.  The LLN
   may be that of the Registering
   Node.  In that case, a hub-and-spoke network, a mesh-under or a route-over network.

   The proxy-ND operation can co-exist with IPv6 ND over the Backbone.
   The proxy state can be distributed across multiple 6BBR needs attached to bridge a
   same Backbone.  A 6LN may move freely from an LLN anchored at one
   6BBR to an LLN anchored at another 6BBR on the unicast packets
   (Bridging proxy), same Backbone and
   retain any or that all of the 6BBR on IPv6 Addresses that the backbone, in which case
   the 6BBRs needs 6LN has formed.

   The registration to route the unicast packets (Routing proxy). a proxy service is done via a NS/NA(EARO)
   exchange.  The
   IPv6 ND 6BBR operation is minimized as the number of 6LNs grows in the
   LLN.  This meets the requirements in Appendix B.6 resembles that of
   [I-D.ietf-6lo-rfc6775-update] "Requirements Related to Scalability",
   as long has the 6BBRs are dimensioned a Mobile IPv6 (MIPv6)
   [RFC6275] Home Agent.  The combination if a 6BBR and a MIPv6 HA
   enables a full mobility support for 6LNs, inside and outside the number of registrations
   links that each needs to support.

   In form the case of Low-Power IEEE STD. 802.11, a subnet.

                 |
               +-----+
               |     | Gateway (default) Router
               |     |
               +-----+
                  |
                  |           Backbone Link
            +-------------------------+----------------------+
            |                         |                      |
         +------+                 +------+                +------+
         | 6BBR may be collocated
   with |                 | 6BBR |                | 6BBR |
         |      |                 |      |                |      |
         +------+                 +------+                +------+
            o                     o   o  o                  o o
        o o   o  o            o o   o  o  o             o  o  o  o o
       o  o o  o o            o   o  o  o  o            o  o  o o o
       o   o  o  o               o    o  o               o  o   o
         o   o o                    o  o                     o o

         LLN                        LLN                      LLN

               Figure 1: Backbone Link and Backbone Routers

   Each Backbone Router (6BBR) maintains an abstract Binding Table of
   its Registered Nodes.  The Binding Tables form a standalone AP distributed database
   of 6LNs that reside on the LLNs or a CAPWAP [RFC5415] wireless controller.  Then on the wireless client (STA) makes IPv6 Backbone, and use of this specification an
   extension to register
   its IPv6 address(es) ND to exchange that information across the 6BBR over the wireless medium.
   Backbone.  In the
   case RPL, the RPL root that process:

      The Extended Address Registration Option (EARO) defined in
      [RFC8505] is collocated with a 6LoWPAN Border Router
   (6LBR), and either collocated with or connected to used in the 6BBR ND exchanges over an
   IPv6 Link.  The 6LBR makes use of this specification to register the
   6LNs on their behalf to Backbone between
      the 6BBR.

3.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are 6BBRs to be interpreted as described in BCP
   14 [RFC2119] .

   In this document, readers will encounter terms and concepts that are
   discussed in the following documents:

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

   o  "IPv6 Stateless Address Autoconfiguration" [RFC4862],

   o  "Multi-Link Subnet Issues" [RFC4903],

   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],

   o  ,"Mobility Support in IPv6" [RFC6275],

   o  "Neighbor Discovery Proxies (ND Proxy)" [RFC4389]

   o  "Optimistic help distinguish duplication from movement.
      Optionally, Extended Duplicate Address Detection" [RFC4429], Messages (EDAR and
   o  "Registration Extensions for 6LoWPAN Neighbor Discovery"
      [I-D.ietf-6lo-rfc6775-update]

   This document EDAC)
      can also uses terminology from [RFC7102] and
   [I-D.ietf-6lo-rfc6775-update], and introduces be used between the following
   terminology:

   Sleeping Proxy

         A 6BBR acts as and a Sleeping Proxy 6LBR if it answers ND Neighbor
         Solicitation over one is present on
      the Backbone.  Address duplication is detected using the ROVR
      field, and conflicting registrations to different 6BBRs by a same
      owner 6LR are resolved using the TID field.

      The Link Layer Address (LLA) that the 6BBR advertises for the backbone
      Registered Address on behalf of the Registered
         Node.

   Unicasting  Proxy

         A Unicasting Proxy forwards NS messages to Node over the Registering
         Node, transforming Layer-2 multicast into unicast.

   Routing proxy

         A routing proxy advertises its own MAC address as the TLLA in
         the proxied NAs over the backbone, as opposed to that of the
         node
      Backbone may be that performs the registration.

   Bridging proxy

         A Bridging proxy advertises the MAC address of the node that
         performs the registration as the TLLA Registering Node; in the proxied NAs over
         the backbone.  In that case, the MAC address and
      6BBR needs to bridge the mobility
         of 6LN is still visible across unicast packets (Bridging Proxy).
      Alternatively, the bridged backbone fabric.

   Primary BBR

         The BBR LLA can be that will defend a Registered Address for the purpose of DAD over the backbone.

   Secondary BBR

         A BBR other than 6BBR on the Primary BBR to Backbone
      interface, in which an address is
         registered.  A Secondary Router MAY advertise the address over case the backbone 6BBRs receives at Layer-2 and proxy for it.

4.  Overview

   The services specified and
      needs to route at Layer-3 the unicast packets (Routing Proxy).
      This is discussed in this document assist more details in Section 3.6 and Section 3.7,
      respectively.

3.1.  Access Link

   This specification also applies to (hub-and-spoke) Access Links such
   as (Low-Power) IEEE STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD.
   802.15.1 (Bluetooth) [IEEEstd802151].  Figure 2 illustrates an ODAD-
   complient (see Section 3.8) example of a 6LN to move freely
   from that forms an LLN anchored at one 6BBR IPv6
   Address and registers it to an LLN anchored at another a 6BBR
   on the same backbone and keep any or all of the acting as a 6LR [RFC8505].

       6LoWPAN Node        6BBR          6LBR            default
          (STA)            (AP)                           Router
            |(Wireless) LLN |       IPv6 addresses that
   the 6LN has formed. ND Backbone        |
               +-----+
            |               | Gateway (default) Router         (Ethernet)            |
            |
               +-----+       RS      |              |           Backbone Link
            +-------------------------+----------------------+                |
            |-------------->|              |                |
         +------+                 +------+                +------+
            | 6BBR  (multicast)  |              | 6BBR                |
            | 6BBR               |              |                |
            |  RA(PIO)      |              |                |
            |<--------------|              |                |
            | (L2 unicast)  |              |                |
            |               |              |                |
            |  NS(EARO)     |              |                |
            |-------------->|              |                |
            | (optimistic)  |              |                |
            |               | Extended DAR |                |
            |               |------------->|                |
            |               | Extended DAC |                |
            |               |<-------------|                |
            |               |         NS-DAD(EARO)          |
            |               |------------------------------>|
            |               |------->   (multicast)         |
            |               |--------------------->         |
            |               |   RS(no SLLAO, for ODAD)      |
            |               |------------------------------>|
            |               |   (if no BCE) NS-LOOKUP       |
            |               |<------------------------------|
            |               |    NA(SLLAO, not(O), EARO)    |
            |               |------------------------------>|
            |               |         RA(unicast)           |
            |               |<------------------------------|
            |               |              |                |
            |         IPv6 Packets in optimistic mode       |
            |<--------------------------------------------->|
            |               |              |                |
            |  NA(EARO)     |DAD <timeout> |                |
            |<--------------|              |                |
            |               |              |                |
         +------+                 +------+                +------+
            o                     o   o  o                  o o
        o o   o  o            o o   o  o  o             o  o  o  o o
       o  o o  o o            o   o  o  o  o            o  o  o o o
       o   o  o  o               o    o  o               o  o   o
         o   o o                    o  o                     o o

         LLN                        LLN                      LLN

   Figure 1: Backbone Link and Backbone Routers

   Each Backbone Router (6BBR) maintains 2: Initial Registration Flow to a Binding Table 6BBR acting as Routing Proxy

3.2.  Route-Over Mesh

   In the case of its
   Registered Nodes.  The Binding Tables form a distributed database of
   wireless 6LNs that reside on the LLNs or on Route-Over Mesh, e.g., using RPL [RFC6550], the backbone, and use an
   extension to IPv6 ND
   6TiSCH architecture [I-D.ietf-6tisch-architecture] suggests to exchange that information across
   collocate the Backbone
   as described below.

   The Extended Address Registration Option (EARO) defined in
   [I-D.ietf-6lo-rfc6775-update] RPL root with a 6LoWPAN Border Router (6LBR), which is used in
   either collocated with or connected to the ND exchanges 6BBR over an IPv6 Link.

   Figure 3 illustrates the
   backbone between initial IPv6 signaling that enables a 6LN to
   form a Global or a Unique-Local Address and register it to the 6BBRs 6LBR
   using [RFC8505].  The 6LBR also leverages [RFC8505] to enable register the registration for routing and
   proxy services, as well as distinguish duplication from movement.

   Address duplication is detected using the ROVR field in the EARO.  In
   case of conflicting registrations to multiple 6BBRs from the same
   node, the Transaction ID (TID) in the EARO enables 6BBRs to determine
   the latest registration for that 6LN.

   6BBRs perform ND proxy operations over the backbone,
   6LNs on behalf of their Registered Nodes.  Registration behalf to a proxy service is done via
   a NS/NA(EARO) exchange.  6BBR operation resembles that of a Mobile
   IPv6 (MIPv6) [RFC6275] Home Agent.  This enables mobility support for
   6LNs; if they move outside of the network delimited by the Backbone
   link, then they make use of a Home Agent.  Home Agent functionality
   can easily be collocated with a 6BBR on the same backbone interface
   of a router.

   The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
   specification details how an address can be used before a Duplicate
   Address Detection (DAD) is complete, and mandates that an address
   that is TENTATIVE should not be associated to a Source Link-Layer
   Address Option in a Neighbor Solicitation message.  This
   specification makes use of ODAD to create a temporary proxy state in
   the 6BBR until DAD is completed over the backbone.  This way, the
   specification allows proxy state distribution across multiple obtain proxy-ND services.

       6LoWPAN Node        6LR             6LBR            6BBR
   and co-existence with
       (mesh leaf)     (mesh router)   (mesh root)
            |               |               |               |
            |  6LoWPAN ND   |6LoWPAN ND+RPL | 6LoWPAN ND    | IPv6 ND over the backbone.

5.
            |   LLN link    |Route-Over mesh|Ethernet/serial| Backbone Router Routing Operations
            |
               +-----+               |               |/Internal call | Gateway (default) Router
            |  IPv6 ND RS   |
               +-----+               | /64               |      Backbone Link
            +-------------------+-------------------+
            |-------------->|               | /64               | /64
            |----------->   | /64
         +------+            +------+           +------+               | 6BBR               |
            |------------------>            | 6BBR               |
            | 6BBR  IPv6 ND RA   |               |               |
            |<--------------|               |               |
            |               |    <once>     |               |
            |  NS(EARO)     |               |               |
            |-------------->|               |               |
            | 6LoWPAN ND    | Extended DAR  |               |
            |               |-------------->|               |
            |               |               |  NS(EARO)     |
            |               |               |-------------->|
            |               |               |  (proxied)    | NS-DAD
            |               |               |               |------>
            |               |               |               | (EARO)
            |               |               |               |
            |               |               |  NA(EARO)     |<timeout>
            |               |               |<--------------|
            |               | Extended DAC  |               |
            |               |<--------------|               |
            |  NA(EARO)     |               |               |
            |<--------------|               |               |
            |               |               |               |
         +------+            +------+           +------+
            o              o o  o                 o o
        o o   o  o       o o   o  o  o         o  o  o  o o
       o  o o  o o       o   o  o  o  o        o  o  o o o
       o   o  o  o          o    o  o           o  o   o
         o   o o               o  o                 o o

         LLN: N*/128        LLN: M*/128       LLN: P*/128

         Figure 2: Example Routing Configuration for 3 LLNs 3: Initial Registration Flow over Route-Over Mesh

3.3.  MultiLink Subnet Consistency

   The Backbone and the federated LLN Links are considered as different
   Links in the ML Subnet

5.1.  Over MultiLink Subnet, even if multiple LLNs are attached to
   a same 6BBR.  Multicast ND messages are link-scoped and MUST NOT be
   forwarded across the Backbone Link Routers.

   A 6BBR prefix that is used across a specific kind of Border Router that performs proxy
   Neighbor Discovery on its backbone interface on behalf of registered
   6LNs on its LLN interfaces.

   On MultiLink Subnet may still be
   advertised as on-link over the backbone side, Backbone, by setting the 6BBR advertises "L" bit in
   the prefixes of Prefix Information Option (PIO) in RA messages ([RFC4861]), in
   order to support classical IPv6 hosts; but the LLNs
   for which it serves MultiLink Subnet
   prefix MUST be advertised as a proxy.  Some restrictions of not-onlink in RAs sent towards the attached
   LLNs will apply to LLN.

   Nodes located inside the backbone.  In particular, subnet will not perform the IPv6 Path MTU SHOULD be
   set to
   Discovery [RFC8201] between one another.  For that reason, the MTU
   must have a same value on the backbone Backbone and all attached LLNs.  The
   scalability of  To
   achieve this, the multilink subnet [RFC4903] requires 6BBR MUST use the same MTU value that broadcast
   operations are avoided as much is used in
   RAs over the Backbone in the RAs that it transmits towards the LLN
   links.

3.4.  Registering Node

   A Registering Node MUST implement [RFC6775] as possible updated by [RFC8505]
   in order to interact with a 6BBR.  As such, it does not depend on
   multicast RAs to discover the backbone as well. 6LR(s).

   The 6BBR uses an EARO Registering Node MUST accept multicast RAs, but those are
   expected to be rare within in the NS-DAD LLN is the best practices
   ([RFC7772]) are followed.

   The Registering Node SHOULD comply with the Simple Procedures for
   Detecting Network Attachment in IPv6 [RFC6059] (DNA procedures) to
   assert movements, and support Packet-Loss Resiliency for Router
   Solicitations [RFC7559] in order to make the multicast NA unicast RS messages more
   reliable.

   The Registering Node signals that it generates over the Backbone Link on behalf of requires IPv6 proxy-ND services
   from a Registered
   Node.  The 6BBR places an EARO in its unicast NA messages, if and
   only if by registering the NS/NA that stimulates it had corresponding IPv6 Address with an EARO in it and
   NS(EARO) message with the 'R'
   bit set. flag set ([RFC8505]).  It may be the
   actual owner of the IPv6 Address or a 6LBR that performs the
   registration on its behalf in a Route-Over mesh.

   The 6BBR Registering Node SHOULD use unicast or register all of its Global Unicast and
   Unique-Local IPv6 Addresses to the solicited-node multicast address
   (SNMA) [RFC4291] 6BBRs.  Failure to defend its Registered register a
   subset of Addresses may result in its Binding
   Table those Addresses being unreachable
   by other parties if the 6BBR cancels the NS(LOOKUP) over the backbone.  In particular, LLN or
   to selected LLN nodes that are known to register their addresses.

3.5.  Using IPv6 ND Over the Backbone Link

   On the Backbone side, the 6BBR MUST join the SNMA group that
   corresponds to a Registered Address as soon as it creates an entry
   for that address, Address, and maintain conserve its SNMA membership as long as it
   maintains that the associated entry.

   Optimistic DAD (ODAD) [RFC4429] SHOULD be supported by  The 6BBR uses either the 6BBRs SNMA or
   plain unicast to defend the Registered Addresses in
   their proxy activity its Binding
   Table over the backbone.  A Backbone.

   The 6BBR supporting ODAD advertises and defends the Registered Addresses over the
   Backbone using the IPv6 ND protocol [RFC4861].  It MUST
   join uses an EARO
   in the SNMA of a Tentative address. NS(DAD) and NA messages that it generates over the Backbone
   Link for the Registered Address.  A 6BBR NA message generated in Routing Proxy mode MAY advertise response
   to a NS(LOOKUP) MUST NOT have the Registered IPv6
   Address with override (O) bit set.  A proxied NS
   MUST NOT contain an SLLAO to avoid the confusion with a registration.

   A 6BBR Link Layer Address, and may asynchronously update Neighbor Cache
   Entries (NCE) the NCEs in correspondent nodes over
   the backbone, Backbone, e.g., in case of a movement.  This is achieved using a
   gratuitous NA(Override).  This method may fail if NA with the override (O) bit set, that may be sent unicast
   to each individual correspondent, or multicast
   message is not received, and correspondent to all nodes may maintain an
   incorrect neighbor state, which they will eventually discover through
   Neighbor Unreachability Detection (NUD).  For slow movements, the NUD
   procedure defined (more in [RFC4861] may time out too quickly,
   Section 3.7 and Section 3.6).

   A 6LBR may optionally be deployed over the
   support of [RFC7048] Backbone.  When that is recommended in all 6LNs in
   the network.

   Multicast should be avoided as much as possible even on case, the backbone
   [I-D.ietf-mboned-ieee802-mcast-problems].  Although hosts can
   participate using legacy IPv6 ND, all 6LNs connected 6BBR uses an EDAR/EDAC echange to check for duplication
   or movement as prescribed in [RFC8505].  If this registration is
   duplicate or not the backbone
   SHOULD support [I-D.ietf-6man-rs-refresh], which also requires freshest, then the
   support 6LBR replies with a status
   code of [RFC7559].

5.2.  Proxy Operations Over 1 ("Duplicate Address") or 3 ("Moved"), respectively.  If
   this registration is the LLN Interface

   6LNs on freshest, then the LLN follow [RFC6775] and do not depend 6LBR replies with a
   status code of 0; in that case, if there was an existing registration
   on multicast RAs
   to discover routers.  6LNs SHOULD accept multicast RAs [RFC7772], but
   those are expected an old 6BBR, then the 6LBR also sends an asynchronous EDAC with a
   status of 4 ("Removed") to be rare within in the LLN. old 6BBR.  Note that an alternate
   protocol such as LISP [RFC6830] may be used to provide an equivalent
   service.

   Nodes SHOULD follow
   the Simple Procedures for Detecting Network Attachment in IPv6
   [RFC6059] (DNA procedures) implementing this specification is expected to assert movements, co-exist on a
   same Backbone Link with nodes implementing classical IPv6 ND
   [RFC4861] and support Packet-
   Loss Resiliency for Router Solicitations [RFC7559] to make snooping [I-D.bi-savi-wlan].  It results that the
   unicast RS more reliable.

   A 6LN signals fact
   that it requires IPv6 ND proxy services from there is a 6BBR by
   registering 6LBR or an alternate protocol that is deployed on the corresponding
   Backbone does not mean that all IPv6 Address with an NS(EARO) message addresses are known there; the
   fact that a unicast DAD succeeds with the 'R' flag set.  The 6LN 6LBR does not mean that performs the registration (the
   Registering Node)
   address is not duplicate, and, unless administratively overridden,
   6BBRs must still perform classical IPv6 ND DAD after an EDAC with a
   status code of 0.

   For slow movements, the Neighbor Unreachability Detection (NUD)
   procedure defined in [RFC4861] may be time out too quickly, and the owner
   support of [RFC7048] is recommended for all nodes in the IPv6 Address (the
   Registered Node) or a 6LBR that performs the registration on its
   behalf.

5.2.1. subnet.

3.6.  Routing Proxy Operations

   When operating as a Routing Proxy, the BBR installs host routes
   (/128) to the Registered Addresses within the LLN, via the
   Registering Node as identified by 6BBR MUST use the Source Layer-2
   Address and on its Backbone Interface in the TLLA and SLLA
   option in options, when
   present, of the NS(EARO) messages. RS, NS and NA messages that it generates to advertise
   the Registered Addresses.  In that case, the MAC address Addresses of the 6LN is
   6LNs do not need to be visible at Layer-2 over the backbone.  The Backbone to
   maintain end-to-end IP connectivity, but the NCEs of the
   correspondents must be updated when the owner registers to a
   different 6BBR.

   This technique is useful when the churn on the Backbone fabric
   associated to wireless mobility becomes expensive, e.g., when the
   Layer-2 topology is virtualized over a wide area IP underlay.  In
   order to maintain IP connectivity, the 6BBR installs a connected host
   route towards to the Registered Node over Address on the interface
   toward LLN interface, via the 6LN, and routes unicast packets to
   Registering Node as identified by the 6LN.

   The Routing Proxy 6BBR handles Source Address and the ND protocol over SLLA
   option in the backbone on
   behalf of NS(EARO) messages.

   This technique is also useful when the Registered Nodes, using its own LLN uses a MAC address in format
   that is different from that on the TLLA
   and SLLA options in proxied NS and NA messages. Backbone (e.g., EUI-64 vs. EUI-
   48).

   For each Registered Address, multiple peer Nodes on the backbone Backbone may
   have resolved the
   address Address with the 6BBR MAC address, Address, maintaining that
   mapping in their Neighbor cache.

   For each Registered Address, the  The 6BBR SHOULD maintain a list of
   the peers on the backbone Backbone which have associated its MAC address Address with
   the Registered Address.  If that Registered Address moves from an old
   to a different new 6BBR, the first old 6BBR SHOULD unicast a gratuitous NA(Override) NA with the
   Override (O) bit set to each such peer, to supply the MAC address LLA of the new
   6BBR in the TLLA option for the Address.

5.2.2.  Bridging Proxy Operations

   A Bridging Proxy can be implemented in a Layer-3 switch, or in a
   wireless Access Point that acts as an IPv6 Host.  In the latter case,

   If the SLLA option in 6BBR fails to maintain this list, then it MAY send the proxied
   gratuitous NA messages is that of the Registering
   Node, and with the 6BBR acts Override (O) bit set as a Layer-2 bridge for unicast packets to
   the Registered Address.  The MAC address in the S/TLLA is multicast message
   that of will possibly hit all the
   Registering Node, which is nodes on the Backbone, whether they
   maintain an NCE or not necessarily for the Registered Node.  When
   a 6LN moves within Address.

   If a LLN mesh, it may attach correspondent fails to a different 6LBR
   acting as Registering Node, and the MAC address advertised over receive the
   backbone might change.

   If gratuitous NA, it will keep
   sending traffic to a registration moves from one 6BBR to which the next, but the
   Registering Node does not change, as indicated by the S/TLLA option
   in the ND exchanges, there is no need node was previously
   registered.  That old 6BBR having removed its host route to update the Neighbor Caches
   of the peer's Nodes on
   Registered Address, it will look it up over the backbone.  On backbone, resolve the other hand, if
   with the LLA
   changes, of the 6BBR SHOULD inform all new 6BBR, and forward the relevant peers as described
   above, packet to update the affected Neighbor Caches.  In the same fashion,
   if the Registering Node changes with a new registration, the correct
   6BBR.  The old 6BBR SHOULD also issue a redirect message [RFC4861] is
   order to update the affected Neighbor Caches over cache of the backbone.

6.  Backbone Router correspondent.

3.7.  Bridging Proxy Operations

   The LLNs attached to each 6BBR are considered different Links

   A Bridging Proxy can be implemented in a
   multi-link subnet.  The prefix Layer-3 switch, or in a
   wireless Access Point or wireless Controller that is used may still be advertised acts as on-link a Layer-2
   Bridge for unicast packets from/to the Registered Address.  The
   Bridging Proxy appears as an IPv6 Host on the backbone to support legacy 6LNs.  Multicast ND
   messages are link-scoped and not forwarded across Backbone whereas the backbone
   routers.

   By default, a 6BBR operates as a Sleeping Proxy,
   Routing Proxy described in Section 3.6 is an IPv6 router operating as follows:

   o  Create
   a new entry in border router between Links of a Binding Table for MultiLink Subnet.

   When operating as a new Registered Bridging Proxy, the 6BBR MUST use the Registering
   Node's Layer-2 Address in the TLLA and ensure SLLA options, when present,
   of, respectively, the RS, NS and NA messages that it generates to
   advertise the Registered Addresses.  The Registering Node's Layer-2
   address is not a duplicate over found in the SLLA of the registration NS(EARO), and
   maintained in the abstract Binding Table.

   If the Registering Node is the owner of the backbone

   o  Defend a Registered Address Address, then
   its mobility does not impact existing NCEs over the backbone using Backbone.  If it
   is not, then when the 6LN selects another Registering Node, the new
   Registering Node SHOULD send a multicast NA messages with the Override (O) bit
   set on behalf of the sleeping 6LN

   o  Advertise a Registered Address over the backbone using NA
      messages, asynchronously or as a response to a Neighbor
      Solicitation messages.

   o  To deliver packets arriving from fix the LLN, use Neighbor
      Solicitation messages to look up existing NCEs across the destination over Backbone.  This method may
   fail if the
      backbone.

   o  Forward packets between multicast message is not received, in which case one or
   more correspondent nodes on the LLN Backbone may maintain an obsolete NCE
   and traffic to the backbone.

   o  Verify liveliness when needed for a stale registration.

   A 6BBR Registered Address may act as a Sleeping Proxy only be lost for a Registered Address that while.  When
   this condition happens, it is REACHABLE, or TENTATIVE in which case eventually be discovered and solved
   through the answer Neighbor Unreachability Detection (NUD) procedure defined
   in [RFC4861].

3.8.  Leveraging Optimistic DAD

   The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
   specification details how an IPv6 Address can be used before a
   Duplicate Address Detection (DAD) is delayed.  In
   any other state, the Sleeping Proxy operates as complete.

   ODAD provides a Unicasting Proxy.

   The 6BBR does set of rules that guarantee that this behavior may
   not act on ND Messages over harm an existing state should the backbone unless they
   are relevant to new Address effectively be a Registered Node on the LLN side, saving wireless
   interference.  On
   duplicate.  This specification leverages ODAD to avoid delays in
   installing the LLN side, Neighbor Cache Entry (NCE) in the prefixes associated 6BBRs and the
   default router in order to obtain immediate connectivity to the
   MultiLink Subnet are presented as not on-link, so address resolution
   for other hosts do not occur.
   registered node.

   This specification RECOMMENDS to support ODAD to create an optimistic
   proxy state in the 6BBR until DAD is completed over the Backbone.  As
   shown in Figure 2, if the 6BBR is aware of the Link-Layer Address
   (LLA) of a Unicasting Proxy, router, then the 6BBR forwards NS lookup messages sends a Router Sollicitation (RS),
   sourced with the Registered Address, to the
   Registering Node, transforming Layer-2 multicast into unicast.  This known router(s).  The RS
   MUST be sent without a Source LLA Option (SLLAO), to ensure that a
   preexisting NCE in the router is not possible in UNREACHABLE state, so affected.

   Following the NS messages are
   multicasted, ODAD flows, the router may then send a unicast RA to
   the Registered Address, and rate-limited.  Retries are possible, in the process of doing so, it may
   resolve it using an
   exponential back-off to protect the medium. NS(LOOKUP) message.  In other states, the
   messages are forwarded to response, the Registering Node as unicast Layer-2
   messages.  In TENTATIVE state, 6BBR sends
   a NA with the NS message override (O) bit that is either held till DAD
   completes, or dropped if DAD does not complete.

6.1.  Primary set (per [RFC4429]), and Secondary BBRs

   A 6BBR MAY be primary or secondary.  The primary is
   an EARO option.  If the backbone router that has supports this specification, then it
   can determine the highest EUI-64 address freshest EARO option in case of all the 6BBRs that
   share a registration for conflicting
   NA(EARO) messages, using section 5.2.1 of [RFC8505].  If the NA(EARO)
   is the freshest or only answer then the default router creates a same Registered Address, BCE
   with the same
   ROVR and same Transaction ID, SLLAO of the EUI-64 address being considered as
   an unsigned 64bit integer.  A given 6BBR (in Routing Proxy mode) or that of the
   Registering Node (in Bridging Proxy mode) and traffic from/to the
   Registered Address can be primary for flow immediately.

4.  Updating RFC 4861

   This specification adds the EARO as a given
   address possible option in RS, NS(DAD)
   and secondary for another address, regardless of whether or NA messages over the backbone.  Note that [RFC8505] requires that
   the registration NS(EARO) contains an SLLAO.  Note that an NS(DAD)
   does not contain an SLLAO and thus cannot be confused with a
   registration.

5.  Updating RFC 8505

   This specification adds the addresses belong capability to the same 6LN.  The primary Backbone
   Router is insert IPv6 ND options in charge of protecting the address for DAD over the
   Backbone.  Any of
   the Primary EDAR and Secondary EDAC messages.  In particular, a 6BBR may claim acting as a 6LR
   for the
   address over Registered Address can insert an SLLAO in the backbone, since they are all capable EDAR to route from the backbone
   6LBR in order to the 6LN; the address appears on the backbone avoid a lookup back.

6.  6BBR detailed Operations

   By default, a 6BBR operates as an
   anycast address.

6.2. a Sleeping Proxy, as follows:

   o  Create a new entry in a Binding Table

   Each 6BBR maintains for a Binding Table, using IPv6 ND over the backbone
   to detect duplication.  Another document
   [I-D.ietf-6lo-rfc6775-update] provides details about how the EARO is
   used between 6LRs new Registered Address
      and 6LBRs by way of DAR/DAC messages within the
   LLN.  Addresses in a LLN ensure that can be reachable from the backbone by
   way of Address is not a 6BBR MUST be registered to that 6BBR.

   A false positive duplicate detection may arise over the backbone, for
   instance if Backbone

   o  Defend a 6LN's Registered Address is registered to more than one
   LBR, or if the 6LN has moved.  Both situations are handled by over the
   6BBR transparently to the 6LN.  In Backbone using NA messages
      with the former case, one LBR becomes
   primary to defend Override bit set on behalf of the address sleeping 6LN

   o  Advertise a Registered Address over the backbone while Backbone using NA
      messages, asynchronously or as a response to a Neighbor
      Solicitation messages.

   o  To deliver packets arriving from the others
   become secondary and may still forward packets.  In LLN, use Neighbor
      Solicitation messages to look up the latter case destination over the LBR that receives
      Backbone.

   o  Forward packets between the newest registration becomes primary because
   of LLN and the TID.

   Only one 6LN Backbone.

   o  Verify liveliness when needed for a stale registration.

   A 6BBR may register act as a given Address at Sleeping Proxy only for a particular 6BBR.
   However, that Registered Address may be registered to Multiple 6BBRs
   for higher availability.

   Over that
   is REACHABLE, or TENTATIVE in which case the LLN, Binding Table management answer is delayed.  In
   any other state, the Sleeping Proxy operates as follows:

      De-registrations (newer TID, same ROVR, null Lifetime) are
      accepted and acknowledged with a status of 4 (TBD); Unicasting Proxy.

   The 6BBR does not act on ND Messages over the entry is
      deleted;

      Newer registrations (newer TID, same ROVR, non-null Lifetime) Backbone unless they
   are
      acknowledged with relevant to a status of 0 (success); the binding is updated
      with Registered Node on the new TID, LLN side, saving wireless
   interference.  On the Registration Lifetime and LLN side, the Registering
      Node; in TENTATIVE state prefixes associated to the acknowledgement is held and may be
      overwritten; in
   MultiLink Subnet are presented as not on-link, so Address resolution
   for other states the Registration-Lifetime timer is
      restarted and the entry is placed in REACHABLE state.

      Identical registrations (same TID, same ROVR) from hosts do not occur.

   As a same Unicasting Proxy, the 6BBR forwards NS lookup messages to the
   Registering Node Node, transforming Layer-2 multicast into unicast.  This
   is not possible in UNREACHABLE state, so the NS messages are acknowledged with a status of 0 (success).
      If they
   multicasted, and rate-limited.  Retries are not identical, possible, using an error SHOULD be logged.
   exponential back-off to protect the medium.  In other states, the
   messages are forwarded to the Registering Node as unicast Layer-2
   messages.  In TENTATIVE state, the response NS message is either held till DAD
   completes, or dropped if DAD does not complete.

6.1.  Primary and may be overwritten, but
      it MUST Secondary 6BBRs

   A 6BBR MAY be eventually produced and it carries primary or secondary.  The primary is the result of Backbone
   router that has the
      DAD process;

      Older registrations (older TID, same ROVR) from a Registering Node
      are ignored;

      Identical and older registrations (not-newer TID, same ROVR) from
      a different Registering Node are acknowledged with a status highest EUI-64 Address of 3
      (moved); this may be rate limited to protect all the medium;

      Any 6BBRs that
   share a registration for a different same Registered Node (different ROVR)
      are acknowledged Address, with a status of 1 (duplicate).

6.3.  Registration the same
   ROVR and Binding Table Entry Creation

   Upon receiving a registration same Transaction ID, the EUI-64 Address being considered as
   an unsigned 64bit integer.  A given 6BBR can be primary for a new address with an NS(EARO) with given
   Address and secondary for another Address, regardless of whether or
   not the 'R' bit set, Addresses belong to the 6BBR performs DAD same 6LN.  The primary Backbone
   Router is in charge of protecting the Address for DAD over the backbone, placing
   Backbone.  Any of the
   new address as target in Primary and Secondary 6BBR may claim the NS-DAD message.  The EARO
   Address over the Backbone, since they are all capable to route from
   the
   registration MUST be placed unchanged in Backbone to the NS-DAD message, and 6LN; the Address appears on the Backbone as an
   Neighbor Cache entry created in TENTATIVE state for
   anycast Address.

6.2.  Binding Table

   Each 6BBR maintains a duration of
   TENTATIVE_DURATION.  The NS-DAD message is sent multicast Binding Table, using IPv6 ND over the
   backbone Backbone
   to detect duplication.  Another document [RFC8505] provides details
   about how the SNMA associated with the registered address, unless
   that operation EARO is known to be costly, used between 6LRs and 6LBRs by way of DAR/DAC
   messages within the 6BBR has an indication LLN.  Addresses in a LLN that can be reachable
   from another source (such as the Backbone by way of a Neighbor Cache entry) 6BBR MUST be registered to that 6BBR.

   A false positive duplicate detection may arise over the Backbone, for
   instance if a 6LN's Registered Address was known on is registered to more than one
   LBR, or if the backbone; in 6LN has moved.  Both situations are handled by the latter
   6BBR transparently to the 6LN.  In the former case, an
   NS-DAD message may be sent as a Layer-2 unicast one LBR becomes
   primary to defend the MAC Address
   that was associated with over the Registered Address. Backbone while the others
   become secondary and may still forward packets.  In TENTATIVE state after EARO with 'R' bit set:

   1.  The entry is removed if an NA is received over the backbone for latter case
   the Registered LBR that receives the newest registration becomes primary because
   of the TID.

   Only one 6LN may register a given Address with no EARO, or containing an EARO with at a
       status of 1 (duplicate) particular 6BBR.
   However, that indicates an existing registration Registered Address may be registered to Multiple 6BBRs
   for another 6LN.  The ROVR and TID fields in the EARO received
       over higher availability.

   Over the backbone LLN, Binding Table management is as follows:

      De-registrations (newer TID, same ROVR, null Lifetime) are ignored.  A
      accepted and acknowledged with a status of 1 is returned in the
       EARO of the NA back to 4 (TBD); the Registering Node;

   2.  The entry is also removed if an NA with an ARO option
      deleted;

      Newer registrations (newer TID, same ROVR, non-null Lifetime) are
      acknowledged with a status of 3 (moved), or a NS with an ARO option that indicates a
       newer registration for 0 (success); the same Registered Node, binding is received over
       the backbone for updated
      with the Registered Address.  A status of 3 is
       returned in new TID, the NA(EARO) back to Registration Lifetime and the Registering
      Node;

   3.  When a registration is updated but not deleted, e.g. from a newer
       registration, in TENTATIVE state the DAD process on acknowledgement is held and may be
      overwritten; in other states the backbone continues Registration-Lifetime timer is
      restarted and the
       running timers entry is placed in REACHABLE state.

      Identical registrations (same TID, same ROVR) from a same
      Registering Node are not restarted;

   4.  Other NS (including DAD acknowledged with no EARO) and NA from the backbone a status of 0 (success).
      If they are not acknowledged in identical, an error SHOULD be logged.  In
      TENTATIVE state.  To cover legacy 6LNs
       that do not support ODAD, state, the list of their origins MAY response is held and may be stored overwritten, but
      it MUST be eventually produced and then, if it carries the TENTATIVE_DURATION timer elapses, result of the 6BBR MAY
       send each such legacy 6LN
      DAD process;

      Older registrations (older TID, same ROVR) from a unicast NA.

   5.  When the TENTATIVE_DURATION timer elapses, Registering Node
      are ignored;

      Identical and older registrations (not-newer TID, same ROVR) from
      a status 0 (success)
       is returned in different Registering Node are acknowledged with a NA(EARO) back status of 3
      (moved); this may be rate limited to protect the Registering Node(s), and
       the entry goes to REACHABLE state medium;

      Any registration for the a different Registered Node (different ROVR)
      are acknowledged with a status of 1 (duplicate).

6.3.  Registration Lifetime.
       The 6BBR MUST send and Binding Table Entry Creation

   Upon receiving a multicast NA(EARO) to registration for a new Address with an NS(EARO) with
   the SNMA associated to 'R' bit set, the Registered Address 6BBR performs DAD over the backbone with Backbone, placing the Override bit
       set so
   new Address as to take over target in the binding NS(DAD) message.  The EARO from other 6BBRs.

6.4.  Defending Addresses

   If a 6BBR has the
   registration MUST be placed unchanged in the NS(DAD) message, and an
   Neighbor Cache entry created in REACHABLE TENTATIVE state for a Registered Address:

   o  If the 6BBR is primary, or does not support the function duration of
      primary, it MUST defend that address
   TENTATIVE_DURATION.  The NS(DAD) message is sent multicast over the backbone upon
      receiving NS, either if
   Backbone to the NS does not carry an EARO, or if an
      EARO is present SNMA associated with the registered Address, unless
   that indicates a different Registering Node
      (different ROVR).  The 6BBR sends a NA message with the Override
      bit set operation is known to be costly, and the NA carries 6BBR has an EARO if and only if indication
   from another source (such as a Neighbor Cache entry) that the NS-DAD did
      so.  When present,
   Registered Address was known on the EARO Backbone; in the NA(Override) that is latter case, an
   NS(DAD) message may be sent in
      response as a Layer-2 unicast to the NS(EARO) carries MAC Address
   that was associated with the Registered Address.

   In TENTATIVE state after EARO with 'R' bit set:

   1.  The entry is removed if an NA is received over the Backbone for
       the Registered Address with no EARO, or containing an EARO with a
       status of 1 (duplicate), and
      the (duplicate) that indicates an existing registration
       for another 6LN.  The ROVR and TID fields in the EARO are obfuscated with null or
      random values to avoid network scanning and impersonation attacks.

   o  If the 6BBR receives an NS(EARO) for a newer registration, received
       over the
      6BBR updates Backbone are ignored.  A status of 1 is returned in the entry and
       EARO of the routing state to forward packets NA back to the new 6BBR, but keeps the Registering Node;

   2.  The entry REACHABLE.  Afterwards, the 6BBR
      MAY use REDIRECT messages to reroute traffic for the Registered
      Address to the new 6BBR.

   o  If the 6BBR receives is also removed if an NA(EARO) for a newer registration, the
      6BBR removes its entry and sends a NA(EARO) NA with an ARO option with a
       status of 3
      (MOVED) to (moved), or a NS with an ARO option that indicates a
       newer registration for the Registering same Registered Node, if the Registering Node is
      different from received over
       the Registered Node.  The 6BBR cleans up existing
      Neighbor Cache entries in peer nodes as discussed Backbone for the Registered Address.  A status of 3 is
       returned in Section 5.1,
      by unicasting the NA(EARO) back to each such peer, or one broadcast NA(Override).

   o  If the 6BBR receives Registering Node;

   3.  When a NS(LOOKUP) for registration is updated but not deleted, e.g. from a Registered Address, it
      answers immediately with an NA newer
       registration, the DAD process on behalf of the Registered Node,
      without polling it.  There is Backbone continues and the
       running timers are not restarted;

   4.  Other NS (including DAD with no need of an EARO EARO) and NA from the Backbone
       are not acknowledged in TENTATIVE state.  To cover legacy 6LNs
       that exchange.

   o do not support ODAD, the list of their origins MAY be stored
       and then, if the TENTATIVE_DURATION timer elapses, the 6BBR MAY
       send each such legacy 6LN a unicast NA.

   5.  When the Registration-Lifetime TENTATIVE_DURATION timer elapses, a status 0 (success)
       is returned in a NA(EARO) back to the Registering Node(s), and
       the entry goes to
      STALE REACHABLE state for a duration of STABLE_STALE_DURATION in LLNs that
      keep stable addresses such as LWPANs, and UNSTABLE_STALE_DURATION
      in LLNs where addresses are renewed rapidly, e.g. for privacy
      reasons.

   The STALE state enables tracking of the backbone peers that have Registration Lifetime.
       The 6BBR MUST send a
   Neighbor Cache entry pointing multicast NA(EARO) to this 6BBR in case the Registered
   Address shows up later.  If SNMA associated to
       the Registered Address is claimed by
   another 6LN on over the backbone, Backbone with an NS-DAD or an NA, the 6BBR does
   not defend Override bit
       set so as to take over the address.  In STALE state:

   o  If STALE_DURATION elapses, binding from other 6BBRs.

6.4.  Defending Addresses

   If a 6BBR has an entry in REACHABLE state for a Registered Address:

   o  If the 6BBR removes is primary, or does not support the entry.

   o  Upon function of
      primary, it MUST defend that Address over the Backbone upon
      receiving an NA(Override) NS, either if the NS does not carry an EARO, or if an
      EARO is present that indicates a different Registering Node
      (different ROVR).  The 6BBR removes its entry and sends a NA(EARO) NA message with the Override
      bit set and the NA carries an EARO if and only if the NS(DAD) did
      so.  When present, the EARO in the NA(Override) that is sent in
      response to the NS(EARO) carries a status of 4 (removed) to 1 (duplicate), and
      the Registering
      Node. ROVR and TID fields in the EARO are obfuscated with null or
      random values to avoid network scanning and impersonation attacks.

   o  If the 6BBR receives a NS(LOOKUP) an NS(EARO) for a Registered Address, newer registration, the
      6BBR MUST send an NS(NUD) following rules in [RFC7048] updates the entry and the routing state to forward packets to
      the
      Registering Node targeting new 6BBR, but keeps the entry REACHABLE.  Afterwards, the 6BBR
      MAY use REDIRECT messages to reroute traffic for the Registered
      Address prior to
      answering.  If the NUD succeeds, the operation in REACHABLE state
      applies. new 6BBR.

   o  If the NUD fails, 6BBR receives an NA(EARO) for a newer registration, the
      6BBR refrains from answering removes its entry and sends a NA(EARO) with a status of 3
      (MOVED) to the
      lookup.  The NUD SHOULD be used by Registering Node, if the Registering Node to
      indicate liveness of is
      different from the Registered Node, if they are different
      nodes.

7.  Security Considerations

   This specification applies to LLNS Node.  The 6BBR cleans up existing
      Neighbor Cache entries in which the link layer is
   protected, either peer nodes as discussed in Section 3.5,
      by means of physical unicasting to each such peer, or IP security for one broadcast NA(Override).

   o  If the
   Backbone Link or MAC sublayer cryptography.  In particular, 6BBR receives a NS(LOOKUP) for a Registered Address, it
      answers immediately with an NA on behalf of the LLN
   MAC Registered Node,
      without polling it.  There is required to provide secure unicast to/from no need of an EARO in that exchange.

   o  When the Backbone Router
   and secure Broadcast from Registration-Lifetime timer elapses, the Backbone Router in entry goes to
      STALE state for a way duration of STABLE_STALE_DURATION in LLNs that prevents
   tampering with or replaying the RA messages.
      keep stable Addresses such as LWPANs, and UNSTABLE_STALE_DURATION
      in LLNs where Addresses are renewed rapidly, e.g. for privacy
      reasons.

   The use STALE state enables tracking of EUI-64 for forming the Interface ID Backbone peers that have a
   Neighbor Cache entry pointing to this 6BBR in case the link local
   address prevents Registered
   Address shows up later.  If the usage of Secure ND ([RFC3971] and [RFC3972]) and
   address privacy techniques.  Additional protection against address
   theft Registered Address is provided claimed by [I-D.ietf-6lo-ap-nd], which guarantees
   another 6LN on the
   ownership of Backbone, with an NS(DAD) or an NA, the ROVR.

   When 6BBR does
   not defend the ownership of Address.  In STALE state:

   o  If STALE_DURATION elapses, the ROVR cannot be assessed, this specification
   limits 6BBR removes the cases where entry.

   o  Upon receiving an NA(Override) the ROVR 6BBR removes its entry and
      sends a NA(EARO) with a status of 4 (removed) to the TID are Registering
      Node.

   o  If the 6BBR receives a NS(LOOKUP) for a Registered Address, the
      6BBR MUST send an NS(NUD) following rules in [RFC7048] to the
      Registering Node targeting the Registered Address prior to
      answering.  If the NUD succeeds, the operation in REACHABLE state
      applies.  If the NUD fails, the 6BBR refrains from answering the
      lookup.  The NUD SHOULD be used by the Registering Node to
      indicate liveness of the Registered Node, if they are different
      nodes.

7.  Security Considerations

   This specification applies to LLNS in which the link layer is
   protected, either by means of physical or IP security for the
   Backbone Link or MAC sublayer cryptography.  In particular, the LLN
   MAC is required to provide 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.

   The use of EUI-64 for forming the Interface ID in the link local
   Address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
   Address privacy techniques.  Additional protection against Address
   theft is provided by [I-D.ietf-6lo-ap-nd], which guarantees the
   ownership of the ROVR.

   When the ownership of the ROVR cannot be assessed, this specification
   limits the cases where the ROVR and the TID are multicasted, and
   obfuscates them in responses to attempts to take over an address. Address.

8.  Protocol Constants

   This Specification uses the following constants:

   TENTATIVE_DURATION:        800 milliseconds

   STABLE_STALE_DURATION:     24 hours

   UNSTABLE_STALE_DURATION:   5 minutes

   DEFAULT_NS_POLLING:        3 times

9.  IANA Considerations

   This document has no request to IANA.

10.  Future Work

   Future documents may extend this specification by allowing the 6BBR
   to redistribute host routes in routing protocols that would operate
   over the backbone, Backbone, or in MIPv6, or FMIP, or the Locator/ID Separation
   Protocol (LISP) [RFC6830] to support mobility on behalf of the 6LNs,
   etc...

11.  Acknowledgments

   Kudos

   Many thanks to Eric Levy-Abegnoli who designed the First Hop Security
   infrastructure at Cisco. Dorothy Stanley, Thomas Watteyne and Jerome Henry for
   their various contributions.

12.  References

12.1.  Normative References

   [I-D.ietf-6lo-rfc6775-update]
              Thubert, P., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for 6LoWPAN Neighbor
              Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
              progress), June 2018.

   [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>.

   [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>.

   [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>.

   [RFC6059]  Krishnan, S. and G. Daley, "Simple Procedures for
              Detecting Network Attachment in IPv6", RFC 6059,
              DOI 10.17487/RFC6059, November 2010,
              <https://www.rfc-editor.org/info/rfc6059>.

   [RFC6775]  Shelby, Z.,

   [RFC6550]  Winter, T., Ed., Chakrabarti, S., Nordmark, E., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and C.
              Bormann, 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>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
              "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
              DOI 10.17487/RFC8201, July 2017,
              <https://www.rfc-editor.org/info/rfc8201>.

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

12.2.  Informative References

   [I-D.bi-savi-wlan]
              Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for
              WLAN", draft-bi-savi-wlan-16 (work in progress), November
              2018.

   [I-D.ietf-6lo-ap-nd]
              Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
              "Address Protected Neighbor Discovery for Low-power and
              Lossy Networks", draft-ietf-6lo-ap-nd-08 (work in
              progress), October 2018.

   [I-D.ietf-6man-rs-refresh]
              Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6
              Neighbor Discovery Optional RS/RA Refresh", draft-ietf-
              6man-rs-refresh-02 (work in progress), October 2016.

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-15 draft-ietf-6tisch-architecture-17 (work
              in progress), October November 2018.

   [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-02 draft-ietf-mboned-ieee802-mcast-problems-04 (work
              in progress), August November 2018.

   [I-D.nordmark-6man-dad-approaches]
              Nordmark, E., "Possible approaches to make DAD more robust
              and/or efficient", draft-nordmark-6man-dad-approaches-02
              (work in progress), October 2015.

   [I-D.yourtchenko-6man-dad-issues]
              Yourtchenko, A. and E. Nordmark, "A survey of issues
              related to IPv6 Duplicate Address Detection", draft-
              yourtchenko-6man-dad-issues-01 (work in progress), March
              2015.

   [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>.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
              2006, <https://www.rfc-editor.org/info/rfc4389>.

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

   [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>.

   [RFC5415]  Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
              Ed., "Control And Provisioning of Wireless Access Points
              (CAPWAP) Protocol Specification", RFC 5415,
              DOI 10.17487/RFC5415, March 2009,
              <https://www.rfc-editor.org/info/rfc5415>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [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>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <https://www.rfc-editor.org/info/rfc6830>.

   [RFC7048]  Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
              Detection Is Too Impatient", RFC 7048,
              DOI 10.17487/RFC7048, January 2014,
              <https://www.rfc-editor.org/info/rfc7048>.

   [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>.

   [RFC7559]  Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss
              Resiliency for Router Solicitations", RFC 7559,
              DOI 10.17487/RFC7559, May 2015,
              <https://www.rfc-editor.org/info/rfc7559>.

   [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
              Consumption of Router Advertisements", BCP 202, RFC 7772,
              DOI 10.17487/RFC7772, February 2016,
              <https://www.rfc-editor.org/info/rfc7772>.

   [RFC8273]  Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
              per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
              <https://www.rfc-editor.org/info/rfc8273>.

12.3.  External Informative References

   [IEEEstd8021]
              IEEE standard for Information Technology, "IEEE Standard
              for Information technology -- Telecommunications and
              information exchange between systems Local and
              metropolitan area networks Part 1: Bridging and
              Architecture".

   [IEEEstd80211]
              IEEE standard for Information Technology, "IEEE Standard
              for Information technology -- Telecommunications and
              information exchange between systems Local and
              metropolitan area networks-- Specific requirements Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications".

   [IEEEstd802151]
              IEEE standard for Information Technology, "IEEE Standard
              for Information Technology - Telecommunications and
              Information Exchange Between Systems - Local and
              Metropolitan Area Networks - Specific Requirements. - Part
              15.1: Wireless Medium Access Control (MAC)
              Metropolitan Area Networks - Specific Requirements. - Part
              15.1: Wireless Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications for Wireless Personal Area
              Networks (WPANs)".

   [IEEEstd802154]
              IEEE standard for Information Technology, "IEEE Standard
              for Local and metropolitan area networks -- Part 15.4:
              Low-Rate Wireless Personal Area Networks (LR-WPANs)".

Appendix A.  Applicability and Requirements Served

   This document specifies proxy-ND functions that can be used to
   federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single
   MultiLink Subnet.  The proxy-ND functions enable IPv6 ND services for
   Duplicate Address Detection (DAD) and Address lookup that do not
   require broadcasts over the LLNs.

   The term LLN is used loosely 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 listed in Appendix B.3 of [RFC8505]
   "Requirements Related to Various Low-Power Link Types".

   Each LLN in the subnet is anchored at an IPv6 Backbone Router (6BBR).
   The Backbone Routers interconnect the LLNs and advertise the
   Addresses of the 6LNs over the Backbone Link using proxy-ND
   operations.

   This specification updates IPv6 ND over the Backbone to distinguish
   Address movement from duplication and eliminate stale state in the
   Backbone routers and Backbone nodes once a 6LN has roamed.  In this
   way, mobile nodes may roam rapidly from one 6BBR to the next and
   requirements in Appendix B.1 of [RFC8505] "Requirements Related to
   Mobility" are met.

   Any 6LN may register its IPv6 Addresses and thereby obtain proxy-ND
   services over the Backbone, providing a solution to the requirements
   expressed in Appendix B.4 of [RFC8505] "Requirements Related to Proxy
   Operations".

   The IPv6 ND operation is minimized as the number of 6LNs grows in the
   LLN.  This meets the requirements in Appendix B.6 of [RFC8505]
   "Requirements Related to Scalability", as long has the 6BBRs are
   dimensioned for the number of registrations that each needs to
   support.

   In the case of a (Low-Power) Wi-Fi access link, a 6BBR may be
   collocated with the Access Point (AP), or with a Fabric Edge (FE) or
   a CAPWAP [RFC5415] Wireless LAN Controller (WLC).  In that case, the
   wireless client (STA) is the 6LN [RFC8505] that makes use of this
   specification to register its IPv6 Address(es) to the 6BBR acting as
   Routing Registrar.  The 6LBR can be centralized and either connected
   to the Backbone Link or reachable over IP.  The 6BBR proxy-ND
   operations eliminate the need for wireless nodes to respond
   synchronously when a lookup is performed for their IPv6 Addresses.
   This provides the function of a Sleep Proxy for ND
   [I-D.nordmark-6man-dad-approaches].

   For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154],
   the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how
   a 6LoWPAN ND host could connect to the Internet via a RPL mesh
   Network, but doing so requires extensions to the 6LOWPAN ND protocol
   to support mobility and reachability in a secure and Physical
              Layer (PHY) Specifications for Wireless Personal Area
              Networks (WPANs)".

   [IEEEstd802154]
              IEEE standard for Information Technology, "IEEE Standard manageable
   environment.  The extensions detailed in this document also work for Local and metropolitan area networks -- Part 15.4:
              Low-Rate Wireless Personal Area Networks (LR-WPANs)".
   the 6TiSCH architecture, serving the requirements listed in
   Appendix A.  Changes from revision 07 B.2 of [RFC8505] "Requirements Related to revision 08

   This section lists the changes between draft-ietf-6lo-backbone-router
   revisions ...-07.txt Routing
   Protocols".

   The registration mechanism may be seen as a more reliable alternate
   to snooping [I-D.bi-savi-wlan].  It can be noted that registration
   and ...-08.txt.

   o  Reorganized snooping are not mutually exclusive.  Snooping may be used in
   conjunction with the order registration for nodes that do not register
   their IPv6 Addresses.  The 6BBR assumes that if a node registers at
   least one IPv6 Address to it, then the node registers all of presentation its
   Addresses to the 6BBR.  With this assumption, the 6BBR can possibly
   cancel all undesirable multicast NS messages that would otherwise
   have been delivered to that node.

   The scalability of some sections so the MultiLink Subnet [RFC4903] requires that
      related material is closer together.

   o  Added "Future Work" section.

   o  Added this section detailing recent changes.

   o  Used '6LN' when LLN node is meant.

   o  Updated bibliographic citations.
   multicast/broadcast operations are avoided as much as possible even
   on the Backbone [I-D.ietf-mboned-ieee802-mcast-problems].  Although
   hosts can connect to the Backbone using classical IPv6 ND operations,
   multicast RAs can be saved by using [I-D.ietf-6man-rs-refresh], which
   also requires the support of [RFC7559].

Authors' Addresses
   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   MOUGINS - Sophia Antipolis  06254
   FRANCE

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

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

   Email: charliep@computer.org

   Eric Levy-Abegnoli
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   MOUGINS - Sophia Antipolis  06254
   FRANCE

   Phone: +33 497 23 26 20
   Email: elevyabe@cisco.com