6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     cisco
Intended status: Standards Track                       February 23, 2018                              C. Perkins
Expires: August 27, March 7, 2019                                         Futurewei
                                                       September 3, 2018

                          IPv6 Backbone Router
                   draft-ietf-6lo-backbone-router-06
                   draft-ietf-6lo-backbone-router-07

Abstract

   This specification proposes proxy operations for IPv6 Neighbor
   Discovery on behalf of devices located on broadcast-inefficient

   Backbone Routers placed at the wireless networks.  A broadcast-efficient edge of a backbone running classical
   IPv6 Neighbor Discovery federates link
   interconnect multiple wireless links at Layer-3 to form a large
   MultiLink Subnet, but so that the broadcast domain of the backbone does
   not need to extend to the wireless links for the purpose of ND operation.
   Backbone Routers placed at the wireless edge of the backbone proxy
   the ND operation and route packets from/to registered nodes, and
   wireless links.  Wireless nodes register or are
   proxy-registered to the a Backbone Router to setup establish IPv6 Neighbor
   Discovery proxy services in a fashion that is essentially
   similar to a classical Layer-2 association. services, and the Backbone Router takes care of the
   ND operation on behalf of registered nodes and ensures and routes
   towards the registered addresses over the wireless interface.

Status of This Memo

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   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on August 27, 2018. March 7, 2019.

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability and Requirements Served . . . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6   5
   4.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Backbone Router Routing Operations  . . . . . . . . . . . . .   9   8
     5.1.  Over the Backbone Link  . . . . . . . . . . . . . . . . .  10   9
     5.2.  Over the LLN Link . . . . . . . . . . . . . . . . . . . .  11  10
   6.  BackBone  Backbone Router Proxy Operations  . . . . . . . . . . . . . .  13  11
     6.1.  Registration and Binding State Creation . . . . . . . . .  15  14
     6.2.  Defending Addresses . . . . . . . . . . . . . . . . . . .  17  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18  16
   8.  Protocol Constants  . . . . . . . . . . . . . . . . . . . . .  18  16
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18  17
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  19  17
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19  17
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19  17
     11.2.  Informative References . . . . . . . . . . . . . . . . .  20  18
     11.3.  External Informative References  . . . . . . . . . . . .  23
   Appendix A.  Requirements . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . .  24
     A.1.  Requirements Related to Mobility . . . . . . . . . . . .  24
     A.2.  Requirements Related to Routing Protocols . . . . . . . .  25
     A.3.  Requirements Related to  22

1.  Introduction

   One of the Variety of Low-Power Link
           types . . . . . . . . . . . . . . . . . . . . . . . . . .  26
     A.4.  Requirements Related to Proxy Operations  . . . . . . . .  26
     A.5.  Requirements Related to Security  . . . . . . . . . . . .  27
     A.6.  Requirements Related to Scalability . . . . . . . . . . .  28
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   One of the key services provided by IEEE std. 802.1 [IEEEstd8021]
   Ethernet Bridging is an efficient and reliable broadcast service, and
   multiple applications and protocols have been built that heavily
   depend on that feature for their core operation.  But a wide range key services provided by IEEE STD. 802.1 [IEEEstd8021]
   Ethernet Bridging is an efficient and reliable broadcast service, and
   multiple applications and protocols have been built that heavily
   depend on that feature for their core operation.  Unfortunately, a
   wide range of wireless networks do not provide the solid and cheap economical broadcast
   capabilities of Ethernet Bridging, and Bridging; protocols designed for bridged
   networks that rely on broadcast often exhibit disappointing
   behaviours when applied unmodified to a wireless medium.

   IEEE std. 802.11

   Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended
   Service Set (ESS) effectively act as bridges, but, bridges.  However, in order to ensure a
   solid connectivity to the devices and protect the medium against
   harmful broadcasts, they refrain from relying on broadcast-
   intensive broadcast-intensive
   protocols such as Transparent Bridging on the wireless side.
   Instead, an association process is used to register proactively the
   MAC addresses of the wireless device (STA) to the AP,
   and then AP.  Then, the APs
   proxy the bridging operation and cancel the broadcasts.

   Classical

   The IPv6 [RFC8200] Neighbor Discovery [RFC4861] [RFC4862] Protocol
   (NDP) operations are reactive and rely heavily on multicast
   operations
   transmissions to locate an on-link correspondent and ensure address
   uniqueness, which is a pillar that sustains the whole IP
   architecture.
   uniqueness.  When the Duplicate Address Detection [RFC4862] (DAD)
   mechanism was designed, it was a natural match with the efficient
   broadcast operation of Ethernet Bridging, but with the unreliable Bridging.  However, since broadcast that is typical of
   can be unreliable over wireless media, DAD is bound to fail often fails to discover
   duplications [I-D.yourtchenko-6man-dad-issues].  In other
   words, because the broadcast service is unreliable,  DAD usually appears
   to work on wireless media media, not because address duplication is
   detected and solved as designed, but because the use of 64-bit
   Interface IDs makes duplication is into a very rare
   event as a side effect of the sheer amount of entropy in 64-bits
   Interface IDs.

   In the real world, event.

   IPv6 multicast messages are effectively broadcast,
   so they usually broadcast over the wireless
   medium.  They are processed by most if not all wireless nodes over
   the ESS fabric even when very few if any of the nodes is effectively
   listening are subscribed
   to the multicast address.  It results that  Consequently a simple Neighbor
   Solicitation (NS) lookup message [RFC4861], that is supposedly
   targeted to a very small group of nodes, ends up polluting can consume the whole
   wireless bandwidth across the fabric
   [I-D.vyncke-6man-mcast-not-efficient].  In other words, the  The reactive IPv6 ND
   operation leads to undesirable power consumption in battery-
   operated battery-operated
   devices.

   The inefficiencies of using radio broadcasts to support IPv6 NDP lead
   the community to consider (again) splitting the
   suggest restricting broadcast domain
   between the wired and transmissions over the wireless access
   links.  One classical way
   to achieve this is to split  This can be done by splitting the subnet in multiple ones,
   and at the in extreme provide cases providing a /64 per wireless device.  Another
   way is to proxy take over (proxy) the Layer-3 protocols that rely on
   broadcast operation at the boundary of the wired and wireless
   domains, effectively emulating the Layer-2 association at layer-3.  To that effect, Layer-3.  Indeed, the current
   IEEE std. STD. 802.11 [IEEEstd80211] specifications require the capability to perform ARP and ND
   proxy [RFC4389] functions at the Access Points (APs).

   But for (APs) but the lack a comprehensive
   specification for the ND proxy and
   in particular the lack of an equivalent to an association process,
   implementations have to operations is still missing.

   Current devices rely on snooping for acquiring the related detecting association state,
   which is unsatisfactory in a lossy and mobile conditions.  With
   snooping, a state (e.g. a new IPv6 address) may not be discovered or
   a change of state (e.g. a movement) may be missed, leading to
   unreliable connectivity.

   In the context of

   WPAN devices (i.e., those implementing IEEE std. STD. 802.15.4 [IEEEstd802154], the step of
   considering the radio as a medium that is different from Ethernet was
   already taken with the publication
   [IEEEstd802154]) can make use of Neighbor Discovery Optimization for
   IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
   [RFC6775].
   [RFC6775] which treats the wireless medium as different from
   Ethernet.  RFC 6775 is updated as [I-D.ietf-6lo-rfc6775-update]; the
   update includes changes that are required by this document.

   This specification applies that same thinking to other wireless links such as Low-Power
   IEEE std. STD. 802.11 (Wi-Fi) and IEEE std. STD. 802.15.1 (Bluetooth)
   [IEEEstd802151], and extends [RFC6775] to enable proxy operation by
   the 6BBR so as to decouple the broadcast domain in the
   backbone from the wireless links. 6BBR.  The proxy operation can be
   maintained asynchronous so that on the BBR eliminates the need for
   low-power nodes or nodes that are deep in a mesh do not need to be bothered respond
   synchronously when a lookup is performed for their addresses, effectively implementing the ND
   contribution to addresses.  This
   provides the concept function of a Sleep Proxy for ND
   [I-D.nordmark-6man-dad-approaches].

2.  Applicability and Requirements Served

   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. 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 has poor delivery ratio or requires high 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 all the multicast operations more in use cases that are related to classical ND ([RFC4861],
   [RFC4862]) and plague the wireless medium. involve mobility.

   This specification updates and generalizes 6LoWPAN ND to a broader
   range of Low power and Lossy Networks (LLNs) with a solid support for
   Duplicate Address Detection (DAD) and address lookup that does not
   require broadcasts over the LLNs.  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. STD.
   802.11AH and IEEE std. STD. 802.15.4 wireless meshes, so as to address the
   requirements listed in Appendix A.3 B.3 of [I-D.ietf-6lo-rfc6775-update]
   "Requirements Related to the Variety of Low-Power Link types".

   The scope of this draft is a Backbone Link that federates enable the federation of
   multiple LLNs as into a single IPv6 MultiLink Subnet.  Each LLN in the subnet
   is anchored at an IPv6 Backbone Router (6BBR).  The Backbone Routers
   interconnect the LLNs over the Backbone Link and emulate that advertise the addresses of the LLN nodes are present on the Backbone
   using proxy-ND operations.  This specification extends IPv6 ND over
   the backbone to discriminate distinguish address movement from duplication and
   eliminate stale state in the backbone routers and backbone nodes once
   a LLN node has roamed.  This  In this way, mobile nodes may roam rapidly
   from a one 6BBR to the next and requirements in Appendix A.1 B.1 of
   [I-D.ietf-6lo-rfc6775-update]"Requirements Related to Mobility" are
   met.

   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 A.4. B.4 of
   [I-D.ietf-6lo-rfc6775-update] "Requirements Related to Proxy
   Operations".

   The Link Layer Address (LLA) that is returned as Target LLA (TLLA) in
   Neighbor Advertisements (NA) messages by the 6BBR on behalf of the
   Registered Node over the backbone may be that of the Registering
   Node, in which case
   Node.  In that case, the 6BBR needs to bridge the unicast packets
   (Bridging proxy), or that of the 6BBR on the backbone, in which case
   the 6BBRs needs to route the unicast packets (Routing proxy).  In the
   latter case, the 6BBR may maintain maintains the list of correspondents to which
   it has advertised its own MAC address on behalf of the LLN node
   and the node.  The
   IPv6 ND operation is minimized as the number of nodes scale up in the
   LLN.  This enables to meet meets the requirements in Appendix A.6 B.6 of
   [I-D.ietf-6lo-rfc6775-update] "Requirements Related to Scalability",
   as long has the 6BBRs are dimensioned for the number of registration registrations
   that each needs to support.

   In the context of the

   For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154],
   the 6TiSCH architecture [I-D.ietf-6tisch-architecture] introduces describes how
   a 6LoWPAN ND host could connect to the Internet via a RPL mesh
   Network, but this doing so requires additions to the 6LOWPAN ND protocol
   to support mobility and reachability in a secured secure and manageable
   environment.  This
   specification document details the new operations that are required to
   implement such additions for the 6TiSCH architecture
   architecture, and serves the requirements listed in Appendix A.2. B.2 of
   [I-D.ietf-6lo-rfc6775-update] "Requirements Related to Routing
   Protocols".

   In the case of Low-Power IEEE std. STD. 802.11, a 6BBR may be collocated
   with a standalone AP or a CAPWAP [RFC5415] wireless controller, and controller.  Then
   the wireless client (STA) leverages makes use of this specification to register
   its IPv6 address(es) to the 6BBR over the wireless medium.  In the
   case of a 6TiSCH LLN mesh, the RPL root is collocated with a 6LoWPAN
   Border Router (6LBR), and either collocated with or connected to the
   6BBR over an IPv6 Link.  The 6LBR leverages makes use of this specification to
   register the LLN nodes on their behalf to the 6BBR.  In the case of
   BTLE, the 6BBR is collocated with the router that implements the BTLE
   central role as discussed in section 2.2 of [RFC7668].

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].

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

   [RFC6775] and "Multi-link Subnet Support in IPv6"
   [I-D.ietf-ipv6-multilink-subnets].

   Readers would benefit from reading "Multi-Link Subnet Issues"
   [RFC4903], ,"Mobility Support in IPv6" [RFC6275], "Neighbor Discovery
   Proxies (ND Proxy)" [RFC4389] and "Optimistic Duplicate Address
   Detection" [RFC4429] prior to this specification for a clear
   understanding of the art in ND-proxying and binding.

   Additionally, this document uses terminology from [RFC7102],
   [I-D.ietf-6lo-rfc6775-update] and [I-D.ietf-6tisch-terminology], and
   introduces the following terminology:

   Sleeping Proxy

         A 6BBR acts as a Sleeping Proxy if it answers ND Neighbor
         Solicitation over the backbone on behalf of the Registered Node whenever possible.  This is the default mode
         for this specification but it may be overridden, for instance
         by configuration, into Unicasting Proxy.
         Node.

   Unicasting  Proxy  As a

         A Unicasting Proxy, the 6BBR Proxy forwards NS messages to the Registering
         Node, transforming Layer-2 multicast into unicast whenever possible. unicast.

   Routing proxy

         A 6BBR acts as a routing proxy if it advertises its own MAC address, as opposed to
         that of the node that performs the registration, as the TLLA in
         the proxied NAs over the backbone.  In that case,

   Bridging proxy

         A Bridging proxy advertises the MAC address of the node is not
         visible at Layer-2 over the backbone and the bridging fabric is
         not aware of the addresses of the LLN devices and their
         mobility.  The 6BBR installs a connected host route towards the
         registered node over the interface to the node, and acts as a
         Layer-3 router for unicast packets to the node.  The 6BBR
         updates the ND Neighbor Cache Entries (NCE) in correspondent
         nodes if the wireless node moves and registers to another 6BBR,
         either with a single broadcast, or with a series of unicast
         NA(O) messages, indicating the TLLA of the new router.

   Bridging proxy  A 6BBR acts as a bridging proxy if it advertises the
         MAC address of the node that performs that
         performs the registration as the TLLA in the proxied NAs over
         the backbone.  In that case, the MAC address and the mobility
         of the node is still visible across the bridged backbone fabric, as is traditionally the
         case with Layer-2 APs.  The 6BBR acts as a Layer-2 bridge for
         unicast packets to the registered node.  The MAC address
         exposed in the S/TLLA is that of the Registering Node, which is
         not necessarily the Registered Device.  When a device moves
         within a LLN mesh, it may end up attached to a different 6LBR
         acting as Registering Node, and the LLA that is exposed over
         the backbone will change.
         fabric.

   Primary BBR

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

   Secondary BBR

         A BBR other than the Primary BBR to which the an address is
         registered.  A Secondary Router MAY advertise the address over
         the backbone and proxy for it.

4.  Overview

   An LLN node can move freely from an LLN anchored at a Backbone Router
   to an LLN anchored at another Backbone Router on the same backbone
   and conserve keep any or all of the IPv6 addresses that it has formed,
   transparently. formed.

                 |
               +-----+
               |     | Other Gateway (default) Router
               |     |
               +-----+
                  |
                  |      Backbone Link
            +--------------------+------------------+
            |                    |                  |
         +-----+             +-----+             +-----+
         |     | Backbone    |     | Backbone    |     | Backbone
         |     | router      |     | router      |     | router
         +-----+             +-----+             +-----+
            o                o   o  o              o o
        o o   o  o       o o   o  o  o         o  o  o  o o
       o  o o  o o       o   o  o  o  o        o  o  o o o
       o   o  o  o          o    o  o           o  o   o
         o   o o               o  o                 o o

         LLN              LLN              LLN

               Figure 1: Backbone Link and Backbone Routers

   The

   Each Backbone Routers maintain an abstract Router (6BBR) maintains a Binding Table of their its
   Registered Nodes.  The Binding Table operates as a distributed
   database of all the wireless Nodes whether they reside on the LLNs or on the
   backbone, and use an extension to the Neighbor Discovery Protocol to
   exchange that information across the Backbone in the
   classical ND reactive fashion. as with IPv6 ND.

   The Extended Address Registration Option (EARO) defined in
   [I-D.ietf-6lo-rfc6775-update] is used to enable the registration for
   routing and proxy option is included options in the ND exchanges over the backbone
   between the 6BBRs to sort out disambiguate duplication from movement.

   Address duplication is sorted out with detected using the Owner Unique-ID ROVR field in the EARO,
   which is a generalization of the EUI-64 that allows different types
   of unique IDs beyond the name space derived from the MAC addresses.
   First-Come First-Serve rules apply, whether the duplication happens
   between LLN nodes as represented by their respective 6BBRs, or
   between an LLN node and a classical node that defends its address over the
   backbone with classical IPv6 ND and does not include the EARO option. EARO.

   In case of conflicting registrations to multiple 6BBRs from a same
   node, a sequence counter called Transaction ID (TID) in the EARO
   enables 6BBRs to sort out determine the latest anchor registration for that node.
   Registrations with a same TID are compatible and maintained, but, in
   case of different TIDs, only the freshest registration is maintained
   and the stale state is eliminated.  The EARO also transports a 'R'
   flag to be used by a 6LN when registering, to indicate that this 6LN
   is not a router and that it will not handle its own reachability.

   With this specification, Backbone Routers perform a ND proxy
   operation over the Backbone Link on behalf of their Registered Nodes.
   The registration to the proxy service is done with a NS/NA(EARO)
   exchange.  The EARO option with a 'R' flag is used in this specification to indicate to
   request the 6BBR that it is expected to perform this proxy operation.  The Backbone
   Router operation is essentially similar to that of a Mobile IPv6
   (MIPv6) [RFC6275] Home Agent.  This enables mobility support for LLN
   nodes that would move outside of the network delimited by the
   Backbone link attach to a Home Agent from that point on.  This also
   enables collocation of Home Agent functionality within Backbone
   Router functionality on the same backbone interface of a router.
   Further specification may extend this be allowing the 6BBR to
   redistribute host routes in routing protocols that would operate over
   the backbone, or in MIPv6 or the Locator/ID Separation Protocol
   (LISP) [RFC6830] to support mobility on behalf of the nodes, etc...

   The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
   specification details how an address can be used before a Duplicate
   Address Detection (DAD) is complete, and insists that an address that
   is TENTATIVE should not be associated to a Source Link-Layer Address
   Option in a Neighbor Solicitation message.  This specification
   leverages makes
   use of ODAD to create a temporary proxy state in the 6BBR till DAD is
   completed over the backbone.  This way, the specification enables to
   distribute proxy states across multiple 6BBR and co-exist with
   classical IPv6
   ND over the backbone.

5.  Backbone Router Routing Operations
                  |
               +-----+
               |     | Other Gateway (default) Router
               |     |
               +-----+
                  | /64
                  |      Backbone Link
            +-------------------+-------------------+
            | /64               | /64               | /64
         +-----+             +-----+             +-----+
         |     | Backbone    |     | Backbone    |     | Backbone
         |     | router      |     | router      |     | router
         +-----+             +-----+             +-----+
            o N*/128       o o  o M*/128          o o P*/128 N * /128          o M * /128          o P * /128
        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 2: Example Routing Configuration for 3 LLNs in the ML Subnet

5.1.  Over the Backbone Link

   The Backbone Router

   A 6BBR is a specific kind of Border Router that performs proxy
   Neighbor Discovery on its backbone interface on behalf of the nodes
   that it has discovered on its LLN interfaces.

   The backbone is expected to be a high speed, reliable Backbone link,
   with affordable and reliable multicast capabilities, such as a
   bridged Ethernet Network, and to allow a full support of classical ND
   as specified in [RFC4861] and subsequent RFCs.  In other words, the
   backbone is not a LLN.

   Still, some restrictions of the attached LLNs will apply

   Some restrictions of the attached LLNs will apply to the backbone.
   In particular, it is expected that the MTU is MUST be set to the same value on the backbone
   and all attached LLNs, and the LLNs.  The scalability of the whole subnet requires
   that broadcast operations are avoided as much as possible on the
   backbone as well.  Unless configured otherwise, in the RAs that it
   sends towards the LLN links, the Backbone Router MUST echo use the same
   MTU that it learns in from RAs over the backbone in the RAs that it sends towards backbone.

   On the LLN links.

   As a router, backbone side, the Backbone Router 6BBR behaves like any other IPv6 router
   on the backbone side. router.
   It has a connected route installed towards advertises on the backbone for the prefixes that are present on that backbone and that
   it proxies for on of the LLN interfaces.

   As LLNs for which it
   serves as a proxy, the proxy.

   The 6BBR uses an EARO option in the NS-DAD and the multicast NA messages
   that it generates over the Backbone Link on behalf of a Registered
   Node, and it places an EARO in its unicast NA messages, if and only
   if the NS/NA that stimulates it had an EARO in it and the 'R' bit
   set.

   When possible, the

   The 6BBR SHOULD use unicast or solicited-node multicast address
   (SNMA) [RFC4291] to defend its Registered Addresses over the
   backbone.  In particular, 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 as long as it maintains that entry,
   whatever the state of the entry.  The expectation is that it is
   possible to get a message delivered to all the nodes on the backbone
   that listen to a particular address and support this specification -
   which includes all the 6BBRs in the MultiLink Subnet - by sending a
   multicast message to the associated SNMA over the backbone.

   The support of

   Optimistic DAD (ODAD) [RFC4429] is recommended for all
   nodes in the backbone and followed SHOULD be supported by the 6BBRs in
   their proxy activity over the backbone.  With ODAD, any optimistic  A node supporting ODAD MUST
   join the SNMA of a Tentative address, which interacts better with this
   specification.

   This specification allows the address.

   A 6BBR in Routing Proxy mode to advertise advertises the Registered IPv6 Address
   with the 6BBR Link Layer Address, and
   attempts to update updates Neighbor Cache Entries
   (NCE) in correspondent nodes over the backbone, using gratuitous
   NA(Override).  This method may fail of if the multicast message is not
   properly received, and correspondent nodes may maintain an incorrect
   neighbor state, which they will eventually discover through Neighbor
   Unreachability Detection (NUD).  Because mobility may be slow,  For slow movements, the NUD
   procedure defined in [RFC4861] may be time out too impatient, quickly, and the
   support of [RFC7048] is recommended in all nodes in the network.

   Since the MultiLink Subnet may grow very large in terms of individual
   IPv6 addresses, multicasts to contain many nodes, multicast
   should be avoided as much as possible even on the backbone.  Though it is possible for plain
   hosts to can participate with using legacy IPv6 ND support, the support by ND, all nodes connected to
   the backbone of [I-D.ietf-6man-rs-refresh] is
   recommended, and this implies the SHOULD support [I-D.ietf-6man-rs-refresh], which also
   requires the support of [RFC7559] as well. [RFC7559].

5.2.  Over the LLN Link

   As a router, the Nodes

   BBRs and Backbone Router operation LLN hosts on the LLN
   follows [RFC6775].  Per that specification, LLN Hosts generally follow [RFC6775] and do not depend on
   multicast RAs to discover routers.  It is still
   generally required for  LLN nodes to SHOULD accept multicast
   RAs [RFC7772], but those are rare on the LLN link.  Nodes are expected to SHOULD
   follow the Simple Procedures for Detecting Network Attachment in IPv6
   [RFC6059] (DNA procedures) to assert movements, and to support the
   Packet-Loss Resiliency for Router Solicitations [RFC7559] to make the
   unicast RS more reliable.

   An

   LLN node signals that it requires IPv6 ND proxy services from a 6BBR
   by registering the corresponding IPv6 Address with an NS(EARO)
   message with the 'R' flag set.  The LLN node that performs the
   registration (the Registering Node) may be the owner of the IPv6
   Address (the Registered Node) or a 6LBR that performs the
   registration on its behalf.

   When operating as a Routing Proxy, the router BBR installs hosts host routes
   (/128) to the Registered Addresses over the LLN links, via the
   Registering Node as identified by the Source Address and the SLLAO SLLA
   option in the NS(EARO) messages.  In that case, the MAC address of
   the node is not visible at Layer-2 over the backbone and the bridging
   fabric is not aware of the addresses of the LLN devices and their
   mobility.  The 6BBR installs a connected host route towards the
   registered node over the interface to the node, and acts as a Layer-3
   router for unicast packets to the node.

   In that mode, the 6BBR handles the ND protocol over the backbone on
   behalf of the Registered Nodes, using its own MAC address in the TLLA
   and SLLA options in proxyed proxied NS and NA messages.  It results that for  For each Registered
   Address, a number of multiple peer Nodes on the backbone may have resolved the
   address with the 6BBR MAC address and keep store that mapping
   stored in their
   Neighbor cache.

   The 6BBR SHOULD maintain, per

   For each Registered Address, the 6BBR SHOULD maintain a list of the
   peers on the backbone to which it answered with it have associated its MAC address, and
   when a binding address with the
   Registered Address.  If that Registered Address moves to a different
   6BBR, it the first 6BBR SHOULD send a unicast a gratuitous NA(O) individually NA(Override) to each of them
   such peer, to inform them that the
   address has moved and pass supply the MAC address of the new 6BBR in the
   TLLAO option.  If the 6BBR can not maintain that list, then it SHOULD
   remember whether that list is empty or not and if not, send a
   multicast NA(O) to all nodes to update the impacted Neighbor Caches
   with the information from TLLA
   option for the new 6BBR.

   The Address.

   A Bridging Proxy is a variation where the BBR function is can be implemented in a Layer-3 switch switch, or an in a
   wireless Access Point that acts as a Host from the IPv6 standpoint, and, in particular, does not
   operate the routing of an IPv6 packets. Host.  In that the latter case,
   the SLLAO SLLA option in the proxied NA messages is that of the Registering Node
   Node, and classical
   bridging operations take place on data frames.

   If a registration moves from one the 6BBR acts as a Layer-2 bridge for unicast packets to
   the next, Registered Address.  The MAC address in the S/TLLA is that of the
   Registering Node, which is not necessarily the Registered Node.  When
   a device moves within a LLN mesh, it may attach to a different 6LBR
   acting as Registering Node, and the MAC address advertised over the
   backbone will change.

   If a registration moves from one 6BBR to the next, but the
   Registering Node does not change, as indicated by the S/TLLAO S/TLLA option
   in the ND exchanges, there is no need to update the Neighbor Caches
   in the peers Nodes on the backbone.  On the other hand, if the LLAO LLA
   changes, the 6BBR SHOULD inform all the relevant peers as described
   above, to update the impacted Neighbor Caches.  In the same fashion,
   if the Registering Node changes with a new registration, the 6BBR
   SHOULD also update the impacted Neighbor Caches over the backbone.

6.  BackBone  Backbone Router Proxy Operations

   This specification enables a Backbone Router to proxy Neighbor
   Discovery operations over the backbone on behalf of the nodes that
   are registered to it, allowing any node on the backbone to reach a
   Registered Node as if it was on-link.  The backbone and the LLNs are
   considered different Links in a MultiLink subnet but the prefix that
   is used may still be advertised as on-link on the backbone to support
   legacy nodes; multicast ND messages are link-scoped and not forwarded
   across the backbone routers.

   ND Messages on the backbone side that do not match to

   By default, a registration
   on the LLN side are not acted upon on the LLN side, which stands
   protected.  On the LLN side, the prefixes associated to the MultiLink
   Subnet are presented 6BBR operates as not on-link, so address resolution for other
   hosts do not occur.

   The default operation in this specification is a Sleeping proxy which
   means: Proxy, as follows:

   o  creating  Create a new entry in an abstract a Binding Table for a new Registered Address
      and validating ensure that the address is not a duplicate over the backbone

   o  defending  Defend a Registered Address over the backbone using NA messages
      with the Override bit set on behalf of the sleeping node whenever
      possible

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

   o  Looking up a destination over the backbone in order to  To deliver packets arriving from the LLN using LLN, use Neighbor
      Solicitation
      messages. messages to look up the destination over the
      backbone.

   o  Forwarding  Forward packets from between the LLN over the backbone, and the other
      way around. backbone.

   o  Eventually triggering a  Verify liveliness verification of when needed for a stale registration.

   A 6BBR may act as a Sleeping Proxy only if the state of the binding
   entry for a Registered Address that
   is REACHABLE, or TENTATIVE in which case the answer is delayed.  In
   any other state, the Sleeping Proxy operates as a Unicasting Proxy.

   The 6BBR does not act on ND Messages over the backbone unless they
   are relevant to a Registered Node on the LLN side, saving wireless
   interference.  On the LLN side, the prefixes associated to the
   MultiLink Subnet are presented as not on-link, so address resolution
   for other hosts do not occur.

   As a Unicasting Proxy, the 6BBR forwards NS lookup messages to the
   Registering Node, transforming Layer-2 multicast into unicast
   whenever possible. unicast.  This
   is not possible in UNREACHABLE state, so the NS messages are
   multicasted, and rate-limited to protect the medium with an exponential back-off. back-off to protect
   the medium.  In other states, The the messages are forwarded to the
   Registering Node as unicast Layer-2 messages.  In TENTATIVE state,
   the NS message is either held till DAD completes, or dropped.

   The draft introduces the optional concept of primary and secondary
   BBRs.  The primary is the backbone router that has the highest EUI-64
   address of all the 6BBRs that share a registration for a same
   Registered Address, with the same Owner Unique ID ROVR and same Transaction ID, the
   EUI-64 address being considered as an unsigned 64bit integer.  The concept is defined with the granularity of an
   address, that is a  A
   given 6BBR can be primary for a given address and secondary or for
   another one, address, regardless on whether or not the addresses belong to
   the same node or not. node.  The primary Backbone Router is in charge of
   protecting the address for DAD over the Backbone.  Any of the Primary
   and Secondary 6BBR may claim the address over the backbone, since
   they are all capable to route from the backbone to the LLN node, and node; the
   address appears on the backbone as an anycast address.

   The Backbone Routers maintain a distributed binding table, using
   classical IPv6
   ND over the backbone to detect duplication.  This specification
   requires that:

   1.  All addresses  Addresses in a LLN that can be reachable from the backbone, including
       IPv6 addresses based on burn-in EUI64 addresses backbone by way
       of a 6BBR MUST be registered to the that 6BBR.

   2.  A Registered Node MUST include the EARO option in an the NS message
       that used to register an when
       registering its addresses to a 6LR; the 6LR.  The 6LR MUST
       propagate that option forward the
       EARO unchanged to the 6LBR in the DAR/DAC
       exchange, and the exchange.  The 6LBR
       MUST propagate that option the EARO unchanged in
       proxy registrations. to 6BBR.

   3.  The 6LR MUST echo respond with the same EARO option in the NA that it uses to
       respond, but NA, except for the
       status filed which is not used in NS
       messages, and significant in NA. field.

   A false positive duplicate detection may arise over the backbone, for
   instance if the Registered Address is registered to more than one
   LBR, or if the node has moved.  Both situations are handled
   gracefully unbeknownst by the
   6BBR transparently to the node.  In the former case, one LBR becomes
   primary to defend the address over the backbone while the others
   become secondary and may still forward packets back and forth. packets.  In the latter case
   the LBR that receives the newest registration wins
   and becomes primary.

   The expectation in this specification is that there is

   Only one node may register a single
   Registering Node given Address at a time per Backbone Router for a given Registered
   Address, but particular 6BBR.
   However, that a Registered Address may be registered to Multiple 6BBRs
   for higher availability.

   Over the LLN, and for any given Registered Address, it Binding Table management is REQUIRED
   that:

      de-registrations as follows:

      De-registrations (newer TID, same OUID, ROVR, null Lifetime) are
      accepted and responded immediately acknowledged with a status of 4; the entry is
      deleted;

      newer

      Newer registrations (newer TID, same OUID, ROVR, non-null Lifetime) are
      accepted and responded
      acknowledged with a status of 0 (success); the entry binding is updated
      with the new TID, the new Registration Lifetime and the
      new Registering Node, if any has changed;
      Node; in TENTATIVE state the
      response acknowledgement is held and may be
      overwritten; in other states the Registration-Lifetime timer is
      restarted and the entry is placed in REACHABLE state.

      identical

      Identical registrations (same TID, same OUID) ROVR) from a same
      Registering Node are not processed but responded acknowledged with a status of 0 (success); (success).
      If they are expected to be identical and not identical, an error may SHOULD be
      logged if not; in logged.  In
      TENTATIVE state, the response is held and may be overwritten, but
      it MUST be eventually produced and it carries the result of the
      DAD process;

      older
      Older registrations (not(newer or equal) (older TID, same OUID) ROVR) from a
      same Registering Node
      are ignored;

      identical

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

      and any

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

6.1.  Registration and Binding State Creation

   Upon receiving a registration for a new address with an NS(EARO) with
   the 'R' bit set, the 6BBR performs a DAD operation over the backbone backbone, placing the
   new address as target in the NS-DAD message.  The EARO from the
   registration MUST be placed unchanged in the NS-DAD message, and an
   Neighbor Cache entry is created in TENTATIVE state for a duration of
   TENTATIVE_DURATION.  The NS-DAD message is sent multicast over the
   backbone to the SNMA address associated with the registered address.
   If address, unless
   that operation is known to be costly, and the 6BBR has an indication
   from another source (such as a NCE) Neighbor Cache entry) that the
   Registered Address was present known on the backbone, that information may be
   leveraged to send backbone; in the latter case, an
   NS-DAD message may be sent as a Layer-2 unicast to the MAC Address
   that was associated with the Registered Address.

   In TENTATIVE state:

   o  the 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 option, EARO, or with an EARO option with a
       status of 1 (duplicate) that indicates an existing registration
       for another LLN node.  The OUID ROVR and TID fields in the EARO option
       received over the backbone are ignored.  A status of 1 is
       returned in the EARO option of the NA back to the Registering Node;

   o  the

   2.  The entry is also removed if an NA with an ARO option with a
       status of 3 (moved), or a NS-DAD with an ARO option that
       indicates a newer registration for the same Registered Node, is
       received over the backbone for the Registered Address.  A status
       of 3 is returned in the NA(EARO) back to the Registering Node;

   o  when

   3.  When a registration is updated but not deleted, e.g. from a newer
       registration, the DAD process on the backbone continues and the
       running timers are not restarted;

   o

   4.  Other NS (including DAD with no EARO option) EARO) and NA from the backbone
       are not responded acknowledged in TENTATIVE state, but state.  To cover legacy nodes
       that do not support ODAD, the list of their origins may MAY be kept in memory stored
       and then, if so, the TENTATIVE_DURATION timer elapses, the 6BBR may MAY
       send
      them each such legacy node a unicast NA with eventually an EARO option when the
      TENTATIVE_DURATION timer elapses, so as to cover legacy nodes that
      do not support ODAD.

   o  When NA.

   5.  When the 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 REACHABLE state for the Registration Lifetime; the
      DAD process is successful and the Lifetime.
       The 6BBR MUST send a multicast NA(EARO) to the SNMA associated to
       the Registered Address over the backbone with the Override bit
       set so as to take over the binding from other 6BBRs.

6.2.  Defending Addresses

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

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

   o  If the 6BBR receives an NS-DAD(EARO) that reflect for a newer registration, the
      6BBR updates the entry and the routing state to forward packets to
      the new 6BBR, but keeps the entry REACHABLE.
      In that phase, it  Afterwards, the 6BBR
      MAY use REDIRECT messages to reroute traffic for the Registered
      Address to the new 6BBR.

   o  If the 6BBR receives an NA(EARO) that reflect for a newer registration, the
      6BBR removes its entry and sends a NA(AERO) NA(EARO) with a status of 3 (moved)
      (MOVED) to the Registering Node, if the Registering Node is
      different from the Registered Node.  If necessary, the  The 6BBR cleans up ND cache existing
      Neighbor Cache Entries in peers peer nodes as discussed in Section 5.1,
      by sending a series of unicast unicasting to the impacted nodes, each such peer, or one broadcast NA(O) to all-nodes. NA(Override).

   o  If the 6BBR received receives a NS(LOOKUP) for a Registered Address, it
      answers immediately with an NA on behalf of the Registered Node,
      without polling it.  There is no need of an EARO in that exchange.

   o  When the Registration-Lifetime timer elapses, the entry goes to
      STALE 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 is a chance to keep track enables tracking of the backbone peers that
   may have an ND cache a
   Neighbor Cache entry pointing on to this 6BBR in case the Registered
   Address shows back up on this or a different 6BBR at a later time.
   In STALE state:

   o later.  If the Registered Address is claimed by
   another node on the backbone, with an NS-DAD or an NA, the 6BBR does
   not defend the address.  In STALE state:

   o  If STALE_DURATION elapses, the 6BBR removes the entry.

   o  Upon receiving an NA(O), or the stale time elapses, NA(Override) the 6BBR removes its entry and
      sends a NA(AERO) NA(EARO) with a status of 4 (removed) to the Registering
      Node.

   o  If the 6BBR received 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 expected to SHOULD be mapped used by the Registering Node
      into a liveliness validation to
      indicate liveness of the Registered Node Node, if they are in
      fact different
      nodes.

7.  Security Considerations

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

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

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

   Kudos to Eric Levy-Abegnoli who designed the First Hop Security
   infrastructure at Cisco.

11.  References

11.1.  Normative References

   [I-D.ietf-6lo-rfc6775-update]
              Thubert, P., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "An Update to "Registration Extensions for 6LoWPAN ND", draft-ietf-6lo-
              rfc6775-update-13 Neighbor
              Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
              progress), February 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>.

   [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>.

   [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>.

   [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>.

11.2.  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-06 draft-ietf-6lo-ap-nd-07 (work in progress),
              February
              September 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 draft-ietf-6lo-nfc-10 (work in progress),
              January
              July 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-13 draft-ietf-6tisch-architecture-14 (work
              in progress), November 2017. April 2018.

   [I-D.ietf-6tisch-terminology]
              Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
              "Terminology
              "Terms Used in IPv6 over the TSCH mode of IEEE 802.15.4e", draft-ietf-6tisch-terminology-09
              draft-ietf-6tisch-terminology-10 (work in progress), June 2017. March
              2018.

   [I-D.ietf-bier-architecture]
              Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
              S. Aldrin, "Multicast using Bit Index Explicit
              Replication", draft-ietf-bier-architecture-08 (work in
              progress), September 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.

   [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.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.vyncke-6man-mcast-not-efficient]
              Vyncke, E., Thubert, P., Levy-Abegnoli, E., and A.
              Yourtchenko, "Why Network-Layer Multicast is Not Always
              Efficient At Datalink Layer", draft-vyncke-6man-mcast-not-
              efficient-01 (work in progress), February 2014.

   [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.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

11.3.  External Informative References

   [IEEEstd8021]
              IEEE standard for Information Technology, "IEEE Standard
              for Information technology-- 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-- 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) 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-- networks -- Part 15.4: Low-
              Rate
              Low-Rate Wireless Personal Area Networks (LR-WPANs)".

Appendix A.  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 A.5 which are deferred to a different
   specification such as [I-D.ietf-6lo-ap-nd].

A.1.  Requirements Related to Mobility

   Due to the unstable nature of LLN links, even in a LLN of immobile
   nodes a 6LoWPAN Node may change its point

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 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 timely 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
   to multiple 6LRs, and this, concurrently.

A.2.  Requirements Related to Routing Protocols

   The point of attachment of a 6LoWPAN Node 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
   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
   [I-D.ietf-bier-architecture] 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 in such a
   fashion that the 6LR MAY 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.

A.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 802.15.4, matching at least the LLN 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].

A.4.  Requirements Related to Proxy Operations

   Duty-cycled devices may not be able to answer themselves to a lookup
   from a node that uses classical 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.

A.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.

   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 impossible.

   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 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 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.

   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.

A.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.

Author's Address

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

   Phone: +33 497 23 26 34 America

   Email: pthubert@cisco.com charliep@computer.org