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6MAN                                                          P. Thubert
Internet-Draft                                          E. Levy-Abegnoli
Intended status: Standards Track                                   Cisco
Expires: April 18, 2014                                 October 17, 2013

Wireless Neighbor Discovery Stateful Address Identification and Location


   This draft proposes an extension to IPv6 Neighbor Discovery to
   exchange Stateful Address Identification and Location between State
   Maintaining Entities located over a backbone link about attached
   nodes that are attached to the backbone via a Wireless Link, in order
   to maintain all the entities up-to-date and maintain reachability as
   the attached nodes move.

Status of this Memo

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

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

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

   This Internet-Draft will expire on April 18, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2

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   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  General Context  . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Efficient ND . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Proxying classical ND  . . . . . . . . . . . . . . . . . . 10
     4.3.  Federating Large LLNs  . . . . . . . . . . . . . . . . . . 11
   5.  New types and formats  . . . . . . . . . . . . . . . . . . . . 12
   6.  Validation Interface Operations  . . . . . . . . . . . . . . . 14
     6.1.  Child to Parent Operations . . . . . . . . . . . . . . . . 15
     6.2.  Parent to Child Operations . . . . . . . . . . . . . . . . 16
       6.2.1.  Address validation and registration  . . . . . . . . . 16
       6.2.2.  Registration update  . . . . . . . . . . . . . . . . . 17
     6.3.  Registration deletion  . . . . . . . . . . . . . . . . . . 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 19
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21

1.  Introduction

   "Neighbor Discovery for IP version 6" [RFC4861] (IPv6 ND) relies
   heavily on multicast signaling messages on the local Link.
   Conceptually, multicast is supposed to avoid broadcast messages, but,
   in most practical cases, its operation at the link level is that of a
   broadcast.  This did not matter much at the time ND was originally
   designed, when an Ethernet network was more or less a single shared
   wire, but since then, large scale switched fabrics, low-power
   sleeping devices, mobile wireless devices and virtual machines have
   changed the landscape dramatically.

   The overhead of multicast in IPv6 ND has become significant and is
   now a major annoyance in multiple scenarios, in particular for
   wireless nodes.  With WIFI, a multicast message will consume the
   wireless link on all Access Points around a switched fabric and will
   be transmitted at the lowest speed possible in order to ensure the
   maximum reception by all other wireless nodes.  This means that in an
   environment where bandwidth is scarce, a single multicast packet may
   consume the bandwidth for hundreds of unicast packets.  Sadly, IPv6
   ND is a major source of multicast messages in wireless devices, since
   such messages are triggered each time a wireless device changes its
   point of attachment.

   A similar situation can be seen in a datacenter, where Virtual
   Machine (VM) mobility also triggers floods of multicast messages,

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   which become a major hassle as the number of VMs grows to the tens of
   thousands and above.  At the IETF, a Working Group was created to
   discuss Address Resolution in Massive Datacenters (ARMD), but the
   work did not go to completion.  The problem with IPv6 ND multicast is
   still present, only getting worse as the scale and degree of mobility
   augments with the massive introduction of new mobile devices such as
   virtualized appliances, IoT and BYOD.

   At the same time, the need to better control the ownership,
   utilization and location of IP addresses has become predominant in
   managed networks.  The Source-Address Validation Improvements (SAVI)
   Working Group has proposed methods to locate, validate the ownership,
   and police the utilization of IPv6 addresses by snooping IPv6 ND and
   DHCP operations.  But snooping requires being on the path of the
   protocols and is limited in particular in and for unicast responses.

   Mobile nodes such as BYOD may change their point of attachment in the
   network but an eventual renumbering can be disruptive to existing
   connections.  Virtual devices - typically VMs in a datacenter - also
   move though in a different fashion, from a physical device to the
   next.  In any case, the need to maintain a same IPv6 address across
   movements implies the creation of very large, eventually multi-link,
   subnets.  In such a large subnet, it might be difficult with the
   existing protocols to differentiate duplication from a rapid sequence
   of movements.  And if it is indeed a sequence of movements, then it
   might be difficult to select the freshest information, and additional
   signaling is required to obtain the actual location of an address in
   a deterministic fashion.

   In a modern managed switched fabric, a number of devices host IPv6
   State Maintaining Entities (6SMEs) that hold Stateful Address
   Identification and Location (SAIL) information about the entity that
   owns an IPv6 address.  A 6SME needs to reascertain periodically the
   state that it maintains and eliminate stale information.  It is of
   common interest between all 6SMEs to share their information and help
   one another learn new state, update existing state and remove stale
   state rapidly.  A Binding Table maintained by a secured registration
   protocol is certainly a more robust basis for 6SME activity than a
   classical  IPv6 NDP  [RFC4861]  Neighbor Cache management coupled
   with protocol snooping as currently found with SAVI [RFC6620].

   Mobile IPv6 [RFC6275] introduced such a registration protocol to
   maintain a tunnel and enable an IPv6 ND proxy operation over a Home
   Network.  Applied to IPv6 Neighbor Discovery, the registration model
   balances the benefits of distributed StateLess Address
   AutoConfiguration (SLAAC) [RFC4862] for scalability and autonomic
   behaviours with the capability to reject or recuse an autoconfigured
   address on an exception basis - based for instance on administrative

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   policies -, which is a desired feature for managed networks that
   classically are operated with DHCPv6  [RFC3115].  In that sense, the
   ND registration allows a scalable hybrid of managed and non-managed
   networks while minimizing the total number of multicast messages
   between hosts, as well as between hosts and routers.

   An IPv6 ND registration mechanism was standardized as Neighbor
   Discovery Optimization for Low-power and Lossy Networks [RFC6775].
   The host to SME router operation is generalized by wireless ND [I-D
   .chakrabarti-nordmark-6man-efficient-nd] for devices that are not
   necessarily attached to a LLN but may still benefit from
   registration.  [RFC6775] also introduces a protocol between SMEs
   based on new ICMP messages.  This draft extends that model in order
   to allow for a distributed, eventually hierarchical set of SMEs to
   share and maintain SAIL states.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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

   Readers may benefit from reading the "RPL: IPv6 Routing Protocol for
   Low-Power and Lossy Networks"  [RFC6550] specification; "Multi-Link
   Subnet Issues" [RFC4903]; "Mobility Support in IPv6"  [RFC6275];
   "Neighbor Discovery Proxies (ND Proxy)"  [RFC4389]; "FCFS SAVI:
   First-Come, First-Served Source Address Validation Improvement for
   Locally Assigned IPv6 Addresses" [RFC6620]; 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 [I-D.ietf-roll-
   terminology], and reuses or introduces the following terminology:

   6LoWPAN Router (6LR): Please refer to [RFC6775].

   6LoWPAN Border Router (6LBR): Please refer to [RFC6775].

   DAR and DAC messages: Please refer to [RFC6775].

   Multi-link subnet: Please refer to  [I-D.ietf-ipv6-multilink-

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   Backbone: A link that forms the core of a multi-link subnet.  All ARs
         and legacy devices are connected to the Backbone and classical
         ND operation ensure connectivity over that link.

   attached link: An abstract link in a multi-link subnet other than the
         backbone.  That link is classically not implemented as a fixed
         wire, and may only provide non-continuous connectivity, in
         particular with support for mobility.  An attached link may be
         for instance a classical WiFi (IEEE802.11) link, a link in a
         wireless mesh network, or an overlay tunnel.

   attached node: A device in a multi-link subnet that is not directly
         connected to the Backbone but reachable via an attached link.

   Backbone Router (BBR): A BBR is an IPv6 router that connects attached
         links to a Backbone link and enables the connectivity of an
         attached node by proxying IPv6 NDP over the Backbone for that
         node, either with the node MAC address, or its own.  The BBR is
         a 6SME that can obtain attachment states from attached nodes by
         different methods, for instance by snooping IPv6 NDP or DHCPv6,
         by learning host routes acting as a RPL root, by accepting ND
         registrations acting as an AR or an IR.

   Stateful Address Identification and Location (SAIL): As opposed to a
         cache entry, a SAIL state is Stateful in that it is obtained
         and maintained through a (secured) registration mechanism.  A
         SAIL state may include for instance a secured identification of
         the owner of the address (e.g.  a trusted token, a public key
         or a certificate), the position of the IPv6 address in the
         network (e.g.  VLAN, Access Switch or Access Point), or the
         mapping of the IPv6 address with a MAC address.  Some of this
         information may be stable, for instance a owner Identification,
         while other may be transient, for instance the Access Point
         identifier in a mobility scenario or the MAC address mapping in
         the case of NDP proxy operations.

    State Maintaining Entity (SME): An entity that hold SAIL
         information.  SMEs are implemented in devices such as security
         appliances such as Network Access Controllers (NACs), SAVI
         switches that protect the ownership of an IPv6 address and
         control the ingress of the network, Wireless LAN Controllers
         (WLCs) that terminate a CAPWAP tunnel and must rapidly re-
         enable reachability for a mobile device both at layer 2 and
         layer 3, as well as overlay terminators such as used for
         network virtualization (NVO3).  Overlay termination may operate
         both at layer 2 or layer 3, and may be found in data centers
         and enterprise networks to support mobility or extend the layer
         2 fabric over a Layer 3 infrastructure, as well as in Service
         Provider networks to support IPv6 mobility.

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   Binding: The association of an IPv6 address with some SAIL state.  A
         registrar maintains a binding table to store and query such

   Registering Node (RN): An IPv6 node that obtains and retains
         ownership of an IPv6 address through the process of IPv6 ND

   Authoritative Registrar (AR): A 6SME that stores authoritative
         information about a registration.  An AR is the reference for
         address and SAIL state binding within its domain of authority,
         e.g.  a specific subset of addresses within a subnet.  There
         can be multiple ARs in a subnet and domains may overlap for
         redundancy and balancing.

   Intermediate Registrar (IR): A 6SME  that stores information about a
         registration as part of the registration flow.  IRs form a
         directed acyclic graph (DAG) that is directed towards ARs.  A
         registration from an RN will be addressed to an IR and will
         follow the IR DAG till it reaches a node that can grant the
         ownership, typically a AR.

   Registration Interface (RIF): The interface between an RN and an IR.
         The RIF is typically implemented using Wireless ND, but can
         also be implicitely implemented by snooping IPv6 ND, e.g.  as
         suggested by SAVI.

   Validation Interface (VIF): The interface between a child IR and a
         parent IR or AR.  The VIF is typically implemented using this
         specification which extends the DAR and DAC messages as defined
         in [RFC6775].

   Determination Interface (DIF): The interface between ARs.  It can be
         implemented using LISP, routing protocol extensions, or using
         IPv6 ND proxy extensions such as suggested by [I-D.thubert-
         6lowpan-backbone-router] .

3.  Overview

   The scope of this draft is a potentially large and potentially multi-
   link subnet [I-D.ietf-ipv6-multilink-subnets] formed by a high speed
   Backbone that federates additional links of heterogeneous MAC/PHY
   types, for instance an Ethernet switched fabric federating a Route-
   Over mesh that may interconnect thousands of LLN devices over
   multiple wireless hops.

   In order to avoid floods of multicast packets inherent to a reactive
   discovery, a node - referred to as a Registering Node (RN) - needs to
   claim its addresses proactively, binding them with its location in
   the network and a Lower Layer Address (LLA), over confirmed exchanges
   with a neighborhood Intermediate Registrar (IR).

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            +-----+                   +-----+
            |     | AR                |     | AR
            |     |                   |     | ND proxy
            +-----+                   +-----+
               |                         |
               |      Backbone Link      |
         |     legacy + proxy | + registration   |
         |              mixed | ND operations    |
      +-----+              +-----+            +-----+
      |     |IR            |     |IR          |     | IR + AR
      |     |ND proxy      |     |            |     | ND proxy
      +-----+              +-----+            +-----+
         |     routing over attached links       |
         |   registration ND operations only     |
      +-----+              +-----+            +-----+
      |     |IR            |     |IR          |     | IR
      |     |--------------|     |------------|     |
      +-----+              +-----+            +-----+

   The IR may confirm the claim with an Authoritative Registrar (AR),
   eventually over a graph of other IRs.  If the ownership is granted,
   the RN may use the address for a lifetime that is associated with the
   grant, at which point it will need to reconfirm the address by
   registering again.

   In the case of a meshed 6LoWPAN [RFC6282] [RFC6775] LLN topology ,
   the neighborhood IR is a 6LoWPAN Router (6LR) and the AR is a 6LoWPAN
   Border Router (6LBR).  When the topology grows, the IPv6 ND
   registration model as described in [RFC6775], with a single AR (the
   6LBR), may not scale.

   With this draft, all registrars maintain an abstract Binding Table of
   their registered addresses.  The Binding Table operates as a
   distributed database of information related to addresses whether the
   address owner reside on the attached links or on the Backbone.  ARs
   use extensions to the Neighbor Discovery Protocol to exchange that
   information across the Backbone either in the classical ND reactive
   fashion, or through a new pub/sub mechanism that is introduced by
   this specification.

   With this specification, multiple IRs and one AR can be deployed so
   as to scale the IPv6 ND registration model yet avoiding any broadcast
   beyond one Layer-2 hop; IRs cover the whole multi-link subnet in a
   fashion that any node in the network has at least one neighborhood IR
   one Layer-2 hop away so it may perform an NDP registration with that
   IR using link local addresses regardless of the link type, wired or

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               |     |  -----.
               |  RN |   RIF |    +-----+       +-----+       +-----+
               +-----+       .->  |     | ----> |     | ----> |     |
                             .->  |  IR | VIF   |  IR | VIF   | AR  |
               +-----+   RIF |    +-----+       +-----+       +-----+
               |     |  -----.                                   ^
               |  RN |                                          DIF
               +-----+                                           v
                                  +-----+       +-----+       +-----+
                 ...              |     | VIF   |     | VIF   |     |
               +-----+       .->  |  IR | ----> |  IR | ----> | AR  |
               |     |   RIF |    +-----+       +-----+       +-----+
               |  RN |  -----.

   IRs and ARs form a DAG directed towards the AR(s); but how this DAG
   is set up is out of scope for this specification.

   If more than one AR is deployed, a strategy (e.g.  a distributed hash
   table (DHT) or a DNS-like hierarchy) and a method to distribute and
   synchronize the individual domains of authority between ARs, must be
   put in place.  Such method is out of scope for this document.  In the
   case where an overlap of domain is acceptable, a protocol must be put
   in place between ARs so as to resolve conflicts, and clean up stale
   states.  Such a protocol is out of scope for this document.

4.  General Context

4.1.  Efficient ND

   [I-D.chakrabarti-nordmark-6man-efficient-nd] updates the
   specification of the RIF interface between the RN and the IR, that
   was initially defined in [RFC6775] for 6LoWPAN devices.  The draft
   details the operation of a IPv6 ND-efficiency-aware Router(NEAR),
   that is the neighborhood IR to which an RN, which is called a
   Efficiency-Aware Host (EAH), registers.  A NEAR is also an AR as it
   has the exclusive authority on the bindings for its registered EAHs.

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               +-----+                   +-----+
               |NEAR | IR                |NEAR | IR
               |     | AR                |     | AR <--.
               +-----+                   +-----+       |
                  |                         |        new NDP
                  |      Backbone Link      |     registration
            +--------------------+------------------+  |
            | legacy + efficient | ND operations    |  |
            |                    |                  |
        +-------+            +-------+          +-------+
        |legacy |            |legacy |          | EAH   | RN
        | host  |            |router |          |       |
        +-------+            +-------+          +-------+

   In the case of a WIFI connection, the NEAR is a BBR for the wireless
   device, and may be collocated with a standalone AP or a Wireless LAN

               +-----+                   +-----+
               |NEAR | IR                |NEAR | IR
               |     | AR                |WLC  | AR <--.
               +-----+                   +-----+      |||
                  |                         |        new NDP
                  |      Backbone Link      |     registration
            +--------------------+------------------+ |||
           | | legacy + proxy   | | ND operations     |||
           | |                  | |                   |||
       o +-----+ o          o +-----+ o           o +-----+ o
      o  |  AP |  o        o  |  AP |  o         o  |  AP |  o
       o +-----+  o         o +-----+ o           o +-----+ o
           o o                  o  o                 o   o
       wireless attached links                    EAH  o  RN

   This specification extends  [I-D.chakrabarti-nordmark-6man-efficient-
   nd], by allowing the separation of IR and AR functions, which are
   collapsed inside the NEAR.  This draft introduces the VIF interface
   between IRs, and between IRs and ARs, as well as the DIF interface
   between ARs with potentially overlapping domain, and other 6SMEs.

   For the purpose of the new NDP registration, [I-D.chakrabarti-
   nordmark-6man-efficient-nd] defines an extended ARO option that is
   advertised by an EAH. The new ARO option includes a sequence counter
   called TID that enables a short term freshness assertion between
   rapid re-registrations of a mobile device, and a unique ID that is
   used for the Duplicate Address Detection (DAD).

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   A 6SME may maintain a state for a longer time than covered by the ARO
   TID, so a coarse age information is be needed to compare old state
   information over the VIF and DIF interfaces.  Additionally, the 6SME
   may qualify information with additional metadata to help resolve
   conflicts.  For instance, in the case of a duplicated IPv6 address,
   additional meta information such as the protocol that was used to
   establish the state (SLAAC vs.  DHCPv6), a device type (trusted
   server vs.  unknown host), or a Secure ND cryptographic address
   ownership validation ([RFC3971], [RFC3972]) can help protect the
   address where it is assigned in a more trusted fashion even if a
   rogue managed to grab the address while the more trusted owner was
   not able to defend it.

   This specification proposes a new ND option that contains such
   information and complements the information in the ARO option for use
   on the VIF and DIF interfaces.

4.2.  Proxying classical ND

   A 6SME such as an IR, a AR or a BBR may proxy classical IPv6 NDP
   [RFC4861] on behalf of a virtual, a wireless, or a low power device
   so as to offload the device, to dampen the network load such as
   induced by the multicast operations of the proxied protocol, or
   simply to attract over the backbone and then relay its traffic to the
   mobile or sleeping device even if the device is not reachable at that
   particular time.

                    Backbone (Home) Link
         | legacy + proxy     | ND operations    |
         |                    |                  |
      +-----+             +-----+             +-----+
      |MIP/ |IR +         |MIP/ |IR +         |MIP/ |IR  <-.
      |HA   |AR           |NEMO |AR           |NEMO |AR    |
      +-----+             +-----+             +-----+   Binding
     // | | \\           // | | \\           // | | \\  Update
    //  | |  \\         //  | |   MN        MR   MN  \\    |
    MN   MN   \\       //   MR                        MN --.
               MN     MN      tunnel-based attached links

   The 6SME may perform the proxy operation on behalf of an original
   device using the original device LLA, or may proxy the Layer-2
   information with their own LLA and either rewrite it later in the
   packets, or route the packet again over an attached link, as
   examplified by a MIPv6  [RFC6275] or a NEMO  [RFC3963] Home Agent

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   The HA is authoritative for any Mobile Node (MN) that successfully
   registers to it through a Binding Update/Ack flow and its domain of
   authority is the subnet(s) on the Home Link, potentially overlapping
   with other HAs.  ND proxy operations are used over the Home Link to
   resolve collisions.

   The MN is thus an RN and the HA cumulates IR, AR and proxy
   functionalities.  With NEMO  [RFC3963], the model is conserved but
   the RN is now a Mobile Router that registers a prefix together with
   its own address, so the operation in the Backbone link is a mix of ND
   proxy and routing.  Network Mobility Home Network Models  [RFC3963]
   provides more information on that model.

4.3.  Federating Large LLNs

   In the case of a large multi-link subnet, this specification expects
   that a Backbone link is deployed to interconnect all the ARs and
   legacy NDP devices.  Each interconnected attached link, whether it is
   a WIFI access, a mesh network, a 6LoWPAN/RPL LLN or an overlaid
   tunnel, is anchored to the Backbone at a Backbone Router (BBR). The
   BBRs interconnect the multi-link subnet over the Backbone Link at
   layer 3, enabling connectivity within the subnet over IP.

               +-----+                   +-----+
               |     | AR                |     | AR
               |     |                   |     |
               +-----+                   +-----+
                  |                         |
                  |      Backbone Link      |
            |     legacy + proxy | + registration   |
            |              mixed | ND operations    |
         +-----+             +-----+             +-----+
         | RPL | BBR         | RPL | BBR         | RPL | BBR
         |root | ND proxy    |root | ND proxy    |root | ND proxy
         +-----+             +-----+             +-----+
       IR o  o  IR o        o   IR  o        o  o  IR  o
        o o IR  o     o     o IR   o  IR  o   o IR  o     IR
       o IR o  IR  o  IR o o   o  o  o  o      o        o    o
       o    IR   o    o     IR    o  IR
          o   o                o  o         LLN attached links

   If the LLN uses a Route-Over model based on RPL [RFC6550], the
   Backbone Router (BBR) that connects the LLN to the Backbone is the
   root for the RPL LLN. The BBR proxies the ND protocol over the
   backbone for the addresses that it has learnt through RPL as host
   routes, using its own LLA and location to attract traffic for the
   attached nodes and route it over the LLN.

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   Over the Backbone, this setup implements the "simple scenario" in
   [I-D.ietf-ipv6-multilink-subnets] whereby the router acts "as an
   asymmetric Neighbor Discovery proxy"; over the RPL-based LLN mesh,
   the setup implements the more "complex scenario" whereby "an
   arbitrary topology exists, and routers within the subnet communicate
   using some means of exchanging host routes".

   [I-D.thubert-6lowpan-backbone-router] describes this mixed model, and
   how a Backbone Router perform ND proxy operation for their attached
   nodes over the The Backbone Link regardless of the mode of
   registration for the attached nodes.  The operation described in the
   draft is compatible with that of a MIPv6 [RFC6275] Home Agent.  This
   enables mobility support for wireless attached nodes that would move
   outside of the network delimited by the Backbone link and back.  In
   any case, it is expected that the registration provides a sequence
   counter, a lifetime and a unique identifier of the attached nodes in
   such a fashion that they can be matched or compared across protocols.

   This specifications indicates how the new ND option can be used in
   conjunction with ND proxy techniques over the Backbone to implement
   the DIF interface.

5.  New types and formats

   This section introduces message formats for all messages used in this

   The specification expects that the protocol running on the LLN can
   provide a sequence number called Transaction ID (TID) that is
   associated to the registration.  When a node registers to multiple
   registrars (IRs or ARs), it is expected that the same TID is used, to
   enable the registrar to correlate the registrations as being a single
   one, and differentiate that situation from a movement.  Otherwise,
   the resolution makes it so that only the most recent registration was
   perceived from the highest TID is kept.

   The specification expects that the protocol running on the LLN can
   provide a unique ID for the owner of the address that is being
   registered.  The Owner Unique ID enables to differentiate a duplicate
   registration from a double registration.  In case of a duplicate, the
   last registration looses.  The Owner Unique ID can be as simple as a
   EUI-64 burnin address, if the device manufacturor is convinced that
   there can not be a manuf error that would cause duplicate EUI64

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   addresses.  Alternatively, the unique ID can be a hash of supposedly
   unique information from multiple orthogonal sources, for instance:

   o  Burn in address.

   o  configured address, id, security keys...

   o  (pseudo) Random number, radio link metrics ...

   In any fashion, it is recommended that the device stores the unique
   ID in persistent memory.  Otherwise, it will be prevented to re-
   register after a reboot that would cause a loss of memory until the
   Backbone Router times out the registration.

   The unique ID and the sequence number are placed in a new ND option
   that is used by the Backbone Routers over the Backbone link to detect
   duplicates and movements.  The option format is as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |     Type      |   Length = 2  |R| rsv         |origin | trust |
     |T|N|  rsv      |     TID       |   Registration age (10 sec)   |
     |                                                               |
     +         ALI                                                   +
     |                                                               |

   Option Fields

   Type: 8-bit identifier of the type of option.

   Length: 2

   R: One bit flag.  Set if the sender is relaying the option received
      from a downstream node, whether a RN or an IR.

   origin : 4-bit unsigned integer.  Indicates the origin of the entry.

      0 - SLACC: Address was auto-configured on the RN [RF4862]

      1 - DHCP: Address was assigned to the RN by DHCP

      2 - LOCAL: Address was manually configured on the RN

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      3 - STATIC: Address was manually configured on the IR as a
         downstream address, i.e.  an address assigned to a downstream

      4 - DATA: Address was gleaned on the first IR as the source of a
         data packet

   trust : 4-bit unsigned integer.  Indicates the level of trust the
      attaching node place in the entry

      0 - NO_TRUST: No particular trust associated with the entry

      1 - L2L3_MATCH: The layer-2 source MAC and Link-layer-Address
         claimed in the registration match

      2 - TRUSTED_BY_POLICY: The address is trusted by policy on the
         attaching node

      3 - AUTHENTICATED The address has been authenticated by a
         cryptographic protocol (CGA, etc.)>

   T: One bit flag.  Set if the next octet is a used as a TID following
      follow section 7 of RPL  [RFC6550]  for sequence counters.  If the
      bit is not set, a unsigned char is expected.

   N: One bit flag.  Set if the device moved.  If not set, the router
      will refrain from sending gratuitous NA(O) over the backbone, for
      instance after the DAD operation upon entry creation.

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

   TID: 1-byte integer; a transaction id that is maintained by the
      device and incremented with each transaction.  it is recommended
      that the device maintains the TID in a persistent storage.  The
      TID is incremented at each registration.

   Registration Age: 2-byte integer; the duration since the last update
      of TID in units of 10 seconds.

   Attaching Location Identifier: A locally unique identifier for the IR
      interface attaching the registering host.

6.  Validation Interface Operations

   The Validation Interface (VIF) is the interface between a child
   Intermediate Registrar (IR) and a parent registrar, whether an
   Intermediate Registrar or Authoritative Registrar (AR). An IR parent
   or upstream chain is defined as the set of IRs along the DAG starting
   from this IR, directed to (and including) the AR. An IR child or
   downstream chain is defined as the set of IRs from this IR an entry
   was learnt from including the IR attaching to the RN. The goal of VIF
   is to perform one or several of the followings:

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   o  Validate a new registration along the parent chain

   o  Record a registration along the parent chain

   o  Update a registration along the parent chain

   o  Cancel a registration along the parent chain

   o  Delete a record along the parent chain

   o  Delete a record along the child chain

6.1.  Child to Parent Operations

   The first IR in the chain (attached to the RN) initiates validation
   and registration of an address registered by the RN or snooped on the
   interface attaching the RN to the node, by building a DAR message,
   including a SLLA and a SAIL option where:

   o  Source of the DAR is an IP address of the IR interface to the next
      IR in the chain.

   o  Destination of the DAR is an IP address of the next IR.

   o  R bit set to zero.  If the IR acts as an RN, the the bit is set to

   o  Origin can take any of the values defined, based on how the
      address was assigned

   o  If the registration was received from the RN (or gleaned) on an IR
      interface administratively trusted, the field "trust" is set to
      TRUSTED_BY_POLICY. Otherwise, if the registration carried CGA
      [RFC3971] credential that the IR successfully verified, the field
      "trust" is set to AUTHENTICATED. Otherwise, if the source mac of
      the registration message received by the IR is identical to the
      Link-Layer Address provided by the message in the SLLA option, the
      trust field is set to L2L3_MATCH.  Otherwise, it is set to

   o  An SLLA option MUST be included in the DAR message along with the
      SAIL option, that contains the Link-Layer address bound to the IP
      address bein registered.

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   While waiting for a response, a TENTATIVE entry is created on the IR.
   Several attributes are stored next to the entry: the EUI64 provided
   by the RN, Link Layer Address provided in the SLLA option, the origin
   and trust values (computed by the IR, based on the registration, and
   local policies), the ALI the registration was received from, the
   lifetime.  In the absence of a DAC response, DAR messages sent in the
   context of VIF fron the IR are retransmitted after 250ms
   [DAR_INTERVAL], up to 2 times [MAX_DAR_RETRANSMIT].  Upon receiving a
   negative response (duplicate address status) or when the maximum
   retransmit is exhausted, the entry is removed from the IR.

   The IR can also initiate update and delete operations.  An update is
   no different from an address validation: the DAR will carry the same
   address and EUI-64 as the one provided in a previous validation,
   while any other attribute such as SLLA option, Lifetime, Origin,
   Trust or ALI will eventually be different from the value previously

   In order to cancel a registration, a DAR is sent, with a lifetime set
   to zero.  It should carry a SAIL option to allow the receiving IR or
   AR to validate the delete.

6.2.  Parent to Child Operations

6.2.1.  Address validation and registration

   Upon receiving a DAR message with a SAIL option, an IR will lookup in
   the local table to verify whether the address already exist.

   If it does not exist, two cases arise.

   1.  The IR is not an AR. It creates the entry as "TENTATIVE",
       together with attributes such as EUI64, IR address it came from,
       origin and trust values.  It then builds and sends a DAR message
       sourced with one address of its interface to the next IR, set
       destination address to the next IR address, sets the R bit to 1
       and copies all other fields    from the received DAR.  It also
       starts a 250ms TENTATIVE_TIMER timer ot 250ms [DAR_INTERVAL].
       Should this timer expire, the DAR is re-transmitted up to 2
       times, then the entry is deleted.  If a negative response (DAC
       with status 1) is received, a DAC with status 1 is sent to the
       downstream IR, and the TENTATIVE entry is deleted.  If a positive
       response (DAC with status 0) is received, the timer
       TENTATIVE_TIMER is stopped, the entry state moved to REACHABLE
       and a DAC with status 0 is sent to downstream IR.

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   2.  The IR is also the AR: it queries other ARs over the DIF
       interface.  While waiting for a response, it may create the entry
       in "TENTATIVE" state.  Upon confirmation from another AR that the
       entry exist elsewhere, the entry in TENTATIVE is deleted, and a
       DAC message is sent back to the source of the DAR message
       (previous IR), with a status set to 1 (Duplicate address).  Upon
       receiving this DAC, each downstream IR deletes its own TENTATIVE
       entry, and sends a DAC, status 1, to the next child IR until it
       reaches the IR attaching the RN, which builds an NA with ARO
       option, and status set to duplicate address.  If the DIF
       interface returns no conflict on the address, the entry state is
       moved to REACHABLE, and a DAC with status 0 is sent to the
       downstream IRs which move their TENTATIVE entry to REACHABLE.
       When the DAC reaches the attaching IR, it send an NA with ARO
       option, status 0 to the RN.

   If the same address carried in the DAR exist on one of the IR or the
   AR, with a different EUI-64 interface identifier, the two entries
   attributes are compared.  A trustlevel value is computed for each
   entry (as a function of the trust value, the origin and the R bit).
   The two trustlevel values are compared numerically as follows:

   1.  If the trustlevel of the existing entry is bigger or equal than
       the one carried by the DAR, the DAR is not propagated, and a DAC
       with status 1 (duplicate address) is sent back to downstream IR,
       up to the attaching IR which sends a NA with an ARO option,
       status 1 to the RN.

   2.  If the trustlevel of the existing entry is strictly smaller that
       the one carried by the DAR, it replaces it, and the DAR is
       propagated towards the upstream IR up to the AR. Again, DAR
       follow the rule of hop-by-hop retransmission and acknowledgment
       already described.

   3.  At the same time, if the entry being replaced was associated with
       a different IR than the one this DAR came from, another DAR, with
       the previous EUI64 value, and a lifetime set to zero is sent to
       downstream IR the previous registration came from.  This message
       causes the downstream IR to remove the entry, provided that the
       EUI64 match, to build and send a DAR to the next IR, and to
       acknowledge the deletion with a DAC, status 0. If the EUI64 don't
       match, it means the entry has already been replaced, and the DAR
       need not to be propagated from this IR.  DAR retransmission
       follow the same pattern already described.  DAC are not
       propagated.  Upon receiving the DAR with lifetime set to zero,
       the attaching IR sends an unsolicited NA to the RN with an ARO
       option, status 1 (duplicate address).

6.2.2.  Registration update

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   An update message is a DAR that carries an address and EUI64
   interface identifier matching an IR or AR table entry, and at least
   one of the following field different from the previously registered
   value: LifeTime, Origin, trust, ALI or IR child.  Upon receiving an
   update, the IR or AR updates its entry and propagate to the upstream
   IR or AR. The AR will in return send a DAC message with a status of 0
   to acknowledge the update.

   If the attribute being updated is the IR address the DAR is coming
   from (child IR), the host has moved to a different downstream IR
   chain, and the entry along the previous chain must be cleaned up.  A
   DAR message, with a lifetime set to zero is sent (and retried if not
   acknowledged) to the old downstream IR. This message causes the
   downstream IR to remove the entry.  The downstream IR should
   propagate the DAR to the next IR in chain, and acknowledge it with a

6.3.  Registration deletion

   A registration deletion can come from the IR attaching to the RN,
   because the RN left the link, from any IR as the result of an
   administrative action, or from the AR because the lifetime has
   expired or again following an administrative action.  In all cases, a
   DAR message with a lifetime set to zero is sent either upstream or
   downstream, retried and acknowledged at each hop along the chain, if
   necessary.  When the deletion is initiated on the IR attaching to the
   RN, a SAIL option MUST be provided to enable any upstream registrar
   to verify that the deletion is coming from the location the RN was
   attached to.  For deletion following the parent chain, the ALI value
   carried in the SAIL option is compared with the ALI value registered
   for this address, and entry is deleted is the two match.  For
   deletion following the child chain, this check is not required.  Upon
   deleting the entry, the IR builds and sends a DAC to acknowledge the
   deletion, then  build and send a DAR to propagate the deletion,
   downstream or upstream.

7.  Security Considerations

   This specification expects that the link layer is sufficiently
   protected, either by means of physical or IP security for the
   Backbone Link or MAC sublayer cryptography.  In particular, it is
   expected that the LLN MAC provides secure unicast to/from the
   Backbone Router and secure BBRoadcast 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.  Considering the envisioned deployments
   and the MAC layer security applied, this is not considered an issue
   at this time.

8.  IANA Considerations

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   A new type is requested for an ND option.

9.  Acknowledgments


10.  References

10.1.  Normative References

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

   [RFC2460]  Deering, S.E. and R.M. Hinden, "Internet Protocol, Version
              6 (IPv6) Specification", RFC 2460, December 1998.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, April 2006.

   [RFC4443]  Conta, A., Deering, S. and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W. and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T. and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J. and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC6282]  Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              September 2011.

   [RFC6550]  Winter, T., Thubert, P., 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, March 2012.

   [RFC6620]  Nordmark, E., Bagnulo, M. and E. Levy-Abegnoli, "FCFS
              SAVI: First-Come, First-Served Source Address Validation
              Improvement for Locally Assigned IPv6 Addresses", RFC
              6620, May 2012.

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   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E. and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.

10.2.  Informative References

              Chakrabarti, S., Nordmark, E. and M. Wasserman,
              "Efficiency aware IPv6 Neighbor Discovery Optimizations",
              Internet-Draft draft-chakrabarti-nordmark-6man-efficient-
              nd-01, November 2012.

              Thaler, D. and C. Huitema, "Multi-link Subnet Support in
              IPv6", Internet-Draft draft-ietf-ipv6-multilink-
              subnets-00, July 2002.

              Vasseur, J., "Terminology in Low power And Lossy
              Networks", Internet-Draft draft-ietf-roll-terminology-12,
              March 2013.

              Thubert, P., "6LoWPAN Backbone Router", Internet-Draft
              draft-thubert-6lowpan-backbone-router-03, February 2013.

   [RFC3115]  Dommety, G. and K. Leung, "Mobile IP Vendor/Organization-
              Specific Extensions", RFC 3115, April 2001.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A. and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B. and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.

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

   [RFC4887]  Thubert, P., Wakikawa, R. and V. Devarapalli, "Network
              Mobility Home Network Models", RFC 4887, July 2007.

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

   [RFC4919]  Kushalnagar, N., Montenegro, G. and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals", RFC
              4919, August 2007.

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   [RFC6275]  Perkins, C., Johnson, D. and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

Authors' Addresses

   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis, 06410

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

   Eric Levy-Abegnoli
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis, 06410

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

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