6lo                                                      P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Updates: 6550, 8505, 9010 (if approved)                   8 October 2021
Intended status: Standards Track
Expires: 11 April 2022


         IPv6 Neighbor Discovery Multicast Address Registration
              draft-thubert-6lo-multicast-registration-02

Abstract

   This document updates RFC 8505 to enable the address registration of
   IPv6 anycast and multicast addresses to a 6LR and updates RFC 6550
   (RPL) add a new Non-Storing multicast mode and support for anycast
   addresses.  This document also extends RFC 9010 to enable the 6LR to
   inject the anycast and multicast addresses in RPL.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   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 11 April 2022.

Copyright Notice

   Copyright (c) 2021 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
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     2.2.  References  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Extending RFC 7400  . . . . . . . . . . . . . . . . . . . . .   8
   5.  Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Updating MOP 3  . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  New Non-Storing Multicast MOP . . . . . . . . . . . . . .   9
     5.3.  RPL Anycast Operation . . . . . . . . . . . . . . . . . .   9
     5.4.  New RPL Target Option Flags . . . . . . . . . . . . . . .  10
   6.  Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  New EARO flag . . . . . . . . . . . . . . . . . . . . . .  11
     6.2.  Registering Extensions  . . . . . . . . . . . . . . . . .  12
   7.  Updating RFC 9010 . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Deployment considerations . . . . . . . . . . . . . . . . . .  13
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   10. Backward Compatibility  . . . . . . . . . . . . . . . . . . .  15
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  New RTO flags  . . . . . . . . . . . . . . . . . . . . .  16
     11.2.  New RPL Mode of Operation  . . . . . . . . . . . . . . .  16
     11.3.  New EARO flags . . . . . . . . . . . . . . . . . . . . .  16
     11.4.  New 6LoWPAN Capability Bits  . . . . . . . . . . . . . .  17
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   13. Normative References  . . . . . . . . . . . . . . . . . . . .  17
   14. Informative References  . . . . . . . . . . . . . . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   The design of Low Power and Lossy Networks (LLNs) is generally
   focused on saving energy, which is the most constrained resource of
   all.  Other design constraints, such as a limited memory capacity,
   duty cycling of the LLN devices and low-power lossy transmissions,
   derive from that primary concern.  The radio (both transmitting or
   simply listening) is a major energy drain and the LLN protocols must
   be adapted to allow the nodes to remain sleeping with the radio
   turned off at most times.










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   The "Routing Protocol for Low Power and Lossy Networks" [RFC6550]
   (RPL) to provide IPv6 [RFC8200] routing services within such
   constraints.  To save signaling and routing state in constrained
   networks, the RPL routing is only performed along a Destination-
   Oriented Directed Acyclic Graph (DODAG) that is optimized to reach a
   Root node, as opposed to along the shortest path between 2 peers,
   whatever that would mean in each LLN.

   This trades the quality of peer-to-peer (P2P) paths for a vastly
   reduced amount of control traffic and routing state that would be
   required to operate an any-to-any shortest path protocol.
   Additionally, broken routes may be fixed lazily and on-demand, based
   on dataplane inconsistency discovery, which avoids wasting energy in
   the proactive repair of unused paths.

   Section 12 of [RFC6550] details the "Storing Mode of Operation with
   multicast support" with source-independent multicast routing in RPL.

   The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861]
   [RFC4862] was defined for serial links and shared transit media such
   as Ethernet at a time when broadcast was cheap on those media while
   memory for neighbor cache was expensive.  It was thus designed as a
   reactive protocol that relies on caching and multicast operations for
   the Address Discovery (aka Lookup) and Duplicate Address Detection
   (DAD) of IPv6 unicast addresses.  Those multicast operations
   typically impact every node on-link when at most one is really
   targeted, which is a waste of energy, and imply that all nodes are
   awake to hear the request, which is inconsistent with power saving
   (sleeping) modes.

   The original 6LoWPAN ND, "Neighbor Discovery Optimizations for
   6LoWPAN networks" [RFC6775], was introduced to avoid the excessive
   use of multicast messages and enable IPv6 ND for operations over
   energy-constrained nodes.  [RFC6775] changes the classical IPv6 ND
   model to proactively establish the Neighbor Cache Entry (NCE)
   associated to the unicast address of a 6LoWPAN Node (6LN) in the a
   6LoWPAN Router(s) (6LR) that serves it.  To that effect, [RFC6775]
   defines a new Address Registration Option (ARO) that is placed in
   unicast Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
   messages between the 6LN and the 6LR.

   "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
   updates [RFC6775] into a generic Address Registration mechanism that
   can be used to access services such as routing and ND proxy and
   introduces the Extended Address Registration Option (EARO) for that
   purpose.  This provides a routing-agnostic interface for a host to
   request that the router injects a unicast IPv6 address in the local
   routing protocol and provide return reachability for that address.



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   "Routing for RPL Leaves" [RFC9010] provides the router counterpart of
   the mechanism for a host that implements [RFC8505] to inject its
   unicast Unique Local Addresses (ULAs) and Global Unicast Addresses
   (GUAs) in RPL.  But though RPL also provides multicast routing,
   6LoWPAN ND supports only the registration of unicast addresses and
   there is no equivalent of [RFC9010] to specify the 6LR behavior upon
   the registration of one or more multicast address.

   The "Multicast Listener Discovery Version 2 (MLDv2) for IPv6"
   [RFC3810] enables the router to learn which node listens to which
   multicast address, but as the classical IPv6 ND protocol, MLD relies
   on multicasting Queries to all nodes, which is unfit for low power
   operations.  As for IPv6 ND, it makes sense to let the 6LNs control
   when and how they maintain the state associated to their multicast
   addresses in the 6LR, e.g., during their own wake time.  In the case
   of a constrained node that already implements [RFC8505] for unicast
   reachability, it makes sense to extend to that support to register
   the multicast addresses they listen to.

   This specification extends [RFC8505] and [RFC9010] to add the
   capability for the 6LN to register multicast addresses and for the
   6LR to inject them in the RPL multicast support.

2.  Terminology

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  References

   This document uses terms and concepts that are discussed in:

   *  "Neighbor Discovery for IP version 6" [RFC4861] and "IPv6
      Stateless address Autoconfiguration" [RFC4862],

   *  Neighbor Discovery Optimization for Low-Power and Lossy Networks
      [RFC6775], as well as

   *  "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
      and

   *  "Using RPI Option Type, Routing Header for Source Routes, and
      IPv6-in-IPv6 Encapsulation in the RPL Data Plane" [RFC9008].



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2.3.  Glossary

   This document uses the following acronyms:

   6BBR   6LoWPAN Backbone Router
   6BBR   6LoWPAN Border Router
   6LN    6LoWPAN Node
   6LR    6LoWPAN Router
   6CIO   Capability Indication Option
   AMC    Address Mapping Confirmation
   AMR    Address Mapping Request
   ARO    Address Registration Option
   DAC    Duplicate Address Confirmation
   DAD    Duplicate Address Detection
   DAR    Duplicate Address Request
   EARO   Extended Address Registration Option
   EDAC   Extended Duplicate Address Confirmation
   EDAR   Extended Duplicate Address Request
   DODAG  Destination-Oriented Directed Acyclic Graph
   LLN    Low-Power and Lossy Network
   NA     Neighbor Advertisement
   NCE    Neighbor Cache Entry
   ND     Neighbor Discovery
   NS     Neighbor Solicitation
   ROVR   Registration Ownership Verifier
   RA     Router Advertisement
   RS     Router Solicitation
   TID    Transaction ID

3.  Overview

   [RFC8505] is a pre-requisite to this specification.  A node that
   implements this MUST also implement [RFC8505].  This specification
   does not introduce a new option; it modifies existing options and
   updates the associated behaviors to enable the Registration for
   Multicast Addresses with [RFC8505].

   This specification also extends [RFC6550] and [RFC9010] in the case
   of a route-over multilink subnet based on the RPL routing protocol.
   A 6LR that implements the RPL extensions specified therein MUST also
   implement [RFC9010].

   Figure 1 illustrates the classical situation of an LLN as a single
   IPv6 Subnet, with a 6LoWPAN Border Router (6LBR) that acts as Root
   for RPL operations and maintains a registry of the active
   registrations as an abstract data structure called an Address
   Registrar for 6LoWPAN ND.




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   The LLN may be a hub-and-spoke access link such as (Low-Power) Wi-Fi
   [IEEE Std 802.11] and Bluetooth (Low Energy) [IEEE Std 802.15.1], or
   a Route-Over LLN such as the Wi-SUN mesh [Wi-SUN] that leverages
   6LoWPAN [RFC4919][RFC6282] and RPL [RFC6550] over [IEEE Std
   802.15.4].

                     |
         ----+-------+------------
             |     Wire side
          +------+
          | 6LBR |
          |(Root)|
          +------+
          o  o  o  Wireless side
      o   o o   o  o o
     o  o  o o   o  o  o
    o  o  o   LLN  o   +---+
      o  o   o  o   o  |6LR|
      o o  o o   o     +---+
       o   o   o o o  o    z
      o  o oo o  o        +---+
             o            |6LN|
                          +---+

                          Figure 1: Wireless Mesh

   A leaf acting as a 6LN registers its unicast addresses to a RPL
   router acting as a 6LR, using a unicast NS message with an EARO as
   specified in [RFC8505].  The registration state is periodically
   renewed by the Registering Node, before the lifetime indicated in the
   EARO expires.

   With this specification, the 6LNs can now register for the multicast
   addresses they listen to, using a new M flag in the EARO to signal a
   registration for a multicast address.  Multiple 6LN can register for
   the same multicast address to the same 6LR.  Note the use of the term
   "for", a node registers the unicast addresses that it owns, but
   registers for multicast addresses that it listens to.

   If the R flag is set in the registration of one or more 6LNs for the
   same multicast address, the 6LR injects the multicast address in the
   RPL multicast support, based on the longest registration lifetime
   across those 6LNs.








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   In the RPL "Storing Mode of Operation with multicast support", the
   DAO messages for the multicast address percolate along the RPL
   preferred parent tree and mark a subtree that becomes the multicast
   tree for that multicast address, with 6LNs that registered for it as
   the leaves.

   As prescribed in section 12 of [RFC6550], the 6LR forward the
   multicast packets as individual unicast MAC frames to each child that
   advertised the multicast address in its DAO message.  In most LLNs a
   broadcast is unreliable (no ack) and forces a listener to remain
   awake, so it is expected that the 6LR also delivers the multicast
   packet as individual unicast MAC frames to each of the 6LNs that
   registered for the multicast address.

   In the new RPL "Non-Storing Mode of Operation with multicast support"
   that is introduced here, the DAO messages register multicast
   addresses as Targets, though never as Transit.  The multicast
   distribution is hub-and-spoke from the Root to all the 6LRs that are
   transit for the multicast address, using the same source-routing
   header as for unicast targets attached to the 6LR, but for the
   ultimate entry that is the multicast address.

   With this specification, the 6LNs can also register for the anycast
   addresses they listen to, using a new A flag in the EARO to signal a
   registration for an anycast address.  Multiple 6LN can register for
   the same anycast address to the same 6LR, but the RPL routing ensures
   that only one of the 6LN gets the particular packet.

   It is also possible to leverage this specification between the 6LN
   and the 6LR for the registration of an anycast or a multicast
   addresses in networks that are not necessarily LLNs, and/or where the
   routing protocol between the 6LR and above is not necessarily RPL.

   For instance, it is possible to operate a RPL Instance in the new
   "Non-Storing Mode of Operation with multicast support" and use
   "Multicast Protocol for Low-Power and Lossy Networks (MPL)" [RFC7731]
   for the multicast operation.  MPL floods the DODAG with the multicast
   messages independently of the RPL DODAG topologies.  Two variations
   are possible:

   *  In one possible variation, all the 6LNs set the R flag in the EARO
      for a multicast target, upon which the 6LR sends a unicast DAO
      message to the Root; in that case, the Root can filter the
      multicast messages for which there is no listener and only flood
      the relevant multicasts.

   *  In a simpler variation, the 6LNs do not set the R flag and the
      Root floods all the multicast packets over the whole DODAG.



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4.  Extending RFC 7400

   This specification defines a new capability bit for use in the 6CIO
   as defined by "6LoWPAN-GHC: Generic Header Compression for IPv6 over
   Low-Power Wireless Personal Area Networks (6LoWPANs)" [RFC7400] and
   extended in [RFC8505] for use in IPv6 ND messages.

   The new "Registration for Multicast Address Supported" (M) flag
   indicates to the 6LN that the 6LR accepts multicast address
   registrations as specified in this document and will ensure that
   packets for the multicast Registered Address will be routed to the
   6LNs that registered with the R flag set.

   Figure 2 illustrates the M flag in its suggested position (8,
   counting 0 to 15 in network order in the 16-bit array), to be
   confirmed by IANA.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |   Length = 1  |    Reserved   |M|A|D|L|B|P|E|G|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: New Capability Bits in the 6CIO

   New Option Field:

   M  1-bit flag: "Registration for Multicast and Anycast Addresses
      Supported"

5.  Updating RFC 6550

5.1.  Updating MOP 3

   RPL supports multicast operations in the "Storing Mode of Operation
   with multicast support" (MOP 3) which provides source-independent
   multicast routing in RPL, as prescribed in section 12 of [RFC6550].
   MOP 3 is a storing Mode of Operation.  This operation builds a
   multicast tree within the RPL DODAG for each multicast address.  This
   specification provides additional details for the MOP 3 operation.

   The expectation in MOP 3 is that the unicast traffic also follows the
   Storing Mode of Operation.  But this is rarely the case in LLN
   deployments of RPL where the "Non-Storing Mode of Operation" (MOP 1)
   is the norm.  Though it is preferred to build separate RPL Instances,



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   one in MOP 1 and one in MOP 3, this specification allows to hybrid
   the Storing Mode for multicast and Non-Storing Mode for unicast in
   the same RPL Instance, more in Section 8.

5.2.  New Non-Storing Multicast MOP

   This specification adds a "Non-Storing Mode of Operation with
   multicast support" (MOP to be assigned by IANA) whereby the non-
   storing Mode DAO to the Root may contain multicast addresses in the
   RTO, whereas the Transit Information Option (TIO) can not.  In that
   case, the RPL Root copies the multicast packet to each 6LR that is a
   transit for the multicast target, using the same source routing
   header as for unicast address of a RPL Unaware Leaf (RUL) attached to
   that 6LR.

   For a packet that is generated by the Root, this means that the Root
   builds a source routing header as discussed in section 8.1.3 of
   [RFC9008], but for which the last and only the last address is
   multicast.  For a packet that is not generated by the Root,the Root
   encapsulates the multicast packet as discussed in section 8.2.4 of
   [RFC9008].

   For this new mode as well, this specification allows to enable the
   operation in a MOP 1 brown field, more in Section 8.

5.3.  RPL Anycast Operation

   With multicast, the address has a recognizable format, and a
   multicast packet is to be delivered to all the registered listeners.
   In contrast with anycast, the format of the address may not be
   distinguishable from unicast.  In fact, an external destination
   (address or prefix) that may be injected from multiple border routers
   MUST be injected as anycast in RPL.

   For both multicast and anycast, there is no concept of duplication,
   and there might be multiple registrations from multiple parties, each
   using a different value of the ROVR field that identifies that
   registration.  The 6LR MUST conserve one registration per value of
   the ROVR per multicast or anycast address, but inject the route into
   RPL only once for each address.  Since the registrations are
   considered separate, the check on the TID that acts as registration
   sequence only applies to the registration with the same ROVR.

   The 6LRs that inject multicast and anycast routes into RPL may not be
   synchronized to advertise same value of the Path Sequence in the RPL
   TIO.  It results that the value the Path Sequence is irrelevant when
   the target is anycast or multicast, and that it MUST be ignored.
   Like the 6LR, a RPL router in Storing Mode propagates the route to



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   its parent(s) in DAO messages once and only once for each address,
   but it MUST retain a routing table entry for each of the children
   that advertised the address.  Note that typically the router
   advertises the multicast and anycast addresses only to its preferred
   parents, in which case the resulting routes form a tree down the
   DODAG.

   When forwarding multicast packets down the DODAG, the RPL router MUST
   copy all the children that advertised the address in their DAO
   messages.  In contrast, when forwarding anycast packets down the
   DODAG, the RPL router MUST copy one and only one of the children that
   advertised the address in their DAO messages.  Typically this is done
   through MAC-Layer unicast which makes the operation more reliable.

5.4.  New RPL Target Option Flags

   [RFC6550] recognizes a multicast address by its format (as specified
   in section 2.7 of [RFC4291]) and applies the specified multicast
   operation if the address is recognized as multicast.  This
   specification updates [RFC6550] to add the M and A flags to the RTO
   to indicate that the target address is to be processed as multicast
   or anycast, respectively.

   An RTO that has the M flag set is called a multicast RTO.  An RTO
   that has the A flag set is called an anycast RTO.  An RTO that has
   neither M nor A flag set is called a unicast RTO.  The M and A flags
   are mutually exclusive and MUST NOT be both set.

   The suggested position for the A and M flags are 2 and 3 counting
   from 0 to 7 in network order as shown in Figure 3, based on figure 4
   of [RFC9010] which defines the flags in position 0 and 1:

      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 = 0x05 | Option Length |F|X|A|M|ROVRsz | Prefix Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                Target Prefix (Variable Length)                |
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: Format of the RPL Target Option




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6.  Updating RFC 8505

6.1.  New EARO flag

   Section 4.1 of [RFC8505] defines the EARO as an extension to the ARO
   option defined in [RFC6775].

   This specification adds a new M flag to the EARO flags field to
   signal that the Registered Address is a multicast address.  When both
   the M and the R flags are set, the 6LR that conforms to this
   specification joins the multicast stream, e.g., by injecting the
   address in the RPL multicast support which is extended in this
   specification for Non-Storing Mode.

   This specification adds a new A flag to the EARO flags field to
   signal that the Registered Address is an anycast address.  When both
   the A and the R flags are set, the 6LR that conforms to this
   specification injects the anycast address in the RPL anycast support
   that is introduced in this specification for both Storing and Non-
   Storing Modes.

   Figure 4 illustrates the A and M flags in their suggested positions
   (2 and 3, respectively, counting 0 to 7 in network order in the 8-bit
   array), to be confirmed by IANA.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |    Status     |    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Rsv|A|M| I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...             Registration Ownership Verifier                 ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 4: EARO Option Format

   New and updated Option Fields:

   Rsv  2-bit field: reserved, MUST be set to 0 and ignored by the
      receiver

   A  1-bit flag: "Registration for Anycast Address"

   M  1-bit flag: "Registration for Multicast Address"




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6.2.  Registering Extensions

   With [RFC8505]:

   *  Only unicast addresses can be registered.

   *  The 6LN must register all its ULA and GUA with a NS(EARO).

   *  The 6LN may set the R flag in the EARO to obtain return
      reachability services by the 6LR, e.g., through ND proxy
      operations, or by injecting the route in a route-over subnet.

   *  the 6LR maintains a registration state per Registered Address,
      including an NCE with the Link Layer Address (LLA) of the
      Registered Node (the 6LN here).

   This specification adds the following behavior:

   *  Registration for multicast and anycast addresses is now supported.

   *  The 6LN MUST also register all the IPv6 multicast addresses that
      it listens to and it MUST set the M flag in the EARO for those
      addresses.

   *  The 6LN MAY set the R flag in the EARO to obtain the delivery of
      the multicast packets by the 6LR, e.g., by MLD proxy operations,
      or by injecting the address in a route-over subnet or in the
      Protocol Independent Multicast [RFC7761] protocol.

   *  The 6LN MUST also register all the IPv6 anycast addresses that it
      supports and it MUST set the A flag in the EARO for those
      addresses.

   *  The Registration Ownership Verifier (ROVR) in the EARO identifies
      uniquely a registration within the namespace of the Registered
      Address.  The 6LR MUST maintain a registration state per tuple
      (IPv6 address, ROVR) for both anycast and multicast types of
      address, since multiple 6LNs may register for the same address of
      these types.

7.  Updating RFC 9010

   With [RFC9010]:

   *  The 6LR injects only unicast routes in RPL

   *  upon a registration with the R flag set to 1 in the EARO, the 6LR
      injects the address in the RPL unicast support.



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   *  Upon receiving a packet directed to a unicast address for which it
      has an active registration, the 6LR delivers the packet as a
      unicast layer-2 frame to the LLA the nodes that registered the
      unicast address.

   This specification adds the following behavior:

   *  Upon a registration with the R and the M flags set to 1 in the
      EARO, the 6LR injects the address in the RPL multicast support.

   *  Upon receiving a packet directed to a multicast address for which
      it has at least one registration, the 6LR delivers a copy of the
      packet as a unicast layer-2 frame to the LLA of each of the nodes
      that registered to that multicast address.

8.  Deployment considerations

   With this specification, a RPL DODAG forms a realm, and multiple RPL
   DODAGs may federated in a single RPL Instance administratively.  This
   means that a multicast address that needs to span a RPL DODAG MUST
   use a scope of Realm-Local whereas a multicast address that needs to
   span a RPL Instance MUST use a scope of Admin-Local as discussed in
   section 3 of "IPv6 Multicast Address Scopes" [RFC7346].

   "IPv6 Addressing of IPv4/IPv6 Translators" [RFC6052] enables to embed
   IPv4 addresses in IPv6 addresses.  The Root of a DODAG may leverage
   that technique to translate IPv4 traffic in IPv6 and route along the
   RPL domain.  When encapsulating an packet with an IPv4 multicast
   Destination Address, it MUST use form a multicast address and use the
   appropriate scope, Realm-Local or Admin-Local.

   "Unicast-Prefix-based IPv6 Multicast Addresses" [RFC3306] enables to
   form 2^32 multicast addresses from a single /64 prefix.  If an IPv6
   prefix is associated to an Instance or a RPL DODAG, this provides a
   namespace that can be used in any desired fashion.  It is for
   instance possible for a standard defining organization to form its
   own registry and allocate 32-bit values from that namespace to
   network functions or device types.  When used within a RPL deployment
   that is associated with a /64 prefix the IPv6 multicast addresses can
   be automatically derived from the prefix and the 32-bit value for
   either a Realm-Local or an Admin-Local multicast address as needed in
   the configuration.

   IN a "green field" deployment where all nodes support this
   specification, it is possible to deploy a single RPL Instance using a
   multicast MOP for unicast, multicast and anycast addresses.





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   In a "brown field" where legacy devices that do not support this
   specification co-exist with upgraded devices, it is RECOMMENDED to
   deploy one RPL Instance in any Mode of Operation (typically MOP 1)
   for unicast that legacy nodes can join, and a separate RPL Instance
   dedicated to multicast and anycast operations using a multicast MOP.

   To deploy a Storing Mode multicast operation using MOP 3 in a RPL
   domain, it is required that there is enough density of RPL routers
   that support MOP 3 to build a DODAG that covers all the potential
   listeners and include the spanning multicast trees that are needed to
   distribute the multicast flows.  This might not be the case when
   extending the capabilities of an existing network.

   In the case of the new Non-Storing multicast MOP, arguably the new
   support is only needed at the 6LRs that will accept multicast
   listeners.  It is still required that each listener can reach at
   least one such 6LR, so the upgraded 6LRs must be deployed to cover
   all the 6LN that need multicast services.

   Using separate RPL Instances for in the one hand unicast traffic and
   in the other hand anycast and multicast traffic allows to use
   different objective function, one favoring the link quality up for
   unicast collection and one favoring downwards link quality for
   multicast distribution.

   But this might be impractical in some use cases where the signaling
   and the state to be installed in the devices are very constrained,
   the upgraded devices are too sparse, or the devices do not support
   more multiple instances.

   When using a single RPL Instance, MOP 3 expects the Storing Mode of
   Operation for both unicast and multicast, which is an issue in
   constrained networks that typically use MOP 1 for unicast.  This
   specification allows a mixed mode that is signaled as MOP 1 in the
   DIO messages for backward compatibility, where limited multicast and/
   or anycast is available, under the following conditions:

   *  There MUST be enough density of 6LRs that support the mixed mode
      to cover the all the 6LNs that require multicast or anycast
      services.  In Storing Mode, there MUST be enough density or 6LR
      that support the mixed mode to also form a DODAG to the Root.

   *  The RPL routers that support the mixed mode and are configured to
      operate in in accordance with the desired operation in the
      network.

   *  The MOP signaled in the RPL DODAG Information Object (DIO)
      messages is MOP 1 to enable the legacy nodes to operate as leaves.



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   *  The support of multicast and/or anycast in the RPL Instance SHOULD
      be signaled by the 6LRs to the 6LN using a 6CIO, see Section 4.

   *  Alternatively, the support of multicast in the RPL domain can be
      globally known by other means such as configuration or external
      information such as support of a version of an industry standard
      that mandates it.  In that case, all the routers MUST support the
      mixed mode.

9.  Security Considerations

   This specification extends [RFC8505], and the security section of
   that document also applies to this document.  In particular, the link
   layer SHOULD be sufficiently protected to prevent rogue access.

10.  Backward Compatibility

   A legacy 6LN will not register multicast addresses and the service
   will be the same when the network is upgraded.  A legacy 6LR will not
   set the M flag in the 6CIO and an upgraded 6LN will not register
   multicast addresses.

   As detailed in Section 8, it is possible to add multicast on an
   existing MOP 1 deployment,

   The combination of a multicast address and the M flag set to 0 in an
   RTO in a MOP 3 RPL Instance is understood by the receiver that
   supports this specification (the parent) as an indication that the
   sender (child) does not support this specification, but the RTO is
   accepted and processed as if the M flag was set for backward
   compatibility.

   When the DODAG is operated in MOP 3, a legacy node will not set the M
   flag and still expect multicast service as specified in section 12 of
   [RFC6550].  In MOP 3 an RTO that is received with a target that is
   multicast and the M bit set to 0 MUST be considered as multicast and
   MUST be processed as if the M flag is set.

11.  IANA Considerations

   Note to RFC Editor, to be removed: please replace "This RFC"
   throughout this document by the RFC number for this specification
   once it is allocated.  Also, the I Field is defined in RFC 9010 but
   we failed to insert it in the subregistry and the flags appear as
   unspecified though they are.






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   IANA is requested to make changes under the "Internet Control Message
   Protocol version 6 (ICMPv6) Parameters" [IANA.ICMP] and the "Routing
   Protocol for Low Power and Lossy Networks (RPL)" [IANA.RPL]
   registries, as follows:

11.1.  New RTO flags

   IANA is requested to make additions to the "RPL Target Option Flags"
   [IANA.RPL.RTO.FLG] subregistry of the "Routing Protocol for Low Power
   and Lossy Networks (RPL)" registry as indicated in Table 1:

   +---------------+---------------------------------------+-----------+
   | Bit Number    | Meaning                               | Reference |
   +---------------+---------------------------------------+-----------+
   | 2 (suggested) | A flag: Target is an Anycast Address  | This RFC  |
   +---------------+---------------------------------------+-----------+
   | 3 (suggested) | M flag: Target is a Multicast         | This RFC  |
   |               | Address                               |           |
   +---------------+---------------------------------------+-----------+

                           Table 1: New RTO flags

11.2.  New RPL Mode of Operation

   IANA is requested to make an addition to the "Mode of Operation"
   [IANA.RPL.MOP] subregistry of the "Routing Protocol for Low Power and
   Lossy Networks (RPL)" registry as indicated in Table 2:

       +---------------+-------------------------------+-----------+
       | Value         | Description                   | Reference |
       +---------------+-------------------------------+-----------+
       | 5 (suggested) | Non-Storing Mode of Operation | This RFC  |
       |               | with multicast support        |           |
       +---------------+-------------------------------+-----------+

                     Table 2: New RPL Mode of Operation

11.3.  New EARO flags

   IANA is requested to make additions to the "Address Registration
   Option Flags" [IANA.ICMP.ARO.FLG] of the "Internet Control Message
   Protocol version 6 (ICMPv6) Parameters" registry as indicated in
   Table 3:








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           +---------------+-----------------------+-----------+
           | ARO flag      | Meaning               | Reference |
           +---------------+-----------------------+-----------+
           | 2 (suggested) | A flag: Registration  | This RFC  |
           |               | for Anycast Address   |           |
           +---------------+-----------------------+-----------+
           | 3 (suggested) | M flag: Registration  | This RFC  |
           |               | for Multicast Address |           |
           +---------------+-----------------------+-----------+
           | 4 and 5       | "I" Field             | RFC 8505  |
           +---------------+-----------------------+-----------+

                           Table 3: New ARO flags

11.4.  New 6LoWPAN Capability Bits

   IANA is requested to make an addition to the "6LoWPAN Capability
   Bits" [IANA.ICMP.6CIO] subregistry subregistry of the "Internet
   Control Message Protocol version 6 (ICMPv6) Parameters" registry as
   indicated in Table 4:

    +----------------+------------------------------------+-----------+
    | Capability Bit | Meaning                            | Reference |
    +----------------+------------------------------------+-----------+
    | 8 (suggested)  | M flag: Registration for Multicast | This RFC  |
    |                | and Anycast Addresses Supported    |           |
    +----------------+------------------------------------+-----------+

                    Table 4: New 6LoWPAN Capability Bits

12.  Acknowledgments


13.  Normative References

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

   [RFC3306]  Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
              Multicast Addresses", RFC 3306, DOI 10.17487/RFC3306,
              August 2002, <https://www.rfc-editor.org/info/rfc3306>.

   [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>.




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   [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>.

   [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>.

   [RFC7346]  Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
              DOI 10.17487/RFC7346, August 2014,
              <https://www.rfc-editor.org/info/rfc7346>.

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

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

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

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





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   [RFC9010]  Thubert, P., Ed. and M. Richardson, "Routing for RPL
              (Routing Protocol for Low-Power and Lossy Networks)
              Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
              <https://www.rfc-editor.org/info/rfc9010>.

   [IANA.ICMP]
              IANA, "IANA Registry for ICMPv6", IANA,
              https://www.iana.org/assignments/icmpv6-parameters/
              icmpv6-parameters.xhtml.

   [IANA.ICMP.ARO.FLG]
              IANA, "IANA Sub-Registry for the ARO Flags", IANA,
              https://www.iana.org/assignments/icmpv6-parameters/
              icmpv6-parameters.xhtml#icmpv6-adress-registration-option-
              flags.

   [IANA.ICMP.6CIO]
              IANA, "IANA Sub-Registry for the 6LoWPAN Capability Bits",
              IANA, https://www.iana.org/assignments/icmpv6-parameters/
              icmpv6-parameters.xhtml#sixlowpan-capability-bits.

   [IANA.RPL] IANA, "IANA Registry for the RPL",
              IANA, https://www.iana.org/assignments/rpl/rpl.xhtml.

   [IANA.RPL.RTO.FLG]
              IANA, "IANA Sub-Registry for the RTO Flags", IANA,
              https://www.iana.org/assignments/rpl/rpl.xhtml#rpl-target-
              option-flags.

   [IANA.RPL.MOP]
              IANA, "IANA Sub-Registry for the RPL Mode of Operation",
              IANA, https://www.iana.org/assignments/rpl/rpl.xhtml#mop.

14.  Informative References

   [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>.

   [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>.






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   [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>.

   [RFC7731]  Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power
              and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731,
              February 2016, <https://www.rfc-editor.org/info/rfc7731>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,
              <https://www.rfc-editor.org/info/rfc6052>.

   [RFC9008]  Robles, M.I., Richardson, M., and P. Thubert, "Using RPI
              Option Type, Routing Header for Source Routes, and IPv6-
              in-IPv6 Encapsulation in the RPL Data Plane", RFC 9008,
              DOI 10.17487/RFC9008, April 2021,
              <https://www.rfc-editor.org/info/rfc9008>.

   [Wi-SUN]   Heile, B., (Remy), B. L., Zhang, M., and C. E. Perkins,
              "Wi-SUN FAN Overview", Work in Progress, Internet-Draft,
              draft-heile-lpwan-wisun-overview-00, 3 July 2017,
              <https://datatracker.ietf.org/doc/html/draft-heile-lpwan-
              wisun-overview-00>.

   [IEEE Std 802.15.4]
              IEEE standard for Information Technology, "IEEE Std
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks".

   [IEEE Std 802.11]
              IEEE standard for Information Technology, "IEEE Standard
              802.11 - IEEE Standard for Information Technology -
              Telecommunications and information exchange between
              systems Local and metropolitan area networks - Specific
              requirements - Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications.",
              <https://ieeexplore.ieee.org/document/9363693>.





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   [IEEE Std 802.15.1]
              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)".

Author's Address

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

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































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