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In: In_Last_Call
ROLL                                                     P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Updates: 6550, 6775, 8505 (if approved)                    M. Richardson
Intended status: Standards Track                               Sandelman
Expires: 12 April 2021                                    9 October 2020


                         Routing for RPL Leaves
                   draft-ietf-roll-unaware-leaves-22

Abstract

   This specification updates RFC6550, RFC6775, and RFC8505, to provide
   routing services to RPL Unaware Leaves that implement 6LoWPAN ND and
   the extensions therein.

Status of This Memo

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

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

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

   This Internet-Draft will expire on 12 April 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   5
     2.2.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  References  . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  RPL External Routes and Dataplane Artifacts . . . . . . . . .   7
   4.  6LoWPAN Neighbor Discovery  . . . . . . . . . . . . . . . . .   8
     4.1.  RFC 6775 Address Registration . . . . . . . . . . . . . .   8
     4.2.  RFC 8505 Extended Address Registration  . . . . . . . . .   8
       4.2.1.  R Flag  . . . . . . . . . . . . . . . . . . . . . . .   9
       4.2.2.  TID, "I" Field and Opaque Fields  . . . . . . . . . .   9
       4.2.3.  ROVR  . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . .  10
       4.3.1.  RFC 7400 Capability Indication Option . . . . . . . .  10
   5.  Requirements on the RPL-Unware Leaf . . . . . . . . . . . . .  11
     5.1.  Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . .  11
     5.2.  Support of IPv6 Encapsulation . . . . . . . . . . . . . .  12
     5.3.  Support of the HbH Header . . . . . . . . . . . . . . . .  12
     5.4.  Support of the Routing Header . . . . . . . . . . . . . .  12
   6.  Enhancements to RFC 6550  . . . . . . . . . . . . . . . . . .  12
     6.1.  Updated RPL Target Option . . . . . . . . . . . . . . . .  13
     6.2.  New Flag in the RPL DODAG Configuration Option  . . . . .  14
     6.3.  Updated RPL Status  . . . . . . . . . . . . . . . . . . .  15
   7.  Enhancements to draft-ietf-roll-efficient-npdao . . . . . . .  16
   8.  Enhancements to RFC 6775 and RFC8505  . . . . . . . . . . . .  17
   9.  Protocol Operations for Unicast Addresses . . . . . . . . . .  17
     9.1.  General Flow  . . . . . . . . . . . . . . . . . . . . . .  18
     9.2.  Detailed Operation  . . . . . . . . . . . . . . . . . . .  20
       9.2.1.  Perspective of the 6LN Acting as RUL  . . . . . . . .  20
       9.2.2.  Perspective of the 6LR Acting as Border Router  . . .  22
       9.2.3.  Perspective of the RPL Root . . . . . . . . . . . . .  26
       9.2.4.  Perspective of the 6LBR . . . . . . . . . . . . . . .  27
   10. Protocol Operations for Multicast Addresses . . . . . . . . .  27
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  29
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     12.1.  Fixing the Address Registration Option Flags . . . . . .  31
     12.2.  Resizing the ARO Status values . . . . . . . . . . . . .  31
     12.3.  New DODAG Configuration Option Flag  . . . . . . . . . .  31
     12.4.  RPL Target Option Registry . . . . . . . . . . . . . . .  31
     12.5.  New Subregistry for the RPL Non-Rejection Status
            values . . . . . . . . . . . . . . . . . . . . . . . . .  32
     12.6.  New Subregistry for the RPL Rejection Status values  . .  32
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  33
   14. Normative References  . . . . . . . . . . . . . . . . . . . .  33
   15. Informative References  . . . . . . . . . . . . . . . . . . .  35
   Appendix A.  Example Compression  . . . . . . . . . . . . . . . .  36



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   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

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 IETF produced the "Routing Protocol for Low Power and Lossy
   Networks" [RFC6550] (RPL) to provide IPv6 [RFC8200] routing services
   within such constraints.  RPL belongs to the class of Distance-Vector
   protocols, which, compared to link-state protocols, limit the amount
   of topological knowledge that needs to be installed and maintained in
   each node, and does not require convergence to avoid micro-loops.

   To save signaling and routing state in constrained networks, RPL
   allows a path stretch (see [RFC6687]), whereby 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 a given
   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.

   For many of the nodes, though not all, the DODAG provides multiple
   forwarding solutions towards the Root of the topology via so-called
   parents.  RPL is designed to adapt to fuzzy connectivity, whereby the
   physical topology cannot be expected to reach a stable state, with a
   lazy control that creates the routes proactively, but may only fix
   them reactively, upon actual traffic.  The result is that RPL
   provides reachability for most of the LLN nodes, most of the time,
   but may not converge in the classical sense.

   RPL can be deployed in conjunction with IPv6 Neighbor Discovery (ND)
   [RFC4861] [RFC4862] and 6LoWPAN ND [RFC6775] [RFC8505] to maintain
   reachability within a Non-Broadcast Multi- (NBMA) Multi-Link subnet.

   In that mode, IPv6 addresses are advertised individually as Host
   routes.  Some nodes may act as Routers and participate in the
   forwarding operations whereas others will only terminate packets,
   acting as Hosts in the data-plane.  In [RFC6550] terms, an IPv6 Host
   [RFC8504] that is reachable over the RPL network is called a Leaf.




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   [USEofRPLinfo] introduces the terms RPL-Aware-Leaf (RAL) and RPL-
   Unaware Leaf (RUL).  A RAL is a Leaf that injects Host routes in RPL
   to manage the reachability of its IPv6 addresses.  Conversely, a RUL
   does not participate to RPL and cannot inject routes.  Section 5
   details a Host-to-Router interface that the RUL needs to implement to
   advertise its IPv6 addresses to a Router that supports this
   specification.  The document specifies how the Router injects those
   addresses as Host routes in the RPL network on behalf of the RUL.

   This specification leverages the Address Registration mechanism
   defined in 6LoWPAN ND to enable a 6LoWPAN Node (6LN) acting as a RUL
   to interface with a 6LoWPAN Router (6LR) that is RPL-Aware router,
   and request that the router injects a Host route for the Registered
   Address in RPL on its behalf.  A RUL may be unable to participate
   because it is very energy-constrained, or because it is unsafe to let
   it inject routes in RPL, in which case using 6LowPAN ND as the
   interface for the RUL limits the surface of the possible attacks and
   optionally protects the address ownership.

   The RPL Non-Storing Mode mechanism is used to extend the routing
   state with connectivity to the RULs even when the DODAG is operated
   in Storing Mode.  The unicast packet forwarding operation by the 6LR
   serving a RUL is described in section 4.1 of [USEofRPLinfo].

   Examples of possible RULs include lightly powered sensors such as
   window smash sensor (alarm system), and kinetically powered light
   switches.  Other applications of this specification may include a
   smart grid network that controls appliances - such as washing
   machines or the heating system - in the home.  Appliances may not
   participate to the RPL protocol operated in the Smartgrid network but
   can still interact with the Smartgrid for control and/or metering.

   This document is organized as follows:

   *  Section 3 and Section 4 present salient aspects of RPL and 6LoWPAN
      ND, respectively, that are leveraged in this specification to
      provide connectivity to a RUL across a RPL network.

   *  Section 5 lists the expectations that a RUL needs to match in
      order to be served by a RPL router that complies with this
      specification.

   *  Section 6, Section 7, and Section 8 present the changes made to
      [RFC6550], [EFFICIENT-NPDAO], [RFC6775] and [RFC8505].

   *  Section 9 and Section 10 present the operation of this
      specification for unicast and multicast flows, respectively, and
      Section 11 presents associated security considerations.



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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.  Glossary

   This document often uses the following acronyms:

   AR:  Address Resolution (aka Address Lookup)
   ARQ:  Automatic Repeat reQuest
   6CIO:  6LoWPAN Capability Indication Option
   6LN:  6LoWPAN Node (a Low Power Host or Router)
   6LR:  6LoWPAN Router
   (E)ARO:  (Extended) Address Registration Option
   (E)DAR:  (Extended) Duplicate Address Request
   (E)DAC:  (Extended) Duplicate Address Confirmation
   DAD:  Duplicate Address Detection
   DAO:  Destination Advertisement Object (a RPL message)
   DCO:  Destination Cleanup Object (a RPL message)
   DIS:  DODAG Information solicitation (a RPL message)
   DIO:  DODAG Information Object (a RPL message)
   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
   RA:  Router Advertisement
   ROVR:  Registration Ownership Verifier
   RPI:  RPL Packet Information
   RAL:  RPL-Aware Leaf
   RAN:  RPL-Aware Node (either a RPL Router or a RPL-Aware Leaf)
   RUL:  RPL-Unaware Leaf
   TID:  Transaction ID (a sequence counter in the EARO)











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2.3.  References

   The Terminology used in this document is consistent with and
   incorporates that described in "Terms Used in Routing for Low-Power
   and Lossy Networks (LLNs)" [RFC7102].  A glossary of classical
   6LoWPAN acronyms is given in Section 2.2.  Other terms in use in LLNs
   are found in "Terminology for Constrained-Node Networks" [RFC7228].
   This specification uses the terms 6LN and 6LR to refer specifically
   to nodes that implement the 6LN and 6LR roles in 6LoWPAN ND and does
   not expect other functionality such as 6LoWPAN Header Compression
   [RFC6282] from those nodes.

   "RPL", the "RPL Packet Information" (RPI), "RPL Instance" (indexed by
   a RPLInstanceID) are defined in "RPL: IPv6 Routing Protocol for
   Low-Power and Lossy Networks" [RFC6550].  The RPI is the abstract
   information that RPL defines to be placed in data packets, e.g., as
   the RPL Option [RFC6553] within the IPv6 Hop-By-Hop Header.  By
   extension, the term "RPI" is often used to refer to the RPL Option
   itself.  The DODAG Information solicitation (DIS), Destination
   Advertisement Object (DAO) and DODAG Information Object (DIO)
   messages are also specified in [RFC6550].  The Destination Cleanup
   Object (DCO) message is defined in [EFFICIENT-NPDAO].

   This document uses the terms RPL-Unaware Leaf (RUL) and RPL Aware
   Leaf (RAL) consistently with [USEofRPLinfo].  The term RPL-Aware Node
   (RAN) is introduced to refer to a node that is either an RAL or a RPL
   Router.  As opposed to a RUL, a RAN manages the reachability of its
   addresses and prefixes by injecting them in RPL by itself.

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

   Classical IPv6 ND:  "Neighbor Discovery for IP version 6" [RFC4861]
      and "IPv6 Stateless Address Autoconfiguration" [RFC4862],

   6LoWPAN:  "Problem Statement and Requirements for IPv6 over Low-Power
      Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606] and
      "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
      Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
      and

   6LoWPAN ND:  Neighbor Discovery Optimization for Low-Power and Lossy
      Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor
      Discovery" [RFC8505], and "Address Protected Neighbor Discovery
      for Low-power and Lossy Networks" [AP-ND].






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3.  RPL External Routes and Dataplane Artifacts

   Section 4.1 of [USEofRPLinfo] provides a set of rules detailed below
   that must be followed for routing packets from and to a RUL.

   A 6LR that acts as a border Router for external routes advertises
   them using Non-Storing Mode DAO messages that are unicast directly to
   the Root, even if the DODAG is operated in Storing Mode.  Non-Storing
   Mode routes are not visible inside the RPL domain and all packets are
   routed via the Root.  The RPL Root tunnels the packets directly to
   the 6LR that advertised the external route, which decapsulates and
   forwards the original (inner) packet.

   The RPL Non-Storing MOP signaling and the associated IP-in-IP
   encapsulated packets appear as normal traffic to the intermediate
   Routers.  The support of external routes only impacts the Root and
   the 6LR.  It can be operated with legacy intermediate Routers and
   does not add to the amount of state that must be maintained in those
   Routers.  A RUL is an example of a destination that is reachable via
   an external route that happens to be also a Host route.

   The RPL data packets always carry a Hop-by-Hop Header to transport a
   RPL Packet Information (RPI) [RFC6550].  So unless the RUL originates
   its packets with an RPI, the 6LR needs to tunnel them to the Root to
   add the RPI.  As a rule of a thumb and except for the very special
   case above, the packets from and to a RUL are always encapsulated
   using an IP-in-IP tunnel between the Root and the 6LR that serves the
   RUL (see sections 7 and 8 of [USEofRPLinfo] for details).

   In Non-Storing Mode, packets going down carry a Source Routing Header
   (SRH).  The IP-in-IP encapsulation, the RPI and the SRH are
   collectively called the "RPL artifacts" and can be compressed using
   [RFC8138].  Appendix A presents an example compressed format for a
   packet forwarded by the Root to a RUL in a Storing Mode DODAG.

   The inner packet that is forwarded to the RUL may carry some RPL
   artifacts, e.g., an RPI if the original packet was generated with it,
   and an SRH in a Non-Storing Mode DODAG.  [USEofRPLinfo] expects the
   RUL to support the basic "IPv6 Node Requirements" [RFC8504].  In
   particular the RUL is expected to ignore the RPL artifacts that are
   either consumed or not applicable to a Host.

   A RUL is not expected to support the compression method defined in
   [RFC8138].  For that reason, the border router uncompresses the
   packet before forwarding over an external route to a RUL
   [USEofRPLinfo].





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4.  6LoWPAN Neighbor Discovery

4.1.  RFC 6775 Address Registration

   The classical "IPv6 Neighbor Discovery (IPv6 ND) Protocol" [RFC4861]
   [RFC4862] was defined for serial links and transit media such as
   Ethernet.  It is a reactive protocol that relies heavily on multicast
   operations for Address Discovery (aka Lookup) and Duplicate Address
   Detection (DAD).

   "Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775]
   adapts IPv6 ND for operations over energy-constrained LLNs.  The main
   functions of [RFC6775] are to proactively establish the Neighbor
   Cache Entry (NCE) in the 6LR and to prevent address duplication.  To
   that effect, [RFC6775] introduces a new unicast Address Registration
   mechanism that contributes to reducing the use of multicast messages
   compared to the classical IPv6 ND protocol.

   [RFC6775] defines a new Address Registration Option (ARO) that is
   carried in the unicast Neighbor solicitation (NS) and Neighbor
   Advertisement (NA) messages between the 6LoWPAN Node (6LN) and the
   6LoWPAN Router (6LR).  It also defines the Duplicate Address Request
   (DAR) and Duplicate Address Confirmation (DAC) messages between the
   6LR and the 6LoWPAN Border Router (6LBR).  In an LLN, the 6LBR is the
   central repository of all the Registered Addresses in its domain and
   the source of truth for uniqueness and ownership.

4.2.  RFC 8505 Extended Address Registration

   "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
   updates the behavior of RFC 6775 to enable a generic Address
   Registration to services such as routing and ND proxy, and defines
   the Extended Address Registration Option (EARO) as shown in Figure 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      |     Length    |    Status     |    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Rsvd | I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...             Registration Ownership Verifier                 ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: EARO Option Format



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4.2.1.  R Flag

   [RFC8505] introduces the R Flag in the EARO.  The Registering Node
   sets the R Flag to indicate whether the 6LR should ensure
   reachability for the Registered Address.  If the R Flag is not set,
   then the Registering Node handles the reachability of the Registered
   Address by other means.  In a RPL network, this means that either it
   is a RAN that injects the route by itself or that it uses another RPL
   Router for reachability services.

   This document specifies how the R Flag is used in the context of RPL.
   A RPL Leaf that implements the 6LN functionality in [RFC8505]
   requires reachability services for an IPv6 address if and only if it
   sets the R Flag in the NS(EARO) used to register the address to a 6LR
   acting as a RPL border Router.  Upon receiving the NS(EARO), the RPL
   Router generates a DAO message for the Registered Address if and only
   if the R flag is set.

   Section 9.2 specifies additional operations when R flag is set in an
   EARO that is placed either in an NS or an NA message.

4.2.2.  TID, "I" Field and Opaque Fields

   When the T Flag is set, the EARO includes a sequence counter called
   Transaction ID (TID), that is needed to fill the Path Sequence Field
   in the RPL Transit Option.  This is the reason why the support of
   [RFC8505] by the RUL, as opposed to only [RFC6775] is a prerequisite
   for this specification (more in Section 5.1).  The EARO also
   transports an Opaque field and an associated "I" field that describes
   what the Opaque field transports and how to use it.

   Section 9.2.1 specifies the use of the "I" field and the Opaque field
   by a RUL.

4.2.3.  ROVR

   Section 5.3 of [RFC8505] introduces the Registration Ownership
   Verifier (ROVR) field of variable length from 64 to 256 bits.  The
   ROVR is a replacement of the EUI-64 in the ARO [RFC6775] that was
   used to identify uniquely an Address Registration with the Link-Layer
   address of the owner but provided no protection against spoofing.

   "Address Protected Neighbor Discovery for Low-power and Lossy
   Networks" [AP-ND] leverages the ROVR field as a cryptographic proof
   of ownership to prevent a rogue third party from registering an
   address that is already owned and enable the 6LR to block traffic
   that is not sourced at a owned address.




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   This specification does not address how the protection by [AP-ND]
   could be extended for use in RPL.  On the other hand, it adds the
   ROVR to the DAO to build the proxied EDAR at the Root (see
   Section 6.1), which means that nodes that are aware of the Host route
   are also aware of the ROVR associated to the Target Address.

4.3.  RFC 8505 Extended DAR/DAC

   [RFC8505] updates the DAR/DAC messages into the Extended DAR/DAC to
   carry the ROVR field.  The EDAR/EDAC exchange takes place between the
   6LR and the 6LBR.  It is triggered by an NS(EARO) message from a 6LN
   to create, refresh, and delete the corresponding state in the 6LBR.
   The exchange is protected by the retry mechanism (ARQ) specified in
   8.2.6 of [RFC6775], though in an LLN, a duration longer than the
   RETRANS_TIMER [RFC4861] of 1 second may be necessary to cover the
   Turn Around Trip delay between the 6LR and the 6LBR.

   RPL [RFC6550] specifies a periodic DAO from the 6LN all the way to
   the Root that maintains the routing state in the RPL network for the
   lifetime indicated by the source of the DAO.  This means that for
   each address, there are two keep-alive messages that traverse the
   whole network, one to the Root and one to the 6LBR.

   This specification avoids the periodic EDAR/EDAC exchange across the
   LLN.  The 6LR turns the periodic NS(EARO) from the RUL into a DAO
   message to the Root on every refresh, but it only generates the EDAR
   upon the first registration, for the purpose of DAD, which must be
   verified before the address is injected in RPL.  Upon the DAO
   message, the Root proxies the EDAR exchange to refresh the state at
   the 6LBR on behalf of the 6LR, as illustrated in Figure 7.

4.3.1.  RFC 7400 Capability Indication Option

   "6LoWPAN-GHC: Generic Header Compression for IPv6 over Low-Power
   Wireless Personal Area Networks (6LoWPANs)" [RFC7400] defines the
   6LoWPAN Capability Indication Option (6CIO) that enables a node to
   expose its capabilities in Router Advertisement (RA) messages.

   [RFC8505] defines a number of bits in the 6CIO, in particular:

   L:  Node is a 6LR.
   E:  Node is an IPv6 ND Registrar -- i.e., it supports registrations
      based on EARO.
   P:  Node is a Routing Registrar, -- i.e., an IPv6 ND Registrar that
      also provides reachability services for the Registered Address.






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

                            Figure 2: 6CIO flags

   A 6LR that can provide reachability services for a RUL in a RPL
   network as specified in this document MUST include a 6CIO in its RA
   messages and set the L, P and E flags as prescribed by [RFC8505].

5.  Requirements on the RPL-Unware Leaf

   This document provides RPL routing for a RUL.  This section describes
   the minimal RPL-independent functionality that the RUL needs to
   implement to obtain routing services for its addresses.

5.1.  Support of 6LoWPAN ND

   To obtain routing services from a Router that implements this
   specification, a RUL needs to implement [RFC8505] and set the "R" and
   "T" flags in the EARO as discussed in Section 4.2.1 and
   Section 4.2.3, respectively.  Section 9.2.1 specifies new behaviors
   for the RUL, e.g., when the R Flag set in a NS(EARO) is not echoed in
   the NA(EARO), which indicates that the route injection failed.

   The RUL is expected not to request routing services from a Router
   that does not originate RA messages with a CIO that has the L, P, and
   E flags all set as discussed in Section 4.3.1, unless configured to
   do so.  It is suggested that the RUL also implements [AP-ND] to
   protect the ownership of its addresses.

   A RUL that may attach to multiple 6LRs is expected to prefer those
   that provide routing services.  The RUL needs to register to all the
   6LRs from which it desires routing services.

   Parallel Address Registrations to several 6LRs should be performed in
   a rapid sequence, using the same EARO for the same Address.  Gaps
   between the Address Registrations will invalidate some of the routes
   till the Address Registration finally shows on those routes.

   [RFC8505] introduces error Status values in the NA(EARO) which can be
   received synchronously upon an NS(EARO) or asynchronously.  The RUL
   needs to support both cases and should refrain from using the address
   when the Status Value indicates a rejection (see Section 6.3).



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5.2.  Support of IPv6 Encapsulation

   Section 2.1 of [USEofRPLinfo] defines the rules for tunneling either
   to the final destination (e.g., a RUL) or to its attachment Router
   (designated as 6LR).  To terminate the IP-in-IP tunnel, the RUL, as
   an IPv6 Host, must be able to decapsulate the tunneled packet and
   either drop the inner packet if it is not the final destination, or
   pass it to the upper layer for further processing.  Unless it is
   aware by other means that the RUL can handle IP-in-IP properly, which
   is not mandated by [RFC8504], the Root terminates the IP-in-IP tunnel
   at the parent 6LR.  It is thus not necessary for a RUL to support IP-
   in-IP decapsulation.

5.3.  Support of the HbH Header

   A RUL is expected to process an Option Type in a Hop-by-Hop Header as
   prescribed by section 4.2 of [RFC8200].  An RPI with an Option Type
   of 0x23 [USEofRPLinfo] is thus skipped when not recognized.

5.4.  Support of the Routing Header

   A RUL is expected to process an unknown Routing Header Type as
   prescribed by section 4.4 of [RFC8200].  This implies that the Source
   Routing Header with a Routing Type of 3 [RFC6554] is ignored when the
   Segments Left is zero, and the packet is dropped otherwise.

6.  Enhancements to RFC 6550

   This document specifies a new behavior whereby a 6LR injects DAO
   messages for unicast addresses (see Section 9) and multicast
   addresses (see Section 10) on behalf of leaves that are not aware of
   RPL.  The RUL addresses are exposed as external targets [RFC6550].
   Conforming to [USEofRPLinfo], an IP-in-IP encapsulation between the
   6LR and the RPL Root is used to carry the RPL artifacts and remove
   them when forwarding outside the RPL domain, e.g., to a RUL.

   This document also synchronizes the liveness monitoring at the Root
   and the 6LBR.  The same value of lifetime is used for both, and a
   single keep-alive message, the RPL DAO, traverses the RPL network.  A
   new behavior is introduced whereby the RPL Root proxies the EDAR
   message to the 6LBR on behalf of the 6LR (more in Section 8), for any
   Leaf node that implements the 6LN functionality in [RFC8505].









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   Section 6.7.7 of [RFC6550] introduces the RPL Target Option, which
   can be used in RPL Control messages such as the DAO message to signal
   a destination prefix.  This document adds the capabilities to
   transport the ROVR field (see Section 4.2.3) and the IPv6 Address of
   the prefix advertiser when the Target is a shorter prefix.  Their use
   is signaled respectively by a new ROVR Size field being non-zero and
   a new "Advertiser address in Full" 'F' flag set, more in Section 6.1.

   This specification defines the new "Root Proxies EDAR/EDAC" (P) flag
   and encodes it in one of these reserved flags of the RPL DODAG
   Configuration option, more in Section 6.2.

   The RPL Status defined in section 6.5.1 of [RFC6550] for use in the
   DAO-ACK message is extended to be placed in DCO messages
   [EFFICIENT-NPDAO] as well.  Furthermore, this specification enables
   to carry the EARO Status defined for 6LoWPAN ND in RPL DAO and DCO
   messages, embedded in a RPL Status, more in Section 6.3.

6.1.  Updated RPL Target Option

   This specification updates the RPL Target Option to transport the
   ROVR that was also defined for 6LoWPAN ND messages.  This enables the
   RPL Root to generate the proxied EDAR message to the 6LBR.

   The new 'F' flag is set to indicate that the Target Prefix field
   contains the IPv6 address of the advertising node, in which case the
   length of the Target Prefix field is 128 bits regardless of the value
   of the Prefix Length field.  If the 'F' flag is reset, the Target
   Prefix field MUST be aligned to the next byte boundary after the size
   (expressed in bits) indicated by the Prefix Length field.  Padding
   bits are reserved and set to 0 per section 6.7.7 of [RFC6550].

   With this specification the ROVR is the remainder of the RPL Target
   Option.  The size of the ROVR is indicated in a new ROVR Size field
   that is encoded to map one-to-one with the Code Suffix in the EDAR
   message (see table 4 of [RFC8505]).  The ROVR Size field is taken
   from the flags field, which is an update to the RPL Target Option
   Flags IANA registry.

   The updated format is illustrated in Figure 3.  It is backward
   compatible with the Target Option in [RFC6550].  It SHOULD be used as
   a replacement in new implementations in all MOPs in preparation for
   upcoming Route Ownership Validation mechanisms based on the ROVR,
   unless the device or the network is so constrained that this is not
   feasible.






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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x05 | Option Length |ROVRsz |F|Flags| Prefix Length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                Target Prefix (Variable Length)                |
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
     ...            Registration Ownership Verifier (ROVR)           ...
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 3: Updated Target Option

   New fields:

   ROVRsz (ROVR Size):  Indicates the Size of the ROVR.  It MAY be 1, 2,
      3, or 4, indicating a ROVR size of 64, 128, 192, or 256 bits,
      respectively.  A value if 0 thus denotes a legacy Target Option.

   F:  1-bit flag.  Set to indicate that Target Prefix field contains an
      address of prefix advertiser in full.

   Registration Ownership Verifier (ROVR):  This is the same field as in
      the EARO, see [RFC8505]

6.2.  New Flag in the RPL DODAG Configuration Option

   The DODAG Configuration Option is defined in Section 6.7.6 of
   [RFC6550].  Its purpose is extended to distribute configuration
   information affecting the construction and maintenance of the DODAG,
   as well as operational parameters for RPL on the DODAG, through the
   DODAG.  As shown in Figure 4, the Option was originally designed with
   4 bit positions reserved for future use as Flags.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Type = 0x04 |Opt Length = 14| |P| | |A|       ...           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                     +
                                     <- Flags ->

            Figure 4: DODAG Configuration Option (Partial View)






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   This specification defines a new flag "Root Proxies EDAR/EDAC" (P).
   The 'P' bit is encoded in position 1 of the reserved Flags in the
   DODAG Configuration Option (counting from bit 0 as the most
   significant bit) and set to 0 in legacy implementations as specified
   respectively in Sections 20.14 and 6.7.6 of [RFC6550].

   The 'P' bit is set to indicate that the Root performs the proxy
   operation, which implies that it supports this specification and the
   updated RPL Target Option (see Section 6.1).

   Section 4.3 of [USEofRPLinfo] updates [RFC6550] to indicate that the
   definition of the Flags applies to Mode of Operation (MOP) values
   zero (0) to six (6) only.  For a MOP value of 7, the Root is expected
   to perform the proxy operation by default.

   The RPL DODAG Configuration Option is typically placed in a DODAG
   Information Object (DIO) message.  The DIO message propagates down
   the DODAG to form and then maintain its structure.  The DODAG
   Configuration Option is copied unmodified from parents to children.
   [RFC6550] states that "Nodes other than the DODAG Root MUST NOT
   modify this information when propagating the DODAG Configuration
   option".  Therefore, a legacy parent propagates the T Flag as set by
   the Root, and when the T Flag is set, it is transparently flooded to
   all the nodes in the DODAG.

6.3.  Updated RPL Status

   The RPL Status is defined in section 6.5.1 of [RFC6550] for use in
   the DAO-ACK message and values are assigned as follows:

               +---------+--------------------------------+
               | Range   | Meaning                        |
               +---------+--------------------------------+
               | 0       | Success/Unqualified acceptance |
               +---------+--------------------------------+
               | 1-127   | Not an outright rejection      |
               +---------+--------------------------------+
               | 128-255 | Rejection                      |
               +---------+--------------------------------+

                     Table 1: RPL Status per RFC 6550

   The 6LoWPAN ND Status was defined for use in the EARO, see section
   4.1 of [RFC8505].  This specification enables to carry the 6LoWPAN ND
   Status values in RPL DAO and DCO messages, embedded in the RPL Status
   field.





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   To achieve this, the range of the EARO Status values is reduced to
   0-63, which updates the IANA registry created for [RFC6775].  This
   reduction ensures that the values fit within a RPL Status as shown in
   Figure 5.  See Section 12.2, Section 12.5, and Section 12.6 for the
   respective IANA declarations.

                               0 1 2 3 4 5 6 7
                              +-+-+-+-+-+-+-+-+
                              |E|A|StatusValue|
                              +-+-+-+-+-+-+-+-+

                        Figure 5: RPL Status Format

   This specification updates the RPL Status with subfields as indicated
   below:

   E:  1-bit flag.  Set to indicate a rejection.  When not set, a Status
      Value of 0 indicates Success/Unqualified acceptance and other
      values indicate "not an outright rejection" as per RFC 6550.

   A:  1-bit flag.  Indicates the type of the RPL Status Value.

   Status Value:  6-bit unsigned integer.  If the 'A' flag is set this
      field transports a Status Value defined for IPv6 ND EARO.  When
      the 'A' flag is not set, the Status Value is defined for RPL.

   When building a DCO or a DAO-ACK message upon an IPv6 ND NA or a EDAC
   message, the RPL Root MUST copy the 6LoWPAN ND Status Code unchanged
   in the RPL Status Value and set the 'A' flag.  The RPL Root MUST set
   the 'E' flag for all rejection and unknown Status Codes.  The Status
   Codes in range 1-10 [RFC8505] are all considered rejections.

   Reciprocally, upon a DCO or a DAO-ACK message from the RPL Root with
   a RPL Status that has the 'A' flag set, the 6LR MUST copy the RPL
   Status Value unchanged in the Status field of the EARO when
   generating an NA to the RUL.

7.  Enhancements to draft-ietf-roll-efficient-npdao

   [EFFICIENT-NPDAO] defines the DCO message for RPL Storing Mode only,
   with a link-local scope.  All nodes in the RPL network are expected
   to support the specification since the message in processed hop by
   hop along the path this is being cleaned up.








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   This specification extends the use of the DCO message to the Non-
   Storing MOP, whereby the DCO is sent end-to-end by the Root directly
   to the RAN that injected the DAO message for the considered target.
   In that case, intermediate nodes do not need to support
   [EFFICIENT-NPDAO]; they forward the DCO message as a plain IPv6
   packet between the Root and the RAN.

   This specification leverages the Non-Storing DCO between the Root and
   the 6LR that serves as attachment Router for a RUL.  A 6LR and a Root
   that support this specification MUST implement the Non-Storing DCO.

8.  Enhancements to RFC 6775 and RFC8505

   This document updates [RFC6775] and [RFC8505] to reduce the range of
   the ND Status Codes down to 64 values.

   This document also changes the behavior of a 6LR acting as RPL Router
   and of a 6LN acting as RUL in the 6LoWPAN ND Address Registration as
   follows:

   *  If the RPL Root advertises the capability to proxy the EDAR/EDAC
      exchange to the 6LBR, the 6LR refrains from sending the keep-alive
      EDAR message.  If it is separated from the 6LBR, the Root
      regenerates the EDAR message to the 6LBR periodically, upon a DAO
      message that signals the liveliness of the address.

   *  The use of the R Flag is extended to the NA(EARO) to confirm
      whether the route was installed.

9.  Protocol Operations for Unicast Addresses

   The description below assumes that the Root sets the 'P' bit in the
   DODAG Configuration Option and performs the EDAR proxy operation.

   If the 'P' bit is reset, the 6LR MUST generate the periodic EDAR
   messages and process the returned status as specified in [RFC8505].
   If the EDAC indicates success, the rest of the flow takes place as
   presented but without the proxied EDAR/EDAC exchange.

   Section 9.1 provides an overview of the route injection in RPL,
   whereas Section 9.2 offers more details from the perspective of the
   different nodes involved in the flow.









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9.1.  General Flow

   This specification eliminates the need to exchange keep-alive
   Extended Duplicate Address messages, EDAR and EDAC, all the way from
   a 6LN to the 6LBR across a RPL mesh.  Instead, the EDAR/EDAC exchange
   with the 6LBR is proxied by the RPL Root upon the DAO message that
   refreshes the RPL routing state.  The first EDAR upon a new
   Registration cannot be proxied, though, as it serves for the purpose
   of DAD, which must be verified before the address is injected in RPL.

   In a RPL network where the function is enabled, refreshing the state
   in the 6LBR is the responsibility of the Root.  Consequently, only
   addresses that are injected in RPL will be kept alive at the 6LBR by
   the RPL Root.  Since RULs are advertised using Non-Storing Mode, the
   DAO message flow and the keep alive EDAR/EDAC can be nested within
   the Address (re)Registration flow.  Figure 6 illustrates that, for
   the first Registration, both the DAD and the keep-alive EDAR/EDAC
   exchanges happen in the same sequence.

           6LN/RUL   <-ND->   6LR   <-RPL->  Root   <-ND->     6LBR
              |                |              |                   |
              |   NS(EARO)     |              |                   |
              |--------------->|                                  |
              |                |          Extended DAR            |
              |                |--------------------------------->|
              |                |                                  |
              |                |          Extended DAC            |
              |                |<---------------------------------|
              |                |      DAO     |                   |
              |                |------------->|                   |
              |                |              |       EDAR        |
              |                |              |------------------>|
              |                |              |       EDAC        |
              |                |              |<------------------|
              |                |    DAO-ACK   |                   |
              |                |<-------------|                   |
              |   NA(EARO)     |              |                   |
              |<---------------|              |                   |
              |                |              |                   |

                   Figure 6: First RUL Registration Flow

   This flow requires that the lifetimes and sequence counters in
   6LoWPAN ND and RPL are aligned.

   ITo achieve this, the Path Sequence and the Path Lifetime in the DAO
   message are taken from the Transaction ID and the Address
   Registration lifetime in the NS(EARO) message from the 6LN.



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   On the first Address Registration, illustrated in Figure 6 for RPL
   Non-Storing Mode, the Extended Duplicate Address exchange takes place
   as prescribed by [RFC8505].  If the exchange fails, the 6LR returns
   an NA message with a negative status to the 6LN, the NCE is not
   created, and the address is not injected in RPL.  Otherwise, the 6LR
   creates an NCE and injects the Registered Address in the RPL routing
   using a DAO/DAO-ACK exchange with the RPL DODAG Root.

   An Address Registration refresh is performed by the 6LN to maintain
   the NCE in the 6LR alive before the lifetime expires.  Upon the
   refresh of a registration, the 6LR reinjects the corresponding route
   in RPL before it expires, as illustrated in Figure 7.

          6LN/RUL   <-ND->   6LR   <-RPL->  Root   <-ND->      6LBR
             |                |              |                   |
             |   NS(EARO)     |              |                   |
             |--------------->|              |                   |
             |                |      DAO     |                   |
             |                |------------->|                   |
             |                |              |       EDAR        |
             |                |              |------------------>|
             |                |              |       EDAC        |
             |                |              |<------------------|
             |                |    DAO-ACK   |                   |
             |                |<-------------|                   |
             |   NA(EARO)     |              |                   |
             |<---------------|              |                   |

                    Figure 7: Next RUL Registration Flow

   This is what causes the RPL Root to refresh the state in the 6LBR,
   using an EDAC message.  In case of an error in the proxied EDAR flow,
   the error is returned in the DAO-ACK using a RPL Status with the 'A'
   flag set that imbeds a 6LoWPAN Status Value as discussed in
   Section 6.3.

   The 6LR may receive a requested DAO-ACK after it received an
   asynchronous DCO, but the negative Status in the DCO supersedes a
   positive Status in the DAO-ACK regardless of the order in which they
   are received.  Upon the DAO-ACK - or the DCO if one arrives first -
   the 6LR responds to the RUL with an NA(EARO).

   An issue may be detected later, e.g., the address moves to a
   different DODAG with the 6LBR attached to a different 6LoWPAN
   Backbone Router (6BBR), see Figure 5 in section 3.3 of [6BBR].  The
   6BBR may send a negative ND status, e.g., in an asynchronous NA(EARO)
   to the 6LBR.




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   [6BBR] expects that the 6LBR is collocated with the RPL Root, but if
   not, the 6LBR MUST forward the Status Code to the originator of the
   EDAR, either the 6LR or the RPL Root that proxies for it.  The ND
   Status Code is mapped in a RPL Status Value by the RPL Root, and then
   back by the 6LR.

   Figure 8 illustrates this in the case where the 6LBR and the Root are
   not collocated, and the Root proxies the EDAR messages.

      6LN/RUL  <-ND->  6LR  <-RPL->  Root  <-ND->  6LBR  <-ND->  6BBR
         |              |             |              |             |
         |              |             |              |   NA(EARO)  |
         |              |             |              |<------------|
         |              |             |     EDAC     |             |
         |              |             |<-------------|             |
         |              |     DCO     |              |             |
         |              |<------------|              |             |
         |   NA(EARO)   |             |              |             |
         |<-------------|             |              |             |
         |              |             |              |             |

                        Figure 8: Asynchronous Issue

   If the Root does not proxy, then the EDAC with a negative status
   reaches the 6LR directly.  In that case, the 6LR MUST clean up the
   route using a DAO with a Lifetime of zero, and it MUST propagate the
   status back to the RUL in a NA(EARO) with the R Flag not set.

   The RUL may terminate the registration at any time by using a
   Registration Lifetime of 0.  This specification requires that the RPL
   Target Option transports the ROVR.  This way, the same flow as the
   heartbeat flow is sufficient to inform the 6LBR using the Root as
   proxy, as illustrated in Figure 7.

   Any combination of the logical functions of 6LR, Root, and 6LBR might
   be collapsed in a single node.

9.2.  Detailed Operation

9.2.1.  Perspective of the 6LN Acting as RUL

   This specification does not alter the operation of a 6LoWPAN ND-
   compliant 6LN/RUL, which is expected to operate as follows:

   1.  The 6LN obtains an IPv6 global address, either using Stateless
       Address Autoconfiguration (SLAAC) [RFC4862] based on a Prefix
       Information Option (PIO) [RFC4861] found in an RA message, or
       some other means, such as DHCPv6 [RFC8415].



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   2.  Once it has formed an address, the 6LN registers its address and
       refreshes its registration periodically, early enough within the
       Lifetime of the previous Address Registration, as prescribed by
       [RFC6775], to refresh the NCE before the lifetime indicated in
       the EARO expires.  It MUST set the T Flag.  The TID is
       incremented each time and wraps in a lollipop fashion (see
       section 5.2.1 of [RFC8505], which is fully compatible with
       section 7.2 of [RFC6550]).

   3.  As stated in section 5.2 of [RFC8505], the 6LN can register to
       more than one 6LR at the same time.  In that case, it uses the
       same EARO for all of the parallel Address Registrations, with the
       exception of the Registration Lifetime field and the setting of
       the R flag that may differ.  The 6LN SHOULD send the NS(EARO), if
       any, that maintain a registration active (i.e., with a non-zero
       Registration Lifetime) and ensure that one succeeds before it
       sends an NS(EARO) that terminates another registration, to avoid
       the churn related to transient route invalidation in the RPL
       network.

   4.  Following section 5.1 of [RFC8505], a 6LN acting as a RUL sets
       the R Flag in the EARO of its registration(s) for which it
       requires routing services.  If the R Flag is not echoed in the
       NA, the RUL SHOULD attempt to use another 6LR.  The RUL SHOULD
       send the registration(s) with the R Flag set and ensure that one
       succeeds before it sends the registrations with the flag reset.
       In case of a conflict with the preceding rule on lifetime, the
       rule on lifetime has precedence.

   5.  The 6LN may use any of the 6LRs to which it registered as the
       default gateway.  Using a 6LR to which the 6LN is not registered
       may result in packets dropped at the 6LR by a Source Address
       Validation function (SAVI) [RFC7039] so it is not recommended.

   Even without support for RPL, the RUL may be configured with an
   opaque value to be provided to the routing protocol.  If the RUL has
   knowledge of the RPL Instance the packet should be injected into,
   then it SHOULD set the Opaque field in the EARO to the RPLInstanceID,
   else it MUST leave the Opaque field to zero.

   Regardless of the setting of the Opaque field, the 6LN MUST set the
   "I" field to zero to signal "topological information to be passed to
   a routing process", as specified in section 5.1 of [RFC8505].








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   A RUL is not expected to produce RPL artifacts in the data packets,
   but it may do so.  For instance, if the RUL has minimal awareness of
   the RPL Instance then it can build an RPI.  A RUL that places an RPI
   in a data packet MUST indicate the RPLInstanceID of the RPL Instance
   where the packet should be forwarded.  All the flags and the Rank
   field are set to zero as specified by section 11.2 of [RFC6550].

9.2.2.  Perspective of the 6LR Acting as Border Router

   As prescribed by [RFC8505], the 6LR generates an EDAR message upon
   reception of a valid NS(EARO) message for the registration of a new
   IPv6 address by a 6LN.  If the initial EDAR/EDAC exchange succeeds,
   then the 6LR installs an NCE for the Registration Lifetime.  For the
   registration refreshes, if the RPL Root has indicated that it proxies
   the keep-alive EDAR/EDAC exchange with the 6LBR (see Section 6), the
   6LR MUST refrain from sending the keep-alive EDAR.

   If the R Flag is set in the NS(EARO), the 6LR SHOULD inject the Host
   route in RPL, unless this is barred for other reasons, such as the
   saturation of the RPL parents.  The 6LR MUST use a RPL Non-Storing
   Mode signaling and the updated Target Option (see Section 6.1).  The
   6LR MUST request a DAO-ACK by setting the 'K' flag in the DAO
   message.  Success injecting the route to the RUL's address is
   indicated by the 'E' flag set to 0 in the RPL status of the DAO-ACK
   message.

   The Opaque field in the EARO provides a mean to signal which RPL
   Instance is to be used for the DAO advertisements and the forwarding
   of packets sourced at the Registered Address when there is no RPI in
   the packet.

   As described in [RFC8505], if the "I" field is zero, then the Opaque
   field is expected to carry the RPLInstanceID suggested by the 6LN;
   otherwise, there is no suggested Instance.  If the 6LR participates
   in the suggested RPL Instance, then the 6LR MUST use that RPL
   Instance for the Registered Address.

   If there is no suggested RPL Instance or else if the 6LR does not
   participate to the suggested Instance, it is expected that the
   packets coming from the 6LN "can unambiguously be associated to at
   least one RPL Instance" [RFC6550] by the 6LR.

   The DAO message advertising the Registered Address MUST be
   constructed as follows:







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   1.  The Registered Address is signaled as the Target Prefix in the
       updated Target Option in the DAO message; the Prefix Length is
       set to 128 but the 'F' flag is not set since the advertiser is
       not the RUL.  The ROVR field is copied unchanged from the EARO
       (see Section 6.1).

   2.  The 6LR indicates one of its global or unique-local IPv6 unicast
       addresses as the Parent Address in the RPL Transit Information
       Option (TIO) associated with the Target Option

   3.  The 6LR sets the External 'E' flag in the TIO to indicate that it
       is redistributing an external target into the RPL network

   4.  the Path Lifetime in the TIO is computed from the Registration
       Lifetime in the EARO.  This operation converts seconds to the
       Lifetime Units used in the RPL operation.  This creates the
       deployment constraint that the Lifetime Unit is reasonably
       compatible with the expression of the Registration Lifetime.
       e.g., a Lifetime Unit of 0x4000 maps the most significant byte of
       the Registration Lifetime to the Path Lifetime.

       In that operation, the Path Lifetime must be rounded, if needed,
       to the upper value to ensure that the path has a longer lifetime
       than the registration.

       Note that if the Registration Lifetime is 0, then the Path
       Lifetime is also 0 and the DAO message becomes a No-Path DAO,
       which cleans up the routes down to the RUL's address; this also
       causes the Root as a proxy to send an EDAR message to the 6LBR
       with a Lifetime of 0.

   5.  the Path Sequence in the TIO is set to the TID value found in the
       EARO option.

   Upon receiving or timing out the DAO-ACK after an implementation-
   specific number of retries, the 6LR MUST send the corresponding
   NA(EARO) to the RUL.  Upon receiving an asynchronous DCO message, if
   a DAO-ACK is pending then the 6LR MUST wait for the DAO-ACK to send
   the NA(EARO) and deliver the status found in the DCO, else it MUST
   send an asynchronous NA(EARO) to the RUL immediately.

   The 6LR MUST set the R Flag in the NA(EARO) back if and only if the
   'E' flag is reset, indicating that the 6LR injected the Registered
   Address in the RPL routing successfully and that the EDAR proxy
   operation succeeded.






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   If the 'A' flag in the RPL Status is set, the embedded Status Value
   is passed back to the RUL in the EARO Status.  If the 'E' flag is
   also set, the registration failed for 6LoWPAN ND related reasons, and
   the NCE is removed.

   An error injecting the route causes the 'E' flag to be set.  If the
   error is not related to ND, the 'A' flag is not set.  In that case,
   the registration succeeds, but the RPL route is not installed.  So
   the NA(EARO) is returned with a positive status but the R Flag not
   set, which means that the 6LN obtained a binding but no route.

   If the 'A' flag is not set in the RPL Status of the DAO-ACK, then the
   6LoWPAN ND operation succeeded, and an EARO Status of 0 (Success)
   MUST be returned to the 6LN.  The EARO Status of 0 MUST also be used
   if the 6LR did not attempt to inject the route but could create the
   binding after a successful EDAR/EDAC exchange or refresh it.

   If the 'E' flag is set in the RPL Status of the DAO-ACK, then the
   route was not installed and the R flag MUST NOT be set in the
   NA(EARO).  The R flag MUST NOT be set if the 6LR did not attempt to
   inject the route.

   In a network where Address Protected Neighbor Discovery (AP-ND) is
   enabled, in case of a DAO-ACK or a DCO indicating transporting an
   EARO Status Value of 5 (Validation Requested), the 6LR MUST challenge
   the 6LN for ownership of the address, as described in section 6.1 of
   [AP-ND], before the Registration is complete.  This flow, illustrated
   in Figure 9, ensures that the address is validated before it is
   injected in the RPL routing.

   If the challenge succeeds, then the operations continue as normal.
   In particular, a DAO message is generated upon the NS(EARO) that
   proves the ownership of the address.  If the challenge failed, the
   6LR rejects the registration as prescribed by AP-ND and may take
   actions to protect itself against DoS attacks by a rogue 6LN, see
   Section 11.















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   6LN                                       6LR        Root        6LBR
    |                                         |           |           |
    |<--------------- RA ---------------------|           |           |
    |                                         |           |           |
    |------ NS EARO (ROVR=Crypto-ID) -------->|           |           |
    |                                         |           |           |
    |<- NA EARO(status=Validation Requested) -|           |           |
    |                                         |           |           |
    |----- NS EARO and Proof-of-ownership  -->|                       |
    |                                         |--------- EDAR ------->|
    |                                         |                       |
    |                                         |<-------- EDAC --------|
    |                                         |                       |
    |                                         |           |           |
    |                                         |-- DAO --->|           |
    |                                         |           |-- EDAR -->|
    |                                         |           |           |
    |                                         |           |<-- EDAC --|
    |                                         |<- DAO-ACK-|           |
    |                                         |           |           |
    |<----------- NA EARO (status=0)----------|           |           |
    |                                         |           |           |
                                        ...
    |                                         |           |           |
    |------ NS EARO (ROVR=Crypto-ID) -------->|           |           |
    |                                         |-- DAO --->|           |
    |                                         |           |-- EDAR -->|
    |                                         |           |           |
    |                                         |           |<-- EDAC --|
    |                                         |<- DAO-ACK-|           |
    |<----------- NA EARO (status=0)----------|           |           |
    |                                         |           |           |
                                        ...

                        Figure 9: Address Protection

   The 6LR may at any time send a unicast asynchronous NA(EARO) with the
   R Flag reset to signal that it stops providing routing services, and/
   or with the EARO Status 2 "Neighbor Cache full" to signal that it
   removes the NCE.  It may also send a final RA, unicast or multicast,
   with a Router Lifetime field of zero, to signal that it stops serving
   as Router, as specified in section 6.2.5 of [RFC4861].  This may
   happen upon a DCO or a DAO-ACK message indicating the path is already
   removed; else the 6LR SHOULD remove the Host route to the 6LN using a
   DAO message with a Path Lifetime of zero.






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   A valid NS(EARO) message with the R Flag not set and a Registration
   Lifetime that is not zero signals that the 6LN wishes to maintain the
   binding but does not require the routing services from the 6LR (any
   more).  Upon this message, if, due to previous NS(EARO) with the R
   Flag set, the 6LR was injecting the Host route to the Registered
   Address in RPL using DAO messages, then the 6LR MUST invalidate the
   Host route in RPL using a DAO with a Path Lifetime of zero.  It is up
   to the Registering 6LN to maintain the corresponding route from then
   on, either keeping it active via a different 6LR or by acting as a
   RAN and managing its own reachability.

9.2.3.  Perspective of the RPL Root

   A RPL Root MUST set the 'P' bit in the RPL DODAG Configuration Option
   of the DIO messages that it generates (see Section 6) to signal that
   it proxies the EDAR/EDAC exchange and supports the Updated RPL Target
   option.

   Upon reception of a DAO message, for each updated RPL Target Option
   (see Section 6.1) that creates or updates an existing RPL state, the
   Root MUST notify the 6LBR by using a proxied EDAR/EDAC exchange.  If
   if the RPL Root and the 6LBR are integrated, an internal API can be
   used.

   The EDAR message MUST be constructed as follows:

   1.  The Target IPv6 address from the RPL Target Option is placed in
       the Registered Address field of the EDAR message;

   2.  the Registration Lifetime is adapted from the Path Lifetime in
       the TIO by converting the Lifetime Units used in RPL into units
       of 60 seconds used in the 6LoWPAN ND messages;

   3.  the TID value is set to the Path Sequence in the TIO and
       indicated with an ICMP code of 1 in the EDAR message;

   4.  The ROVR in the RPL Target Option is copied as is in the EDAR and
       the ICMP Code Suffix is set to the appropriate value as shown in
       Table 4 of [RFC8505] depending on the size of the ROVR field.

   Upon receiving an EDAC message from the 6LBR, if a DAO is pending,
   then the Root MUST send a DAO-ACK back to the 6LR.  Else, if the
   Status in the EDAC message is not "Success", then it MUST send an
   asynchronous DCO to the 6LR.

   In either case, the EDAC Status is embedded in the RPL Status with
   the 'A' flag set.




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   The proxied EDAR/EDAC exchange MUST be protected with a timer of an
   appropriate duration and a number of retries, that are
   implementation-dependent, and SHOULD be configurable since the Root
   and the 6LBR are typically nodes with a higher capacity and
   manageability than 6LRs.  Upon timing out, the Root MUST send an
   error back to the 6LR as above, either using a DAO-ACK or a DCO, as
   appropriate, with the 'A' and 'E' flags set in the RPL status, and a
   RPL Status Value of of "6LBR Registry Saturated" [RFC8505].

9.2.4.  Perspective of the 6LBR

   The 6LBR is unaware that the RPL Root is not the new attachment 6LR
   of the RUL, so it is not impacted by this specification.

   Upon reception of an EDAR message, the 6LBR acts as prescribed by
   [RFC8505] and returns an EDAC message to the sender.

10.  Protocol Operations for Multicast Addresses

   Section 12 of [RFC6550] details the RPL support for multicast flows.
   This support is not source-specific and only operates as an extension
   to the Storing Mode of Operation for unicast packets.  Note that it
   is the RPL model that the multicast packet is passed as a Layer-2
   unicast to each of the interested children.  This remains true when
   forwarding between the 6LR and the listener 6LN.

   "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810]
   provide an interface for a listener to register to multicast flows.
   In the MLD model, the Router is a "querier", and the Host is a
   multicast listener that registers to the querier to obtain copies of
   the particular flows it is interested in.

   The equivalent of the first Address Registration happens as
   illustrated in Figure 10.  The 6LN, as an MLD listener, sends an
   unsolicited Report to the 6LR.  This enables it to start receiving
   the flow immediately, and causes the 6LR to inject the multicast
   route in RPL.

   This specification does not change MLD but will operate more
   efficiently if the asynchronous messages for unsolicited Report and
   Done are sent by the 6LN as Layer-2 unicast to the 6LR, in particular
   on wireless.

   The 6LR acts as a generic MLD querier and generates a DAO with the
   Multicast Address as the Target Prefix as described in section 12 of
   [RFC6550].  As for the Unicast Host routes, the Path Lifetime
   associated to the Target is mapped from the Query Interval, and set
   to be larger to account for variable propagation delays to the Root.



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   The Root proxies the MLD exchange as a listener with the 6LBR acting
   as the querier, so as to get packets from a source external to the
   RPL domain.

   Upon a DAO with a Target option for a multicast address, the RPL Root
   checks if it is already registered as a listener for that address,
   and if not, it performs its own unsolicited Report for the multicast
   address as sescribed in section 5.1 of [RFC3810].  The report is
   source independent, so there is no Source Address listed.

      6LN/RUL                6LR             Root                   6LBR
         |                    |               |                       |
         | unsolicited Report |               |                       |
         |------------------->|               |                       |
         |     <L2 ack>       |               |                       |
         |                    | DAO           |                       |
         |                    |-------------->|                       |
         |                    |    DAO-ACK    |                       |
         |                    |<--------------|                       |
         |                    |               | <if not done already> |
         |                    |               |  unsolicited Report   |
         |                    |               |---------------------->|
         |                    |               |                       |

                Figure 10: First Multicast Registration Flow

   The equivalent of the registration refresh is pulled periodically by
   the 6LR acting as querier.  Upon the timing out of the Query
   Interval, the 6LR sends a Multicast Address Specific Query to each of
   its listeners, for each Multicast Address, and gets a Report back
   that is mapped into a DAO one by one.  Optionally, the 6LR MAY send a
   General Query, where the Multicast Address field is set to zero.  In
   that case, the multicast packet is passed as a Layer-2 unicast to
   each of the interested children. .

   Upon a Report, the 6LR generates a DAO with as many Target Options as
   there are Multicast Address Records in the Report message, copying
   the Multicast Address field in the Target Prefix of the RPL Target
   Option.  The DAO message is a Storing Mode DAO, passed to a selection
   of the 6LR's parents.

   Asynchronously to this, a similar procedure happens between the Root
   and a router such as the 6LBR that serves multicast flows on the Link
   where the Root is located.  Again the Query and Report messages are
   source independent.  The Root lists exactly once each Multicast
   Address for which it has at least one active multicast DAO state,
   copying the multicast address in the DAO state in the Multicast
   Address field of the Multicast Address Records in the Report message.



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   This is illustrated in Figure 11:

      6LN/RUL                6LR             Root                6LBR
         |                    |               |                    |
         |       Query        |               |                    |
         |<-------------------|               |                    |
         |       Report       |               |                    |
         |------------------->|               |                    |
         |                    | DAO           |                    |
         |                    |-------------->|                    |
         |                    |    DAO-ACK    |                    |
         |                    |<--------------|                    |
         |                    |               |       Query        |
         |                    |               |<-------------------|
         |                    |               |       Report       |
         |                    |               |------------------->|
         |                    |               |                    |

                     Figure 11: Next Registration Flow

   Note that any of the functions 6LR, Root and 6LBR might be collapsed
   in a single node, in which case the flow above happens internally,
   and possibly through internal API calls as opposed to messaging.

11.  Security Considerations

   It is worth noting that with [RFC6550], every node in the LLN is RPL-
   aware and can inject any RPL-based attack in the network.  This
   specification isolates edge nodes that can only interact with the RPL
   Routers using 6LoWPAN ND, meaning that they cannot perform RPL
   insider attacks.

   The LLN nodes depend on the 6LBR and the RPL participants for their
   operation.  A trust model must be put in place to ensure that the
   right devices are acting in these roles, so as to avoid threats such
   as black-holing, (see [RFC7416] section 7), Denial-Of-Service attacks
   whereby a rogue 6LR creates a high churn in the RPL network by
   advertising and removing many forged addresses, or bombing attack
   whereby an impersonated 6LBR would destroy state in the network by
   using the "Removed" Status code.

   This trust model could be at a minimum based on a Layer-2 Secure
   joining and the Link-Layer security.  This is a generic 6LoWPAN
   requirement, see Req5.1 in Appendix of [RFC8505].

   In a general manner, the Security Considerations in [RFC7416]
   [RFC6775], and [RFC8505] apply to this specification as well.




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   The Link-Layer security is needed in particular to prevent Denial-Of-
   Service attacks whereby a rogue 6LN creates a high churn in the RPL
   network by constantly registering and deregistering addresses with
   the R Flag set in the EARO.

   [AP-ND] updated 6LoWPAN ND with the called Address-Protected Neighbor
   Discovery (AP-ND).  AP-ND protects the owner of an address against
   address theft and impersonation attacks in a Low-Power and Lossy
   Network (LLN).  Nodes supporting th extension compute a cryptographic
   identifier (Crypto-ID), and use it with one or more of their
   Registered Addresses.  The Crypto-ID identifies the owner of the
   Registered Address and can be used to provide proof of ownership of
   the Registered Addresses.  Once an address is registered with the
   Crypto-ID and a proof of ownership is provided, only the owner of
   that address can modify the registration information, thereby
   enforcing Source Address Validation.  [AP-ND] reduces even more the
   attack perimeter that is available to the edge nodes and its use is
   suggested in this specification.

   Additionally, the trust model could include a role validation to
   ensure that the node that claims to be a 6LBR or a RPL Root is
   entitled to do so.

   The Opaque field in the EARO enables the RUL to suggest a
   RPLInstanceID where its traffic is placed.  This opens to attacks
   where a RPL instance would be reserved for critical traffic, e.g.,
   with a specific bandwidth reservation, that the additional traffic
   generated by a rogue may disrupt.  This may be alleviated by
   traditional access control mechanisms where the 6LR shapes the
   incoming traffic from the 6LN.

   At the time of this writing, RPL does not have a Route Ownership
   Validation model whereby it is possible to validate the origin of an
   address that is injected in a DAO.  This specification makes a first
   step in that direction by allowing the Root to challenge the RUL via
   the 6LR that serves it.

   [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor
   node to invalidate a route on behalf of the target node.  In that
   case, the RPL Status in the DCO has the 'A' flag not set, and a
   NA(EARO) is returned to the 6LN with the R flag not set.  This
   encourages the 6LN to try another 6LR.  If a 6LR exists that does not
   use the rogue common ancestor, then the 6LN will eventually succeed
   gaining reachability over the RPL network in spite of the rogue node.







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12.  IANA Considerations

12.1.  Fixing the Address Registration Option Flags

   Section 9.1 of [RFC8505] creates a Registry for the 8-bit Address
   Registration Option Flags field.  IANA is requested to rename the
   first column of the table from "ARO Status" to "Bit number".

12.2.  Resizing the ARO Status values

   Section 12 of [RFC6775] creates the Address Registration Option
   Status Values Registry with a range 0-255.

   This specification reduces that range to 0-63, see Section 6.3.

   IANA is requested modify the Address Registration Option Status
   Values Registry so that the upper bound of the unassigned values is
   63.  This document should be added as a reference.  The registration
   procedure does not change.

12.3.  New DODAG Configuration Option Flag

   This specification updates the Registry that was created for
   [RFC6550] as the registry for "DODAG Configuration Option Flags" and
   updated as the registry for "DODAG Configuration Option Flags for MOP
   0..6" by [USEofRPLinfo], by allocating one new Flag as follows:

        +---------------+----------------------------+-----------+
        | Bit Number    | Capability Description     | Reference |
        +---------------+----------------------------+-----------+
        | 1 (suggested) | Root Proxies EDAR/EDAC (P) | THIS RFC  |
        +---------------+----------------------------+-----------+

               Table 2: New DODAG Configuration Option Flag

12.4.  RPL Target Option Registry

   Section 20.15 of [RFC6550] creates a Registry for the 8-bit "RPL
   Target Option Flags" field.  IANA is requested to reduce the size of
   the field in the Registry to 4 bits.  Section 6.1 also defines a new
   entry in the Registry as follows:










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      +---------------+--------------------------------+-----------+
      | Bit Number    | Capability Description         | Reference |
      +---------------+--------------------------------+-----------+
      | 1 (suggested) | Advertiser address in Full (F) | THIS RFC  |
      +---------------+--------------------------------+-----------+

                   Table 3: RPL Target Option Registry

12.5.  New Subregistry for the RPL Non-Rejection Status values

   This specification creates a new Subregistry for the RPL Non-
   Rejection Status values for use in the RPL DAO-ACK and DCO messages
   with the 'A' flag reset, under the RPL registry.

   *  Possible values are 6-bit unsigned integers (0..63).

   *  Registration procedure is "IETF Review" [RFC8126].

   *  Initial allocation is as indicated in Table 4:

         +-------+--------------------------+-------------------+
         | Value | Meaning                  | Reference         |
         +-------+--------------------------+-------------------+
         | 0     | Unqualified acceptance   | THIS RFC          |
         +-------+--------------------------+-------------------+
         | 1     | No routing-entry for the | [EFFICIENT-NPDAO] |
         |       | indicated Target found   |                   |
         +-------+--------------------------+-------------------+

               Table 4: Acceptance values of the RPL Status

12.6.  New Subregistry for the RPL Rejection Status values

   This specification creates a new Subregistry for the RPL Rejection
   Status values for use in the RPL DAO-ACK and DCO messages with the
   'A' flag reset, under the RPL registry.

   *  Possible values are 6-bit unsigned integers (0..63).

   *  Registration procedure is "IETF Review" [RFC8126].

   *  Initial allocation is as indicated in Table 5:









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               +-------+-----------------------+-----------+
               | Value | Meaning               | Reference |
               +-------+-----------------------+-----------+
               | 0     | Unqualified rejection | THIS RFC  |
               +-------+-----------------------+-----------+

                Table 5: Rejection values of the RPL Status

13.  Acknowledgments

   The authors wish to thank Ines Robles, Georgios Papadopoulos and
   especially Rahul Jadhav and Alvaro Retana for their reviews and
   contributions to this document.

14.  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>.

   [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>.

   [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>.

   [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>.

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




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

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

   [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>.

   [RFC8504]  Chown, T., Loughney, J., and T. Winters, "IPv6 Node
              Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
              January 2019, <https://www.rfc-editor.org/info/rfc8504>.

   [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>.

   [AP-ND]    Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
              "Address Protected Neighbor Discovery for Low-power and
              Lossy Networks", Work in Progress, Internet-Draft, draft-
              ietf-6lo-ap-nd-23, 30 April 2020,
              <https://tools.ietf.org/html/draft-ietf-6lo-ap-nd-23>.

   [USEofRPLinfo]
              Robles, 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", Work in
              Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-41,
              21 September 2020, <https://tools.ietf.org/html/draft-
              ietf-roll-useofrplinfo-41>.









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   [EFFICIENT-NPDAO]
              Jadhav, R., Thubert, P., Sahoo, R., and Z. Cao, "Efficient
              Route Invalidation", Work in Progress, Internet-Draft,
              draft-ietf-roll-efficient-npdao-18, 15 April 2020,
              <https://tools.ietf.org/html/draft-ietf-roll-efficient-
              npdao-18>.

15.  Informative References

   [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>.

   [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>.

   [RFC6553]  Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
              Power and Lossy Networks (RPL) Option for Carrying RPL
              Information in Data-Plane Datagrams", RFC 6553,
              DOI 10.17487/RFC6553, March 2012,
              <https://www.rfc-editor.org/info/rfc6553>.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
              Routing Header for Source Routes with the Routing Protocol
              for Low-Power and Lossy Networks (RPL)", RFC 6554,
              DOI 10.17487/RFC6554, March 2012,
              <https://www.rfc-editor.org/info/rfc6554>.

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

   [RFC7039]  Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
              "Source Address Validation Improvement (SAVI) Framework",
              RFC 7039, DOI 10.17487/RFC7039, October 2013,
              <https://www.rfc-editor.org/info/rfc7039>.

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




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   [RFC8138]  Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
              "IPv6 over Low-Power Wireless Personal Area Network
              (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
              April 2017, <https://www.rfc-editor.org/info/rfc8138>.

   [RFC8415]  Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
              RFC 8415, DOI 10.17487/RFC8415, November 2018,
              <https://www.rfc-editor.org/info/rfc8415>.

   [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>.

   [RFC6687]  Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur,
              Ed., "Performance Evaluation of the Routing Protocol for
              Low-Power and Lossy Networks (RPL)", RFC 6687,
              DOI 10.17487/RFC6687, October 2012,
              <https://www.rfc-editor.org/info/rfc6687>.

   [RFC7416]  Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
              and M. Richardson, Ed., "A Security Threat Analysis for
              the Routing Protocol for Low-Power and Lossy Networks
              (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
              <https://www.rfc-editor.org/info/rfc7416>.

   [RFC8025]  Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
              RFC 8025, DOI 10.17487/RFC8025, November 2016,
              <https://www.rfc-editor.org/info/rfc8025>.

   [6BBR]     Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
              Backbone Router", Work in Progress, Internet-Draft, draft-
              ietf-6lo-backbone-router-20, 23 March 2020,
              <https://tools.ietf.org/html/draft-ietf-6lo-backbone-
              router-20>.

Appendix A.  Example Compression

   Figure 12 illustrates the case in Storing Mode where the packet is
   received from the Internet, then the Root encapsulates the packet to
   insert the RPI and deliver to the 6LR that is the parent and last hop
   to the final destination, which is not known to support [RFC8138].






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   +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-...
   |11110001|SRH-6LoRH| RPI-  |IP-in-IP| NH=1      |11110CPP| UDP | UDP
   |Page 1  |Type1 S=0| 6LoRH | 6LoRH  |LOWPAN_IPHC| UDP    | hdr |Payld
   +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-...
            <-4 bytes->                <-        RFC 6282        ->
                                       <-     No RPL artifact ...

           Figure 12: Encapsulation to Parent 6LR in Storing Mode

   The difference with the example presented in Figure 19 of [RFC8138]
   is the addition of a SRH-6LoRH before the RPI-6LoRH to transport the
   compressed address of the 6LR as the destination address of the outer
   IPv6 header.  In the [RFC8138] example the destination IP of the
   outer header was elided and was implicitly the same address as the
   destination of the inner header.  Type 1 was arbitrarily chosen, and
   the size of 0 denotes a single address in the SRH.

   In Figure 12, the source of the IP-in-IP encapsulation is the Root,
   so it is elided in the IP-in-IP 6LoRH.  The destination is the parent
   6LR of the destination of the inner packet so it cannot be elided.
   If the DODAG is operated in Storing Mode, it is the single entry in
   the SRH-6LoRH and the SRH-6LoRH Size is encoded as 0.  The SRH-6LoRH
   is the first 6LoRH in the chain.  In this particular example, the 6LR
   address can be compressed to 2 bytes so a Type of 1 is used.  It
   results that the total length of the SRH-6LoRH is 4 bytes.

   In Non-Storing Mode, the encapsulation from the Root would be similar
   to that represented in Figure 12 with possibly more hops in the SRH-
   6LoRH and possibly multiple SRH-6LoRHs if the various addresses in
   the routing header are not compressed to the same format.  Note that
   on the last hop to the parent 6LR, the RH3 is consumed and removed
   from the compressed form, so the use of Non-Storing Mode vs.  Storing
   Mode is indistinguishable from the packet format.

   The SRH-6LoRHs are followed by RPI-6LoRH and then the IP-in-IP 6LoRH.
   When the IP-in-IP 6LoRH is removed, all the 6LoRH Headers that
   precede it are also removed.  The Paging Dispatch [RFC8025] may also
   be removed if there was no previous Page change to a Page other than
   0 or 1, since the LOWPAN_IPHC is encoded in the same fashion in the
   default Page 0 and in Page 1.  The resulting packet to the
   destination is the inner packet compressed with [RFC6282].

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200



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   06254 Mougins - Sophia Antipolis
   France

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


   Michael C. Richardson
   Sandelman Software Works

   Email: mcr+ietf@sandelman.ca
   URI:   http://www.sandelman.ca/







































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