[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-thubert-roll-unaware-leaves) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

ROLL                                                     P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Updates: 6550, 6775, 8505 (if approved)                    M. Richardson
Intended status: Standards Track                               Sandelman
Expires: 15 July 2021                                    11 January 2021


                         Routing for RPL Leaves
                   draft-ietf-roll-unaware-leaves-29

Abstract

   This specification updates RFC6550, RFC6775, and RFC8505.  It
   provides a mechanism for a host that implements a routing-agnostic
   interface based on 6LoWPAN Neighbor Discovery to obtain reachability
   services across a network that leverages RFC6550 for its routing
   operations.

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 15 July 2021.

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
   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.



Thubert & Richardson      Expires 15 July 2021                  [Page 1]


Internet-Draft             RPL Unaware Leaves               January 2021


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   6
     2.2.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  References  . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  RPL External Routes and Dataplane Artifacts . . . . . . . . .   8
   4.  6LoWPAN Neighbor Discovery  . . . . . . . . . . . . . . . . .   9
     4.1.  RFC 6775 Address Registration . . . . . . . . . . . . . .   9
     4.2.  RFC 8505 Extended Address Registration  . . . . . . . . .  10
       4.2.1.  R Flag  . . . . . . . . . . . . . . . . . . . . . . .  10
       4.2.2.  TID, "I" Field and Opaque Fields  . . . . . . . . . .  11
       4.2.3.  Route Ownership Verifier  . . . . . . . . . . . . . .  11
     4.3.  RFC 8505 Extended DAR/DAC . . . . . . . . . . . . . . . .  11
       4.3.1.  RFC 7400 Capability Indication Option . . . . . . . .  12
   5.  Requirements on the RPL-Unware leaf . . . . . . . . . . . . .  13
     5.1.  Support of 6LoWPAN ND . . . . . . . . . . . . . . . . . .  13
     5.2.  Support of IPv6 Encapsulation . . . . . . . . . . . . . .  14
     5.3.  Support of the Hop-by-Hop Header  . . . . . . . . . . . .  14
     5.4.  Support of the Routing Header . . . . . . . . . . . . . .  14
   6.  Enhancements to RFC 6550  . . . . . . . . . . . . . . . . . .  14
     6.1.  Updated RPL Target Option . . . . . . . . . . . . . . . .  15
     6.2.  Additional Flag in the RPL DODAG Configuration Option . .  17
     6.3.  Updated RPL Status  . . . . . . . . . . . . . . . . . . .  18
   7.  Enhancements to draft-ietf-roll-efficient-npdao . . . . . . .  20
   8.  Enhancements to RFC6775 and RFC8505 . . . . . . . . . . . . .  20
   9.  Protocol Operations for Unicast Addresses . . . . . . . . . .  20
     9.1.  General Flow  . . . . . . . . . . . . . . . . . . . . . .  21
     9.2.  Detailed Operation  . . . . . . . . . . . . . . . . . . .  24
       9.2.1.  Perspective of the 6LN Acting as RUL  . . . . . . . .  24
       9.2.2.  Perspective of the 6LR Acting as Border router  . . .  25
       9.2.3.  Perspective of the RPL Root . . . . . . . . . . . . .  30
       9.2.4.  Perspective of the 6LBR . . . . . . . . . . . . . . .  31
   10. Protocol Operations for Multicast Addresses . . . . . . . . .  31
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  34
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
     12.1.  Fixing the Address Registration Option Flags . . . . . .  35
     12.2.  Resizing the ARO Status values . . . . . . . . . . . . .  36
     12.3.  New RPL DODAG Configuration Option Flag  . . . . . . . .  36
     12.4.  RPL Target Option Registry . . . . . . . . . . . . . . .  36
     12.5.  New Subregistry for RPL Non-Rejection Status values  . .  37
     12.6.  New Subregistry for RPL Rejection Status values  . . . .  37
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  38
   14. Normative References  . . . . . . . . . . . . . . . . . . . .  38
   15. Informative References  . . . . . . . . . . . . . . . . . . .  39
   Appendix A.  Example Compression  . . . . . . . . . . . . . . . .  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42



Thubert & Richardson      Expires 15 July 2021                  [Page 2]


Internet-Draft             RPL Unaware Leaves               January 2021


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 Multiple-Access (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 receive/originate
   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.




Thubert & Richardson      Expires 15 July 2021                  [Page 3]


Internet-Draft             RPL Unaware Leaves               January 2021


   Section 2 of [USEofRPLinfo] defines the terms RPL leaf, RPL-Aware-
   leaf (RAL) and RPL-Unaware Leaf (RUL).  A RPL leaf is a host attached
   to one or more RPL router(s); as such, it relies on the RPL router(s)
   to forward its traffic across the RPL domain but does not forward
   traffic from another node.  As opposed to the RAL, the RUL does not
   participate to RPL, and relies on its RPL router(s) also to inject
   the routes to its IPv6 addresses in the RPL domain.

   A RUL may be unable to participate because it is very energy-
   constrained, code-space constrained, or because it would be unsafe to
   let it inject routes in RPL.  Using 6LoWPAN ND as opposed to RPL as
   the host-to-router interface limits the surface of the possible
   attacks by the RUL against the RPL domain.  If all RULs and RANs use
   6LoWPAN ND for Neighbor Discovery, it is also possible to protect the
   address ownership of all nodes, including the RULs.

   This document specifies how the router injects the host routes in the
   RPL domain on behalf of the RUL.  Section 5 details how the RUL can
   leverage 6LoWPAN ND to obtain the routing services from the router.
   In that model, the RUL is also a 6LoWPAN Node (6LN) and the RPL-Aware
   router is also a 6LoWPAN Router (6LR).  Using the 6LoWPAN ND Address
   Registration mechanism, the RUL signals that the router must inject a
   host route for the Registered Address.

            ------+---------
                  |          Internet
                  |
               +-----+
               |     | <------------- 6LBR / RPL Root
               +-----+                     ^
                  |                        |
            o    o   o  o                  | RPL
        o o   o  o   o  o     o    o       |
       o  o o  o o    o   o  o   o  o      |  +
       o   o      o     o   o   o    o     |
      o  o   o  o   o  o    o    o  o      | 6LoWPAN ND
         o  o  o  o        o   o           |
        o       o            o    o        v
      o      o     o <------------- 6LR / RPL Border router
                                           ^
                                           | 6LoWPAN ND only
                                           v
                   u <------------- 6LN / RPL-Unaware Leaf

                Figure 1: Injecting Routes on behalf of RULs






Thubert & Richardson      Expires 15 July 2021                  [Page 4]


Internet-Draft             RPL Unaware Leaves               January 2021


   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 severely energy constrained 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 specification can be deployed incrementally in a network that
   implements [USEofRPLinfo].  Only the Root and the 6LRs that connect
   the RULs need to be upgraded.  The RPL routers on path will only see
   unicast IPv6 traffic between the Root and the 6LR.

   This document is organized as follows:

   *  Section 3 and Section 4 present in a non-normative fashion the
      salient aspects of RPL and 6LoWPAN ND, respectively, that are
      leveraged in this specification to provide connectivity to a 6LN
      acting as a RUL across a RPL network.

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

   *  Section 6 presents the changes made to [RFC6550]; a new behavior
      is introduced whereby the 6LR advertises the 6LN's addresses in a
      RPL DAO message based on the ND registration by the 6LN, and the
      RPL root performs the EDAR/EDAC exchange with the 6LoWPAN Border
      Router (6LBR) on behalf of the 6LR; modifications are introduced
      to some RPL options and to the RPL Status to facilitate the
      integration of the protocols.

   *  Section 7 presents the changes made to [EFFICIENT-NPDAO]; the use
      of the DCO message is extended to the Non-Storing MOP to report
      asynchronous issues from the Root to the 6LR.

   *  Section 8 presents the changes made to [RFC6775] and [RFC8505];
      The range of the ND status codes is reduced down to 64 values, and
      the remaining bits in the original status field are now reserved.

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



Thubert & Richardson      Expires 15 July 2021                  [Page 5]


Internet-Draft             RPL Unaware Leaves               January 2021


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 uses the following acronyms:

   6CIO:  6LoWPAN Capability Indication Option
   6LN:  6LoWPAN Node (a Low Power host or router)
   6LR:  6LoWPAN router
   6LBR:  6LoWPAN Border 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)
   DIO:  DODAG Information Object (a RPL message)
   DODAG:  Destination-Oriented Directed Acyclic Graph
   LLN:  Low-Power and Lossy Network
   MOP:  RPL Mode of Operation
   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
   SRH:  Source-Routing Header
   TID:  Transaction ID (a sequence counter in the EARO)
   TIO:  Transit Information Option










Thubert & Richardson      Expires 15 July 2021                  [Page 6]


Internet-Draft             RPL Unaware Leaves               January 2021


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), "up", "down" 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 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), RPL-Aware Node
   (RAN) and RPL aware Leaf (RAL) consistently with [USEofRPLinfo].  A
   RAN is either a 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], "Address Protected Neighbor Discovery for
      Low-power and Lossy Networks" [RFC8928], and "IPv6 Backbone
      Router" [RFC8929].





Thubert & Richardson      Expires 15 July 2021                  [Page 7]


Internet-Draft             RPL Unaware Leaves               January 2021


3.  RPL External Routes and Dataplane Artifacts

   RPL was initially designed to build stub networks whereby the only
   border router would be the RPL Root (typically collocated with the
   6LBR) and all the nodes in the stub would be RPL-Aware.  But
   [RFC6550] was also prepared to be extended for external routes
   (targets in RPL parlance) with the External 'E' flag in the Transit
   Information Option (TIO).  External targets enable to reach
   destinations that are outside the RPL domain and connected to the RPL
   domain via RPL border routers that are not the Root.  Section 4.1 of
   [USEofRPLinfo] provides a set of rules summarized below that must be
   followed for routing packets to and from an external destination.  A
   RUL is a special case of an external target that is also a host
   directly connected to the RPL domain.

   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 data packets directly
   to the 6LR that advertised the external route, which decapsulates and
   forwards the original (inner) packets.

   The RPL Non-Storing MOP signaling and the associated IPv6-in-IPv6
   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 typically carry a Hop-by-Hop Header with a RPL
   Option [RFC6553] that contains the Packet Information (RPI) defined
   in section 11.2 of [RFC6550].  Unless the RUL already placed a RPL
   Option in outer header chain, the packets from and to the RUL are
   encapsulated using an IPv6-in-IPv6 tunnel between the Root and the
   6LR that serves the RUL (see sections 7 and 8 of [USEofRPLinfo] for
   details).  If the packet from the RUL has an RPI, the 6LR as a RPL
   border router rewrites the RPI to indicate the selected Instance and
   set the flags, but it does not need to encapsulate the packet (see
   Section 9.2.2) .

   In Non-Storing Mode, packets going down carry a Source Routing Header
   (SRH).  The IPv6-in-IPv6 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.




Thubert & Richardson      Expires 15 July 2021                  [Page 8]


Internet-Draft             RPL Unaware Leaves               January 2021


   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] and in
   particular the mandates in Sections 4.2 and 4.4 of [RFC8200].  As
   such, the RUL is expected to ignore the RPL artifacts that may be
   left over, either an SRH with zero Segments Left or a RPL Option in
   the Hop-by-Hop Header, which can be skipped when not recognized, see
   Section 5 for more.

   A RUL is not expected to support the compression method defined in
   [RFC8138].  For that reason, the border router (the 6LR here)
   uncompresses the packet before forwarding it over an external route
   to a RUL [USEofRPLinfo].

4.  6LoWPAN Neighbor Discovery

   This section goes through the 6LoWPAN ND mechanisms that this
   specification leverages, as a non-normative reference to the reader.
   The full normative text is to be found in [RFC6775], [RFC8505], and
   [RFC8928].

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 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.





Thubert & Richardson      Expires 15 July 2021                  [Page 9]


Internet-Draft             RPL Unaware Leaves               January 2021


4.2.  RFC 8505 Extended Address Registration

   "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
   updates RFC 6775 into a generic Address Registration mechanism that
   can be used to access services such as routing and ND proxy.  To that
   effect, [RFC8505] defines the Extended Address Registration Option
   (EARO), shown in Figure 2:


      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 2: EARO Option Format

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 set to 0,
   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 from [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 to 1.

   Section 9.2 specifies additional operations when R flag is set to 1
   in an EARO that is placed either in an NS or an NA message.








Thubert & Richardson      Expires 15 July 2021                 [Page 10]


Internet-Draft             RPL Unaware Leaves               January 2021


4.2.2.  TID, "I" Field and Opaque Fields

   When the T Flag is set to 1, 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)/; this requirement is fully
   explained 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.  Route Ownership Verifier

   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" [RFC8928] leverages the ROVR field as a cryptographic proof
   of ownership to prevent a rogue third party from registering an
   address that is already owned.  The use of ROVR field enables the 6LR
   to block traffic that is not sourced at an owned address.

   This specification does not address how the protection by [RFC8928]
   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 specified in
   Section 8.2.6 of [RFC6775], though in an LLN, a duration longer than
   the default value of the RetransTimer (RETRANS_TIMER) [RFC4861] of 1
   second may be necessary to cover the round trip delay between the 6LR
   and the 6LBR.






Thubert & Richardson      Expires 15 July 2021                 [Page 11]


Internet-Draft             RPL Unaware Leaves               January 2021


   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 8 in
   Section 9.1.

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.

       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 3: 6CIO flags

   A 6LR that provides reachability services for a RUL in a RPL network
   as specified in this document includes a 6CIO in its RA messages and
   set the L, P and E flags to 1 as prescribed by [RFC8505]; this is
   fully explained in Section 9.2.







Thubert & Richardson      Expires 15 July 2021                 [Page 12]


Internet-Draft             RPL Unaware Leaves               January 2021


5.  Requirements on the RPL-Unware leaf

   This document describes how RPL routing can be extended to reach a
   RUL.  This section specifies 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 sets the "R"
   and "T" flags in the EARO to 1 as discussed in Section 4.2.1 and
   Section 4.2.2, respectively.  Section 9.2.1 specifies new behaviors
   for the RUL, e.g., when the R Flag set to 1 in a NS(EARO) is not
   echoed in the NA(EARO), which indicates that the route injection
   failed.

   The RUL is expected to request routing services from a router only if
   that router originates RA messages with a 6CIO that has the L, P, and
   E flags all set to 1 as discussed in Section 4.3.1, unless configured
   to do so.  It is suggested that the RUL also implements [RFC8928] 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 refrain from using the address when
   the Status value indicates a rejection (see Section 6.3).















Thubert & Richardson      Expires 15 July 2021                 [Page 13]


Internet-Draft             RPL Unaware Leaves               January 2021


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).  In order to terminate the IPv6-in-IPv6 tunnel,
   the RUL, as an IPv6 host, would have to be capable of decapsulating
   the tunneled packet and either drop the encapsulated packet if it is
   not the final destination, or pass it to the upper layer for further
   processing.  As indicated in section 4.1 of [USEofRPLinfo], this is
   not mandated by [RFC8504], and the IPv6-in-IPv6 tunnel from the Root
   is terminated at the parent 6LR.  It is thus not necessary for a RUL
   to support IPv6-in-IPv6 decapsulation.

5.3.  Support of the Hop-by-Hop 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, which has a Routing Type of 3 [RFC6554], is ignored
   when the Segments Left is zero.  When the Segments Left is non-zero,
   the RUL discards the packet and send an ICMP Parameter Problem, Code
   0, message to the packet's Source Address, pointing to the
   unrecognized Routing Type.

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 IPv6-in-IPv6 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 (see Section 8), for any
   leaf node that implements the 6LN functionality in [RFC8505].






Thubert & Richardson      Expires 15 July 2021                 [Page 14]


Internet-Draft             RPL Unaware Leaves               January 2021


   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 to 1, see
   Section 6.1.

   This specification defines a new flag, "Root Proxies EDAR/EDAC" (P),
   in the RPL DODAG Configuration option, see 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, see Section 6.3.

   Section 12 of [RFC6550] details the RPL support for multicast flows
   when the RPLInstance is operated in the MOP of 3 ("Storing Mode of
   Operation with multicast support").  This specification extends the
   RPL Root operation to proxy-relay the MLDv2 [RFC3810] operation
   between the RUL and the 6LR, see Section 10.

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 Target Prefix of the RPL Target Option is left (high bit)
   justified and contains the advertised prefix; its size may be smaller
   than 128 when it indicates a Prefix route.  The Prefix Length field
   signals the number of bits that correspond to the advertised Prefix;
   it is 128 for a host route or less in the case of a Prefix route.
   This remains unchanged.

   This specification defines the new 'F' flag.  When it is set to 1,
   the size of the Target Prefix field MUST be 128 bits and it MUST
   contain an IPv6 address of the advertising node taken from the
   advertised Prefix.  In that case, the Target Prefix field carries two
   distinct pieces of information: a route that can be a host route or a
   Prefix route depending on the Prefix Length, and an IPv6 address that
   can be used to reach the advertising node and validate the route.







Thubert & Richardson      Expires 15 July 2021                 [Page 15]


Internet-Draft             RPL Unaware Leaves               January 2021


   If the 'F' flag is set to 0, the Target Prefix field can be shorter
   than 128 bits and it MUST be aligned to the next byte boundary after
   the end of the prefix.  Any additional bits in the rightmost octet
   are filled with padding bits.  Padding bits are reserved and set to 0
   as specified in 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 4.  It is backward
   compatible with the Target Option in [RFC6550].  It is recommended
   that the updated format 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.

      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|Flg|ROVRsz | Prefix Length |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                Target Prefix (Variable Length)                |
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 4: Updated Target Option

   New fields:

   F:  1-bit flag.  Set to 1 to indicate that Target Prefix field
      contains the complete (128 bit) IPv6 address of the advertising
      node.

   X:  1-bit flag.  Set to 1 to request that the Root performs a proxy
      EDAR/EDAC exchange.

      The 'X' flag can only be set to 1 if the DODAG is operating in
      Non-Storing Mode and if the Root sets the "Root Proxies EDAR/EDAC
      (P)" flag to 1 in the DODAG Configuration Option, see Section 6.2.



Thubert & Richardson      Expires 15 July 2021                 [Page 16]


Internet-Draft             RPL Unaware Leaves               January 2021


      The 'X' flag can be set for host routes to RULs and RANs; it can
      also be set for internal prefix routes if the 'F' flag is set,
      using the node's address in the Target Prefix field to form the
      EDAR, but it cannot be used otherwise.

   Flg (Flags):  The 2 bits remaining unused in the Flags field are
      reserved for flags.  The field MUST be initialized to zero by the
      sender and MUST be ignored by the receiver.

   ROVRsz (ROVR Size):  Indicates the Size of the ROVR.  It MUST be set
      to 1, 2, 3, or 4, indicating a ROVR size of 64, 128, 192, or 256
      bits, respectively.

      If a legacy Target Option is used, then the value must remain 0,
      as specified in [RFC6550].

      In case of a value above 4, the size of the ROVR is undetermined
      and this node cannot validate the ROVR; an implementation SHOULD
      propagate the whole Target Option upwards as received to enable
      the verification by an ancestor that would support the upgraded
      ROVR.

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

6.2.  Additional 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.  This 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|       ...           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                     +
                                     |4 bits |

            Figure 5: DODAG Configuration Option (Partial View)

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



Thubert & Richardson      Expires 15 July 2021                 [Page 17]


Internet-Draft             RPL Unaware Leaves               January 2021


   The 'P' flag is set to 1 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
   from zero (0) to six (6) only.  For a MOP value of 7, the
   implementation MUST consider that the Root performs the proxy
   operation.

   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 'P' Flag as set
   by the Root, and when the 'P' Flag is set to 1, 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 adds a capability to allow the
   carriage of 6LoWPAN ND Status values in RPL DAO and DCO messages,
   embedded in the RPL Status field.










Thubert & Richardson      Expires 15 July 2021                 [Page 18]


Internet-Draft             RPL Unaware Leaves               January 2021


   To achieve this, the range of the ARO/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 6.  See Section 12.2, Section 12.5, and Section 12.6 for the
   respective IANA declarations.  This ask is reasonable because the
   associated registry relies on standards action for registration and
   only values up to 10 are currently allocated.

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

                        Figure 6: RPL Status Format

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

   E:  1-bit flag. set to 1 to indicate a rejection.  When set to 0, 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 to 1 this field transports a value defined
      for the 6LoWPAN ND EARO Status.

      When the 'A' flag is set to 0, this field transports a Status
      Value 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 to 1.  The RPL Root MUST
   set the 'E' flag to 1 for all rejection and unknown status codes.
   The status codes in the 1-10 range [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.








Thubert & Richardson      Expires 15 July 2021                 [Page 19]


Internet-Draft             RPL Unaware Leaves               January 2021


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 is processed hop-by-
   hop along the path that is being cleaned up.

   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.

   In the case of a RUL, the 6LR that serves the RUL acts as the RAN
   that receives the Non-Storing DCO.  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 RFC6775 and RFC8505

   This document updates [RFC6775] and [RFC8505] to reduce the range of
   the ND status codes down to 64 values.  The two most significant
   (leftmost) bits if the original ND status field are now reserved,
   they MUST be set to zero by the sender and ignored by the receiver.

   This document also updates 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' flag in the
   DODAG Configuration Option and performs the EDAR proxy operation
   presented in Section 4.3 .






Thubert & Richardson      Expires 15 July 2021                 [Page 20]


Internet-Draft             RPL Unaware Leaves               January 2021


   If the 'P' flag is set to 0, 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.

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 7 illustrates that, for
   the first Registration, both the DAD and the keep-alive EDAR/EDAC
   exchanges happen in the same sequence.

          6LN/RUL            6LR   <6LR*>   Root               6LBR
             |<---Using ND--->|<--Using RPL->|<-----Using ND---->|
             |                |<-----------Using ND------------->|
             |                |              |                   |
             |   NS(EARO)     |              |                   |
             |--------------->|                                  |
             |                |            EDAR                  |
             |                |--------------------------------->|
             |                |                                  |
             |                |             EDAC                 |
             |                |<---------------------------------|
             |                |                                  |
             |                |   DAO(X=0)   |                   |
             |                |------------->|                   |
             |                |                                  |
             |                |    DAO-ACK   |                   |
             |                |<-------------|                   |
             |   NA(EARO)     |              |                   |
             |<---------------|              |                   |
             |                |              |                   |



Thubert & Richardson      Expires 15 July 2021                 [Page 21]


Internet-Draft             RPL Unaware Leaves               January 2021


                   Figure 7: First RUL Registration Flow

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

   To 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.

   On the first Address Registration, illustrated in Figure 7 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 non-zero 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 keep 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 8.

          6LN/RUL   <-ND->   6LR   <-RPL->  Root   <-ND->      6LBR
             |                |              |                   |
             |   NS(EARO)     |              |                   |
             |--------------->|              |                   |
             |                |   DAO(X=1)   |                   |
             |                |------------->|                   |
             |                |              |       EDAR        |
             |                |              |------------------>|
             |                |              |       EDAC        |
             |                |              |<------------------|
             |                |    DAO-ACK   |                   |
             |                |<-------------|                   |
             |   NA(EARO)     |              |                   |
             |<---------------|              |                   |

                    Figure 8: 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 to 1 that imbeds a 6LoWPAN Status value as discussed in
   Section 6.3.







Thubert & Richardson      Expires 15 July 2021                 [Page 22]


Internet-Draft             RPL Unaware Leaves               January 2021


   The 6LR may receive a requested DAO-ACK after it received an
   asynchronous Non-Storing DCO, but the non-zero 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 [RFC8929].
   The 6BBR may send a negative ND status, e.g., in an asynchronous
   NA(EARO) to the 6LBR.

   [RFC8929] 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.  Note that a legacy RAN that receives a Non-Storing
   DCO that it does not support will ignore it silently, as specified in
   section 6 of [RFC6550].  The result is that it may ignore for a while
   that it is no more reachable.  The situation will be cleared upon the
   next Non-Storing DAO exchange if the error is returned in a DAO-ACK.

   Figure 9 illustrates this in the case where the 6LBR and the Root are
   not collocated, and the Root proxies the EDAR/EDAC flow.

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

                        Figure 9: Asynchronous Issue

   If the Root does not proxy, then the EDAC with a non-zero 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 set to 0.








Thubert & Richardson      Expires 15 July 2021                 [Page 23]


Internet-Draft             RPL Unaware Leaves               January 2021


   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 8.

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

9.2.  Detailed Operation

   The following section specify respectively the behaviour of the 6LN
   Acting as RUL, the 6LR Acting as Border router and serving the 6LN,
   the RPL Root and the 6LBR in the control flows that enable RPL
   routing back to the RUL.

9.2.1.  Perspective of the 6LN Acting as RUL

   This specification builds on the operation of a 6LoWPAN ND-compliant
   6LN/RUL, which is expected to operate as follows:

   1.  The 6LN selects a 6LR that provides reachability services for a
       RUL.  This is signaled by a 6CIO in the RA messages with the L, P
       and E flags set to 1 as prescribed by [RFC8505].

   2.  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].

   3.  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 sets the T Flag to 1 as prescribed in
       [RFC8505].  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]).

   4.  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 may cancel a subset of its
       registrations, or transfer a registration from one or more old
       6LR(s) to one or more new 6LR(s).  To do so, the 6LN sends a
       series of NS(EARO) messages, all with the same TID, with a zero
       Registration Lifetime to the old 6LR(s) and with a non-zero



Thubert & Richardson      Expires 15 July 2021                 [Page 24]


Internet-Draft             RPL Unaware Leaves               January 2021


       Registration Lifetime to the new 6LR(s).  In that process, the
       6LN SHOULD send the NS(EARO) with a non-zero Registration
       Lifetime and ensure that at least one succeeds before it sends an
       NS(EARO) that terminates another registration.  This avoids the
       churn related to transient route invalidation in the RPL network
       above the common parent of the involved 6LRs.

   5.  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 MUST consider that establishing the routing services
       via this 6LR failed and it SHOULD attempt to use another 6LR.
       The RUL SHOULD ensure that one registration succeeds before
       setting the R Flag to 0.  In case of a conflict with the
       preceding rule on lifetime, the rule on lifetime has precedence.

   6.  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,
   otherwise it MUST leave the Opaque field as 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].

   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 SHOULD indicate the RPLInstanceID of the RPL
   Instance where the packet should be forwarded.  It is up to the 6LR
   (e.g., by policy) to use the RPLInstanceID information provided by
   the RUL or rewrite it to the selected RPLInstanceID for forwarding
   inside the RPL domain.  All the flags and the Rank field are set to 0
   as specified by section 11.2 of [RFC6550].

9.2.2.  Perspective of the 6LR Acting as Border router

   A 6LR that provides 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 to 1 as prescribed by [RFC8505].





Thubert & Richardson      Expires 15 July 2021                 [Page 25]


Internet-Draft             RPL Unaware Leaves               January 2021


   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.

   If the R Flag is set to 1 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 SHOULD refrain from setting the 'X' flag to
   avoid a redundant EDAR/EDAC flow to the 6LBR.  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.

   For the registration refreshes, if the RPL Root sets the 'P' flag in
   the DODAG Configuration Option to 1, then the 6LR MUST refrain from
   sending the keep-alive EDAR; instead, it MUST set the 'X' flag to 1
   in the Target Option of the DAO messages, to request that the Root
   proxies the keep-alive EDAR/EDAC exchange with the 6LBR (see
   Section 6); if the 'P' flag is set to 0 then the 6LR MUST set the 'X'
   flag to 0 and handle the EDAR/EDAC flow itself.

   The Opaque field in the EARO provides a means 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, e.g., using a policy
   that maps the 6-tuple into an Instance.

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

   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 set to 0 since the advertiser is
       not the RUL.  The ROVR field is copied unchanged from the EARO
       (see Section 6.1).



Thubert & Richardson      Expires 15 July 2021                 [Page 26]


Internet-Draft             RPL Unaware Leaves               January 2021


   2.  The 6LR indicates one of its global or unique-local IPv6 unicast
       addresses as the Parent Address in the 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 set to ensure that
       the path has a longer lifetime than the registration and covers
       in addition the round trip time to the Root.

       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, it
   MUST send an asynchronous NA(EARO) to the RUL immediately, but still
   be capable of processing the DAO-ACK if one is pending.

   The 6LR MUST set the R Flag to 1 in the NA(EARO) back if and only if
   the 'E' flag in the RPL Status is set to 0, indicating that the 6LR
   injected the Registered Address in the RPL routing successfully and
   that the EDAR proxy operation succeeded.

   If the 'A' flag in the RPL Status is set to 1, the embedded Status
   value is passed back to the RUL in the EARO Status.  If the 'E' flag
   is also set to 1, the registration failed for 6LoWPAN-ND-related
   reasons, and the NCE is removed.








Thubert & Richardson      Expires 15 July 2021                 [Page 27]


Internet-Draft             RPL Unaware Leaves               January 2021


   An error injecting the route causes the 'E' flag to be set to 1.  If
   the error is not related to ND, the 'A' flag is set to 0.  In that
   case, the registration succeeds, but the RPL route is not installed.
   So the NA(EARO) is returned with a status indicating success but the
   R Flag set to 0, which means that the 6LN obtained a binding but no
   route.

   If the 'A' flag is set to 0 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 to 1 in the RPL Status of the DAO-ACK, then
   the route was not installed and the R flag MUST be set to 0 in the
   NA(EARO).  The R flag MUST be set to 0 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 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 [RFC8928],
   before the Registration is complete.  This flow, illustrated in
   Figure 10, 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.



















Thubert & Richardson      Expires 15 July 2021                 [Page 28]


Internet-Draft             RPL Unaware Leaves               January 2021


   6LN                                       6LR        Root        6LBR
    |                                         |           |           |
    |<--------------- RA ---------------------|           |           |
    |                                         |           |           |
    |------ NS EARO (ROVR=Crypto-ID) -------->|           |           |
    |                                         |           |           |
    |<- NA EARO(status=Validation Requested) -|           |           |
    |                                         |           |           |
    |----- NS EARO and Proof-of-ownership  -->|                       |
    |                                         |           |           |
    |                                <validate the Proof> |           |
    |                                                     |           |
    |<----------- NA EARO (status=10)---<if failed>       |           |
    |                                                     |           |
    |                                       <else>        |           |
    |                                         |           |           |
    |                                         |--------- EDAR ------->|
    |                                         |                       |
    |                                         |<-------- EDAC --------|
    |                                         |                       |
    |                                         |           |           |
    |                                         |-DAO(X=0)->|           |
    |                                         |           |           |
    |                                         |<- DAO-ACK-|           |
    |                                         |           |           |
    |<----------- NA EARO (status=0)----------|           |           |
    |                                         |           |           |
                                        ...
    |                                         |           |           |
    |------ NS EARO (ROVR=Crypto-ID) -------->|           |           |
    |                                         |-DAO(X=1)->|           |
    |                                         |           |-- EDAR -->|
    |                                         |           |           |
    |                                         |           |<-- EDAC --|
    |                                         |<- DAO-ACK-|           |
    |<----------- NA EARO (status=0)----------|           |           |
    |                                         |           |           |
                                        ...

                       Figure 10: Address Protection











Thubert & Richardson      Expires 15 July 2021                 [Page 29]


Internet-Draft             RPL Unaware Leaves               January 2021


   The 6LR may at any time send a unicast asynchronous NA(EARO) with the
   R Flag set to 0 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 is ceasing to
   serve 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 MUST remove the host route to the 6LN
   using a DAO message with a Path Lifetime of zero.

   A valid NS(EARO) message with the R Flag set to 0 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 to 1, 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.

   When forwarding a packet from the RUL into the RPL domain, if the
   packet does not have an RPI then the 6LR MUST encapsulate the packet
   to the Root, and add an RPI.  If there is an RPI in the packet, the
   6LR MUST rewrite the RPI but it does not need to encapsulate.

9.2.3.  Perspective of the RPL Root

   A RPL Root MUST set the 'P' flag to 1 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) with the 'X' flag set to 1, the Root MUST notify
   the 6LBR by using a proxied EDAR/EDAC exchange; if the RPL Root and
   the 6LBR are integrated, an internal API can be used instead.

   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;





Thubert & Richardson      Expires 15 July 2021                 [Page 30]


Internet-Draft             RPL Unaware Leaves               January 2021


   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.  Otherwise, 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 to 1.

   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 to 1 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 activated by the MOP of 3 ("Storing Mode of Operation
   with multicast support") in the DIO messages that form the DODAG.
   This section also applies if and only if the MOP of the RPLInstance
   is 3.

   The RPL support of multicast 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.






Thubert & Richardson      Expires 15 July 2021                 [Page 31]


Internet-Draft             RPL Unaware Leaves               January 2021


   "Multicast Listener Discovery Version 2 (MLDv2) for IPv6" [RFC3810]
   provides 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 11.  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.
   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 described 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 |               |                       |
         |------------------->|               |                       |
         |                    | DAO           |                       |
         |                    |-------------->|                       |
         |                    |    DAO-ACK    |                       |
         |                    |<--------------|                       |
         |                    |               | <if not done already> |
         |                    |               |  unsolicited Report   |
         |                    |               |---------------------->|
         |                    |               |                       |

                Figure 11: First Multicast Registration Flow





Thubert & Richardson      Expires 15 July 2021                 [Page 32]


Internet-Draft             RPL Unaware Leaves               January 2021


   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.

   This is illustrated in Figure 12:

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

                     Figure 12: 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.





Thubert & Richardson      Expires 15 July 2021                 [Page 33]


Internet-Draft             RPL Unaware Leaves               January 2021


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 improves the situation by isolating 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 status code of 4 ("Removed").

   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 B.5 of [RFC8505].

   In a general manner, the Security Considerations in [RFC6550],
   [RFC7416] [RFC6775], and [RFC8505] apply to this specification as
   well.

   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 to 1 in the EARO.

   [RFC8928] 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 the 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.  [RFC8928] 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 (e.g.,
   using a role-based authorization) to ensure that the node that claims
   to be a 6LBR or a RPL Root is entitled to do so.




Thubert & Richardson      Expires 15 July 2021                 [Page 34]


Internet-Draft             RPL Unaware Leaves               January 2021


   The Opaque field in the EARO enables the RUL to suggest a
   RPLInstanceID where its traffic is placed.  It is also possible for
   an attacker RUL to include an RPI in the packet.  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.  The attack may be
   alleviated by traditional access control and traffic shaping
   mechanisms where the 6LR controls the incoming traffic from the 6LN.
   More importantly, the 6LR is the node that injects the traffic in the
   RPL domain, so it has the final word on which RPLInstance is to be
   used for the traffic coming from the RUL, per its own policy.  In
   particular, a policy can override the formal language that forces to
   use the Opaque field or to rewrite the RPI provided by the RUL, in a
   situation where the network administrator finds it relevant.

   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.

   Section 6.1 indicates that when the length of the ROVR field is
   unknown, the RPL Target Option must be passed on as received in RPL
   storing Mode.  This creates a possible opening for using DAO messages
   as a covert channel.  Note that DAO messages are rare and the
   overusing that channel could be detected.  An implementation SHOULD
   notify the network management when a RPL Target Option is receives
   with an unknown ROVR field size, to ensure that the situation is
   known to the network administrator.

   [EFFICIENT-NPDAO] introduces the ability for a rogue common ancestor
   node to invalidate a route on behalf of the target node.  In this
   case, the RPL Status in the DCO has the 'A' flag set to 0, and a
   NA(EARO) is returned to the 6LN with the R flag set to 0.  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.

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".






Thubert & Richardson      Expires 15 July 2021                 [Page 35]


Internet-Draft             RPL Unaware Leaves               January 2021


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 to 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 RPL DODAG Configuration Option Flag

   IANA is requested to assign a flag from the "DODAG Configuration
   Option Flags for MOP 0..6" [USEofRPLinfo] registry as follows:

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

               Table 2: New DODAG Configuration Option Flag

   IANA is requested to add [this document] as a reference for MOP 7 in
   the RPL Mode of Operation registry.

12.4.  RPL Target Option Registry

   This document modifies the "RPL Target Option Flags" registry
   initially created in Section 20.15 of [RFC6550] . The registry now
   includes only 4 bits (Section 6.1) and should point to this document
   as an additional reference.  The registration procedure does not
   change.

   Section 6.1 also defines 2 new entries in the Registry as follows:

      +---------------+--------------------------------+-----------+
      | Bit Number    | Capability Description         | Reference |
      +---------------+--------------------------------+-----------+
      | 0 (suggested) | Advertiser address in Full (F) | THIS RFC  |
      +---------------+--------------------------------+-----------+
      | 1 (suggested) | Proxy EDAR Requested (X)       | THIS RFC  |
      +---------------+--------------------------------+-----------+

                   Table 3: RPL Target Option Registry




Thubert & Richardson      Expires 15 July 2021                 [Page 36]


Internet-Draft             RPL Unaware Leaves               January 2021


12.5.  New Subregistry for 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, DCO, and DCO-ACK
   messages with the 'A' flag set to 0, 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 / RFC 6550 |
         +-------+------------------------+---------------------+
         | 1..63 | Unassigned             |                     |
         +-------+------------------------+---------------------+

               Table 4: Acceptance values of the RPL Status

12.6.  New Subregistry for 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 set to 0, 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:

           +-------+-----------------------+-------------------+
           | Value | Meaning               | Reference         |
           +-------+-----------------------+-------------------+
           | 0     | Unqualified rejection | THIS RFC          |
           +-------+-----------------------+-------------------+
           | 1     | No routing entry      | [EFFICIENT-NPDAO] |
           +-------+-----------------------+-------------------+
           | 2..63 | Unassigned            |                   |
           +-------+-----------------------+-------------------+

                Table 5: Rejection values of the RPL Status






Thubert & Richardson      Expires 15 July 2021                 [Page 37]


Internet-Draft             RPL Unaware Leaves               January 2021


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.  Also many thanks to Eric Vyncke,
   Erik Kline, Murray Kucherawy, Peter Van der Stok, Carl Wallace, Barry
   Leiba, Julien Meuric, and especially Benjamin Kaduk and Elwyn Davies,
   for their reviews and useful comments during the IETF Last Call and
   the IESG review sessions.

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>.

   [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>.



Thubert & Richardson      Expires 15 July 2021                 [Page 38]


Internet-Draft             RPL Unaware Leaves               January 2021


   [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>.

   [RFC8928]  Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
              "Address-Protected Neighbor Discovery for Low-Power and
              Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
              2020, <https://www.rfc-editor.org/info/rfc8928>.

   [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-43,
              10 January 2021, <https://tools.ietf.org/html/draft-ietf-
              roll-useofrplinfo-43>.

   [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






Thubert & Richardson      Expires 15 July 2021                 [Page 39]


Internet-Draft             RPL Unaware Leaves               January 2021


   [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>.

   [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>.








Thubert & Richardson      Expires 15 July 2021                 [Page 40]


Internet-Draft             RPL Unaware Leaves               January 2021


   [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>.

   [RFC8929]  Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
              "IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
              November 2020, <https://www.rfc-editor.org/info/rfc8929>.

Appendix A.  Example Compression

   Figure 13 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].

   +-+ ... -+-+ ... +-+- ... -+-+ ... -+-+-+ ... +-+-+ ... -+ ... +-...
   |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 13: Encapsulation to Parent 6LR in Storing Mode




Thubert & Richardson      Expires 15 July 2021                 [Page 41]


Internet-Draft             RPL Unaware Leaves               January 2021


   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 13, the source of the IPv6-in-IPv6 encapsulation is the
   Root, so it is elided in the IPv6-in-IPv6 6LoRH.  The destination is
   the parent 6LR of the destination of the encapsulated 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 13 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 IPv6-in-IPv6
   6LoRH.  When the IPv6-in-IPv6 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 encapsulated packet compressed with [RFC6282].

Authors' Addresses

   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






Thubert & Richardson      Expires 15 July 2021                 [Page 42]


Internet-Draft             RPL Unaware Leaves               January 2021


   Michael C. Richardson
   Sandelman Software Works

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














































Thubert & Richardson      Expires 15 July 2021                 [Page 43]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/