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ROLL Working Group                                             M. Robles
Internet-Draft                                             UTN-FRM/Aalto
Updates: 6553, 6550, 8138 (if approved)                    M. Richardson
Intended status: Standards Track                                     SSW
Expires: December 10, 2020                                    P. Thubert
                                                                   Cisco
                                                            June 8, 2020


Using RPI Option Type, Routing Header for Source Routes and IPv6-in-IPv6
                  encapsulation in the RPL Data Plane
                    draft-ietf-roll-useofrplinfo-39

Abstract

   This document looks at different data flows through LLN (Low-Power
   and Lossy Networks) where RPL (IPv6 Routing Protocol for Low-Power
   and Lossy Networks) is used to establish routing.  The document
   enumerates the cases where RFC6553 (RPI Option Type), RFC6554
   (Routing Header for Source Routes) and IPv6-in-IPv6 encapsulation is
   required in data plane.  This analysis provides the basis on which to
   design efficient compression of these headers.  This document updates
   RFC6553 adding a change to the RPI Option Type.  Additionally, this
   document updates RFC6550 defining a flag in the DIO Configuration
   option to indicate about this change and updates [RFC8138] as well to
   consider the new Option Type when the RPL Option is decompressed.

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 December 10, 2020.








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Copyright Notice

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

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology and Requirements Language . . . . . . . . . . . .   5
   3.  RPL Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Updates to RFC6553, RFC6550 and RFC8138 . . . . . . . . . . .   7
     4.1.  Updates to RFC6550: Advertising External Routes with Non-
           Storing Mode Signaling. . . . . . . . . . . . . . . . . .   7
     4.2.  Updates to RFC6553: Indicating the new RPI Option Type. .   8
     4.3.  Updates to RFC6550: Indicating the new RPI in the
           DODAG Configuration option Flag.  . . . . . . . . . . . .  11
     4.4.  Updates to RFC8138: Indicating the way to decompress with
           the new RPI Option Type.  . . . . . . . . . . . . . . . .  12
   5.  Sample/reference topology . . . . . . . . . . . . . . . . . .  14
   6.  Use cases . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   7.  Storing mode  . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.1.  Storing Mode: Interaction between Leaf and Root . . . . .  20
       7.1.1.  SM: Example of Flow from RAL to Root  . . . . . . . .  21
       7.1.2.  SM: Example of Flow from Root to RAL  . . . . . . . .  22
       7.1.3.  SM: Example of Flow from Root to RUL  . . . . . . . .  22
       7.1.4.  SM: Example of Flow from RUL to Root  . . . . . . . .  24
     7.2.  SM: Interaction between Leaf and Internet.  . . . . . . .  25
       7.2.1.  SM: Example of Flow from RAL to Internet  . . . . . .  25
       7.2.2.  SM: Example of Flow from Internet to RAL  . . . . . .  27
       7.2.3.  SM: Example of Flow from RUL to Internet  . . . . . .  28
       7.2.4.  SM: Example of Flow from Internet to RUL. . . . . . .  29
     7.3.  SM: Interaction between Leaf and Leaf . . . . . . . . . .  30
       7.3.1.  SM: Example of Flow from RAL to RAL . . . . . . . . .  30
       7.3.2.  SM: Example of Flow from RAL to RUL . . . . . . . . .  31
       7.3.3.  SM: Example of Flow from RUL to RAL . . . . . . . . .  33
       7.3.4.  SM: Example of Flow from RUL to RUL . . . . . . . . .  34
   8.  Non Storing mode  . . . . . . . . . . . . . . . . . . . . . .  35



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     8.1.  Non-Storing Mode: Interaction between Leaf and Root . . .  37
       8.1.1.  Non-SM: Example of Flow from RAL to root  . . . . . .  37
       8.1.2.  Non-SM: Example of Flow from root to RAL  . . . . . .  38
       8.1.3.  Non-SM: Example of Flow from root to RUL  . . . . . .  39
       8.1.4.  Non-SM: Example of Flow from RUL to root  . . . . . .  40
     8.2.  Non-Storing Mode: Interaction between Leaf and Internet .  41
       8.2.1.  Non-SM: Example of Flow from RAL to Internet  . . . .  41
       8.2.2.  Non-SM: Example of Flow from Internet to RAL  . . . .  43
       8.2.3.  Non-SM: Example of Flow from RUL to Internet  . . . .  44
       8.2.4.  Non-SM: Example of Flow from Internet to RUL  . . . .  45
     8.3.  Non-SM: Interaction between leaves  . . . . . . . . . . .  46
       8.3.1.  Non-SM: Example of Flow from RAL to RAL . . . . . . .  46
       8.3.2.  Non-SM: Example of Flow from RAL to RUL . . . . . . .  49
       8.3.3.  Non-SM: Example of Flow from RUL to RAL . . . . . . .  51
       8.3.4.  Non-SM: Example of Flow from RUL to RUL . . . . . . .  52
   9.  Operational Considerations of supporting
       RUL-leaves  . . . . . . . . . . . . . . . . . . . . . . . . .  53
   10. Operational considerations of introducing 0x23  . . . . . . .  54
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  54
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  55
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  58
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  59
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  59
     14.2.  Informative References . . . . . . . . . . . . . . . . .  60
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  62

1.  Introduction

   RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
   [RFC6550] is a routing protocol for constrained networks.  [RFC6553]
   defines the RPL Option carried within the IPv6 Hop-by-Hop Header to
   carry the RPLInstanceID and quickly identify inconsistencies (loops)
   in the routing topology.  The RPL Option is commonly referred to as
   the RPL Packet Information (RPI) though the RPI is really the
   abstract information that is defined in [RFC6550] and transported in
   the RPL Option.  RFC6554 [RFC6554] defines the "RPL Source Route
   Header" (RH3), an IPv6 Extension Header to deliver datagrams within a
   RPL routing domain, particularly in non-storing mode.

   These various items are referred to as RPL artifacts, and they are
   seen on all of the data-plane traffic that occurs in RPL routed
   networks; they do not in general appear on the RPL control plane
   traffic at all which is mostly Hop-by-Hop traffic (one exception
   being DAO messages in non-storing mode).

   It has become clear from attempts to do multi-vendor
   interoperability, and from a desire to compress as many of the above




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   artifacts as possible that not all implementers agree when artifacts
   are necessary, or when they can be safely omitted, or removed.

   The ROLL WG analysized how [RFC2460] rules apply to storing and non-
   storing use of RPL.  The result was 24 data plane use cases.  They
   are exhaustively outlined here in order to be completely unambiguous.
   During the processing of this document, new rules were published as
   [RFC8200], and this document was updated to reflect the normative
   changes in that document.

   This document updates [RFC6553], changing the value of the Option
   Type of the RPL Option to make [RFC8200] routers ignore this option
   when not recognized.

   A Routing Header Dispatch for 6LoWPAN (6LoRH)([RFC8138]) defines a
   mechanism for compressing RPL Option information and Routing Header
   type 3 (RH3) [RFC6554], as well as an efficient IPv6-in-IPv6
   technique.

   Since some of the uses cases here described, use IPv6-in-IPv6
   encapsulation.  It MUST take in consideration, when encapsulation is
   applied, the RFC6040 [RFC6040], which defines how the explicit
   congestion notification (ECN) field of the IP header should be
   constructed on entry to and exit from any IPV6-in-IPV6 tunnel.
   Additionally, it is recommended the reading of
   [I-D.ietf-intarea-tunnels] that explains the relationship of IP
   tunnels to existing protocol layers and the challenges in supporting
   IP tunneling.

   Non-constrained uses of RPL are not in scope of this document, and
   applicability statements for those uses may provide different advice,
   E.g.  [I-D.ietf-anima-autonomic-control-plane].

1.1.  Overview

   The rest of the document is organized as follows: Section 2 describes
   the used terminology.  Section 3 provides a RPL Overview.  Section 4
   describes the updates to RFC6553, RFC6550 and RFC 8138.  Section 5
   provides the reference topology used for the uses cases.  Section 6
   describes the uses cases included.  Section 7 describes the storing
   mode cases and section 8 the non-storing mode cases.  Section 9
   describes the operational considerations of supporting RPL-unaware-
   leaves.  Section 10 depicts operational considerations for the
   proposed change on RPI Option Type, section 11 the IANA
   considerations and then section 12 describes the security aspects.






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2.  Terminology and 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.

   Terminology defined in [RFC7102] applies to this document: LLN, RPL,
   RPL domain and ROLL.

   RPL Leaf: An IPv6 host that is attached to a RPL router and obtains
   connectivity through a RPL Destination Oriented Directed Acyclic
   Graph (DODAG).  As an IPv6 node, a RPL Leaf is expected to ignore a
   consumed Routing Header and as an IPv6 host, it is expected to ignore
   a Hop-by-Hop header.  It results that a RPL Leaf can correctly
   receive a packet with RPL artifacts.  On the other hand, a RPL Leaf
   is not expected to generate RPL artifacts or to support IP-in-IP
   encapsulation.  For simplification, this document uses the standalone
   term leaf to mean a RPL leaf.

   RPL Packet Information (RPI): The abstract information that [RFC6550]
   places in IP packets.  The term is commonly used, including in this
   document, to refer to the RPL Option [RFC6553] that transports that
   abstract information in an IPv6 Hob-by-Hop Header.

   RPL-aware-node (RAN): A device which implements RPL.  Please note
   that the device can be found inside the LLN or outside LLN.

   RPL-Aware-Leaf(RAL): A RPL-aware-node that is also a RPL Leaf.

   RPL-unaware-node: A device which does not implement RPL, thus the
   device is not-RPL-aware.  Please note that the device can be found
   inside the LLN.

   RPL-Unaware-Leaf(RUL): A RPL-unaware-node that is also a RPL Leaf.

   6LoWPAN Node (6LN): [RFC6775] defines it as: "A 6LoWPAN node is any
   host or router participating in a LoWPAN.  This term is used when
   referring to situations in which either a host or router can play the
   role described.".  In this document, a 6LN acts as a leaf.

   6LoWPAN Router (6LR): [RFC6775] defines it as:" An intermediate
   router in the LoWPAN that is able to send and receive Router
   Advertisements (RAs) and Router Solicitations (RSs) as well as
   forward and route IPv6 packets.  6LoWPAN routers are present only in
   route-over topologies."




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   6LoWPAN Border Router (6LBR): [RFC6775] defines it as:"A border
   router located at the junction of separate 6LoWPAN networks or
   between a 6LoWPAN network and another IP network.  There may be one
   or more 6LBRs at the 6LoWPAN network boundary.  A 6LBR is the
   responsible authority for IPv6 prefix propagation for the 6LoWPAN
   network it is serving.  An isolated LoWPAN also contains a 6LBR in
   the network, which provides the prefix(es) for the isolated network."

   Flag Day: In this document, refers to a transition that involves
   having a network with different values of RPI Option Type.

   Non-Storing Mode (Non-SM): RPL mode of operation in which the RPL-
   aware-nodes send information to the root about their parents.  Thus,
   the root knows the topology.  Because the root knows the topology,
   the intermediate 6LRs do not maintain routing state and source
   routing is needed.

   Storing Mode (SM): RPL mode of operation in which RPL-aware-nodes
   (6LRs) maintain routing state (of the children) so that source
   routing is not needed.

   Note: Due to lack of space in some figures (tables) we refer to IPv6-
   in-IPv6 as IP6-IP6.

3.  RPL Overview

   RPL defines the RPL Control messages (control plane), a new ICMPv6
   [RFC4443] message with Type 155.  DIS (DODAG Information
   Solicitation), DIO (DODAG Information Object) and DAO (Destination
   Advertisement Object) messages are all RPL Control messages but with
   different Code values.  A RPL Stack is shown in Figure 1.




















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   +--------------+
   | Upper Layers |
   |              |
   +--------------+
   |   RPL        |
   |              |
   +--------------+
   |   ICMPv6     |
   |              |
   +--------------+
   |   IPv6       |
   |              |
   +--------------+
   |   6LoWPAN    |
   |              |
   +--------------+
   |   PHY-MAC    |
   |              |
   +--------------+

                           Figure 1: RPL Stack.

   RPL supports two modes of Downward traffic: in storing mode (SM), it
   is fully stateful; in non-storing mode (Non-SM), it is fully source
   routed.  A RPL Instance is either fully storing or fully non-storing,
   i.e. a RPL Instance with a combination of storing and non-storing
   nodes is not supported with the current specifications at the time of
   writing this document.

4.  Updates to RFC6553, RFC6550 and RFC8138

4.1.  Updates to RFC6550: Advertising External Routes with Non-Storing
      Mode Signaling.

   Section 6.7.8. of [RFC6550] introduces the 'E' flag that is set to
   indicate that the 6LR that generates the DAO redistributes external
   targets into the RPL network.  An external Target is a Target that
   has been learned through an alternate protocol, for instance a route
   to a prefix that is outside the RPL domain but reachable via a 6LR.
   Being outside of the RPL domain, a node that is reached via an
   external target cannot be guaranteed to ignore the RPL artifacts and
   cannot be expected to process the [RFC8138] compression correctly.
   This means that the RPL artifacts should be contained in an IP-in-IP
   encapsulation that is removed by the 6LR, and that any remaining
   compression should be expanded by the 6LR before it forwards a packet
   outside the RPL domain.





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   This specification updates [RFC6550] to RECOMMEND that external
   targets are advertised using Non-Storing Mode DAO messaging even in a
   Storing-Mode network.  This way, external routes are not advertised
   within the DODAG and all packets to an external target reach the Root
   like normal Non-Storing Mode traffic.  The Non-Storing Mode DAO
   informs the Root of the address of the 6LR that injects the external
   route, and the root uses IP-in-IP encapsulation to that 6LR, which
   terminates the IP-in-IP tunnel and forwards the original packet
   outside the RPL domain free of RPL artifacts.  In the other
   direction, for traffic coming from an external target into the LLN,
   the parent (6LR) that injects the traffic always encapsulates to the
   root.  This whole operation is transparent to intermediate routers
   that only see traffic between the 6LR and the Root, and only the Root
   and the 6LRs that inject external routes in the network need to be
   upgraded to add this function to the network.

   A RUL is a special case of external target when the target is
   actually a host and it is known to support a consumed Routing Header
   and to ignore a HbH header as prescribed by [RFC8200].  The target
   may have been learned through an external routing protocol or may
   have been registered to the 6LR using [RFC8505].

   In order to enable IP-in-IP all the way to a 6LN, it is beneficial
   that the 6LN supports decapsulating IP-in-IP, but that is not assumed
   by [RFC8504].  If the 6LN is a RUL, the Root that encapsulates a
   packet SHOULD terminate the tunnel at a parent 6LR unless it is aware
   that the RUL supports IP-in-IP decapsulation.

   A node that is reachable over an external route is not expected to
   support [RFC8138].  Whether a decapsulation took place or not and
   even when the 6LR is delivering the packet to a RUL, the 6LR that
   injected an external route MUST uncompress the packet before
   forwarding over that external route.

4.2.  Updates to RFC6553: Indicating the new RPI Option Type.

   This modification is required in order to be able to send, for
   example, IPv6 packets from a RPL-Aware-Leaf to a RPL-unaware node
   through Internet (see Section 7.2.1), without requiring IPv6-in-IPv6
   encapsulation.

   [RFC6553] (Section 6, Page 7) states as shown in Figure 2, that in
   the Option Type field of the RPL Option, the two high order bits must
   be set to '01' and the third bit is equal to '1'.  The first two bits
   indicate that the IPv6 node must discard the packet if it doesn't
   recognize the Option Type, and the third bit indicates that the
   Option Data may change in route.  The remaining bits serve as the
   Option Type.



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   +-------+-------------------+----------------+-----------+
   |  Hex  |    Binary Value   |   Description  | Reference |
   + Value +-------------------+                +           +
   |       | act | chg |  rest |                |           |
   +-------+-----+-----+-------+----------------+-----------+
   |  0x63 |  01 |  1  | 00011 |   RPL Option   | [RFC6553] |
   +-------+-----+-----+-------+----------------+-----------+

                   Figure 2: Option Type in RPL Option.

   This document illustrates that it is not always possible to know for
   sure at the source that a packet will only travel within the RPL
   domain or may leave it.

   At the time [RFC6553] was published, leaking a Hop-by-Hop header in
   the outer IPv6 header chain could potentially impact core routers in
   the internet.  So at that time, it was decided to encapsulate any
   packet with a RPL Option using IPv6-in-IPv6 in all cases where it was
   unclear whether the packet would remain within the RPL domain.  In
   the exception case where a packet would still leak, the Option Type
   would ensure that the first router in the Internet that does not
   recognize the option would drop the packet and protect the rest of
   the network.

   Even with [RFC8138], where the IPv6-in-IPv6 header is compressed,
   this approach yields extra bytes in a packet; this means consuming
   more energy, more bandwidth, incurring higher chances of loss and
   possibly causing a fragmentation at the 6LoWPAN level.  This impacts
   the daily operation of constrained devices for a case that generally
   does not happen and would not heavily impact the core anyway.

   While intention was and remains that the Hop-by-Hop header with a RPL
   Option should be confined within the RPL domain, this specification
   modifies this behavior in order to reduce the dependency on IPv6-in-
   IPv6 and protect the constrained devices.  Section 4 of [RFC8200]
   clarifies the behaviour of routers in the Internet as follows: "it is
   now expected that nodes along a packet's delivery path only examine
   and process the Hop-by-Hop Options header if explicitly configured to
   do so".

   When unclear about the travel of a packet, it becomes preferable for
   a source not to encapsulate, accepting the fact that the packet may
   leave the RPL domain on its way to its destination.  In that event,
   the packet should reach its destination and should not be discarded
   by the first node that does not recognize the RPL Option.  But with
   the current value of the Option Type, if a node in the Internet is
   configured to process the Hop-by-Hop header, and if such node
   encounters an option with the first two bits set to 01 and conforms



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   to [RFC8200], it will drop the packet.  Host systems should do the
   same, irrespective of the configuration.

   Thus, this document updates the Option Type of the RPL Option
   [RFC6553], abusively naming it RPI Option Type for simplicity, to
   (Figure 3): the two high order bits MUST be set to '00' and the third
   bit is equal to '1'.  The first two bits indicate that the IPv6 node
   MUST skip over this option and continue processing the header
   ([RFC8200] Section 4.2) if it doesn't recognize the Option Type, and
   the third bit continues to be set to indicate that the Option Data
   may change en route.  The rightmost five bits remain at 0x3(00011).
   This ensures that a packet that leaves the RPL domain of an LLN (or
   that leaves the LLN entirely) will not be discarded when it contains
   the RPL Option.

   With the new Option Type, if an IPv6 (intermediate) node (RPL-not-
   capable) receives a packet with a RPL Option, it should ignore the
   Hop-by-Hop RPL Option (skip over this option and continue processing
   the header).  This is relevant, as it was mentioned previously, in
   the case that there is a flow from RAL to Internet (see
   Section 7.2.1).

   This is a significant update to [RFC6553].

   +-------+-------------------+-------------+------------+
   |  Hex  |    Binary Value   | Description | Reference  |
   + Value +-------------------+             +            +
   |       | act | chg |  rest |             |            |
   +-------+-----+-----+-------+-------------+------------+
   |  0x23 |  00 |  1  | 00011 |  RPL Option |[RFCXXXX](*)|
   +-------+-----+-----+-------+-------------+------------+

      Figure 3: Revised Option Type in RPL Option. (*)represents this
                                 document

   Without the signaling described below, this change would otherwise
   create a lack of interoperation (flag day) for existing networks
   which are currently using 0x63 as the RPI Option Type value.  A move
   to 0x23 will not be understood by those networks.  It is suggested
   that RPL implementations accept both 0x63 and 0x23 when processing
   the header.

   When forwarding packets, implementations SHOULD use the same value of
   RPI Type as was received.  This is required because the RPI Option
   Type does not change en route ([RFC8200] - Section 4.2).  It allows
   the network to be incrementally upgraded and allows the DODAG root to
   know which parts of the network have been upgraded.




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   When originating new packets, implementations SHOULD have an option
   to determine which value to originate with, this option is controlled
   by the DIO option described below.

   The change of RPI Option Type from 0x63 to 0x23, makes all [RFC8200]
   Section 4.2 compliant nodes tolerant of the RPL artifacts.  There is
   therefore no longer a necessity to remove the artifacts when sending
   traffic to the Internet.  This change clarifies when to use IPv6-in-
   IPv6 headers, and how to address them: The Hop-by-Hop Options header
   containing the RPI MUST always be added when 6LRs originate packets
   (without IPv6-in-IPv6 headers), and IPv6-in-IPv6 headers MUST always
   be added when a 6LR finds that it needs to insert a Hop-by-Hop
   Options header containing the RPL Option.  The IPv6-in-IPv6 header is
   to be addressed to the RPL root when on the way up, and to the end-
   host when on the way down.

   In the non-storing case, dealing with not-RPL aware leaf nodes is
   much easier as the 6LBR (DODAG root) has complete knowledge about the
   connectivity of all DODAG nodes, and all traffic flows through the
   root node.

   The 6LBR can recognize not-RPL aware leaf nodes because it will
   receive a DAO about that node from the 6LR immediately above that
   not-RPL aware node.

   The non-storing mode case does not require the type change from 0x63
   to 0x23, as the root can always create the right packet.  The type
   change does not adversely affect the non-storing case.

4.3.  Updates to RFC6550: Indicating the new RPI in the DODAG
      Configuration option Flag.

   In order to avoid a Flag Day caused by lack of interoperation between
   new RPI Option Type (0x23) and old RPI Option Type (0x63) nodes, this
   section defines a flag in the DIO Configuration option, to indicate
   when the new RPI Option Type can be safely used.  This means, the
   flag is going to indicate the value of Option Type that the network
   will be using for the RPL Option.  Thus, when a node joins to a
   network will know which value to use.  With this, RPL-capable nodes
   know if it is safe to use 0x23 when creating a new RPL Option.  A
   node that forwards a packet with an RPI MUST NOT modify the Option
   Type of the RPL Option.

   This is done using a DODAG Configuration option flag which will
   signal "RPI 0x23 enable" and propagate through the network.
   Section 6.3.1. of [RFC6550] defines a 3-bit Mode of Operation (MOP)
   in the DIO Base Object.  The flag is defined only for MOP value
   between 0 to 6.  For a MOP value of 7 or above, the flag MAY indicate



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   something different and MUST NOT be interpreted as "RPI 0x23 enable"
   unless the specification of the MOP indicates to do so.

   As stated in [RFC6550] the DODAG Configuration option is present in
   DIO messages.  The DODAG Configuration option distributes
   configuration information.  It is generally static, and does not
   change within the DODAG.  This information is configured at the DODAG
   root and distributed throughout the DODAG with the DODAG
   Configuration option.  Nodes other than the DODAG root do not modify
   this information when propagating the DODAG Configuration option.

   Currently, the DODAG Configuration option in [RFC6550] states: "the
   unused bits MUST be initialize to zero by the sender and MUST be
   ignored by the receiver".  If the flag is received with a value zero
   (which is the default), then new nodes will remain in RFC6553
   Compatible Mode; originating traffic with the old-RPI Option Type
   (0x63) value.  If the flag is received with a value of 1, then the
   value for the RPL Option MUST be set to 0x23.

   Bit number three of the flag field in the DODAG Configuration option
   is to be used as shown in Figure 4 (which is the same as Figure 39 in
   Section 11 and is shown here for convenience):


                +------------+-----------------+---------------+
                | Bit number |   Description   |   Reference   |
                +------------+-----------------+---------------+
                |      3     | RPI 0x23 enable | This document |
                +------------+-----------------+---------------+


    Figure 4: DODAG Configuration option Flag to indicate the RPI-flag-
                                   day.

   In the case of reboot, the node (6LN or 6LR) does not remember the
   RPI Option Type (i.e., whether or not the flag is set), so the node
   will not trigger DIO messages until a DIO message is received
   indicating the RPI value to be used.  The node will use the value
   0x23 if the network supports this feature

4.4.  Updates to RFC8138: Indicating the way to decompress with the new
      RPI Option Type.

   This modification is required in order to be able to decompress the
   RPL Option with the new Option Type of 0x23.

   RPI-6LoRH header provides a compressed form for the RPL RPI; see
   [RFC8138], Section 6. A node that is decompressing this header MUST



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   decompress using the RPI Option Type that is currently active: that
   is, a choice between 0x23 (new) and 0x63 (old).  The node will know
   which to use based upon the presence of the flag in the DODAG
   Configuration option defined in Section 4.3.  E.g.  If the network is
   in 0x23 mode (by DIO option), then it should be decompressed to 0x23.

   [RFC8138] section 7 documents how to compress the IPv6-in-IPv6
   header.

   There are potential significant advantages to having a single code
   path that always processes IPv6-in-IPv6 headers with no conditional
   branches.

   In Storing Mode, the scenarios where the flow goes from RAL to RUL
   and RUL to RUL include compression of the IPv6-in-IPv6 and RPI
   headers.  The use of the IPv6-in-IPv6 header is MANDATORY in this
   case, and it SHOULD be compressed with [RFC8138] section 7.  Figure 5
   illustrates the case in Storing mode where the packet is received
   from the Internet, then the root encapsulates the packet to insert
   the RPI.  In that example, the leaf is not known to support RFC 8138,
   and the packet is encapsulated to the 6LR that is the parent and last
   hop to the final destination.

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

            Figure 5: RPI Inserted by the Root in Storing Mode

   In Figure 5, the source of the IPv6-in-IPv6 encapsulation is the
   Root, so it is elided in the IP-in-IP 6LoRH.  The destination is the
   parent 6LR of the destination of the inner packet so it cannot be
   elided.  It is placed as the single entry in an SRH-6LoRH as the
   first 6LoRH.  There is a single entry so the SRH-6LoRH Size is 0.  In
   that example, the type is 1 so the 6LR address is compressed to 2
   bytes.  It results that the total length of the SRH-6LoRH is 4 bytes.
   Follows the RPI-6LoRH and then the IP-in-IP 6LoRH.  When the IP-in-IP
   6LoRH is removed, all the router headers that precede it are also
   removed.  The Paging Dispatch [RFC8025] may also be removed if there
   was no previous Page change to a Page other than 0 or 1, since the
   LOWPAN_IPHC is encoded in the same fashion in the default Page 0 and
   in Page 1.  The resulting packet to the destination is the inner
   packet compressed with [RFC6282].





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5.  Sample/reference topology

   A RPL network in general is composed of a 6LBR, a Backbone Router
   (6BBR), a 6LR and a 6LN as a leaf logically organized in a DODAG
   structure.

   Figure 6 shows the reference RPL Topology for this document.  The
   letters above the nodes are there so that they may be referenced in
   subsequent sections.  In the figure, 6LR represents a full router
   node.  The 6LN is a RPL aware router, or host (as a leaf).
   Additionally, for simplification purposes, it is supposed that the
   6LBR has direct access to Internet and is the root of the DODAG, thus
   the 6BBR is not present in the figure.

   The 6LN leaves (RAL) marked as (F, H and I) are RPL nodes with no
   children hosts.

   The leaves marked as RUL (G and J) are devices which do not speak RPL
   at all (not-RPL-aware), but uses Router-Advertisements, 6LowPAN DAR/
   DAC and 6LoWPAN ND only to participate in the network [RFC8505].  In
   the document these leaves (G and J) are also referred to as a RUL.

   The 6LBR ("A") in the figure is the root of the Global DODAG.




























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                     +------------+
                     |  INTERNET  ----------+
                     |            |         |
                     +------------+         |
                                            |
                                            |
                                            |
                                          A |
                                      +-------+
                                      |6LBR   |
                          +-----------|(root) |-------+
                          |           +-------+       |
                          |                           |
                          |                           |
                          |                           |
                          |                           |
                          | B                         |C
                      +---|---+                   +---|---+
                      |  6LR  |                   |  6LR  |
            +---------|       |--+             +---       ---+
            |         +-------+  |             |  +-------+  |
            |                    |             |             |
            |                    |             |             |
            |                    |             |             |
            |                    |             |             |
            | D                  |  E          |             |
          +-|-----+          +---|---+         |             |
          |  6LR  |          |  6LR  |         |             |
          |       |    +------       |         |             |
          +---|---+    |     +---|---+         |             |
              |        |         |             |             |
              |        |         +--+          |             |
              |        |            |          |             |
              |        |            |          |             |
              |        |            |        I |          J  |
           F  |        | G          | H        |             |
        +-----+-+    +-|-----+  +---|--+   +---|---+     +---|---+
        |  RAL  |    | RUL   |  | RAL  |   |  RAL  |     | RUL   |
        |  6LN  |    |  6LN  |  | 6LN  |   |  6LN  |     |  6LN  |
        +-------+    +-------+  +------+   +-------+     +-------+


                    Figure 6: A reference RPL Topology.








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6.  Use cases

   In the data plane a combination of RFC6553, RFC6554 and IPv6-in-IPv6
   encapsulation are going to be analyzed for a number of representative
   traffic flows.

   This document assumes that the LLN is using the no-drop RPI Option
   Type of 0x23.

   The use cases describe the communication in the following cases: -
   Between RPL-aware-nodes with the root (6LBR) - Between RPL-aware-
   nodes with the Internet - Between RUL nodes within the LLN (e.g. see
   Section 7.1.4) - Inside of the LLN when the final destination address
   resides outside of the LLN (e.g. see Section 7.2.3).

   The uses cases are as follows:

   Interaction between Leaf and Root:

      RAL to root

      root to RAL

      RUL to root

      root to RUL

   Interaction between Leaf and Internet:

      RAL to Internet

      Internet to RAL

      RUL to Internet

      Internet to RUL

   Interaction between leaves:

      RAL to RAL

      RAL to RUL

      RUL to RAL

      RUL to RUL





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   This document is consistent with the rule that a Header cannot be
   inserted or removed on the fly inside an IPv6 packet that is being
   routed.  This is a fundamental precept of the IPv6 architecture as
   outlined in [RFC8200].

   As the rank information in the RPI artifact is changed at each hop,
   it will typically be zero when it arrives at the DODAG root.  The
   DODAG root MUST force it to zero when passing the packet out to the
   Internet.  The Internet will therefore not see any SenderRank
   information.

   Despite being legal to leave the RPI artifact in place, an
   intermediate router that needs to add an extension header (e.g.  RH3
   or RPL Option) MUST still encapsulate the packet in an (additional)
   outer IP header.  The new header is placed after this new outer IP
   header.

   A corollary is that an intermediate router can remove an RH3 or RPL
   Option only if it is placed in an encapsulating IPv6 Header that is
   addressed TO this intermediate router.  When doing the above, the
   whole encapsulating header must be removed.  (A replacement may be
   added).  This sometimes can result in outer IP headers being
   addressed to the next hop router using link-local address.

   Both the RPL Option and the RH3 headers may be modified in very
   specific ways by routers on the path of the packet without the need
   to add and remove an encapsulating header.  Both headers were
   designed with this modification in mind, and both the RPL RH3 and the
   RPL Option are marked mutable but recoverable: so an IPsec AH
   security header can be applied across these headers, but it can not
   secure the values which mutate.

   The RPI MUST be present in every single RPL data packet.

   Prior to [RFC8138], there was significant interest in creating an
   exception to this rule and removing the RPI for downward flows in
   non-storing mode.  This exception covered a very small number of
   cases, and caused significant interoperability challenges while
   adding significant in the code and tests.  The ability to compress
   the RPI down to three bytes or less removes much of the pressure to
   optimize this any further [I-D.ietf-anima-autonomic-control-plane].

   Throughout the following subsections, the examples are described in
   more details in the first subsections, and more concisely in the
   later ones.

   The uses cases are delineated based on the following IPV6 and RPL
   mandates:



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      The RPI has to be in every packet that traverses the LLN.

      - Because of the above requirement, packets from the Internet have
      to be encapsulated.

      - A Header cannot be inserted or removed on the fly inside an IPv6
      packet that is being routed.

      - Extension headers may not be added or removed except by the
      sender or the receiver.

      - RPI and RH3 headers may be modified by routers on the path of
      the packet without the need to add and remove an encapsulating
      header.

      - an RH3 or RPL Option can only be removed by an intermediate
      router if it is placed in an encapsulating IPv6 Header, which is
      addressed to the intermediate router.

      - Non-storing mode requires downstream encapsulation by root for
      RH3.

   The uses cases are delineated based on the following assumptions:

      This document assumes that the LLN is using the no-drop RPI Option
      Type (0x23).

      - Each IPv6 node (including Internet routers) obeys [RFC8200], so
      that 0x23 RPI Option Type can be safely inserted.

      - All 6LRs obey [RFC8200].

      - The RPI is ignored at the IPv6 dst node (RUL).

      - In the uses cases, we assume that the RAL supports IP-in-IP
      encapsulation.

      - In the uses cases, we dont assume that the RUL supports IP-in-IP
      encapsulation.

      - For traffic leaving a RUL, if the RUL adds an opaque RPI then
      the description of the RAL applies.

      - The description for RALs applies to RAN in general.

      - Non-constrained uses of RPL are not in scope of this document.

      - Compression is based on [RFC8138].



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      - The flow label [RFC6437] is not needed in RPL.

7.  Storing mode

   In storing mode (SM) (fully stateful), the sender can determine if
   the destination is inside the LLN by looking if the destination
   address is matched by the DIO's Prefix Information Option (PIO)
   option.

   The following table (Figure 7) itemizes which headers are needed in
   each of the following scenarios.  It indicates whether an IPv6-in-
   IPv6 header must be added and what destination it must be addressed
   to: (1) the final destination (the RAL node that is the target
   (tgt)), (2) the "root", or (3) the 6LR parent of a RUL.

   In cases where no IPv6-in-IPv6 header is needed, the column states
   "No", and the destination is N/A (Not Applicable).  If the IPv6-in-
   IPv6 header is needed, the column shows "must".

   In all cases, the RPI is needed, since it identifies inconsistencies
   (loops) in the routing topology.  In general, the RH3 is not needed
   because it is not used in storing mode.  However, there is one
   scenario (from the root to the RUL in SM) where the RH3 can be used
   to point at the RUL (Figure 11).

   The leaf can be a router 6LR or a host, both indicated as 6LN.  The
   root refers to the 6LBR (see Figure 6).
























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   +---------------------+--------------+------------+----------------+
   | Interaction between |   Use Case   |IPv6-in-IPv6|IPv6-in-IPv6 dst|
   +---------------------+--------------+------------+----------------+
   |                     |  RAL to root |    No      |      N/A       |
   +                     +--------------+------------+----------------+
   |     Leaf - Root     |  root to RAL |    No      |      N/A       |
   +                     +--------------+------------+----------------+
   |                     | root to RUL  |   must     |       6LR      |
   +                     +--------------+------------+----------------+
   |                     | RUL to root  |   must     |       root     |
   +---------------------+--------------+------------+----------------+
   |                     |  RAL to Int  |   may      |      root      |
   +                     +--------------+------------+----------------+
   |   Leaf - Internet   |  Int to RAL  |   must     |      RAL (tgt) |
   +                     +--------------+------------+----------------+
   |                     |  RUL to Int  |   must     |       root     |
   +                     +--------------+------------+----------------+
   |                     |  Int to RUL  |   must     |       6LR      |
   +---------------------+--------------+------------+----------------+
   |                     |  RAL to RAL  |    No      |      N/A       |
   |  Leaf - Leaf        +--------------+------------+----------------+
   |                     |  RAL to RUL  |    No(up)  |      N/A       |
   |                     +              +------------+----------------+
   |                     |              | must(down) |      6LR       |
   |                     +--------------+------------+----------------+
   |                     |  RUL to RAL  |   must(up) |      root      |
   |                     |              +------------+----------------+
   |                     |              | must(down) |      RAL       |
   |                     +--------------+------------+----------------+
   |                     |  RUL to RUL  |   must(up) |      root      |
   |                     |              +------------+----------------+
   |                     |              | must(down) |      6LR       |
   |---------------------+--------------+------------+----------------+

      Figure 7: Table of IPv6-in-IPv6 encapsulation in Storing mode.

7.1.  Storing Mode: Interaction between Leaf and Root

   In this section is described the communication flow in storing mode
   (SM) between,

      RAL to root

      root to RAL

      RUL to root

      root to RUL



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7.1.1.  SM: Example of Flow from RAL to Root

   In storing mode, RFC 6553 (RPI) is used to send RPL Information
   instanceID and rank information.

   In this case the flow comprises:

   RAL (6LN) --> 6LR_i --> root(6LBR)

   For example, a communication flow could be: Node F (6LN) --> Node D
   (6LR_i) --> Node B (6LR_i)--> Node A root(6LBR)

   The RAL (Node F) inserts the RPI, and sends the packet to 6LR (Node
   D) which decrements the rank in the RPI and sends the packet up.
   When the packet arrives at 6LBR (Node A), the RPI is removed and the
   packet is processed.

   No IPv6-in-IPv6 header is required.

   The RPI can be removed by the 6LBR because the packet is addressed to
   the 6LBR.  The RAL must know that it is communicating with the 6LBR
   to make use of this scenario.  The RAL can know the address of the
   6LBR because it knows the address of the root via the DODAGID in the
   DIO messages.

   The Figure 8 summarizes what headers are needed for this use case.

   +-----------+-----+-------+------+
   |   Header  | RAL | 6LR_i | 6LBR |
   |           | src |       |  dst |
   +-----------+-----+-------+------+
   |   Added   | RPI |   --  |  --  |
   |  headers  |     |       |      |
   +-----------+-----+-------+------+
   |  Modified |  -- |  RPI  |  --  |
   |  headers  |     |       |      |
   +-----------+-----+-------+------+
   |  Removed  |  -- |   --  |  RPI |
   |  headers  |     |       |      |
   +-----------+-----+-------+------+
   | Untouched |  -- |   --  |  --  |
   |  headers  |     |       |      |
   +-----------+-----+-------+------+

       Figure 8: SM: Summary of the use of headers from RAL to root






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7.1.2.  SM: Example of Flow from Root to RAL

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RAL (6LN)

   For example, a communication flow could be: Node A root(6LBR) -->
   Node B (6LR_i) --> Node D (6LR_i) --> Node F (6LN)

   In this case the 6LBR inserts RPI and sends the packet down, the 6LR
   is going to increment the rank in RPI (it examines the RPLInstanceID
   to identify the right forwarding table), the packet is processed in
   the RAL and the RPI removed.

   No IPv6-in-IPv6 header is required.

   The Figure 9 summarizes what headers are needed for this use case.

   +-----------+------+-------+-----+
   |   Header  | 6LBR | 6LR_i | RAL |
   |           |  src |       | dst |
   +-----------+------+-------+-----+
   |   Added   |  RPI |   --  |  -- |
   |  headers  |      |       |     |
   +-----------+------+-------+-----+
   |  Modified |  --  |  RPI  |  -- |
   |  headers  |      |       |     |
   +-----------+------+-------+-----+
   |  Removed  |  --  |   --  | RPI |
   |  headers  |      |       |     |
   +-----------+------+-------+-----+
   | Untouched |  --  |   --  |  -- |
   |  headers  |      |       |     |
   +-----------+------+-------+-----+

       Figure 9: SM: Summary of the use of headers from root to RAL

7.1.3.  SM: Example of Flow from Root to RUL

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)

   For example, a communication flow could be: Node A (6LBR) --> Node B
   (6LR_i) --> Node E (6LR_n) --> Node G (RUL)

   6LR_i (Node B) represents the intermediate routers from the source
   (6LBR) to the destination (RUL), 1 <= i <= n, where n is the total



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   number of routers (6LR) that the packet goes through from the 6LBR
   (Node A) to the RUL (Node G).

   The 6LBR will encapsulate the packet in an IPv6-in-IPv6 header, and
   prepend an RPI.  The IPv6-in-IPv6 header is addressed to the 6LR
   parent of the RUL (6LR_n).  The 6LR parent of the RUL removes the
   header and sends the packet to the RUL.

   The Figure 10 summarizes what headers are needed for this use case.

   +-----------+---------+---------+---------+-----+
   |   Header  |   6LBR  |  6LR_i  |  6LR_n  | RUL |
   |           |   src   |         |         | dst |
   +-----------+---------+---------+---------+-----+
   |   Added   | IP6-IP6 |    --   |    --   |  -- |
   |  headers  |   RPI   |         |         |     |
   +-----------+---------+---------+---------+-----+
   |  Modified |    --   |         |     --  |  -- |
   |  headers  |         |   RPI   |         |     |
   +-----------+---------+---------+---------+-----+
   |  Removed  |    --   |    --   | IP6-IP6 |  -- |
   |  headers  |         |         |   RPI   |     |
   +-----------+---------+---------+---------+-----+
   | Untouched |    --   | IP6-IP6 |    --   |  -- |
   |  headers  |         |         |         |     |
   +-----------+---------+---------+---------+-----+

       Figure 10: SM: Summary of the use of headers from root to RUL

   IP-in-IP encapsulation MAY be avoided for Root to RUL communication.
   In SM, it can be replaced by a loose RH3 header that indicates the
   RUL, in which case the packet is routed to the 6LR as a normal SM
   operation, then the 6LR forwards to the RUL based on the RH3, and the
   RUL ignores both the consumed RH3 and the RPI, as in Non-Storing
   Mode.

   The Figure 11 summarizes what headers are needed for this scenario.














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   +-----------+----------+--------------+----------------+----------+
   |   Header  |   6LBR   |     6LR_i    |      6LR_n     |   RUL    |
   |           |    src   | i=(1,..,n-1) |                |   dst    |
   |           |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   |   Added   | RPI, RH3 |      --      |       --       |    --    |
   |  headers  |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   |  Modified |    --    |     RPI      |     RPI        |    --    |
   |  headers  |          |              | RH3(consumed)  |          |
   +-----------+----------+--------------+----------------+----------+
   |  Removed  |    --    |      --      |    --          |    --    |
   |  headers  |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   | Untouched |    --    |     RH3      |       --       | RPI, RH3 |
   |  headers  |          |              |                |  (both   |
   |           |          |              |                | ignored) |
   +-----------+----------+--------------+----------------+----------+

   Figure 11: SM: Summary of the use of headers from root to RUL without
                               encapsulation

7.1.4.  SM: Example of Flow from RUL to Root

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR)

   For example, a communication flow could be: Node G (RUL) --> Node E
   (6LR_1)--> Node B (6LR_i)--> Node A root(6LBR)

   6LR_i represents the intermediate routers from the source (RUL) to
   the destination (6LBR), 1 <= i <= n, where n is the total number of
   routers (6LR) that the packet goes through from the RUL to the 6LBR.

   When the packet arrives from the RUL (Node G) to 6LR_1 (Node E), the
   6LR_1 will insert encapsulate the packet in an IPv6-in-IPv6 header
   and prepend an RPI.  The IPv6-in-IPv6 header is addressed to the root
   (Node A).  The root removes the header and processes the packet.

   The Figure 12 shows the table that summarizes what headers are needed
   for this use case where the IPv6-in-IPv6 header is addressed to the
   root (Node A).








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  +-----------+------+--------------+----------------+-----------------+
  |   Header  | RUL  |     6LR_1    |     6LR_i      |       6LBR dst  |
  |           | src  |              |                |                 |
  |           | node |              |                |                 |
  +-----------+------+--------------+----------------+-----------------+
  |   Added   |  --  |   IP6-IP6    |                |         --      |
  |  headers  |      |     RPI      |    --          |                 |
  +-----------+------+--------------+----------------+-----------------+
  |  Modified |  --  |      --      |       RPI      |         --      |
  |  headers  |      |              |                |                 |
  +-----------+------+--------------+----------------+-----------------+
  |  Removed  |  --  |      --      |      ---       |     IP6-IP6     |
  |  headers  |      |              |                |       RPI       |
  +-----------+------+--------------+----------------+-----------------+
  | Untouched |  --  |      --      |      IP6-IP6   |         --      |
  |  headers  |      |              |                |                 |
  +-----------+------+--------------+----------------+-----------------+

      Figure 12: SM: Summary of the use of headers from RUL to root.

7.2.  SM: Interaction between Leaf and Internet.

   In this section is described the communication flow in storing mode
   (SM) between,

      RAL to Internet

      Internet to RAL

      RUL to Internet

      Internet to RUL

7.2.1.  SM: Example of Flow from RAL to Internet

   In this case the flow comprises:

   RAL (6LN) --> 6LR_i --> root (6LBR) --> Internet

   For example, the communication flow could be: Node F (RAL) --> Node D
   (6LR_i)--> Node B (6LR_i)--> Node A root(6LBR) --> Internet

   6LR_i represents the intermediate routers from the source (RAL) to
   the root (6LBR), 1 <= i <= n, where n is the total number of routers
   (6LR) that the packet goes through from the RAL to the 6LBR.






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   RPL information from RFC 6553 may go out to Internet as it will be
   ignored by nodes which have not been configured to be RPI aware.  No
   IPv6-in-IPv6 header is required.

   On the other hand, the RAL may insert the RPI encapsulated in a IPv6-
   in-IPv6 header to the root.  Thus, the root removes the RPI and send
   the packet to the Internet.

   Note: In this use case, it is used a node as a leaf, but this use
   case can be also applicable to any RPL-aware-node type (e.g. 6LR)

   The Figure 13 summarizes what headers are needed for this use case
   when there is no encapsulation.  Note that the RPI is modified by
   6LBR to set the SenderRank to zero in case that it is not already
   zero.  The Figure 14 summarizes what headers are needed when
   encapsulation to the root takes place.

   +-----------+-----+-------+------+-----------+
   |   Header  | RAL | 6LR_i | 6LBR |  Internet |
   |           | src |       |      |    dst    |
   +-----------+-----+-------+------+-----------+
   |   Added   | RPI |   --  |  --  |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   |  Modified |  -- |  RPI  |  RPI |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   |  Removed  |  -- |   --  |  --  |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   | Untouched |  -- |   --  |  --  |    RPI    |
   |  headers  |     |       |      | (Ignored) |
   +-----------+-----+-------+------+-----------+

     Figure 13: SM: Summary of the use of headers from RAL to Internet
                           with no encapsulation















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   +-----------+----------+--------------+--------------+--------------+
   |   Header  | RAL      |    6LR_i     |  6LBR        | Internet dst |
   |           | src      |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |   Added   | IP6-IP6  |     --       |      --      |         --   |
   |  headers  |   RPI    |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Modified |    --    |     RPI      |     --       |         --   |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Removed  |    --    |      --      |   IP6-IP6    |     --       |
   |  headers  |          |              |     RPI      |              |
   +-----------+----------+--------------+--------------+--------------+
   | Untouched |    --    |    IP6-IP6   |      --      |         --   |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+

     Figure 14: SM: Summary of the use of headers from RAL to Internet
                  with encapsulation to the root (6LBR).

7.2.2.  SM: Example of Flow from Internet to RAL

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> RAL (6LN)

   For example, a communication flow could be: Internet --> Node A
   root(6LBR) --> Node B (6LR_1) --> Node D (6LR_n) --> Node F (RAL)

   When the packet arrives from Internet to 6LBR the RPI is added in a
   outer IPv6-in-IPv6 header (with the IPv6-in-IPv6 destination address
   set to the RAL) and sent to 6LR, which modifies the rank in the RPI.
   When the packet arrives at the RAL the RPI is removed and the packet
   processed.

   The Figure 15 shows the table that summarizes what headers are needed
   for this use case.














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   +-----------+----------+--------------+--------------+--------------+
   |   Header  | Internet |     6LBR     |     6LR_i    |     RAL dst  |
   |           | src      |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |   Added   |    --    | IP6-IP6(RPI) |      --      |         --   |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Modified |    --    |      --      |      RPI     |         --   |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Removed  |    --    |      --      |      --      | IP6-IP6(RPI) |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+
   | Untouched |    --    |      --      |      --      |         --   |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+

    Figure 15: SM: Summary of the use of headers from Internet to RAL.

7.2.3.  SM: Example of Flow from RUL to Internet

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_i -->root (6LBR) --> Internet

   For example, a communication flow could be: Node G (RUL)--> Node E
   (6LR_1)--> Node B (6lR_i) --> Node A root(6LBR) --> Internet

   The node 6LR_1 (i=1) will add an IPv6-in-IPv6(RPI) header addressed
   to the root such that the root can remove the RPI before passing
   upwards.  In the intermediate 6LR, the rank in the RPI is modified.

   The originating node will ideally leave the IPv6 flow label as zero
   so that the packet can be better compressed through the LLN.  The
   6LBR will set the flow label of the packet to a non-zero value when
   sending to the Internet, for details check [RFC6437].

   The Figure 16 shows the table that summarizes what headers are needed
   for this use case.












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   +---------+-------+------------+-------------+-------------+--------+
   |  Header | IPv6  |   6LR_1    |    6LR_i    |     6LBR    |Internet|
   |         |  src  |            | [i=2,...,n] |             |  dst   |
   |         | node  |            |             |             |        |
   |         | (RUL) |            |             |             |        |
   +---------+-------+------------+-------------+-------------+--------+
   |  Added  |   --  |IP6-IP6(RPI)|     --      |      --     |    --  |
   | headers |       |            |             |             |        |
   +---------+-------+------------+-------------+-------------+--------+
   | Modified|   --  |    --      |      RPI    |      --     |    --  |
   | headers |       |            |             |             |        |
   +---------+-------+------------+-------------+-------------+--------+
   | Removed |   --  |    --      |     --      | IP6-IP6(RPI)|    --  |
   | headers |       |            |             |             |        |
   +---------+-------+------------+-------------+-------------+--------+
   |Untouched|   --  |    --      |     --      |      --     |    --  |
   | headers |       |            |             |             |        |
   +---------+-------+------------+-------------+-------------+--------+

    Figure 16: SM: Summary of the use of headers from RUL to Internet.

7.2.4.  SM: Example of Flow from Internet to RUL.

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)

   For example, a communication flow could be: Internet --> Node A
   root(6LBR) --> Node B (6LR_i)--> Node E (6LR_n) --> Node G (RUL)

   The 6LBR will have to add an RPI within an IPv6-in-IPv6 header.  The
   IPv6-in-IPv6 is addressed to the 6LR parent of the RUL.

   Further details about this are mentioned in
   [I-D.ietf-roll-unaware-leaves], which specifies RPL routing for a 6LN
   acting as a plain host and not being aware of RPL.

   The 6LBR may set the flow label on the inner IPv6-in-IPv6 header to
   zero in order to aid in compression [RFC8138][RFC6437].

   The Figure 17 shows the table that summarizes what headers are needed
   for this use case.









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   +---------+-------+------------+--------------+-------------+-------+
   |  Header |Inter- |   6LBR     |     6LR_i    |     6LR_n   | RUL   |
   |         | net   |            |[i=1,..,n-1]  |             | dst   |
   |         | src   |            |              |             |       |
   |         |       |            |              |             |       |
   +---------+-------+------------+--------------+-------------+-------+
   | Inserted|   --  |IP6-IP6(RPI)|   --         |      --     |   --  |
   | headers |       |            |              |             |       |
   +---------+-------+------------+--------------+-------------+-------+
   | Modified|   --  |    --      |      RPI     |      --     |   --  |
   | headers |       |            |              |             |       |
   +---------+-------+------------+--------------+-------------+-------+
   | Removed |   --  |    --      |   --         | IP6-IP6(RPI)|   --  |
   | headers |       |            |              |             |       |
   +---------+-------+------------+--------------+-------------+-------+
   |Untouched|   --  |    --      |      --      |      --     |   --  |
   | headers |       |            |              |             |       |
   +---------+-------+------------+--------------+-------------+-------+

    Figure 17: SM: Summary of the use of headers from Internet to RUL.

7.3.  SM: Interaction between Leaf and Leaf

   In this section is described the communication flow in storing mode
   (SM) between,

      RAL to RAL

      RAL to RUL

      RUL to RAL

      RUL to RUL

7.3.1.  SM: Example of Flow from RAL to RAL

   In [RFC6550] RPL allows a simple one-hop optimization for both
   storing and non-storing networks.  A node may send a packet destined
   to a one-hop neighbor directly to that node.  See section 9 in
   [RFC6550].

   When the nodes are not directly connected, then in storing mode, the
   flow comprises:

   RAL src (6LN) --> 6LR_ia --> common parent (6LR_x) --> 6LR_id --> RAL
   dst (6LN)





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   For example, a communication flow could be: Node F (RAL src)--> Node
   D (6LR_ia)--> Node B (6LR_x) --> Node E (6LR_id) --> Node H (RAL dst)

   6LR_ia (Node D) represents the intermediate routers from source to
   the common parent (6LR_x) (Node B), 1 <= ia <= n, where n is the
   total number of routers (6LR) that the packet goes through from RAL
   (Node F) to the common parent 6LR_x (Node B).

   6LR_id (Node E) represents the intermediate routers from the common
   parent (6LR_x) (Node B) to destination RAL (Node H), 1 <= id <= m,
   where m is the total number of routers (6LR) that the packet goes
   through from the common parent (6LR_x) to destination RAL (Node H).

   It is assumed that the two nodes are in the same RPL domain (that
   they share the same DODAG root).  At the common parent (Node B), the
   direction flag ('O' flag) of the RPI is changed (from decreasing
   ranks to increasing ranks).

   While the 6LR nodes will update the RPI, no node needs to add or
   remove the RPI, so no IPv6-in-IPv6 headers are necessary.

   The Figure 18 summarizes what headers are needed for this use case.

   +-----------+-----+--------+---------+--------+-----+
   |   Header  | RAL | 6LR_ia |  6LR_x  | 6LR_id | RAL |
   |           | src |        | (common |        | dst |
   |           |     |        | parent) |        |     |
   +-----------+-----+--------+---------+--------+-----+
   |   Added   | RPI |   --   |    --   |   --   |  -- |
   |  headers  |     |        |         |        |     |
   +-----------+-----+--------+---------+--------+-----+
   |  Modified |  -- |   RPI  |   RPI   |   RPI  |  -- |
   |  headers  |     |        |         |        |     |
   +-----------+-----+--------+---------+--------+-----+
   |  Removed  |  -- |   --   |    --   |   --   | RPI |
   |  headers  |     |        |         |        |     |
   +-----------+-----+--------+---------+--------+-----+
   | Untouched |  -- |   --   |    --   |   --   |  -- |
   |  headers  |     |        |         |        |     |
   +-----------+-----+--------+---------+--------+-----+

       Figure 18: SM: Summary of the Use of Headers from RAL to RAL

7.3.2.  SM: Example of Flow from RAL to RUL

   In this case the flow comprises:





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   RAL src (6LN) --> 6LR_ia --> common parent (6LBR - The root-) -->
   6LR_id --> RUL (IPv6 dst node)

   For example, a communication flow could be: Node F (RAL)--> Node D
   --> Node B--> Node A -->Node B --> Node E --> Node G (RUL)

   6LR_ia represents the intermediate routers from source (RAL) to the
   common parent (the Root), 1 <= ia <= n, where n is the total number
   of routers (6LR) that the packet goes through from RAL to the Root.

   6LR_id (Node E) represents the intermediate routers from the Root
   (Node B) to destination RUL (Node G).  In this case, 1 <= id <= m,
   where m is the total number of routers (6LR) that the packet goes
   through from the Root down to the destination RUL.

   In this case, the packet from the RAL goes to 6LBR because the route
   to the RUL is not injected into the RPL-SM.  Thus, the RAL inserts an
   RPI (RPI1) addressed to the root(6LBR).  The root does not removes
   the RPI1 (the root cannot remove an RPI if there is no
   encapsulation).  The root inserts an RPI2 encapsulated to the 6LR
   parent of the RUL, which removes the RPI2 before pasing the packet to
   the RUL.

   The Figure 19 summarizes what headers are needed for this use case.

   +----------+-------+-------+---------+---------+---------+---------+
   |  Header  | RAL   |6LR_ia |   6LBR  |  6LR_id |  6LR_m  | RUL     |
   |          | src   |       |         |         |         | dst     |
   |          | node  |       |         |         |         | node    |
   +----------+-------+-------+---------+---------+---------+---------+
   |  Added   |       |       | IP6-IP6 |    --   |    --   |  --     |
   | headers  | RPI1  |  --   |  (RPI2) |         |         |         |
   |          |       |       |         |         |         |         |
   +----------+-------+-------+---------+---------+---------+---------+
   | Modified |  --   |       |    --   |         |         |  --     |
   | headers  |       |  RPI1 |         |   RPI2  |  --     |         |
   |          |       |       |         |         |         |         |
   +----------+-------+-------+---------+---------+---------+---------+
   | Removed  |  --   |  --   |         |    --   | IP6-IP6 |  --     |
   | headers  |       |       |   --    |         |  (RPI2) |         |
   |          |       |       |         |         |         |         |
   +----------+-------+-------+---------+---------+---------+---------+
   |Untouched |  --   |  --   |  RPI1   |   RPI1  |   RPI1  | RPI1    |
   | headers  |       |       |         |         |         |(Ignored)|
   |          |       |       |         |         |         |         |
   +----------+-------+-------+---------+---------+---------+---------+

       Figure 19: SM: Summary of the Use of Headers from RAL to RUL



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7.3.3.  SM: Example of Flow from RUL to RAL

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_ia --> 6LBR --> 6LR_id --> RAL dst (6LN)

   For example, a communication flow could be: Node G (RUL)--> Node E
   --> Node B --> Node A --> Node B --> Node D --> Node F (RAL)

   6LR_ia (Node E) represents the intermediate routers from source (RUL)
   (Node G) to the root (Node A).  In this case, 1 <= ia <= n, where n
   is the total number of routers (6LR) that the packet goes through
   from source to the root.

   6LR_id represents the intermediate routers from the root (Node A) to
   destination RAL (Node F).  In this case, 1 <= id <= m, where m is the
   total number of routers (6LR) that the packet goes through from the
   root to the destination RAL.

   The 6LR_ia (ia=1) (Node E) receives the packet from the RUL (Node G)
   and inserts the RPI (RPI1) encapsulated in a IPv6-in-IPv6 header to
   the root.  The root removes the outer header including the RPI (RPI1)
   and inserts a new RPI (RPI2) addressed to the destination RAL (Node
   F).

   The Figure 20 shows the table that summarizes what headers are needed
   for this use case.
























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  +-----------+------+---------+---------+---------+---------+---------+
  |   Header  | RUL  |  6LR_1  |  6LR_ia |   6LBR  |  6LR_id |   RAL   |
  |           | src  |         |         |         |         |   dst   |
  |           | node |         |         |         |         |   node  |
  +-----------+------+---------+---------+---------+---------+---------+
  |   Added   |  --  | IP6-IP6 |    --   | IP6-IP6 |    --   |    --   |
  |  headers  |      |  (RPI1) |         |  (RPI2) |         |         |
  |           |      |         |         |         |         |         |
  +-----------+------+---------+---------+---------+---------+---------+
  |  Modified |  --  |         |         |    --   |         |    --   |
  |  headers  |      |   --    |  RPI1   |         |   RPI2  |         |
  |           |      |         |         |         |         |         |
  +-----------+------+---------+---------+---------+---------+---------+
  |  Removed  |  --  |         |    --   | IP6-IP6 |    --   | IP6-IP6 |
  |  headers  |      |  --     |         |  (RPI1) |         | (RPI2)  |
  |           |      |         |         |         |         |         |
  +-----------+------+---------+---------+---------+---------+---------+
  | Untouched |  --  |  --     |    --   |    --   |    --   |    --   |
  |  headers  |      |         |         |         |         |         |
  +-----------+------+---------+---------+---------+---------+---------+

       Figure 20: SM: Summary of the use of headers from RUL to RAL.

7.3.4.  SM: Example of Flow from RUL to RUL

   In this case the flow comprises:

   RUL (IPv6 src node)--> 6LR_1--> 6LR_ia --> 6LBR --> 6LR_id --> RUL
   (IPv6 dst node)

   For example, a communication flow could be: Node G (RUL src)--> Node
   E --> Node B --> Node A (root) --> Node C --> Node J (RUL dst)

   Internal nodes 6LR_ia (e.g: Node E or Node B) is the intermediate
   router from the RUL source (Node G) to the root (6LBR) (Node A).  In
   this case, 1 <= ia <= n, where n is the total number of routers (6LR)
   that the packet goes through from the RUL to the root. 6LR_1 refers
   when ia=1.

   6LR_id (Node C) represents the intermediate routers from the root
   (Node A) to the destination RUL dst node (Node J).  In this case, 1
   <= id <= m, where m is the total number of routers (6LR) that the
   packet goes through from the root to destination RUL.

   The 6LR_1 (Node E) receives the packet from the RUL (Node G) and
   inserts the RPI (RPI), encapsulated in an IPv6-in-IPv6 header
   directed to the root.  The root removes the outer header including




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   the RPI (RPI1) and inserts a new RPI (RPI2) addressed to the 6LR
   father of the RUL.

   The Figure 21 shows the table that summarizes what headers are needed
   for this use case.

  +---------+----+-------------+--------+---------+--------+-------+---+
  | Header  |RUL |   6LR_1     | 6LR_ia |   6LBR  | 6LR_id |6LR_n  |RUL|
  |         |src |             |        |         |        |       |dst|
  |         |    |             |        |         |        |       |   |
  +---------+----+-------------+--------+---------+--------+-------+---+
  | Added   | -- |IP6-IP6(RPI1)|   --   | IP6-IP6 |   --   | --    | --|
  | Headers |    |             |        |  (RPI2) |        |       |   |
  +---------+----+-------------+--------+---------+--------+-------+---+
  |Modified | -- |     --      |        |    --   |        | --    | --|
  |headers  |    |             |  RPI1  |         |  RPI2  |       |   |
  +---------+----+-------------+--------+---------+--------+-------+---+
  | Removed | -- |     --      |   --   | IP6-IP6 |   --   |IP6-IP6| --|
  | headers |    |             |        |  (RPI1) |        | (RPI2)|   |
  +---------+----+-------------+--------+---------+--------+-------+---+
  |Untouched| -- |     --      |   --   |    --   |   --   | --    | --|
  | headers |    |             |        |         |        |       |   |
  +---------+----+-------------+--------+---------+--------+-------+---+

       Figure 21: SM: Summary of the use of headers from RUL to RUL

8.  Non Storing mode

   In Non Storing Mode (Non-SM) (fully source routed), the 6LBR (DODAG
   root) has complete knowledge about the connectivity of all DODAG
   nodes, and all traffic flows through the root node.  Thus, there is
   no need for all nodes to know about the existence of RPL-unaware
   nodes.  Only the 6LBR needs to act if compensation is necessary for
   not-RPL aware receivers.

   The table (Figure 22) summarizes what headers are needed in the
   following scenarios, and indicates when the RPI, RH3 and IPv6-in-IPv6
   header are to be inserted.  The last column depicts the target
   destination of the IPv6-in-IPv6 header: 6LN (indicated by "RAL"), 6LR
   (parent of a RUL) or the root.  In cases where no IPv6-in-IPv6 header
   is needed, the column indicates "No".  There is no expectation on RPL
   that RPI can be omitted, because it is needed for routing, quality of
   service and compression.  This specification expects that an RPI is
   always present.  The term "may(up)" means that the IPv6-in-IPv6
   header may be necessary in the upwards direction.  The term
   "must(up)" means that the IPv6-in-IPv6 header must be present in the
   upwards direction.  The term "must(down)" means that the IPv6-in-IPv6
   header must be present in the downward direction.



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   The leaf can be a router 6LR or a host, both indicated as 6LN
   (Figure 6).  In the table (Figure 22) the (1) indicates a 6tisch case
   [RFC8180], where the RPI may still be needed for the RPLInstanceID to
   be available for priority/channel selection at each hop.

   The root always have to encapuslate on the way down

  +--- ------------+-------------+-----+-----+--------------+----------+
  |  Interaction   |   Use Case  | RPI | RH3 | IPv6-in-IPv6 | IP-in-IP |
  |     between    |             |     |     |              |    dst   |
  +----------------+-------------+-----+-----+--------------+----------+
  |                | RAL to root | Yes |  No |      No      |    No    |
  |                +-------------+-----+-----+--------------+----------+
  |  Leaf - Root   | root to RAL | Yes | Yes |      No      |    No    |
  |                +-------------+-----+-----+--------------+----------+
  |                | root to RUL | Yes | Yes |     must     |    6LR   |
  |                |             | (1) |     |              |          |
  |                +-------------+-----+-----+--------------+----------+
  |                | RUL to root | Yes |  No |     must     |   root   |
  +----------------+-------------+-----+-----+--------------+----------+
  |                |  RAL to Int | Yes |  No |    may(up)   |   root   |
  |                +-------------+-----+-----+--------------+----------+
  |Leaf - Internet |  Int to RAL | Yes | Yes |     must     |    RAL   |
  |                +-------------+-----+-----+--------------+----------+
  |                |  RUL to Int | Yes |  No |     must     |   root   |
  |                +-------------+-----+-----+--------------+----------+
  |                |  Int to RUL | Yes | Yes |     must     |    6LR   |
  +----------------+-------------+-----+-----+--------------+----------+
  |                |  RAL to RAL | Yes | Yes |    may(up)   |   root   |
  |                |             |     |     +--------------+----------+
  |                |             |     |     |  must(down)  |    RAL   |
  |  Leaf - Leaf   +-------------+-----+-----+--------------+----------+
  |                |  RAL to RUL | Yes | Yes |    may(up)   |   root   |
  |                |             |     |     +--------------+----------+
  |                |             |     |     |  must(down)  |    6LR   |
  |                +-------------+-----+-----+--------------+----------+
  |                |  RUL to RAL | Yes | Yes |   must(up)   |   root   |
  |                |             |     |     +--------------+----------+
  |                |             |     |     |  must(down)  |    RAL   |
  |                +-------------+-----+-----+--------------+----------+
  |                |  RUL to RUL | Yes | Yes |   must(up)   |   root   |
  |                |             |     |     +--------------+----------+
  |                |             |     |     |  must(down)  |    6LR   |
  +----------------+-------------+-----+-----+--------------+----------+

   Figure 22: Table that shows headers needed in Non-Storing mode: RPI,
                     RH3, IPv6-in-IPv6 encapsulation.




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8.1.  Non-Storing Mode: Interaction between Leaf and Root

   In this section is described the communication flow in Non Storing
   Mode (Non-SM) between,

      RAL to root

      root to RAL

      RUL to root

      root to RUL

8.1.1.  Non-SM: Example of Flow from RAL to root

   In non-storing mode the leaf node uses default routing to send
   traffic to the root.  The RPI must be included since it contains the
   rank information, which is used to avoid/detect loops.

   RAL (6LN) --> 6LR_i --> root(6LBR)

   For example, a communication flow could be: Node F --> Node D -->
   Node B --> Node A (root)

   6LR_i represents the intermediate routers from source to destination.
   In this case, 1 <= i <= n, where n is the total number of routers
   (6LR) that the packet goes through from source (RAL) to destination
   (6LBR).

   This situation is the same case as storing mode.

   The Figure 23 summarizes what headers are needed for this use case.



















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                    +-----------+-----+-------+------+
                    |   Header  | RAL | 6LR_i | 6LBR |
                    |           | src |       |  dst |
                    +-----------+-----+-------+------+
                    |   Added   | RPI |   --  |  --  |
                    |  headers  |     |       |      |
                    +-----------+-----+-------+------+
                    |  Modified |  -- |  RPI  |  --  |
                    |  headers  |     |       |      |
                    +-----------+-----+-------+------+
                    |  Removed  |  -- |   --  |  RPI |
                    |  headers  |     |       |      |
                    +-----------+-----+-------+------+
                    | Untouched |  -- |   --  |  --  |
                    |  headers  |     |       |      |
                    +-----------+-----+-------+------+

     Figure 23: Non-SM: Summary of the use of headers from RAL to root

8.1.2.  Non-SM: Example of Flow from root to RAL

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RAL (6LN)

   For example, a communication flow could be: Node A (root) --> Node B
   --> Node D --> Node F

   6LR_i represents the intermediate routers from source to destination.
   In this case, 1 <= i <= n, where n is the total number of routers
   (6LR) that the packet goes through from source (6LBR) to destination
   (RAL).

   The 6LBR inserts an RH3, and an RPI.  No IPv6-in-IPv6 header is
   necessary as the traffic originates with a RPL aware node, the 6LBR.
   The destination is known to be RPL-aware because the root knows the
   whole topology in non-storing mode.

   The Figure 24 summarizes what headers are needed for this use case.












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   +-----------+----------+----------+----------+
   |   Header  |   6LBR   |   6LR_i  |    RAL   |
   |           |    src   |          |    dst   |
   +-----------+----------+----------+----------+
   |   Added   | RPI, RH3 |    --    |    --    |
   |  headers  |          |          |          |
   +-----------+----------+----------+----------+
   |  Modified |    --    | RPI, RH3 |    --    |
   |  headers  |          |          |          |
   +-----------+----------+----------+----------+
   |  Removed  |    --    |    --    | RPI, RH3 |
   |  headers  |          |          |          |
   +-----------+----------+----------+----------+
   | Untouched |    --    |    --    |    --    |
   |  headers  |          |          |          |
   +-----------+----------+----------+----------+

     Figure 24: Non-SM: Summary of the use of headers from root to RAL

8.1.3.  Non-SM: Example of Flow from root to RUL

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)

   For example, a communication flow could be: Node A (root) --> Node B
   --> Node E --> Node G (RUL)

   6LR_i represents the intermediate routers from source to destination.
   In this case, 1 <= i <= n, where n is the total number of routers
   (6LR) that the packet goes through from source (6LBR) to destination
   (RUL).

   In the 6LBR, the RH3 is added; it is then modified at each
   intermediate 6LR (6LR_1 and so on), and it is fully consumed in the
   last 6LR (6LR_n) but is left in place.  When the RPI is added, the
   RUL, which does not understand the RPI, will ignore it (per
   [RFC8200]); thus, encapsulation is not necessary.

   The Figure 25 depicts the table that summarizes what headers are
   needed for this use case.










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   +-----------+----------+--------------+----------------+----------+
   |   Header  |   6LBR   |     6LR_i    |      6LR_n     |   RUL    |
   |           |    src   | i=(1,..,n-1) |                |   dst    |
   |           |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   |   Added   | RPI, RH3 |      --      |       --       |    --    |
   |  headers  |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   |  Modified |    --    |   RPI, RH3   |      RPI,      |    --    |
   |  headers  |          |              | RH3(consumed)  |          |
   +-----------+----------+--------------+----------------+----------+
   |  Removed  |    --    |      --      |    --          |    --    |
   |  headers  |          |              |                |          |
   +-----------+----------+--------------+----------------+----------+
   | Untouched |    --    |      --      |       --       | RPI, RH3 |
   |  headers  |          |              |                |  (both   |
   |           |          |              |                | ignored) |
   +-----------+----------+--------------+----------------+----------+

     Figure 25: Non-SM: Summary of the use of headers from root to RUL

8.1.4.  Non-SM: Example of Flow from RUL to root

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR) dst

   For example, a communication flow could be: Node G --> Node E -->
   Node B --> Node A (root)

   6LR_i represents the intermediate routers from source to destination.
   In this case, 1 <= i <= n, where n is the total number of routers
   (6LR) that the packet goes through from source (RUL) to destination
   (6LBR).  For example, 6LR_1 (i=1) is the router that receives the
   packets from the RUL.

   In this case, the RPI is added by the first 6LR (6LR_1) (Node E),
   encapsulated in an IPv6-in-IPv6 header, and modified in the
   subsequent 6LRs in the flow.  The RPI and the entire packet are
   consumed by the root.

   The Figure 26 shows the table that summarizes what headers are needed
   for this use case.








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  +---------+----+-----------------+-----------------+-----------------+
  |         |RUL |                 |                 |                 |
  |  Header |src |      6LR_1      |      6LR_i      |     6LBR dst    |
  |         |node|                 |                 |                 |
  +---------+----+-----------------+-----------------+-----------------+
  |  Added  | -- |IPv6-in-IPv6(RPI)|        --       |        --       |
  | headers |    |                 |                 |                 |
  +---------+----+-----------------+-----------------+-----------------+
  | Modified| -- |        --       |       RPI       |        --       |
  | headers |    |                 |                 |                 |
  +---------+----+-----------------+-----------------+-----------------+
  | Removed | -- |        --       |        --       |IPv6-in-IPv6(RPI)|
  | headers |    |                 |                 |                 |
  +---------+----+-----------------+-----------------+-----------------+
  |Untouched| -- |        --       |        --       |        --       |
  | headers |    |                 |                 |                 |
  +---------+----+-----------------+-----------------+-----------------+

     Figure 26: Non-SM: Summary of the use of headers from RUL to root

8.2.  Non-Storing Mode: Interaction between Leaf and Internet

   This section will describe the communication flow in Non Storing Mode
   (Non-SM) between:

      RAL to Internet

      Internet to RAL

      RUL to Internet

      Internet to RUL

8.2.1.  Non-SM: Example of Flow from RAL to Internet

   In this case the flow comprises:

   RAL (6LN) src --> 6LR_i --> root (6LBR) --> Internet dst

   For example, a communication flow could be: Node F (RAL) --> Node D
   --> Node B --> Node A --> Internet

   6LR_i represents the intermediate routers from source to destination,
   1 <= i <= n, where n is the total number of routers (6LR) that the
   packet goes through from source (RAL) to 6LBR.






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   In this case, the encapsulation from the RAL to the root is optional.
   The simplest case is when the RPI gets to the Internet (as the
   Figure 27 shows it), knowing that the Internet is going to ignore it.

   The IPv6 flow label should be set to zero to aid in compression
   [RFC8138], and the 6LBR will set it to a non-zero value when sending
   towards the Internet [RFC6437].

   The Figure 27 summarizes what headers are needed for this use case
   when no encapsulation is used.  The Figure 28 summarizes what headers
   are needed for this use case when encapsulation to the root is used.

   +-----------+-----+-------+------+-----------+
   |   Header  | RAL | 6LR_i | 6LBR |  Internet |
   |           | src |       |      |    dst    |
   +-----------+-----+-------+------+-----------+
   |   Added   | RPI |   --  |  --  |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   |  Modified |  -- |  RPI  |  RPI |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   |  Removed  |  -- |   --  |  --  |     --    |
   |  headers  |     |       |      |           |
   +-----------+-----+-------+------+-----------+
   | Untouched |  -- |   --  |  --  |    RPI    |
   |  headers  |     |       |      | (Ignored) |
   +-----------+-----+-------+------+-----------+

   Figure 27: Non-SM: Summary of the use of headers from RAL to Internet
                           with no encapsulation




















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   +-----------+--------------+--------------+--------------+----------+
   |   Header  |      RAL     |     6LR_i    |     6LBR     | Internet |
   |           |      src     |              |              |    dst   |
   +-----------+--------------+--------------+--------------+----------+
   |   Added   | IPv6-in-IPv6 |      --      |      --      |    --    |
   |  headers  |     (RPI)    |              |              |          |
   +-----------+--------------+--------------+--------------+----------+
   |  Modified |      --      |              |      --      |    --    |
   |  headers  |              |     RPI      |              |          |
   +-----------+--------------+--------------+--------------+----------+
   |  Removed  |      --      |      --      | IPv6-in-IPv6 |    --    |
   |  headers  |              |              |     (RPI)    |          |
   +-----------+--------------+--------------+--------------+----------+
   | Untouched |      --      |      --      |      --      |    --    |
   |  headers  |              |              |              |          |
   +-----------+--------------+--------------+--------------+----------+

   Figure 28: Non-SM: Summary of the use of headers from RAL to Internet
                      with encapsulation to the root

8.2.2.  Non-SM: Example of Flow from Internet to RAL

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> RAL dst (6LN)

   For example, a communication flow could be: Internet --> Node A
   (root) --> Node B --> Node D --> Node F (RAL)

   6LR_i represents the intermediate routers from source to destination,
   1 <= i <= n, where n is the total number of routers (6LR) that the
   packet goes through from 6LBR to destination (RAL).

   The 6LBR must add an RH3 header.  As the 6LBR will know the path and
   address of the target node, it can address the IPv6-in-IPv6 header to
   that node.  The 6LBR will zero the flow label upon entry in order to
   aid compression [RFC8138].

   The Figure 29 summarizes what headers are needed for this use case.












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   +-----------+----------+--------------+--------------+--------------+
   |   Header  | Internet |     6LBR     |     6LR_i    |      RAL     |
   |           |    src   |              |              |      dst     |
   +-----------+----------+--------------+--------------+--------------+
   |   Added   |    --    | IPv6-in-IPv6 |      --      |      --      |
   |  headers  |          |  (RH3, RPI)  |              |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Modified |    --    |      --      | IPv6-in-IPv6 |      --      |
   |  headers  |          |              |  (RH3, RPI)  |              |
   +-----------+----------+--------------+--------------+--------------+
   |  Removed  |    --    |      --      |      --      | IPv6-in-IPv6 |
   |  headers  |          |              |              |  (RH3, RPI)  |
   +-----------+----------+--------------+--------------+--------------+
   | Untouched |    --    |      --      |      --      |      --      |
   |  headers  |          |              |              |              |
   +-----------+----------+--------------+--------------+--------------+

   Figure 29: Non-SM: Summary of the use of headers from Internet to RAL

8.2.3.  Non-SM: Example of Flow from RUL to Internet

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_i -->root (6LBR) --> Internet
   dst

   For example, a communication flow could be: Node G --> Node E -->
   Node B --> Node A --> Internet

   6LR_i represents the intermediate routers from source to destination,
   1 <= i <= n, where n is the total number of routers (6LRs) that the
   packet goes through from the source (RUL) to the 6LBR, e.g., 6LR_1
   (i=1).

   In this case the flow label is recommended to be zero in the RUL.  As
   RPL headers are added in the RUL packet, the first 6LR (6LR_1) will
   add an RPI inside a new IPv6-in-IPv6 header.  The IPv6-in-IPv6 header
   will be addressed to the root.  This case is identical to the
   storing-mode case (see Section 7.2.3).

   The Figure 30 shows the table that summarizes what headers are needed
   for this use case.









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   +---------+----+-------------+--------------+--------------+--------+
   |  Header |RUL |    6LR_1    |     6LR_i    |     6LBR     |Internet|
   |         |src |             |  [i=2,..,n]  |              |  dst   |
   |         |node|             |              |              |        |
   +---------+----+-------------+--------------+--------------+--------+
   |  Added  | -- |IP6-IP6(RPI) |      --      |      --      |   --   |
   | headers |    |             |              |              |        |
   +---------+----+-------------+--------------+--------------+--------+
   | Modified| -- |     --      |     RPI      |      --      |   --   |
   | headers |    |             |              |              |        |
   +---------+----+-------------+--------------+--------------+--------+
   | Removed | -- |     --      |      --      | IP6-IP6(RPI) |   --   |
   | headers |    |             |              |              |        |
   +---------+----+-------------+--------------+--------------+--------+
   |Untouched| -- |     --      |      --      |      --      |   --   |
   | headers |    |             |              |              |        |
   +---------+----+-------------+--------------+--------------+--------+

   Figure 30: Non-SM: Summary of the use of headers from RUL to Internet

8.2.4.  Non-SM: Example of Flow from Internet to RUL

   In this case the flow comprises:

   Internet src --> root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)

   For example, a communication flow could be: Internet --> Node A
   (root) --> Node B --> Node E --> Node G

   6LR_i represents the intermediate routers from source to destination,
   1 <= i <= n, where n is the total number of routers (6LR) that the
   packet goes through from 6LBR to RUL.

   The 6LBR must add an RH3 header inside an IPv6-in-IPv6 header.  The
   6LBR will know the path, and will recognize that the final node is
   not a RPL capable node as it will have received the connectivity DAO
   from the nearest 6LR.  The 6LBR can therefore make the IPv6-in-IPv6
   header destination be the last 6LR.  The 6LBR will set to zero the
   flow label upon entry in order to aid compression [RFC8138].

   The Figure 31 shows the table that summarizes what headers are needed
   for this use case.









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  +----------+--------+------------------+-----------+-----------+-----+
  |  Header  |Internet|       6LBR       |   6LR_i   |   6LR_n   | RUL |
  |          |   src  |                  |           |           | dst |
  +----------+--------+------------------+-----------+-----------+-----+
  |  Added   |   --   | IP6-IP6(RH3,RPI) |     --    |     --    |  -- |
  | headers  |        |                  |           |           |     |
  +----------+--------+------------------+-----------+-----------+-----+
  | Modified |   --   |        --        |  IP6-IP6  |     --    |  -- |
  | headers  |        |                  | (RH3,RPI) |           |     |
  +----------+--------+------------------+-----------+-----------+-----+
  | Removed  |   --   |        --        |     --    |  IP6-IP6  |  -- |
  | headers  |        |                  |           | (RH3,RPI) |     |
  +----------+--------+------------------+-----------+-----------+-----+
  |Untouched |   --   |        --        |     --    |     --    |  -- |
  | headers  |        |                  |           |           |     |
  +----------+--------+------------------+-----------+-----------+-----+

     Figure 31: Non-SM: Summary of the use of headers from Internet to
                                   RUL.

8.3.  Non-SM: Interaction between leaves

   In this section is described the communication flow in Non Storing
   Mode (Non-SM) between,

      RAL to RAL

      RAL to RUL

      RUL to RAL

      RUL to RUL

8.3.1.  Non-SM: Example of Flow from RAL to RAL

   In this case the flow comprises:

   RAL src --> 6LR_ia --> root (6LBR) --> 6LR_id --> RAL dst

   For example, a communication flow could be: Node F (RAL src)--> Node
   D --> Node B --> Node A (root) --> Node B --> Node E --> Node H (RAL
   dst)

   6LR_ia represents the intermediate routers from source to the root, 1
   <= ia <= n, where n is the total number of routers (6LR) that the
   packet goes through from RAL to the root.





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   6LR_id represents the intermediate routers from the root to the
   destination, 1 <= id <= m, where m is the total number of the
   intermediate routers (6LR).

   This case involves only nodes in same RPL domain.  The originating
   node will add an RPI to the original packet, and send the packet
   upwards.

   The originating node may put the RPI (RPI1) into an IPv6-in-IPv6
   header addressed to the root, so that the 6LBR can remove that
   header.  If it does not, then the RPI1 is forwarded down from the
   root in the inner header to no avail.

   The 6LBR will need to insert an RH3 header, which requires that it
   add an IPv6-in-IPv6 header.  It removes the RPI(RPI1), as it was
   contained in an IPv6-in-IPv6 header addressed to it.  Otherwise,
   there may be an RPI buried inside the inner IP header, which should
   get ignored.  The root inserts an RPI (RPI2) alongside the RH3.

   Networks that use the RPL P2P extension [RFC6997] are essentially
   non-storing DODAGs and fall into this scenario or scenario
   Section 8.1.2, with the originating node acting as 6LBR.

   The Figure 32 shows the table that summarizes what headers are needed
   for this use case when encapsulation to the root takes place.

   The Figure 33 shows the table that summarizes what headers are needed
   for this use case when there is no encapsulation to the root.  Note
   that in the Modified headers row, going up in each 6LR_ia only the
   RPI1 is changed.  Going down, in each 6LR_id the IPv6 header is
   swapped with the RH3 so both are changed alongside with the RPI2.




















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   +---------+-------+----------+------------+----------+------------+
   |  Header | RAL   |   6LR_ia |    6LBR    | 6LR_id   |     RAL    |
   |         | src   |          |            |          |     dst    |
   +---------+-------+----------+------------+----------+------------+
   |  Added  |IP6-IP6|          |  IP6-IP6   |  --      |     --     |
   | headers |(RPI1) |   --     |(RH3-> RAL, |          |            |
   |         |       |          |   RPI2)    |          |            |
   +---------+-------+----------+------------+----------+------------+
   | Modified|  --   |          |    --      | IP6-IP6  |    --      |
   | headers |       |   RPI1   |            |(RH3,RPI2)|            |
   +---------+-------+----------+------------+----------+------------+
   | Removed |    -- |    --    |   IP6-IP6  |  --      |  IP6-IP6   |
   | headers |       |          |   (RPI1)   |          |   (RH3,    |
   |         |       |          |            |          |   RPI2)    |
   +---------+-------+----------+------------+----------+------------+
   |Untouched|    -- |    --    |    --      |  --      |    --      |
   | headers |       |          |            |          |            |
   +---------+-------+----------+------------+----------+------------+

   Figure 32: Non-SM: Summary of the Use of Headers from RAL to RAL with
                        encapsulation to the root.

   +-----------+------+--------+---------+---------+---------+
   |   Header  |  RAL | 6LR_ia |   6LBR  |  6LR_id |   RAL   |
   +-----------+------+--------+---------+---------+---------+
   |  Inserted | RPI1 |   --   | IP6-IP6 |    --   |    --   |
   |  headers  |      |        |  (RH3,  |         |         |
   |           |      |        |   RPI2) |         |         |
   +-----------+------+--------+---------+---------+---------+
   |  Modified |  --  |  RPI1  |    --   | IP6-IP6 |    --   |
   |  headers  |      |        |         |  (RH3,  |         |
   |           |      |        |         |   RPI2) |         |
   +-----------+------+--------+---------+---------+---------+
   |  Removed  |  --  |   --   |    --   |    --   | IP6-IP6 |
   |  headers  |      |        |         |         |  (RH3,  |
   |           |      |        |         |         |   RPI2) |
   |           |      |        |         |         |         |
   +-----------+------+--------+---------+---------+---------+
   | Untouched |  --  |   --   |   RPI1  |   RPI1  |   RPI1  |
   |  headers  |      |        |         |         |(Ignored)|
   +-----------+------+--------+---------+---------+---------+

     Figure 33: Non-SM: Summary of the Use of Headers from RAL to RAL
                    without encapsulation to the root.







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8.3.2.  Non-SM: Example of Flow from RAL to RUL

   In this case the flow comprises:

   RAL --> 6LR_ia --> root (6LBR) --> 6LR_id --> RUL (IPv6 dst node)

   For example, a communication flow could be: Node F (RAL) --> Node D
   --> Node B --> Node A (root) --> Node B --> Node E --> Node G (RUL)

   6LR_ia represents the intermediate routers from source to the root, 1
   <= ia <= n, where n is the total number of intermediate routers (6LR)

   6LR_id represents the intermediate routers from the root to the
   destination, 1 <= id <= m, where m is the total number of the
   intermediate routers (6LRs).

   As in the previous case, the RAL (6LN) may insert an RPI (RPI1)
   header which must be in an IPv6-in-IPv6 header addressed to the root
   so that the 6LBR can remove this RPI.  The 6LBR will then insert an
   RH3 inside a new IPv6-in-IPv6 header addressed to the last 6LR_id
   (6LR_id = m) alongside the insertion of RPI2.

   If the originating node does not not put the RPI (RPI1) into an IPv6-
   in-IPv6 header addressed to the root.  Then, the RPI1 is forwarded
   down from the root in the inner header to no avail.

   The Figure 34 shows the table that summarizes what headers are needed
   for this use case when encapsulation to the root takes place.  The
   Figure 35 shows the table that summarizes what headers are needed for
   this use case when no encapsulation to the root takes place.





















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  +-----------+---------+---------+---------+---------+---------+------+
  |   Header  |   RAL   |  6LR_ia |   6LBR  |  6LR_id |  6LR_m  | RUL  |
  |           |   src   |         |         |         |         | dst  |
  |           |   node  |         |         |         |         | node |
  +-----------+---------+---------+---------+---------+---------+------+
  |   Added   | IP6-IP6 |         | IP6-IP6 |    --   |    --   |  --  |
  |  headers  |  (RPI1) | --      |  (RH3,  |         |         |      |
  |           |         |         |   RPI2) |         |         |      |
  +-----------+---------+---------+---------+---------+---------+------+
  |  Modified |    --   |         |    --   | IP6-IP6 |         |  --  |
  |  headers  |         |  RPI1   |         |  (RH3,  |  --     |      |
  |           |         |         |         |   RPI2) |         |      |
  +-----------+---------+---------+---------+---------+---------+------+
  |  Removed  |    --   |    --   | IP6-IP6 |    --   | IP6-IP6 |  --  |
  |  headers  |         |         |  (RPI1) |         |  (RH3,  |      |
  |           |         |         |         |         |   RPI2) |      |
  +-----------+---------+---------+---------+---------+---------+------+
  | Untouched |    --   |    --   |    --   |    --   |    --   |  --  |
  |  headers  |         |         |         |         |         |      |
  +-----------+---------+---------+---------+---------+---------+------+

   Figure 34: Non-SM: Summary of the use of headers from RAL to RUL with
                        encapsulation to the root.

   +-----------+------+--------+---------+---------+---------+---------+
   |   Header  |  RAL | 6LR_ia |   6LBR  |  6LR_id |  6LR_n  |   RUL   |
   |           |  src |        |         |         |         |   dst   |
   |           | node |        |         |         |         |   node  |
   +-----------+------+--------+---------+---------+---------+---------+
   |  Inserted | RPI1 |   --   | IP6-IP6 |    --   |    --   |    --   |
   |  headers  |      |        |  (RH3,  |         |         |         |
   |           |      |        |   RPI2) |         |         |         |
   +-----------+------+--------+---------+---------+---------+---------+
   |  Modified |  --  |  RPI1  |    --   | IP6-IP6 |    --   |    --   |
   |  headers  |      |        |         |  (RH3,  |         |         |
   |           |      |        |         |   RPI2) |         |         |
   +-----------+------+--------+---------+---------+---------+---------+
   |  Removed  |  --  |   --   |    --   |    --   | IP6-IP6 |    --   |
   |  headers  |      |        |         |         |  (RH3,  |         |
   |           |      |        |         |         |   RPI2) |         |
   +-----------+------+--------+---------+---------+---------+---------+
   | Untouched |  --  |   --   |   RPI1  |   RPI1  |   RPI1  |   RPI1  |
   |  headers  |      |        |         |         |         |(Ignored)|
   +-----------+------+--------+---------+---------+---------+---------+


     Figure 35: Non-SM: Summary of the use of headers from RAL to RUL
                    without encapsulation to the root.



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8.3.3.  Non-SM: Example of Flow from RUL to RAL

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_ia --> root (6LBR) --> 6LR_id
   --> RAL dst (6LN)

   For example, a communication flow could be: Node G (RUL)--> Node E
   --> Node B --> Node A (root) --> Node B --> Node E --> Node H (RAL)

   6LR_ia represents the intermediate routers from source to the root, 1
   <= ia <= n, where n is the total number of intermediate routers (6LR)

   6LR_id represents the intermediate routers from the root to the
   destination, 1 <= id <= m, where m is the total number of the
   intermediate routers (6LR).

   In this scenario the RPI (RPI1) is added by the first 6LR (6LR_1)
   inside an IPv6-in-IPv6 header addressed to the root.  The 6LBR will
   remove this RPI, and add it's own IPv6-in-IPv6 header containing an
   RH3 header and an RPI (RPI2).

   The Figure 36 shows the table that summarizes what headers are needed
   for this use case.

   +----------+------+---------+---------+---------+---------+---------+
   |  Header  | RUL  |  6LR_1  |  6LR_ia |   6LBR  |  6LR_id |   RAL   |
   |          | src  |         |         |         |         |   dst   |
   |          | node |         |         |         |         |   node  |
   +----------+------+---------+---------+---------+---------+---------+
   |  Added   |  --  | IP6-IP6 |    --   | IP6-IP6 |    --   |    --   |
   | headers  |      |  (RPI1) |         |  (RH3,  |         |         |
   |          |      |         |         |   RPI2) |         |         |
   +----------+------+---------+---------+---------+---------+---------+
   | Modified |  --  |         |         |    --   | IP6-IP6 |    --   |
   | headers  |      |  --     |  RPI1   |         |  (RH3,  |         |
   |          |      |         |         |         |   RPI2) |         |
   +----------+------+---------+---------+---------+---------+---------+
   | Removed  |  --  |         |    --   | IP6-IP6 |    --   | IP6-IP6 |
   | headers  |      | --      |         |  (RPI1) |         |  (RH3,  |
   |          |      |         |         |         |         |   RPI2) |
   +----------+------+---------+---------+---------+---------+---------+
   |Untouched |  --  | --      |    --   |    --   |    --   |    --   |
   | headers  |      |         |         |         |         |         |
   +----------+------+---------+---------+---------+---------+---------+

     Figure 36: Non-SM: Summary of the use of headers from RUL to RAL.




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8.3.4.  Non-SM: Example of Flow from RUL to RUL

   In this case the flow comprises:

   RUL (IPv6 src node) --> 6LR_1 --> 6LR_ia --> root (6LBR) --> 6LR_id
   --> RUL (IPv6 dst node)

   For example, a communication flow could be: Node G --> Node E -->
   Node B --> Node A (root) --> Node C --> Node J

   6LR_ia represents the intermediate routers from source to the root, 1
   <= ia <= n, where n is the total number of intermediate routers (6LR)

   6LR_id represents the intermediate routers from the root to the
   destination, 1 <= id <= m, where m is the total number of the
   intermediate routers (6LR).

   This scenario is the combination of the previous two cases.

   The Figure 37 shows the table that summarizes what headers are needed
   for this use case.

   +---------+------+-------+-------+---------+-------+---------+------+
   |  Header | RUL  | 6LR_1 | 6LR_ia|   6LBR  |6LR_id |  6LR_m  | RUL  |
   |         | src  |       |       |         |       |         | dst  |
   |         | node |       |       |         |       |         | node |
   +---------+------+-------+-------+---------+-------+---------+------+
   |  Added  |  --  |IP6-IP6|  --   | IP6-IP6 |  --   |    --   |  --  |
   | headers |      | (RPI1)|       |  (RH3,  |       |         |      |
   |         |      |       |       |   RPI2) |       |         |      |
   +---------+------+-------+-------+---------+-------+---------+------+
   | Modified|  --  |  --   |       |    --   |IP6-IP6|    --   |  --  |
   | headers |      |       |  RPI1 |         | (RH3, |         |      |
   |         |      |       |       |         |  RPI2)|         |      |
   +---------+------+-------+-------+---------+-------+---------+------+
   | Removed |  --  |  --   |  --   | IP6-IP6 |  --   | IP6-IP6 |  --  |
   | headers |      |       |       |  (RPI1) |       |  (RH3,  |      |
   |         |      |       |       |         |       |   RPI2) |      |
   +---------+------+-------+-------+---------+-------+---------+------+
   |Untouched|  --  |  --   |  --   |    --   |  --   |    --   |  --  |
   | headers |      |       |       |         |       |         |      |
   +---------+------+-------+-------+---------+-------+---------+------+

     Figure 37: Non-SM: Summary of the use of headers from RUL to RUL







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9.  Operational Considerations of supporting RUL-leaves

   Roughly half of the situations described in this document involve
   leaf ("host") nodes that do not speak RPL.  These nodes fall into two
   further categories: ones that drop a packet that have RPI or RH3
   headers, and ones that continue to process a packet that has RPI and/
   or RH3 headers.

   [RFC8200] provides for new rules that suggest that nodes that have
   not been configured (explicitly) to examine Hop-by-Hop headers,
   should ignore those headers, and continue processing the packet.
   Despite this, and despite the switch from 0x63 to 0x23, there may be
   hosts that are pre-RFC8200, or simply intolerant.  Those hosts will
   drop packets that continue to have RPL artifacts in them.  In
   general, such hosts can not be easily supported in RPL LLNs.

   There are some specific cases where it is possible to remove the RPL
   artifacts prior to forwarding the packet to the leaf host.  The
   critical thing is that the artifacts have been inserted by the RPL
   root inside an IPv6-in-IPv6 header, and that the header has been
   addressed to the 6LR immediately prior to the leaf node.  In that
   case, in the process of removing the IPv6-in-IPv6 header, the
   artifacts can also be removed.

   The above case occurs whenever traffic originates from the outside
   the LLN (the "Internet" cases above), and non-storing mode is used.
   In non-storing mode, the RPL root knows the exact topology (as it
   must create the RH3 header) and therefore knows which 6LR is prior to
   the leaf.  For example, in Figure 6, Node E is the 6LR prior to leaf
   Node G, or Node C is the 6LR prior to leaf Node J.

   traffic originating from the RPL root (such as when the data
   collection system is co-located on the RPL root), does not require an
   IPv6-in-IPv6 header (in storing or non-storing mode), as the packet
   is originating at the root, and the root can insert the RPI and RH3
   headers directly into the packet, as it is formed.  Such a packet is
   slightly smaller, but only can be sent to nodes (whether RPL aware or
   not), that will tolerate the RPL artifacts.

   An operator that finds itself with a high amount of traffic from the
   RPL root to RPL-not-aware-leaves, will have to do IPv6-in-IPv6
   encapsulation if the leaf is not tolerant of the RPL artifacts.  Such
   an operator could otherwise omit this unnecessary header if it was
   certain of the properties of the leaf.

   As storing mode can not know the final path of the traffic,
   intolerant (that drop packets with RPL artifacts) leaf nodes can not
   be supported.



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10.  Operational considerations of introducing 0x23

   This section describes the operational considerations of introducing
   the new RPI Option Type of 0x23.

   During bootstrapping the node gets the DIO with the information of
   RPI Option Type, indicating the new RPI in the DODAG Configuration
   option Flag.  The DODAG root is in charge to configure the current
   network to the new value, through DIO messages and when all the nodes
   are set with the new value.  The DODAG should change to a new DODAG
   version.  In case of rebooting, the node does not remember the RPI
   Option Type.  Thus, the DIO is sent with a flag indicating the new
   RPI Option Type.

   The DODAG Configuration option is contained in a RPL DIO message,
   which contains a unique DTSN counter.  The leaf nodes respond to this
   message with DAO messages containing the same DTSN.  This is a normal
   part of RPL routing; the RPL root therefore knows when the updated
   DODAG Configuration option has been seen by all nodes.

   Before the migration happens, all the RPL-aware nodes should support
   both values .  The migration procedure it is triggered when the DIO
   is sent with the flag indicating the new RPI Option Type.  Namely, it
   remains at 0x63 until it is sure that the network is capable of 0x23,
   then it abruptly change to 0x23.  This options allows to send packets
   to not-RPL nodes, which should ignore the option and continue
   processing the packets.

   As mentioned previously, indicating the new RPI in the DODAG
   Configuration option flag is a way to avoid the flag day (lack of
   interoperation) in a network using 0x63 as the RPI Option Type value.
   It is suggested that RPL implementations accept both 0x63 and 0x23
   RPI Option type values when processing the header to enable
   interoperability.

11.  IANA Considerations

   This document updates the registration made in [RFC6553] Destination
   Options and Hop-by-Hop Options registry from 0x63 to 0x23 as shown in
   Figure 38.











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   +-------+-------------------+------------------------+---------- -+
   |  Hex  |    Binary Value   |       Description      | Reference  |
   + Value +-------------------+                        +            +
   |       | act | chg |  rest |                        |            |
   +-------+-----+-----+-------+------------------------+------------+
   |  0x23 |  00 |  1  | 00011 |       RPL Option       |[RFCXXXX](*)|
   +-------+-----+-----+-------+------------------------+------------+
   |  0x63 |  01 |  1  | 00011 | RPL Option(DEPRECATED) | [RFC6553]  |
   |       |     |     |       |                        |[RFCXXXX](*)|
   +-------+-----+-----+-------+------------------------+------------+

     Figure 38: Option Type in RPL Option.(*)represents this document

   DODAG Configuration option is updated as follows (Figure 39):


                 +------------+-----------------+---------------+
                 | Bit number |   Description   |   Reference   |
                 +------------+-----------------+---------------+
                 |      3     | RPI 0x23 enable | This document |
                 +------------+-----------------+---------------+


   Figure 39: DODAG Configuration option Flag to indicate the RPI-flag-
                                   day.

12.  Security Considerations

   The security considerations covered in [RFC6553] and [RFC6554] apply
   when the packets are in the RPL Domain.

   The IPv6-in-IPv6 mechanism described in this document is much more
   limited than the general mechanism described in [RFC2473].  The
   willingness of each node in the LLN to decapsulate packets and
   forward them could be exploited by nodes to disguise the origin of an
   attack.

   While a typical LLN may be a very poor origin for attack traffic (as
   the networks tend to be very slow, and the nodes often have very low
   duty cycles), given enough nodes, LLNs could still have a significant
   impact, particularly if attack is targeting another LLN.
   Additionally, some uses of RPL involve large backbone ISP scale
   equipment [I-D.ietf-anima-autonomic-control-plane], which may be
   equipped with multiple 100Gb/s interfaces.

   Blocking or careful filtering of IPv6-in-IPv6 traffic entering the
   LLN as described above will make sure that any attack that is mounted
   must originate from compromised nodes within the LLN.  The use of



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   BCP38 [BCP38] filtering at the RPL root on egress traffic will both
   alert the operator to the existence of the attack, as well as drop
   the attack traffic.  As the RPL network is typically numbered from a
   single prefix, which is itself assigned by RPL, BCP38 filtering
   involves a single prefix comparison and should be trivial to
   automatically configure.

   There are some scenarios where IPv6-in-IPv6 traffic should be allowed
   to pass through the RPL root, such as the IPv6-in-IPv6 mediated
   communications between a new Pledge and the Join Registrar/
   Coordinator (JRC) when using [I-D.ietf-anima-bootstrapping-keyinfra]
   and [I-D.ietf-6tisch-dtsecurity-zerotouch-join].  This is the case
   for the RPL root to do careful filtering: it occurs only when the
   Join Coordinator is not co-located inside the RPL root.

   With the above precautions, an attack using IPv6-in-IPv6 tunnels can
   only be by a node within the LLN on another node within the LLN.
   Such an attack could, of course, be done directly.  An attack of this
   kind is meaningful only if the source addresses are either fake or if
   the point is to amplify return traffic.  Such an attack, could also
   be done without the use of IPv6-in-IPv6 headers using forged source
   addresses.  If the attack requires bi-directional communication, then
   IPv6-in-IPv6 provides no advantages.

   Whenever IPv6-in-IPv6 headers are being proposed, there is a concern
   about creating security issues.  In the Security Considerations
   section of [RFC2473], it was suggested that tunnel entry and exit
   points can be secured by securing the IPv6 path between them.  This
   recommendation is not practical for RPL networks.  [RFC5406] goes
   into some detail on what additional details would be needed in order
   to "Use IPsec".  Use of ESP would prevent [RFC8138] compression
   (compression must occur before encryption), and [RFC8138] compression
   is lossy in a way that prevents use of AH.  These are minor issues.
   The major issue is how to establish trust enough such that IKEv2
   could be used.  This would require a system of certificates to be
   present in every single node, including any Internet nodes that might
   need to communicate with the LLN.  Thus, using IPsec requires a
   global PKI in the general case.

   More significantly, the use of IPsec tunnels to protect the IPv6-in-
   IPv6 headers would in the general case scale with the square of the
   number of nodes.  This is a lot of resource for a constrained nodes
   on a constrained network.  In the end, the IPsec tunnels would be
   providing only BCP38-like origin authentication!  That is, IPsec
   provides a transitive guarantee to the tunnel exit point that the
   tunnel entry point did BCP38 on traffic going in.  Just doing origin
   filtering per BCP 38 at the entry and exit of the LLN provides a
   similar level of security without all the scaling and trust problems



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   related to IPv6 tunnels as discussed in RFC 2473.  IPsec is not
   recommended.

   An LLN with hostile nodes within it would not be protected against
   impersonation with the LLN by entry/exit filtering.

   The RH3 header usage described here can be abused in equivalent ways
   (to disguise the origin of traffic and attack other nodes) with an
   IPv6-in-IPv6 header to add the needed RH3 header.  As such, the
   attacker's RH3 header will not be seen by the network until it
   reaches the end host, which will decapsulate it.  An end-host should
   be suspicious about an RH3 header which has additional hops which
   have not yet been processed, and SHOULD ignore such a second RH3
   header.

   In addition, the LLN will likely use [RFC8138] to compress the IPv6-
   in-IPv6 and RH3 headers.  As such, the compressor at the RPL-root
   will see the second RH3 header and MAY choose to discard the packet
   if the RH3 header has not been completely consumed.  A consumed
   (inert) RH3 header could be present in a packet that flows from one
   LLN, crosses the Internet, and enters another LLN.  As per the
   discussion in this document, such headers do not need to be removed.
   However, there is no case described in this document where an RH3 is
   inserted in a non-storing network on traffic that is leaving the LLN,
   but this document should not preclude such a future innovation.  It
   should just be noted that an incoming RH3 must be fully consumed, or
   very carefully inspected.

   The RPI, if permitted to enter the LLN, could be used by an attacker
   to change the priority of a packet by selecting a different
   RPLInstanceID, perhaps one with a higher energy cost, for instance.
   It could also be that not all nodes are reachable in an LLN using the
   default RPLInstanceID, but a change of RPLInstanceID would permit an
   attacker to bypass such filtering.  Like the RH3, an RPI is to be
   inserted by the RPL root on traffic entering the LLN by first
   inserting an IPv6-in-IPv6 header.  The attacker's RPI therefore will
   not be seen by the network.  Upon reaching the destination node the
   RPI has no further meaning and is just skipped; the presence of a
   second RPI will have no meaning to the end node as the packet has
   already been identified as being at it's final destination.

   The RH3 and RPIs could be abused by an attacker inside of the network
   to route packets on non-obvious ways, perhaps eluding observation.
   This usage appears consistent with a normal operation of [RFC6997]
   and can not be restricted at all.  This is a feature, not a bug.






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   [RFC7416] deals with many other threats to LLNs not directly related
   to the use of IPv6-in-IPv6 headers, and this document does not change
   that analysis.

   Nodes within the LLN can use the IPv6-in-IPv6 mechanism to mount an
   attack on another part of the LLN, while disguising the origin of the
   attack.  The mechanism can even be abused to make it appear that the
   attack is coming from outside the LLN, and unless countered, this
   could be used to mount a Distributed Denial Of Service attack upon
   nodes elsewhere in the Internet.  See [DDOS-KREBS] for an example of
   such attacks already seen in the real world.

   If an attack comes from inside of LLN, it can be alleviated with SAVI
   (Source Address Validation Improvement) using [RFC8505] with
   [I-D.ietf-6lo-ap-nd].  The attacker will not be able to source
   traffic with an address that is not registered, and the registration
   process checks for topological correctness.  Notice that there is an
   L2 authentication in most of the cases.  If an attack comes from
   outside LLN IPv6-in- IPv6 can be used to hide inner routing headers,
   but by construction, the RH3 can typically only address nodes within
   the LLN.  That is, an RH3 with a CmprI less than 8 , should be
   considered an attack (see RFC6554, section 3).

   Nodes outside of the LLN will need to pass IPv6-in-IPv6 traffic
   through the RPL root to perform this attack.  To counter, the RPL
   root SHOULD either restrict ingress of IPv6-in-IPv6 packets (the
   simpler solution), or it SHOULD walk the IP header extension chain
   until it can inspect the upper-layer-payload as described in
   [RFC7045].  In particular, the RPL root SHOULD do [BCP38] processing
   on the source addresses of all IP headers that it examines in both
   directions.

   Note: there are some situations where a prefix will spread across
   multiple LLNs via mechanisms such as the one described in
   [I-D.ietf-6lo-backbone-router].  In this case the BCP38 filtering
   needs to take this into account, either by exchanging detailed
   routing information on each LLN, or by moving the BCP38 filtering
   further towards the Internet, so that the details of the multiple
   LLNs do not matter.

13.  Acknowledgments

   This work is done thanks to the grant given by the StandICT.eu
   project.

   A special BIG thanks to C.  M.  Heard for the help with the
   Section 4.  Much of the redaction in that section is based on his
   comments.



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   Additionally, the authors would like to acknowledge the review,
   feedback, and comments of (alphabetical order): Dominique Barthel,
   Robert Cragie, Simon Duquennoy, Ralph Droms, Cenk Guendogan, Rahul
   Jadhav, Benjamin Kaduk, Matthias Kovatsch, Gustavo Mercado,
   Subramanian Moonesamy, Marcela Orbiscay, Charlie Perkins, Cristian
   Perez, Alvaro Retana, Peter van der Stok, Xavier Vilajosana, Eric
   Vyncke and Thomas Watteyne.

14.  References

14.1.  Normative References

   [BCP38]    Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <https://www.rfc-editor.org/info/bcp38>.

   [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>.

   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, DOI 10.17487/RFC6040, November
              2010, <https://www.rfc-editor.org/info/rfc6040>.

   [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>.

   [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>.

   [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>.








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   [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>.

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,
              <https://www.rfc-editor.org/info/rfc7045>.

   [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>.

   [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>.

   [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>.

14.2.  Informative References

   [DDOS-KREBS]
              Goodin, D., "Record-breaking DDoS reportedly delivered by
              >145k hacked cameras", September 2016,
              <http://arstechnica.com/security/2016/09/botnet-of-145k-
              cameras-reportedly-deliver-internets-biggest-ddos-ever/>.

   [I-D.ietf-6lo-ap-nd]
              Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
              "Address Protected Neighbor Discovery for Low-power and
              Lossy Networks", draft-ietf-6lo-ap-nd-23 (work in
              progress), April 2020.




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   [I-D.ietf-6lo-backbone-router]
              Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
              Backbone Router", draft-ietf-6lo-backbone-router-20 (work
              in progress), March 2020.

   [I-D.ietf-6tisch-dtsecurity-zerotouch-join]
              Richardson, M., "6tisch Zero-Touch Secure Join protocol",
              draft-ietf-6tisch-dtsecurity-zerotouch-join-04 (work in
              progress), July 2019.

   [I-D.ietf-anima-autonomic-control-plane]
              Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
              Control Plane (ACP)", draft-ietf-anima-autonomic-control-
              plane-24 (work in progress), March 2020.

   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-41 (work in progress), April 2020.

   [I-D.ietf-intarea-tunnels]
              Touch, J. and M. Townsley, "IP Tunnels in the Internet
              Architecture", draft-ietf-intarea-tunnels-10 (work in
              progress), September 2019.

   [I-D.ietf-roll-unaware-leaves]
              Thubert, P. and M. Richardson, "Routing for RPL Leaves",
              draft-ietf-roll-unaware-leaves-15 (work in progress),
              April 2020.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <https://www.rfc-editor.org/info/rfc2473>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC5406]  Bellovin, S., "Guidelines for Specifying the Use of IPsec
              Version 2", BCP 146, RFC 5406, DOI 10.17487/RFC5406,
              February 2009, <https://www.rfc-editor.org/info/rfc5406>.



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   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [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>.

   [RFC6997]  Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
              J. Martocci, "Reactive Discovery of Point-to-Point Routes
              in Low-Power and Lossy Networks", RFC 6997,
              DOI 10.17487/RFC6997, August 2013,
              <https://www.rfc-editor.org/info/rfc6997>.

   [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>.

   [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>.

   [RFC8180]  Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
              IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
              Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180,
              May 2017, <https://www.rfc-editor.org/info/rfc8180>.

   [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>.

Authors' Addresses

 Maria Ines Robles
 Universidad Tecno. Nac.(UTN)-FRM, Argentina / Aalto University, Finland

 Email: mariainesrobles@gmail.com







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   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7
   CA

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


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

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
































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