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Versions: (draft-robles-roll-useofrplinfo) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16

ROLL Working Group                                             M. Robles
Internet-Draft                                                  Ericsson
Updates: 6553, 6550 (if approved)                          M. Richardson
Intended status: Standards Track                                     SSW
Expires: January 4, 2018                                      P. Thubert
                                                                   Cisco
                                                            July 3, 2017


              When to use RFC 6553, 6554 and IPv6-in-IPv6
                    draft-ietf-roll-useofrplinfo-16

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 RFC 6553, RFC 6554 and IPv6-in-IPv6
   encapsulation is required.  This analysis provides the basis on which
   to design efficient compression of these headers.  Additionally, this
   document updates the RFC 6553 adding a change to the RPL Option Type
   and the RFC 6550 to indicate about this change.

Status of This Memo

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

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

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

   This Internet-Draft will expire on January 4, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   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
   2.  Terminology and Requirements Language . . . . . . . . . . . .   4
     2.1.  hop-by-hop IPv6-in-IPv6 headers . . . . . . . . . . . . .   5
   3.  Updates to RFC6553 and RFC 6550 . . . . . . . . . . . . . . .   5
     3.1.  Updates to RFC 6553 . . . . . . . . . . . . . . . . . . .   5
     3.2.  Updates to RFC 6550 . . . . . . . . . . . . . . . . . . .   6
   4.  Sample/reference topology . . . . . . . . . . . . . . . . . .   7
   5.  Use cases . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Storing mode  . . . . . . . . . . . . . . . . . . . . . . . .  12
     6.1.  Storing Mode: Interaction between Leaf and Root . . . . .  13
       6.1.1.  SM: Example of Flow from RPL-aware-leaf to root . . .  14
       6.1.2.  SM: Example of Flow from root to RPL-aware-leaf . . .  15
       6.1.3.  SM: Example of Flow from root to not-RPL-aware-leaf .  15
       6.1.4.  SM: Example of Flow from not-RPL-aware-leaf to root .  16
     6.2.  Storing Mode: Interaction between Leaf and Internet . . .  17
       6.2.1.  SM: Example of Flow from RPL-aware-leaf to Internet .  17
       6.2.2.  SM: Example of Flow from Internet to RPL-aware-leaf .  18
       6.2.3.  SM: Example of Flow from not-RPL-aware-leaf to
               Internet  . . . . . . . . . . . . . . . . . . . . . .  19
       6.2.4.  SM: Example of Flow from Internet to non-RPL-aware-
               leaf  . . . . . . . . . . . . . . . . . . . . . . . .  20
     6.3.  Storing Mode: Interaction between Leaf and Leaf . . . . .  21
       6.3.1.  SM: Example of Flow from RPL-aware-leaf to RPL-aware-
               leaf  . . . . . . . . . . . . . . . . . . . . . . . .  21
       6.3.2.  SM: Example of Flow from RPL-aware-leaf to non-RPL-
               aware-leaf  . . . . . . . . . . . . . . . . . . . . .  22
       6.3.3.  SM: Example of Flow from not-RPL-aware-leaf to RPL-
               aware-leaf  . . . . . . . . . . . . . . . . . . . . .  23
       6.3.4.  SM: Example of Flow from not-RPL-aware-leaf to not-
               RPL-aware-leaf  . . . . . . . . . . . . . . . . . . .  24
   7.  Non Storing mode  . . . . . . . . . . . . . . . . . . . . . .  26
     7.1.  Non-Storing Mode: Interaction between Leaf and Root . . .  27
       7.1.1.  Non-SM: Example of Flow from RPL-aware-leaf to root .  28
       7.1.2.  on-SM: Example of Flow from root to RPL-aware-leaf  .  28
       7.1.3.  Non-SM: Example of Flow from root to not-RPL-aware-
               leaf  . . . . . . . . . . . . . . . . . . . . . . . .  29
       7.1.4.  Non-SM: Example of Flow from not-RPL-aware-leaf to
               root  . . . . . . . . . . . . . . . . . . . . . . . .  30
     7.2.  Non-Storing Mode: Interaction between Leaf and Internet .  31



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       7.2.1.  Non-SM: Example of Flow from RPL-aware-leaf to
               Internet  . . . . . . . . . . . . . . . . . . . . . .  31
       7.2.2.  Non-SM: Example of Flow from Internet to RPL-aware-
               leaf  . . . . . . . . . . . . . . . . . . . . . . . .  32
       7.2.3.  Non-SM: Example of Flow from not-RPL-aware-leaf to
               Internet  . . . . . . . . . . . . . . . . . . . . . .  33
       7.2.4.  Non-SM: Example of Flow from Internet to not-RPL-
               aware-leaf  . . . . . . . . . . . . . . . . . . . . .  34
     7.3.  Non-Storing Mode: Interaction between Leafs . . . . . . .  35
       7.3.1.  Non-SM: Example of Flow from RPL-aware-leaf to RPL-
               aware-leaf  . . . . . . . . . . . . . . . . . . . . .  35
       7.3.2.  Non-SM: Example of Flow from RPL-aware-leaf to not-
               RPL-aware-leaf  . . . . . . . . . . . . . . . . . . .  37
       7.3.3.  Non-SM: Example of Flow from not-RPL-aware-leaf to
               RPL-aware-leaf  . . . . . . . . . . . . . . . . . . .  38
       7.3.4.  Non-SM: Example of Flow from not-RPL-aware-leaf to
               not-RPL-aware-leaf  . . . . . . . . . . . . . . . . .  39
   8.  Observations about the cases  . . . . . . . . . . . . . . . .  40
     8.1.  Storing mode  . . . . . . . . . . . . . . . . . . . . . .  40
     8.2.  Non-Storing mode  . . . . . . . . . . . . . . . . . . . .  41
   9.  6LoRH Compression cases . . . . . . . . . . . . . . . . . . .  41
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  42
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  44
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  45
     13.2.  Informative References . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  48

1.  Introduction

   RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
   [RFC6550] is a routing protocol for constrained networks.  RFC 6553
   [RFC6553] defines the "RPL option" (RPI), carried within the IPv6
   Hop-by-Hop header to quickly identify inconsistencies (loops) in the
   routing topology.  RFC 6554 [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 implementors agree when artifacts
   are necessary, or when they can be safely omitted, or removed.

   An interim meeting went through the 24 cases defined here to discover
   if there were any shortcuts, and this document is the result of that
   discussion.  This document clarify what is correct and incorrect
   behaviour.

   The related document A Routing Header Dispatch for 6LoWPAN (6LoRH)
   [I-D.ietf-roll-routing-dispatch] defines a method to compress RPL
   Option information and Routing Header type 3 [RFC6554], an efficient
   IP-in-IP technique, and use cases proposed for the
   [Second6TischPlugtest] involving 6loRH.

2.  Terminology and Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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

   RPL-node: It is device which implements RPL, thus we can say that the
   device is RPL-capable or RPL-aware.  Please note that the device can
   be found inside the LLN or outside LLN.  In this document a RPL-node
   which is a leaf of a DODAG is called RPL-aware-leaf.

   RPL-not-capable: It is device which do not implement RPL, thus we can
   say that the device is not-RPL-aware.  Please note that the device
   can be found inside the LLN.  In this document a not-RPL-aware node
   which is a leaf of a DODAG is called not-RPL-aware-leaf.

   pledge: a new device which seeks admission to a network. (from
   [I-D.ietf-anima-bootstrapping-keyinfra])

   Join Registrar and Coordinator (JRC): a device which brings new nodes
   (pledges) into a network. (from
   [I-D.ietf-anima-bootstrapping-keyinfra])

   Flag day: A "flag day" is a procedure in which the network, or a part
   of it, is changed during a planned outage, or suddenly, causing an
   outage while the network recovers [RFC4192]








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2.1.  hop-by-hop IPv6-in-IPv6 headers

   The term "hop-by-hop IPv6-in-IPv6" header refers to: adding a header
   that originates from a node to an adjacent node, using the addresses
   (usually the GUA or ULA, but could use the link-local addresses) of
   each node.  If the packet must traverse multiple hops, then it must
   be decapsulated at each hop, and then re-encapsulated again in a
   similar fashion.

3.  Updates to RFC6553 and RFC 6550

3.1.  Updates to RFC 6553

   [RFC6553] states as showed below, that in the Option Type field of
   the RPL Option header, 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 en route.  The remaining bits serve as the option type.


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


                   Figure 1: Option Type in RPL Option.

   Recent changes in [I-D.ietf-6man-rfc2460bis], state: "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".  Processing of the Hop-by-Hop Options header (by IPv6
   intermediate nodes) is now optional, but if they are configured to
   process the header, and if such nodes encounter an option with the
   first two bits set to 01, they will drop the packet (if they conform
   [I-D.ietf-6man-rfc2460bis]).  The hosts should do the same,
   irrespective of the configuration.

   Based on That, if an IPv6 (intermediate) node (RPL-not-capable)
   receives a packet with an RPL Option, it should ignore the HBH RPL
   option (skip over this option and continue processing the header).

   Thus, this document updates the Option Type field to: 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
   (Section 4.2.[I-D.ietf-6man-rfc2460bis] ) if it doesn't recognize the



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   option type, and the third bit continues to be set to indicate that
   the Option Data may change en route.  The remaining bits serve as the
   option type and remain as 0x3.  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 [RFC6553] RPL Hop-by-Hop
   option known as RPI.  This is an update to [RFC6553].


          Hex Value     Binary Value
                        act  chg  rest     Description        Reference
          ---------     ---  ---  -------  -----------------  ----------
            0x23         00    1   00011   RPL Option         [RFCXXXX]


        Figure 2: Proposed change to the Option Type in RPL Option.

   This change creates a flag day for existing networks which are
   currently using 0x63 as the RPI value.  A move to 0x23 will not be
   understood by those networks.  It is suggested that implementations
   accept both 0x63 and 0x23 when processing.  When forwarding packets,
   implementations SHOULD use the same value as it was received.  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.

   A network which is switching from straight 6lowpan compression
   mechanism to those described in [I-D.ietf-roll-routing-dispatch] will
   experience a flag day in the data compression anyway, and if possible
   this change can be deployed at the same time.

3.2.  Updates to RFC 6550

   In order to avoid a flag day caused by lack of interoperation between
   new RPI (0x23) and old RPI (0x63) nodes, the new nodes need to be
   told that there are old RPI nodes present.  This can be done via a
   new DIO Option which will propogate through the network.  Failure to
   receive this flag will cause dual mode nodes to originate traffic
   with the old-RPI (0x63) value.

   DIO Option: 0x05 RPI 0x23 enable MCRXXX

   Flags: 8-bit unused field reserved for flags.  The field MUST be
   initialized to zero by the sender and MUST be ignored by the
   receiver.

   We propose to use a bit flag as follows:





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             +----+----+----+----+----+----+----+----+
             |    |    |    |    |    |    |    |    |
             |    |    |    |    |    |    |    | FR |
             |    |    |    |    |    |    |    |    |
             +----+----+----+----+----+----+----+----+




            Figure 3: A DIO Flag to indicate the RPI-flag-day.

   FR(RPI-flag-day): the flag with values of 1 indicates that RPL Option
   field is set to "00", values of 0 indicates that RPL Option field is
   set to "01"

4.  Sample/reference topology

   A RPL network in general is composed of a 6LBR (6LoWPAN Border
   Router), Backbone Router (6BBR), 6LR (6LoWPAN Router) and 6LN
   (6LoWPAN Node) as leaf logically organized in a DODAG structure.
   (Destination Oriented Directed Acyclic Graph).

   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 showed in Figure 1.

   RPL supports two modes of Downward traffic: in storing mode (RPL-SM),
   it is fully stateful or an in non-storing (RPL-NSM), 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.

















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

                           Figure 4: RPL Stack.






























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



                    Figure 5: A reference RPL Topology.

   Figure 2 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, a 6LR is a router.  A 6LN can be



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   a router or a host.  The 6LN leaves (Raf - "RPL aware leaf"-) marked
   as (F and I) are RPL hosts that does not have forwarding capability.
   The 6LN leaf (H) is a RPL router.  The leafs marked as ~Raf "not-RPL
   aware leaf" (G and J) are devices which do not speak RPL at all (not-
   RPL-aware), but uses Router-Advertisements, 6LowPAN DAR/DAC and
   efficient-ND only to participate in the network [RFC6775].  In the
   document these leafs (G and J) are often named IPv6 node.  The 6LBR
   in the figure is the root of the Global DODAG.

5.  Use cases

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

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

   The uses cases describe the communication between RPL-aware-nodes,
   with the root (6LBR), and with Internet.  This document also describe
   the communication between nodes acting as leaf that does not
   understand RPL and they are part of hte LLN.  We name these nodes as
   not-RPL-aware-leaf.(e.g. section 5.4- Flow from not-RPL-aware-leaf to
   root) We describe also how is the communication inside of the LLN
   when it has the final destination addressed outside of the LLN e.g.
   with destination to Internet. (e.g. section 5.7- Flow from not-RPL-
   aware-leaf to Internet)

   The uses cases comprise as follow:

   Interaction between Leaf and Root:

      RPL-aware-leaf to root

      root to RPL-aware-leaf

      not-RPL-aware-leaf to root

      root to not-RPL-aware-leaf

   Interaction between Leaf and Internet:

      RPL-aware-leaf to Internet

      Internet to RPL-aware-leaf

      not-RPL-aware-leaf to Internet




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      Internet to not-RPL-aware-leaf

   Interaction between Leafs:

      RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)

      RPL-aware-leaf to not-RPL-aware-leaf (non-storing)

      not-RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)

      not-RPL-aware-leaf to not-RPL-aware-leaf (non-storing)

   This document assumes 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
   [RFC2460].  Extensions may not be added or removed except by the
   sender or the receiver.

   But, options in the Hop-by-Hop Option Header whose option type has
   the first two bits set to '00' MUST ignored when received by a host
   or router that does not understand that option ( Section 4.2
   [I-D.ietf-6man-rfc2460bis]).

   This means that when the no-drop RPI option code 0x23 is used, a
   packet that leaves the RPL domain of an LLN (or that leaves the LLN
   entirely) will not be discarded when it contains the [RFC6553] RPL
   Hop-by-Hop option known as RPI.  Thus, the RPI Hop-by-Hop option MAY
   be left in place even if the end host does not understand it.

   NOTE: There is some possible security risk when the RPI information
   is released to the Internet.  At this point this is a theoretical
   situation.  It is clear that the RPI option would waste some network
   bandwidth when it escapes.

   An intermediate router that needs to add an extension header (SHR3 or
   RPI Option) must encapsulate the packet in an (additional) outer IP
   header.  The new header can be placed is placed after this new outer
   IP header.

   A corollory is that an SHR3 or RPI 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.  When it does so, 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 addresses.

   Both RPI and RH3 headers may be modified in very specific ways by
   routers on the path of the packet without the need to add to remove



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   an encapsulating header.  Both headers were designed with this
   modification in mind, and both the RPL RH 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.

   RPI should be present in every single RPL data packet.  There is one
   exception in non-storing mode: when a packet is going down from the
   root.  In a downward non-storing mode, the entire route is written,
   so there can be no loops by construction, nor any confusion about
   which forwarding table to use (as the root has already made all
   routing decisions).  There still may be cases (such as in 6tisch)
   where the instanceID portion of the RPI header may still be needed to
   pick an appropriate priority or channel at each hop.

   In the tables present in this document, the term "RPL aware leaf" is
   has been shortened to "Raf", and "not-RPL aware leaf" has been
   shortened to "~Raf" to make the table fit in available space.

   The earlier examples are more extensive to make sure that the process
   is clear, while later examples are more concise.

6.  Storing mode

   In storing mode (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 PIO option.

   The following table summarizes what headers are needed in the
   following scenarios, and indicates when the IP-in-IP header must be
   inserted on a hop-by-hop basis, and when it can target the
   destination node directly.  There are these possible situations: hop-
   by-hop necessary (indicated by "hop"), or destination address
   possible (indicated by "dst").  In all cases hop by hop can be used.
   In cases where no IP-in-IP header is needed, the column is left
   blank.

   In all cases the RPI headers are needed, since it identifies
   inconsistencies (loops) in the routing topology.  In all cases the
   RH3 is not need because we do not indicate the route in storing mode.

   The leaf can be a router 6LR or a host, both indicated as 6LN
   (Figure 2).








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           +---------------------+--------------+----------+--------------+
           | Interaction between |   Use Case   | IP-in-IP | IP-in-IP dst |
           +---------------------+--------------+----------+--------------+
           |                     |  Raf to root |    No    |      --      |
           +                     +--------------+----------+--------------+
           |     Leaf - Root     |  root to Raf |    No    |      --      |
           +                     +--------------+----------+--------------+
           |                     | root to ~Raf |    No    |      --      |
           +                     +--------------+----------+--------------+
           |                     | ~Raf to root |    Yes   |     root     |
           +---------------------+--------------+----------+--------------+
           |                     |  Raf to Int  |    No    |      --      |
           +                     +--------------+----------+--------------+
           |   Leaf - Internet   |  Int to Raf  |   Yes    |      Raf     |
           +                     +--------------+----------+--------------+
           |                     |  ~Raf to Int |    Yes   |     root     |
           +                     +--------------+----------+--------------+
           |                     |  Int to ~Raf |    Yes   |      hop     |
           +---------------------+--------------+----------+--------------+
           |                     |  Raf to Raf  |    No    |      --      |
           +                     +--------------+----------+--------------+
           |                     |  Raf to ~Raf |    No    |      --      |
           +     Leaf - Leaf     +--------------+----------+--------------+
           |                     |  ~Raf to Raf |    Yes   |      dst     |
           +                     +--------------+----------+--------------+
           |                     | ~Raf to ~Raf |    Yes   |      hop     |
           +---------------------+--------------+----------+--------------+



             Figure 6: IP-in-IP encapsulation in Storing mode.

6.1.  Storing Mode: Interaction between Leaf and Root

   In this section we are going to describe the communication flow in
   storing mode (SM) between,

      RPL-aware-leaf to root

      root to RPL-aware-leaf

      not-RPL-aware-leaf to root

      root to not-RPL-aware-leaf







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6.1.1.  SM: Example of Flow from RPL-aware-leaf to root

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

   As stated in Section 16.2 of [RFC6550]  a RPL-aware-leaf node does
   not generally issue DIO messages; a leaf node accepts DIO messages
   from upstream.  (When the inconsistency in routing occurs, a leaf
   node will generate a DIO with an infinite rank, to fix it).  It may
   issue DAO and DIS messages though it generally ignores DAO and DIS
   messages.

   In this case the flow comprises:

   RPL-aware-leaf (6LN) --> 6LR_i --> root(6LBR)

   For example, the communication flow would be: Node F --> Node E -->
   Node B --> Node A root(6LBR)

   6LR_i (Node E and Node B) are the intermediate routers from source to
   destination.  In this case, "1 <= i >= n", n is the number of routers
   (6LR) that the packet go through from source (6LN) to destination
   (6LBR).

   As it was mentioned In this document 6LRs, 6LBR are always full-
   fledge RPL routers.

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

   No IP-in-IP header is required.

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












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                +-------------------+-----+-------+------+
                | Header            | 6LN | 6LR_i | 6LBR |
                +-------------------+-----+-------+------+
                | Inserted headers  | RPI | --    | --   |
                | Removed headers   | --  | --    | RPI  |
                | Re-added headers  | --  | --    | --   |
                | Modified headers  | --  | RPI   | --   |
                | Untouched headers | --  | --    | --   |
                +-------------------+-----+-------+------+

    Storing: Summary of the use of headers from RPL-aware-leaf to root

6.1.2.  SM: Example of Flow from root to RPL-aware-leaf

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LBR) to destination (6LN).

   In this case the 6LBR inserts RPI header and sends the packet down,
   the 6LR is going to increment the rank in RPI (examines instanceID
   for multiple tables), the packet is processed in 6LN and RPI removed.

   No IP-in-IP header is required.

                +-------------------+------+-------+------+
                | Header            | 6LBR | 6LR_i | 6LN  |
                +-------------------+------+-------+------+
                | Inserted headers  | RPI  | --    | --   |
                | Removed headers   | --   | --    | RPI  |
                | Re-added headers  | --   | --    | --   |
                | Modified headers  | --   | RPI   | --   |
                | Untouched headers | --   | --    | --   |
                +-------------------+------+-------+------+

    Storing: Summary of the use of headers from root to RPL-aware-leaf

6.1.3.  SM: Example of Flow from root to not-RPL-aware-leaf

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)



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   For example, the communication flow would be: Node A root(6LBR) -->
   Node B --> Node E --> Node G

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LBR) to destination (IPv6).

   As the RPI extension can be ignored by the not-RPL-aware leaf, this
   situation is identical to the previous scenario.

           +-------------------+------+-------+----------------+
           | Header            | 6LBR | 6LR_i | IPv6           |
           +-------------------+------+-------+----------------+
           | Inserted headers  | RPI  | --    | --             |
           | Removed headers   | --   | --    | --             |
           | Re-added headers  | --   | --    | --             |
           | Modified headers  | --   | RPI   | --             |
           | Untouched headers | --   | --    | RPI (Ignored)  |
           +-------------------+------+-------+----------------+

    Storing: Summary of the use of headers from root to not-RPL-aware-
                                   leaf

6.1.4.  SM: Example of Flow from not-RPL-aware-leaf to root

   In this case the flow comprises:

   not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i --> root (6LBR)

   For example, the communication flow would be: Node G --> Node E -->
   Node B --> Node A root(6LBR)

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from source (IPv6) to destination (6LBR).  For
   example, 6LR_1 (i=1) is the router that receives the packets from the
   IPv6 node (Node G).

   When the packet arrives from IPv6 node (Node G) to 6LR_1 (Node E),
   the 6LR_1 will insert a RPI header, encapsuladed in a IPv6-in-IPv6
   header.  The IPv6-in-IPv6 header can be addressed to the next hop
   (Node B), or to the root (Node A).  The root removes the header and
   processes the packet.








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   +------------+------+---------------+---------------+---------------+
   | Header     | IPv6 | 6LR_1         | 6LR_i         | 6LBR          |
   +------------+------+---------------+---------------+---------------+
   | Inserted   | --   | IP-in-IP(RPI) | --            | --            |
   | headers    |      |               |               |               |
   | Removed    | --   | --            | --            | IP-in-IP(RPI) |
   | headers    |      |               |               |               |
   | Re-added   | --   | --            | --            | --            |
   | headers    |      |               |               |               |
   | Modified   | --   | --            | IP-in-IP(RPI) | --            |
   | headers    |      |               |               |               |
   | Untouched  | --   | --            | --            | --            |
   | headers    |      |               |               |               |
   +------------+------+---------------+---------------+---------------+

     Storing: Summary of the use of headers from not-RPL-aware-leaf to
                                   root

6.2.  Storing Mode: Interaction between Leaf and Internet

   In this section we are going to describe the communication flow in
   storing mode (SM) between,

      RPL-aware-leaf to Internet

      Internet to RPL-aware-leaf

      not-RPL-aware-leaf to Internet

      Internet to not-RPL-aware-leaf

6.2.1.  SM: Example of Flow from RPL-aware-leaf to Internet

   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.

   In this case the flow comprises:

   RPL-aware-leaf (6LN) --> 6LR_i --> root (6LBR) --> Internet

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LN) to 6LBR.

   No IP-in-IP header is required.



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

       +-------------------+------+-------+------+----------------+
       | Header            | 6LN  | 6LR_i | 6LBR | Internet       |
       +-------------------+------+-------+------+----------------+
       | Inserted headers  | RPI  | --    | --   | --             |
       | Removed headers   | --   | --    | --   | --             |
       | Re-added headers  | --   | --    | --   | --             |
       | Modified headers  | --   | RPI   | --   | --             |
       | Untouched headers | --   | --    | RPI  | RPI (Ignored)  |
       +-------------------+------+-------+------+----------------+

       Storing: Summary of the use of headers from RPL-aware-leaf to
                                 Internet

6.2.2.  SM: Example of Flow from Internet to RPL-aware-leaf

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from 6LBR to destination(6LN).

   When the packet arrives from Internet to 6LBR the RPI header is added
   in a outer IPv6-in-IPv6 header and sent to 6LR, which modifies the
   rank in the RPI.  When the packet arrives at 6LN the RPI header is
   removed and the packet processed.


















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   +----------+---------+--------------+---------------+---------------+
   | Header   | Interne | 6LBR         | 6LR_i         | 6LN           |
   |          | t       |              |               |               |
   +----------+---------+--------------+---------------+---------------+
   | Inserted | --      | IP-in-       | --            | --            |
   | headers  |         | IP(RPI)      |               |               |
   | Removed  | --      | --           | --            | IP-in-IP(RPI) |
   | headers  |         |              |               |               |
   | Re-added | --      | --           | --            | --            |
   | headers  |         |              |               |               |
   | Modified | --      | --           | IP-in-IP(RPI) | --            |
   | headers  |         |              |               |               |
   | Untouche | --      | --           | --            | --            |
   | d        |         |              |               |               |
   | headers  |         |              |               |               |
   +----------+---------+--------------+---------------+---------------+

    Storing: Summary of the use of headers from Internet to RPL-aware-
                                   leaf

6.2.3.  SM: Example of Flow from not-RPL-aware-leaf to Internet

   In this case the flow comprises:

   not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i -->root (6LBR) -->
   Internet

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from source(IPv6) to 6LBR.

   The 6LR_1 (i=1) node will add an IP-in-IP(RPI) header addressed
   either to the root, or hop-by-hop such that the root can remove the
   RPI header before passing upwards.

   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.









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   +---------+-----+-------------+-------------+-------------+---------+
   | Header  | IPv | 6LR_1       | 6LR_i       | 6LBR        | Interne |
   |         | 6   |             | [i=2,..,n]_ |             | t       |
   +---------+-----+-------------+-------------+-------------+---------+
   | Inserte | --  | IP-in-      | --          | --          | --      |
   | d       |     | IP(RPI)     |             |             |         |
   | headers |     |             |             |             |         |
   | Removed | --  | --          | --          | IP-in-      | --      |
   | headers |     |             |             | IP(RPI)     |         |
   | Re-     | --  | --          | --          | --          | --      |
   | added   |     |             |             |             |         |
   | headers |     |             |             |             |         |
   | Modifie | --  | --          | IP-in-      | --          | --      |
   | d       |     |             | IP(RPI)     |             |         |
   | headers |     |             |             |             |         |
   | Untouch | --  | --          | --          | --          | --      |
   | ed      |     |             |             |             |         |
   | headers |     |             |             |             |         |
   +---------+-----+-------------+-------------+-------------+---------+

     Storing: Summary of the use of headers from not-RPL-aware-leaf to
                                 Internet

6.2.4.  SM: Example of Flow from Internet to non-RPL-aware-leaf

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from 6LBR to not-RPL-aware-leaf (IPv6).  6LR_i
   updates the rank in the RPI.

   The 6LBR will have to add an RPI header within an IP-in-IP header.
   The IP-in-IP can be addressed to the not-RPL-aware-leaf, leaving the
   RPI inside.

   The 6LBR MAY set the flow label on the inner IP-in-IP header to zero
   in order to aid in compression.








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   +-----------+----------+---------------+---------------+------------+
   | Header    | Internet | 6LBR          | 6LR_i         | IPv6       |
   +-----------+----------+---------------+---------------+------------+
   | Inserted  | --       | IP-in-IP(RPI) | --            | --         |
   | headers   |          |               |               |            |
   | Removed   | --       | --            | --            | --         |
   | headers   |          |               |               |            |
   | Re-added  | --       | --            | --            | --         |
   | headers   |          |               |               |            |
   | Modified  | --       | --            | IP-in-IP(RPI) | --         |
   | headers   |          |               |               |            |
   | Untouched | --       | --            | --            | RPI        |
   | headers   |          |               |               | (Ignored)  |
   +-----------+----------+---------------+---------------+------------+

     Storing: Summary of the use of headers from Internet to non-RPL-
                                aware-leaf

6.3.  Storing Mode: Interaction between Leaf and Leaf

   In this section we are going to describe the communication flow in
   storing mode (SM) between,

      RPL-aware-leaf to RPL-aware-leaf

      RPL-aware-leaf to not-RPL-aware-leaf

      not-RPL-aware-leaf to RPL-aware-leaf

      not-RPL-aware-leaf to not-RPL-aware-leaf

6.3.1.  SM: Example of Flow from RPL-aware-leaf to RPL-aware-leaf

   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.  Section 9 in [RFC6550].

   In this case the flow comprises:

   6LN --> 6LR_ia --> common parent (6LR_x) --> 6LR_id --> 6LN

   For example, the communication flow could be: Node F --> Node D -->
   Node B --> Node E --> Node H

   6LR_ia (Node D) are the intermediate routers from source to the
   common parent (6LR_x) (Node B) In this case, "1 <= ia >= n", n is the
   number of routers (6LR) that the packet go through from 6LN (Node F)
   to the common parent (6LR_x).



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   6LR_id (Node E) are the intermediate routers from the common parent
   (6LR_x) (Node B) to destination 6LN (Node H).  In this case, "1 <= id
   >= m", m is the number of routers (6LR) that the packet go through
   from the common parent (6LR_x) to destination 6LN.

   This case is assumed in the same RPL Domain.  In the common parent
   (Node B), the direction of RPI is changed (from increasing to
   decreasing the rank).

   While the 6LR nodes will update the RPI, no node needs to add or
   remove the RPI, so no IP-in-IP headers are necessary.  This may be
   done regardless of where the destination is, as the included RPI will
   be ignored by the receiver.

   +---------------+--------+--------+---------------+--------+--------+
   | Header        | 6LN    | 6LR_ia | 6LR_x (common | 6LR_id | 6LN    |
   |               | src    |        | parent)       |        | dst    |
   +---------------+--------+--------+---------------+--------+--------+
   | Inserted      | RPI    | --     | --            | --     | --     |
   | headers       |        |        |               |        |        |
   | Removed       | --     | --     | --            | --     | RPI    |
   | headers       |        |        |               |        |        |
   | Re-added      | --     | --     | --            | --     | --     |
   | headers       |        |        |               |        |        |
   | Modified      | --     | RPI    | RPI           | RPI    | --     |
   | headers       |        |        |               |        |        |
   | Untouched     | --     | --     | --            | --     | --     |
   | headers       |        |        |               |        |        |
   +---------------+--------+--------+---------------+--------+--------+

     Storing: Summary of the use of headers for RPL-aware-leaf to RPL-
                                aware-leaf

6.3.2.  SM: Example of Flow from RPL-aware-leaf to non-RPL-aware-leaf

   In this case the flow comprises:

   6LN --> 6LR_ia --> common parent (6LR_x) --> 6LR_id --> not-RPL-aware
   6LN (IPv6)

   For example, the communication flow could be: Node F --> Node D -->
   Node B --> Node E --> Node G

   6LR_ia are the intermediate routers from source (6LN) to the common
   parent (6LR_x) In this case, "1 <= ia >= n", n is the number of
   routers (6LR) that the packet go through from 6LN to the common
   parent (6LR_x).




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   6LR_id (Node E) are the intermediate routers from the common parent
   (6LR_x) (Node B) to destination not-RPL-aware 6LN (IPv6) (Node G).
   In this case, "1 <= id >= m", m is the number of routers (6LR) that
   the packet go through from the common parent (6LR_x) to destination
   6LN.

   This situation is identical to the previous situation Section 6.3.1

   +-----------+------+--------+---------------+--------+--------------+
   | Header    | 6LN  | 6LR_ia | 6LR_x(common  | 6LR_id | IPv6         |
   |           | src  |        | parent)       |        |              |
   +-----------+------+--------+---------------+--------+--------------+
   | Inserted  | RPI  | --     | --            | --     | --           |
   | headers   |      |        |               |        |              |
   | Removed   | --   | --     | --            | --     | RPI          |
   | headers   |      |        |               |        |              |
   | Re-added  | --   | --     | --            | --     | --           |
   | headers   |      |        |               |        |              |
   | Modified  | --   | RPI    | RPI           | RPI    | --           |
   | headers   |      |        |               |        |              |
   | Untouched | --   | --     | --            | --     | RPI(Ignored) |
   | headers   |      |        |               |        |              |
   +-----------+------+--------+---------------+--------+--------------+

   Storing: Summary of the use of headers for RPL-aware-leaf to non-RPL-
                                aware-leaf

6.3.3.  SM: Example of Flow from not-RPL-aware-leaf to RPL-aware-leaf

   In this case the flow comprises:

   not-RPL-aware 6LN (IPv6) --> 6LR_ia --> common parent (6LR_x) -->
   6LR_id --> 6LN

   For example, the communication flow could be: Node G --> Node E -->
   Node B --> Node D --> Node F

   6LR_ia (Node E) are the intermediate routers from source (not-RPL-
   aware 6LN (IPv6)) (Node G) to the common parent (6LR_x) (Node B) In
   this case, "1 <= ia >= n", n is the number of routers (6LR) that the
   packet go through from source to the common parent.

   6LR_id (Node D) are the intermediate routers from the common parent
   (6LR_x) (Node B) to destination 6LN (Node F).  In this case, "1 <= id
   >= m", m is the number of routers (6LR) that the packet go through
   from the common parent (6LR_x) to destination 6LN.





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   The 6LR_ia (ia=1) (Node E) receives the packet from the the IPv6 node
   (Node G) and inserts and the RPI header encapsulated in IPv6-in-IPv6
   header.  The IP-in-IP header is addressed to the destination 6LN
   (Node F).

   +--------+------+------------+------------+------------+------------+
   | Header | IPv6 | 6LR_ia     | common     | 6LR_id     | 6LN        |
   |        |      |            | parent     |            |            |
   |        |      |            | (6LRx)     |            |            |
   +--------+------+------------+------------+------------+------------+
   | Insert | --   | IP-in-     | --         | --         | --         |
   | ed hea |      | IP(RPI)    |            |            |            |
   | ders   |      |            |            |            |            |
   | Remove | --   | --         | --         | --         | IP-in-     |
   | d head |      |            |            |            | IP(RPI)    |
   | ers    |      |            |            |            |            |
   | Re-    | --   | --         | --         | --         | --         |
   | added  |      |            |            |            |            |
   | header |      |            |            |            |            |
   | s      |      |            |            |            |            |
   | Modifi | --   | --         | IP-in-     | IP-in-     | --         |
   | ed hea |      |            | IP(RPI)    | IP(RPI)    |            |
   | ders   |      |            |            |            |            |
   | Untouc | --   | --         | --         | --         | --         |
   | hed he |      |            |            |            |            |
   | aders  |      |            |            |            |            |
   +--------+------+------------+------------+------------+------------+

     Storing: Summary of the use of headers from not-RPL-aware-leaf to
                              RPL-aware-leaf

6.3.4.  SM: Example of Flow from not-RPL-aware-leaf to not-RPL-aware-
        leaf

   In this case the flow comprises:

   not-RPL-aware 6LN (IPv6 src)--> 6LR_1--> 6LR_ia --> root (6LBR) -->
   6LR_id --> not-RPL-aware 6LN (IPv6 dst)

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

   Internet 6LR_ia (Node E and Node B) are the intermediate routers from
   source (not-RPL-aware 6LN (IPv6 src))(Node G) to the root (6LBR)
   (Node A) In this case, "1 < ia >= n", n is the number of routers
   (6LR) that the packet go through from IPv6 src to the root.





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   6LR_id (C) are the intermediate routers from the root (Node A) to
   destination (IPv6 dst) (Node J).  In this case, "1 <= id >= m", m is
   the number of routers (6LR) that the packet go through from the root
   to destination (IPv6 dst).

   This flow is identical to Section 6.3.3

   The 6LR_1 (Node E) receives the packet from the the IPv6 node (Node
   G) and inserts the RPI header (RPIa) encapsulated in IPv6-in-IPv6
   header.  The IPv6-in-IPv6 header is addressed to the 6LBR.  The 6LBR
   remove the IPv6-in-IPv6 header and insert another one (RPIb) with
   destination to 6LR_m (Node C) node.

   One of the side-effects of inserting IP-in-IP RPI header at 6LR_1, is
   that now all the packets will go through the 6LBR, even though there
   exists a shorter P2P path to the destination 6LN in storing mode.
   One possible solution is given by the work in
   [I-D.ietf-roll-dao-projection].  Once we have route projection, the
   root can find that this traffic deserves optimization (based on
   volume and path length, or additional knowledge on that particular
   flow) and project a DAO into 6LR_1.






























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   +-------+-----+-----------+-----------+-----------+-----------+-----+
   | Heade | IPv | 6LR_1     | 6LR_ia    | 6LBR      | 6LR_m     | IPv |
   | r     | 6   |           |           |           |           | 6   |
   |       | src |           |           |           |           | dst |
   +-------+-----+-----------+-----------+-----------+-----------+-----+
   | Inser | --  | IP-in-    | --        | IP-in-    | --        | --  |
   | ted h |     | IP(RPI_a) |           | IP(RPI_b) |           |     |
   | eader |     |           |           |           |           |     |
   | s     |     |           |           |           |           |     |
   | Remov | --  | --        | --        | --        | --        | --  |
   | ed he |     |           |           |           |           |     |
   | aders |     |           |           |           |           |     |
   | Re-   | --  | --        | --        | --        | IP-in-    | --  |
   | added |     |           |           |           | IP(RPI_b) |     |
   | heade |     |           |           |           |           |     |
   | rs    |     |           |           |           |           |     |
   | Modif | --  | --        | IP-in-    | --        | IP-in-    | --  |
   | ied h |     |           | IP(RPI_a) |           | IP(RPI_b) |     |
   | eader |     |           |           |           |           |     |
   | s     |     |           |           |           |           |     |
   | Untou | --  | --        | --        | --        | --        | --  |
   | ched  |     |           |           |           |           |     |
   | heade |     |           |           |           |           |     |
   | rs    |     |           |           |           |           |     |
   +-------+-----+-----------+-----------+-----------+-----------+-----+

     Storing: Summary of the use of headers from not-RPL-aware-leaf to
                            non-RPL-aware-leaf

7.  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 non-RPL aware
   nodes.  Only the 6LBR needs to change when there are non-RPL aware
   nodes.

   The following table summarizes what headers are needed in the
   following scenarios, and indicates when the RPI, RH3 and IP-in-IP
   header must be inserted.  There are these possible situations:
   destination address possible (indicated by "dst"), to a 6LR, to a 6LN
   or to the root.  In cases where no IP-in-IP header is needed, the
   column is left blank.

   The leaf can be a router 6LR or a host, both indicated as 6LN
   (Figure 3).




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   +-----------------+--------------+-----+-----+----------+----------+
   |   Interaction   |   Use Case   | RPI | RH3 | IP-in-IP | IP-in-IP |
   |      between    |              |     |     |          |    dst   |
   +-----------------+--------------+-----+-----+----------+----------+
   |                 |  Raf to root | Yes | No  |    No    |    --    |
   +                 +--------------+-----+-----+----------+----------+
   |   Leaf - Root   |  root to Raf | Opt | Yes |    No    |    --    |
   +                 +--------------+-----+-----+----------+----------+
   |                 | root to ~Raf | No  | Yes |    Yes   |    6LR   |
   +                 +--------------+-----+-----+----------+----------+
   |                 | ~Raf to root | Yes | No  |    Yes   |   root   |
   +-----------------+--------------+-----+-----+----------+----------+
   |                 |  Raf to Int  | Yes | No  |    Yes   |   root   |
   +                 +--------------+-----+-----+----------+----------+
   | Leaf - Internet |  Int to Raf  | Opt | Yes |   Yes    |    dst   |
   +                 +--------------+-----+-----+----------+----------+
   |                 |  ~Raf to Int | Yes | No  |    Yes   |   root   |
   +                 +--------------+-----+-----+----------+----------+
   |                 |  Int to ~Raf | Opt | Yes |    Yes   |    6LR   |
   +-----------------+--------------+-----+-----+----------+----------+
   |                 |  Raf to Raf  | Yes | Yes |    Yes   | root/dst |
   +                 +--------------+-----+-----+----------+----------+
   |                 |  Raf to ~Raf | Yes | Yes |    Yes   | root/6LR |
   +   Leaf - Leaf   +--------------+-----+-----+----------+----------+
   |                 |  ~Raf to Raf | Yes | Yes |    Yes   | root/6LN |
   +                 +--------------+-----+-----+----------+----------+
   |                 | ~Raf to ~Raf | Yes | Yes |    Yes   | root/6LR |
   +-----------------+--------------+-----+-----+----------+----------+

     Figure 7: Headers needed in Non-Storing mode: RPI, RH3, IP-in-IP
                              encapsulation.

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

   In this section we are going to describe the communication flow in
   Non Storing Mode (Non-SM) between,

      RPL-aware-leaf to root

      root to RPL-aware-leaf

      not-RPL-aware-leaf to root

      root to not-RPL-aware-leaf







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7.1.1.  Non-SM: Example of Flow from RPL-aware-leaf to root

   In non-storing mode the leaf node uses default routing to send
   traffic to the root.  The RPI header must be included to avoid/detect
   loops.

   RPL-aware-leaf (6LN) --> 6LR_i --> root(6LBR)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LN) to destination (6LBR).

   This situation is the same case as storing mode.

                +-------------------+-----+-------+------+
                | Header            | 6LN | 6LR_i | 6LBR |
                +-------------------+-----+-------+------+
                | Inserted headers  | RPI | --    | --   |
                | Removed headers   | --  | --    | RPI  |
                | Re-added headers  | --  | --    | --   |
                | Modified headers  | --  | RPI   | --   |
                | Untouched headers | --  | --    | --   |
                +-------------------+-----+-------+------+

     Non Storing: Summary of the use of headers from RPL-aware-leaf to
                                   root

7.1.2.  on-SM: Example of Flow from root to RPL-aware-leaf

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LBR) to destination (6LN).

   The 6LBR will insert an RH3, and may optionally insert an RPI header.
   No IP-in-IP header is necessary as the traffic originates with an RPL
   aware node, the 6LBR.  The destination is known to RPL-aware because,
   the root knows the whole topology in non-storing mode.




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        +-------------------+-----------------+-------+----------+
        | Header            | 6LBR            | 6LR_i | 6LN      |
        +-------------------+-----------------+-------+----------+
        | Inserted headers  | (opt: RPI), RH3 | --    | --       |
        | Removed headers   | --              | --    | RH3,RPI  |
        | Re-added headers  | --              | --    | --       |
        | Modified headers  | --              | RH3   | --       |
        | Untouched headers | --              | --    | --       |
        +-------------------+-----------------+-------+----------+

    Non Storing: Summary of the use of headers from root to RPL-aware-
                                   leaf

7.1.3.  Non-SM: Example of Flow from root to not-RPL-aware-leaf

   In this case the flow comprises:

   root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LBR) to destination (IPv6).

   In 6LBR the RH3 is added, modified in each intermediate 6LR (6LR_1
   and so on) and it is fully consumed in the last 6LR (6LR_n), but left
   there.  If RPI is left present, the IPv6 node which does not
   understand it will ignore it (following 2460bis), thus encapsulation
   is not necesary.  Due the complete knowledge of the topology at the
   root, the 6LBR is able to address the IP-in-IP header to the last
   6LR.


















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   +---------------+-------------+---------------+--------------+------+
   | Header        | 6LBR        | 6LR_i(i=1)    | 6LR_n(i=n)   | IPv6 |
   +---------------+-------------+---------------+--------------+------+
   | Inserted      | (opt: RPI), | --            | --           | --   |
   | headers       | RH3         |               |              |      |
   | Removed       | --          | RH3           | --           | --   |
   | headers       |             |               |              |      |
   | Re-added      | --          | --            | --           | --   |
   | headers       |             |               |              |      |
   | Modified      | --          | (opt: RPI),   | (opt: RPI),  | --   |
   | headers       |             | RH3           | RH3          |      |
   | Untouched     | --          | --            | --           | RPI  |
   | headers       |             |               |              |      |
   +---------------+-------------+---------------+--------------+------+

     Non Storing: Summary of the use of headers from root to not-RPL-
                                aware-leaf

7.1.4.  Non-SM: Example of Flow from not-RPL-aware-leaf to root

   In this case the flow comprises:

   not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i --> root (6LBR)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from source (IPv6) to destination (6LBR).  For
   example, 6LR_1 (i=1) is the router that receives the packets from the
   IPv6 node.

   In this case the RPI is added by the first 6LR (6LR1) (Node E),
   encapsulated in an IP-in-IP header, and is modified in the followings
   6LRs.  The RPI and entire packet is consumed by the root.















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   +------------+------+---------------+---------------+---------------+
   | Header     | IPv6 | 6LR_1         | 6LR_i         | 6LBR          |
   +------------+------+---------------+---------------+---------------+
   | Inserted   | --   | IP-in-IP(RPI) | --            | --            |
   | headers    |      |               |               |               |
   | Removed    | --   | --            | --            | IP-in-IP(RPI) |
   | headers    |      |               |               |               |
   | Re-added   | --   | --            | --            | --            |
   | headers    |      |               |               |               |
   | Modified   | --   | --            | IP-in-IP(RPI) | --            |
   | headers    |      |               |               |               |
   | Untouched  | --   | --            | --            | --            |
   | headers    |      |               |               |               |
   +------------+------+---------------+---------------+---------------+

   Non Storing: Summary of the use of headers from not-RPL-aware-leaf to
                                   root

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

   In this section we are going to describe the communication flow in
   Non Storing Mode (Non-SM) between,

      RPL-aware-leaf to Internet

      Internet to RPL-aware-leaf

      not-RPL-aware-leaf to Internet

      Internet to not-RPL-aware-leaf

7.2.1.  Non-SM: Example of Flow from RPL-aware-leaf to Internet

   In this case the flow comprises:

   RPL-aware-leaf (6LN) --> 6LR_i --> root (6LBR) --> Internet

   For example, the communication flow could be: Node F --> Node D -->
   Node B --> Node A --> Internet

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from source (6LN) to 6LBR.

   This case is identical to storing-mode case.






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

       +-------------------+------+-------+------+----------------+
       | Header            | 6LN  | 6LR_i | 6LBR | Internet       |
       +-------------------+------+-------+------+----------------+
       | Inserted headers  | RPI  | --    | --   | --             |
       | Removed headers   | --   | --    | --   | --             |
       | Re-added headers  | --   | --    | --   | --             |
       | Modified headers  | --   | RPI   | --   | --             |
       | Untouched headers | --   | --    | RPI  | RPI (Ignored)  |
       +-------------------+------+-------+------+----------------+

     Non Storing: Summary of the use of headers from RPL-aware-leaf to
                                 Internet

7.2.2.  Non-SM: Example of Flow from Internet to RPL-aware-leaf

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 <= i >= n", n is the number of routers (6LR) that the
   packet go through from 6LBR to destination(6LN).

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

   The RPI may be added or not, it is optional.















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   +--------+-------+----------------+----------------+----------------+
   | Header | Inter | 6LBR           | 6LR_i          | 6LN            |
   |        | net   |                |                |                |
   +--------+-------+----------------+----------------+----------------+
   | Insert | --    | IP-in-IP(RH3,o | --             | --             |
   | ed hea |       | pt:RPI)        |                |                |
   | ders   |       |                |                |                |
   | Remove | --    | --             | --             | IP-in-IP(RH3,o |
   | d head |       |                |                | pt:RPI)        |
   | ers    |       |                |                |                |
   | Re-    | --    | --             | --             | --             |
   | added  |       |                |                |                |
   | header |       |                |                |                |
   | s      |       |                |                |                |
   | Modifi | --    | --             | IP-in-IP(RH3,o | --             |
   | ed hea |       |                | pt:RPI)        |                |
   | ders   |       |                |                |                |
   | Untouc | --    | --             | --             | --             |
   | hed he |       |                |                |                |
   | aders  |       |                |                |                |
   +--------+-------+----------------+----------------+----------------+

     Non Storing: Summary of the use of headers from Internet to RPL-
                                aware-leaf

7.2.3.  Non-SM: Example of Flow from not-RPL-aware-leaf to Internet

   In this case the flow comprises:

   not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i -->root (6LBR) -->
   Internet

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from source(IPv6) to 6LBR. e.g 6LR_1 (i=1).

   In this case the flow label is recommended to be zero in the IPv6
   node.  As RPL headers are added in the IPv6 node, the first 6LR
   (6LR_1) will add an RPI header inside a new IP-in-IP header.  The IP-
   in-IP header will be addressed to the root.  This case is identical
   to the storing-mode case (Section 5.7).







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   +---------+-----+-------------+-------------+-------------+---------+
   | Header  | IPv | 6LR_1       | 6LR_i       | 6LBR        | Interne |
   |         | 6   |             | [i=2,..,n]_ |             | t       |
   +---------+-----+-------------+-------------+-------------+---------+
   | Inserte | --  | IP-in-      | --          | --          | --      |
   | d       |     | IP(RPI)     |             |             |         |
   | headers |     |             |             |             |         |
   | Removed | --  | --          | --          | IP-in-      | --      |
   | headers |     |             |             | IP(RPI)     |         |
   | Re-     | --  | --          | --          | --          | --      |
   | added   |     |             |             |             |         |
   | headers |     |             |             |             |         |
   | Modifie | --  | --          | IP-in-      | --          | --      |
   | d       |     |             | IP(RPI)     |             |         |
   | headers |     |             |             |             |         |
   | Untouch | --  | --          | --          | --          | --      |
   | ed      |     |             |             |             |         |
   | headers |     |             |             |             |         |
   +---------+-----+-------------+-------------+-------------+---------+

   Non Storing: Summary of the use of headers from not-RPL-aware-leaf to
                                 Internet

7.2.4.  Non-SM: Example of Flow from Internet to not-RPL-aware-leaf

   In this case the flow comprises:

   Internet --> root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)

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

   6LR_i are the intermediate routers from source to destination.  In
   this case, "1 < i >= n", n is the number of routers (6LR) that the
   packet go through from 6LBR to not-RPL-aware-leaf (IPv6).

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









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   +--------+-------+----------------+------------+-------------+------+
   | Header | Inter | 6LBR           | 6LR_1      | 6LR_i(i=2,. | IPv6 |
   |        | net   |                |            | .,n)        |      |
   +--------+-------+----------------+------------+-------------+------+
   | Insert | --    | IP-in-IP(RH3,o | --         | --          | --   |
   | ed hea |       | pt:RPI)        |            |             |      |
   | ders   |       |                |            |             |      |
   | Remove | --    | --             | --         | IP-in-      | --   |
   | d head |       |                |            | IP(RH3,     |      |
   | ers    |       |                |            | RPI)        |      |
   | Re-    | --    | --             | --         | --          | --   |
   | added  |       |                |            |             |      |
   | header |       |                |            |             |      |
   | s      |       |                |            |             |      |
   | Modifi | --    | --             | IP-in-     | IP-in-      | --   |
   | ed hea |       |                | IP(RH3,    | IP(RH3,     |      |
   | ders   |       |                | RPI)       | RPI)        |      |
   | Untouc | --    | --             | --         | --          | RPI  |
   | hed he |       |                |            |             |      |
   | aders  |       |                |            |             |      |
   +--------+-------+----------------+------------+-------------+------+

    NonStoring: Summary of the use of headers from Internet to non-RPL-
                                aware-leaf

7.3.  Non-Storing Mode: Interaction between Leafs

   In this section we are going to describe the communication flow in
   Non Storing Mode (Non-SM) between,

      RPL-aware-leaf to RPL-aware-leaf

      RPL-aware-leaf to not-RPL-aware-leaf

      not-RPL-aware-leaf to RPL-aware-leaf

      not-RPL-aware-leaf to not-RPL-aware-leaf

7.3.1.  Non-SM: Example of Flow from RPL-aware-leaf to RPL-aware-leaf

   In this case the flow comprises:

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

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





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   6LR_ia are the intermediate routers from source to the root In this
   case, "1 <= ia >= n", n is the number of routers (6LR) that the
   packet go through from 6LN to the root.

   6LR_id are the intermediate routers from the root to the destination.
   In this case, "1 <= ia >= m", m is the number of the intermediate
   routers (6LR).

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

   The originating node SHOULD put the RPI into an IP-in-IP header
   addressed to the root, so that the 6LBR can remove that header.  If
   it does not, then additional resources are wasted on the way down to
   carry the useless RPI option.

   The 6LBR will need to insert an RH3 header, which requires that it
   add an IP-in-IP header.  It SHOULD be able to remove the RPI, as it
   was contained in an IP-in-IP header addressed to it.  Otherwise,
   there MAY be an RPI header buried inside the inner IP header, which
   should get ignored.

   Networks that use the RPL P2P extension [RFC6997] are essentially
   non-storing DODAGs and fall into this scenario or scenario
   Section 7.1.2, with the originating node acting as 6LBR.

























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   +---------+-------------+------+--------------+-------+-------------+
   | Header  | 6LN src     | 6LR_ | 6LBR         | 6LR_i | 6LN dst     |
   |         |             | ia   |              | d     |             |
   +---------+-------------+------+--------------+-------+-------------+
   | Inserte | IP-in-      | --   | IP-in-IP(RH3 | --    | --          |
   | d       | IP(RPI1)    |      | to 6LN, opt  |       |             |
   | headers |             |      | RPI2)        |       |             |
   | Removed | --          | --   | IP-in-       | --    | IP-in-      |
   | headers |             |      | IP(RPI1)     |       | IP(RH3, opt |
   |         |             |      |              |       | RPI2)       |
   | Re-     | --          | --   | --           | --    | --          |
   | added   |             |      |              |       |             |
   | headers |             |      |              |       |             |
   | Modifie | --          | RPI1 | --           | RPI2  | --          |
   | d       |             |      |              |       |             |
   | headers |             |      |              |       |             |
   | Untouch | --          | --   | --           | --    | --          |
   | ed      |             |      |              |       |             |
   | headers |             |      |              |       |             |
   +---------+-------------+------+--------------+-------+-------------+

   Non Storing: Summary of the use of headers for RPL-aware-leaf to RPL-
                                aware-leaf

7.3.2.  Non-SM: Example of Flow from RPL-aware-leaf to not-RPL-aware-
        leaf

   In this case the flow comprises:

   6LN --> 6LR_ia --> root (6LBR) --> 6LR_id --> not-RPL-aware (IPv6)

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

   6LR_ia are the intermediate routers from source to the root In this
   case, "1 <= ia >= n", n is the number of intermediate routers (6LR)

   6LR_id are the intermediate routers from the root to the destination.
   In this case, "1 <= ia >= m", m is the number of the intermediate
   routers (6LR).

   As in the previous case, the 6LN will insert an RPI (RPI_1) header
   which MUST be in an IP-in-IP header addressed to the root so that the
   6LBR can remove this RPI.  The 6LBR will then insert an RH3 inside a
   new IP-in-IP header addressed to the 6LN destination node.  The RPI
   is optional from 6LBR to 6LR_id (RPI_2).





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   +--------+-----------+------------+-------------+------------+------+
   | Header | 6LN       | 6LR_1      | 6LBR        | 6LR_id     | IPv6 |
   +--------+-----------+------------+-------------+------------+------+
   | Insert | IP-in-    | --         | IP-in-      | --         | --   |
   | ed hea | IP(RPI1)  |            | IP(RH3, opt |            |      |
   | ders   |           |            | RPI_2)      |            |      |
   | Remove | --        | --         | IP-in-      | IP-in-     | --   |
   | d head |           |            | IP(RPI_1)   | IP(RH3,    |      |
   | ers    |           |            |             | opt RPI_2) |      |
   | Re-    | --        | --         | --          | --         | --   |
   | added  |           |            |             |            |      |
   | header |           |            |             |            |      |
   | s      |           |            |             |            |      |
   | Modifi | --        | IP-in-     | --          | IP-in-     | --   |
   | ed hea |           | IP(RPI_1)  |             | IP(RH3,    |      |
   | ders   |           |            |             | opt RPI_2) |      |
   | Untouc | --        | --         | --          | --         | opt  |
   | hed he |           |            |             |            | RPI_ |
   | aders  |           |            |             |            | 2    |
   +--------+-----------+------------+-------------+------------+------+

     Non Storing: Summary of the use of headers from RPL-aware-leaf to
                            not-RPL-aware-leaf

7.3.3.  Non-SM: Example of Flow from not-RPL-aware-leaf to RPL-aware-
        leaf

   In this case the flow comprises:

   not-RPL-aware 6LN (IPv6) --> 6LR_ia --> root (6LBR) --> 6LR_id -->
   6LN

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

   6LR_ia are the intermediate routers from source to the root In this
   case, "1 <= ia >= n", n is the number of intermediate routers (6LR)

   6LR_id are the intermediate routers from the root to the destination.
   In this case, "1 <= ia >= m", m is the number of the intermediate
   routers (6LR).

   This scenario is mostly identical to the previous one.  The RPI is
   added by the first 6LR (6LR_1) inside an IP-in-IP header addressed to
   the root.  The 6LBR will remove this RPI, and add it's own IP-in-IP
   header containing an RH3 header and optional RPI (RPI_2).





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   +--------+-----+------------+-------------+------------+------------+
   | Header | IPv | 6LR_1      | 6LBR        | 6LR_id     | 6LN        |
   |        | 6   |            |             |            |            |
   +--------+-----+------------+-------------+------------+------------+
   | Insert | --  | IP-in-     | IP-in-      | --         | --         |
   | ed hea |     | IP(RPI_1)  | IP(RH3, opt |            |            |
   | ders   |     |            | RPI_2)      |            |            |
   | Remove | --  | --         | IP-in-      | --         | IP-in-     |
   | d head |     |            | IP(RPI_1)   |            | IP(RH3,    |
   | ers    |     |            |             |            | opt RPI_2) |
   | Re-    | --  | --         | --          | --         | --         |
   | added  |     |            |             |            |            |
   | header |     |            |             |            |            |
   | s      |     |            |             |            |            |
   | Modifi | --  | --         | --          | IP-in-     | --         |
   | ed hea |     |            |             | IP(RH3,    |            |
   | ders   |     |            |             | opt RPI_2) |            |
   | Untouc | --  | --         | --          | --         | --         |
   | hed he |     |            |             |            |            |
   | aders  |     |            |             |            |            |
   +--------+-----+------------+-------------+------------+------------+

   Non Storing: Summary of the use of headers from not-RPL-aware-leaf to
                              RPL-aware-leaf

7.3.4.  Non-SM: Example of Flow from not-RPL-aware-leaf to not-RPL-
        aware-leaf

   In this case the flow comprises:

   not-RPL-aware 6LN (IPv6 src)--> 6LR_ia --> root (6LBR) --> 6LR_id -->
   not-RPL-aware (IPv6 dst)

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

   6LR_ia are the intermediate routers from source to the root In this
   case, "1 <= ia >= n", n is the number of intermediate routers (6LR)

   6LR_id are the intermediate routers from the root to the destination.
   In this case, "1 <= ia >= m", m is the number of the intermediate
   routers (6LR).

   This scenario is the combination of the previous two cases.







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   +---------+-----+--------------+---------------+-------------+------+
   | Header  | IPv | 6LR_1        | 6LBR          | 6LR_id      | IPv6 |
   |         | 6   |              |               |             | dst  |
   |         | src |              |               |             |      |
   +---------+-----+--------------+---------------+-------------+------+
   | Inserte | --  | IP-in-       | IP-in-IP(RH3) | --          | --   |
   | d       |     | IP(RPI_1)    |               |             |      |
   | headers |     |              |               |             |      |
   | Removed | --  | --           | IP-in-        | IP-in-      | --   |
   | headers |     |              | IP(RPI_1)     | IP(RH3, opt |      |
   |         |     |              |               | RPI_2)      |      |
   | Re-     | --  | --           | --            | --          | --   |
   | added   |     |              |               |             |      |
   | headers |     |              |               |             |      |
   | Modifie | --  | --           | --            | --          | --   |
   | d       |     |              |               |             |      |
   | headers |     |              |               |             |      |
   | Untouch | --  | --           | --            | --          | --   |
   | ed      |     |              |               |             |      |
   | headers |     |              |               |             |      |
   +---------+-----+--------------+---------------+-------------+------+

   Non Storing: Summary of the use of headers from not-RPL-aware-leaf to
                            not-RPL-aware-leaf

8.  Observations about the cases

8.1.  Storing mode

   [I-D.ietf-roll-routing-dispatch] shows that the hop-by-hop IP-in-IP
   header can be compressed using IP-in-IP 6LoRH (IP-in-IP-6LoRH) header
   as described in Section 7 of the document.

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

   Thanks to the change of the RPI option type from 0x63 to 0x23, there
   is no longer any uncertainty about when to use an IP-in-IP header in
   the storing mode.  A Hop-by-Hop Options Header containing the RPI
   option SHOULD always be added when 6LRs originate packets (without
   IP-in-IP headers), and IP-in-IP headers should always be added
   (addressed to the root when on the way up, to the end-host when on
   the way down) when a 6LR find that it needs to insert a Hop-by-Hop
   Options Header containing the RPI option.

   In order to support the above two cases with full generality, the
   different situations (always do IP-in-IP vs never use IP-in-IP)
   should be signaled in the RPL protocol itself.



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8.2.  Non-Storing mode

   In the non-storing case, dealing with non-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 non-RPL aware leaf nodes because it will
   receive a DAO about that node from the 6LN immediately above that
   node.  This means that the non-storing mode case can avoid ever using
   hop-by-hop IP-in-IP headers.

   Unlike in the storing mode case, there is no need for all nodes to
   know about the existence of non-RPL aware nodes.  Only the 6LBR needs
   to change when there are non-RPL aware nodes.  Further, in the non-
   storing case, the 6LBR is informed by the DAOs when there are non-RPL
   aware nodes.

9.  6LoRH Compression cases

   The [I-D.ietf-roll-routing-dispatch] proposes a compression method
   for RPI, RH3 and IPv6-in-IPv6.

   In Storing Mode, for the examples of Flow from RPL-aware-leaf to non-
   RPL-aware-leaf and non-RPL-aware-leaf to non-RPL-aware-leaf comprise
   an IP-in-IP and RPI compression headers.  The type of this case is
   critical since IP-in-IP is encapsulating a RPI header.


   +--+-----+---+--------------+-----------+-------------+-------------+
   |1 | 0|0 |TSE| 6LoRH Type 6 | Hop Limit | RPI - 6LoRH | LOWPAN IPHC |
   +--+-----+---+--------------+-----------+-------------+-------------+


                    Figure 8: Critical IP-in-IP (RPI).

10.  IANA Considerations

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











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


                   Figure 9: Option Type in RPL Option.

   Todo: Add the Updates to RFC 6550.

11.  Security Considerations

   The security considerations covering of [RFC6553] and [RFC6554] apply
   when the packets get into RPL Domain.

   The IPIP 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.

   Nodes outside of the LLN will need to pass IPIP traffic through the
   RPL root to perform this attack.  To counter, the RPL root SHOULD
   either restrict ingress of IPIP packets (the simpler solution), or it
   SHOULD do a deep packet inspection wherein it walks 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
   ([RFC2827]) 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 described in
   [I-D.ietf-6lo-backbone-router].  In this case the BCP38 filtering
   needs to take this into account.

   Nodes with the LLN can use the IPIP 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.

   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, they could still have a significant
   impact, particularly if the attack was on another LLN!  Additionally,
   some uses of RPL involve large backbone ISP scale equipment



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   [I-D.ietf-anima-autonomic-control-plane], which may be equipped with
   multiple 100Gb/s interfaces.

   Blocking or careful filtering of IPIP traffic entering the LLN as
   described above will make sure that any attack that is mounted must
   originate compromised nodes within the LLN.  The use of 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 IPIP traffic SHOULD be allowed to pass
   through the RPL root, such as the IPIP 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-secure-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 IPIP tunnels will 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 IPIP headers using forged source addresses.
   If the attack requires bi-directional communication, then IPIP
   provides no advantages.

   [RFC2473] suggests that tunnel entry and exit points can be secured,
   via the "Use IPsec".  This solution has all the problems that
   [RFC5406] goes into.  In an LLN such a solution would degenerate into
   every node having a tunnel with every other node.  It would provide a
   small amount of origin address authentication at a very high cost;
   doing BCP38 at every node (linking layer-3 addresses to layer-2
   addresses, and to already present layer-2 cryptographic mechanisms)
   would be cheaper should RPL be run in an environment where hostile
   nodes are likely to be a part of the LLN.

   The RH3 header usage described here can be abused in equivalent ways
   with an IPIP 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 a RH3 header which has additional hops which have
   not yet been processed, and SHOULD ignore such a second RH3 header.





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   In addition, the LLN will likely use [I-D.ietf-roll-routing-dispatch]
   to compress the IPIP 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 header, if permitted to enter the LLN, could be used by an
   attacker to change the priority of a packet by selecting a different
   RPL instanceID, 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 instanceID, but a change of instanceID would permit an
   attacker to bypass such filtering.  Like the RH3, an RPI header is to
   be inserted by the RPL root on traffic entering the LLN by first
   inserting an IPIP header.  The attacker's RPI header therefore will
   not be seen by the network.  Upon reaching the destination node the
   RPI header has no further meaning and is just skipped; the presence
   of a second RPI header 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 RPI headers could be abused by an attacker inside of the
   network to route packets on non-obvious ways, perhaps eluding
   observation.  This usage is in fact part of [RFC6997] and can not be
   restricted at all.  This is a feature, not a bug.

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

12.  Acknowledgments

   This work is partially funded by the FP7 Marie Curie Initial Training
   Network (ITN) METRICS project (grant agreement No.  607728).

   The authors would like to acknowledge the review, feedback, and
   comments of (alphabetical order): Robert Cragie, Simon Duquennoy,
   Cenk Guendogan, C.  M.  Heard, Rahul Jadhav, Peter van der Stok,
   Xavier Vilajosana and Thomas Watteyne.






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13.  References

13.1.  Normative References

   [I-D.ietf-6man-rfc2460bis]
              Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", draft-ietf-6man-rfc2460bis-13 (work
              in progress), May 2017.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://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, <http://www.rfc-editor.org/info/rfc2473>.

   [RFC2827]  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, <http://www.rfc-editor.org/info/rfc2827>.

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

   [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,
              <http://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,
              <http://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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc7045>.

   [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,
              <http://www.rfc-editor.org/info/rfc7416>.

13.2.  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-backbone-router]
              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-03 (work in progress), January 2017.

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work
              in progress), January 2017.

   [I-D.ietf-6tisch-dtsecurity-secure-join]
              Richardson, M., "6tisch Secure Join protocol", draft-ietf-
              6tisch-dtsecurity-secure-join-01 (work in progress),
              February 2017.

   [I-D.ietf-anima-autonomic-control-plane]
              Behringer, M., Eckert, T., and S. Bjarnason, "An Autonomic
              Control Plane", draft-ietf-anima-autonomic-control-
              plane-06 (work in progress), March 2017.








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   [I-D.ietf-anima-bootstrapping-keyinfra]
              Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
              S., and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-06 (work in progress), May 2017.

   [I-D.ietf-roll-dao-projection]
              Thubert, P. and J. Pylakutty, "Root initiated routing
              state in RPL", draft-ietf-roll-dao-projection-01 (work in
              progress), March 2017.

   [I-D.ietf-roll-routing-dispatch]
              Thubert, P., Bormann, C., Toutain, L., and R. Cragie,
              "6LoWPAN Routing Header", draft-ietf-roll-routing-
              dispatch-05 (work in progress), October 2016.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              DOI 10.17487/RFC4192, September 2005,
              <http://www.rfc-editor.org/info/rfc4192>.

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

   [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,
              <http://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,
              <http://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, <http://www.rfc-editor.org/info/rfc7102>.

   [Second6TischPlugtest]
              "2nd 6Tisch Plugtest", <http://www.ietf.org/mail-
              archive/web/6tisch/current/pdfgDMQcdCkRz.pdf>.





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Authors' Addresses

   Maria Ines Robles
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: maria.ines.robles@ericsson.com


   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
   Village d'Entreprises Green Side 400, Avenue de Roumanille
   Batiment T3, Biot - Sophia Antipolis    06410
   France

   Email: pthubert@cisco.com























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