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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6971

Internet Engineering Task Force                          U. Herberg, Ed.
Internet-Draft                                                   Fujitsu
Intended status: Experimental                                A. Cardenas
Expires: November 8, 2013                  University of Texas at Dallas
                                                                 T. Iwao
                                                                 Fujitsu
                                                                  M. Dow
                                                               Freescale
                                                             S. Cespedes
                                                                U. Icesi
                                                             May 7, 2013


          Depth-First Forwarding in Unreliable Networks (DFF)
                         draft-cardenas-dff-14

Abstract

   This document specifies the "Depth-First Forwarding" (DFF) protocol
   for IPv6 networks, a data forwarding mechanism that can increase
   reliability of data delivery in networks with dynamic topology and/or
   lossy links.  The protocol operates entirely on the forwarding plane,
   but may interact with the routing plane.  DFF forwards data packets
   using a mechanism similar to a "depth-first search" for the
   destination of a packet.  The routing plane may be informed of
   failures to deliver a packet or loops.  This document specifies the
   DFF mechanism both for IPv6 networks (as specified in RFC2460) and in
   addition also for LoWPAN "mesh-under" networks (as specified in
   RFC4944).  The design of DFF assumes that the underlying link layer
   provides means to detect if a packet has been successfully delivered
   to the next hop or not.  It is applicable for networks with little
   traffic, and is used for unicast transmissions only.

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."




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   This Internet-Draft will expire on November 8, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.2.  Experiments to be conducted  . . . . . . . . . . . . . . .  6
   2.  Notation and Terminology . . . . . . . . . . . . . . . . . . .  7
     2.1.  Notation . . . . . . . . . . . . . . . . . . . . . . . . .  7
     2.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  9
   4.  Protocol Overview and Functioning  . . . . . . . . . . . . . . 11
     4.1.  Information Sets Overview  . . . . . . . . . . . . . . . . 12
     4.2.  Signaling Overview . . . . . . . . . . . . . . . . . . . . 12
   5.  Protocol Dependencies  . . . . . . . . . . . . . . . . . . . . 13
   6.  Information Sets . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Symmetric Neighbor List  . . . . . . . . . . . . . . . . . 14
     6.2.  Processed Set  . . . . . . . . . . . . . . . . . . . . . . 14
   7.  Packet Header Fields . . . . . . . . . . . . . . . . . . . . . 15
   8.  Protocol Parameters  . . . . . . . . . . . . . . . . . . . . . 16
   9.  Data Packet Generation and Processing  . . . . . . . . . . . . 16
     9.1.  Data Packets Entering the DFF Routing Domain . . . . . . . 17
     9.2.  Data Packet Processing . . . . . . . . . . . . . . . . . . 18
   10. Unsuccessful Packet Transmission . . . . . . . . . . . . . . . 20
   11. Determining the Next Hop for a Packet  . . . . . . . . . . . . 21
   12. Sequence Numbers . . . . . . . . . . . . . . . . . . . . . . . 22
   13. Modes of Operation . . . . . . . . . . . . . . . . . . . . . . 22
     13.1. Route-Over . . . . . . . . . . . . . . . . . . . . . . . . 23
       13.1.1.  Mapping of DFF Terminology to IPv6 Terminology  . . . 23
       13.1.2.  Packet Format . . . . . . . . . . . . . . . . . . . . 23
     13.2. Mesh-Under . . . . . . . . . . . . . . . . . . . . . . . . 25
       13.2.1.  Mapping of DFF Terminology to LoWPAN Terminology  . . 25
       13.2.2.  Packet Format . . . . . . . . . . . . . . . . . . . . 26
   14. Scope Limitation of DFF  . . . . . . . . . . . . . . . . . . . 27
     14.1. Route-Over MoP . . . . . . . . . . . . . . . . . . . . . . 29
     14.2. Mesh-Under MoP . . . . . . . . . . . . . . . . . . . . . . 30
   15. MTU Exceedance . . . . . . . . . . . . . . . . . . . . . . . . 32
   16. Security Considerations  . . . . . . . . . . . . . . . . . . . 32
     16.1. Attacks Out of Scope . . . . . . . . . . . . . . . . . . . 32
     16.2. Protection Mechanisms of DFF . . . . . . . . . . . . . . . 32
     16.3. Attacks In Scope . . . . . . . . . . . . . . . . . . . . . 33
       16.3.1.  Denial of Service . . . . . . . . . . . . . . . . . . 33
       16.3.2.  Packet Header Modification  . . . . . . . . . . . . . 33
         16.3.2.1.  Return Flag Tampering . . . . . . . . . . . . . . 34
         16.3.2.2.  Duplicate Flag Tampering  . . . . . . . . . . . . 34
         16.3.2.3.  Sequence Number Tampering . . . . . . . . . . . . 34
   17. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 35
   18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
   19. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     19.1. Normative References . . . . . . . . . . . . . . . . . . . 35



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     19.2. Informative References . . . . . . . . . . . . . . . . . . 36
   Appendix A.  Examples  . . . . . . . . . . . . . . . . . . . . . . 37
     A.1.  Example 1: Normal Delivery . . . . . . . . . . . . . . . . 37
     A.2.  Example 2: Forwarding with Link Failure  . . . . . . . . . 37
     A.3.  Example 3: Forwarding with Missed Link Layer
           Acknowledgment . . . . . . . . . . . . . . . . . . . . . . 38
     A.4.  Example 4: Forwarding with a Loop  . . . . . . . . . . . . 39
   Appendix B.  Deployment Experience . . . . . . . . . . . . . . . . 40
     B.1.  Deployments in Japan . . . . . . . . . . . . . . . . . . . 40
     B.2.  Kit Carson Electric Cooperative  . . . . . . . . . . . . . 40
     B.3.  Simulations  . . . . . . . . . . . . . . . . . . . . . . . 40
     B.4.  Open Source Implementation . . . . . . . . . . . . . . . . 40
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41






































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1.  Introduction

   This document specifies the Depth-First Forwarding (DFF) protocol for
   IPv6 networks, both for IPv6 forwarding ([RFC2460], henceforth
   denoted "route-over"), and also for "mesh-under" forwarding using the
   LoWPAN adaptation layer ([RFC4944]).  The protocol operates entirely
   on the forwarding plane, but may interact with the routing plane.
   The purpose of DFF is to increase reliability of data delivery in
   networks with dynamic topologies and/or lossy links.

   DFF forwards data packets using a "depth-first search" for the
   destination of the packets.  DFF relies on an external neighborhood
   discovery mechanism which lists neighbors of a router that may be
   attempted as next hops for a data packet.  In addition, DFF may use
   information from the Routing Information Base (RIB) for deciding in
   which order to try to send the packet to the neighboring routers.

   If the packet makes no forward progress using the first selected next
   hop, DFF will successively try all neighbors of the router.  If none
   of the next hops successfully receives or forwards the packet, DFF
   returns the packet to the previous hop, which in turn tries to send
   it to alternate neighbors.

   As network topologies do not necessarily form trees, loops can occur.
   Therefore, DFF contains a loop detection and avoidance mechanism.

   DFF may provide information, which may - by a mechanism outside of
   this specification - be used for updating cost of routes in the RIB
   based on failed or successful delivery of packets through alternative
   next hops.  Such information may also be used by a routing protocol.

   DFF assumes that the underlying link layer provides means to detect
   if a packet has been successfully delivered to the next hop or not,
   is designed for networks with little traffic, and is used for unicast
   transmissions only.

1.1.  Motivation

   In networks with dynamic topologies and/or lossy links, even frequent
   exchanges of control messages between routers for updating the
   routing tables cannot guarantee that the routes correspond to the
   effective topology of the network at all times.  Packets may not be
   delivered to their destination because the topology has changed since
   the last routing protocol update.

   More frequent routing protocol updates can mitigate that problem to a
   certain extent, however this requires additional signaling, consuming
   channel and router resources (e.g., when flooding control messages



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   through the network).  This is problematic in networks with lossy
   links, where further control traffic exchange can worsen the network
   stability because of collisions.  Moreover, additional control
   traffic exchange may drain energy from battery-driven routers.

   The data-forwarding mechanism specified in this document allows for
   forwarding data packets along alternate paths for increasing
   reliability of data delivery, using a depth-first search.  The
   objective is to decrease the necessary control traffic overhead in
   the network, and at the same time to increase delivery success rates.

   As this specification is intended for experimentation, the mechanism
   is also specified for forwarding on the LoWPAN adaption layer
   (according to Section 11 of [RFC4944]), in addition to IPv6
   forwarding as specified in [RFC2460].  Other than different header
   formats, the DFF mechanism for route-over and mesh-under is similar,
   and is therefore first defined in general, and then more specifically
   for both IPv6 route-over forwarding (as specified in Section 13.1),
   and for LoWPAN adaptation layer mesh-under (as specified in
   Section 13.2).

1.2.  Experiments to be conducted

   This document is presented as an Experimental specification that can
   increase reliability of data delivery in networks with dynamic
   topology and/or lossy links.  It is anticipated that, once sufficient
   operational experience has been gained, this specification will be
   revised to progress it on to the Standards Track.  This experiment is
   intended to be tried in networks that meet the applicability
   described in Section 3, and with the scope limitations set out in
   Section 14.  While experimentation is encouraged in such networks,
   operators should exercise caution before attempting this experiment
   in other types of network as the stability of interaction between DFF
   and routing in those networks has not been established.

   Experience reports regarding DFF implementation and deployment are
   encouraged particularly with respect to:

   o  Optimal values for the parameter P_HOLD_TIME, depending on the
      size of the network, the topology and the amount of traffic
      originated per router.  The longer a Processed Tuple is hold, the
      more memory is consumed on a router.  Moreover, if a tuple is hold
      too long, a sequence number wrap-around may occur, and a new
      packet may have the same sequence number as one indicated in an
      old Processed Tuple.  However, if the tuple is expired too soon
      (before the packet has been completed its path to the
      destination), it may be mistakenly detected as new packet instead
      of one already seen.



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   o  Optimal values for the parameter MAX_HOP_LIMIT, depending on the
      size of the network, the topology, and the lossyness of the link
      layer.  MAX_HOP_LIMIT makes sure that packets do not unnecessarily
      traverse in the network; it may be used to limit the "detour" of
      packets that is acceptable.  The value may also be based on a per-
      packet-basis if hop-count information is available from the RIB or
      routing protocol.  In such a case, the hop-limit for the packet
      may be a percentage (e.g., 200%) of the hop-count value indicated
      in the routing table.

   o  Optimal methods to increase cost of a route when a loop or lost L2
      ACK is detected by DFF.  While this is not specified as a
      normative part of this document, it may be of interest in an
      experiment to find good values of how much to increase link cost
      in the RIB or routing protocol.

   o  Performance of using DFF in combination with different routing
      protocols, such as reactive and proactive protocols.  This also
      implies how routes are updated by the RIB / routing protocol when
      informed by DFF about loops or broken links.


2.  Notation and Terminology

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

   Additionally, this document uses the notation in Section 2.1 and the
   terminology in Section 2.2.

2.1.  Notation

   The following notations are used in this document:

   List:  A list of elements is defined as [] for an empty list,
      [element] for a list with one element, and [element1, element2,
      ...] for a list with multiple elements.

   Concatenation of lists:  If L1 and L2 are lists, then L1@L2 is a new
      list with first all elements of L1, followed by all elements of L2
      in that order.

   Byte order:  All packet formats in this specification use network
      byte order (most significant octet first) for all fields.  The
      most significant bit in an octet is numbered bit 0, and the least
      significant bit of an octet is numbered bit 7.



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   Assignment:  a := b
      An assignment operator, whereby the left side (a) is assigned the
      value of the right side (b).

   Comparison:  c = d
      A comparison operator, returning true if the value of the left
      side (c) is equal to the value of the right side (d).

   Flags:  This specification uses multiple 1-bit flags.  A value of '0'
      of a flag means 'false', a value of '1' means 'true'.

2.2.  Terminology

   The terms "route-over" and "mesh-under", introduced in [RFC6775] are
   used in this document, where "route-over" is not only limited to
   6LoWPANs but applies to general IPv6 networks:

   Mesh-under:  A topology where nodes are connected to a [6LoWPAN
      Border Router] 6LBR through a mesh using link-layer forwarding.
      Thus, in a mesh-under configuration, all IPv6 hosts in a LoWPAN
      are only one IP hop away from the 6LBR.  This topology simulates
      the typical IP-subnet topology with one router with multiple nodes
      in the same subnet.

   Route-over:  A topology where hosts are connected to the 6LBR through
      the use of intermediate layer-3 (IP) routing.  Here, hosts are
      typically multiple IP hops away from a [6LoWPAN Router] 6LBR.  The
      route-over topology typically consists of a 6LBR, a set of 6LRs,
      and hosts.

   The following terms are used in this document.  As the DFF mechanism
   is specified both for route-over IPv6 and for mesh-under LoWPAN
   adaptation layer, the terms are generally defined in this section,
   and then specifically mapped for each of the different modes of
   operation in Section 13.

   Depth-first search:  "Depth-first search (DFS) is an algorithm for
      traversing or searching a tree, tree structure, or graph.  One
      starts at the root (selecting some node as the root in the graph
      case) and explores as far as possible along each branch before
      backtracking" [DFS_wikipedia].  In this document, the algorithm
      for traversing a graph is applied to forwarding packets in a
      computer network, with nodes being routers.

   Routing Information Base (RIB):  A table stored in the user-space of
      an operating system of a router or host.  The table lists routes
      to network destinations, as well as associated metrics with these
      routes.



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   Mode of Operation (MoP):  The DFF mechanism specified in this
      document can either be used as "route-over" IPv6 forwarding
      mechanism (Mode of Operation: "route-over"), or as "mesh-under"
      LoWPAN adaptation layer (Mode of Operation: "mesh-under").

   Packet:  An IPv6 Packet (for "route-over" MoP) or a "LoWPAN
      encapsulated packet" (for "mesh-under" MoP) containing an IPv6
      Packet as payload.

   Packet Header:  An IPv6 extension header (for "route-over" MoP) or a
      LoWPAN header (for "mesh-under" MoP).

   Address:  An IPv6 address (for "route-over" MoP), or a 16-bit short
      or EUI-64 link layer address (for "mesh-under" MoP).

   Originator:  The router which added the DFF header (specified in
      Section 7) to a Packet.

   Originator Address:  An Address of the Originator.  This Address
      SHOULD be an Address configured on the interface which transmits
      the Packet, selected according to [RFC6724].

   Destination:  The router or host to which a Packet is finally
      destined.  In case this router or host is outside of the routing
      domain in which DFF is used, the Destination is the router that
      removes the DFF header (specified in Section 7) from the Packet.
      This case is described in Section 14.1.

   Destination Address:  An Address to which the Packet is sent.

   Next Hop:  An Address of the next hop router to which the Packet is
      sent along the path to the Destination.

   Previous Hop:  The Address of the previous hop router from which a
      Packet has been received.  In case the Packet has been received by
      a router from outside of the routing domain where DFF is used
      (i.e., no DFF header is contained in the Packet), the Originator
      Address of the router adding the DFF header to the Packet is used
      as the Previous Hop.

   Hop Limit:  An upper bound how many times the Packet may be
      forwarded.


3.  Applicability Statement

   This document specifies DFF, a packet forwarding mechanism intended
   for use in networks with dynamic topology and/or lossy links with the



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   purpose of increasing reliability of data delivery.  The protocol's
   applicability is determined by its characteristics, which are that
   this protocol:

   o  Is applicable for use in IPv6 networks, either as "route-over"
      forwarding mechanism using IPv6 ([RFC2460]), or as "mesh-under"
      forwarding mechanism using the frame format for transmission of
      IPv6 packets defined in [RFC4944].

   o  Assumes addresses used in the network are either IPv6 addresses
      (if the protocol is used as "route-over"), or 16-bit short or
      EUI-64 link layer addresses, as specified in [RFC4944] if the
      protocol is used as "mesh-under".  In "mesh-under" mode, mixed 16-
      bit and EUI-64 addresses within one DFF routing domain are allowed
      (if conform with [RFC4944]), as long as DFF is limited to be used
      within one PAN (Personal Area Network).  It is assumed that the
      "route-over" mode and "mesh-under" mode are mutually exclusive in
      the same routing domain.

   o  Assumes that the underlying link layer provides means to detect if
      a Packet has been successfully delivered to the Next Hop or not
      (e.g., by L2 ACK messages).  Examples for such underlying link
      layers are IEEE 802.15.4 or IEEE 802.11.

   o  Is applicable in networks with lossy links and/or with a dynamic
      topology.  In networks with very stable links and fixed topology,
      DFF will not bring any benefit (but also not be harmful, other
      than the additional overhead for the Packet header).

   o  Works in a completely distributed manner, and does not depend on
      any central entity.

   o  Is applicable for networks with little traffic in terms of numbers
      of Packets per second, since each recently forwarded Packet
      increases the state on a router.  The amount of traffic per time
      that is supported by DFF depends on the memory resources of the
      router running DFF, on the density of the network, on the loss
      rate of the channel, and the maximum hop limit for each Packet:
      for each recently seen Packet, a list of Next Hops that the Packet
      has been sent to is stored in memory.  The stored entries can be
      deleted after an expiration time, so that only recently received
      Packets require storage on the router.  Implementations are
      advised to measure and report rates of packets in the network, and
      also to report memory usage.  Thus, operators can determine memory
      exhaustion because of growing Information Sets or problems because
      of too rapid sequence number wrap-around.





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   o  Is applicable for dense topologies with multiple paths between
      each source and each destination.  Certain topologies are less
      suitable for DFF: topologies that can be partitioned by the
      removal of a single router or link, topologies with multiple stub
      routers that each have a single link to the network, topologies
      with only a single path to a destination, or topologies where the
      "detour" that a Packet makes during the depth-first search in
      order to reach the destination would be too long.  Note that the
      number of retransmissions of a Packet that stipulate a "too long"
      path depends on the underlying link layer (capacity and
      probability of Packet loss), as well as how much bandwidth is
      required for data traffic by applications running in the network.
      In such topologies, the Packet may never reach the Destination,
      and therefore unnecessary transmissions of data Packets may occur
      until the Hop Limit of the Packet reaches zero and the Packet is
      dropped.  This may consume channel and router resources.

   o  Is used for unicast transmissions only (not for anycast or
      multicast).

   o  Is for use within stub networks, and for traffic between a router
      inside the routing domain in which DFF is used and a known border
      router.  Examples of such networks are LoWPANs.  Scope limitations
      are described in Section 14.


4.  Protocol Overview and Functioning

   When a Packet is to be forwarded by a router using DFF, the router
   creates a list of candidate Next Hops for that Packet.  This list
   (created per packet) is ordered, and Section 11 provides
   recommendations of how to order the list, e.g., first listing Next
   Hops listed in the RIB, if available, ordered in increasing cost,
   followed by other neighbors provided by an external neighborhood
   discovery.  DFF proceeds to forward the Packet to the Next Hop listed
   first in the list.  If the transmission was not successful (as
   determined by the underlying link layer) or if the Packet was
   "returned" by a Next Hop to which it had been sent before, the router
   will try to forward the Packet to the next Next Hop on the list.  A
   router "returns" a Packet to the router from which it was originally
   received, once it has unsuccessfully tried to forward the Packet to
   all elements in the candidate Next Hop list.  If the Packet is
   eventually returned to the Originator of the Packet, and after the
   Originator has exhausted all of its Next Hops for the Packet, the
   Packet is dropped.

   For each recently forwarded Packet, a router running DFF stores
   information about the Packet as entry in an information set, denoted



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   Processed Set. Each entry in the Processed Set contains a sequence
   number, included in the Packet Header, identifying the Packet (refer
   to Section 12 for further details on the sequence number).
   Furthermore, the entry contains a list of Next Hops to which the
   Packet has been sent.  This list of recently forwarded Packets also
   allows for avoiding loops when forwarding a Packet.  Entries in the
   Processed Set expire after a given expiration timeout, and are
   removed.

4.1.  Information Sets Overview

   This specification requires a single set on each router, the
   Processed Set. The Processed Set stores the sequence number, the
   Originator Address, the Previous Hop and a list of Next Hops, to
   which the Packet has been sent, for each recently seen Packet.
   Entries in the set are removed after a predefined time-out.  Each
   time a Packet is forwarded to a Next Hop, that Next Hop is added to
   the list of Next Hops of the entry for the Packet.

   Note that an implementation of this protocol may maintain the
   information of the Processed Set in the indicated form, or in any
   other organization which offers access to this information.  In
   particular, it is not necessary to remove Tuples from a Set at the
   exact time indicated, only to behave as if the Tuples were removed at
   that time.

   In addition to the Processed Set, a list of symmetric neighbors must
   be provided by an external neighborhood discovery mechanism, or may
   be determined from the RIB (e.g., if the RIB provides routes to
   adjacent routers, and if these one-hop routes are verified to be
   symmetric).

4.2.  Signaling Overview

   Information is needed on a per-packet basis by a router running DFF
   that receives a Packet.  This information is encoded in the Packet
   Header that is specified in this document as IPv6 Hop-by-Hop Options
   extension header and as LoWPAN header respectively, for the intended
   "route-over" and "mesh-under" Modes of Operations.  This DFF header
   contains a sequence number used for uniquely identifying a Packet,
   and two flags: RET (for "return") and DUP (for "duplicated").

   While a router successively tries sending a data Packet to one or
   more of its neighbors, RET = 0.  If none of the transmissions of the
   Packet to the neighbors of a router have succeeded, the Packet is
   returned to the router from which the Packet has been first received,
   indicated by setting the return flag (RET := 1).  The RET flag is
   required to discern between a deliberately returned Packet and a



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   looping Packet: if a router receives a Packet with RET = 1 (and DUP =
   0 or DUP = 1) that it has already forwarded, the Packet was
   deliberately returned, and the router will continue to successively
   send the Packet to routers from the candidate Next Hop list.  If that
   Packet has RET = 0, the router assumes that the Packet is looping and
   returns it to the router from which it last received it.  An external
   mechanism may use this information for increasing the route cost of
   the route to the Destination using the Next Hop which resulted in the
   loop in the RIB or the routing protocol.  It is out of scope of this
   document to specify such a mechanism.  Note that once DUP is set to
   1, loop detection is not possible any more as the flag is not reset
   any more.  Therefore, a Packet may loop if the RIBs of routers in the
   domain are inconsistent, until hop limit has reached 0.

   Whenever a Packet transmission to a neighbor has failed (as
   determined by the underlying link layer, e.g., using L2 ACKs), the
   duplicate (DUP) flag is set in the Packet Header for the following
   transmissions.  The rationale is that the Packet may have been
   successfully received by the neighbor and only the L2 ACK has been
   lost, resulting in possible duplicates of the Packet in the network.
   The DUP flag tags such a possible duplicate.  The DUP flag is
   required to discern between a duplicated Packet and a looping Packet:
   if a router receives a Packet with DUP = 1 (and RET = 0) that it has
   already forwarded, the Packet is not considered looping, and
   successively forwarded to the next router from the candidate Next Hop
   list.  If the received Packet has DUP = 0 (and RET = 0), the router
   assumes that the Packet is looping, sets RET := 1, and returns it to
   the Previous Hop. Again, an external mechanism may use this
   information for increasing route costs and/or informing the routing
   protocol.

   The reason for not dropping received duplicated Packets (with DUP =
   1) is that a duplicated Packet may during its path again be
   duplicated if another L2 ACK is lost.  However, when DUP is already
   set to 1, it is not possible discerning the duplicate from the
   duplicate of the duplicate.  As a consequence, loop detection is not
   possible after the second lost L2 ACK on the path of a Packet.
   However, if duplicates are simply dropped, it is possible that the
   Packet was actually a looping packet (and not a duplicate), and so
   the Depth First Search would be interrupted.


5.  Protocol Dependencies

   DFF MAY use information from the Routing Information Base (RIB),
   specifically for determining an order of preference for to which next
   hops a packet should be forwarded (e.g., the packet may be forwarded
   first to neighbors that are listed in the RIB as next hops to the



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   destination, preferring those with the lowest route cost).
   Section 11 provides recommendations about the order of preference for
   the next hops of a packet.

   DFF MUST have access to a list of symmetric neighbors for each
   router, provided by a mechanism such as, e.g., NHDP [RFC6130].  That
   neighborhood discovery protocol is not specified in this document.


6.  Information Sets

   This section specifies the information sets used by DFF.

6.1.  Symmetric Neighbor List

   DFF MUST have access to a list of Addresses of symmetric neighbors of
   the router.  This list can be provided by an external neighborhood
   discovery mechanism, or alternatively may be determined from the RIB
   (e.g., if the RIB provides routes to adjacent routers, and if these
   one-hop routes are verified to be symmetric).  The list of Addresses
   of symmetric neighbors is not specified within this document.  The
   Addresses in the list are used to construct a list of candidate Next
   Hops for a Packet, as specified in Section 11.

6.2.  Processed Set

   Each router maintains a Processed Set in order to support the loop
   detection functionality.  The Processed Set lists sequence numbers of
   previously received Packets, as well as a list of Next Hops to which
   the Packet has been sent successively as part of the depth-first
   forwarding mechanism.  To protect against this situation, it is
   recommended that an implementation retains the Processed Set in non-
   volatile storage if such is provided by the router.

   The set consists of Processed Tuples

      (P_orig_address, P_seq_number, P_prev_hop,
      P_next_hop_neighbor_list, P_time)

   where

      P_orig_address is the Originator Address of the received Packet;

      P_seq_number is the sequence number of the received Packet;







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      P_prev_hop is the Address of the Previous Hop of the Packet;

      P_next_hop_neighbor_list is a list of Addresses of Next Hops to
      which the Packet has been sent previously, as part of the depth-
      first forwarding mechanism, as specified in Section 9.2;

      P_time specifies when this Tuple expires and MUST be removed.

   The consequences when no or not enough non-volatile storage is
   available on a router (e.g., because of limited resources) or when an
   implementation chooses not to make the Processed Set persistent, are
   that Packets that are already in a loop caused by the routing
   protocol may continue to loop until the hop limit is exhausted.  Non-
   looping Packets may be sent to Next Hops that have already received
   the Packet previously and will return the Packet, leading to some
   unnecessary retransmissions.  This effect is only temporary and
   applies only for Packets already traversing the network.


7.  Packet Header Fields

   This section specifies the information required by DFF in the Packet
   Header.  Note that, depending on whether DFF is used in the "route-
   over" MoP or in the "mesh-under" MoP, the DFF header is either an
   IPv6 Hop-by-Hop Options extension header (as specified in
   Section 13.1.2) or a LoWPAN header (as specified in Section 13.2.2).
   Section 13.1.2 and Section 13.2.2 specify the precise order, format
   and encoding of the fields that are listed in this section.

   Version (VER)  - This 2-bit value indicates the version of DFF that
      is used.  This specification defines value 00.  Packets with other
      values of the version MUST be forwarded using forwarding as
      defined in [RFC2460] and [RFC4944] for route-over and mesh-under
      MoP respectively.

   Duplicate Packet Flag (DUP)  - This 1-bit flag is set in the DFF
      header of a Packet, when that Packet is being re-transmitted due
      to a signal from the link-layer that the original transmission
      failed, as specified in Section 9.2.  Once the flag is set to 1,
      it MUST NOT be modified by routers forwarding the Packet.

   Return Packet Flag (RET)  - The 1-bit flag MUST be set to 1 prior to
      sending the Packet back to the Previous Hop. Upon receiving a
      packet with RET = 1, and before sending it to a new Candidate Next
      Hop, that flag MUST be set to 0 as specified in Section 9.2.






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   Sequence Number  - A 16-bit field, containing an unsigned integer
      sequence number generated by the Originator, unique to each router
      for each Packet to which the DFF has been added, as specified in
      Section 12.  The Originator Address concatenated with the sequence
      number represents an identifier of previously seen data Packets.
      Refer to Section 12 for further information about sequence
      numbers.


8.  Protocol Parameters

   The parameters used in this specification are listed in this section.
   These parameters are configurable, do not need to be stored in non-
   volatile storage, and can be varied by implementations at run time.
   Default values for the parameters depend on the network size,
   topology, link layer and traffic patterns.  Part of the
   experimentation described in Section 1.2 is to determine suitable
   default values.

   P_HOLD_TIME  - Is the time period after which a newly created or
      modified Processed Tuple expires and MUST be deleted.  An
      implementation SHOULD use a value for P_HOLD_TIME that is high
      enough that the Processed Tuple for a Packet is still in memory on
      all forwarding routers while the Packet is transiting the routing
      domain.  The value SHOULD at least be MAX_HOP_LIMIT times the
      expected time to send a Packet to a router on the same link.  The
      value MUST be lower than the time it takes until the same sequence
      number is reached again after a wrap-around on the router
      identified by P_orig_address of the Processed Tuple.

   MAX_HOP_LIMIT  - Is the initial value of Hop Limit, and therefore the
      maximum number of times that a Packet is forwarded in the routing
      domain.  When choosing the value of MAX_HOP_LIMIT, the size of the
      network, the distance between source and destination in number of
      hops, and the maximum possible "detour" of a Packet SHOULD be
      considered (compared to the shortest path).  Such information MAY
      be used from the RIB, if provided.


9.  Data Packet Generation and Processing

   The following sections specify the process of handling a Packet
   entering the DFF routing domain (i.e., without DFF header) in
   Section 9.1, as well as forwarding a data Packet from another router
   running DFF in Section 9.2.






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9.1.  Data Packets Entering the DFF Routing Domain

   This section applies for any data Packets upon their first entry into
   a routing domain, in which DFF is used.  This occurs when a new data
   Packet is generated on this router, or when a data Packet is
   forwarded from outside the routing domain (i.e., from a host attached
   to this router or from a router outside the routing domain in which
   DFF is used).  Before such a data Packet (henceforth denoted "current
   Packet") is transmitted, the following steps MUST be executed:

   1.  If required, encapsulate the Packet as specified in Section 14.

   2.  Add the DFF header to the current Packet (to the outer header if
       the Packet has been encapsulated), with:

       *  DUP := 0;

       *  RET := 0;

       *  Sequence Number := a new sequence number of the Packet (as
          specified in Section 12).

   3.  Check that the Packet does not exceed the MTU as specified in
       Section 15.  In case it does, execute the procedures listed in
       Section 15 and do not further process the Packet.

   4.  Select the Next Hop (henceforth denoted "next_hop") for the
       current Packet, as specified in Section 11.

   5.  Add a Processed Tuple to the Processed Set with:

       *  P_orig_address := the Originator Address of the current
          Packet;

       *  P_seq_number := the sequence number of the current Packet;

       *  P_prev_hop := the Originator Address of the current Packet;

       *  P_next_hop_neighbor_list := [next_hop];

       *  P_time := current time + P_HOLD_TIME.

   6.  Pass the current Packet to the underlying link layer for
       transmission to next_hop.  If the transmission fails (as
       determined by the link layer), the procedures in Section 10 MUST
       be executed.





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9.2.  Data Packet Processing

   When a Packet (henceforth denoted the "current Packet") is received
   by a router, then the following tasks MUST be performed:

   1.  If the Packet Header is malformed (i.e., the header format is not
       as expected by this specification), drop the Packet.

   2.  Otherwise, if the Destination Address of the Packet matches an
       Address of an interface of this router, deliver the Packet to
       upper layers and do not further process the Packet as specified
       below.

   3.  Decrement the value of the Hop Limit field by one (1).

   4.  Drop the Packet if Hop Limit is decremented to zero and do not
       further process the Packet as specified below.

   5.  If no Processed Tuple (henceforth denoted the "current tuple")
       exists in the Processed Set, with:

       +  P_orig_address = the Originator Address of the current Packet,
          AND;

       +  P_seq_number = the sequence number of the current Packet.

       Then:

       1.  Add a Processed Tuple (henceforth denoted the "current
           tuple") with:

           +  P_orig_address := the Originator Address of the current
              Packet;

           +  P_seq_number := the sequence number of the current Packet;

           +  P_prev_hop := the Previous Hop Address of the current
              Packet;

           +  P_next_hop_neighbor_list := [];

           +  P_time := current time + P_HOLD_TIME.

       2.  Set RET to 0 in the DFF header.







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       3.  Select the Next Hop (henceforth denoted "next_hop") for the
           current Packet, as specified in Section 11.

       4.  P_next_hop_neighbor_list := P_next_hop_neighbor_list@
           [next_hop].

       5.  Pass the current Packet to the underlying link layer for
           transmission to next_hop.  If the transmission fails (as
           determined by the link layer), the procedures in Section 10
           MUST be executed.

   6.  Otherwise, if a tuple exists:

       1.  If the return flag of the current Packet is not set (RET = 0)
           (i.e., a loop has been detected):

           1.  Set RET := 1.

           2.  Pass the current Packet to the underlying link layer for
               transmission to the Previous Hop.

       2.  Otherwise, if the return flag of the current Packet is set
           (RET = 1):

           1.  If the Previous Hop of the Packet is not contained in
               P_next_hop_neighbor_list of the current tuple, drop the
               Packet.

           2.  If the Previous Hop of the Packet (i.e., the address of
               the router from which the current Packet has just been
               received) is equal to P_prev_hop of current tuple (i.e.,
               the address of the router from which the current Packet
               has been first received), drop the Packet.

           3.  Set RET := 0.

           4.  Select the Next Hop (henceforth denoted "next_hop") for
               the current Packet, as specified in Section 11.

           5.  Modify the current tuple:

               -  P_next_hop_neighbor_list := P_next_hop_neighbor_list@
                  [next_hop];

               -  P_time := current time + P_HOLD_TIME.






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           6.  If the selected Next Hop is equal to P_prev_hop of the
               current tuple, as specified in Section 11, (i.e., all
               Candidate Next Hops have been unsuccessfully tried), set
               RET := 1.  If this router (i.e., the router receiving the
               current packet) has the same Address as the Originator
               Address of the current Packet, drop the Packet.

           7.  Pass the current Packet to the underlying link layer for
               transmission to next_hop.  If transmission fails (as
               determined by the link layer), the procedures in
               Section 10 MUST be executed.


10.  Unsuccessful Packet Transmission

   DFF requires that the underlying link layer provides information as
   to whether a Packet is successfully received by the Next Hop. Absence
   of such a signal is interpreted as delivery failure of the Packet
   (henceforth denoted the "current Packet").  Note that the underlying
   link layer MAY retry sending the Packet multiple times (e.g., using
   exponential back-off) before determining that the Packet has not been
   successfully received by the Next Hop. Whenever Section 9 explicitly
   requests it in case of such a delivery failure, the following steps
   are executed:

   1.  Set the duplicate flag (DUP) of the DFF header of the current
       Packet to 1.

   2.  Select the Next Hop (henceforth denoted "next_hop") for the
       current Packet, as specified in Section 11.

   3.  Find the Processed Tuple (the "current tuple") in the Processed
       Set, with:

       +  P_orig_address = the Originator Address of the current Packet,
          AND;

       +  P_seq_number = the sequence number of the current Packet,

   4.  If no current tuple is found, drop the Packet.

   5.  Otherwise, modify the current tuple:

       *  P_next_hop_neighbor_list := P_next_hop_neighbor_list@
          [next_hop];

       *  P_time := current time + P_HOLD_TIME.




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   6.  If the selected next_hop is equal to P_prev_hop of the current
       tuple, as specified in Section 11 (i.e., all neighbors have been
       unsuccessfully tried):

       *  RET := 1

       *  Decrement the value of the Hop Limit field by one (1).  Drop
          the Packet if Hop Limit is decremented to zero.

   7.  Otherwise

       *  RET := 0

   8.  Transmit the current Packet to next_hop.  If transmission fails
       (determined by the link layer), and if the next_hop does not
       equal P_prev_hop from the current tuple, the procedures in
       Section 10 MUST be executed.


11.  Determining the Next Hop for a Packet

   When forwarding a Packet, a router determines a valid Next Hop for
   that Packet as specified in this section.  As a Processed Tuple was
   either existing when receiving the Packet (henceforth denoted the
   "current Packet"), or otherwise was created, it can be assumed the a
   Processed Tuple for that Packet (henceforth denoted the "current
   tuple") is available.

   The Next Hop is chosen from a list of candidate Next Hops in order of
   decreasing priority.  This list is created per Packet.  The maximum
   candidate Next Hop List for a Packet contains all the neighbors of
   the router (as determined from an external neighborhood discovery
   process), except for the Previous Hop of the current Packet.  A
   smaller list MAY be used, if desired, and the exact selection of the
   size of the candidate Next Hop List is a local decision in each
   router, which does not affect interoperability.  Selecting a smaller
   list may reduce the path length of a Packet traversing the network
   and reduce required state in the Processed Set, but may result in
   valid paths that are not explored.  If information from the RIB is
   used, then the candidate Next Hop list MUST contain at least the Next
   Hop, indicated in the RIB as the Next Hop on the shortest path to the
   destination, and SHOULD contain all Next Hops, indicated to the RIB
   as Next Hops on paths to the destination.  If a Next Hop from the RIB
   equals the Previous Hop of the current Packet, it MUST NOT be added
   to the candidate Next Hop list.

   The list MUST NOT contain Addresses which are listed in
   P_next_hop_neighbor_list of the current tuple, in order to avoid



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   sending the Packet to the same neighbor multiple times.  Moreover, an
   Address MUST NOT appear more than once in the list, for the same
   reason.  Also, Addresses of an interface of this router MUST NOT be
   added to the list.

   The list has an order of preference, where Next Hops at the top of
   the list being the ones that Packets are sent to first in the depth-
   first processing specified in Section 9.1 and Section 9.2.  The
   following order is RECOMMENDED, with the elements listed on top
   having the highest preference:

   1.  The neighbor that is indicated in the RIB as the Next Hop on the
       shortest path to the destination of the current Packet;

   2.  Other neighbors indicated in the RIB as Next Hops on path to the
       destination of the current Packet;

   3.  All other symmetric neighbors (except the Previous Hop of the
       current Packet).

   Additional information from the RIB or the list of symmetric
   neighbors MAY be used for determining the order, such as route cost
   or link quality.

   If the candidate Next Hop list created as specified in this section
   is empty, the selected Next Hop MUST be P_prev_hop of the current
   tuple; this case applies when returning the Packet to the Previous
   Hop.


12.  Sequence Numbers

   Whenever a router generates a Packet or forwards a Packet on behalf
   of a host or a router outside the routing domain where DFF is used, a
   sequence number MUST be created and included in the DFF header.  This
   sequence number MUST be unique locally on each router where it is
   created.  A sequence number MUST start at 0 for the first Packet to
   which the DFF header is added, and then increase in steps of 1 for
   each new Packet.  The sequence number MUST NOT be greater than 65535
   and MUST wrap around to 0.


13.  Modes of Operation

   DFF can be used either as "route-over" IPv6 forwarding protocol, or
   alternatively as "mesh-under" data forwarding protocol for the LoWPAN
   adaptation layer ([RFC4944]).  Previous sections have specified the
   DFF mechanism in general; specific differences for each MoP are



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   specified in this section.

13.1.  Route-Over

   This section maps the general terminology from Section 2.2 to the
   specific terminology when using the "route-over" MoP.

13.1.1.  Mapping of DFF Terminology to IPv6 Terminology

   The following terms are those listed in Section 2.2, and their
   meaning is explicitly defined when DFF is used in the "route-over"
   MoP:

   Packet  - An IPv6 packet, as specified in [RFC2460].

   Packet Header  - An IPv6 extension header, as specified in [RFC2460].

   Address  - An IPv6 address, as specified in [RFC4291].

   Originator Address  - The Originator Address corresponds to the
      Source address field of the IPv6 header as specified in [RFC2460].

   Destination Address  - The Destination Address corresponds to the
      Destination field of the IPv6 header as specified in [RFC2460].

   Next Hop  - The Next Hop is the IPv6 address of the next hop to which
      the Packet is sent; the link layer address from that IP address is
      resolved by a mechanism such as ND [RFC4861].  The link layer
      address is then used by L2 as destination.

   Previous Hop  - The Previous Hop is the IPv6 address from the
      interface of the previous hop from which the Packet has been
      received.

   Hop Limit  - The Hop Limit corresponds to the Hop Limit field in the
      IPv6 header as specified in [RFC2460].

13.1.2.  Packet Format

   In the "route-over" MoP, all IPv6 Packets MUST conform with the
   format specified in [RFC2460].

   The DFF header, as specified below, is an IPv6 Extension Hop-by-Hop
   Options header, and is depicted in Figure 1 (where DUP is abbreviated
   to D, and RET is abbreviated to R because of the limited space in the
   figure).  This document specifies a new option to be used inside the
   Hop-by-Hop Options header, which contains the DFF fields (DUP and RET
   flags and sequence number, as specified in Section 7).



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   [RFC6564] specifies:

      New options for the existing Hop-by-Hop Header SHOULD NOT be
      created or specified unless no alternative solution is feasible.
      Any proposal to create a new option for the existing Hop-by-Hop
      Header MUST include a detailed explanation of why the hop-by-hop
      behavior is absolutely essential in the document proposing the new
      option with hop-by-hop behavior.

   [RFC6564] recommends to use Destination Headers instead of Hop-by-Hop
   Option headers.  Destination Headers are only read by the destination
   of an IPv6 packet, not by intermediate routers.  However, the
   mechanism specified in this document relies on intermediate routers
   reading and editing the header.  Specifically, the sequence number
   and the DUP and RET flags are read by each router running the DFF
   protocol.  Modifying the DUP flag and RET flag is essential for this
   protocol to tag duplicate or returned Packets.  Without the DUP flag,
   a duplicate Packet cannot be discerned from a looping Packet, and
   without the RET flag, a returned Packet cannot be discerned from a
   looping Packet.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Next Header  |  Hdr Ext Len  |  OptTypeDFF   | OptDataLenDFF |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |VER|D|R|0|0|0|0|        Sequence Number        |      Pad1     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                         Figure 1: IPv6 DFF Header

   Field definitions of the DFF header are as follows:

   Next Header  - 8-bit selector.  Identifies the type of header
      immediately following the Hop-by-Hop Options header.  As specified
      in [RFC2460].

   Hdr Ext Len  - 8-bit unsigned integer.  Length of the Hop-by-Hop
      Options header in 8-octet units, not including the first 8 octets.
      As specified in [RFC2460].  This value is set to 0 (zero).

   OptTypeDFF  - 8-bit identifier of the type of option as specified in
      [RFC2460].  This value is set to IP_DFF.  The two high order bits
      of the option type MUST be set to '11' and the third bit is equal
      to '1'.  With these bits, according to [RFC2460], routers that do
      not understand this option on a received Packet discard the packet
      and, only if the packet's Destination Address was not a multicast



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      address, send an ICMP Parameter Problem, Code 2, message to the
      packet's Source Address, pointing to the unrecognized Option Type.
      Also, according to [RFC2460], the values within the option are
      expected to change en route.

   OptDataLenDFF  - 8-bit unsigned integer.  Length of the Option Data
      field of this option, in octets as specified in [RFC2460].  This
      value is set to 2 (two).

   DFF fields  - A 2-bit version field (abbreviated as VER), the DUP
      (abbreviated as D) and RET (abbreviated as R) flags follow after
      Mesh Forw, as specified in Section 7.  The version specified in
      this document is 00.  All other bits (besides VER, DUP, and RET)
      of this octet are reserved and MUST be set to 0.

   Sequence Number  - A 16-bit field, containing an unsigned integer
      sequence number, as specified in Section 7.

   Pad1  - Since the Hop-by-Hop Options header must have a length of
      multiples of 8 octets, a Pad1 option is used, as specified in
      [RFC2460].  All bits of this octet are 0.

13.2.  Mesh-Under

   This section maps the general terminology from Section 2.2 to the
   specific terminology when using the "mesh-under" MoP.

13.2.1.  Mapping of DFF Terminology to LoWPAN Terminology

   The following terms are those listed in Section 2.2 (besides "Mode of
   Operation"), and their meaning is explicitly defined when DFF is used
   in the "mesh-under" MoP:

   Packet  - A "LoWPAN encapsulated packet" (as specified in [RFC4944],
      which contains an IPv6 packet as payload.

   Packet Header  - A LoWPAN header, as specified in [RFC4944].

   Address  - A 16-bit short or EUI-64 link layer address, as specified
      in [RFC4944].

   Originator Address  - The Originator Address corresponds to the
      Originator Address field of the Mesh Addressing header as
      specified in [RFC4944].







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   Destination Address  - The Destination Address corresponds to the
      Final Destination field of the Mesh Addressing header as specified
      in [RFC4944].

   Next Hop  - The Next Hop is the destination address of a frame
      containing a LoWPAN encapsulated packet, as specified in
      [RFC4944].

   Previous Hop  - The Previous Hop is the source address of the frame
      containing a LoWPAN encapsulated packet, as specified in
      [RFC4944].

   Hop Limit  - The Hop Limit corresponds to the Deep Hops Left field in
      the Mesh Addressing header as specified in [RFC4944].

13.2.2.  Packet Format

   In the "mesh-under" MoP, all IPv6 Packets MUST conform with the
   format specified in [RFC4944].  All data Packets exchanged by routers
   using this specification MUST contain the Mesh Addressing header as
   part of the LoWPAN encapsulation, as specified in [RFC4944].

   The DFF header, as specified below, MUST follow the Mesh Addressing
   header.  After these two headers, any other LoWPAN header, e.g.,
   header compression or fragmentation headers, MAY also be added before
   the actual payload.  Figure 2 depicts the Mesh Addressing header
   defined in [RFC4944], and Figure 3 depicts the DFF header.

                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |1 0|V|F|HopsLft| DeepHopsLeft  |orig. address, final address...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 2: Mesh Addressing Header


                          1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 1| Mesh Forw |VER|D|R|0|0|0|0|        sequence number        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                   Figure 3: Header for DFF data Packets

   Field definitions of the Mesh Addressing header are as specified in



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   [RFC4944].  When adding that header to the LoWPAN encapsulation on
   the Originator, the fields of the Mesh Addressing header MUST be set
   to the following values:

   o  V := 0 if the Originator Address is an IEEE extended 64-bit
      address (EUI-64); otherwise, V := 1 if it is a short 16-bit
      address.

   o  F := 0 if the Final Destination Address is an IEEE extended 64-bit
      address (EUI-64); otherwise, F := 1 if it is a short 16-bit
      address.

   o  Hops Left := 0xF (i.e., reserved value indicating that the Deep
      Hops Left field is following);

   o  Deep Hops Left := MAX_HOP_LIMIT.

   Field definitions of the DFF header are as follows:

   Mesh Forw  - A 6-bit identifier that allows for the use of different
      mesh forwarding mechanisms.  As specified in [RFC4944], additional
      mesh forwarding mechanisms should use the reserved dispatch byte
      values following LOWPAN_BCO; therefore, 0 1 MUST precede Mesh
      Forw.  The value of Mesh Forw is LOWPAN_DFF.

   DFF fields  - A 2-bit version field (abbreviated as VER), the DUP
      (abbreviated as D) and RET (abbreviated as R) flags follow after
      Mesh Forw, as specified in Section 7.  The version specified in
      this document is 00.  All other bits (besides VER, DUP, and RET)
      of this octet are reserved and MUST be set to 0.

   Sequence Number  - A 16-bit field, containing an unsigned integer
      sequence number, as specified in Section 7.


14.  Scope Limitation of DFF

   The forwarding mechanism specified in this document MUST be limited
   in scope to the routing domain in which DFF is used.  That also
   implies that any headers specific to DFF do not traverse the
   boundaries of the routing domain.  This section specifies, both for
   the "route-over" MoP and the "mesh-under" MoP, how to limit the scope
   of DFF to the routing domain in which it is used.

   Figure 4 to Figure 7 depict four different cases for source and
   destination of traffic with regards to the scope of the routing
   domain in which DFF is used.  Section 14.2 and Section 14.1 specify
   how routers limit the scope of DFF for the "route-over" MoP and the



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   "mesh-under" MoP respectively for these cases.  In these sections,
   all nodes "inside the routing domain" are routers and use DFF, and
   may also be sources or destinations.  Sources or destinations
   "outside the routing domain" do not run DFF and are either hosts
   attached to a router in the routing domain that is running DFF, or
   are themselves routers but outside the routing domain and not running
   DFF.

                        +-----------------+
                        |                 |
                        |  (S) ----> (D)  |
                        |                 |
                        +-----------------+
                        Routing Domain


         Figure 4: Traffic within the routing domain (from S to D)


                        +-----------------+
                        |                 |
                        |  (S) --------> (R) --------> (D)
                        |                 |
                        +-----------------+
                        Routing Domain


    Figure 5: Traffic from within the routing domain to outside of the
                           domain (from S to D)


                        +-----------------+
                        |                 |
         (S) --------> (R) --------> (D)  |
                        |                 |
                        +-----------------+
                        Routing Domain


      Figure 6: Traffic from outside the routing domain to inside the
                           domain (from S to D)










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                        +-----------------+
                        |                 |
         (S) --------> (R1) -----------> (R2) --------> (D)
                        |                 |
                        +-----------------+
                        Routing Domain


     Figure 7: Traffic from outside the routing domain, traversing the
        domain and then to the outside of the domain  (from S to D)

14.1.  Route-Over MoP

   In Figure 4, both the source and destination of the traffic are
   routers within the routing domain.  If traffic is originated at S,
   the DFF header is added to the IPv6 header (as specified in
   Section 13.1.2).  The Originator Address is set to S and the
   Destination Address is set to D. The Packet is forwarded to D using
   this specification.  When router D receives the Packet, it processes
   the payload of the IPv6 Packet in upper layers.  This case assumes
   that S has knowledge that D is in the routing domain, e.g., because
   of administrative setting based on the IP address of the Destination.
   If S has no knowledge about whether D is in the routing domain, IPv6-
   in-IPv6 tunnels as specified in [RFC2473] MUST be used.  These cases
   are described in the following paragraphs.

   In Figure 5, the source of the traffic (S) is within the routing
   domain, and the destination (D) is outside of the routing domain.
   The IPv6 Packet, originated at S, MUST be encapsulated according to
   [RFC2473] (IPv6-in-IPv6 tunnels), and the DFF header added to the
   outer IPv6 header.  S chooses the next router that should process the
   Packet as the tunnel exit-point (R).  Administrative setting, as well
   as information from a routing protocol may be used to determine the
   tunnel exit-point.  If no information is available which router to
   choose as tunnel exit-point, the Next Hop MUST be used as tunnel
   exit-point.  In some cases, the tunnel exit-point will be the final
   router along a path towards the Packet's Destination, and the Packet
   will only traverse a single tunnel (e.g., if R is a known border
   router then S can choose R as tunnel exit- point).  In other cases,
   the tunnel exit-point will not be the final router along the path to
   D, and the Packet may traverse multiple tunnels to reach the
   Destination; note that in this case, the DFF mechanism is only used
   inside each IPv6-in-IPv6 tunnel.  The Originator Address of the
   Packet is set to S and the Destination Address is set to the tunnel
   exit-point (in the outer IPv6 header).  The Packet is forwarded to
   the tunnel exit-point using this specification (potentially using
   multiple consecutive IPv6-in-IPv6 tunnels).  When router R receives
   the Packet, it decapsulates the IPv6 Packet and forwards the inner



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   IPv6 Packet to D, using normal IPv6 forwarding as specified in
   [RFC2460].

   In Figure 6, the source of the traffic (S) is outside of the routing
   domain, and the destination (D) is inside of the routing domain.  The
   IPv6 Packet, originated at S, is forwarded to R using normal IPv6
   forwarding as specified in [RFC2460].  Router R MUST encapsulate the
   IPv6 Packet according to [RFC2473], and add the DFF header (as
   specified in Section 13.1.2) to the outer IPv6 header.  Like in the
   previous case, R has to select a tunnel exit-point; if it knows that
   D is in the routing domain (e.g., based on administrative settings),
   it SHOULD select D as the tunnel exit-point.  In case it does not
   have any information which exit-point to select, it MUST use the Next
   Hop as tunnel exit-point, limiting the effectiveness of DFF to inside
   each IPv6-in-IPv6 tunnel.  The Originator Address of the Packet is
   set to R, the Destination Address to the tunnel exit-point (both in
   the outer IPv6 header), the sequence number in the DFF header is
   generated locally on R. The Packet is forwarded to D using this
   specification.  When router D receives the Packet, it decapsulates
   the inner IPv6 Packet and processes the payload of the inner IPv6
   Packet in upper layers.

   This mechanism is typically not used in transit networks; therefore,
   this case is discouraged, but described nevertheless for
   completeness: In Figure 7, both the source of the traffic (S) and the
   destination (D) are outside of the routing domain.  The IPv6 Packet,
   originated at S, is forwarded to R1 using normal IPv6 forwarding as
   specified in [RFC2460].  Router R1 MUST encapsulate the IPv6 Packet
   according to [RFC2473] and add the DFF header (as specified in
   Section 13.1.2).  R1 selects a tunnel exit-point like in the previous
   cases; if R2 is, e.g., a known border router, then R1 can select R2
   as tunnel exit-point.  The Originator Address is set to R1, the
   Destination Address to the tunnel exit-point (both in the outer IPv6
   header), the sequence number in the DFF header is generated locally
   on R1.  The Packet is forwarded to the tunnel exit-point using this
   specification (potentially traversing multiple consecutive IPv6-in-
   IPv6 tunnels).  When router R2 receives the Packet, it decapsulates
   the inner IPv6 Packet and forwards the inner IPv6 Packet to D, using
   normal IPv6 forwarding as specified in [RFC2460].

14.2.  Mesh-Under MoP

   In Figure 4, both the source and destination of the traffic are
   routers within the routing domain.  If traffic is originated at
   router S, the LoWPAN encapsulated Packet is created from the IPv6
   packet as specified in [RFC4944].  Then, the Mesh Addressing header
   and the DFF header (as specified in Section 13.2.2) are added to the
   LoWPAN encapsulation on router S. The Originator Address is set to S



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   and the Destination Address is set to D. The Packet is then forwarded
   using this specification.  When router D receives the Packet, it
   processes the payload of the Packet in upper layers.

   In Figure 5, the source of the traffic (S) is within the routing
   domain, and the destination (D) is outside of the routing domain
   (which is known by S to be outside the routing domain because D uses
   a different IP prefix from the PAN).  The LoWPAN encapsulated Packet,
   originated at router S, is created from the IPv6 packet as specified
   in [RFC4944].  Then, the Mesh Addressing header and the DFF header
   (as specified in Section 13.2.2) are added to the LoWPAN
   encapsulation on router S. The Originator Address is set to S and the
   Destination Address is set to R, which is a known border router of
   the PAN.  The Packet is then forwarded using this specification.
   When router R receives the Packet, it restores the IPv6 packet from
   the LoWPAN encapsulated Packet and forwards it to D, using normal
   IPv6 forwarding as specified in [RFC2460].

   In Figure 6, the source of the traffic (S) is outside of the routing
   domain, and the destination (D) is inside of the routing domain.  The
   IPv6 packet, originated at S, is forwarded to R using normal IPv6
   forwarding as specified in [RFC2460].  Router R (which is a known
   border router to the PAN) creates the LoWPAN encapsulated Packet from
   the IPv6 packet as specified in [RFC4944].  Then, R adds the Mesh
   Addressing header and the DFF header (as specified in
   Section 13.2.2).  The Originator Address is set to R, the Destination
   Address to D, the sequence number in the DFF header is generated
   locally on R. The Packet is forwarded to D using this specification.
   When router D receives the Packet, it restores the IPv6 packet from
   the LoWPAN encapsulated Packet and processes the payload in upper
   layers.

   As LoWPANs are typically no transit networks, this case is
   discouraged, but described nevertheless for completeness: In
   Figure 7, both the source of the traffic (S) and the destination (D)
   are outside of the routing domain.  The IPv6 packet, originated at S,
   is forwarded to R1 using normal IPv6 forwarding as specified in
   [RFC2460].  Router R1 (which is a known border router of the PAN)
   creates the LoWPAN encapsulated Packet from the IPv6 Packet as
   specified in [RFC4944].  Then, it adds the Mesh Addressing header and
   the DFF header (as specified in Section 13.2.2).  The Originator
   Address is set to R1, the Destination Address to R2 (which is another
   border router towards the Destination), the sequence number in the
   DFF header is generated locally on R1.  The Packet is forwarded to R2
   using this specification.  When router R2 receives the Packet, it
   restores the IPv6 packet from the LoWPAN encapsulated Packet and
   forwards the IPv6 packet to D, using normal IPv6 forwarding as
   specified in [RFC2460].



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15.  MTU Exceedance

   When adding the DFF header as specified in Section 9.1 or when
   encapsulating the Packet as specified in Section 14, the Packet size
   may exceed the MTU.  This is described in Section 5 of [RFC2460].
   When the Packet size of a Packet to be forwarded by DFF exceeds the
   MTU, the following steps are executed:

   1.  The router MUST discard the Packet.

   2.  The router MAY log the event locally (depending on the storage
       capabilities of the router).

   3.  The router MUST send back an ICMP Packet Too Big to the source of
       the Packet reporting back the Next Hop MTU considering the
       additional overhead of adding the headers.


16.  Security Considerations

   Based on the recommendations in [RFC3552], this section describes
   security threats to DFF, lists which attacks are out of scope, which
   attacks DFF is susceptible to, and which attacks DFF protects
   against.

16.1.  Attacks Out of Scope

   As DFF is a data forwarding protocol, any security issues concerning
   the payload of the Packets are not considered in this section.

   It is the responsibility of upper layers to use appropriate security
   mechanisms (IPsec, TLS, ...) according to application requirements.
   As DFF does not modify the contents of IP datagrams, other than the
   DFF header (which is a Hop-by-Hop Options extension header in the
   "route-over" MoP, and therefore not protected by IPsec), no special
   considerations for IPsec have to be addressed.

   Any attack that is not specific to DFF, but that applies in general
   to the link layer (e.g., wireless, PLC), is out of scope.  In
   particular, these attacks are: Eavesdropping, Packet insertion,
   Packet replaying, Packet deletion, and man-in-the-middle attacks.
   Appropriate link-layer encryption can mitigate part of these attacks
   and is therefore RECOMMENDED.

16.2.  Protection Mechanisms of DFF

   DFF itself does not provide any additional integrity, confidentiality
   or authentication.  Therefore, the level of protection of DFF depends



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   on the underlying link layer security as well as protection of the
   payload by upper layer security (e.g., IPsec).

   In the following sections, whenever encrypting or digitally signing
   Packets is suggested for protecting DFF, it is assumed that routers
   are not compromised.

16.3.  Attacks In Scope

   This section discusses security threats to DFF, and for each
   describes whether (and how) DFF is affected by the threat.  DFF is
   designed to be used in lossy and unreliable networks.  Predominant
   examples of lossy networks are wireless networks, where routers send
   Packets via broadcast.  The attacks listed below are easier to
   exploit in wireless media, but can also be observed in wired
   networks.

16.3.1.  Denial of Service

   Denial of Service attacks are possible when using DFF by either
   exceeding the storage on a router, or by exceeding the available
   bandwidth of the channel.  As DFF does not contain any algorithms
   with high complexity, it is unlikely that the processing power of the
   router could be exhausted by an attack on DFF.

   The storage of a router can be exhausted by increasing the size of
   the Processed Set, i.e., by adding new tuples, or by increasing the
   size of each tuple.  New tuples can be added by injecting new Packets
   in the network, or by forwarding overheard Packets.

   Another possible DoS attack is to send Packets to a non-existing
   Address in the network.  DFF would perform a depth-first search until
   the Hop Limit has reached zero.  Is is therefore RECOMMENDED to set
   the Hop Limit to a value that limits the path length.

   If security provided by the link layer is used, this attack can be
   mitigated if the malicious router does not possess valid credentials,
   since other routers would not forward data through the malicious
   router.

16.3.2.  Packet Header Modification

   The following attacks can be exploited by modifying the Packet Header
   information, unless additional security (such as link layer security)
   is used:






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16.3.2.1.  Return Flag Tampering

   A malicious router may tamper the "return" flag of a DFF Packet, and
   send it back to the previous hop, but only if that router had been
   selected as next hop by the receiving router before (as specified in
   Section 9.2).  If the malicious router had not been selected as next
   hop, then a returned Packet is dropped by the receiving router.  If,
   otherwise, the malicious router had been selected as next hop by the
   receiving router, and the malicious router has set the return flag,
   the receiving router would then try alternative neighbors.  This may
   lead to Packets never reaching their Destination, as well as
   unnecessary depth-first search in the network (bandwidth exhaustion /
   energy drain).

   This attack can be mitigated by using appropriate security of the
   underlying link layer.

16.3.2.2.  Duplicate Flag Tampering

   A malicious router may modify the Duplicate Flag of a Packet that it
   forwards.

   If it changes the flag from 0 to 1, the Packet would be detected as
   duplicate by other routers in the network and not as looping packet.

   If the Duplicate Flag is set from 1 to 0, and a router receives that
   Packet for the second time (i.e., it has already received a Packet
   with the same Originator Address and sequence number before), it will
   wrongly detect a loop.

   This attack can be mitigated by using appropriate security of the
   underlying link layer.

16.3.2.3.  Sequence Number Tampering

   A malicious router may modify the sequence number of a Packet that it
   forwards.

   In particular, if the sequence number is modified to a number of
   another, previously sent, Packet of the same Originator, this Packet
   may wrongly be perceived as looping packet.

   This attack can be mitigated by using appropriate security of the
   underlying link layer.







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17.  IANA Considerations

   IANA is requested to allocate a value from the Dispatch Type Field
   registry for LOWPAN_DFF.

   IANA is requested to allocate a value from the Destination Options
   and Hop-by-Hop Options registry for IP_DFF.  The first three bits of
   that value MUST be 111.


18.  Acknowledgements

   Jari Arkko (Ericsson), Antonin Bas (Ecole Polytechnique), Thomas
   Clausen (Ecole Polytechnifque), Yuichi Igarashi (Hitachi), Kazuya
   Monden (Hitachi), Geoff Mulligan (Proto6), Hiroki Satoh (Hitachi),
   Ganesh Venkatesh (Mobelitix), and Jiazi Yi (Ecole Polytechnique)
   provided useful reviews of the draft and discussions which helped to
   improve this document.

   The authors also would like to thank Ralph Droms, Adrian Farrel,
   Stephen Farrell, Ted Lemon, Alvaro Retana, Dan Romascanu, and Martin
   Stiemerling for their reviews during IETF LC and IESG evaluation.


19.  References

19.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC6130]  Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
              Network (MANET) Neighborhood Discovery Protocol (NHDP)",
              RFC 6130, April 2011.




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   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, April 2012.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

19.2.  Informative References

   [DFF_paper1]
              Cespedes, S., Cardenas, A., and T. Iwao, "Comparison of
              Data Forwarding Mechanisms for AMI Networks",  2012 IEEE
              Innovative Smart Grid Technologies Conference (ISGT),
              January 2012.

   [DFF_paper2]
              Iwao, T., Iwao, T., Yura, M., Nakaya, Y., Cardenas, A.,
              Lee, S., and R. Masuoka, "Dynamic Data Forwarding in
              Wireless Mesh Networks",  First IEEE International
              Conference on Smart Grid Communications (SmartGridComm),
              October 2010.

   [DFS_wikipedia]
              "Dynamic Data Forwarding in Wireless Mesh Networks",  http
              ://en.wikipedia.org/w/
              index.php?title=Depth-first_search&oldid=549733112,
              March 2013.

   [KCEC_press_release]
              Kit Carson Electric Cooperative (KCEC), "DFF deployed by
              KCEC (Press Release)",  http://www.kitcarson.com/
              index.php?option=com_content&view=article&id=45&Itemid=1,
              2011.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.




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Appendix A.  Examples

   In this section, some example network topologies are depicted, using
   the DFF mechanism for data forwarding.  In these examples, it is
   assumed that a routing protocol is running which adds or inserts
   entries into the RIB.

A.1.  Example 1: Normal Delivery

   Figure 8 depicts a network topology with seven routers A to G, with
   links between them as indicated by lines.  It is assumed that router
   A sends a Packet to G, through B and D, according to the routing
   protocol.

                                        +---+
                                    +---+ D +-----+
                                    |   +---+     |
                            +---+   |             |
                        +---+ B +---+             |
                        |   +---+   |             |
                      +-+-+         |   +---+   +-+-+
                      | A |         +---+ E +---+ G +
                      +-+-+             +---+   +-+-+
                        |   +---+                 |
                        +---+ C +---+             |
                            +---+   |             |
                                    |   +---+     |
                                    +---+ F +-----+
                                        +---+

                   Figure 8: Example 1: normal delivery

   If no link fails in this topology, and no loop occurs, then DFF
   forward the Packet along the Next Hops listed in each of the routers
   RIB along the path towards the destination.  Each router adds a
   Processed Tuple for the incoming Packet, and selects the Next Hop as
   specified in Section 11, i.e., it will first select the next hop for
   router G as determined by the routing protocol.

A.2.  Example 2: Forwarding with Link Failure

   Figure 9 depicts the same topology as the Example 1, but both links
   between B and D and between B and E are unavailable (e.g., because of
   wireless link characteristics).







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                                        +---+
                                    XXX-+ D +-----+
                                    X   +---+     |
                            +---+   X             |
                        +---+ B +---+             |
                        |   +---+   X             |
                      +-+-+         X   +---+   +-+-+
                      | A |         XXXX+ E +---+ G +
                      +-+-+             +---+   +-+-+
                        |   +---+                 |
                        +---+ C +---+             |
                            +---+   |             |
                                    |   +---+     |
                                    +---+ F +-----+
                                        +---+

                     Figure 9: Example 2: link failure

   When B receives the Packet from router A, it adds a Processed Tuple,
   and then tries to forward the Packet to D. Once B detects that the
   Packet cannot be successfully delivered to D because it does not
   receive link layer ACKs, it will follow the procedures listed in
   Section 10, by setting the DUP flag to 1, selecting E as new next
   hop, adding E to the list of next hops in the Processed Tuple, and
   then forwarding the Packet to E.

   As the link to E also fails, B will again follow the procedure in
   Section 10.  As all possible next hops (D and E) are listed in the
   Processed Tuple, B will set the RET flag in the Packet and return it
   to A.

   A determines that it already has a Processed Tuple for the returned
   Packet, reset the RET flag of the Packet and select a new next hop
   for the Packet.  As B is already in the list of next hops in the
   Processed Tuple, it will select C as next hop and forward the Packet
   to it.  C will then forward the Packet to F, and F delivers the
   Packet to its Destination G.

A.3.  Example 3: Forwarding with Missed Link Layer Acknowledgment

   Figure 10 depicts the same topology as the Example 1, but the link
   layer acknowledgments from C to A are lost (e.g., because the link is
   uni-directional).  It is assumed that A prefers a path to G through C
   and F.







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                                        +---+
                                    +---+ D +-----+
                                    |   +---+     |
                            +---+   |             |
                        +---+ B +---+             |
                        |   +---+   |             |
                      +-+-+         |   +---+   +-+-+
                      | A |         +---+ E +---+ G +
                      +-+-+             +---+   +-+-+
                        .   +---+                 |
                        +...+ C +---+             |
                            +---+   |             |
                                    |   +---+     |
                                    +---+ F +-----+
                                        +---+

          Figure 10: Example 3: missed link layer acknowledgment

   While C successfully receives the Packet from A, A does not receive
   the L2 ACK and assumes the Packet has not been delivered to C.
   Therefore, it sets the DUP flag of the Packet to 1, in order to
   indicate that this Packet may be a duplicate.  Then, it forwards the
   Packet to B.

A.4.  Example 4: Forwarding with a Loop

   Figure 11 depicts the same topology as the Example 1, but there is a
   loop from D to A, and A sends the Packet to G through B and D.

                        +-----------------+
                        |                 |
                        |               +-+-+
                        |           +---+ D +
                        |           |   +---+
                       \|/  +---+   |
                        +---+ B +---+
                        |   +---+   |
                      +-+-+         |   +---+   +-+-+
                      | A |         +---+ E +---+ G +
                      +-+-+             +---+   +-+-+
                        |   +---+                 |
                        +---+ C +---+             |
                            +---+   |             |
                                    |   +---+     |
                                    +---+ F +-----+
                                        +---+

                        Figure 11: Example 4: loop



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   When A receives the Packet through the loop from D, it will find a
   Processed Tuple for the Packet.  Router A will set the RET flag and
   return the Packet to D, which in turn will return it to B. B will
   then select E as next hop, which will then forward it to G.


Appendix B.  Deployment Experience

   DFF has been deployed and experimented with both in real deployments
   and in network simulations, as described in the following.

B.1.  Deployments in Japan

   The majority of the large Advanced Metering Infrastructure (AMI)
   deployments using DFF are located in Japan, but the data of these
   networks is property of Japanese utilities and cannot be disclosed.

B.2.  Kit Carson Electric Cooperative

   DFF has been deployed at Kit Carson Electric Cooperative (KCEC), a
   non-profit organization distributing electricity to about 30,000
   customers in New Mexico.  As described in a press release
   [KCEC_press_release], DFF is running on currently about 2000 electric
   meters.  All meters are connected through a mesh network using an
   unreliable, wireless medium.  DFF is used together with a distance
   vector routing protocol.  Metering data from each meter is sent
   towards a gateway periodically every 15 minutes.  The data delivery
   reliability is over 99%.

B.3.  Simulations

   DFF has been evaluated in Ns2 and OMNEST simulations, in conjunction
   with a distance vector routing protocol.  The performance of DFF has
   been compared to using only the routing protocol without DFF.  The
   results published in peer-reviewed academic papers
   ([DFF_paper1][DFF_paper2]) show significant improvements of the
   Packet delivery ratio compared to using only the distance vector
   protocol.

B.4.  Open Source Implementation

   Fujitsu Laboratories of America is currently working on an open
   source implementation of DFF, which is to be released in early 2013,
   and which allows for interoperability testings of different DFF
   implementations.  The implementation is written in Java, and can be
   used both on real machines and in the Ns2 simulator.





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Authors' Addresses

   Ulrich Herberg (editor)
   Fujitsu
   1240 E. Arques Avenue, M/S 345
   Sunnyvale, CA  94085
   US

   Phone: +1 408 530-4528
   Email: ulrich.herberg@us.fujitsu.com


   Alvaro A. Cardenas
   University of Texas at Dallas
   School of Computer Science, 800 West Campbell Rd, EC 31
   Richardson, TX  75080-3021
   US

   Email: alvaro.cardenas@me.com


   Tadashige Iwao
   Fujitsu
   Shiodome City Center, 5-2, Higashi-shimbashi 1-chome, Minato-ku
   Tokyo,
   JP

   Phone: +81-44-754-3343
   Email: smartnetpro-iwao_std@ml.css.fujitsu.com


   Michael L. Dow
   Freescale
   6501 William Cannon Drive West
   Austin, TX  78735
   USA

   Phone: +1 512 895 4944
   Email: m.dow@freescale.com












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   Sandra L. Cespedes
   U. Icesi
   Calle 18 No. 122-135 Pance
   Cali, Valle
   Colombia

   Phone:
   Email: scespedes@icesi.edu.co











































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