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Network Working Group                                         T. Clausen
Internet-Draft                                      A. Colin de Verdiere
Intended status: Standards Track                                   J. Yi
Expires: October 24, 2012                       LIX, Ecole Polytechnique
                                                              A. Niktash
                                               Maxim Integrated Products
                                                             Y. Igarashi
                                                                H. Satoh
                                        Hitachi, Ltd., Yokohama Research
                                                              Laboratory
                                                              U. Herberg
                                         Fujitsu Laboratories of America
                                                               C. Lavenu
                                                                 EDF R&D
                                                                  T. Lys
                                                                    ERDF
                                                          April 22, 2012


    The LLN On-demand Ad hoc Distance-vector Routing Protocol - Next
                          Generation (LOADng)
                      draft-clausen-lln-loadng-04

Abstract

   This document describes the LLN Ad hoc On-Demand - Next Generation
   (LOADng) distance vector routing protocol, a reactive routing
   protocol intended for use in Low power and Lossy Networks (LLN).  The
   protocol is derived from AODV (RFC3561) and extended for use in LLNs.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, except to format it
   for publication as an RFC or to translate it into languages other
   than English.

   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 October 24, 2012.

Copyright Notice

   Copyright (c) 2012 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
   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 . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Terminology and Notation . . . . . . . . . . . . . . . . . . .  6
     2.1.  Notations  . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.1.  Elements . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.2.  Variables  . . . . . . . . . . . . . . . . . . . . . .  7
       2.1.3.  Conventions  . . . . . . . . . . . . . . . . . . . . .  7
     2.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol Overview and Functioning  . . . . . . . . . . . . . .  8
     4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.  Routers and Interfaces . . . . . . . . . . . . . . . . . . 10
     4.3.  Information Base Overview  . . . . . . . . . . . . . . . . 10
     4.4.  Signaling Overview . . . . . . . . . . . . . . . . . . . . 11
   5.  Protocol Parameters and Constants  . . . . . . . . . . . . . . 12
   6.  Information Base . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  Routing Set  . . . . . . . . . . . . . . . . . . . . . . . 14
     6.2.  Local Interface Set  . . . . . . . . . . . . . . . . . . . 15
     6.3.  Blacklisted Neighbor Set . . . . . . . . . . . . . . . . . 15
     6.4.  Destination Address Set  . . . . . . . . . . . . . . . . . 15
     6.5.  Pending Acknowledgment Set . . . . . . . . . . . . . . . . 16
   7.  LOADng Router Sequence Numbers . . . . . . . . . . . . . . . . 16
   8.  Packet Format  . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  TLV Block  . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.2.  Message Format . . . . . . . . . . . . . . . . . . . . . . 19
       8.2.1.  RREQ and RREP Message Format . . . . . . . . . . . . . 19
       8.2.2.  RREP_ACK Message Format  . . . . . . . . . . . . . . . 20
       8.2.3.  RERR Message Format  . . . . . . . . . . . . . . . . . 21
   9.  Route Maintenance  . . . . . . . . . . . . . . . . . . . . . . 21
   10. Unidirectional Link Handling . . . . . . . . . . . . . . . . . 23



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     10.1. Blacklist Usage  . . . . . . . . . . . . . . . . . . . . . 23
   11. Common Rules for RREQ and RREP Messages  . . . . . . . . . . . 24
     11.1. Identifying Invalid RREQ or RREP Messages  . . . . . . . . 24
     11.2. RREQ and RREP Message Processing . . . . . . . . . . . . . 25
     11.3. Updating Routing Tuples In Response to RREQ and RREP . . . 27
   12. Route Requests (RREQs) . . . . . . . . . . . . . . . . . . . . 27
     12.1. RREQ Generation  . . . . . . . . . . . . . . . . . . . . . 28
     12.2. RREQ Processing  . . . . . . . . . . . . . . . . . . . . . 29
     12.3. RREQ Forwarding  . . . . . . . . . . . . . . . . . . . . . 29
     12.4. RREQ Transmission  . . . . . . . . . . . . . . . . . . . . 30
   13. Route Replies (RREPs)  . . . . . . . . . . . . . . . . . . . . 30
     13.1. RREP Generation  . . . . . . . . . . . . . . . . . . . . . 30
     13.2. RREP Processing  . . . . . . . . . . . . . . . . . . . . . 31
     13.3. RREP Forwarding  . . . . . . . . . . . . . . . . . . . . . 32
     13.4. RREP Transmission  . . . . . . . . . . . . . . . . . . . . 32
   14. Route Errors (RERRs) . . . . . . . . . . . . . . . . . . . . . 32
     14.1. Identifying Invalid RERR Messages  . . . . . . . . . . . . 33
     14.2. RERR Generation  . . . . . . . . . . . . . . . . . . . . . 33
     14.3. RERR Processing  . . . . . . . . . . . . . . . . . . . . . 33
     14.4. RERR Forwarding  . . . . . . . . . . . . . . . . . . . . . 34
     14.5. RERR Transmission  . . . . . . . . . . . . . . . . . . . . 35
   15. Route Reply Acknowledgments (RREP_ACKs)  . . . . . . . . . . . 35
     15.1. RREP_ACK Generation  . . . . . . . . . . . . . . . . . . . 35
     15.2. RREP_ACK Processing  . . . . . . . . . . . . . . . . . . . 36
     15.3. RREP_ACK Forwarding  . . . . . . . . . . . . . . . . . . . 36
     15.4. RREP_ACK Transmission  . . . . . . . . . . . . . . . . . . 36
   16. Metrics  . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     16.1. The <= Comparison Operator . . . . . . . . . . . . . . . . 37
     16.2. Specifying New Metrics . . . . . . . . . . . . . . . . . . 37
     16.3. Default Metric: Hop Count With Weak Links  . . . . . . . . 38
       16.3.1. R_dist Definition  . . . . . . . . . . . . . . . . . . 38
       16.3.2. Weak Link Definition . . . . . . . . . . . . . . . . . 38
       16.3.3. Required TLVs  . . . . . . . . . . . . . . . . . . . . 38
       16.3.4. The <= Comparison Operator . . . . . . . . . . . . . . 38
   17. Security Considerations  . . . . . . . . . . . . . . . . . . . 38
     17.1. Confidentiality  . . . . . . . . . . . . . . . . . . . . . 39
     17.2. Integrity  . . . . . . . . . . . . . . . . . . . . . . . . 40
     17.3. Channel Jamming and State Explosion  . . . . . . . . . . . 41
     17.4. Interaction with External Routing Domains  . . . . . . . . 42
   18. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 43
     18.1. Multicast Addresses  . . . . . . . . . . . . . . . . . . . 43
     18.2. Packet Types . . . . . . . . . . . . . . . . . . . . . . . 43
     18.3. TLV Types  . . . . . . . . . . . . . . . . . . . . . . . . 43
     18.4. Metrics  . . . . . . . . . . . . . . . . . . . . . . . . . 43
     18.5. Error Codes  . . . . . . . . . . . . . . . . . . . . . . . 44
   19. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 44
   20. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 45
   21. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45



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     21.1. Normative References . . . . . . . . . . . . . . . . . . . 45
     21.2. Informative References . . . . . . . . . . . . . . . . . . 45
   Appendix A.  LOADng Control Packet Illustrations . . . . . . . . . 46
     A.1.  RREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
     A.2.  RREP . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
     A.3.  RREP_ACK . . . . . . . . . . . . . . . . . . . . . . . . . 47
     A.4.  RERR . . . . . . . . . . . . . . . . . . . . . . . . . . . 47












































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1.  Introduction

   The LLN On-demand Ad hoc Distance-vector Routing Protocol - Next
   Generation (LOADng) is a routing protocol, derived from AODV
   [RFC3561] and extended for use in Low power and Lossy Networks
   (LLNs).  As a reactive protocol, the basic operations of LOADng
   include generation of Route Requests (RREQs) by a router (originator)
   for when discovering a route to a destination, forwarding of such
   RREQs until they reach the destination router, generation of Route
   Replies (RREPs) upon receipt of an RREQ by the indicated destination,
   and unicast hop-by-hop forwarding of these RREPs towards the
   originator.  If a route is detected broken, i.e., if forwarding of a
   data packet to the recorded next hop on the route to the destination
   is detected to fail, a Route Error (RERR) message is returned to the
   originator of that data packet.

   Compared to [RFC3561], LOADng is simplified as follows:

   o  Only the destination is permitted to respond to an RREQ;
      intermediate routers are explicitly prohibited from responding to
      RREQs, even if they may have active routes to the sought
      destination, and all messages (RREQ or RREPs) generated by a given
      router share a single unique, monotonically increasing sequence
      number.  This also eliminates Gratuitous RREPs while ensuring loop
      freedom.  The rationale for this simplification is reduced
      complexity of protocol operation and reduced message sizes.

   o  A LOADng Router does not maintain a precursor list, thus when
      forwarding of a data packet to the recorded next hop on the route
      to the destination fails, an RERR is sent only to the originator
      of that data packet.  The rationale for this simplification is an
      assumption that few overlapping routes are in use concurrently in
      a given network.

   Compared to [RFC3561], LOADng is extended as follows:

   o  Optimized Flooding is supported, reducing the overhead incurred by
      RREQ generation and flooding.  If no optimized flooding operation
      is specified for a given deployment, classical flooding is used by
      default.

   o  Different address lengths are supported - from full 16 octet IPv6
      addresses over 6 octet Ethernet MAC addresses and 4 octet IPv4
      addresses to shorter 1 and 2 octet addresses.  The only
      requirement is, that within a given routing domain, all addresses
      are of the same address length.





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   o  Control messages can include TLV (Type-Length-Value) elements,
      permitting protocol extensions to be developed.

   LOADng supports routing using arbitrary metrics, which can be
   specified as extensions using the TLV mechanism.  In order to provide
   a "fallback", in case a router on a route does not understand a given
   metric, LOADng always provides a default "hop-count-with-weak-links"
   metric - the philosophy being that "any route, even if not with the
   metric desired, is better than no route".

2.  Terminology and Notation

   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 notations in Section 2.1 and the
   terminology defined in Section 2.2.

2.1.  Notations

   The following notations, for elements and variables, are used in this
   document.

   This format uses 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
   [Stevens].

2.1.1.  Elements

   This specification defines elements.  An element is a group of any
   number of consecutive bits that together form a syntactic entity
   represented using the notation <element>.  Each element in this
   document is defined as either:

   o  a specifically sized field of bits OR

   o  a composite element, composed of other <element>s.

   A composite element is defined as follows:

              <element> := specification

   where, on the right hand side following :=, specification is
   represented using the regular expression syntax defined in
   [SingleUNIX].  Only the following notation is used:



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   <element1><element2> -  Indicates that <element1> is immediately
      followed by <element2>.

   (<element1><element2>) -  Indicates a grouping of the elements
      enclosed by the parentheses.

   ? -  Zero or one occurrences of the preceding element or group.

   * -  Zero or more occurrences of the preceding element or group.

2.1.2.  Variables

   Variables are introduced into the specification solely as a means to
   clarify the description.  The following two notations are used:

   <foo> -  If <foo> is an unsigned integer field, then <foo> is also
      used to represent the value of that field.

   bar -  A variable, usually obtained through calculations based on the
      value(s) of element(s).

2.1.3.  Conventions

   This document uses the following notational conventions:

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

   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).

2.2.  Terminology

   This document uses the following terminology:

   LOADng Router -  A router that implements this routing protocol.  A
      LOADng router can be equipped with one or multiple distinct
      interfaces.

   Interface -  A router's attachment to a communications medium.  An
      interface is assigned one or more addresses.

   Packet -  The top level entity in this specification.  A packet
      contains a Packet Header and zero or one message.







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   Message -  The fundamental entity carrying protocol information, in
      the form of address objects and TLVs.

   Link Cost -  The cost (weight) between a pair of LOADng Routers,
      determined by a LOADng Router upon receipt of a packet.

   Route Cost -  The sum of the Link Costs for the links that an RREQ or
      RREP has crossed.

   Weak Link -  A link that is marginally usable, i.e., which MAY be
      used if no other links are available, but which SHOULD be avoided
      if at all possible - even if it entails ultimately longer routes.
      As an example, a Weak Link might be defined as a link with a
      nominatively high bit-rate (thus, a priori attractive) while
      suffering a significant loss-rate.

3.  Applicability Statement

   This protocol:

   o  Is a reactive routing protocol for Low power and Lossy Networks
      (LLNs).

   o  Supports the use of optimized flooding for RREQs.

   o  Enables any router in the LLN to discover bi-directional routes to
      destinations in the LLN (i.e., any other router, as well as hosts
      or networks attached to that router).

   o  Supports addresses of any length, from 16 octets to a single
      octet.

   o  Is layer-agnostic, i.e., may be used at layer 3 as a "route over"
      routing protocol, or at layer 2 as a "mesh under" routing
      protocol.

   o  Supports per-destination route maintenance; if a destination
      becomes unreachable, rediscovery of that single (bi-directional)
      route is performed, without need for global topology
      recalculation.

4.  Protocol Overview and Functioning

   The objective of this protocol is for each LOADng Router to,
   independently:

   o  Discover a bi-directional route to any destination in the network.




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   o  Establish routes only when there is data traffic to be sent along
      that route.

   o  Maintain a route only for as long as it is an active route, i.e.,
      there is traffic using the route.

   o  Generate control traffic based on network events only: when a new
      route is required, or when an active route is detected broken.
      Specifically, this protocol does not require periodic signaling.

4.1.  Overview

   These objectives are achieved, for each LOADng Router, by performing
   the following tasks:

   o  When having a data packet to deliver to a destination, for which
      no tuple in the routing table exists, generate a Route Request
      (RREQ) encoding the destination address, and transmit this to all
      of its neighbors.

   o  Upon receiving an RREQ, install or refresh a tuple in the routing
      table towards the originator address from the RREQ, as well as to
      the neighbor LOADng Router from which the RREQ was received.  This
      will install the Reverse Route (towards the originator address
      from the RREQ).

   o  Upon receiving an RREQ, inspect the indicated destination address:

      *  If that address is an address in the Destination Address Set of
         the LOADng Router, generate a Route Reply (RREP), which is
         unicast in a hop-by-hop fashion along the installed Reverse
         Route.

      *  If that address is not an address in the Destination Address
         Set of the LOADng Router, consider the RREQ as a candidate for
         forwarding.

   o  When an RREQ is considered a candidate for forwarding, retransmit
      it according to the flooding operation, specified for the network.

   o  Upon receiving an RREP, install a route towards the originator
      address from the RREP, as well as to the neighbor LOADng Router,
      from which that RREP was received.  This will install the Forward
      Route (towards the originator address from the RREP).  The
      originator address is either an address from the Local Interface
      Set of the LOADng Router, or an address from its Destination
      Address Set (i.e. an address of a host attached to that router).




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   o  Upon receiving an RREP, forward it, as unicast, to the recorded
      next hop along the corresponding Reverse Route until the RREP gets
      to the LOADng Router that has the destination address from the
      RREP in its Local Interface Set or Destination Address Set.

   A router generating an RREQ specifies which metric it desires.
   Routers receiving an RREQ will process it and update route cost
   information in the RREQ according to that metric, if they can.  All
   routers, however, will update information in the RREQ so as to be
   able to support the "hop-count-with-weak-links" default metric.  If a
   router is not able to understand the specified metric in an RREQ, it
   will change the metric type in the RREQ to "hop-count-with-weak-
   links" so as to ensure that it be indicated what metric is supported
   by the path taken by that copy of the RREQ.

4.2.  Routers and Interfaces

   In order for a LOADng Router to participate in a LLN, it MUST have at
   least one, and possibly more, LOADng interfaces.  Each LOADng
   interface:

   o  Is configured with one or more interface addresses.

   In addition to a set of LOADng interfaces as described above, each
   LOADng Router:

   o  Has a number of router parameters.

   o  Has an Information Base.

   o  Generates and processes RREQ, RREP, RREP_ACK and RERR messages,
      according to this specification.

4.3.  Information Base Overview

   Necessary protocol state is recorded by way of five information sets:
   the "Routing Set", the "Local Interface Set", the "Blacklisted
   Neighbor Set", the "Destination Address Set", and the "Pending
   Acknowledgment Set".

   The Routing Set contains tuples, each representing the next-hop on,
   and the cost of, a route towards a destination address.
   Additionally, the Routing Set records the sequence number of the last
   message, received from the destination.  This information is
   extracted from the message (RREQ or RREP) that generated the tuple so
   as to enable routing.  The routing table is to be updated using this
   Routing Set. (A router MAY choose to use any or all destination
   addresses in the Routing Set to update the routing table, this



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   selection is outside the scope of this specification.)

   The Local Interface Set contains tuples, each representing a local
   interface of the router.  Each tuple contains a list of one or more
   addresses of that interface.

   The Blacklisted Neighbor Set contains tuples representing neighbor
   LOADng Routers with which unidirectional connectivity has been
   recently detected.

   The Destination Address Set contains tuples representing addresses,
   for which the LOADng Router is responsible; i.e., be addresses of
   this LOADng Router, or of hosts and networks directly attached to
   this router and which use it to connect to the LLN.  These addresses
   may in particular belong to devices which do not implement LOADng,
   and thus cannot process LOADng messages.  This router SHOULD provide
   connectivity to these addresses by generating RREPs in response to
   RREQs directed towards them.

   The Pending Acknowledgment Set contains tuples, representing
   transmitted RREPs for which an RREP_ACK is expected, but where this
   RREP_ACK has not yet been received.

   The Routing Set, the Blacklisted Neighbor Set and the Pending
   Acknowledgment Set are updated by this protocol.  The Destination
   Address Set is used, but not updated, by this protocol.

4.4.  Signaling Overview

   This protocol generates and processes the following routing messages:

   Route Request (RREQ) -  Generated by a LOADng Router when it has a
      data packet to deliver to a given destination, but when it does
      not have an available tuple in its Routing Set indicating a route
      to that destination.  An RREQ contains:

      *  The address (destination) to which a Forward Route is to be
         discovered by way of soliciting the LOADng Router with that
         destination address in its Local Interface Set or in its
         Destination Address Set to generate an RREP.

      *  The address for which a Reverse Route is to be installed
         (originator) by RREQ forwarding and processing, i.e., the
         source address of the data packet which triggered the RREQ
         generation.

      *  The sequence number of the LOADng Router, generating the RREQ.




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      An RREQ is flooded through the network, according to the flooding
      operation specified for the network.

   Route Reply (RREP) -  Generated as a response to an RREQ by the
      LOADng Router which has the address (destination) from the RREQ in
      its Local Interface Set or in its Destination Address Set. An RREP
      is sent in unicast towards the originator of that RREQ.  An RREP
      contains:

      *  The address (originator) to which a Forward Route is to be
         installed when forwarding the RREP.

      *  The address (destination) towards which the RREP is to be sent.
         More precisely, the destination address indicates the unicast
         route which the RREP follows.

      *  The sequence number of the LOADng Router, generating the RREP.

   Route Reply Acknowledgment (RREP_ACK) -  Generated by a LOADng Router
      as a response to an RREP, in order to signal to the neighbor that
      transmitted the RREP that the RREP was successfully received.
      Receipt of an RREP_ACK indicates that the link between these two
      neighboring LOADng Routers is bidirectional.  An RREP_ACK is
      unicast to the neighbor from which the RREP has arrived, and is
      not forwarded.  RREP_ACKs are generated only in response to an
      RREP which, by way of a flag, has explicitly indicated that an
      RREP_ACK is desired.

   Route Error (RERR) -  Generated by a LOADng Router when a link on an
      active route to a destination is detected as broken by way of
      inability to forward a data packet towards that destination.  An
      RERR is unicast to the source of the undeliverable data packet.

5.  Protocol Parameters and Constants

   The following router parameters and constants are used in this
   specification.

   LL-LLN-Routers -  is a link-local-scoped multicast address of a
      group, which all LOADng Routers MUST join if LOADng is used as
      route-over protocol using IP.

   NET_TRAVERSAL_TIME -  is the maximum time that a packet is expected
      to take when traversing from one end of the network to the other.







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   RREQ_RETRIES -  is the maximum number of subsequent RREQs that a
      particular router may generate in order to discover a route to a
      destination, before declaring that destination unreachable.

   RREQ_RATELIMIT -  is the maximum number of RREQs that a particular
      router is allowed to send per time interval.

   R_HOLD_TIME -  is the minimum time a Routing Tuple SHOULD be kept in
      the Routing Set after it was last refreshed.  This MAY be a
      network-wide constant, but MAY also be a variable whose value is
      defined by an auxiliary mechanism, e.g., by an extension to this
      protocol.

   MAX_DIST -  is the value (tuple) representing the maximum possible
      distance (R_dist field).

   RREP_ACK_REQUIRED -  is a boolean flag, which indicates (if set) that
      the router is configured to expect that each RREP it sends be
      confirmed by an RREP_ACK or (if cleared) that no RREP_ACK is
      expected.

   RREP_ACK_TIMEOUT -  is the minimum time after transmission of an
      RREP, that a LOADng Router SHOULD wait for an RREP_ACK from a
      neighbor LOADng Router, before considering that the link to this
      neighbor is unidirectional.

   B_HOLD_TIME -  is the time during which the link between the neighbor
      LOADng Router and this LOADng Router MUST be considered as non-
      bidirectional, and that therefore RREQs received from that
      neighbor LOADng Router MUST be ignored after being added.
      B_HOLD_TIME should be greater than 2 x NET_TRAVERSAL_TIME x
      RREQ_RETRIES, to ensure that subsequent RREQs will reach the
      destination via a route, excluding this link.

   USE_BIDIRECTIONAL_LINK_ONLY -  is a boolean flag, which indicates if
      the LOADng Router only uses verified bi-directional links for data
      packet forwarding.  It is set by default.  If cleared, then the
      LOADng Router can use links which have not been verified to be bi-
      directional.

   HOP_COUNT_WITH_WEAK_LINKS -  is the value representing the default
      hop count with weak links metric, see Section 16.

6.  Information Base

   Each LOADng Router maintains an Information Base, containing the
   information sets necessary for protocol operation, as described in
   the following sections.  The organization of information into these



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   information sets is non-normative, given so as to facilitate
   description of message generation, forwarding and processing rules in
   this specification.  An implementation may choose any representation
   or structure for when maintaining this information.

6.1.  Routing Set

   The Routing Set records the next hop on the route to each known
   destination, when such a route is known.  It consists of Routing
   Tuples:

   (R_dest_addr, R_next_addr, R_dist, R_metric,
      R_seq_num, R_valid_time,  R_bidirectional, R_local_iface_addr)

   where:

   R_dest_addr -  is the address of the destination, either the address
      of an interface of a destination LOADng Router, or the address of
      an interface reachable via the destination LOADng Router, but
      which is outside the LLN.

   R_next_addr -  is the address of the "next hop" on the selected route
      to the destination.

   R_dist -  is the distance associated with the selected route to the
      destination with address R_dest_addr.  R_dist is a tuple
      containing Route Cost, Weak Links and (depending on the metric
      used) additional fields; see Section 16.

   R_metric -  specifies how R_dist is defined and calculated, as well
      as the comparison operator '<=' for determining which of two route
      costs is lower.  This is specified in Section 16.

   R_seq_num -  is the value of the <seq-num> field of the RREQ or RREP
      which installed or last updated this tuple.  For the routing
      tuples installed by previous hop information of RREQ or RREP,
      R_seq_num MUST be set to -1.

   R_valid_time -  specifies the time until which the information
      recorded in this tuple is considered valid.

   R_bidirectional -  is a boolean flag, which specifies if the routing
      tuple is verified as representing a bi-directional route.  Data
      traffic SHOULD only be routed through a routing tuple with
      R_bidirectional flag equals TRUE, unless the router is configured
      as accepting routes without bi-directionality verification
      explicitly by setting the USE_BIDIRECTIONAL_LINK_ONLY to FALSE.




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   R_local_iface_addr -  is the address of the local interface, through
      which the destination can be reached.

6.2.  Local Interface Set

   A router's Local Interface Set records its local interfaces.  It
   consists of Local Interface Tuples, one per interface:

               (I_local_iface_addr_list)

   where:

   I_local_iface_addr_list -  is an unordered list of the network
      addresses of this interface.

   The implementation MUST initialize the Local Interface Set with at
   least one tuple containing at least one address of an interface.
   Moreover, the implementation MUST update the Local Interface Set if
   there is a change of the interfaces of a LOADng router (i.e. a new
   interface, a removed interface, or a change of addresses of an
   interface).

6.3.  Blacklisted Neighbor Set

   The Blacklisted Neighbor Set records the neighbor interface addresses
   of a LOADng Router, with which connectivity has been detected to be
   unidirectional.  Specifically, the Blacklisted Neighbor Set records
   neighbors from which an RREQ has been received (i.e., through which a
   Forward Route would possible) but to which it has been determined
   that it is not possible to communicate (i.e., forwarding Route
   Replies via this neighbor fails, rendering installing the Forward
   Route impossible).  It consists of Blacklisted Neighbor Tuples:

               (B_neighbor_address, B_valid_time)

   where:

   B_neighbor_address -  is the address of the blacklisted neighbor
      interface.

   B_valid_time -  specifies the time until which the information
      recorded in this tuple is considered valid.

6.4.  Destination Address Set

   The Destination Address Set records addresses, for which a LOADng
   Router will generate RREPs in response to received RREQs, in addition
   to its own interface addresses (as listed in the Local Interface



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   Set).  The Destination Address Set thus represents those destinations
   (i.e. hosts), for which this LOADng Router is providing connectivity.
   It consists of destination address tuples:

               (D_address)

   where:

   D_address -  is the address of a destination (a host or a network),
      attached to this LOADng Router and for which this LOADng Router
      provides connectivity through the LLN.

   The Destination Address Set is used for generating signaling, but is
   not itself updated by signaling specified in this document.  Updates
   to the Destination Address Set are due to changes of the environment
   of a LOADng Router - hosts or external networks being connected to or
   disconnected from a LOADng Router.  The Destination Address Set may
   be administrationally provisioned, or provisioned by external
   protocols.

6.5.  Pending Acknowledgment Set

   The Pending Acknowledgment Set contains information about RREPs which
   have been transmitted with the ACK_REQUIRED flag set, and for which
   an RREP_ACK has not yet been received.  It consists of Pending
   Acknowledgment Tuples:

               (P_next_hop, P_originator, P_seq_num, P_ack_timeout)

   where:

   P_next_hop -  is the address of the neighbor interface to which the
      RREP was sent.

   P_originator -  is the address of the originator of the RREP.

   P_seq_num -  corresponds to the <seq-num> field of the sent RREP.

   P_ack_timeout -  is the time after which the neighbor is considered
      not to have a bidirectional link to this router and MUST be added
      to the Blacklisted Neighbor Set; the tuple MUST then be discarded.

7.  LOADng Router Sequence Numbers

   Each LOADng Router maintains a single sequence number, which must be
   included in each RREQ or RREP message it generates.  Each router MUST
   make sure that no two messages (both RREQ and RREP) are generated
   with the same sequence number, and MUST generate sequence numbers



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   such that these are monotonically increasing.  This sequence number
   is used as freshness information for when comparing routes to the
   router having generated the message.

   However, with a limited number of bits for representing sequence
   numbers, wrap-around (that the sequence number is incremented from
   the maximum possible value to zero) will occur.  To prevent this from
   interfering with the operation of the protocol, the following MUST be
   observed.  The term MAXVALUE designates in the following the largest
   possible value for a sequence number.  The sequence number S1 is said
   to be "greater than" (denoted '>') the sequence number S2 if:

      S2 < S1 AND S1 - S2 <= MAXVALUE/2 OR

      S1 < S2 AND S2 - S1 > MAXVALUE/2

8.  Packet Format

   The packet format, used by this protocol, is described in this
   section using the notational conventions described in Section 2.
   Example packets are illustrated in Appendix A.

   The general format for all packets, generated, forwarded and
   processed by this specification, is as follows:


       <packet> := <type>
                   <addr-length>
                   <tlv-block>
                   <message>

   where:

   <type>  is an 8 bit unsigned integer field and specifies the type of
      the <message> field, specified in Section 8.2.

   <addr-length>  is a 4 bit unsigned integer field, encoding the length
      of the destination and originator addresses of the <message> field
      (<destination> and <originator>) as follows:

         <addr-length> := the length of an address in octets - 1

      <addr-length> is thus 1 for 16 bit short addresses [RFC4944], 3
      for IPv4 addresses, 7 for 64 bit extended addresses [RFC4944] or
      15 for IPv6 addresses.






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   <tlv-block>  is specified in Section 8.1.

   <message>  is specified in Section 8.2.

8.1.  TLV Block

   The TLV Block contains zero or more Type-Length-Value elements
   (TLVs).  A TLV allows the association of an arbitrary attribute with
   a packet.  The attribute (value) is made up from an integer number of
   consecutive octets.  Different attributes have different types;
   attributes which are unknown when parsing can be skipped, as
   specified by flags associated with a given TLV.


      <tlv-block> := <tlv-count>
                     (<tlv-type><tlv-flags><tlv-length><tlv-value>)*

   where:

   <tlv-count>  is a 4 bit unsigned integer field, specifying the number
      of TLVs included.

   <tlv-type>  is an 8 bit unsigned integer field, specifying the type
      of the TLV.

   <tlv-flags>  is an 8 bit field specifying processing and forwarding
      rules related to the TLV processing:

      bit 0 (difunknown):  If cleared (0), indicates that if a LOADng
         Router does not understand the <tlv-type>, then it MAY process
         the packet, and all TLVs with <tlv-type> fields which it
         understands.  If set (1), indicates that if a LOADng Router
         does not understand the <tlv-type>, then it MUST NOT process or
         forward the packet and the packet MUST be silently dropped.

      bit 1 (rifunknown):  If cleared (0), indicates that if a LOADng
         Router does not understand the <tlv-type>, then it MAY keep the
         TLV when processing (which is then determined by the value of
         the pifunknown flag) and (for packets, intended to be
         forwarded) forwarding.  If set (1), indicates that if a LOADng
         Router does not understand the <tlv-type>, it MUST remove the
         TLV from the packet prior to processing and (for packets,
         intended to be forwarded) forwarding.

         difunknown and rifunknown flags MUST NOT be set (1) in the same
         time.





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      bit 2-7 (RESERVED):  SHOULD be set to zero on transmission and
         SHOULD be ignored upon receipt.

   <tlv-length>  is an 8 bit unsigned integer field that equals or is
      greater than 0, specifying the length of the following <tlv-value>
      field in octets.

   <tlv-value>  is a field of length <length> octets.

8.2.  Message Format

   This section specifies the format of the <message> field for message
   types RREQ, RREP, RREP_ACK and RERR.

8.2.1.  RREQ and RREP Message Format

   The format of Route Request (RREQ) and Route Reply (RREP) messages is
   identical, RREQ and RREP messages being distinguished by the <type>
   field in the packet.  They are as follows:


       <message> := <seq-num>
                    <metric>
                    <flags>
                    <weak-links>
                    <hop-count>
                    <originator>
                    <destination>

   where:

   <seq-num>  is a 16 bit unsigned integer field, containing the
      sequence number (see Section 7) of the LOADng Router, generating
      the RREQ or RREP message.

   <metric>  is an 8 bit unsigned integer field and specifies how the
      route cost is to be calculated, as well as the comparison operator
      '<=' used for when determining which among two route costs is
      lower.  The route cost calculation MAY be based on the <weak-
      links> and <hop-count> fields of the packet.  It MAY also use
      additional information, encoded in TLVs.

   <flags>  is a 4 bit unsigned integer field and specifies the
      interpretation of the remainder of the message.







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      For RREQ messages:

         bit 0-3 (RESERVED):  SHOULD be set to zero on transmission and
            SHOULD be ignored upon receipt.

      For RREP messages:

         bit 0 (ackrequired):  When set ('1'), an RREP_ACK MUST be
            generated by the recipient of an RREP if the RREP is
            successfully processed.  When cleared ('0'), an RREP_ACK
            MUST NOT be generated in response to processing of the RREP.

         bit 1-3 (RESERVED):  SHOULD be set to zero on transmission and
            SHOULD be ignored upon receipt.

   <weak-links>  is a 4 bit unsigned integer field and specifies the
      total number of weak links on the route from the originator to the
      destination.  This field MAY be updated when a packet is
      forwarded, see Section 11.2.

   <hop-count>  is an 8 bit unsigned integer field and specifies the
      total number of hops which the packet has traversed from the
      <originator> to the <destination>.  This field MUST be updated,
      when a packet is forwarded, see Section 12.3 and Section 13.3.

   <originator>  is an identifier of <address-length> + 1 octets,
      specifying the interface address for which this message was
      generated, and to which a route is supplied by this message.  For
      an RREQ, the route supplied corresponds to the "reverse route",
      whereas for an RREP the route supplied corresponds to the "forward
      route".  In case the message is generated on a LOADng router on
      behalf of an attached host, the <originator> address corresponds
      to an interface address of that host, otherwise it corresponds to
      an address of the sending interface of the LOADng router.

   <destination>  is an identifier of <address-length> + 1 octets,
      specifying the address to which the RREQ or RREP should be sent.
      (I.e., for an RREQ, this address would be the interface address
      for which a route is sought.  For an RREP, this address is
      equivalent to the <originator> address of the RREQ that triggered
      the RREP.)

8.2.2.  RREP_ACK Message Format

   The format of a Route Reply Acknowledgment (RREP_ACK) message is as
   follows:





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       <message> := <seq-num>
                    <originator>

   where:

   <seq-num>  is a 16 bit unsigned integer field and contains the value
      of the <seq-num> field from the RREP for which this RREP_ACK is
      sent.

   <originator>  is an identifier of <address-length> + 1 octets and
      contains the value of the <originator> field from the RREP for
      which this RREP_ACK is sent.

8.2.3.  RERR Message Format

   The format of a Route Error (RERR) message is as follows:


       <message> := <error-code>
                    <originator>
                    <destination>

   where:

   <error-code>  is an 8 bit unsigned integer field and specifies the
      reason for the error message being generated, according to
      Table 4.

   <originator>  is an identifier of <address-length> + 1 octets,
      specifying the source address of a data packet, for which delivery
      to <destination> failed.  The unicast destination of the RERR
      message is the LOADng Router which has <destination> listed in a
      Local Interface Tuple or in a Destination Address Tuple.

   <destination>  is an identifier of <address-length> + 1 octets,
      specifying the address of the destination, which has become
      unreachable, and for which an error is reported.

9.  Route Maintenance

   Tuples in the Routing Set are maintained by way of five different
   mechanisms:

   o  RREQ/RREP exchange, specified in Section 12 and Section 13.

   o  Data traffic delivery success.





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   o  Data traffic delivery failure.

   o  External signals indicating that a tuple in the Routing Set
      necessitates updating.

   o  Information expiration.

   Routing Tuples in the Routing Set contain a validity time, which
   specifies the time until which the information recorded in this tuple
   is considered valid.  After this time, the information in such tuples
   is to be considered as invalid, for the processing specified in this
   document.

   Routing Tuples for actively used routes (i.e., a route via which
   traffic is currently transiting) SHOULD NOT be removed, unless there
   is evidence that they no longer provide connectivity - i.e., unless a
   link on that route has broken.

   To this end, one or more of the following mechanisms (non-exhaustive
   list) MAY be used:

   o  If a lower layer mechanism provides signals, such as when delivery
      to a presumed neighbor LOADng Router fails, this signal MAY be
      used to indicate that a link has broken, trigger early expiration
      of a Routing Tuple from the Routing Set, and to initiate Route
      Error Signaling (see Section 14).  Conversely, absence of such a
      signal when attempting delivery MAY be interpreted as validation
      that the corresponding Routing Tuple(s) are valid, and their
      R_valid_time refreshed correspondingly.  Note that when using such
      a mechanism, care should be taken to prevent that an intermittent
      error (e.g., an incidental wireless collision) triggers corrective
      action and signaling.  This depends on the nature of the signals,
      provided by the lower layer, but can include the use of a
      hysteresis function or other statistical mechanisms.

   o  Conversely, for each successful delivery of a packet to a neighbor
      or a destination, if signaled by a lower layer or a transport
      mechanism, or each positive confirmation of the presence of a
      neighbor by way of an external neighbor discovery protocol, MAY be
      interpreted as validation that the corresponding Routing Tuple(s)
      are valid, and their R_valid_time refreshed correspondingly.

   Furthermore, a LOADng Router may experience that a route currently
   used for forwarding data packets is no longer operational, and must
   act to either rectify this situation locally (Section 13) or signal
   this situation to the source of the data packets for which delivery
   was unsuccessful (Section 14).




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10.  Unidirectional Link Handling

   Each LOADng Router MUST monitor the bidirectionality of the links to
   its neighbors and set the R_bidirectional flag of related routing
   tuples when processing Route Replies (RREP).  To this end, one or
   more of the following mechanisms MAY be used (non exhaustive list):

   o  If a lower layer mechanism provides signals, such as when delivery
      to a presumed neighbor LOADng Router fails, this signal MAY be
      used to detect that a link to this neighbor is broken or is
      unidirectional; the LOADng Router MUST then blacklist the
      neighbor, see Section 10.1.

   o  If a mechanism such as NDP [RFC4861] is available, the LOADng
      Router MAY use it.

   o  RREP_ACK message exchange, as described in Section 15.

   o  Upper-layer mechanisms, such as transport-layer acknowledgments,
      MAY be used to detect unidirectional or broken links.

   When a LOADng Router detects, via one of these mechanisms, that a
   link to a LOADng neighbor router is unidirectional or broken, the
   router MUST blacklist this neighbor, see Section 10.1.  Conversely,
   if a LOADng Router detects via one of these mechanisms that a
   previously blacklisted LOADng Router has a bidirectional link to this
   router, it MAY remove it from the blacklist before the <B_valid_time>
   of the corresponding tuple.

10.1.  Blacklist Usage

   The Blacklist is maintained according to Section 6.3.  When a LOADng
   Router is detected to have a unidirectional link to the LOADng
   Router, it is blacklisted, i.e., a tuple (B_neighbor_address,
   B_valid_time) is created thus:

   o  B_neighbor_address := the address of the blacklisted neighbor

   o  B_valid_time := current_time + B_HOLD_TIME

   When a LOADng neighbor router is blacklisted, i.e., when there is a
   corresponding (B_neighbor_address, B_valid_time) tuple in the
   Blacklisted Neighbor Set, it is temporarily not considered as a
   neighbor, and thus:

   o  Every RREQ received from this neighbor MUST be discarded;





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11.  Common Rules for RREQ and RREP Messages

   RREQ and RREP messages, both, supply routes between their recipients
   and the originator of the RREQ or RREP message.  The two message
   types therefore share common processing rules, and differ only in the
   following:

   o  RREQ messages are multicast or broadcast, intended to be received
      by all LOADng Routers in the network, whereas RREP messages are
      all unicast, intended to be received only by routers on a specific
      route towards a specific destination.

   o  Receipt of an RREQ message MAY trigger generation of an RREP
      message.

   o  Receipt of an RREP message MAY trigger generation of an RREP_ACK
      message.

   For the purpose of the processing description in this section, the
   following additional notation is used:

   <= is the comparison operator specified by the <metrics> field in the
      RREQ or RREP message and described in Section 16.

   received-route-cost  is a variable, representing the cost of the
      route, as calculated based on the received message, see
      Section 16.

   used-metric  is a variable, representing the metric used for
      calculating received-route-cost, see Section 16.

   previous-hop  is the address of the LOADng Router, from which the
      RREQ or RREP message was received.

   >  is the comparison operator for <seq-num> specified in Section 8.

11.1.  Identifying Invalid RREQ or RREP Messages

   A received RREQ or RREP message is invalid, and MUST be discarded
   without further processing, if any of the following conditions are
   true:

   o  The address length specified by this message (i.e., <addr-length>
      + 1) differs from the length of the address(es) of this router.

   o  The address contained in the <originator> field is an address of
      this router.




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   o  There is a tuple in the Routing Set where:

      *  R_dest_addr = <originator>

      *  R_seq_num > <seq-num>

   o  For RREQ messages only, an RREQ MUST be considered invalid if the
      previous-hop is blacklisted (i.e. its address is in a tuple in the
      Blacklisted Neighbor Set, see Section 10.1).

   A LOADng Router MAY recognize additional reasons for identifying that
   an RREQ or RREP message is invalid for processing, e.g., to allow a
   security protocol to perform verification of signatures and prevent
   processing of unverifiable RREQ or RREP message by this protocol.

11.2.  RREQ and RREP Message Processing

   A received, and valid, RREQ or RREP message is processed as follows:

   1.  Included TLVs are processed/removed/updated according to their
       specification.

   2.  If the RREQ or RREP message was received over a "weak link",
       increment the <weak-links> field in the received RREQ or RREP by
       one.

   3.  If the <metric>, indicated in the message, is known to this
       LOADng Router, then:

       *  Set the variable used-metric to the value of <metric>.

   4.  Otherwise, if the <metric>, indicated in the message, is unknown
       to this LOADng Router:

       *  Set the variable used-metric to HOP_COUNT_WITH_WEAK_LINKS.

   5.  Set the variable received-route-cost to the route cost,
       calculated according to used-metric.

   6.  Find the Routing Tuple (henceforth, matching Routing Tuple)
       where:

       *  R_dest_addr = <originator>

       *  R_metric = used-metric






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   7.  If no matching Routing Tuple is found, then create a new matching
       Routing Tuple (the "reverse route" for RREQ messages or "forward
       route" for RREP messages) with:

       *  R_dest_addr := <originator>

       *  R_next_addr := previous-hop

       *  R_metric := used-metric

       *  R_dist := MAX_DIST

       *  R_seq_num := -1

       *  R_valid_time := current time + R_HOLD_TIME

       *  R_bidirectional := FALSE

       *  R_local_iface_addr := the interface address through which the
          packet was received.

   8.  The matching Routing Tuple, existing or new, is compared to the
       received RREQ or RREP message:

       1.  If

           +  received-route-cost < R_dist; AND

           +  R_seq_num = <seq-num>

           OR

           +  <seq-num> > R_seq_num

           Then:

           +  The message is used for updating the Routing Set according
              to Section 11.3.

           +  If there is no matching Routing Tuple in the Routing Set
              with R_dest_addr = previous-hop, create a new matching
              Routing Tuple with:

              -  R_dest_addr := previous-hop

              -  R_next_addr := previous-hop





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              -  R_metric := HOP_COUNT_WITH_WEAK_LINKS

              -  R_dist := (HC, WL), where HC = 1 and WL = 1 if the
                 message was received over a "weak link".  Otherwise, WL
                 = 0

              -  R_seq_num := -1

              -  R_valid_time := current time + R_HOLD_TIME

              -  R_bidirectional := TRUE, if the processed message is an
                 RREP, otherwise FALSE.

              -  R_local_iface_addr := the interface address through
                 which the packet was received.

       2.  Otherwise, the RREQ or RREP message is not processed further,
           and is not considered for forwarding.

11.3.  Updating Routing Tuples In Response to RREQ and RREP

   A Routing Tuple in the Routing Set is updated when a received RREQ or
   RREP message provides a better route to the <originator> than the
   route current recorded for a given metric.  The Routing Tuple, where:

   o  R_dest_addr = <originator>; AND

   o  R_metric = used-metric

   is updated thus:

   o  R_next_addr := previous-hop

   o  R_dist := received-route-cost

   o  R_seq_num := <seq-num>

   o  R_valid_time := current time + R_HOLD_TIME

   o  R_bidirectional := TRUE, if the message being processed is an
      RREP.

12.  Route Requests (RREQs)

   Route Requests (RREQs) are generated by a LOADng Router when it has
   data packets to deliver to a destination for which it has no matching
   bi-directional tuple in the Routing Set (i.e., with R_bidirectional
   set to TRUE).  Only when the router is configured explicitly as being



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   able to use routing tuples without bi-directionality verification
   (i.e., with R_bidirectional set to FALSE) by setting
   USE_BIDIRECTIONAL_LINK_ONLY flag to FALSE, can the router use the
   routing tuple without initiating an RREQ.  The RREQ is transmitted to
   all directly reachable neighbor LOADng Routers.

   After originating an RREQ, a LOADng Router waits for a corresponding
   RREP.  If no such RREP is received within 2*NET_TRAVERSAL_TIME
   milliseconds, the LOADng Router MAY issue a new RREQ for the sought
   destination (with an incremented seq_num) up to a maximum of
   RREQ_RETRIES times.  A LOADng Router SHOULD NOT originate more than
   RREQ_RATELIMIT RREQs per second.  A LOADng Router MAY use mechanisms
   such as exponential backoff to determine the rate at which it
   originates RREQs.

12.1.  RREQ Generation

   A packet with an RREQ message is generated according to Section 8.2
   with the following content:

   o  <type> := RREQ;

   o  <addr-length> set to the length of the address, as specified in
      Section 8;

   o  <metric> set to indicate how route costs are to be calculated and
      compared, according to Table 3;

   o  <weak-links> := 0;

   o  <seq-num> set to the next unused sequence number, maintained by
      this router;

   o  <hop-count> := 1;

   o  <destination> := the address to which a route is sought;

   o  <originator> := one address of the LOADng Router interface that
      generates the RREQ.  If the LOADng Router is generating RREQ on
      behalf of a host connected to this LOADng Router, the sender
      address of the host is used;

   o  TLVs, as neccessary for the <metric> (if any), see Section 16.








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12.2.  RREQ Processing

   On receiving an RREQ message, a LOADng Router MUST process the
   message according to this section:

   1.  If the message is invalid for processing, as defined in
       Section 11.1, the message MUST be discarded without further
       processing.  The message is not considered for forwarding.

   2.  Otherwise, the message is processed according to Section 11.2.

   3.  If the <hop-count> field equals MAX_HOP_COUNT (i.e., 255), or the
       <weak-links> field equals MAX_WEAK_LINKS (i.e., 15), the message
       is not considered for forwarding.

   4.  If <destination> in the RREQ message is not listed in
       I_local_iface_addr_list of any Local Interface Tuple, or does
       correspond to D_address of any Destination Address Tuple of this
       LOADng Router, then the message is considered for forwarding
       according to Section 12.3.

   5.  Otherwise, an RREP can be generated, see Section 13.1.  The RREQ
       is not considered for forwarding.

12.3.  RREQ Forwarding

   An RREQ, considered for forwarding, MUST be updated as follows, prior
   to it being transmitted:

   1.  <metric> := used-metric (as set in Section 11.2)

   2.  <hop-count> := <hop-count> + 1

   3.  TLVs used by <metric> updated according to the specification of
       <metric> included in the RREQ, see Section 16.

   An RREQ is forwarded according to the flooding operation, specified
   for the network.  This MAY be by way of classic flooding, or the
   flooding operation for a given network MAY employ a reduced relay set
   mechanism such as [SMF] or any other information diffusion mechanism
   such as [RFC6206].  Care must be taken that NET_TRAVERSAL_TIME is
   chosen so as to accommodate for the maximum time that may take for an
   RREQ to traverse the network, accounting for in-router delays
   incurring due to or imposed by such algorithms.







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12.4.  RREQ Transmission

   RREQs, initially generated or forwarded, are sent to all neighbor
   LOADng Routers.  If LOADng is operating as an IP routing protocol,
   the destination address for this RREQ MUST be the link local
   multicast address LL-LLN-Routers, and the source address MUST be the
   address of the interface over which the RREQ is sent.

   When an RREQ is transmitted, all receiving LOADng Routers will
   process the RREQ message and MAY consider the RREQ message for
   forwarding at the same, or at almost the same, time.  If using data
   link and physical layers that are subject to packet loss due to
   collisions, such RREQ messages SHOULD be jittered as described in
   [RFC5148].

13.  Route Replies (RREPs)

   Route Replies (RREPs) are generated by a LOADng Router in response to
   an RREQ, and is sent by the LOADng Router which has, in either its
   Destination Address Set or in its Local Interface Set, the address
   which is contained in the <destination> element of the received RREQ.
   RREPs are sent, hop by hop, in unicast towards the originator of the
   corresponding RREQ, along the Reverse Route installed by that RREQ.
   A router, upon forwarding an RREP, installs the Forward Route towards
   the <destination>.

   Thus, with forwarding of RREQs installing the Reverse Route and
   forwarding of RREPs installing the Forward Route, bi-directional
   routes are provided between the <originator> and <destination>
   indicated in the RREQ.

13.1.  RREP Generation

   At least one RREP MUST be generated in response to a (set of)
   received RREQ messages with identical (<originator>,<seq-num>).  An
   RREP can be generated immediately as a response to each RREQ
   processed, or can be generated after a certain delay after the
   arrival of the first RREQ, in order to use the "best" received RREQ
   (received over lowest-cost route, over the route with least Weak
   Links etc).  A LOADng Router MAY generate further RREPs for
   subsequent RREQs received with the same (<originator>,<seq-num>)
   pairs, if these indicate a better route.  The content of an RREP is
   as follows:

   o  <type> := RREP;

   o  <flag> bit-0 ackrequired flag set to ('1') if RREP_ACK is required
      by the router (i.e. if RREP_ACK_REQUIRED is set to TRUE).



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      Otherwise, bit-0 is cleared ('0');

   o  <addr-length> set to the length of the address, as specified in
      Section 8;

   o  <seq-num> set to the next unused sequence number, maintained by
      this LOADng Router;

   o  <metric> set to the same value as the <metric> in the
      corresponding RREQ;

   o  <weak-links> := 0;

   o  <hop-count> := 1;

   o  <destination> := the address to which this RREP message is to be
      sent; this corresponds to the <originator> address from the RREQ
      message, in response to which this RRREP message is generated;

   o  <originator> := the address of the LOADng Router, generating the
      RREP.  If the LOADng Router is generating RREP on behalf of the
      hosts connected to it, or on behalf of one of the addresses
      contained in the routers Destination Address Set, the host address
      is used.

   o  TLVs, as neccessary for the <metric> (if any), see Section 16.

   The specification of the TLVs included in the <tlv-block> of the RREQ
   responsible to generate the RREP MUST stipulate if, and under which
   conditions, these are to be included in the <tlv-block> of the RREP.

13.2.  RREP Processing

   On receiving an RREP message, a LOADng Router MUST process the
   message according to this section:

   1.  If the message is invalid for processing, as defined in
       Section 11.1, the message MUST be discarded without further
       processing.  The message is not considered for forwarding.

   2.  Otherwise, the message is processed according to Section 11.2.

   3.  If the RREP message has the ackrequired flag set, an RREP_ACK
       message MUST be sent to the previous-hop, according to
       Section 15.1.

   4.  If the <hop-count> field equals MAX_HOP_COUNT (i.e., 255), or the
       <weak-links> field equals MAX_WEAK_LINKS (i.e., 15), the message



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       is not considered for forwarding.

   5.  If the <destination> in the RREP message is not listed in
       I_local_iface_addr_list of any Local Interface Tuple and does not
       correspond to D_address of any Destination Address Tuple of this
       LOADng Router, the RREP message is considered for forwarding
       according to Section 13.3.

13.3.  RREP Forwarding

   An RREP message, considered for forwarding, MUST be updated as
   follows, prior to it being transmitted:

   1.  <metric> := used-metric (as set in Section 11.2)

   2.  <hop-count> := <hop-count> + 1

   3.  TLVs used by <metric> updated according to the specification of
       <metric> included in the RREQ, see Section 16.

   4.  If this LOADng Router is configured to use RREP_ACKs in order to
       check the bidirectionality of the links (i.e.  RREP_ACK_REQUIRED
       is set to TRUE), the ackrequired flag MUST be set to (1),
       according to Section 15.

   The RREP message is then unicast to the next hop towards the
   <destination> indicated in the RREP.

13.4.  RREP Transmission

   An RREP is, ultimately, destined for the LOADng Router listed in the
   <destination> field, and is forwarded in unicast towards this LOADng
   Router.  The RREP MUST, however, be transmitted so as to allow it to
   be processed in each intermediate LOADng Router to:

   o  Install proper forward routes;

   o  Permit that <hop-count> and <weak-links> be updated to reflect the
      route; AND

   o  Permit that TLVs included may be processed/added/removed according
      to their specification.

14.  Route Errors (RERRs)

   If a LOADng Router fails to deliver a data packet to a next hop or a
   destination, it MUST generate a Route Error (RERR), and send this
   RERR along the Reverse Route towards the source of the data packet



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   for which delivery was unsuccessful (to the last router along the
   Reverse Route, if the data packet was originated by a host behind
   that router).

14.1.  Identifying Invalid RERR Messages

   A LOADng Router MAY recognize reasons, external to this
   specification, for identifying that an RERR message is invalid for
   processing, e.g., to allow a security protocol to perform
   verification of signatures and prevent processing of unverifiable
   RERR message by this protocol.

14.2.  RERR Generation

   A packet with an RERR message is generated by the LOADng Router,
   detecting the link breakage, with the following content:

   o  <type> := RERR;

   o  <error-code> := the most appropriate error code from among those
      recorded in Table 4;

   o  <addr-length> := the length of the address, as specified in
      Section 8;

   o  <originator> := the source address from the unsuccessfully
      delivered data packet.

   o  <destination> := the destination address from the unsuccessfully
      delivered data packet.

14.3.  RERR Processing

   For the purpose of the processing description below, the following
   additional notation is used:

   previous-hop  is the address of the LOADng Router, from which the
      RERR was received.

   Upon receiving an RERR, a LOADng Router MUST perform the following
   steps:

   1.  Included TLVs are processed/removed/updated according to their
       specification.

   2.  Find the Routing Tuple (henceforth "matching Routing Tuple") in
       the Routing Set where:




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       *  R_dest_addr = <destination>

       *  R_next_addr = previous-hop

   3.  If no matching Routing Tuple is found, the RERR is not processed
       further, and is not considered for forwarding.

   4.  Otherwise, if one matching Routing Tuple is found, this matching
       Routing Tuple is updated as follows:

       *  R_valid_time := expired

       The RERR message is, then, considered for forwarding.

14.4.  RERR Forwarding

   An RERR is, ultimately, destined for the LOADng Router on which the
   address from the <originator> field is listed in
   I_local_iface_addr_list of any Local Interface Tuple or which
   corresponds to D_address of any Destination Address Tuple.

   An RERR, considered for forwarding is therefore processed as follows:

   1.  Find the Destination Address Tuple (henceforth, matching
       Destination Address Tuple) in the Destination Address Set where:

       *  D_address = the address from the <originator> field of the
          RERR.

   2.  If one or more matching Destination Address Tuples are found, the
       RERR message is discarded and not retransmitted, as it has
       reached the final destination.

   3.  Otherwise, find the Local Interface Tuple (henceforth, matching
       Local Interface Tuple) in the Local Interface Set where:

       *  I_local_iface_addr_list contains the address from the
          <originator> field of the RERR.

   4.  If a matching Local Interface Tuple is found, the RERR message is
       discarded and not retransmitted, as it has reached the final
       destination.

   5.  Otherwise, if no matching Destination Address Tuples or Local
       Interface Tuples are found, the RERR message is transmitted
       according to Section 14.5.





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14.5.  RERR Transmission

   An RERR is transmitted, as unicast, to the LOADng Router, recorded
   the next hop for the <originator> indicated in the RERR message.  The
   RERR MUST be transmitted hop-by-hop such that it can be processed in
   each intermediate LOADng Router.  This serves to:

   o  Allow intermediate routers to update their Routing Sets, i.e.,
      remove tuples for this destination.

   o  Permit that TLVs included may be processed/added/removed according
      to their specification.

15.  Route Reply Acknowledgments (RREP_ACKs)

   A LOADng Router SHOULD use RREP_ACK exchange to monitor
   bidirectionality of links with neighbor routers, except if another
   mechanism, as described in Section 10, provides for such
   bidirectionality information.

   A LOADng Router MUST signal in a transmitted RREP that it is
   expecting an RREP_ACK, by setting the ackrequired flag in the RREP.
   When doing so, the LOADng Router MUST also add a tuple (P_next_hop,
   P_originator, P_seq_num, P_ack_timeout) to the Pending Acknowledgment
   Set, and set P_ack_timeout to RREP_ACK_TIMEOUT.

15.1.  RREP_ACK Generation

   Upon reception of an RREP message with the ackrequired flag set, a
   LOADng Router MUST generate an RREP_ACK and send this RREP_ACK in
   unicast to the neighbor which originated the RREP.

   A packet with an RREP_ACK message is generated by a LOADng Router
   with the following content:

   o  <type> := RREP_ACK;

   o  <addr-length> := the length of the address, as specified in
      Section 8;

   o  <seq-num> := the <seq-num> field of the received RREP;

   o  <originator> := the <originator> field of the received RREP.








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15.2.  RREP_ACK Processing

   On receiving an RREP_ACK from a LOADng neighbor router, a LOADng
   Router MUST do the following:

   1.  The TLV fields are added/removed/updated according to their
       specification.

   2.  Find the Routing Tuple (henceforth, matching Routing Tuple)
       where:

       *  R_dest_addr = previous-hop;

       and update the tuple with:

       *  R_bidirectional := TRUE

   3.  Check whether a corresponding RREP is pending, i.e. if the
       Pending Acknowledgment Set contains a tuple (P_next_hop,
       P_originator, P_seq_num, P_ack_timeout) such as:

       *  P_next_hop is the address of the LOADng neighbor router from
          which the RREP_ACK was received.

       *  P_originator corresponds to the <originator> field of the
          RREP_ACK.

       *  P_seq_num corresponds to the <seq-num> field of the RREP_ACK.

   4.  If such a tuple exists, then the RREP has been correctly
       acknowledged and the tuple MUST be discarded.

   5.  Otherwise, i.e. if no such tuple exists, then no further
       processing is required.

15.3.  RREP_ACK Forwarding

   An RREP_ACK is intended only for a specific direct neighbor, and MUST
   NOT be forwarded.

15.4.  RREP_ACK Transmission

   An RREP_ACK is transmitted, in unicast, to the neighbor LOADng Router
   from which the RREP was received.







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16.  Metrics

   This specification enables the use of different metrics for when
   calculating route costs, and specifies one particularly simplified
   such metric in Section 16.3, for use as a default ensuring
   interoperability even if routers in a network are configured to use
   different metrics.  It is encouraged that more appropriate metrics be
   developed for different deployment environments.

16.1.  The <= Comparison Operator

   The objective of the <= comparison operator is to be able to
   determine which of two routes is "better", i.e., which route has the
   lowest cost.  A link between a pair of interfaces may have a nominal
   and administratively assigned cost associated (such as, for example,
   representing a nominal bandwidth), however may also have a dynamic
   component making a link with an otherwise low cost a less attractive
   choice for when establishing a new route (such as, for example, if a
   high loss-rate is experienced across that link).

16.2.  Specifying New Metrics

   When defining a metric, the following considerations SHOULD be taken
   into consideration, and MUST be taken into consideration when
   requesting a code-point from IANA for the 1-8 range of the Cost Types
   registry defined in Table 3:

   o  The definition of the R_dist field, as well as the value of
      MAX_DIST.

   o  The mechanism for determining when a link qualifies as a "Weak
      Link".  Examples include when an SNR or SIR is above/below a given
      threshold, etc.  This MAY be by way of lower-layer information,
      message statistics or any other means.

   o  The required TLVs for calculating the route cost, as well as the
      mechanism for determining how to update those fields when an RREP
      or RREQ is transmitted over an interface.

   o  The <= comparison operator, which MUST specify a strict ordering
      of the R_dist space, i.e.  R_dist1 can always be compared to
      R_dist2 and (R_dist1 <= R_dist2 && R_dist2 <= R_dist1) if and only
      if R_dist1 = R_dist2.








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16.3.  Default Metric: Hop Count With Weak Links

   This section specifies a simple "Hop-Count-With-Weak-Links" metric,
   which is both the default metric provided for interoperability, and
   is intended to exemplify of how to specify metrics in general.  It
   represents a simple "hop count" based cost, permitting avoiding weak
   links.  It is RECOMMENDED to define a more appropriate metric for the
   environment in which the protocol is to operate.

16.3.1.  R_dist Definition

   R_dist := (HC, WL) where HC is the Hop Count, and WL the number of
   Weak Links.  MAX_DIST := (255, 15).

16.3.2.  Weak Link Definition

   A link is considered a weak link when information is available from a
   lower layer, indicating that the link falls below an acceptable
   threshold according to that lower layer specification.  For IEEE
   802.15.4, for example, this can be derived from the Link Quality
   Indicator.

   Otherwise, if such information is not available from a lower layer, a
   link is never considered a Weak Link.

16.3.3.  Required TLVs

   This metric requires no TLVs.

16.3.4.  The <= Comparison Operator

   Let (HC, WL) be the pair (hop-count, weak-links) received in one RREQ
   or RREP, and let (HC', WL') be the pair (hop-count, weak-links)
   received in another RREQ or RREP.  The comparison operator <= is then
   defined as:

       (HC,WL) <= (HC',WL') if and only if:

                                  WL < WL'; OR
                                  WL == WL' AND HC <= HC'

17.  Security Considerations

   Currently, this protocol does not specify any special security
   measures.  As a reactive routing protocol, this protocol is a
   potential target for various attacks.  Various possible
   vulnerabilities are discussed in this section.




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   By way of (i) enabling inclusion of TLVs and (ii) permitting that
   LOADng recognizes external reasons for rejecting RREQ, RREP, RREP_ACK
   and RERR messages, development of security measures, appropriate for
   a given deployment, is however supported.  This architecture is a
   result of the observation that with respect to security in LOADng
   routed networks, "one size rarely fits all".  This, as LOADng
   deployment domains have varying security requirements ranging from
   "unbreakable" to "virtually none", depending on, e.g., physical
   access to the network, or on security available on other layers.  The
   virtue of this approach is that LOADng routing protocol
   specifications (and implementations) can remain "generic", with
   extensions providing proper deployment-domain specific security
   mechanisms.

17.1.  Confidentiality

   This protocol floods Route Requests (RREQs) to all the LOADng routers
   in the network, when there is traffic to deliver to a given
   destination.  Hence, if used in an unprotected network (such as an
   unprotected wireless network):

   o  Part of the network topology is revealed to anyone who listens,
      specifically (i) the identity (and existence) of the source LOADng
      router; (ii) the identity of the destination; and (iii) the fact
      that a path exists between the source LOADng router and the LOADng
      router from which the RREQ was received.

   o  The network traffic patterns are revealed to anyone who listens to
      the LOADng control traffic, specifically which pairs of devices
      communicate.  If, for example, a majority of traffic originates
      from or terminates in a specific LOADng router, this may indicate
      that this LOADng router has a central role in the network.

   This protocol also unicasts Route Replies (RREPs) from the
   destination of an RREQ to the originator of that same RREQ.  Hence,
   if used in an unprotected network (such as an unprotected wireless
   network):

   o  Part of the network topology is revealed to anyone who is near or
      on the unicast path of the RREP (such as within radio range of
      LOADng routers on the unicast path in an unprotected wireless
      network), specifically that a path from the originator (of the
      RREP) to the destination (of the RREP) exists.

   Finally, this protocol unicasts Route Errors (RERRs) when an
   intermediate router detects that the path from a source to a
   destination is no longer available.  Hence, if used in an unprotected
   network (such as an unprotected wireless network):



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   o  A disruption of the network topology is revealed to anyone who is
      near or on the unicast path of the RERR (such as within radio
      range of LOADng routers on the unicast path in an unprotected
      wireless network), specifically that a path from the originator
      (of the RERR) to the destination (of the RERR) has been disrupted.

   This protocol signaling behavior enables, for example, an attacker to
   identify central devices in the network (by monitoring RREQs) so as
   to target an attack, and (by way of monitoring RERRs) to measure the
   success of an attack.

17.2.  Integrity

   A LOADng router injects topological information into the network by
   way of transmitting RREQ and RREP messages, and removes installed
   topological information by way of transmitting RERR messages.  If
   some routers for some reason, malice or malfunction, inject invalid
   control traffic, network integrity may be compromised.  Therefore,
   message authentication is recommended.

   Different such situations may occur, for instance:

   1.  A router generates RREQ messages, pretending to be another
       router;

   2.  A router generates RREP messages, pretending to be another
       router;

   3.  A router generates RERR messages, pretending to be another
       router;

   4.  A router generates RERR messages, indicating that a link on a
       path to a destination is broken;

   5.  A router forwards altered control messages;

   6.  A router does not forward control messages;

   7.  A router forwards RREPs and RREQs, but does not forward unicast
       data traffic;

   8.  A router "replays" previously recorded control messages from
       another router.

   Authentication of the originator LOADng router for control messages
   (for situations 1, 2 and 3) and on individual links announced in the
   control message (for situation 2 and 4) may be used as a
   countermeasure.  However, to prevent routers from repeating old (and



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   correctly authenticated) information (situation 8), temporal
   information is required, requiring a router to positively identify
   such a delayed message.

   In general, integrity check values and other required security
   information may be transmitted as a separate Message Type, or
   signatures and security information may be transmitted within the
   control messages, using the TLV mechanism.  Either option permits
   that "secured" and "unsecured" routers can coexist in the same
   network, if desired.

   Specifically, if LOADng is used on the IP layer, the authenticity of
   entire control messages can be established through employing IPsec
   authentication headers, whereas authenticity of individual links
   (situations 2 and 4) require additional security information to be
   distributed.

17.3.  Channel Jamming and State Explosion

   A reactive protocol, LOADng control messages are generated in
   response to network events.  For RREQs, such an event is that a data
   packet is present in a router which does not have a route to the
   destination of the data packet, or that the router receives an RERR
   message, invalidating a route.  For RREPs, such an event is receipt
   of an RREQ corresponding to a destination owned by the LOADng router.
   A router, forwarding an RREQ or an RREP records state, for the
   reverse and forward routes, respectively.  If some routers for some
   reason, malice or malfunction, generates excessive RREQ, RREP or
   RERRs, otherwise correctly functioning LOADng routers may fall victim
   to either "indirect jamming" (being "tricked" into generating
   excessive control traffic) or an explosion in the state necessary for
   maintaining protocol state (potentially, exhausting the available
   memory resources).

   Different such situations may occur, for instance:

   1.  A router, within a short time, generates RREQs to an excessive
       amount of destinations in the network (possibly all destinations,
       possibly even destinations not present in the network), causing
       intermediate routers to allocate state for the forward routes.

   2.  A router generates excessively frequent RREQs to the same
       (existing) destination, causing the corresponding LOADng router
       to generate excessive RREPs.

   3.  A router generates RERRs for a destination to the source LOADng
       router for traffic to that destination, causing that LOADng
       router to flood renewed RREQs.



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   For situation 1, the state required for recording forward and/or
   reverse routes may exceed the memory available in the intermediate
   LOADng routers - to the detriment of being able of recording state
   for other routes.  This, in particular, if a LOADng router generates
   RREQs for destinations "not present in the network".

   A router which, within a short time, generates RREPs to an excessive
   amount of destinations in the network (possibly all destinations,
   possibly even destinations not present in the network), will not have
   the same network-wide effect: an intermediate router receiving an
   RREP for a destination for which no reverse route exists will neither
   attempt forwarding the RREP nor allocate state for the forward route.

   For situations 1, 2, and 3, a possible countermeasure is to rate-
   limit the number of control messages that a LOADng router forwards on
   behalf of another LOADng router.  Such a rate limit should take into
   consideration the expected normal traffic for a given LOADng
   deployment.  Authentication may furthermore be used so as to prohibit
   a LOADng router from forwarding control traffic from any non-
   authenticated router (with the assumption being that an authenticated
   router is not expected to exhibit such rogue behavior).

17.4.  Interaction with External Routing Domains

   This protocol does provide a basic mechanism for a LOADng router to
   be able to discover routes to external routing domains: a LOADng
   router configured to "own" a given set of addresses will respond to
   RREQs for destinations with these addresses, and can - by whatever
   protocols governing the routing domain wherein these addresses exist
   - provide paths to these addresses.

   When operating routers connecting a LOADng domain to an external
   routing domain, destinations inside the LOADng domain can be injected
   into the external domain, if the routing protocol governing that
   domain so permits.  Care MUST be taken to not allow potentially
   insecure and untrustworthy information to be injected into the
   external domain.

   In case LOADng is used on the IP layer, a RECOMMENDED way of
   extending connectivity from an external routing domain to a LOADng
   routed domain is to assign an IP prefix (under the authority of the
   routers/gateways connecting the LOADng routing domain with the
   external routing domain) exclusively to that LOADng routing domain,
   and to statically configure gateways to advertise routes for that
   prefix into the external domain.  Within the LOADng domain, gateways
   SHOULD only generate RREPs for destinations which are not part of
   that prefix; this is in particularly important if a gateway otherwise
   provides connectivity to "a default route".



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18.  IANA Considerations

18.1.  Multicast Addresses

   IANA is requested to allocate LL-LLN-ROUTERS well-known, link-scoped
   multicast addresses for both IPv4 and IPv6.

18.2.  Packet Types

   IANA is requested to create a new registry for packet types, with
   initial assignments and allocation policies as specified in Table 1.

   +---------+-------------------------------------+-------------------+
   |   Type  | Description                         | Allocation Policy |
   +---------+-------------------------------------+-------------------+
   |    0    | Route Request (RREQ)                |                   |
   |    1    | Route Reply (RREP)                  |                   |
   |    2    | Route Error (RERR)                  |                   |
   |    3    | Route Reply Acknowledgment          |                   |
   |         | (RREP_ACK)                          |                   |
   |  4-251  | Unassigned                          | Expert Review     |
   | 252-255 | Unassigned                          | Experimental Use  |
   +---------+-------------------------------------+-------------------+

                           Table 1: Packet Types

18.3.  TLV Types

   IANA is requested to create a new registry for TLV types, with
   initial assignments and allocation policies as specified in Table 2.

               +---------+-------------+-------------------+
               |   Type  | Description | Allocation Policy |
               +---------+-------------+-------------------+
               |  0-251  | Unassigned  | Expert Review     |
               | 252-255 | Unassigned  | Experimental Use  |
               +---------+-------------+-------------------+

                            Table 2: TLV Types

18.4.  Metrics

   IANA is requested to create a new registry for Metrics, with initial
   assignments and allocation policies as specified in Table 3.







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   +---------+----------------------------------------+----------------+
   |   Code  | Description                            | Allocation     |
   |         |                                        | Policy         |
   +---------+----------------------------------------+----------------+
   |    0    | Hop Count While Avoiding Weak Links    |                |
   |         | (Section 16)                           |                |
   |  1-251  | Unassigned                             | Expert Review  |
   | 252-255 | Unassigned                             | Experimental   |
   |         |                                        | Use            |
   +---------+----------------------------------------+----------------+

                             Table 3: Metrics

   When assigning a new Metric, the specification requesting that
   assignment MUST specify the way in which each LOADng Router
   calculates the <hop-count> field and TLVs for calculating the route
   cost in RREQs and RREPs, as well as the criteria for incrementing the
   <weak-links> field in RREQs and RREPs.  The specification MUST also
   specify the comparison operation '<=' for determining, from among two
   RREQs (or RREPs) for the same destination, which message represents
   the shortest route; note that this comparison operation SHOULD
   involve the <hop-count> field and MAY use other information such as
   <weak-links> or content of specific TLV types included in the RREQ or
   RREP.

18.5.  Error Codes

   IANA is requested to create a new registry for Error Codes, with
   initial assignments and allocation policies as specified in Table 4.

           +---------+--------------------+-------------------+
           |   Code  | Description        | Allocation Policy |
           +---------+--------------------+-------------------+
           |    0    | No available route |                   |
           |  1-251  | Unassigned         | Expert Review     |
           | 252-255 | Unassigned         | Experimental Use  |
           +---------+--------------------+-------------------+

                           Table 4: Error Codes

19.  Contributors

   This specification is the result of the joint efforts of the
   following contributors -- listed alphabetically.

   o  Alberto Camacho, LIX, France, <alberto@albertocamacho.com>





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   o  Thomas Heide Clausen, LIX, France, <T.Clausen@computer.org>

   o  Axel Colin de Verdiere, LIX, France, <axel@axelcdv.com>

   o  Kenneth Garey, Maxim Integrated Products, USA,
      <kenneth.garey@maxim-ic.com>

   o  Ulrich Herberg, Fujitsu Laboratories of America, USA
      <ulrich.herberg@us.fujitsu.com>

   o  Yuichi Igarashi, Hitachi Ltd, Yokohama Research Laboratory, Japan,
      <yuichi.igarashi.hb@hitachi.com>

   o  Afshin Niktash, Maxim Integrated Products, USA,
      <afshin.niktash@maxim-ic.com>

   o  Hiroki Satoh, Hitachi Ltd, Yokohama Research Laboratory, Japan,
      <hiroki.satoh.yj@hitachi.com>

   o  Jiazi Yi, LIX, France, <jiazi@jiaziyi.com>

20.  Acknowledgments

   The authors would like to acknowledge the team behind AODV, specified
   in RFC3561 for their contributions.  The authors would also like to
   acknowledge the efforts of K. Kim (picosNet Corp/Ajou University), S.
   Daniel Park (Samsung Electronics), G. Montenegro (Microsoft
   Corporation), S. Yoo (Ajou University) and N. Kushalnagar (Intel
   Corp.) for their work on an initial version of a specification, from
   which this protocol is derived.

21.  References

21.1.  Normative References

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

21.2.  Informative References

   [RFC3561]     Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
                 Demand Distance Vector (AODV) Routing", RFC 3561,
                 July 2003.

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




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   [RFC6206]     Levis, P., Clausen, T., Gnawali, O., and J. Ko, "The
                 Trickle Algorithm", RFC 6206, March 2011.

   [SMF]         Macker, J., "Simplified Multicast Forwarding",
                 draft-ietf-manet-smf-14 (work in progress), March 2012.

   [RFC5148]     Clausen, T., Dearlove, C., and B. Adamson, "Jitter
                 Considerations in Mobile Ad Hoc Networks (MANETs)",
                 RFC 5148, February 2008.

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

   [Stevens]     Stevens, W., "TCP/IP Illustrated  Volume 1 - The
                 Protocols", 1994.

   [SingleUNIX]  IEEE Std 1003.1, The Open Group, and ISO/IEC JTC1/SC22/
                 WG15, "Single UNIX Specification, Version 3, 2004
                 Edition", April 2004.

Appendix A.  LOADng Control Packet Illustrations

   This section presents example packets following this specification.

A.1.  RREQ

   This figure depicts the format of a sample packet with an RREQ
   message using IPv4 addresses.  The packet is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      RREQ     |   3   |   0   |       Sequence number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Metric    |   0   |  WL   |   Hop-count   | Originator ...|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |...  address (IPv4)                            | Destination...|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |...  address (IPv4)                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


A.2.  RREP

   This figure depicts the format of a sample packet with an RREP
   message using IPv4 addresses, with the ackrequired flag set.  The
   packet is as follows:



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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      RREQ     |   3   |   0   |       Sequence number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Metric    |1|  0  |  WL   |   Hop-count   | Originator ...|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |...  address (IPv4)                            | Destination...|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |...  address (IPv4)                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


A.3.  RREP_ACK

   This figure depicts the format of a sample packet with an RREP_ACK
   message using IPv4 addresses, as follows:


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     R_ACK     |   3   |   0   |         Sequence number       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Originator address (IPv4)                    |
     +-+-+--+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


A.4.  RERR

   This figure depicts the format of a sample packet with an RERR
   message using IPv4 addresses, as follows:



     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     RERR      |   3   |   0   |  Error code   | Originator ...|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |...  address (IPv4)                            | Destination...|
    +-+-+--+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |...  address (IPv4)                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







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Authors' Addresses

   Thomas Heide Clausen
   LIX, Ecole Polytechnique

   Phone: +33 6 6058 9349
   EMail: T.Clausen@computer.org
   URI:   http://www.ThomasClausen.org/


   Axel Colin de Verdiere
   LIX, Ecole Polytechnique

   Phone: +33 6 1264 7119
   EMail: axel@axelcdv.com
   URI:   http://www.axelcdv.com/


   Jiazi Yi
   LIX, Ecole Polytechnique

   Phone: +33 1 6933 4031
   EMail: jiazi@jiaziyi.com
   URI:   http://www.jiaziyi.com/


   Afshin Niktash
   Maxim Integrated Products

   Phone: +1 94 9450 1692
   EMail: afshin.niktash@maxim-ic.com
   URI:   http://www.Maxim-ic.com/


   Yuichi Igarashi
   Hitachi, Ltd., Yokohama Research Laboratory

   Phone: +81 45 860 3083
   EMail: yuichi.igarashi.hb@hitachi.com
   URI:   http://www.hitachi.com/











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   Hiroki Satoh
   Hitachi, Ltd., Yokohama Research Laboratory

   Phone: +81 44 959 0205
   EMail: hiroki.satoh.yj@hitachi.com
   URI:   http://www.hitachi.com/


   Ulrich Herberg
   Fujitsu Laboratories of America

   Phone: +1 408 530 4528
   EMail: ulrich@herberg.name
   URI:   http://www.herberg.name/


   Cedric Lavenu
   EDF R&D

   Phone: +33 1 4765 2729
   EMail: cedric-2.lavenu@edf.fr
   URI:   http://www.edf.fr/


   Thierry Lys
   ERDF

   Phone: +33 1 8197 6777
   EMail: thierry.lys@erdfdistribution.fr
   URI:   http://www.erdfdistribution.fr/





















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