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Versions: (draft-ietf-manet-dymo) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 draft-perkins-manet-aodvv2

Mobile Ad hoc Networks Working Group                          C. Perkins
Internet-Draft                                                 Futurewei
Intended status: Standards Track                              S. Ratliff
Expires: July 3, 2015                                            Idirect
                                                              J. Dowdell
                                                Airbus Defence and Space
                                                           L. Steenbrink
                                           HAW Hamburg, Dept. Informatik
                                                       December 30, 2014


                Dynamic MANET On-demand (AODVv2) Routing
                       draft-ietf-manet-aodvv2-06

Abstract

   The revised Ad Hoc On-demand Distance Vector (AODVv2) routing
   protocol is intended for use by mobile routers in wireless, multihop
   networks.  AODVv2 determines unicast routes among AODVv2 routers
   within the network in an on-demand fashion, offering rapid
   convergence in dynamic topologies.

Status of This Memo

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

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

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

   This Internet-Draft will expire on July 3, 2015.

Copyright Notice

   Copyright (c) 2014 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



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   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.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Data Elements and Notational Conventions  . . . . . . . . . .   8
   4.  Applicability Statement . . . . . . . . . . . . . . . . . . .   8
   5.  AODVv2 Message Transmission . . . . . . . . . . . . . . . . .  10
   6.  Data Structures . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Route Table Entry . . . . . . . . . . . . . . . . . . . .  10
     6.2.  Bidirectional Connectivity and Blacklists . . . . . . . .  12
     6.3.  Router Clients and Client Networks  . . . . . . . . . . .  13
     6.4.  Sequence Numbers  . . . . . . . . . . . . . . . . . . . .  13
     6.5.  Metrics . . . . . . . . . . . . . . . . . . . . . . . . .  14
       6.5.1.  The Cost() function . . . . . . . . . . . . . . . . .  15
       6.5.2.  The LoopFree() function . . . . . . . . . . . . . . .  15
       6.5.3.  Default Metric type . . . . . . . . . . . . . . . . .  16
       6.5.4.  Alternate Metrics . . . . . . . . . . . . . . . . . .  16
     6.6.  RREQ Table: Received RREQ Messages  . . . . . . . . . . .  16
   7.  AODVv2 Operations on Route Table Entries  . . . . . . . . . .  18
     7.1.  Evaluating Incoming Routing Information . . . . . . . . .  18
     7.2.  Applying Route Updates To Route Table Entries . . . . . .  19
     7.3.  Route Table Entry Timeouts  . . . . . . . . . . . . . . .  20
   8.  Routing Messages RREQ and RREP (RteMsgs)  . . . . . . . . . .  20
     8.1.  Route Discovery Retries and Buffering . . . . . . . . . .  21
     8.2.  RteMsg Structure  . . . . . . . . . . . . . . . . . . . .  22
     8.3.  RREQ Generation . . . . . . . . . . . . . . . . . . . . .  23
     8.4.  RREP Generation . . . . . . . . . . . . . . . . . . . . .  24
     8.5.  Handling a Received RteMsg  . . . . . . . . . . . . . . .  24
       8.5.1.  Additional Handling for Incoming RREQ . . . . . . . .  25
       8.5.2.  Additional Handling for Incoming RREP . . . . . . . .  26
     8.6.  Suppressing Redundant RREQ messages . . . . . . . . . . .  26
   9.  Route Maintenance and RERR Messages . . . . . . . . . . . . .  27
     9.1.  Maintaining Route Lifetimes During Packet Forwarding  . .  27
     9.2.  Next-hop Router Adjacency Monitoring  . . . . . . . . . .  28
     9.3.  RERR Generation . . . . . . . . . . . . . . . . . . . . .  28
       9.3.1.  Case 1: Undeliverable Packet  . . . . . . . . . . . .  29
       9.3.2.  Case 2: Broken Link . . . . . . . . . . . . . . . . .  30
     9.4.  Receiving and Handling RERR Messages  . . . . . . . . . .  30
   10. Representing AODVv2 data elements using RFC 5444  . . . . . .  32
   11. Simple Internet Attachment  . . . . . . . . . . . . . . . . .  33
   12. Multiple Interfaces . . . . . . . . . . . . . . . . . . . . .  34
   13. AODVv2 Control Message Generation Limits  . . . . . . . . . .  35



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   14. Optional Features . . . . . . . . . . . . . . . . . . . . . .  35
     14.1.  Expanding Rings Multicast  . . . . . . . . . . . . . . .  35
     14.2.  Intermediate RREP  . . . . . . . . . . . . . . . . . . .  35
     14.3.  Precursor Lists and Notifications  . . . . . . . . . . .  35
       14.3.1.  Overview . . . . . . . . . . . . . . . . . . . . . .  36
       14.3.2.  Precursor Notification Details . . . . . . . . . . .  36
     14.4.  Multicast RREP Response to RREQ  . . . . . . . . . . . .  37
     14.5.  RREP_ACK . . . . . . . . . . . . . . . . . . . . . . . .  37
     14.6.  Message Aggregation  . . . . . . . . . . . . . . . . . .  37
   15. Administratively Configurable Parameters and Timer Values . .  38
     15.1.  Timers . . . . . . . . . . . . . . . . . . . . . . . . .  38
     15.2.  Protocol constants . . . . . . . . . . . . . . . . . . .  39
     15.3.  Administrative (functional) controls . . . . . . . . . .  39
     15.4.  Other administrative parameters and lists  . . . . . . .  39
   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  40
     16.1.  AODVv2 Message Types Specification . . . . . . . . . . .  40
     16.2.  Message TLV Type Specification . . . . . . . . . . . . .  40
     16.3.  Address Block TLV Specification  . . . . . . . . . . . .  41
     16.4.  Metric Type Number Allocation  . . . . . . . . . . . . .  41
   17. Security Considerations . . . . . . . . . . . . . . . . . . .  41
   18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  43
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  43
     19.1.  Normative References . . . . . . . . . . . . . . . . . .  43
     19.2.  Informative References . . . . . . . . . . . . . . . . .  44
   Appendix A.  Example Algorithms for AODVv2 Protocol Operations  .  45
     A.1.  Subroutines for AODVv2 Protocol Operations  . . . . . . .  47
     A.2.  Example Algorithms for AODVv2 RREQ Operations . . . . . .  48
       A.2.1.  Generate_RREQ . . . . . . . . . . . . . . . . . . . .  48
       A.2.2.  Receive_RREQ  . . . . . . . . . . . . . . . . . . . .  49
       A.2.3.  Regenerate_RREQ . . . . . . . . . . . . . . . . . . .  50
     A.3.  Example Algorithms for AODVv2 RREP Operations . . . . . .  51
       A.3.1.  Generate_RREP . . . . . . . . . . . . . . . . . . . .  52
       A.3.2.  Receive_RREP  . . . . . . . . . . . . . . . . . . . .  53
       A.3.3.  Regenerate_RREP . . . . . . . . . . . . . . . . . . .  54
       A.3.4.  Consume_RREP  . . . . . . . . . . . . . . . . . . . .  55
     A.4.  Example Algorithms for AODVv2 RERR Operations . . . . . .  55
       A.4.1.  Generate_RERR . . . . . . . . . . . . . . . . . . . .  55
       A.4.2.  Receive_RERR  . . . . . . . . . . . . . . . . . . . .  56
       A.4.3.  Regenerate_RERR . . . . . . . . . . . . . . . . . . .  57
     A.5.  Example Algorithms for AODVv2 RREP-Ack Operations . . . .  59
       A.5.1.  Generate_RREP_Ack . . . . . . . . . . . . . . . . . .  59
       A.5.2.  Consume_RREP_Ack  . . . . . . . . . . . . . . . . . .  59
       A.5.3.  Timeout_RREP_Ack  . . . . . . . . . . . . . . . . . .  59
   Appendix B.  Example RFC 5444-compliant packet formats  . . . . .  59
     B.1.  RREQ Message Format . . . . . . . . . . . . . . . . . . .  60
     B.2.  RREP Message Format . . . . . . . . . . . . . . . . . . .  62
     B.3.  RERR Message Format . . . . . . . . . . . . . . . . . . .  64
     B.4.  RREP_ACK Message Format . . . . . . . . . . . . . . . . .  65



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   Appendix C.  Changes since revision ...-05.txt  . . . . . . . . .  65
   Appendix D.  Changes since revision ...-04.txt  . . . . . . . . .  66
   Appendix E.  Changes since revision ...-03.txt  . . . . . . . . .  67
   Appendix F.  Changes since revision ...-02.txt  . . . . . . . . .  67
   Appendix G.  Multi-homing Considerations  . . . . . . . . . . . .  68
   Appendix H.  Shifting Network Prefix Advertisement Between AODVv2
                Routers  . . . . . . . . . . . . . . . . . . . . . .  68
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  68

1.  Overview

   The revised Ad Hoc On-demand Distance Vector (AODVv2) routing
   protocol [formerly named DYMO] enables on-demand, multihop unicast
   routing among AODVv2 routers in mobile ad hod networks
   [MANETs][RFC2501].  The basic operations of the AODVv2 protocol are
   route discovery and route maintenance.  Route discovery is performed
   when an AODVv2 router must transmit a packet towards a destination
   for which it does not have a route.  Route maintenance is performed
   to avoid prematurely expunging routes from the route table, and to
   avoid dropping packets when a route breaks.

   During route discovery, the originating AODVv2 router (RREQ_Gen)
   multicasts a Route Request message (RREQ) to find a route toward some
   target destination.  Using a hop-by-hop regeneration algorithm, each
   AODVv2 router receiving the RREQ message records a route toward the
   originator.  When the target's AODVv2 router (RREP_Gen) receives the
   RREQ, it records a route toward RREQ_Gen and generates a Route Reply
   (RREP) unicast toward RREQ_Gen.  Each AODVv2 router that receives the
   RREP stores a route toward the target, and again unicasts the RREP
   toward the originator.  When RREQ_Gen receives the RREP, routes have
   then been established between RREQ_Gen (the originating AODVv2
   router) and RREP_Gen (the target's AODVv2 router) in both directions.

   Route maintenance consists of two operations.  In order to maintain
   routes, AODVv2 routers extend route lifetimes upon successfully
   forwarding a packet.  When a data packet is received to be forwarded
   but there is no valid route for the destination, then the AODVv2
   router of the source of the packet is notified via a Route Error
   (RERR) message.  Each upstream router that receives the RERR marks
   the route as broken.  Before such an upstream AODVv2 router could
   forward a packet to the same destination, it would have to perform
   route discovery again for that destination.  RERR messages are also
   used to notify upstream routers when routes break (say, due to loss
   of a link to a neighbor).

   AODVv2 uses sequence numbers to assure loop freedom [Perkins99],
   similarly to AODV.  Sequence numbers enable AODVv2 routers to
   determine the temporal order of AODVv2 route discovery messages,



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   thereby avoiding use of stale routing information.  See Section 10
   for the mapping of AODVv2 data elements to RFC 5444 Address Block,
   Address TLV, and Message TLV formats.

2.  Terminology

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

   This document uses terminology from [RFC5444].

   This document defines the following terms:

   Adjacency
      A bi-directional relationship between neighboring AODVv2 routers
      for the purpose of exchanging routing information.  Not every pair
      of neighboring routers will necessarily form an adjacency.
      Monitoring of adjacencies where packets are being forwarded is
      required (see Section 9.2).
   AODVv2 Router
      An IP addressable device in the ad-hoc network that performs the
      AODVv2 protocol operations specified in this document.
   AODVv2 Sequence Number (SeqNum)
      Same as Sequence Number.
   Client Interface
      An interface that directly connects Router Clients to the Router.
   Current_Time
      The current time as maintained by the AODVv2 router.
   Data Element
      A named object used within AODVv2 protocol messages
   Disregard
      Ignore for further processing (see Section 5).
   Handling Router (HandlingRtr)
      HandlingRtr denotes the AODVv2 router receiving and handling an
      AODVv2 message.
   Incoming Link
      A link over which an AODVv2 Router has received a message from an
      adjacent router.
   MANET
      A Mobile Ad Hoc Network as defined in [RFC2501].
   MetricList
      A MetricList is a list of Metrics associated with the addresses in
      an AddressList.
   Node
      An IP addressable device in the ad-hoc network.  A node may be an
      AODVv2 router, or it may be a device in the network that does not



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      perform any AODVv2 protocol operations.  All nodes in this
      document are either AODVv2 Routers or else Router Clients.
   OrigAddr
      The IP address of the Originating Node used as a data element
      within AODVv2 messages.
   Originating Node (OrigNode)
      The Originating Node is the node that launched the application
      requiring communication with the Target Address.  If OrigNode is a
      Router Client, its AODVv2 router (RREQ_Gen) has the responsibility
      to generate a AODVv2 RREQ message on behalf of OrigNode as
      necessary to discover a route.
   PrefixLengthList
      A PrefixLengthList is the list of prefix lengths associated with
      the addresses in an AddressList.
   Reactive
      A protocol operation is called "reactive" if it is performed only
      in reaction to specific events.  As used in this document,
      "reactive" is synonymous with "on-demand".
   Routable Unicast IP Address
      A routable unicast IP address is a unicast IP address that is
      scoped sufficiently to be forwarded by a router.  Globally-scoped
      unicast IP addresses and Unique Local Addresses (ULAs) [RFC4193]
      are examples of routable unicast IP addresses.
   Route Error (RERR)
      A RERR message is used to indicate that an AODVv2 router does not
      have a route toward one or more particular destinations.
   Route Reply (RREP)
      A RREP message is used to establish a route between the Target
      Address and the Originating Address, at all the AODVv2 routers
      between them.
   Route Request (RREQ)
      An AODVv2 router uses a RREQ message to discover a valid route to
      a particular destination address, called the Target Address.  An
      AODVv2 router processing a RREQ receives routing information for
      the Originating Address.
   Router Client
      A node that requires the services of an AODVv2 router for route
      discovery and maintenance.  An AODVv2 router is always its own
      client, so that its list of client IP addresses is never empty.
   Router Interface
      An interface supporting the transmission or reception of Router
      Messages.
   RREP Generating Router (RREP_Gen)
      The RREP Generating Router is the AODVv2 router that serves
      TargNode.  RREP_Gen generates the RREP message to advertise a
      route towards TargAddr from OrigAddr.
   RREQ Generating Router (RREQ_Gen)




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      The RREQ Generating Router is the AODVv2 router that serves
      OrigNode.  RREQ_Gen generates the RREQ message to discover a route
      for TargAddr.
   Sequence Number (SeqNum)
      A Sequence Number is an unsigned integer maintained by an AODVv2
      router to avoid re-use of stale messages.  The router associates
      SeqNum with an IP address of one of its network interfaces.  The
      value zero (0) is reserved to indicate that the Sequence Number
      for an address is unknown.
   SeqNumList
      A SeqNumList is the list of Sequence Numbers associated with the
      addresses in an AddressList.
   TargAddr
      The IP address of the Target Node used as a data element within
      AODVv2 messages.
   Target Node (TargNode)
      The Target Node denotes the node hosting the IP address towards
      which a route is needed.
   Unreachable Addr (UnreachableAddr)
      An UnreachableAddr is an address for which a valid route is not
      known.
   upstream
      In the direction from TargAddr to OrigAddr.
   Valid route
      A route that can be used for forwarding; in other words a route
      that is not Broken or Expired.

























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3.  Data Elements and Notational Conventions

   This document uses the Data Elements and conventions found in Table 1
   and Table 2.

    +---------------+-------------------------------------------------+
    | Data Elements | Meaning                                         |
    +---------------+-------------------------------------------------+
    | msg_hop_limit | Number of hops allowable for the message.       |
    | msg_hop_count | Number of hops traversed so far by the message. |
    | AckReq        | Acknowledgement Requested for RREP              |
    | MetricType    | Metric Type for Metric data element             |
    | PktSource     | The IP address which is unreachable.            |
    | AddressList   | A list of IP addresses                          |
    | SeqNum        | Sequence Number                                 |
    | SeqNumList    | Sequence Number List                            |
    | Metric        | Metric value for route to associated IP address |
    | OrigSeqNum    | Originating Node Sequence Number                |
    | TargSeqNum    | Target Node Sequence Number                     |
    +---------------+-------------------------------------------------+

                                  Table 1

   +------------------------+------------------------------------------+
   | Notation               | Meaning                                  |
   +------------------------+------------------------------------------+
   | Route[Address]         | A route table entry towards Address      |
   | Route[Address].{field} | A field in a route table entry           |
   | --                     | --                                       |
   | RREQ_Gen               | AODVv2 router originating an RREQ        |
   | RREP_Gen               | AODVv2 router responding to an RREQ      |
   | RteMsg                 | Either RREQ or RREP                      |
   | RteMsg.{field}         | Field in RREQ or RREP                    |
   | AdvRte                 | a route advertised in an incoming RteMsg |
   | HandlingRtr            | Handling Router                          |
   | UnreachableAddr        | Unreachable Addr                         |
   +------------------------+------------------------------------------+

                                  Table 2

4.  Applicability Statement

   The AODVv2 routing protocol is a reactive routing protocol designed
   for stub (i.e., non-transit) or disconnected (i.e., from the
   Internet) mobile ad hoc networks (MANETs).  AODVv2 handles a wide
   variety of mobility patterns by determining routes on-demand.  AODVv2
   also handles a wide variety of traffic patterns.  In networks with a
   large number of routers, AODVv2 is best suited for relatively sparse



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   traffic scenarios where any particular router forwards packets to
   only a small percentage of the AODVv2 routers in the network, due to
   the on-demand nature of route discovery and route maintenance.
   AODVv2 supports routers with multiple interfaces, as long as each
   interface has its own (unicast routeable) IP address; the set of all
   network interfaces supporting AODVv2 is administratively configured
   in a list (namely, AODVv2_INTERFACES).

   Although AODVv2 is closely related to AODV [RFC3561], and shares some
   features of DSR [RFC4728], AODVv2 is not interoperable with either of
   those other two protocols.

   AODVv2 is applicable to memory constrained devices, since only a
   little routing state is maintained in each AODVv2 router.  Routes
   that are not needed for forwarding data do not have to be maintained,
   in contrast to proactive routing protocols that require routing
   information to all routers within the MANET be maintained.

   In addition to routing for its own local applications, each AODVv2
   router can also route on behalf of other non-routing nodes (in this
   document, "Router Clients"), reachable via Client Interfaces.  Each
   AODVv2 router, if serving router clients other than itself, SHOULD be
   configured with information about the IP addresses of its clients,
   using any suitable method.  In the initial state, no AODVv2 router is
   required to have information about the relationship between any other
   AODVv2 router and its Router Clients (see Section 6.3).

   The coordination among multiple AODVv2 routers to distribute routing
   information correctly for a shared address (i.e. an address that is
   advertised and can be reached via multiple AODVv2 routers) is not
   described in this document.  The AODVv2 router operation of shifting
   responsibility for a routing client from one AODVv2 router to another
   is described in Appendix H.  Address assignment procedures are
   entirely out of scope for AODVv2.  A Router Client SHOULD NOT be
   served by more than one AODVv2 router at any one time.

   AODVv2 routers perform route discovery to find a route toward a
   particular destination.  AODVv2 routers MUST must be configured to
   respond to RREQs for themselves and their clients.  When AODVv2 is
   the only protocol interacting with the forwarding table, AODVv2 MAY
   be configured to perform route discovery for all unknown unicast
   destinations.

   AODVv2 only supports bidirectional links.  In the case of possible
   unidirectional links, blacklists (see Section 6.2) SHOULD be used, or
   other means (e.g. adjacency establishment with only neighboring
   routers that have bidirectional communication as indicated by NHDP
   [RFC6130]) of assuring and monitoring bi-directionality are



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   recommended.  Otherwise, persistent packet loss or persistent
   protocol failures could occur.  The cost of bidirectional link L
   (denoted Cost(L)) may depend upon the direction across the link for
   which the cost is measured.  If received over a link that is
   unidirectional, metric information from incoming AODVv2 messages MUST
   NOT be used for route table updates.

   The routing algorithm in AODVv2 may be operated at layers other than
   the network layer, using layer-appropriate addresses.  The routing
   algorithm makes use of some persistent state; if there is no
   persistent storage available for this state, recovery can impose a
   performance penalty (e.g., in case of AODVv2 router reboots).

5.  AODVv2 Message Transmission

   In its default mode of operation, AODVv2 sends messages using the
   parameters for port number and IP protocol specified in [RFC5498].
   By default, AODVv2 messages are sent with the IP destination address
   set to the link-local multicast address LL-MANET-Routers [RFC5498]
   unless otherwise specified.  Therefore, all AODVv2 routers MUST
   subscribe to LL-MANET-Routers [RFC5498] to receive AODVv2 messages.
   In order to reduce multicast overhead, regenerated multicast packets
   in MANETs SHOULD be done according to methods specified in [RFC6621].
   AODVv2 does not specify which method should be used to restrict the
   set of AODVv2 routers that have the responsibility to regenerate
   multicast packets.  Note that multicast packets MAY be sent via
   unicast.  For example, this may occur for certain link-types (non-
   broadcast media), for manually configured router adjacencies, or in
   order to improve robustness.

   The IPv4 TTL (IPv6 Hop Limit) field for all packets containing AODVv2
   messages is set to 255.  If a packet is received with a value other
   than 255, any AODVv2 message contained in the packet MUST be
   disregarded by AODVv2.  This mechanism, known as "The Generalized TTL
   Security Mechanism" (GTSM) [RFC5082] helps to assure that packets
   have not traversed any intermediate routers.

   IP packets containing AODVv2 protocol messages SHOULD be given
   priority queuing and channel access.

6.  Data Structures

6.1.  Route Table Entry

   The route table entry is a conceptual data structure.
   Implementations MAY use any internal representation so long as it
   provides access to the information specified below.




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   A route table entry has the following fields:

   Route.Address
      An address or address prefix of a node
   Route.PrefixLength
      The length of the address or prefix.  If the value of
      Route.PrefixLength is less than the length of addresses in the
      address family used by the AODVv2 routers, the associated address
      is a routing prefix, rather than an address.  A PrefixLength is
      stored for every route in the route table.
   Route.SeqNum
      The Sequence Number associated with Route.Address, as obtained
      from the last packet that successfully updated this route table
      entry.
   Route.NextHopAddress
      The IP address of the adjacent AODVv2 router used for the path
      toward the Route.Address
   Route.NextHopInterface
      The interface used to send packets toward Route.Address
   Route.LastUsed
      The time that this route was last used
   Route.ExpirationTime
      The time at which this route must expire
   Route.MetricType
      The type of the metric for the route towards Route.Address
   Route.Metric
      The cost of the route towards Route.Address expressed in units
      consistent with Route.MetricType
   Route.State
      The last *known* state of the route.  Route.State is one of the
      following: Active, Idle, Expired, or Broken.
   Route.Timed
      The Route.Timed flag is true if the route was specified to have a
      specific lifetime for use.
   Route.Precursors (optional)
      A list of upstream nodes using the route.

   A route table entry (i.e., a route) is in one of the following
   states:

   Active
      An Active route is in current use for forwarding packets.  An
      Active route is maintained continuously by AODVv2 and is
      considered to remain active as long as it is used at least once
      during every ACTIVE_INTERVAL, or if the Route.Timed flag is true.
      When a route that is not a timed route is no longer active the
      route becomes an Idle route.
   Idle



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      An Idle route can be used for forwarding packets, even though it
      is not in current use.  If an Idle route is used to forward a
      packet, it becomes an Active route once again.  After an Idle
      route remains idle for MAX_IDLETIME, it becomes an Expired route.
   Expired
      After a route has been idle for too long, it expires, and may no
      longer be used for forwarding packets.  An Expired route is not
      used for forwarding, but the sequence number information can be
      maintained until the destination sequence number has had no
      updates for MAX_SEQNUM_LIFETIME; after that time, old sequence
      number information is considered no longer valuable and the
      Expired route MUST BE expunged.
   Broken
      A route marked as Broken cannot be used for forwarding packets but
      still has valid destination sequence number information.  When the
      link to a route's next hop is broken, the route is marked as being
      Broken, and afterwards the route MAY NOT be used.
   Timed
      The expiration of a Timed route is controlled by the
      Route.ExpirationTime time of the route table entry (instead of
      MAX_IDLETIME).  Until that time, a Timed route can be used for
      forwarding packets.  A route is indicated to be a Timed route by
      the setting of the Route.Timed flag in the route table entry.
      Afterwards, the route MAY be expunged; otherwise the route must be
      must be marked as Expired.

   MAX_SEQNUM_LIFETIME is the time after a reboot during which an AODVv2
   router MUST NOT transmit any routing messages.  Thus, if all other
   AODVv2 routers expunge routes to the rebooted router after that time
   interval, the rebooted AODVv2 router's sequence number will not be
   considered stale by any other AODVv2 router in the MANET.

6.2.  Bidirectional Connectivity and Blacklists

   To avoid repeated failure of Route Discovery, an AODVv2 router
   (HandlingRtr) handling a RREP message MUST attempt to verify
   connectivity towards RREQ_Gen.  This MAY be done by including the
   Acknowledgement Request (AckReq) data element in the RREP.  In reply
   to an AckReq, an RREP_ACK message message MUST be sent.  If the
   verification is not received within UNICAST_MESSAGE_SENT_TIMEOUT,
   HandlingRtr MUST put the upstream neighbor in the blacklist.  RREQs
   received from a blacklisted router, or any router over a link that is
   known to be incoming-only, MUST NOT be regenerated by HandlingRtr.
   However, the upstream neighbor SHOULD NOT be permanently blacklisted;
   after a certain time (MAX_BLACKLIST_TIME), it SHOULD once again be
   considered as a viable upstream neighbor for route discovery
   operations.




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   For this purpose, a list of blacklisted routers along with their time
   of removal SHOULD be maintained:

   Blacklist.Router
      An IP address of the router that did not verify bidirectional
      connectivity.
   Blacklist.RemoveTime
      The time at which Blacklist.Router MAY be removed from the
      blacklist.

6.3.  Router Clients and Client Networks

   An AODVv2 router may offer routing services to other nodes that are
   not AODVv2 routers; such nodes are defined as Router Clients in this
   document.

   For this purpose, CLIENT_ADDRESSES must be configured on each AODVv2
   router with the following information:

   Client IP address
      The IP address of the node that requires routing service from the
      AODVv2 router.
   Client Prefix Length
      The length of the routing prefix associated with the client IP
      address.

   If the Client Prefix Length is not the full length of the Client IP
   address, then the prefix defines a Client Network.  If an AODVv2
   router is configured to serve a Client Network, then the AODVv2
   router MUST serve every node that has an address within the range
   defined by the routing prefix of the Client Network.  The list of
   Routing Clients for an AODVv2 router is never empty, since an AODVv2
   router is always its own client as well.

6.4.  Sequence Numbers

   Sequence Numbers allow AODVv2 routers to evaluate the freshness of
   routing information.  Each AODVv2 router in the network MUST maintain
   its own sequence number.  Each RREQ and RREP generated by an AODVv2
   router includes that sequence number.  Each AODVv2 router MUST make
   sure that its sequence number is unique and monotonically increasing.
   This can be achieved by incrementing it with every RREQ or RREP it
   generates.

   Every router receiving a RREQ or RREP can thus use the Sequence
   Number of a RREQ or RREP as information concerning the freshness of
   the packet's route update: if the new packet's Sequence Number is




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   lower than the one already stored in the route table, its information
   is considered stale.

   As a consequence, loop freedom is assured.

   If the router has multiple network interfaces, it can use the same
   SeqNum for the IP addresses of all of them, or it can assign
   different SeqNums for use with different IP addresses.  However, the
   router MUST NOT use multiple SeqNums for any particular IP address.
   A Router Client has the same SeqNum as the IP address of the network
   interface that the AODVv2 router uses to forward packets to that
   Router Client.  Similarly, a route to a subnet has the same SeqNum as
   the IP address of the network interface that the AODVv2 router uses
   to forward packets to that subnet.  The Sequence Number guarantees
   the temporal order of routing information to maintain loop-free
   routes, and fulfills the same role as the "Destination Sequence
   Number" of DSDV [Perkins94], and as the AODV Sequence Number in RFC
   3561[RFC3561].

   An AODVv2 router increments its SeqNum as follows.  Most of the time,
   SeqNum is incremented by simply adding one (1).  But when the SeqNum
   has the value of the largest possible number representable as a
   16-bit unsigned integer (i.e., 65,535), it MUST be incremented by
   setting to one (1).  In other words, the sequence number after 65,535
   is 1.

   An AODVv2 router SHOULD maintain its SeqNum in persistent storage.
   If an AODVv2 router's SeqNum is lost, it MUST take the following
   actions to avoid the danger of routing loops.  First, the AODVv2
   router MUST set Route.State = Broken for each entry.  Furthermore the
   AODVv2 router MUST wait for at least MAX_SEQNUM_LIFETIME before
   transmitting or regenerating any AODVv2 RREQ or RREP messages.  If an
   AODVv2 protocol message is received during this waiting period, the
   AODVv2 router SHOULD perform normal route table entry updates, but
   not forward the message to other nodes.  If a data packet is received
   for forwarding to another destination during this waiting period, the
   AODVv2 router MUST transmit a RERR message indicating that no route
   is available.  At the end of the waiting period the AODVv2 router
   sets its SeqNum to one (1) and begins performing AODVv2 protocol
   operations again.

6.5.  Metrics

   Metrics describe the quality of a route or a link.  They can take
   various aspects into account, such as latency, delay, financial,
   energy, etc.  Whenever an AODV router receives metric information in
   an incoming message, the value of the metric is as measured by the




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   transmitting router, and does not reflect the cost of traversing the
   incoming link.

   Each routing table entry is associated with metric information.  When
   presented with information which may update a route, deciding whether
   to use the information involves evaluating the metric.  For some
   metrics, a maximum value is defined, namely MAX_METRIC[i] where 'i'
   is the Metric Type.  AODVv2 does not store routes in its route table
   that cost more than MAX_METRIC[i].

   Each metric has to have a Metric Type, and the Metric Type is
   allocated by IANA as specified in [RFC6551].  Apart from its default
   metric type, which is detailed in Section 6.5.3, AODVv2 enables the
   use of generic metrics, whose data type depends on the metric used.
   The Metric Type is specified by the MetricType TLV of each RteMsg.
   As a natural result of the way routes are looked up according to
   conformant metric type, all intermediate routers handling a RteMsg
   will assign the same metric type to all metric information in the
   RteMsg.

6.5.1.  The Cost() function

   In order to simplify the description of storing accumulated route
   costs in the route table, a Cost() function is defined.  This
   function returns the Cost of traversing a Route ('Cost(R)') or a Link
   ('Cost(L)').  The specification of Cost(L) for metric types other
   than DEFAULT_METRIC_TYPE is beyond the scope of this document.

6.5.2.  The LoopFree() function

   Since determining loop freedom is known to depend on comparing the
   Cost(R) of route update information to the Cost(R) of an existing
   stored route using the same metric, AODVv2 must also be able to
   invoke an abstract routine which in this document is called
   "LoopFree(R1, R2)".  LoopFree(R1, R2) returns TRUE when, (under the
   assumption of nondecreasing SeqNum during Route Discovery) given that
   R2 is loop-free and Cost(R2) is the cost of route R2, Cost(R1) is
   known to guarantee loop freedom of the route R1.  In this document,
   an AODVv2 router will only invoke LoopFree (AdvRte, Route), for
   routes AdvRte and Route which use the same metric to the same
   destination.  AdvRte is the route advertised in an incoming RREQ or
   RREP, and is used as parameter R1 for LoopFree.  Route is a route
   already existing in the AODVv2 router's route table, and is used as
   parameter R2 for LoopFree.







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6.5.3.  Default Metric type

   HopCount is still the default metric for use in MANETs,
   notwithstanding the above objections.  Therefore, the default Metric
   Type DEFAULT_METRIC_TYPE is Hop Count.  It is also the only metric
   described in detail by this protocol.  With this metric, Cost(L) is
   always 1, and Cost(R) is simply the hop count between the router and
   the destination.

   MAX_METRIC[DEFAULT_METRIC_TYPE] is defined to be MAX_HOPCOUNT.
   MAX_HOPCOUNT MUST be larger than the AODVv2 network diameter.
   Otherwise, AODVv2 protocol messages may not reach their intended
   destinations.

   Using Metric Type DEFAULT_METRIC_TYPE, LoopFree (AdvRte, Route) is
   TRUE when Cost(AdvRte) <= Cost(Route).  The specification of Cost(R)
   and LoopFree(AdvRte, Route) for metric types other than
   DEFAULT_METRIC_TYPE is beyond the scope of this document.

6.5.4.  Alternate Metrics

   Some applications may require metric information other than Hop
   Count, which has traditionally been the default metric associated
   with routes in MANET.  It is well known that reliance on Hop Count
   can cause selection of the worst possible route in many situations.
   For this reason, it is important to enable route selection based on
   metric information other than Hop Count -- in other words, based on
   "alternate metrics".

   The range and data type of each such alternate metric may be
   different.  For instance, the data type might be integers, or
   floating point numbers, or restricted subsets thereof.  It is out of
   the scope of this document to specify for alternate metrics the
   Cost(L) and Cost(R) functions, or their return type.

6.6.  RREQ Table: Received RREQ Messages

   Two incoming RREQ messages are considered to be "comparable" if they
   were generated by the same AODVv2 router in order to discover a route
   for the same destination with the same metric type.  According to
   that notion of comparability, when RREQ messages are flooded in a
   MANET, an AODVv2 router may well receive comparable RREQ messages
   from more than one of its neighbors.  A router, after receiving an
   RREQ message, MUST check against previous RREQs to assure that its
   response message would contain information that is not redundant (see
   Section 8.6 regarding suppression of redundant RREQ messages).
   Otherwise, multicast RREQs are likely to be regenerated again and




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   again with almost no additional benefit, but generating a great deal
   of unnecessary signaling traffic and interference.

   To avoid transmission of redundant RREQ messages, while still
   enabling the proper handling of earlier RREQ messages that may have
   somehow been delayed in the network, it is needed for each AODVv2
   router to keep a list of the certain information about RREQ messages
   which it has recently received.

   This list is called the AODVv2 Received RREQ Table -- or, more
   briefly, the RREQ Table.  Two AODVv2 RREQ messages are comparable if:

   o  they have the same metric type
   o  they have the same OrigAddr and TargAddr

   Each entry in the RREQ Table has the following fields:

   o  OrigAddr
   o  TargAddr
   o  OrigNode Sequence Number
   o  TargNode Sequence Number (if present in RREQ)
   o  Metric Type
   o  Metric
   o  Timestamp

   The RREQ Table is maintained so that no two entries in the RREQ
   Table are comparable -- that is, all RREQs represented in the RREQ
   Table either have a different OrigAddr, different TargAddr, or
   different metric types.  If two RREQs have the same metric type,
   OrigAddr, and TargAddr, the information from the one with the older
   Sequence Number is not needed in the table; in case they have the
   same Sequence Number, the one with the greater Metric value is not
   needed; in case they have the same Metric as well, it does not matter
   which table entry is maintained.  Whenever a RREQ Table entry is
   updated, its Timestamp field should also be updated to reflect the
   Current_Time.

   When optional multicast RREP (see Section 14.4) is used to enable
   selection from among multiple possible return routes, an AODVv2
   router can eliminate redundant RREP messages using the analogous
   mechanism along with a RREP Table.  The description in this section
   only refers to RREQ multicast messages.

   Protocol handling of RERR messages eliminates the need for tracking
   RERR messages, since the rules for RERR regeneration prevent the
   phenomenon of redundant retansmission that affects RREQ and RREP
   multicast.




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7.  AODVv2 Operations on Route Table Entries

   In this section, operations are specified for updating the route
   table due to timeouts and route updates within AODVv2 messages.
   Route update information in AODVv2 messages includes IP addresses,
   along with the SeqNum and prefix length associated with each IP
   address, and including the Metric measured from the node transmitting
   the AODVv2 message to the IP address in the route update.  A RREQ
   message advertises a route to OrigAddr, and a RREP message
   analogously advertises a route to TargAddr.  In this section, RteMsg
   is either RREQ or RREP, and AdvRte is the route advertised by the
   RteMsg.  All SeqNum comparisons use signed 16-bit arithmetic.

7.1.  Evaluating Incoming Routing Information

   If the incoming RteMsg does not have a Metric Type data element, then
   the metric information contained by AdvRte is considered to be of
   type DEFAULT_METRIC_TYPE -- in other words, 3 (for HopCount) unless
   changed by administrative action.  The AODVv2 router (HandlingRtr)
   checks the advertised route (AdvRte) to see whether the AdvRte should
   be used to update an existing route table entry.  HandlingRtr
   searches its route table to see if there is a route table entry with
   the same Metric Type as the AdvRte, matching AdvRte.Address.  If not,
   HandlingRtr creates a route table entry for AdvRte.Address as
   described in Section 7.2.  Otherwise, HandlingRtr compares the
   incoming routing information for AdvRte against the already stored
   routing information in the route table entry (Route) for
   AdvRte.Address, as described next.

   Route[AdvRte.Address] uses the same metric type as the incoming
   routing information, and the route entry contains Route.SeqNum,
   Route.Metric, and Route.State.  Define AdvRte.SeqNum and
   AdvRte.Metric to be the corresponding routing information for
   Route.Address in the incoming RteMsg.  Define AdvRte.Cost to be
   (AdvRte.Metric + Cost(L)), where L is the link from which the
   incoming message was received.  The incoming routing information is
   classified as follows:

   1.  Stale::  AdvRte.SeqNum < Route.SeqNum :
      If AdvRte.SeqNum < Route.SeqNum the incoming information is stale.
      Using stale routing information is not allowed, since that might
      result in routing loops.  In this case, HandlingRtr MUST NOT
      update the route table entry using the routing information for
      AdvRte.Address.
   2.  Unsafe against loops::  (TRUE != LoopFree (AdvRte, Route)) :
      If AdvRte is not Stale (as in (1) above), AdvRte.Cost is next
      considered to insure loop freedom.  If (TRUE != LoopFree (AdvRte,
      Route)) (see Section 6.5), then the incoming AdvRte information is



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      not guaranteed to prevent routing loops, and it MUST NOT be used
      to update any route table entry.
   3.  More costly::
      (AdvRte.Cost >= Route.Metric) && (Route.State != Broken)
      When AdvRte.SeqNum is the same as in a valid route table entry,
      and LoopFree (AdvRte, Route) assures loop freedom, incoming
      information still does not offer any improvement over the existing
      route table information if AdvRte.Cost >= Route.Metric.  Using
      such incoming routing information to update a route table entry is
      not recommended.
   4.  Offers improvement::
      Advertised routing information that does not match any of the
      above criteria is better than existing route table information and
      SHOULD be used to improve the route table.  The following pseudo-
      code illustrates whether advertised routing information should be
      used to update an existing route table entry as described in
      Section 7.2.

   (AdvRte.SeqNum > Route.SeqNum) OR
       ((AdvRte.SeqNum == Route.SeqNum) AND
                [(AdvRte.Cost < Route.Metric) OR
                 ((Route.State == Broken) && LoopFree (AdvRte, Route))])

      The above logic corresponds to placing the following conditions
      (compared to the existing route table entry) on the advertised
      route update before it can be used:

      *  it is more recent, or
      *  it is not stale and is less costly, or
      *  it can safely repair a broken route.

7.2.  Applying Route Updates To Route Table Entries

   To apply the route update, a route table entry for AdvRte.Address is
   either found to already exist in the route table, or else a new route
   table entry for AdvRte.Address is created and inserted into the route
   table.  If the route table entry already exists, and the state is
   Expired or Broken, then the state is reset to be Idle.  If the route
   table entry had to be created, the state is set to be Active.  The
   route table entry is populated with the following information:

   o  If AdvRte.PrefixLength exists, then Route.PrefixLength :=
      AdvRte.PrefixLength.  Otherwise, Route.PrefixLength := maximum
      length for address family (either 32 or 128).
   o  Route.SeqNum := AdvRte.SeqNum
   o  Route.NextHopAddress := IP.SourceAddress (i.e., an address of the
      node from which the RteMsg was received)




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   o  Route.NextHopInterface is set to the interface on which RteMsg was
      received
   o  Route.MetricType := AdvRte.MetricType
   o  Route.Metric := AdvRte.Cost
   o  Route.LastUsed := Current_Time
   o  If RteMsg.VALIDITY_TIME is included, then
      Route.Timed := TRUE and Route.ExpirationTime := Current_Time +
      RteMsg.VALIDITY_TIME.  Otherwise, Route.ExpirationTime :=
      Current_Time + (ACTIVE_INTERVAL + MAX_IDLETIME).

   With these assignments to the route table entry, a route has been
   made available, and the route can be used to send any buffered data
   packets and subsequently to forward any incoming data packets for
   Route.Address.  An updated route entry also fulfills any outstanding
   route discovery (RREQ) attempts for Route.Address.

7.3.  Route Table Entry Timeouts

   During normal operation, AODVv2 does not require any explicit
   timeouts to manage the lifetime of a route.  However, the route table
   entry MUST be examined before using it to forward a packet, as
   discussed in Section 9.1.  Any required expiry or deletion can occur
   at that time.  Alternatively, timers and timeouts MAY be implemented
   to achieve the same effect.

   At any time, the route table can be examined and route table entries
   can be expunged according to their current state at the time of
   examination, as follows.

   o  An Active route MUST NOT be expunged.
   o  An Idle route SHOULD NOT be expunged.
   o  An Expired route MAY be expunged (least recently used first).
   o  A route MUST be expunged if (Current_Time - Route.LastUsed) >=
      MAX_SEQNUM_LIFETIME.
   o  A route MUST be expunged if Current_Time >= Route.ExpirationTime

   If precursor lists are maintained for the route (as described in
   Section 14.3) then the precursor lists must also be expunged at the
   same time that the route itself is expunged.

8.  Routing Messages RREQ and RREP (RteMsgs)

   AODVv2 message types RREQ and RREP are together known as Routing
   Messages (RteMsgs) and are used to discover a route between an
   Originating and Target Addr, denoted by OrigAddr and TargAddr.  The
   constructed route is bidirectional, enabling packets to flow between
   OrigAddr and TargAddr.  RREQ and RREP have similar information and
   function, but have some differences in their rules for handling.



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   When a node receives a RREQ or a RREP, the node then creates or
   updates a route to the OrigAddr or the TargAddr respectively.  The
   main difference between the two messages is that RREQ messages are
   typically multicast to solicit a RREP, whereas RREP is typically
   unicast as a response to RREQ.

   When an AODVv2 router needs to forward a data packet from a node
   (with IP address OrigAddr) in its set of router clients, and it does
   not have a forwarding route toward the packet's IP destination
   address (TargAddr), the AODVv2 router (RREQ_Gen) generates a RREQ (as
   described in Section 8.3) to discover a route toward TargAddr.
   Subsequently RREQ_Gen awaits reception of an RREP message (see
   Section 8.4) or other route table update (see Section 7.2) to
   establish a route toward TargAddr.  The RREQ message contains routing
   information to enable RREQ recipients to route packets back to
   OrigAddr, and the RREP message contains routing information enabling
   RREP recipients to route packets to TargAddr.

8.1.  Route Discovery Retries and Buffering

   After issuing a RREQ, as described above RREQ_Gen awaits a RREP
   providing a bidirectional route toward the Target Address.  If the
   RREP is not received within RREQ_WAIT_TIME, RREQ_Gen MAY retry the
   Route Discovery by generating another RREQ.  Route Discovery SHOULD
   be considered to have failed after DISCOVERY_ATTEMPTS_MAX and the
   corresponding wait time for a RREP response to the final RREQ.  After
   the attempted Route Discovery has failed, RREQ_Gen MUST wait at least
   RREQ_HOLDDOWN_TIME before attempting another Route Discovery to the
   same destination.

   To reduce congestion in a network, repeated attempts at route
   discovery for a particular Target Address SHOULD utilize a binary
   exponential backoff.

   Data packets awaiting a route SHOULD be buffered by RREQ_Gen.  This
   buffer SHOULD have a fixed limited size (BUFFER_SIZE_PACKETS or
   BUFFER_SIZE_BYTES).  Determining which packets to discard first is a
   matter of policy at each AODVv2 router; in the absence of policy
   constraints, by default older data packets SHOULD be discarded first.
   Buffering of data packets can have both positive and negative effects
   (albeit usually positive).  Nodes without sufficient memory available
   for buffering SHOULD be configured to disable buffering by
   configuring BUFFER_SIZE_PACKETS == 0 and BUFFER_SIZE_BYTES == 0.
   Doing so will affect the latency required for launching TCP
   applications to new destinations.

   If a route discovery attempt has failed (i.e., DISCOVERY_ATTEMPTS_MAX
   attempts have been made without receiving a RREP) to find a route



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   toward the Target Address, any data packets buffered for the
   corresponding Target Address MUST BE dropped and a Destination
   Unreachable ICMP message (Type 3) SHOULD be delivered to the source
   of the data packet.  The code for the ICMP message is 1 (Host
   unreachable error).  If RREQ_Gen is not the source (OrigNode), then
   the ICMP is sent to OrigAddr.

8.2.  RteMsg Structure

   RteMsgs have the following general format:

       +---------------------------------------------------------------+
       |                  msg_hop_limit, msg_hop_count                 |
       +---------------------------------------------------------------+
       |                      AckReq, MetricType                       |
       +---------------------------------------------------------------+
       |               AddressList := {OrigAddr,TargAddr}              |
       +---------------------------------------------------------------+
       |         Address Prefix Length for OrigAddr OR TargAddr        |
       +---------------------------------------------------------------+
       |           SeqNumList (OrigSeqNum AND/OR TargSeqNum)           |
       +---------------------------------------------------------------+
       |         MetricList (Metric for OrigAddr OR TargAddr)         |
       +---------------------------------------------------------------+

            Figure 1: RREQ and RREP (RteMsg) message structure

   RteMsg Data Elements

      msg_hop_limit
         The remaining number of hops allowed for dissemination of the
         RteMsg message.
      msg_hop_count
         The number of hops already traversed during dissemination of
         the RteMsg message.
      AckReq
         (RREP Only) Acknowledgement Requested by sender (optional).
      MetricType
         If MetricType != DEFAULT_METRIC_TYPE, the MetricType associated
         with route to OrigAddr or TargAddr.
      AddressList
         AddressList contains OrigAddr and TargAddr.
      OrigSeqNum AND/OR TargSeqNum
         At least one of OrigSeqNum or TargSeqNum is REQUIRED and
         carries the destination sequence number(s) associated with
         OrigNode or TargNode respectively.
      MetricList




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         The MetricList data element is REQUIRED, and carries the route
         metric information associated with either OrigAddr or TargAddr
         (but not both).

   RteMsgs carry information about OrigAddr and TargAddr, as identified
   in the context of the RREQ_Gen.  Either the OrigSeqNum or TargSeqNum
   MUST appear.  Both MAY appear in the same RteMsg when SeqNum is
   available for both OrigAddr and TargAddr.

   If the OrigSeqNum data element appears, then it MUST apply only to
   OrigAddr.  The other address in the Address List is TargAddr.

   If the TargSeqNum data element appears, then it MUST apply only to
   TargAddr.  The other address in the AddressList is OrigAddr.

8.3.  RREQ Generation

   RREQ_Gen (the AODVv2 router generating the RREQ and associated data
   elements on behalf of its client OrigNode) follows the steps in this
   section.  OrigAddr MUST be a unicast address.  The order of data
   elements is illustrated schematically in Figure 1.  RREQ_Gen SHOULD
   include TargSeqNum, if a previous value of the TargNode's SeqNum is
   known (e.g., from an invalid route table entry using longest-prefix
   matching).  If TargSeqNum is not included, AODVv2 routers handling
   the RREQ assume that RREQ_Gen does not have that information.

   1.  RREQ_Gen MUST increment the SeqNum for OrigAddr by one (1)
       according to the rules specified in Section 6.4.  This assures
       that each node receiving the RREQ will update its route table
       using the information in the RREQ.
   2.  msg_hop_limit SHOULD be set to MAX_HOPCOUNT.
   3.  msg_hop_count, if included, MUST be set to 0.

       *  This RFC 5444 constraint causes certain RREQ payloads to incur
          additional enlargement (otherwise, msg_hop_count could often
          be used as the metric).
   4.  AddressList := {OrigAddr, TargAddr}
   5.  If Route[OrigAddr].PrefixLength is equal to the number of bits in
       the addresses of the RREQ (32 for IPv4, 128 for IPv6), then no
       PrefixLengthList is included.  Otherwise, PrefixLengthList :=
       {Route[OrigAddr].PrefixLength, null}.
   6.  OrigSeqNum := OrigAddr's SeqNum number
   7.  If known, TargSeqNum := Route[TargAddr].SeqNum
   8.  RREQ.MetricList := {Route[OrigAddr].Metric, null}

   By default, the RREQ message is multicast to LL-MANET-Routers.  An
   example RREQ message format is illustrated in Appendix B.1.




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8.4.  RREP Generation

   This section specifies the generation of an RREP by an AODVv2 router
   (RREP_Gen) that provides connectivity for TargAddr, thus enabling the
   establishment of a route between OrigAddr and TargAddr.  If TargAddr
   is not a unicast IP address, the RREP MUST NOT be generated, and
   processing for the RREQ is complete.  Before transmitting a RREP, the
   routing information of the RREQ is processed as specified in
   Section 7.2; after such processing, RREP_Gen has an updated route to
   OrigAddr as well as TargAddr.  The basic format of an RREP conforms
   to the structure for RteMsgs as shown in Figure 1.

   RREP_Gen creates data elements and generates the RREP as follows:

   1.  RREP_Gen checks the RREQ against recently received RREQ messages
       as specified in Section 8.6.  If a previously received RREQ has
       made the information in the incoming RREQ to be redundant, no
       RREP is generated and processing is complete.
   2.  RREP_Gen MUST increment TargAddr's SeqNum by one (1) according to
       the rules specified in Section 6.4.
   3.  msg_hop_count, if included, MUST be set to 0.
   4.  msg_hop_limit SHOULD be set to RREQ.msg_hop_count.
   5.  If (DEFAULT_METRIC_TYPE != Route[TargAddr].MetricType) then
       include the MetricType data element and set MetricType :=
       Route[TargAddr].MetricType
   6.  AddressList := {OrigAddr, TargAddr}
   7.  TargSeqNum := Route[TargAddr].SeqNum
   8.  If Route[TargAddr].PrefixLength is equal to the number of bits in
       the addresses of the RREQ (32 for IPv4, 128 for IPv6), then no
       PrefixLengthList is included in the RREP.  Otherwise,
       PrefixLengthList := {null, Route[TargAddr].PrefixLength}
   9.  MetricList := {null, Route[TargAddr].Metric}}

   By default, the RREP message is unicast to OrigAddr.  An example
   message format for RREP is illustrated in Appendix B.2.

8.5.  Handling a Received RteMsg

   Before an AODVv2 router can make use of a received RteMsg (i.e., RREQ
   or RREP), the router must verify that the RteMsg is valid according
   to the following steps.  First the router extracts the data elements
   from the message (see Section 10).  RteMsg_Metric is the single
   Metric.  In this section (unless qualified by additional description)
   all occurrences of the term "router" refer to the AODVv2 router
   handling the received RteMsg.

   1.  A router MUST handle RteMsgs only from neighbors as specified in
       Section 5.  RteMsgs from other sources MUST be disregarded.



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   2.  The router verifies that the RteMsg contains the required data
       elements: msg_hop_limit, OrigAddr, TargAddr, RteMsg_Metric, and
       either OrigSeqNum or TargSeqNum.  If the required data elements
       are absent, the message is disregarded.
   3.  The router checks that OrigAddr and TargAddr are routable unicast
       addresses.  If not, the message is disregarded.
   4.  If the MetricType is absent, the router uses DEFAULT_METRIC_TYPE
       for the metric type.  Otherwise the router verifies that the
       MetricType is known; if not, the message is disregarded.

       *  DISCUSSION: or, can change Metric data element to use
          HopCount, e.g., measured from msg_hop_count.
   5.  If (MAX_METRIC[MetricType] - Cost(L)) <= RteMsg_Metric, where L
       denotes the incoming link, the RteMsg is disregarded.

   An AODVv2 router handles a valid RteMsg as follows:

   1.  The router MUST process the advertised route for OrigAddr or
       TargAddr contained in the RteMsg as specified in Section 7.1.
   2.  If msg_hop_limit is zero (0), no further action is taken, and the
       RteMsg is not regenerated.  Otherwise, the router MUST decrement
       msg_hop_limit.
   3.  If the RteMsg.msg_hop_count is present, and MAX_HOPCOUNT <=
       msg_hop_count, then no further action is taken.  Otherwise, the
       router MUST increment msg_hop_count.

   Further actions to regenerate an updated RteMsg depend upon whether
   the incoming RteMsg is an RREP or an RREQ.

8.5.1.  Additional Handling for Incoming RREQ

   o  By sending a RREQ, a router advertises that it will forward
      packets to the OrigAddr contained in the RteMsg according to the
      information enclosed.  The router MAY choose not to regenerate the
      RREQ, though not regenerating the RREQ could decrease connectivity
      in the network or result in nonoptimal paths.  The circumstances
      under which a router might choose not to re-transmit a RREQ are
      not specified in this document.  Some examples might include the
      following:

      *  The router is already heavily loaded and does not want to
         advertise routing for more traffic
      *  The router recently transmitted the same routing information
         (e.g. in a RREQ advertising the same metric) Section 8.6
      *  The router is low on energy and has to reduce energy expended
         for sending protocol messages or packet forwarding





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      Unless the router is prepared to advertise the new route, it halts
      processing.
   o  If the upstream router sending a RREQ is in the Blacklist, and
      Current_Time < Blacklist.RemoveTime, then the router receiving
      that RREQ MUST NOT transmit any outgoing RteMsg, and processing is
      complete.
   o  Otherwise, if the upstream router is in the Blacklist, and
      Current_Time >= Blacklist.RemoveTime, then the upstream router
      SHOULD be removed from the Blacklist, and message processing
      continued.
   o  The incoming RREQ MUST be checked against previously received
      information from the RREQ Table (Section 8.6).  If the information
      in the incoming RteMsg is redundant, then then no further action
      is taken.
   o  If TargNode is a client of the router receiving the RREQ, then the
      router generates a RREP message as specified in Section 8.4, and
      subsequently processing for the RREQ is complete.  Otherwise,
      processing continues as follows.
   o  If (DEFAULT_METRIC_TYPE != Route[OrigAddr].MetricType) then
      include the MetricType data element and assign MetricType :=
      Route[OrigAddr].MetricType
   o  Metric := Route[OrigAddr].Metric
   o  The RREQ (with updated fields as specified above>) SHOULD be
      multicast the IP address LL-MANET-Routers [RFC5498].  If the RREQ
      is unicast, the IP.DestinationAddress is set to
      Route[RREQ.TargAddr].NextHopAddress.

8.5.2.  Additional Handling for Incoming RREP

   The OrigAddr and TargAddr data elements are extracted from the
   AddressList of the incoming RREP, for instance according to the
   format of message elements as shown in Section 10.

   o  If no forwarding route exists to OrigAddr, then a RERR SHOULD be
      transmitted to TargAddr.  Otherwise, if HandlingRtr is not
      RREQ_Gen then the outgoing RREP is sent to the
      Route.NextHopAddress for OrigAddr.
   o  If HandlingRtr is RREQ_Gen then the RREP satisfies RREQ_Gen's
      earlier RREQ, and RREP processing is completed.  Any packets
      buffered for OrigAddr should be transmitted.

8.6.  Suppressing Redundant RREQ messages

   Since RREQ messages are multicast, there are common circumstances
   under which an AODVv2 router might transmit a redundant response
   (RREQ or RREP), duplicating the information transmitted in response
   to some other recent RREQ (see Section 6.6).  Before responding, an
   AODVv2 router MUST suppress such RREQ messages.  This is done by



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   checking the list of recently received RREQs to determine whether the
   incoming RREQ is redundant, as follows:

   o  The AODVv2 router searches the RREQ Table for recent entries with
      the same OrigAddr, TargAddr, and MetricType.  If not, the incoming
      RREQ message is not suppressed, and a new entry for the incoming
      RREQ is created in the RREQ Table.
   o  If there is such an entry, and the incoming RREQ has a newer
      sequence number, the incoming RREQ is not suppressed, and the
      existing table entry MUST be updated to reflect the new Sequence
      Number and Metric.
   o  Similarly, if the Sequence Numbers are the same, and the incoming
      RREQ offers a better Metric, the incoming RREQ is not suppressed,
      and the RREQ Table entry MUST be updated to reflect the new
      Metric.
   o  Otherwise, the incoming RREQ is suppressed.

9.  Route Maintenance and RERR Messages

   AODVv2 routers attempt to maintain active routes.  When a routing
   problem is encountered, an AODVv2 router (denoted RERR_Gen) sends the
   RERR to quickly notify upstream routers.  Two kinds of routing
   problems can trigger generation of a RERR message.  The first case
   happens when the router receives a packet but does not have a route
   for the destination of the packet.  The second case happens
   immediately upon detection of a broken link (see Section 9.2) for an
   Active route.

9.1.  Maintaining Route Lifetimes During Packet Forwarding

   Before using a route to forward a packet, an AODVv2 router MUST check
   the status of the route as follows.

   o  If the route is marked has been marked as Broken, it cannot be
      used for forwarding.
   o  If Current_Time > Route.ExpirationTime, the route table entry has
      expired, and cannot be used for forwarding.
   o  Similarly, if (Route.ExpirationTime == MAXTIME), and if
      (Current_Time - Route.LastUsed) > (ACTIVE_INTERVAL +
      MAX_IDLETIME), the route has expired, and cannot be used for
      forwarding.
   o  Furthermore, if Current_Time - Route.LastUsed >
      MAX_SEQNUM_LIFETIME, the route table entry MUST be expunged.

   If any of the above route error conditions hold true, the route
   cannot be used to forward the packet, and an RERR message MUST be
   generated (see Section 9.3).




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   Otherwise, Route.LastUsed := Current_Time, and the packet is
   forwarded to the route's next hop.

   Optionally, if a precursor list is maintained for the route, see
   Section 14.3 for precursor lifetime operations.

9.2.  Next-hop Router Adjacency Monitoring

   Neighboring routers MAY form an adjacency based on AODVv2 messages,
   other protocols (e.g.  NDP [RFC4861] or NHDP [RFC6130]), or manual
   configuration.  Loss of a routing adjacency may also be indicated by
   similar information.  AODVv2 routers SHOULD monitor connectivity to
   adjacent routers along active routes.  This monitoring can be
   accomplished by one or several mechanisms, including:

   o  Neighborhood discovery [RFC6130]
   o  Route timeout
   o  Lower layer trigger that a link is broken
   o  TCP timeouts
   o  Promiscuous listening
   o  Other monitoring mechanisms or heuristics

   If a next-hop AODVv2 router has become unreachable, RERR_Gen follows
   the procedures in Section 9.3.2.

9.3.  RERR Generation

   An RERR message is generated by a AODVv2 router (i.e., RERR_Gen) in
   order to notify upstream routers that packets cannot be delivered to
   one or more destinations.  An RERR message has the following general
   structure:

       +---------------------------------------------------------------+
       |                  msg_hop_limit, msg_hop_count                 |
       +---------------------------------------------------------------+
       |                     PktSource, MetricType                     |
       +---------------------------------------------------------------+
       |                   Unreachable Address List                    |
       +---------------------------------------------------------------+
       |             Unreachable Address PrefixLength List             |
       +---------------------------------------------------------------+
       |            Unreachable Address Sequence Number List           |
       +---------------------------------------------------------------+

                     Figure 2: RERR message structure

   RERR Data Elements




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      msg_hop_limit
         The remaining number of hops allowed for dissemination of the
         RERR message.
      msg_hop_count
         The number of hops already traversed during dissemination of
         the RERR message.
      PktSource
         The IP address of the unreachable destination triggering RERR
         generation.
      MetricType
         If MetricType != DEFAULT_METRIC_TYPE, the MetricType associated
         with routes affected by a broken link.
      AddressList
         A list of IP addresses not reachable by the AODVv2 router
         transmitting the RERR.
      PrefixLengthList
         The list of prefix lengths associated with the addresses in the
         Unreachable Address List.
      SeqNumList
         The list of destination sequence numbers associated with the
         Unreachable Address List.

   There are two kinds of events indicating that packets cannot be
   delivered to certain destinations.  The two cases differ in the way
   that the neighboring IP destination address for the RERR is chosen,
   and in the way that the set of UnreachableAddrs is identified.

   In both cases, the msg_hop_limit MUST be included and SHOULD be set
   to MAX_HOPCOUNT.  msg_hop_count SHOULD be included and set to 0, to
   facilitate use of various route repair strategies including expanding
   rings multicast and Intermediate RREP [I-D.perkins-irrep].

9.3.1.  Case 1: Undeliverable Packet

   The first case happens when the router receives a packet from another
   AODVv2 router but does not have a valid route for the destination of
   the packet.  In this case, there is exactly one UnreachableAddr to be
   included in the RERR's AddressList (either the Destination Address of
   the IP header from a data packet, or the OrigAddr found in the
   AddressList of an RREP message).  The RERR SHOULD be sent to the
   multicast address LL-MANET-Routers, but RERR_Gen MAY instead send the
   RERR to the next hop towards the source IP address of the packet
   which was undeliverable.  For unicast RERR, the PktSource data
   element MUST be included, containing the the source IP address of the
   undeliverable packet, or TargAddr in case the undeliverable packet
   was an RREP message for a route to TargAddr.  If a Sequence Number
   for UnreachableAddr is known, that Sequence Number SHOULD be included
   in a Seqnum data element the RERR.  Otherwise all nodes handling the



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   RERR will assume their route through RERR_Gen towards the
   UnreachableAddr is no longer valid and mark those routes as broken,
   regardless of the Sequence Number information for those routes.
   RERR_Gen MUST discard the packet or message that triggered generation
   of the RERR.

   If an AODVv2 router receives an ICMP packet from the address of one
   of its client nodes, it simply relays the packet to the ICMP packet's
   destination address, and does not generate any RERR message.

9.3.2.  Case 2: Broken Link

   The second case happens when the link breaks to an active adjacent
   AODVv2 router (i.e., the next hop of an active route).  In this case,
   the RERR MUST be sent to the multicast address LL-MANET-Routers,
   except when the optional feature of maintaining precursor lists is
   used as specified in Section 14.3.  All routes (Active, Idle and
   Expired) that use the broken link MUST be marked as Broken.  The
   AddressList (which will contain the Unreachable Addresses) is
   initialized by first identifying those Active routes which use the
   broken link.  For each such Active Route, Route.Dest is added to the
   AddressList.  After the Active Routes using the broken link have all
   been indicated in the AddressList, Idle routes MAY also be included,
   if allowed by the setting of ENABLE_IDLE_IN_RERR, as long as the
   packet size of the RERR does not exceed the MTU (interface "Maximum
   Transfer Unit") of the physical medium.

   If there are no Unreachable Addresses in the AddressList, no RERR is
   generated.  Otherwise, RERR_Gen generates a new RERR using the
   AddressList.  If any Unreachable Address is associated with a routing
   prefix (i.e., a prefix length shorter than the maximum length for the
   address family), then the AddressList MUST be accompanied by a
   PrefixLengthList; otherwise, if no such entry, the PrefixLengthList
   SHOULD NOT be included.  The value (from the route table) for each
   Unreachable Address's SeqNum MUST be placed in the SeqNum data
   element.

   Every broken route reported in the RERR MUST have the same
   MetricType.  If the MetricType is not DEFAULT_METRIC_TYPE, then the
   RERR message MUST contain a MetricType data element indicating the
   MetricType of the broken route(s).

9.4.  Receiving and Handling RERR Messages

   When an AODVv2 router (HandlingRtr) receives a RERR message, it uses
   the information provided to mark affected routes as broken.  If
   HandlingRtr has neighbors that are using the affected routes, then
   HandlingRtr subsequently sends an RERR message to those neighbors.



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   This regeneration of the RERR message is counted as another "hop" for
   purposes of properly modifying msg_hop_limit and msg_hop_count in the
   RERR message header.

   HandlingRtr examines the incoming RERR to assure that it contains
   msg_hop_limit and at least one Unreachable Address; otherwise, the
   incoming RERR message is disregarded and further processing stopped.
   For each UnreachableAddr, HandlingRtr searches its route table for a
   route using longest prefix matching.  If no such Route is found,
   processing is complete for that UnreachableAddr.  Otherwise,
   HandlingRtr verifies the following:

   1.  The UnreachableAddr is a routable unicast address.
   2.  Route.NextHopAddress is the same as the SourceAddress in the IP
       header of the RERR packet.
   3.  Route.NextHopInterface is the same as the interface on which the
       RERR was received.
   4.  The UnreachableAddr.SeqNum is unknown, OR Route.SeqNum <=
       UnreachableAddr.SeqNum (using signed 16-bit arithmetic).

   If the Route satisfies all of the above conditions, HandlingRtr
   checks whether Route.PrefixLength is the same as the prefix length
   for UnreachableAddr.  If so, HandlingRtr simply sets the state for
   that Route to be Broken.  Otherwise, HandlingRtr creates a new route
   (call it BrokenRoute) with the same PrefixLength as the prefix length
   for UnreachableAddr, and sets Route.State == Broken for BrokenRoute.
   If the prefix length for the new route is shorter than
   Route.PrefixLength, then Route MUST be expunged from the route table
   (since it is a subroute of the larger route which is reported to be
   broken).  If msg_hop_limit is 0, then HandlingRtr takes no further
   action on the RERR message.

   If there are no UnreachableAddrs to be transmitted in an RERR to
   upstream routers, HandlingRtr takes no further action on the RERR
   message.

   Otherwise, msg_hop_limit is decremented by one (1) and processing
   continues as follows:

   o  The UnreachableAddrs data element is included in the RERR.
   o  msg_hop_limit is decremented by one (1).
   o  (Optional) If precursor lists are maintained, the outgoing RERR
      SHOULD be sent to the active precursors of the broken route as
      specified in Section 14.3.
   o  Otherwise, if the incoming RERR message was received at the LL-
      MANET-Routers [RFC5498] multicast address, the outgoing RERR
      SHOULD be sent to LL-MANET-Routers.




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   o  Otherwise, if the PktSource data element is present, and
      HandlingRtr has a Route to PktSource.Addr, then HandlingRtr MUST
      send the outgoing RERR to Route[PktSource.Addr].NextHop.
   o  Otherwise, the outgoing RERR MUST be sent to LL-MANET-Routers.

10.  Representing AODVv2 data elements using RFC 5444

   AODVv2 specifies that all control plane messages between Routers
   SHOULD use the Generalised Mobile Ad-hoc Network Packet and Message
   Format [RFC5444], which provides a multiplexed transport for multiple
   protocols.  AODVv2 therefore specifies Route Messages comprising data
   elements that map to message elements in RFC5444 but, in line with
   the concept of use, does not specify which order the messages should
   be arranged in an RFC5444 packet.  An implementation of an RFC5444
   parser may choose to optimise the content of certain message elements
   to reduce control plane overhead.

   Here is a brief summary of the RFC 5444 format.

      A packet formatted according to RFC 5444 contains zero or more
      messages.
      A message contains a message header, message TLV block, and zero
      or more address blocks.
      Each address block MAY also have an associated TLV block; this TLV
      block MAY encode multiple TLVs.  Each such TLV may include an
      array of values.  The list of TLV values may be associated with
      various subsets of the addresses in the address block.

   If a packet contains only a single AODVv2 message and no packet TLVs,
   it need only include a minimal Packet-Header [RFC5444].  The length
   of an address (32 bits for IPv4 and 128 bits for IPv6) inside an
   AODVv2 message is indicated by the msg-addr-length (MAL) in the msg-
   header, as specified in [RFC5444].

   This section specifies a way to represent the data elements specified
   by AODVv2 within RFC 5444 message format.

   Type-Length-Value structure (TLV)
      A generic way to represent information, conformant to use in
      [RFC5444].

   AODVv2 uses the following RFC5444 message elements:


   o  Message Hop Count, <msg-hop-count>, which should be mapped to the
      <msg-hop-count> element in <msg-header>.
   o  Message Hop Limit, <msg-hop-limit>, which should be mapped to the
      <msg-hop-limit> element in <msg-header>.



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   +---------------------+---------------------------------------------+
   | Data Element        | RFC 5444 Message Representation             |
   +---------------------+---------------------------------------------+
   | msg_hop_limit       | RFC 5444 Message Header <msg-hop-count>     |
   | msg_hop_count       | RFC 5444 Message Header <msg-hop-limit>     |
   | AckReq              | Acknowledgement Requested Message TLV       |
   | MetricType          | Metric Type Message TLV                     |
   | AddressList         | RFC 5444 Address TLV Block                  |
   | PrefixLengthsList   | Included in RFC 5444 Address TLV Block      |
   | MetricList          | Metric Address Block TLV                    |
   | SeqNumList          | Sequence Number Address Block TLV           |
   | OrigSeqNum          | Originating Node Sequence Number Address    |
   |                     | Block TLV                                   |
   | TargSeqNum          | Target Node Sequence Number Address Block   |
   |                     | TLV                                         |
   | OrigAddr            | Included in AddressList                     |
   | TargAddr            | Included in AddressList                     |
   | UnreachableAddr     | Included in AddressList                     |
   | SeqNum              | Included in SeqNumList                      |
   | Metric              | Included in MetricList                      |
   +---------------------+---------------------------------------------+

                                  Table 3

   For handling of messages that contain unknown TLV types, ignore the
   information for processing, but preserve it unmodified for
   forwarding.

11.  Simple Internet Attachment

   Simple Internet attachment means attachment of a stub (i.e., non-
   transit) network of AODVv2 routers to the Internet via a single
   Internet AODVv2 router (called IAR).

   As in any Internet-attached network, AODVv2 routers, and their
   clients, wishing to be reachable from hosts on the Internet MUST have
   IP addresses within the IAR's routable and topologically correct
   prefix (e.g. 191.0.2.0/24).













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        /-------------------------\
       / +----------------+        \
      /  |  AODVv2 Router |         \
      |  |  191.0.2.2/32  |         |
      |  +----------------+         |            Routable
      |                       +-----+--------+   Prefix
      |                       |   Internet   |  /191.0.2/24
      |                       | AODVv2 Router| /
      |                       |  191.0.2.1   |/      /---------------\
      |                       | serving net  +------+    Internet     \
      |                       |  191.0.2/24  |      \                 /
      |                       +-----+--------+       \---------------/
      |         +----------------+  |
      |         |  AODVv2 Router |  |
      |         |  191.0.2.3/32  |  |
      \         +----------------+  /
       \                           /
        \-------------------------/

               Figure 3: Simple Internet Attachment Example

   When an AODVv2 router within the AODVv2 MANET wants to discover a
   route toward a node on the Internet, it uses the normal AODVv2 route
   discovery for that IP Destination Address.  The IAR MUST respond to
   RREQ on behalf of all Internet destinations.

   When a packet from a node on the Internet destined for a node in the
   AODVv2 MANET reaches the IAR, if the IAR does not have a route toward
   that destination it will perform normal AODVv2 route discovery for
   that destination.

12.  Multiple Interfaces

   AODVv2 MAY be used with multiple interfaces; therefore, the
   particular interface over which packets arrive MUST be known whenever
   a packet is received.  Whenever a new route is created, the interface
   through which the route's destination can be reached is also recorded
   in the route table entry.

   When multiple interfaces are available, a node transmitting a
   multicast packet to LL-MANET-Routers MUST send the packet on all
   interfaces that have been configured for AODVv2 operation.

   Similarly, AODVv2 routers MUST subscribe to LL-MANET-Routers on all
   their AODVv2 interfaces.






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13.  AODVv2 Control Message Generation Limits

   To avoid congestion, each AODVv2 router's rate of packet/message
   generation SHOULD be limited.  The rate and algorithm for limiting
   messages (CONTROL_TRAFFIC_LIMITS) is left to the implementor and
   should be administratively configurable.  AODVv2 messages SHOULD be
   discarded in the following order of preference: RREQ, RREP, and
   finally RERR.

14.  Optional Features

   Some optional features of AODVv2, associated with AODV, are not
   required by minimal implementations.  These features are expected to
   apply in networks with greater mobility, or larger node populations,
   or requiring reduced latency for application launches.  The optional
   features are as follows:

   o  Expanding Rings Multicast
   o  Intermediate RREPs (iRREPs): Without iRREP, only the destination
      can respond to a RREQ.
   o  Precursor lists.
   o  Reporting Multiple Unreachable Addresses: a RERR message can carry
      more than one Unreachable Destination Address for cases when a
      single link breakage causes multiple destinations to become
      unreachable from an intermediate router.
   o  RREP_ACK.
   o  Message Aggregation.

14.1.  Expanding Rings Multicast

   For multicast RREQ, msg_hop_limit MAY be set in accordance with an
   expanding ring search as described in [RFC3561] to limit the RREQ
   propagation to a subset of the local network and possibly reduce
   route discovery overhead.

14.2.  Intermediate RREP

   This specification has been published as a separate Internet Draft
   [I-D.perkins-irrep].

14.3.  Precursor Lists and Notifications

   This section specifies an interoperable enhancement to AODVv2 (and
   possibly other reactive routing protocols) enabling more economical
   notifications to traffic sources upon determination that a route
   needed to forward such traffic to its destination has become Broken.





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14.3.1.  Overview

   In many circumstances, there can be several sources of traffic for a
   certain destination.  Each such source of traffic is known as a
   "precursor" for the destination, as well as all upstream routers
   between the forwarding AODVv2 router and the traffic source.  For
   each destination, an AODVv2 router MAY choose to keep track of the
   upstream neighbors that have provided traffic for that destination;
   there is no need to keep track of upstream routers any farther away
   than the next hop.

   Moreover, any particular link to an adjacent AODVv2 router may be a
   path component of multiple routes towards various destinations.  The
   precursors for all destinations using the next hop across any link
   are collectively known as the precursors for that next hop.

   When an AODVv2 router determines that an link to one of its neighbors
   has broken, the AODVv2 router detecting the broken link must mark
   multiple routes as Broken, for each of the newly unreachable
   destinations, as described in Section 9.3.  Each route that relies on
   the newly broken link is no longer valid.  Furthermore, the
   precursors of the broken link should be notified (using RERR) about
   the change in status of their route to a destination relying upon the
   broken next hop.

14.3.2.  Precursor Notification Details

   During normal operation, each AODVv2 router wishing to maintain
   precursor lists as described above, maintains a precursor table and
   updates the table whenever the node forwards traffic to one of the
   destinations in its route table.  For each precursor in the precursor
   list, a record must be maintained to indicate whether the precursor
   has been used for recent traffic (in other words, whether the
   precursor is an Active precursor).  So, when traffic arrives from a
   precursor, the Current_Time is used to mark the time of last use for
   the precursor list element associated with that precursor.

   When an AODVv2 router detects that a link is broken, then for each
   precursor using that next hop, the node MAY notify the precursor
   using either unicast or multicast RERR:

   unicast RERR to each Active precursor
      This option is applicable when there are few Active precursors
      compared to the number of neighboring AODVv2 routers.
   multicast RERR to RERR_PRECURSORS
      RERR_PRECURSORS is, by default, LL-MANET-Routers [RFC5498].  This
      option is typically preferable when there are many precursors,
      since fewer packet transmissions are required.



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   Each upstream neighbor (i.e., precursor) MAY then execute the same
   procedure until all upstream routers have received the RERR
   notification.

14.4.  Multicast RREP Response to RREQ

   The RREQ Target Router (RREP_Gen) MAY, as an alternative to
   unicasting a RREP, be configured to distribute routing information
   about the route toward TargAddr.  That is, RREP_Gen MAY be configured
   respond to a route discovery by generating a RREP, using the
   procedure in Section 8.4, but multicasting the RREP to LL-MANET-
   Routers [RFC5498] (subject to similar suppression algorithm for
   redundant RREP multicasts as described in Section 8.6).  The
   redundant message suppression must occur at every router handling the
   multicast RREP.  Afterwards, RREP_Gen processing for the incoming
   RREQ is complete.

   Broadcast RREP response to incoming RREQ was originally specified to
   handle unidirectional links, but it is expensive.  Due to the
   significant overhead, AODVv2 routers MUST NOT use multicast RREP
   unless configured to do so by setting the administrative parameter
   USE_MULTICAST_RREP.

14.5.  RREP_ACK

   Instead of relying on existing mechanisms for requesting verification
   of link bidirectionality during Route Discovery, RREP_Ack is provided
   as an optional feature and modeled on the RREP_Ack message type from
   AODV [RFC3561].

   Since the RREP_ACK is simply echoed back to the node from which the
   RREP was received, there is no need for other data elements.
   Considerations of packet TTL are as specified in Section 5.  An
   example message format is illustrated in section Appendix B.4.

14.6.  Message Aggregation

   The aggregation of multiple messages into a packet is specified in
   RFC 5444 [RFC5444].

   Implementations MAY choose to briefly delay transmission of messages
   for the purpose of aggregation (into a single packet) or to improve
   performance by using jitter [RFC5148].








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15.  Administratively Configurable Parameters and Timer Values

   AODVv2 uses various configurable parameters of various types:

   o  Timers
   o  Protocol constants
   o  Administrative (functional) controls
   o  Other administrative parameters and lists

   The tables in the following sections show the parameters along their
   definitions and default values (if any).

   Note: several fields have limited size (bits or bytes).  These sizes
   and their encoding may place specific limitations on the values that
   can be set.  For example, <msg-hop-count> is a 8-bit field and
   therefore MAX_HOPCOUNT cannot be larger than 255.

15.1.  Timers

   AODVv2 requires certain timing information to be associated with
   route table entries.  The default values are as follows, subject to
   future experience:

             +------------------------------+---------------+
             |             Name             | Default Value |
             +------------------------------+---------------+
             |       ACTIVE_INTERVAL        | 5 second      |
             |         MAX_IDLETIME         | 200 seconds   |
             |      MAX_BLACKLIST_TIME      | 200 seconds   |
             |     MAX_SEQNUM_LIFETIME      | 300 seconds   |
             |        RREQ_WAIT_TIME        | 2 seconds     |
             | UNICAST_MESSAGE_SENT_TIMEOUT | 1 second      |
             |      RREQ_HOLDDOWN_TIME      | 10 seconds    |
             +------------------------------+---------------+

                     Table 4: Timing Parameter Values

   The above timing parameter values have worked well for small and
   medium well-connected networks with moderate topology changes.

   The timing parameters SHOULD be administratively configurable for the
   network where AODVv2 is used.  Ideally, for networks with frequent
   topology changes the AODVv2 parameters should be adjusted using
   either experimentally determined values or dynamic adaptation.  For
   example, in networks with infrequent topology changes MAX_IDLETIME
   may be set to a much larger value.





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15.2.  Protocol constants

   AODVv2 protocol constants typically do not require changes.  The
   following table lists these constants, along with their values and a
   reference to the specification describing their use.

   +------------------------+--------------------+---------------------+
   | Name                   | Default Value      | Description         |
   +------------------------+--------------------+---------------------+
   | DISCOVERY_ATTEMPTS_MAX | 3                  | Section 8.1         |
   | MAX_HOPCOUNT           | 20 hops            | Section 6.5         |
   | MAX_METRIC[i]          | Specified only for | Section 6.5         |
   |                        | HopCount           |                     |
   | MAXTIME                | [TBD]              | Maximum expressible |
   |                        |                    | clock time          |
   +------------------------+--------------------+---------------------+

                         Table 5: Parameter Values

15.3.  Administrative (functional) controls

   The following administrative controls may be used to change the
   operation of the network, by enabling optional behaviors.  These
   options are not required for correct routing behavior, although they
   may potentially reduce AODVv2 protocol messaging in certain
   situations.  The default behavior is to NOT enable most such options,
   options.  Packet buffering is enabled by default.

      +------------------------+------------------------------------+
      |          Name          | Description                        |
      +------------------------+------------------------------------+
      |  DEFAULT_METRIC_TYPE   | 3 (i.e, Hop Count (see [RFC6551])) |
      |  ENABLE_IDLE_IN_RERR   | Section 9.3.2                      |
      |      ENABLE_IRREP      | Section 8.3                        |
      |   USE_MULTICAST_RREP   | Section 14.4                       |
      +------------------------+------------------------------------+

               Table 6: Administratively Configured Controls

15.4.  Other administrative parameters and lists

   The following table lists contains AODVv2 parameters which should be
   administratively configured for each specific network.








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    +-----------------------+-----------------------+-----------------+
    | Name                  | Default Value         | Cross Reference |
    +-----------------------+-----------------------+-----------------+
    | AODVv2_INTERFACES     |                       | Section 4       |
    | BUFFER_SIZE_PACKETS   | 2                     | Section 8.1     |
    | BUFFER_SIZE_BYTES     | MAX_PACKET_SIZE [TBD] | Section 8.1     |
    | CLIENT_ADDRESSES      | AODVv2_INTERFACES     | Section 6.3     |
    | CONTROL_TRAFFIC_LIMIT | TBD [50 packets/sec?] | Section 13      |
    +-----------------------+-----------------------+-----------------+

                 Table 7: Other Administrative Parameters

16.  IANA Considerations

   This section specifies several RFC 5444 message types, message tlv-
   types, and address tlv-types.  Also, a new registry of 16-bit
   alternate metric types is specified.

16.1.  AODVv2 Message Types Specification

          +----------------------------------------+------------+
          |                  Name                  | Type (TBD) |
          +----------------------------------------+------------+
          |          Route Request (RREQ)          |     10     |
          |           Route Reply (RREP)           |     11     |
          |           Route Error (RERR)           |     12     |
          | Route Reply Acknowledgement (RREP_ACK) |     13     |
          +----------------------------------------+------------+

                       Table 8: AODVv2 Message Types

16.2.  Message TLV Type Specification

   +-----------------------------------+-------+---------+-------------+
   | Name                              |  Type |  Length | Cross       |
   |                                   | (TBD) |    in   | Reference   |
   |                                   |       |  octets |             |
   +-----------------------------------+-------+---------+-------------+
   | AckReq (Acknowledgment Request)   |   10  |    0    | Section 6.2 |
   | PktSource (Packet Source)         |   11  | 4 or 16 | Section 9.3 |
   | MetricType                        |   12  |    1    | Section 8.2 |
   +-----------------------------------+-------+---------+-------------+

                        Table 9: Message TLV Types







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16.3.  Address Block TLV Specification

   +-----------------------------+--------+--------------+-------------+
   | Name                        |  Type  | Length       | Value       |
   |                             | (TBD)  |              |             |
   +-----------------------------+--------+--------------+-------------+
   | Metric                      |   10   | depends on   | Section 8.2 |
   |                             |        | Metric Type  |             |
   | Sequence Number (SeqNum)    |   11   | 2 octets     | Section 8.2 |
   | Originating Node Sequence   |   12   | 2 octets     | Section 8.2 |
   | Number (OrigSeqNum)         |        |              |             |
   | Target Node Sequence Number |   13   | 2 octets     | Section 8.2 |
   | (TargSeqNum)                |        |              |             |
   | VALIDITY_TIME               |   1    | 1 octet      | [RFC5497]   |
   +-----------------------------+--------+--------------+-------------+

                Table 10: Address Block TLV (AddrTLV) Types

16.4.  Metric Type Number Allocation

   Metric types are identified according to the assignments as specified
   in [RFC6551].  The metric type of the Hop Count metric is assigned to
   be 3, in order to maintain compatibility with that existing table of
   values from RFC 6551.  Non-addititve metrics are not supported in
   this draft.

            +-----------------------+----------+-------------+
            |          Name         |   Type   | Metric Size |
            +-----------------------+----------+-------------+
            |      Unallocated      |  0 -- 2  |     TBD     |
            |       Hop Count       | 3 - TBD  |   1 octet   |
            |      Unallocated      | 4 -- 254 |     TBD     |
            |        Reserved       |   255    |  Undefined  |
            +-----------------------+----------+-------------+

                          Table 11: Metric Types

17.  Security Considerations

   The objective of the AODVv2 protocol is for each router to
   communicate reachability information about addresses for which it is
   responsible.  Positive routing information (i.e. a route exists) is
   distributed via RREQ and RREP messages.  Negative routing information
   (i.e. a route does not exist) is distributed via RERRs.  AODVv2
   routers store the information contained in these messages in order to
   properly forward data packets, and they generally provide this
   information to other AODVv2 routers.




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   This section does not mandate any specific security measures.
   Instead, this section describes various security considerations and
   potential avenues to secure AODVv2 routing.

   The most important security mechanisms for AODVv2 routing are
   integrity/authentication and confidentiality.

   In situations where routing information or router identity are
   suspect, integrity and authentication techniques SHOULD be applied to
   AODVv2 messages.  In these situations, routing information that is
   distributed over multiple hops SHOULD also verify the integrity and
   identity of information based on originator of the routing
   information.

   A digital signature could be used to identify the source of AODVv2
   messages and information, along with its authenticity.  A nonce or
   timestamp SHOULD also be used to protect against replay attacks.  S/
   MIME and OpenPGP are two authentication/integrity protocols that
   could be adapted for this purpose.

   In situations where confidentiality of AODVv2 messages is important,
   cryptographic techniques can be applied.

   In certain situations, for example sending a RREP or RERR, an AODVv2
   router could include proof that it has previously received valid
   routing information to reach the destination, at one point of time in
   the past.  In situations where routers are suspected of transmitting
   maliciously erroneous information, the original routing information
   along with its security credentials SHOULD be included.

   Note that if multicast is used, any confidentiality and integrity
   algorithms used MUST permit multiple receivers to handle the message.

   Routing protocols, however, are prime targets for impersonation
   attacks.  In networks where the node membership is not known, it is
   difficult to determine the occurrence of impersonation attacks, and
   security prevention techniques are difficult at best.  However, when
   the network membership is known and there is a danger of such
   attacks, AODVv2 messages must be protected by the use of
   authentication techniques, such as those involving generation of
   unforgeable and cryptographically strong message digests or digital
   signatures.  While AODVv2 does not place restrictions on the
   authentication mechanism used for this purpose, IPsec Authentication
   Message (AH) is an appropriate choice for cases where the nodes share
   an appropriate security association that enables the use of AH.

   In particular, routing messages SHOULD be authenticated to avoid
   creation of spurious routes to a destination.  Otherwise, an attacker



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   could masquerade as that destination and maliciously deny service to
   the destination and/or maliciously inspect and consume traffic
   intended for delivery to the destination.  RERR messages SHOULD be
   authenticated in order to prevent malicious nodes from disrupting
   routes between communicating nodes.

   If the mobile nodes in the ad hoc network have pre-established
   security associations, the purposes for which the security
   associations are created should include that of authorizing the
   processing of AODVv2 control packets.  Given this understanding, the
   mobile nodes should be able to use the same authentication mechanisms
   based on their IP addresses as they would have used otherwise.

   If the mobile nodes in the ad hoc network have pre-established
   security associations, the purposes for which the security
   associations Most AODVv2 messages are transmitted to the multicast
   address LL-MANET-Routers [RFC5498].  It is therefore required for
   security that AODVv2 neighbors exchange security information that can
   be used to insert an ICV [RFC6621] into the AODVv2 message block
   [RFC5444].  This enables hop-by-hop security.  For destination-only
   RREP discovery procedures, AODVv2 routers that share a security
   association SHOULD use the appropriate mechanisms as specified in RFC
   6621.  The establishment of these security associations is out of
   scope for this document.

18.  Acknowledgments

   AODVv2 is a descendant of the design of previous MANET on-demand
   protocols, especially AODV [RFC3561] and DSR [RFC4728].  Changes to
   previous MANET on-demand protocols stem from research and
   implementation experiences.  Thanks to Elizabeth Belding-Royer for
   her long time authorship of AODV.  Additional thanks to Derek Atkins,
   Emmanuel Baccelli, Abdussalam Baryun, Ramon Caceres, Thomas Clausen,
   Christopher Dearlove, Ulrich Herberg, Henner Jakob, Luke Klein-
   Berndt, Lars Kristensen, Tronje Krop, Koojana Kuladinithi, Kedar
   Namjoshi, Alexandru Petrescu, Henning Rogge, Fransisco Ros, Pedro
   Ruiz, Christoph Sommer, Lotte Steenbrink, Romain Thouvenin, Richard
   Trefler, Jiazi Yi, Seung Yi, and Cong Yuan, for their reviews AODVv2
   and DYMO, as well as numerous specification suggestions.

19.  References

19.1.  Normative References

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





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   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, October 2007.

   [RFC5444]  Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
              "Generalized Mobile Ad Hoc Network (MANET) Packet/Message
              Format", RFC 5444, February 2009.

   [RFC5497]  Clausen, T. and C. Dearlove, "Representing Multi-Value
              Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March
              2009.

   [RFC5498]  Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network
              (MANET) Protocols", RFC 5498, March 2009.

   [RFC6551]  Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
              Barthel, "Routing Metrics Used for Path Calculation in
              Low-Power and Lossy Networks", RFC 6551, March 2012.

19.2.  Informative References

   [I-D.perkins-irrep]
              Perkins, C. and I. Chakeres, "Intermediate RREP for
              dynamic MANET On-demand (AODVv2) Routing", draft-perkins-
              irrep-02 (work in progress), November 2012.

   [Perkins94]
              Perkins, C. and P. Bhagwat, "Highly Dynamic Destination-
              Sequenced Distance-Vector Routing (DSDV) for Mobile
              Computers", Proceedings of the ACM SIGCOMM '94 Conference
              on Communications Architectures, Protocols and
              Applications, London, UK, pp. 234-244, August 1994.

   [Perkins99]
              Perkins, C. and E. Royer, "Ad hoc On-Demand Distance
              Vector (AODV) Routing", Proceedings of the 2nd IEEE
              Workshop on Mobile Computing Systems and Applications, New
              Orleans, LA, pp. 90-100, February 1999.

   [RFC2501]  Corson, M. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501, January 1999.

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





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   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4728]  Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source
              Routing Protocol (DSR) for Mobile Ad Hoc Networks for
              IPv4", RFC 4728, February 2007.

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

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

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

   [RFC6621]  Macker, J., "Simplified Multicast Forwarding", RFC 6621,
              May 2012.

Appendix A.  Example Algorithms for AODVv2 Protocol Operations

   The following subsections show example algorithms for protocol
   operations required by AODVv2, including RREQ, RREP, RERR, and RREP-
   ACK.

   Processing for RREQ, RREP, and RERR messages follows the following
   general outline:

   1.  Receive incoming message.
   2.  Update route table as appropriate.
   3.  Respond as needed, often regenerating the incoming message with
       updated information.

   Once the route table has been updated, the information contained
   there is known to be the most recent available information for any
   fields in the outgoing message.  For this reason, the algorithms are
   written as if outgoing message field values are assigned from the
   route table information, even though it is often equally appropriate
   to use fields from the incoming message.

   AODVv2_algorithms:

   o  Process_Routing_Info
   o  Generate_RREQ
   o  Receive_RREQ



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   o  Regenerate_RREQ
   o  Generate_RREP
   o  Receive_RREP
   o  Regenerate_RREP
   o  Generate_RERR
   o  Receive_RERR
   o  Regenerate_RERR
   o  Generate_RREP_Ack
   o  Consume_RREP_Ack()
   o  Timeout RREP_Ack()

   The following lists indicate the meaning of the field names used in
   subsequent sections to describe message processing for the above
   algorithms.

   Incoming RREQ message parameters:

      inRREQ.origIP := originator IP address
      inRREQ.origSeq := originator IP sequence #
      inRREQ.metType := metric type
      inRREQ.origMet := metric to originator
      inRREQ.targIP := target IP address
      inRREQ.targSeq := target sequence # (if known)
      inRREQ.hopLim := msg-hop-limit /* from RFC 5444 header */
      inRREQ.nbrIP := IP address of the neighbor that sent the RREQ

   Outgoing RREQ message parameters:

      outRREQ.origIP := originator IP address
      outRREQ.origSeq := originator IP sequence #
      outRREQ.metType := metric type
      outRREQ.origMet := metric to origNode {initially
      MIN_METRIC[MetType]}
      outRREQ.targIP := target IP address
      outRREQ.targSeq := target sequence # (if known)
      outRREQ.hopLim /* initially MAX_HOPCOUNT at originator */

   Incoming RREP message parameters:

      inRREP.hoplim /* msg-hop-limit from RFC 5444 header */
      inRREP.origIP := originator's IP address
      inRREP.metType := metric type
      inRREP.targIP := target IP address
      inRREP.targSeq := target sequence #
      inRREP.targMet := target's metric {initially MIN_METRIC[MetType]}
      inRREP.PfxLen

   Outgoing RREP message parameters:



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      outRREP.origIP := originator's IP address
      outRREP.metType := metric type
      outRREP.targIP := target IP address
      outRREP.targSeq := target sequence #
      outRREP.targMet := target's metric {starting with zero}
      outRREP.PfxLen
      outRREP.hopLim /* initially MAX_HOPCOUNT at originator */

   Incoming RERR message parameters:

      inRERR.PktSrc := source IP of unforwardable packet (if present)
      inRERR.metType := metric type for routes to unreachable
      destinations
      inRERR.PfxLen[] := prefix lengths for unreachable destinations
      inRERR.LostDest[] := unreachable destinations
      inRERR.LostSeq[] := sequence #s for unreachable destinations

   Outgoing RERR message parameters:

      outRERR.PktSrc := source IP of unforwardable packet (if present)
      outRERR.metType := metric type for routes to unreachable
      destinations
      outRERR.PfxLen[] := prefix lengths for unreachable destinations
      outRERR.LostDest[] := unreachable destinations
      outRERR.LostSeq[] := sequence #s for unreachable destinations

A.1.  Subroutines for AODVv2 Protocol Operations
























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    /* Compare incoming route information to current route, maybe use */
    Process_Routing_Info (dest, seq#, metric_type, metric,
                                                       last_hop_metric)
      /* last_hop_metric: either Cost(inRREQ.netif) or (inRREP.netif) */
    {
  new_metric := metric + last_hop_metric;
  rte := Fetch_Route_Table_Entry (dest, seq#, metric_type);
  if (NULL == rte) {
      rte := Create_Route_Table_Entry
        (dest, seq#, metric_type, new_metric);
  } else if (seq# > rte.seq#) { /* stale rte route entry */
      Update_Route_Table_Entry (rte, seq#, metric_type, new_metric);
  } else if (seq# < rte.seq#) { /* stale incoming route infor */
      return(NULL);
  } else if (rte.state == broken) {  /* when (seq# == rte.seq#) */
      Update_Route_Table_Entry (rte, seq#, metric_type, new_metric);
  } else if (rte.metric > (new_metric) { /* and (seq# == rte.seq#) */
      Update_Route_Table_Entry (rte, seq#, metric_type, new_metric);
  } else {  /* incoming route information is not useful */
      return(NULL);
  }
  return (rte);
    }



A.2.  Example Algorithms for AODVv2 RREQ Operations

A.2.1.  Generate_RREQ






















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      Generate_RREQ {
    /* Marshall parameters */
    outRREQ.origIP := IP address used by application
    outRREQ.origSeq := originating router's sequence #
    outRREQ.metType := (if included) metric type needed by application
    outRREQ.origMet := 0 (default) or MIN_METRIC(Metric_type)
    outRREQ.targIP := target IP address
    outRREQ.targSeq := target sequence # /* if known from route table */
    outRREQ.hopLim := msg-hop-limit   /* RFC 5444 */

    /* build RFC 5444 message header fields */
    {
      msg-type=RREQ (message is of type RREQ)
      MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
      MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
      msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
      msg-hop-limit := MAX_HOPCOUNT
      if (Metric_type == DEFAULT) {
        msg.tlvs-length=0
      } else { /* Metric_type != HopCount */
        /* Build Metric_type Message TLV */
      }
    }

    /* build AddrBlk */
    num-addr := 2
    AddrBlk := {outRREQ.origIP and outRREQ.targIP addresses}

    /* Include each available Sequence Number in appropriate AddrTLV */
      /* put outRREQ.origSeq in OrigSeqNum AddrTLV */
      if (NULL != targSeq) {
        /* put outRREQ.targSeq in TargSeqNum AddrTLV */
      }

    /* Build Metric AddrTLV containing OrigAddr metric */
      /* use MIN_METRIC(metric type) [==0 for default metric type */
      }


A.2.2.  Receive_RREQ











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       Receive_RREQ (inRREQ) {
     /* Extract inRREQ values */
     origRTE = Process_Routing_Info (inRREQ.origIP, inRREQ.origSeq, ...)
     if (inRREQ.targIP belongs to me or my client subnet) {
       Generate_RREP()
     } else if (inRREQ present in RREQ_table) {
       return;   /* don't regenerate RREQ... */
     } else if (inRREQ.nbrIP not present in blacklist) {
       Regenerate_RREQ(origRTE, inRREQ)
     } else if (blacklist_expiration_time > current_time) {
       return;   /* don't regenerate RREQ... */
     } else {
       Remove nbrIP from blacklist;
       Regenerate_RREQ(origRTE, inRREQ)
     }
       }


A.2.3.  Regenerate_RREQ
































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    Regenerate_RREQ (origRTE, inRREQ) { /* called from receive_RREQ() */
  outRREQ.hopLim := inRREQ.hopLim - 1
  if (outRREQ.hopLim == 0) {  /* don't regenerate */
    return()
  }
  /* Marshall parameters */
  outRREQ.origIP := origRTE.origIP
  outRREQ.origSeq := origRTE.origSeq
  outRREQ.origMet := origRTE.origMet
  outRREQ.metType := origRTE.metType
  outRREQ.targIP := inRREQ.targIP
  outRREQ.targSeq := inRREQ.targSeq /* if present */

  /* build RFC 5444 message header fields */
  {
    msg-type=RREQ (message is of type RREQ)
    MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
    MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
    msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
    msg-hop-limit := MAX_METRIC(Metric Type) (default, MAX_HOPCOUNT)
    if (Metric_type == DEFAULT) {
      msg.tlvs-length=0
    } else { /* Metric_type != HopCount */
      /* Build Metric_type Message TLV */
    }
  }

  /* build AddrBlk */
  num-addr := 2
  AddrBlk := {outRREQ.origIP and outRREQ.targIP addresses}

  /* Include each available Sequence Number in its proper AddrTLV */
  /* put outRREQ.origSeq in OrigSeqNum AddrTLV */
  if (NULL != targSeq) {
    /* put outRREQ.targSeq in TargSeqNum AddrTLV */
  }

  /* Build Metric AddrTLV to contain outRREQ.origMet */

    }


A.3.  Example Algorithms for AODVv2 RREP Operations








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A.3.1.  Generate_RREP


       Generate_RREP {
     /* Marshall parameters */
     outRREP.origIP := origRTE.origIP
     metric_type := origRTE.metType  /* if not default */
     if (DEFAULT != metric_type)
       outRREP.metType := metric_type
     outRREP.targIP := inRREQ.targIP
     outRREP.targMet := MIN_METRIC(outRREP.metType) (0  by default)
     my_sequence_# := (1 + my_sequence_#) /* from nonvolatile storage */
     outRREP.targSeq := my_sequence_#

     /* build RFC 5444 message header fields */
     {
       msg-type=RREP
       MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
       MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
       msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
       msg-hop-limit := MAX_HOPCOUNT
       /* Include the AckReq TLV when:
          - previous RREP does not seem to enable any data flow, OR
          - when RREQ is received from same OrigAddr after RREP was
            unicast to targRTE.nextHop
        */
       if (DEFAULT != metric_type) {
         msg.tlvs-length=0
       } else { /* Metric_type != HopCount */
         /* Build Metric_type Message TLV */
       }
     }

     /* build AddrBlk */
     num-addr := 2
     AddrBlk := {outRREQ.origIP and outRREQ.targIP addresses}

     /* put outRREP.TargSeq in TargSeqNum AddrTLV */

     /* Build Metric AddrTLV containing TargAddr metric */
     /* use MIN_METRIC(origRTE.metType) */
       }









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A.3.2.  Receive_RREP


      Receive_RREP (inRREP)
      {
    If (RREP includes AckReq data element) {
      Generate_RREP_Ack()
    }
    /* Extract inRREP values */
    targRTE := Process_Routing_Info (inRREP.targIP, inRREP.targSeq, ...)
    if (inRREP.targIP belongs to me, a client, or a client subnet) {
      Consume_RREP(inRREP)
    } else {
      Regenerate_RREP(targRTE, inRREP)
    }
      }



































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A.3.3.  Regenerate_RREP


       Regenerate_RREP(targRTE, inRREP) {
     outRREP.hopLim := inRREP.hopLim - 1
     if (outRREP.hopLim == 0) {  /* don't regenerate */
       return()
     }
     /* Marshall parameters */
     outRREP.targIP := targRTE.targIP
     outRREP.targSeq := targRTE.targSeq
     outRREP.targMet := targRTE.targMet
     metric_type := origRTE.metType  /* if not default */
     if (DEFAULT != metric_type)
       outRREP.metType := metric_type
     outRREP.origIP := inRREP.origIP
     outRREP.nextHop := targRTE.nextHop

     /* build RFC 5444 message header fields */
     {
       msg-type=RREP (message is of type RREP)
       MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
       MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
       msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
       /* Include the AckReq data element when:
          - previous RREP does not seem to enable any data flow, OR
          - when RREQ is received from same OrigAddr after RREP was
            unicast to targRTE.nextHop
        */
       msg-hop-limit := outRREP.hopLim;
       if (metric_type == DEFAULT) {
         msg.tlvs-length=0
       } else { /* Metric_type != HopCount */
         /* Build Metric_type Message TLV */
       }
     }

     /* build AddrBlk */
     num-addr := 2
     AddrBlk := {outRREQ.origIP and outRREQ.targIP addresses}

     /* put outRREP.targSeq in TargSeqNum AddrTLV */

     /* Build Metric AddrTLV containing TargAddr metric */
       }






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A.3.4.  Consume_RREP


     /* executed by RREQ_Gen */
     /* TargAddr route table entry was updated by Receive_RREP() */
     Consume_RREP() {
       /* Transmit buffered packet(s) (if any) to TargAddr */
     }


A.4.  Example Algorithms for AODVv2 RERR Operations

A.4.1.  Generate_RERR


       Generate_RERR()
       {
     metric_type := DEFAULT;
     switch (error_type) in {
     case (broken_link):
       num-broken-addr=0
       /* find unreachable destinations, seqNums, prefixes */
       for (every rte (route table entry) in route table) {
           if (broken_link == rte.next_hop) {
         rte.state := broken;
         outRERR.LostDest[num-broken-addr] := rte.dest
         outRERR.LostSeq[num-broken-addr] := rte.seq#
         outRERR.PfxLen[num-broken-addr] := rte.pfx
         metric_type := rte.metType
         num-broken-addr := (num-broken-addr+1)
           }
       }
       /* No offending-src for this case */
     case (undeliverable packet):
       offending-src := undeliverable_packet.srcIP
       outRERR.LostDest[] := undeliverable_packet.destIP
       outRERR.LostPfxSiz[] := MAX_PFX_SIZE   /* 31 or 127 */
       num-broken-addr=1
     }

     /* build RFC 5444 message header fields */
     {
       msg-type=RERR (message is of type RERR)
       MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
       MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
       msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
       msg-hop-limit := outRERR.hopLim;
       if (NULL != offending-src) {



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         /* Build PktSource Message TLV */
       }
       if (metric_type != DEFAULT) { /* Metric_type != HopCount */
         /* Build Metric_type Message TLV */
       }
     }

     /* build AddrBlk */
     num-addr := num-broken-addr;
     AddrBlk := outRERR.LostDest[];

     /* Add AddrBlk Seq# TLV */
     Seq#TLV := outRERR.LostSeq[]

     /* only add AddrBlk PfxSiz TLV if prefixes are nondefault */
     for (pfx in outRERR.LostPfx[]) {
       if (pfx != Max_Prefix_Size) { /* 31 for IPv4, 127 for IPv6 */
         PfxSizTLV := outRERR.LostPfx[]
         return;
       }
     }
       }


A.4.2.  Receive_RERR


























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       Receive_RERR (inERR)
       {
     /* Extract inERR values */
     next_hop := inRERR.nbrIP
     offending-src := inRERR.offending-src;  /* NULL if not present */

     precursors[] := NULL;
     num-broken-addr := 0;
     in-broken-addr := 0;
     for (IPaddr := inRERR.LostDest[in-broken-addr]) {
       rte := Fetch_Route_Table_Entry (dest, metric_type);
       if (NULL == rte) {
         continue;
       } else if (rte.nextHop != inRERR.fromIP) {
         continue;
       } else if (NULL != rte.precursors) {
         /* add rte.precursors to precursors */
       } else if (rte.PfxSiz < inRERR.PfxSiz) {
       /***********************************************************
        If the reported prefix from the incoming RERR is *longer*
          than the prefix from Route Table, then create a new route
          with the longer prefix.
          The newly created route will be marked as broken, and used
          to regenerate RERR, NOT using shorter the routing prefix.
          This avoids unnecessarily invalidating the larger subnet.
        **********************************************************/
         rte := Create_Route_Table_Entry (IPaddr, seq#,
           metric_type, new_metric, inRERR.PfxSiz);
       }
       LostDest[num-broken-addr] := rte.Dest;
       Seq#[num-broken-addr] := rte.Seq#;
       PfxSiz[num-broken-addr] := rte.PfxSiz;
       rte.state = broken;
       num-broken-addr := (num-broken-addr + 1);
       in-broken-addr := (in-broken-addr + 1);
     }
     if (num-broken-addr > 0) {
       Regenerate_RERR (offending-src, precursors,
         LostDest[], Seq#[], PfxSiz[])
     }
       }


A.4.3.  Regenerate_RERR







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       Regenerate_RERR (offending-src, precursors,
       LostDest[], LostSeq#[], PfxSiz[])
       {
     /* build RFC 5444 message header fields */
     {
         msg-type=RERR (message is of type RERR)
         MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
         MAL=3 or 15 (Message Address Length [3 for IPv4, 15 for IPv6])
         msg-size=NN (octets -- counting MsgHdr, AddrBlk, and AddrTLVs)
         outRERR.hopLim := inRERR.hopLim - 1
         msg-hop-limit := outRERR.hopLim;

         if (NULL != offending-src) {
         /* Build PktSource Message TLV */
         }
         if (metric_type != DEFAULT) { /* Metric_type != HopCount */
         /* Build Metric_type Message TLV */
         }
     }

     /* build AddrBlk */
     num-addr := num-broken-addr;
     AddrBlk := LostDest[];

     /* Add AddrBlk Seq# TLV */
     Seq#TLV := LostSeq[]

     /* only add AddrBlk PfxSiz TLV if prefixes are nondefault */
     for (pfx in PfxSiz[]) {
       if (pfx != Max_Prefix_Size) { /* 31 for IPv4, 127 for IPv6 */
         PfxSizTLV := PfxSiz[]
       }
     } /* If all are default, don't include PfxSize AddrTLV */

     if (#precursors == 1) {
       unicast RERR to precursor[0];
     } else if (#precursors > 1) {
       multicast RERR to RERR_PRECURSORS;
     } else if (offending-src != NULL) {
       unicast RERR to offending-src;
     } else {
       multicast RERR to RERR_PRECURSORS;
     }
       }







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A.5.  Example Algorithms for AODVv2 RREP-Ack Operations

A.5.1.  Generate_RREP_Ack


       /* To be sent when RREP includes the AckReq TLV */
       Generate_RREP_Ack()
       {
     /* assign RFC 5444 fields */
     msgtype := RREPAck
     MF := 0
     MAL := 3
     msg-size := 4
       }


A.5.2.  Consume_RREP_Ack


       Consume_RREP_Ack()
       {
     /* turn off timeout event for the node sending RREP_Ack */
       }


A.5.3.  Timeout_RREP_Ack


       Timeout_RREP_Ack()
       {
     /* insert unresponsive node into blacklist */
       }


Appendix B.  Example RFC 5444-compliant packet formats

   The following subsections show example RFC 5444-compliant packets for
   AODVv2 message types RREQ, RREP, RERR, and RREP-Ack.  These proposed
   message formats are designed based on expected savings from IPv6
   addressable MANET nodes, and a layout for the Address TLVs that may
   be viewed as natural, even if perhaps not the absolute most compact
   possible encoding.

   For RteMsgs, the msg-hdr fields are followed by at least one and
   optionally two Address Blocks.  The first AddrBlk contains OrigAddr
   and TargAddr.  For each AddrBlk, there must be AddrTLVs of type
   Metric and one of the SeqNum types (i.e, OrigSeqNum, TargSeqNum, or
   Seqnum).



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   There is no Metric Type Message TLV present, so the Metric AddrTLV
   measures HopCount.  The Metric AddrTLV also provides a way for the
   AODV router generating the RREQ or RREP to supply an initial nonzero
   cost for the route to its client node (OrigAddr or TargAddr, for RREQ
   or RREP respectively).

   In all cases, the length of an address (32 bits for IPv4 and 128 bits
   for IPv6) inside an AODVv2 message is indicated by the msg-addr-
   length (MAL) in the msg-header, as specified in [RFC5444].

   The RFC 5444 header preceding AODVv2 messages in this document has
   the format illustrated in Figure 4.

        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
       +-+-+-+-+-+-+-+-+
       | PV=0 |  PF=0  |
       +-+-+-+-+-+-+-+-+

                     Figure 4: RFC 5444 Packet Header

   The fields in Figure 4 are to be interpreted as follows:

   o  PV=0 (Packet Header Version = 0)
   o  PF=0 (Packet Flags = 0)

B.1.  RREQ Message Format

   Figure 5 illustrates an example RREQ message format.






















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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-type=RREQ | MF=4  | MAL=3 |          msg-size=28          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-hop-limit |      msg.tlvs-length=0        |   num-addr=2  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |1|0|0|0|0| Rsv | head-length=3 | Head (bytes for Orig & Target):
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :Head(Orig&Targ)|   Orig.Mid    |  Target.Mid   |addr.TLV.len=11:
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :addr.TLV.len=11|type=OrigSeqNum|0|1|0|1|0|0|Rsv| Index-start=0 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | tlv-length=2  |     Orig.Node Sequence #      |  type=Metric  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|1|0|1|0|0|Rsv| Index-start=0 | tlv-length=1  | OrigAddrHopCt |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 5: Example IPv4 RREQ, with OrigSeqNum and Metric AddrTLVs

   The fields in Figure 5 are to be interpreted as follows:

   o  msg-type=RREQ (first [and only] message is of type RREQ)
   o  MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
   o  MAL=3 (Message Address Length indicator [3 for IPv4, 15 for IPv6])
   o  msg-size=28 (octets -- counting MsgHdr, MsgTLVs, and AddrBlks)
   o  msg-hop-limit (initially MAX_HOPCOUNT by default)
   o  msg.tlvs-length=0 (no Message TLVs)
   o  num-addr=2 (OrigAddr and TargAddr in RteMsg AddrBlock)
   o  AddrBlk flags:

      *  bit 0 (ahashead): 1
      *  bit 1 (ahasfulltail): 0
      *  bit 2 (ahaszerotail): 0
      *  bit 3 (ahassingleprelen): 0
      *  bit 4 (ahasmultiprelen): 0
      *  bits 5-7: RESERVED
   o  head-length=3 (length of head part of each address is 3 octets)
   o  Head (3 initial bytes for both Originating & Target addresses)
   o  Orig.Mid (4th byte of Originating Address)
   o  Target.Mid (4th byte of Target Address)
   o  addr.TLV.len = 11 (length in bytes for OrigSeqNum and Metric TLVs
   o  type=OrigSeqNum (type of first AddrBlk TLV, value 2 octets)
   o  AddrTLV flags for the OrigSeqNum TLV:

      *  bit 0 (thastypeext): 0
      *  bit 1 (thassingleindex): 1
      *  bit 2 (thasmultiindex): 0



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      *  bit 3 (thasvalue): 1
      *  bit 4 (thasextlen): 0
      *  bit 5 (tismultivalue): 0
      *  bits 6-7: RESERVED
   o  Index-start=0 (OrigSeqNum TLV value applies at index 0)
   o  tlv-length=2 (so there is only one TLV value, [1 = 2/2])
   o  Orig.Node Sequence # (TLV value for the OrigSeqNum TLV
   o  type=Metric (AddrTLV type of second AddrBlk TLV, values 1 octet)
   o  AddrTLV flags for Metric_TLV:

      *  bit 0 (thastypeext): 0
      *  bit 1 (thassingleindex): 1
      *  bit 2 (thasmultiindex): 0
      *  bit 3 (thasvalue): 1
      *  bit 4 (thasextlen): 0
      *  bit 5 (tismultivalue): 0
      *  bits 6-7: RESERVED
   o  Index-start=0 (Metric TLV values start at index 0)
   o  tlv-length=1 (so there is only one TLV value, [1 = 1/1])
   o  OrigAddrHopCt (first [and only] TLV value for the Metric TLV)

B.2.  RREP Message Format

   Figure 6 illustrates a packet format for an example RREP message.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-type=RREP | MF=4  | MAL=3 |          msg-size=28          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-hop-limit |      msg.tlvs-length=0        |   num-addr=2  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |1|0|0|0|0| Rsv | head-length=3 | Head (bytes for Orig & Target):
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :Head(Orig&Targ)|   Orig.Mid    |  Target.Mid   |addr.TLV.len=11:
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :addr.TLV.len=11|type=TargSeqNum|0|1|0|1|0|0|Rsv| Index-start=1 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | tlv-length=2  |     Targ.Node Sequence #      |  type=Metric  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|1|0|1|0|0|Rsv| Index-start=1 | tlv-length=1  | TargAddrHopCt |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 6: Example IPv4 RREP, with TargSeqNum TLV and 1 Metric







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   The fields in Figure 6 are to be interpreted as follows:

   o  msg-type=RREP (first [and only] message is of type RREP)
   o  MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
   o  MAL=3 (Message Address Length indicator [3 for IPv4, 15 for IPv6])
   o  msg-size=28 (octets -- counting MsgHdr, MsgTLVs, and AddrBlks)
   o  msg-hop-limit (initially MAX_HOPCOUNT by default)
   o  msg.tlvs-length=0 (no Message TLVs)
   o  num-addr=2 (OrigAddr and TargAddr in RteMsg AddrBlock)
   o  AddrBlk flags:

      *  bit 0 (ahashead): 1
      *  bit 1 (ahasfulltail): 0
      *  bit 2 (ahaszerotail): 0
      *  bit 3 (ahassingleprelen): 0
      *  bit 4 (ahasmultiprelen): 0
      *  bits 5-7: RESERVED
   o  head-length=3 (length of head part of each address is 3 octets)
   o  Head (3 initial bytes for both Originating & Target addresses)
   o  Orig.Mid (4th byte of Originating Address)
   o  Target.Mid (4th byte of Target Address)
   o  addr.TLV.len = 11 (length in bytes for TargSeqNum TLV and Metric
      TLV
   o  type=TargSeqNum (type of first AddrBlk TLV, value 2 octets)
   o  AddrTLV flags for the TargSeqNum TLV:

      *  bit 0 (thastypeext): 0
      *  bit 1 (thassingleindex): 1
      *  bit 2 (thasmultiindex): 0
      *  bit 3 (thasvalue): 1
      *  bit 4 (thasextlen): 0
      *  bit 5 (tismultivalue): 0
      *  bits 6-7: RESERVED
   o  Index-start=1 (TargSeqNum TLV value applies to address at index 1)
   o  tlv-length=2 (there is one TLV value, 2 bytes in length)
   o  Targ.Node Sequence # (value for the TargSeqNum TLV)
   o  type=Metric (AddrTLV type of second AddrBlk TLV, value 1 octet)
   o  AddrTLV flags for the Metric TLV [01010000, same as for TargSeqNum
      TLV]
   o  Index-start=1 (Metric TLV values start at index 1)
   o  tlv-length=1 (there is one TLV value, 1 byte in length)
   o  TargAddrHopCt (first [and only] TLV value for Metric TLV)









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B.3.  RERR Message Format

   Figure 7 illustrates an example RERR message format.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-type=RERR | MF=4  | MAL=3 |          msg-size=24          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | msg-hop-limit |      msg.tlvs-length=0        |   num-addr=2  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |1|0|0|0|0| Rsv | head-length=3 | Head (for both destinations)  :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :Head (3rd byte)|  Mid (Dest_1) | Mid (Dest_2)  | addr.TLV.len=7:
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :addr.TLV.len=7 |  type=SeqNum  |0|0|1|1|0|1|Rsv| tlv-length=4  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        Dest_1 Sequence #      |        Dest_2 Sequence #      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 7: Example IPv4 RERR with Two Unreachable Addresses

   The fields in Figure 7 are to be interpreted as follows:

   o  msg-type=RERR (first [and only] message is of type RERR)
   o  MF=4 (Message Flags = 4 [only msg-hop-limit field is present])
   o  MAL=3 (Message Address Length indicator [3 for IPv4, 15 for IPv6])
   o  msg-size=24 (octets -- counting MsgHdr, MsgTLVs, and AddrBlks)
   o  msg-hop-limit (initially MAX_HOPCOUNT by default)
   o  msg.tlvs-length=0 (no Message TLVs)
   o  num-addr=2 (OrigAddr and TargAddr in RteMsg AddrBlock)
   o  AddrBlk flags == 10000000 [same as RREQ and RREP AddrBlk examples]
   o  head-length=3 (length of head part of each address is 3 octets)
   o  Head (3 initial bytes for both Unreachable Addresses, Dest_1 and
      Dest_2)
   o  Dest_1.Mid (4th byte of Dest_1 IP address)
   o  Dest_2.Mid (4th byte of Dest_2 IP address)
   o  addr.TLV.len = 7 (length in bytes for SeqNum TLV
   o  type=SeqNum (AddrTLV type of AddrBlk TLV, values 2 octets each)
   o  AddrTLV flags for SeqNum TLV:

      *  bit 0 (thastypeext): 0
      *  bit 1 (thassingleindex): 0
      *  bit 2 (thasmultiindex): 1
      *  bit 3 (thasvalue): 1
      *  bit 4 (thasextlen): 0
      *  bit 5 (tismultivalue): 1
      *  bits 6-7: RESERVED



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   o  tlv-length=4 (so there are two TLV values, [2 = 4/2])
   o  Dest_1 Sequence # (first of two TLV values for the SeqNum TLV)
   o  Dest_2 Sequence # (second of two TLV values for the SeqNum TLV)

B.4.  RREP_ACK Message Format

   The figure below illustrates a packet format for an example RREP_ACK
   message.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |msgtype=RREPAck| MF=0  | MAL=3 |          msg-size=4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 8: Example IPv4 RREP_ACK








Appendix C.  Changes since revision ...-05.txt

   This section lists the changes since AODVv2 revision ...-05.txt

   o  Added Lotte Steenbrink as co-author.
   o  Reorganized section on Metrics to improve readability by putting
      specific topics into subsections.
   o  Introduced concept of data element, which is used to clarify the
      method of enabling RFC 5444 representation for AODVv2 data
      elements.  A list of Data Elements was introduced in section 3,
      which provides a better understanding of their role than was
      previously supplied by the table of notational devices.
   o  Replaced instances of OrigNode by OrigAddr whenever the more
      specific meaning is appropriate.  Similarly for instances of other
      node versus address terminology.
   o  Introduced concepts of PrefixLengthList and MetricList in order to
      avoid use of index-based terminology such as OrigNdx and TargNdx.
   o  Added section 5, "AODVv2 Message Transmission", describing the
      intended interface to RFC 5444.
   o  Included within the main body of the specification the mandatory
      setting of the TLV flag thassingleindex for TLVs OrigSeqNum and
      TargSeqNum.
   o  Removed the Route.Timed state.  Created a new flag for route table
      entries known as Route.Timed.  This flag can be set when the route



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      is in the active state.  Previous description would require that
      the route table entry be in two states at the same time, which
      seems to be misleading.  The new flag is used to clarify other
      specification details for Timed routes.
   o  Created table 3 to show the correspondence between AODVv2 data
      elements and RFC 5444 message components.
   o  Replaced "invalid" terminology by the more specific terms "broken"
      or "expired" where appropriate.
   o  Eliminated the instance of duplicate specification for inclusion
      of OrigNode (now, OrigAddr) in the message.
   o  Corrected the terminology to be Mid instead of Tail for the
      trailing address bits of OrigAddr and TargAddr for the example
      message formats in the appendices.
   o  Repaired remaining instances of phraseology that could be
      construed as indicating that AODV only supports a single network
      interface.
   o  Numerous editorial improvements and clarifications.

Appendix D.  Changes since revision ...-04.txt

   This section lists the changes since AODVv2 revision ...-04.txt

   o  Normative text moved out of definitions into the relevant section
      of the body of the specification.
   o  Editorial improvements and improvements to consistent terminology
      were made.  Replaced "retransmit" by the slightly more accurate
      term "regenerate".
   o  Issues were resolved as discussed on the mailing list.
   o  Changed definition of LoopFree as suggested by Kedar Namjoshi and
      Richard Trefler to avoid the failure condition that they have
      described.  In order to make understanding easier, replaced
      abstract parameters R1 by RteMsg and R2 by Route to reduce the
      level of abstraction when the function LoopFree is discussed.
   o  Added text to clarify that different metrics may have different
      data types and different ranges of acceptable values.
   o  Added text to section "RteMsg Structure" to emphasize the proper
      use of RFC 5444.
   o  Included within the main body of the specification the mandatory
      setting of the TLV flag thassingleindex for TLVs OrigSeqNum and
      TargSeqNum.
   o  Made more extensive use of the AdvRte terminology, in order to
      better distinguish between the incoming RREQ or RREP message
      (i.e., RteMsg) versus the route advertised by the RteMsg (i.e.,
      AdvRte).







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Appendix E.  Changes since revision ...-03.txt

   This section lists the changes since AODVv2 revision ...-03.txt

   o  An appendix was added to exhibit algorithmic code for
      implementation of AODVv2 functions.
   o  Numerous editorial improvements and improvements to consistent
      terminology were made.  Terminology related to prefix lengths was
      made consistent.  Some items listed in "Notational Conventions"
      were no longer used, and so deleted.
   o  Issues were resolved as discussed on the mailing list.
   o  Appropriate instances of "may" were changed to "MAY".
   o  Definition inserted for "upstream".
   o  Route.Precursors included as an *optional* route table field
   o  Reworded text to avoid use of "relevant".
   o  Deleted references to "DestOnly" flag.
   o  Refined statements about Metric Type TLV to allow for omission
      when Metric Type == HopCount.
   o  Bulletized list in section 8.1
   o  ENABLE_IDLE_UNREACHABLE renamed to be ENABLE_IDLE_IN_RERR
   o  Transmission and subscription to LL-MANET-Routers converted to
      MUST from SHOULD.

Appendix F.  Changes since revision ...-02.txt

   This section lists the changes since AODVv2 revision ...-02.txt

   o  The "Added Node" feature was removed.  This feature was intended
      to enable additional routing information to be carried within a
      RREQ or a RREP message, thus increasing the amount of topological
      information available to nodes along a routing path.  However,
      enlarging the packet size to include information which might never
      be used can increase congestion of the wireless medium.  The
      feature can be included as an optional feature at a later date
      when better algorithms are understood for determining when the
      inclusion of additional routing information might be worthwhile.
   o  Numerous editorial improvements and improvements to consistent
      terminology were made.  Instances of OrigNodeNdx and TargNodeNdx
      were replaced by OrigNdx and TargNdx, to be consistent with the
      terminology shown in Table 2.
   o  Example RREQ and RREP message formats shown in the Appendices were
      changed to use OrigSeqNum and TargSeqNum message TLVs instead of
      using the SeqNum message TLV.
   o  Inclusion of the OrigNode's SeqNum in the RREP message is not
      specified.  The processing rules for the OrigNode's SeqNum were
      incompletely specified in previous versions of the draft, and very
      little benefit is foreseen for including that information, since
      reverse path forwarding is used for the RREP.



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   o  Additional acknowledgements were included, and contributors names
      were alphabetized.
   o  Definitions in the Terminology section capitalize the term to be
      defined.
   o  Uncited bibliographic entries deleted.
   o  Ancient "Changes" sections were deleted.

Appendix G.  Multi-homing Considerations

   Multi-homing is not supported by the AODVv2 specification.  There has
   been previous work indicating that it can be supported by expanding
   the sequence number to include the AODVv2 router's IP address as a
   parsable field of the SeqNum.  Otherwise, comparing sequence numbers
   would not work to evaluate freshness.  Even when the IP address is
   included, there isn't a good way to compare sequence numbers from
   different IP addresses, but at least a handling node can determine
   whether the two given sequence numbers are comparable.  If the route
   table can store multiple routes for the same destination, then multi-
   homing can work with sequence numbers augmented by IP addresses.

   This non-normative information is provided simply to document the
   results of previous efforts to enable multi-homing.  The intention is
   to simplify the task of future specification if multihoming becomes
   needed for reactive protocol operation.

Appendix H.  Shifting Network Prefix Advertisement Between AODVv2
             Routers

   Only one AODVv2 router within a MANET SHOULD be responsible for a
   particular address at any time.  If two AODVv2 routers dynamically
   shift the advertisement of a network prefix, correct AODVv2 routing
   behavior must be observed.  The AODVv2 router adding the new network
   prefix must wait for any existing routing information about this
   network prefix to be purged from the network.  Therefore, it must
   wait at least ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous AODVv2
   router for this address stopped advertising routing information on
   its behalf.

Authors' Addresses

   Charles E. Perkins
   Futurewei Inc.
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Phone: +1-408-330-4586
   Email: charliep@computer.org



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   Stan Ratliff
   Idirect
   13861 Sunrise Valley Drive, Suite 300
   Herndon, VA  20171
   USA

   Email: ratliffstan@gmail.com


   John Dowdell
   Airbus Defence and Space
   Celtic Springs
   Newport, Wales  NP10 8FZ
   United Kingdom

   Email: john.dowdell486@gmail.com


   Lotte Steenbrink
   HAW Hamburg, Dept. Informatik
   Berliner Tor 7
   D-20099 Hamburg
   Germany

   Email: lotte.steenbrink@haw-hamburg.de


























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