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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: November 14, 2015                                       Idirect
                                                              J. Dowdell
                                                Airbus Defence and Space
                                                           L. Steenbrink
                                           HAW Hamburg, Dept. Informatik
                                                             V. Mercieca
                                                Airbus Defence and Space
                                                            May 13, 2015


           Ad Hoc On-demand Distance Vector (AODVv2) Routing
                       draft-ietf-manet-aodvv2-09

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 November 14, 2015.

Copyright Notice

   Copyright (c) 2015 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



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

Table of Contents

   1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . .  10
   4.  Data Structures . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Interface List  . . . . . . . . . . . . . . . . . . . . .  11
     4.2.  Router Client List  . . . . . . . . . . . . . . . . . . .  11
     4.3.  Neighbor List . . . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Sequence Numbers  . . . . . . . . . . . . . . . . . . . .  13
     4.5.  Multicast Route Message Table . . . . . . . . . . . . . .  14
     4.6.  Route Table Entry . . . . . . . . . . . . . . . . . . . .  15
   5.  Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     5.1.  Cost Function . . . . . . . . . . . . . . . . . . . . . .  17
     5.2.  LoopFree Function . . . . . . . . . . . . . . . . . . . .  17
     5.3.  Default Metric Type . . . . . . . . . . . . . . . . . . .  17
     5.4.  Alternate Metric Types  . . . . . . . . . . . . . . . . .  18
   6.  AODVv2 Protocol Operations  . . . . . . . . . . . . . . . . .  19
     6.1.  Initialization  . . . . . . . . . . . . . . . . . . . . .  19
     6.2.  Adjacency Monitoring  . . . . . . . . . . . . . . . . . .  19
     6.3.  Message Transmission  . . . . . . . . . . . . . . . . . .  21
     6.4.  Route Discovery, Retries and Buffering  . . . . . . . . .  22
     6.5.  Processing Received Route Information . . . . . . . . . .  23
       6.5.1.  Evaluating Route Information  . . . . . . . . . . . .  24
       6.5.2.  Applying Route Updates  . . . . . . . . . . . . . . .  25
     6.6.  Suppressing Redundant Messages  . . . . . . . . . . . . .  27
     6.7.  Route Maintenance . . . . . . . . . . . . . . . . . . . .  28
       6.7.1.  Route State . . . . . . . . . . . . . . . . . . . . .  28
       6.7.2.  Reporting Invalid Routes  . . . . . . . . . . . . . .  29
   7.  AODVv2 Protocol Messages  . . . . . . . . . . . . . . . . . .  30
     7.1.  Route Request (RREQ) Message  . . . . . . . . . . . . . .  30
       7.1.1.  RREQ Generation . . . . . . . . . . . . . . . . . . .  31
       7.1.2.  RREQ Reception  . . . . . . . . . . . . . . . . . . .  33
       7.1.3.  RREQ Regeneration . . . . . . . . . . . . . . . . . .  34
     7.2.  Route Reply (RREP) Message  . . . . . . . . . . . . . . .  35
       7.2.1.  RREP Generation . . . . . . . . . . . . . . . . . . .  36
       7.2.2.  RREP Reception  . . . . . . . . . . . . . . . . . . .  38
       7.2.3.  RREP Regeneration . . . . . . . . . . . . . . . . . .  39
     7.3.  Route Reply Acknowledgement (RREP_Ack) Message  . . . . .  40
       7.3.1.  RREP_Ack Generation . . . . . . . . . . . . . . . . .  40



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       7.3.2.  RREP_Ack Reception  . . . . . . . . . . . . . . . . .  40
     7.4.  Route Error (RERR) Message  . . . . . . . . . . . . . . .  40
       7.4.1.  RERR Generation . . . . . . . . . . . . . . . . . . .  42
       7.4.2.  RERR Reception  . . . . . . . . . . . . . . . . . . .  44
       7.4.3.  RERR Regeneration . . . . . . . . . . . . . . . . . .  45
   8.  RFC 5444 Representation . . . . . . . . . . . . . . . . . . .  46
     8.1.  RREQ  . . . . . . . . . . . . . . . . . . . . . . . . . .  47
       8.1.1.  Message Header  . . . . . . . . . . . . . . . . . . .  47
       8.1.2.  Message TLV Block . . . . . . . . . . . . . . . . . .  47
       8.1.3.  Address Block . . . . . . . . . . . . . . . . . . . .  47
       8.1.4.  Address Block TLV Block . . . . . . . . . . . . . . .  47
     8.2.  RREP  . . . . . . . . . . . . . . . . . . . . . . . . . .  48
       8.2.1.  Message Header  . . . . . . . . . . . . . . . . . . .  48
       8.2.2.  Message TLV Block . . . . . . . . . . . . . . . . . .  49
       8.2.3.  Address Block . . . . . . . . . . . . . . . . . . . .  49
       8.2.4.  Address Block TLV Block . . . . . . . . . . . . . . .  49
     8.3.  RREP_Ack  . . . . . . . . . . . . . . . . . . . . . . . .  50
       8.3.1.  Message Header  . . . . . . . . . . . . . . . . . . .  50
       8.3.2.  Message TLV Block . . . . . . . . . . . . . . . . . .  50
       8.3.3.  Address Block . . . . . . . . . . . . . . . . . . . .  50
       8.3.4.  Address Block TLV Block . . . . . . . . . . . . . . .  50
     8.4.  RERR  . . . . . . . . . . . . . . . . . . . . . . . . . .  50
       8.4.1.  Message Header  . . . . . . . . . . . . . . . . . . .  51
       8.4.2.  Message TLV Block . . . . . . . . . . . . . . . . . .  51
       8.4.3.  Address Block . . . . . . . . . . . . . . . . . . . .  51
       8.4.4.  Address Block TLV Block . . . . . . . . . . . . . . .  51
   9.  Simple Internet Attachment  . . . . . . . . . . . . . . . . .  52
   10. Optional Features . . . . . . . . . . . . . . . . . . . . . .  53
     10.1.  Expanding Rings Multicast  . . . . . . . . . . . . . . .  53
     10.2.  Precursor Lists  . . . . . . . . . . . . . . . . . . . .  54
     10.3.  Intermediate RREP  . . . . . . . . . . . . . . . . . . .  55
     10.4.  Message Aggregation Delay  . . . . . . . . . . . . . . .  55
   11. Configuration . . . . . . . . . . . . . . . . . . . . . . . .  55
     11.1.  Timers . . . . . . . . . . . . . . . . . . . . . . . . .  56
     11.2.  Protocol Constants . . . . . . . . . . . . . . . . . . .  56
     11.3.  Local Settings . . . . . . . . . . . . . . . . . . . . .  57
     11.4.  Network-Wide Settings  . . . . . . . . . . . . . . . . .  58
     11.5.  Optional Feature Settings  . . . . . . . . . . . . . . .  58
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  59
     12.1.  RFC 5444 Message Types . . . . . . . . . . . . . . . . .  59
     12.2.  RFC 5444 Message TLV Types . . . . . . . . . . . . . . .  59
     12.3.  RFC 5444 Address Block TLV Types . . . . . . . . . . . .  59
     12.4.  MetricType Allocation  . . . . . . . . . . . . . . . . .  60
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  60
   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  63
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  63
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  63
     15.2.  Informative References . . . . . . . . . . . . . . . . .  64



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   Appendix A.  Features Required of IP  . . . . . . . . . . . . . .  65
   Appendix B.  Multi-homing Considerations  . . . . . . . . . . . .  65
   Appendix C.  Router Client Relocation . . . . . . . . . . . . . .  66
   Appendix D.  Example Algorithms for AODVv2 Operations . . . . . .  66
     D.1.  General Operations  . . . . . . . . . . . . . . . . . . .  68
       D.1.1.  Check_Route_State . . . . . . . . . . . . . . . . . .  68
       D.1.2.  Process_Routing_Info  . . . . . . . . . . . . . . . .  69
       D.1.3.  Fetch_Route_Table_Entry . . . . . . . . . . . . . . .  69
       D.1.4.  Update_Route_Table_Entry  . . . . . . . . . . . . . .  70
       D.1.5.  Create_Route_Table_Entry  . . . . . . . . . . . . . .  71
       D.1.6.  LoopFree  . . . . . . . . . . . . . . . . . . . . . .  71
       D.1.7.  Fetch_Rte_Msg_Table_Entry . . . . . . . . . . . . . .  72
       D.1.8.  Update_Rte_Msg_Table  . . . . . . . . . . . . . . . .  72
       D.1.9.  Build_RFC_5444_Message_Header . . . . . . . . . . . .  73
     D.2.  RREQ Operations . . . . . . . . . . . . . . . . . . . . .  74
       D.2.1.  Generate_RREQ . . . . . . . . . . . . . . . . . . . .  74
       D.2.2.  Receive_RREQ  . . . . . . . . . . . . . . . . . . . .  75
       D.2.3.  Regenerate_RREQ . . . . . . . . . . . . . . . . . . .  77
     D.3.  RREP Operations . . . . . . . . . . . . . . . . . . . . .  78
       D.3.1.  Generate_RREP . . . . . . . . . . . . . . . . . . . .  78
       D.3.2.  Receive_RREP  . . . . . . . . . . . . . . . . . . . .  79
       D.3.3.  Regenerate_RREP . . . . . . . . . . . . . . . . . . .  80
     D.4.  RREP_Ack Operations . . . . . . . . . . . . . . . . . . .  82
       D.4.1.  Generate_RREP_Ack . . . . . . . . . . . . . . . . . .  82
       D.4.2.  Receive_RREP_Ack  . . . . . . . . . . . . . . . . . .  82
       D.4.3.  Timeout_RREP_Ack  . . . . . . . . . . . . . . . . . .  82
     D.5.  RERR Operations . . . . . . . . . . . . . . . . . . . . .  82
       D.5.1.  Generate_RERR . . . . . . . . . . . . . . . . . . . .  82
       D.5.2.  Receive_RERR  . . . . . . . . . . . . . . . . . . . .  84
       D.5.3.  Regenerate_RERR . . . . . . . . . . . . . . . . . . .  85
   Appendix E.  AODVv2 Draft Updates . . . . . . . . . . . . . . . .  87
     E.1.  Changes between revisions 8 and 9 . . . . . . . . . . . .  87
     E.2.  Changes between revisions 7 and 8 . . . . . . . . . . . .  89
     E.3.  Changes between revisions 6 and 7 . . . . . . . . . . . .  90
     E.4.  Changes between revisions 5 and 6 . . . . . . . . . . . .  92
     E.5.  Changes between revisions 4 and 5 . . . . . . . . . . . .  93
     E.6.  Changes between revisions 3 and 4 . . . . . . . . . . . .  94
     E.7.  Changes between revisions 2 and 3 . . . . . . . . . . . .  94
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  95

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 hoc networks [MANETs]
   [RFC2501].  The basic operations of the AODVv2 protocol are route
   discovery and route maintenance.




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   Route discovery is performed when an AODVv2 router needs to forward a
   packet for one of its clients, but does not have a valid route to the
   packet's destination.  AODVv2 routers use Route Reply and Route
   Request messages to carry route information between the originator of
   the route discovery and the target, establishing a route to both
   endpoints on all intermediate routers.

   Metrics are included in RREQ and RREP messages to represent the cost
   of the routes to the originator and target of the route discovery.
   AODVv2 compares route metrics in a way that ensures loop avoidance.
   AODVv2 also uses sequence numbers to assure loop freedom, enabling
   identification of stale routing information so that it can be
   discarded.

   Route maintenance involves monitoring the router's links and routes
   for changes.  This includes confirming adjacencies with other AODVv2
   routers, issuing Route Error messages if link failures invalidate
   routes, extending and enforcing route timeouts, and reacting to
   received Route Error messages.

   AODVv2 control plane messages use the Generalized MANET Packet/
   Message Format defined in [RFC5444] and the parameters in [RFC5498].
   AODVv2 defines a set of data elements which map to RFC 5444 Address
   Blocks, Address Block TLVs, and Message TLVs.

   Security for authentication of AODVv2 routers and encryption of
   control messages is dealt with by using the recommendations in
   [RFC7182].

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].  In addition, this document uses terminology from
   [RFC5444], and defines the following terms:

   AddressList
      An AODVv2 Data Element (see Table 1).

   Adjacency
      A bi-directional relationship between neighboring AODVv2 routers
      for the purpose of exchanging routing information.

   AckReq
      An AODVv2 Data Element (see Table 1).

   AODVv2 Router



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      An IP addressable device in the ad hoc network that performs the
      AODVv2 protocol operations specified in this document.

   CurrentTime
      The current time as maintained by the AODVv2 router.

   Data Element
      A named object used within AODVv2 protocol messages (see Table 1).

   Disregard
      Ignore for further processing.

   Invalid route
      A route that cannot be used for forwarding.

   MANET
      A Mobile Ad Hoc Network as defined in [RFC2501].

   MetricType
      An AODVv2 Data Element (see Table 1).

   MetricTypeList
      An AODVv2 Data Element (see Table 1).

   Node
      An IP addressable device in the ad hoc network.  All nodes in this
      document are either AODVv2 Routers or Router Clients.

   OrigAddr (Originator Address)
      An AODVv2 Data Element (see Table 1).

   OrigMetric
      An AODVv2 Data Element (see Table 1).

   OrigNode (Originating Node)
      The node that launched the application requiring communication
      with the Target Address.

   OrigSeqNum
      An AODVv2 Data Element (see Table 1).

   PktSource
      An AODVv2 Data Element (see Table 1).

   PrefixLengthList
      An AODVv2 Data Element (see Table 1).

   Reactive



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      A protocol operation is called "reactive" if it is performed only
      in reaction to specific events.  In this document, "reactive" is
      synonymous with "on-demand".

   RERR (Route Error)
      The AODVv2 message type used to indicate that an AODVv2 router
      does not have a route toward one or more particular destinations.

   RERR_Gen (RERR Generating Router)
      The AODVv2 router generating a Route Error message.

   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.

   Router Client
      A node that requires the services of an AODVv2 router.  An AODVv2
      router is also its own client.

   RREP (Route Reply)
      The AODVv2 message type used to reply to a Route Request message.

   RREP_Gen (RREP Generating Router)
      The AODVv2 router responsible for the Target Node of a Route
      Request message, i.e., the router that creates the Route Reply
      message.

   RREQ (Route Request)
      The AODVv2 message type used to discover a route to the Target
      Address and distribute information about the route to the
      Originator Address.

   RREQ_Gen (RREQ Generating Router)
      The AODVv2 router that creates the Route Request message on behalf
      of the Originating Node to discover a route for Target Address.

   RteMsg (Route Message)
      A Route Request (RREQ) or Route Reply (RREP) message.

   Sequence Number (SeqNum)
      One of the sequence numbers maintained by an AODVv2 router to
      indicate freshness of route information.  Used as an AODVv2 Data
      Element (see Table 1).

   SeqNumList
      An AODVv2 Data Element (see Table 1).



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   TargAddr (Target Address)
      An AODVv2 Data Element (see Table 1).

   TargMetric
      An AODVv2 Data Element (see Table 1).

   TargNode (Target Node)
      The node hosting the IP address toward which a route is needed.

   TargSeqNum
      An AODVv2 Data Element (see Table 1).

   Unreachable Address
      An address for which a valid route is not known.

   Upstream
      In the direction from destination to source (from TargAddr to
      OrigAddr).

   Valid route
      A route that can be used for forwarding.

   ValidityTime
      An AODVv2 Data Element (see Table 1).

   This document defines a set of Data Elements in Table 1 which are
   used in AODVv2 messages.  These data elements contain the message
   data which is transferred into RFC 5444 formatted messages
   (Section 8) before sending.






















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   +------------------+------------------------------------------------+
   | Data Elements    | Meaning                                        |
   +------------------+------------------------------------------------+
   | AckReq           | Presence in RREP means acknowledgement is      |
   |                  | requested                                      |
   | AddressList      | A list of IP addresses                         |
   | MetricType       | The metric type for a metric value             |
   | MetricTypeList   | Metric types associated with routes to         |
   |                  | addresses in AddressList, used in RERR         |
   | msg_hop_limit    | Number of hops the message is allowed to       |
   |                  | traverse                                       |
   | msg_hop_count    | Number of hops traversed so far by the message |
   | OrigMetric       | Metric value associated with the route to      |
   |                  | OrigAddr                                       |
   | OrigSeqNum       | Sequence number associated with OrigAddr, used |
   |                  | in RREQ                                        |
   | OrigAddr         | IP address of the Originating Node, the source |
   |                  | address of the packet triggering route         |
   |                  | discovery                                      |
   | PktSource        | Source address of a packet triggering a RERR   |
   |                  | message                                        |
   | PrefixLengthList | A list of routing prefixes associated with     |
   |                  | addresses in AddressList                       |
   | SeqNum           | Sequence number, when used in RERR             |
   | SeqNumList       | A list of generic sequence numbers associated  |
   |                  | with addresses in an AddressList, used in RERR |
   | TargAddr         | IP address of the Target Node, the destination |
   |                  | address for which a route is requested         |
   | TargMetric       | Metric value associated with the route to      |
   |                  | TargAddr                                       |
   | TargSeqNum       | Sequence number associated with TargAddr, used |
   |                  | in RREQ (optional) and RREP                    |
   | ValidityTime     | Length of time a route is offered              |
   +------------------+------------------------------------------------+

                          Table 1: Data Elements

   This document uses the notational conventions in Table 2 to simplify
   the text.












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   +----------------------+--------------------------------------------+
   | Notation             | Meaning                                    |
   +----------------------+--------------------------------------------+
   | Route[Address]       | A route table entry toward Address         |
   | Route[Address].Field | A field in a route table entry toward      |
   |                      | Address                                    |
   | RteMsg               | Either RREQ or RREP                        |
   | RteMsg.Field         | A field in either RREQ or RREP             |
   | AdvRte               | A route advertised in an incoming RteMsg   |
   +----------------------+--------------------------------------------+

                      Table 2: Notational Conventions

3.  Applicability Statement

   The AODVv2 routing protocol is a reactive routing protocol designed
   for stub or disconnected mobile ad hoc networks, i.e., non-transit
   networks or those not connected to the internet.

   AODVv2 handles a wide variety of mobility and traffic patterns by
   determining routes on-demand.  In networks with a large number of
   routers, AODVv2 is best suited for relatively sparse traffic
   scenarios where each router forwards packets to a small percentage of
   other AODVv2 routers in the network.  In this case fewer routes are
   needed, and therefore less control traffic is produced.

   AODVv2 is well suited to reactive scenarios such as emergency and
   disaster relief, where the ability to communicate is more important
   than being assured of secure operations.  For other ad hoc networking
   applications, in which insecure operation could negate the value of
   establishing communication paths, it is important for neighboring
   AODVv2 nodes to establish security associations with one another.

   AODVv2 will not make use of uni-directional links.  Route requests
   from routers which cannot confirm bidirectional connectivity should
   be ignored to avoid persistent packet loss or protocol failures.

   AODVv2 is applicable to memory constrained devices, since only a
   little routing state is maintained in each AODVv2 router.  In
   contrast to proactive routing protocols, which maintain routing
   information for all destinations within the MANET, AODVv2 routes that
   are not needed for forwarding data do not need to be maintained.  On
   routers unable to store persistent AODVv2 state, recovery can impose
   a performance penalty (e.g., in case of AODVv2 router reboot).

   AODVv2 supports routers with multiple interfaces, as long as each
   interface configured for AODVv2 has its own unicast routable IP
   address.  Address assignment procedures are out of scope for AODVv2.



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   Multi-homing is not supported by AODVv2, and therefore a Router
   Client SHOULD NOT be served by more than one AODVv2 router at any one
   time.  Appendix B contains some notes on this topic.

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

   The routing algorithm in AODVv2 may be operated at layers other than
   the network layer, using layer-appropriate addresses.

   AODVv2 can be configured to perform gateway functions when attached
   to the internet.  Such gateway routers will reply to each route
   request generated inside the AODVv2 network as if they were
   responsible for the target address, and may advertise the AODVv2
   network to the internet using procedures out of scope for this
   specification.

4.  Data Structures

4.1.  Interface List

   A list of the interfaces supporting AODVv2 should be configured in
   the AODVv2_INTERFACES list.

4.2.  Router Client List

   An AODVv2 router may provide routing services for its own local
   applications and for other non-routing nodes that are directly
   reachable via its network interfaces.  These nodes, including the
   AODVv2 router itself, are referred to as Router Clients.

   Each AODVv2 router MUST be configured with information about the IP
   addresses of its clients.  If a subnet is configured as a Router
   Client, the AODVv2 router MUST serve every node in that subnet.

   A CLIENT_ADDRESSES list should exist to store information about
   Router Clients, with the following information:

   RouterClient.IPAddress
      The IP address of the client node or subnet that requires routing
      services from the AODVv2 router.

   RouterClient.PrefixLength
      The length, in bits, of the routing prefix associated with the
      client IP address or subnet.





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   The list of Router Clients for an AODVv2 router is never empty, since
   an AODVv2 router is always its own client.  The IP Addresses of the
   router's interfaces will appear in the Router Client list.

   The router MUST respond to Route Requests for all Router Clients.  In
   the initial state, an AODVv2 router is not required to have
   information about the Router Clients of any other AODVv2 router.

   A Router Client SHOULD NOT be served by more than one AODVv2 router
   at any one time.  Shifting responsibility for a Router Client to a
   different AODVv2 router is discussed in Appendix C.

4.3.  Neighbor List

   A neighbor list SHOULD be maintained with information about
   neighboring AODVv2 routers, including an indication of the state of
   the adjacency to the router.  Section 6.2 discusses how to monitor
   adjacency.

   Neighboring routers which cannot confirm adjacency should be marked
   as blacklisted.  Certain AODVv2 messages received from a blacklisted
   router should be ignored.  Routers should be blacklisted for a
   maximum of MAX_BLACKLIST_TIME, but can be removed from the blacklist
   before this time if an indication of adjacency is received.

   Neighbor entries should contain:

   Neighbor.IPAddress
      An IP address of the neighboring router.

   Neighbor.State
      The state of the adjacency (Confirmed, Unknown, or Blacklisted)

   Neighbor.ResetTime
      The time at which this router SHOULD no longer be considered
      blacklisted.  By default this value is calculated at the time the
      router is blacklisted and is equal to CurrentTime +
      MAX_BLACKLIST_TIME.  After this time, the state should be reset to
      Unknown.  While the neighbor is not marked as blacklisted, this
      value SHOULD be set to MAX_TIME.

   Before a neighbor is confirmed, any routes learned through that
   neighbor are marked as Unconfirmed.  When neighbor state is set to
   Confirmed, the Unconfirmed routes using the neighbor as a next hop
   can transition to Idle state (see Section 6.7.1).

   If a neighbor is blacklisted, any routes installed which use that
   neighbor for their next hop should be invalidated.



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   When the link to a neighbor breaks, the neighbor entry should be
   removed and all routes using the neighbor as next hop should be
   invalidated.

4.4.  Sequence Numbers

   Sequence numbers enable AODVv2 routers to determine the temporal
   order of route discovery messages, identifying stale routing
   information so that it can be discarded.  The sequence number
   fulfills the same roles as the "Destination Sequence Number" of DSDV
   [Perkins94], and the AODV Sequence Number in [RFC3561].

   Each AODVv2 router in the network MUST maintain its own sequence
   number as a 16-bit unsigned integer.  All route messages (Route
   Request and Route Reply messages) created by an AODVv2 router include
   the router's sequence number.

   If the router has multiple AODVv2 interfaces, it can maintain
   different sequence numbers for each interface IP address, but the
   router MUST NOT use multiple sequence numbers for any one interface
   IP address.  All route messages created on behalf of Router Clients
   on a particular interface MUST include the sequence number of that
   interface's IP address.

   Each AODVv2 router MUST ensure that its sequence number is strictly
   increasing.  It can ensure this by incrementing the sequence number
   by one (1) whenever a route message is created, except when the
   sequence number is 65,535 (the maximum value of a 16-bit unsigned
   integer), in which case it MUST be reset to one (1).  The value zero
   (0) is reserved to indicate that the sequence number for an address
   is unknown.

   A router receiving a route message uses the sequence number to
   determine the freshness of the route information in the message in
   comparison with any existing information about the same route.  If
   the sequence number stored in the route table is higher than the
   sequence number in the message, the received information is
   considered stale and MUST NOT be used to update the route table.

   As a consequence, loop freedom is assured.

   An AODVv2 router SHOULD maintain its sequence number(s) in persistent
   storage.  If a sequence number is lost, the router must follow the
   procedure in Section 6.1 to safely resume routing operations with a
   new sequence number.






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4.5.  Multicast Route Message Table

   A route message (RteMsg) is either a Route Request and Route Reply
   message.  The Multicast Route Message Table (RteMsg Table) contains
   information about previously received multicast route messages, so
   that when a route message is received, an AODVv2 router can determine
   if the incoming information is redundant, and avoid unnecessary
   regeneration of the route message.  RREQ messages are usually
   multicast.  Future extensions to AODVv2 MAY enable RREP messages to
   be multicast.

   Each entry in the RteMsg Table stores the following information,
   copied from the route message:

   RteMsg.MessageType
      Either RREQ or RREP.

   RteMsg.OrigAddr
      The IP address of the originating node wishing to send a packet.

   RteMsg.TargAddr
      The IP address of the target node, the destination of the packet.

   RteMsg.OrigSeqNum
      The sequence number associated with the originator, if present in
      RteMsg.

   RteMsg.TargSeqNum
      The sequence number associated with the target, if present in
      RteMsg.

   RteMsg.MetricType
      The metric type of the route requested.

   RteMsg.Metric
      The metric value received in the RteMsg.

   RteMsg.Timestamp
      The last time this entry was updated.

   RteMsg.RemoveTime
      The time at which this entry MUST be removed.

   Multicast RteMsgs are considered to be comparable if they have the
   same MessageType, OrigAddr, TargAddr, and MetricType.  The RteMsg
   Table is maintained so that no two entries are comparable, i.e., all
   entries either have different MessageType, different OrigAddr,




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   different TargAddr, or different MetricType.  See Section 6.6 for
   details on updating this table.

   Entries in the RteMsg Table MUST be deleted when the sequence number
   is no longer valid, i.e., after MAX_SEQNUM_LIFETIME.  RemoveTime
   should be set when the sequence number of the entry is updated, i.e.,
   when OrigSeqNum is updated for a RREQ, and when TargSeqNum is updated
   for a RREP.  RemoveTime should be set to CurrentTime +
   MAX_SEQNUM_LIFETIME.  Memory-constrained devices MAY remove the entry
   before this time, but the entry should be maintained for at least
   RteMsg_ENTRY_TIME after the last Timestamp update in order to account
   for long-lived RREQs traversing the network.

4.6.  Route Table Entry

   The route table entry is a conceptual data structure.
   Implementations MAY use any internal representation that provides
   access to the following information:

   Route.Address
      An address or address prefix of a node.

   Route.PrefixLength
      The prefix length, in bits, associated with the address.  If it is
      less than the length of Route.Address, this is a route to the
      subnet on which Route.Address resides.

   Route.SeqNum
      The sequence number associated with Route.Address, obtained from
      the last route message that successfully updated this route table
      entry.

   Route.NextHop
      An IP address of the AODVv2 router used for the next hop on the
      path toward Route.Address.

   Route.NextHopInterface
      The interface used to send packets toward Route.Address.

   Route.LastUsed
      The time this route was last used to forward a packet.

   Route.LastSeqNumUpdate
      The time the sequence number for this route was last updated.

   Route.ExpirationTime
      The time at which this route must be marked as Invalid.




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   Route.MetricType
      The type of metric associated with this route.

   Route.Metric
      The cost of the route toward Route.Address expressed in units
      consistent with Route.MetricType.

   Route.State
      The last known state (Active, Idle, Invalid, or Unconfirmed) of
      the route.

   Route.Precursors (optional feature)
      A list of upstream neighbors using the route (see Section 10.2).

   An AODVv2 route may be valid for a limited time.  In this case,
   Route.ExpirationTime reflects the shortened validity time of the
   route.  If a route is not timed, the expiration time is MAX_TIME.

5.  Metrics

   Metrics measure a cost or quality associated with a route or a link,
   e.g., latency, delay, financial cost, energy, etc.

   AODVv2 enables the use of multiple metric types.  Each metric that
   can be used in AODVv2 has a MetricType number.  Numbers are allocated
   by IANA as specified in [RFC6551] or detailed in Section 12.4.  The
   default metric type is discussed in Section 5.3.  Alternate metrics
   are discussed in Section 5.4.

   An AODVv2 implementation MAY be configured to use a limited set of
   the supported metric types.  In the processing described in
   Section 7, a "known" MetricType can be interpreted as a configured
   MetricType.  If a message is received using an unknown or non-
   configured MetricType it MUST be ignored.  Since the message will not
   be regenerated, other routers which do support the MetricType will
   not be able to route through a router which does not support the
   MetricType.

   For each MetricType, a maximum value is defined, denoted
   MAX_METRIC[MetricType].  AODVv2 cannot store routes that cost more
   than MAX_METRIC[MetricType].

   Metric information reported in incoming route messages describes the
   metric as measured by message sender, and does not reflect the cost
   of traversing the link to that sender.  The receiving router
   calculates the cost of the route from its perspective.  This cost is
   used to determine whether to use incoming information to update an




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   existing route.  If the cost exceeds MAX_METRIC[MetricType], the
   route is ignored.

5.1.  Cost Function

   This document uses the following notation to represent costs:

   o  Cost(L) for link cost

   o  Cost(R) for route cost

   These functions return the cost of traversing a link or a route.
   Cost(L) and Cost(R) for the default metric type are detailed in
   Section 5.3.  The Cost() functions for other metric types are beyond
   the scope of this document.

5.2.  LoopFree Function

   When comparing an advertised route to an existing route for the same
   destination and the same metric type, the metric value should be
   examined to ensure that using the advertised route to update the
   route table will not cause a routing loop to form.

   The function LoopFree(R1, R2) is defined to verify that a route R2 is
   not a part of another route R1.  LoopFree returns TRUE if R2 cannot
   be a sub-section of the route R1.

   An AODVv2 router invokes LoopFree() as part of the process in
   Section 6.5.1.  The advertised route (AdvRte) is used as parameter
   R1, and the stored route (Route) is used as parameter R2.

   The LoopFree(R1,R2) function for the default metric type is detailed
   in Section 5.3.  The LoopFree(R1,R2) functions for other metric types
   are beyond the scope of this document.

5.3.  Default Metric Type

   AODVv2's default metric type (DEFAULT_METRIC_TYPE) is HopCount, and
   is the only metric described in detail in this document.  Alternate
   metrics are discussed in Section 5.4.

   For the HopCount metric:

   o  Cost(L) := 1

   o  Cost(R) := Sum (Cost(L) of each link in the route), i.e., the hop
      count between the router calculating the cost, and the destination
      of the route



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   o  LoopFree(R1, R2) returns TRUE when the cost of R1 is less than or
      equal to the cost of R2, i.e., Cost(R1) <= Cost(R2)

   o  MAX_METRIC[HopCount] := MAX_HOPCOUNT

   The LoopFree function is derived from the fact that route cost
   increases with number of hops.  When examining two routes, the route
   with higher cost may include the route with lower cost as a sub-
   section of its route.  Therefore, an advertised route with higher
   cost than the corresponding stored route could include the stored
   route as a sub-section.  Replacing the stored route with the received
   route could form a routing loop.  LoopFree returns FALSE in this case
   to indicate that an advertised route with higher cost is not to be
   used to update a stored route, even if the stored route is invalid.

   MAX_HOPCOUNT is a constant defined in Section 11.2.  It MUST be
   larger than the AODVv2 network diameter, in order that AODVv2
   protocol messages may reach their intended destinations.

5.4.  Alternate Metric Types

   Some applications may require metric information other than hop
   count.  For this reason, AODVv2 enables route selection based on
   alternate metric types.

   Using non-default metrics in an AODVv2 message requires the inclusion
   of the MetricType data element.

   Alternate metrics may have different types and ranges, for example
   integers or floating point numbers, or restricted subsets thereof.
   Therefore the size of the metric field in route messages may vary.
   See Section 12.4 for further information on MetricType number
   allocation and size.

   Metrics might be classified as additive, concave, convex, or
   multiplicative as discussed in [RFC6551].  Where Cost and LoopFree
   functions can be developed for a metric type, it can be supported by
   AODVv2.

   AODVv2 can support additive metrics using the Cost(R) and
   LoopFree(R1, R2) functions defined for the default metric.  Further,
   any strictly increasing metric can be supported using the LoopFree
   function defined.  It is, however, out of the scope of this document
   to specify for alternate metrics the correct Cost(L), Cost(R), and
   LoopFree() functions.  Where possible these should take into account
   differences in the link cost in each direction.





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6.  AODVv2 Protocol Operations

   The AODVv2 protocol's operations include managing sequence numbers,
   monitoring adjacent AODVv2 routers, performing route discovery and
   dealing with requests from other routers, processing incoming route
   information and updating the route table, suppressing redundant
   messages, maintaining the route table and reporting broken routes.
   These processes are discussed in detail in the following sections.

6.1.  Initialization

   During initialization where the previous sequence number is unknown,
   or if the sequence number is lost at any point, an AODVv2 router
   resets its sequence number(s) to one (1).  However, other AODVv2
   routers may still hold sequence number information this router
   previously issued.  Since sequence number information will be removed
   if there have been no sequence number updates in MAX_SEQNUM_LIFETIME,
   the initializing router must wait for MAX_SEQNUM_LIFETIME before it
   creates any messages containing its sequence number.  It can then be
   sure that the information it sends will not be considered stale.

   Until MAX_SEQNUM_LIFETIME after its sequence number is reset, the
   router SHOULD not create RREQ or RREP messages.

   During this wait period, the router can do the following:

   o  Process information in a received RREQ or RREP message to learn a
      route to the originator or target

   o  Send a RREP_Ack

   o  Regenerate a received RREQ or RREP

   o  Forward data packets to Router Clients, and to other routers, if a
      route exists

   o  Create, process and regenerate RERR messages

6.2.  Adjacency Monitoring

   An adjacency is a bidirectional relationship between neighboring
   AODVv2 routers for the purpose of exchanging routing information.
   Not every pair of neighboring routers will necessarily form an
   adjacency, but AODVv2 routers SHOULD monitor connectivity to
   neighboring AODVv2 routers along potential routes and SHOULD NOT
   establish routes over uni-directional links, since packet losses are
   likely to occur and route establishment can fail.




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   The default approach for monitoring connectivity is to request
   acknowledgement of Route Reply messages.  An acknowledgement proves
   that bidirectional connectivity exists.  See Section 7.2 and
   Section 7.3 for further details on how this is accomplished.  A
   received RREP is also an indication of bidirectional connectivity,
   since a RREP is a reply to a RREQ which previously crossed the link
   in the opposite direction.

   When routers perform other operations such as those from the list
   below, these can be used as additional indications of connectivity:

   o  NHDP HELLO Messages [RFC6130]

   o  Route timeout

   o  Lower layer triggers, e.g. message reception or link status
      notifications

   o  TCP timeouts

   o  Promiscuous listening

   o  Other monitoring mechanisms or heuristics

   For example, receipt of a Neighborhood Discovery Protocol HELLO
   message with the receiving router listed as a neighbor is a signal of
   bidirectional connectivity.  In this case, acknowledgement of a RREP
   message is unnecessary.  Similarly, if AODVv2 receives notification
   of a timeout, this may be due to a disconnection.  The AODVv2 router
   SHOULD attempt to verify connectivity by requesting acknowledgement
   of the next RREP sent to that neighbor.

   The Neighbor List (Section 4.3) gives the last known state of the
   neighbor adjacency, either Confirmed, Unknown, or Blacklisted.  Until
   bidirectionality is confirmed, the state is Unknown, and
   acknowledgement of RREP messages MUST be requested.  If
   bidirectionality is already confirmed, the acknowledgement is
   unnecessary.  If bidirectionality cannot be confirmed, the state is
   Blacklisted.  RREQs received from a blacklisted router, or any router
   over a link that is known to be incoming-only, MUST be disregarded.

   Neighbor state is updated as follows:

   o  If a link to a neighbor is determined to be unidirectional, either
      by failure to acknowledge a RREP, or by some other means, the
      neighbor MUST be marked as blacklisted.





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   o  If a notification indicates that there may be a problem with
      bidirectionality, and the neighbor state is currently Confirmed,
      the state SHOULD be set to Unknown to force acknowledgement of the
      next RREP sent to the neighbor.

   o  If an indication of bidirectional connectivity is received, the
      neighbor state SHOULD be set to Confirmed.

   o  If the reset time is reached, the neighbor state SHOULD be reset
      to Unknown and the neighbor SHOULD again be allowed to participate
      in route discovery.

   If a link to a neighbor is determined to be broken, the neighbor
   entry should be removed.

6.3.  Message Transmission

   In its default mode of operation, AODVv2 sends [RFC5444] formatted
   messages using the parameters for port number and IP protocol
   specified in [RFC5498].  Mapping of AODVv2 data elements to RFC 5444
   is detailed in Section 8.

   Unless otherwise specified, AODVv2 multicast messages are sent to the
   link-local multicast address LL-MANET-Routers [RFC5498].  All AODVv2
   routers MUST subscribe to LL-MANET-Routers [RFC5498] to receive
   AODVv2 messages.

   Implementations are free to choose their own heuristics for reducing
   multicast overhead.  Some methods for doing so are described 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 messages.  Note that multicast messages 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.

   When multiple interfaces are available, a node transmitting a
   multicast message to LL-MANET-Routers MUST send the message on all
   interfaces that have been configured for AODVv2 operation, as given
   in the AODVv2_INTERFACES list (Section 4.1).  Similarly, AODVv2
   routers MUST subscribe to LL-MANET-Routers on all their AODVv2
   interfaces.

   To avoid congestion, each AODVv2 router's rate of message generation
   (CONTROL_TRAFFIC_LIMIT) SHOULD be limited and administratively
   configurable.  The implementation is free to choose the algorithm for
   limiting messages, including prioritizing messages when approaching
   the limit.  AODVv2 messages SHOULD be discarded in the following



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   order: RERR for invalidated routes, RREQ, RREP, RERR for
   undeliverable packet, RREP_Ack.

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

6.4.  Route Discovery, Retries and Buffering

   AODVv2's RREQ and RREP messages are used for route discovery and are
   together known as route messages (RteMsgs).  The main difference
   between the two messages is that, by default, RREQ messages are
   multicast to solicit a RREP, whereas RREP is unicast as a response to
   the RREQ.  The constants used in this section are defined in
   Section 11.

   When an AODVv2 router needs to forward a data packet (with source
   address OrigAddr and destination address TargAddr) from one of its
   Router Clients, it needs a route to the packet's destination.  If no
   route exists, the AODVv2 router generates and multicasts a Route
   Request message (RREQ) using OrigAddr and TargAddr.  The procedure
   for this is described in Section 7.1.1.  The AODVv2 router is
   referred to as RREQ_Gen.

   Data packets awaiting a route MAY be buffered by RREQ_Gen.  Buffering
   of data packets can have both positive and negative effects (albeit
   usually positive).  Real-time traffic, voice, and scheduled delivery
   may suffer if packets are buffered and subjected to delays, but TCP
   connection establishment will benefit if packets are queued while
   route discovery is performed.

   The packet buffer is configured with a fixed limited size of
   BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES.  Determining which packets
   to discard first when the buffer is full is a matter of policy at
   each AODVv2 router; in the absence of policy constraints, older data
   packets SHOULD be discarded first.  Nodes without sufficient memory
   available for buffering SHOULD have buffering disabled by configuring
   BUFFER_SIZE_PACKETS := 0 and BUFFER_SIZE_BYTES := 0.  This will
   affect the latency for launching TCP applications to new
   destinations.

   RREQ_Gen awaits reception of a Route Reply message (RREP) containing
   a route toward TargAddr.  A RREQ from TargAddr would also fulfil the
   request, if adjacency to the next hop is already confirmed.  If a
   route to TargAddr is not learned within RREQ_WAIT_TIME, RREQ_Gen MAY
   retry the route discovery by generating another RREQ with a new
   sequence number.  To reduce congestion in a network, repeated
   attempts at route discovery for a particular target address SHOULD




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   utilize a binary exponential backoff, as described in [RFC3561],
   where the wait time is doubled for each retry.

   The RREQ is received by neighboring AODVv2 routers, and processed and
   regenerated as described in Section 7.1.  Intermediate routers learn
   a potential route to OrigAddr from the RREQ.  The router responsible
   for TargAddr responds by generating a Route Reply message (RREP) and
   sends it back toward RREQ_Gen using the route to OrigAddr learned
   from the RREQ.  Each intermediate router regenerates the RREP and
   unicasts toward OrigAddr.

   Links which are not bidirectional cause problems.  If a RREP is not
   received at an intermediate router, the RREP cannot be regenerated
   and will never reach RREQ_Gen.  However, since routers monitor
   adjacencies (Section 6.2), the loss of the RREP should cause the last
   router which regenerated the RREP to blacklist the router which did
   not receive it.  When a timeout occurs at RREQ_Gen, a new RREQ may be
   regenerated.  When the new RREQ arrives again via the blacklisted
   router, it will be ignored, and the RREQ should discover a different
   path.

   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.  Any data
   packets buffered for TargAddr MUST also be dropped and a Destination
   Unreachable ICMP message (Type 3) with a code of 1 (Host Unreachable
   Error) SHOULD be delivered to the source of the data packet.  The
   source may be an application on RREQ_Gen itself, or on a Router
   Client with address OrigAddr.

   If RREQ_Gen does receive a route message containing a route to
   TargAddr within the timeout, it processes the message according to
   Section 7.  When a valid route is installed, the router can begin
   sending the buffered packets.  Any retry timers for the corresponding
   RREQ SHOULD be cancelled.

   During route discovery, all routers on the path learn a route to both
   OrigAddr and TargAddr, making the constructed route bidirectional.

6.5.  Processing Received Route Information

   All AODVv2 route messages contain a route.  A Route Request (RREQ)
   includes a route to OrigAddr, and a Route Reply (RREP) contains a
   route to TargAddr.





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   All AODVv2 routers that receive a route message can store the route
   contained within it.  Incoming information is first checked to verify
   that it is both safe to use and offers an improvement to existing
   information.  This process is explained in Section 6.5.1.  The route
   table may then be updated according to Section 6.5.2.

   In the processes below, RteMsg is used to denote the route message,
   AdvRte is used to denote the route contained within it, and Route
   denotes a stored routing table entry which matches AdvRte.

   AdvRte has the following properties:

   o  AdvRte.Address := RteMsg.OrigAddr (in RREQ) or RteMsg.TargAddr (in
      RREP)

   o  AdvRte.PrefixLength := RteMsg.OrigPrefixLen (in RREQ) or
      RteMsg.TargPrefixLen (in RREP) if included, or if no prefix length
      was included in RteMsg, the address length, in bits, of
      AdvRte.Address

   o  AdvRte.SeqNum := RteMsg.OrigSeqNum (in RREQ) or RteMsg.TargSeqNum
      (in RREP)

   o  AdvRte.MetricType := RteMsg.MetricType if included, or
      DEFAULT_METRIC_TYPE if not

   o  AdvRte.Metric := RteMsg.Metric

   o  AdvRte.Cost := AdvRte.Metric + Cost(L) using the cost function
      associated with the route's metric type, where L is the link from
      the advertising router

   o  AdvRte.ValidityTime := RteMsg.ValidityTime, if included

   If prefix length information is present, the route describes the
   subnet on which the address resides.

6.5.1.  Evaluating Route Information

   To determine whether the advertised route is to be used to update the
   routing table, the incoming route information MUST be processed as
   follows:

   1.  Search for a routing table entry (Route) matching AdvRte's
       address, prefix length and metric type

       *  If no route exists, AdvRte SHOULD be used to update the
          routing table.



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       *  If a route exists, continue to Step 2.

   2.  Compare sequence numbers

       *  If AdvRte is more recent (AdvRte.SeqNum > Route.SeqNum),
          AdvRte MUST be used to update the routing table.

       *  If AdvRte is stale (AdvRte.SeqNum < Route.SeqNum), AdvRte MUST
          NOT be used to update the routing table.

       *  If the sequence numbers are equal, continue to Step 3.

   3.  Compare route costs

       *  For some metric types, including the default metric specified
          in Section 5.3, the best route is the route with the lowest
          metric value.  For other metric types, the best route may be
          the route with the highest metric.

       *  If AdvRte is better, it SHOULD be used to update the routing
          table because it offers improvement.

       *  If AdvRte is not better (i.e., it is worse or equal) and Route
          is valid, AdvRte MUST NOT be used to update the routing table
          because it does not offer any improvement.

       *  If AdvRte is not better (i.e., it is worse or equal) but Route
          is Invalid, continue to Step 4.

   4.  Check that AdvRte is safe against routing loops (see Section 5.2)

       *  If LoopFree(AdvRte, Route) returns FALSE, AdvRte MUST NOT be
          used to update the routing table because using the incoming
          information might cause a routing loop.

       *  If LoopFree(AdvRte, Route) returns TRUE, AdvRte SHOULD be used
          to update the routing table because it can safely repair the
          existing invalid route.

   If the advertised route SHOULD be used to update the routing table,
   the procedure in Section 6.5.2 is followed.

6.5.2.  Applying Route Updates

   If the RteMsg containing AdvRte is a RREQ, the route is not yet
   confirmed.  It should be stored, so that a corresponding RREP can be
   sent, but should not be used to forward data.  If there is already a
   matching route, this new route should be saved as an additional route



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   using the process below, and can replace the original route when
   adjacency with the next hop is confirmed.

   If no existing route in the route table matches AdvRte on address,
   prefix length and metric type, a new route should be saved using the
   process below.

   A new route table entry is created and initialized as follows:

   o  Route.Address := AdvRte.Address

   o  Route.PrefixLength := AdvRte.PrefixLength (if included), or the
      length, in bits, of Route.Address (32 for IPv4 or 128 for IPv6)

   o  Route.MetricType := AdvRte.MetricType

   o  Route.State := Idle (if the RteMsg is a RREP) or Unconfirmed (if
      the RteMsg is a RREQ)

   In all cases, the other fields of the route table entry are assigned
   as follows:

   o  Route.SeqNum := AdvRte.SeqNum

   o  Route.NextHop := IP.SourceAddress (the address of the router from
      which the AdvRte was received)

   o  Route.NextHopInterface := interface on which RteMsg was received

   o  Route.Metric := AdvRte.Cost

   o  Route.LastUsed := CurrentTime

   o  Route.LastSeqNumUpdate := CurrentTime

   o  Route.ExpirationTime := CurrentTime + AdvRte.ValidityTime if a
      validity time exists, otherwise MAX_TIME

   In addition, if a route already existed but Route.State was Invalid
   before the update, it should be set to Idle (if the RteMsg is a
   RREP).

   If this update results in a valid route which fulfills an existing
   route discovery, the associated timers can be cancelled and any
   buffered packets for this route can be forwarded.






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6.6.  Suppressing Redundant Messages

   When route messages are flooded in a MANET, an AODVv2 router may
   receive multiple similar messages.  Regenerating every one of these
   gives little additional benefit, and generates unnecessary signaling
   traffic and interference.

   Each AODVv2 router stores information about recently received route
   messages in the AODVv2 Multicast RteMsg Table (Section 4.5).
   Received RteMsgs are tested against previously received RteMsgs, and
   if determined to be redundant, regeneration can be avoided.  Where
   necessary, regeneration is performed using the processes in
   Section 7.

   To determine if a received RREQ is redundant:

   1.  Search for an entry in the RteMsg Table with the same
       MessageType, OrigAddr, TargAddr, and MetricType

       *  If there is none, create an entry to store information about
          the received RREQ and regenerate the RREQ.

       *  If there is an entry, update the timestamp field, since
          comparable RteMsgs are still traversing the network, and
          continue to Step 2.

   2.  Compare the sequence numbers

       *  If the entry has a lower OrigSeqNum than the received RREQ,
          update the entry using information from the new RREQ and
          regenerate the RREQ.

       *  If the entry has a higher OrigSeqNum than the received RREQ,
          do not update the entry and do not regenerate the RREQ.

       *  If the entry has the same OrigSeqNum, continue to Step 3.

   3.  Compare the metric values

       *  If the entry has a Metric that is worse than the received
          RREQ, update the entry using information from the new RREQ.

       *  If the entry has a Metric that is better than the received
          RREQ, do not update the entry.

       *  In both cases, the RREQ MAY be suppressed to avoid extra
          control traffic.  However, if the processing of the RREQ
          results in an update to the route table, the RREQ MAY be



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          regenerated to ensure other routers have up-to-date
          information.

6.7.  Route Maintenance

   Route maintenance involves monitoring and updating route state,
   handling route timeouts and reporting routes that become invalid.

   Before using a route to forward a packet, an AODVv2 router MUST check
   the status of the route (Section 6.7.1).  If the route is valid, it
   MUST be marked as Active and its LastUsed timestamp MUST be updated,
   before forwarding the packet to the route's next hop.  If there is no
   valid route, this MUST be reported to the packet's source (see
   Section 6.7.2).

6.7.1.  Route State

   During normal operation, AODVv2 does not require any explicit
   timeouts to manage the lifetime of a route.  At any time, any route
   table entry can be examined and updated according to the rules below.
   Route state should be checked before packet forwarding and before any
   operation based on route state.

   There are four possible states for an AODVv2 route:

   Active
      An Active route is in current use for forwarding packets.  If the
      route is not timed, it becomes Idle if not used within
      ACTIVE_INTERVAL.  A timed route remains Active until its
      expiration time, after which it MAY either be expunged or marked
      as Invalid.

   Idle
      An Idle route has not been used in the last ACTIVE_INTERVAL, but
      can still be used for forwarding packets, in which case it becomes
      an Active route again.  If not used, an Idle route remains idle
      for MAX_IDLETIME before becoming an Invalid route.

   Invalid
      An Invalid route cannot be used for forwarding packets, but the
      sequence number information MAY be maintained until
      MAX_SEQNUM_LIFETIME after the last sequence number update.  This
      allows incoming information to be assessed for freshness.

   Unconfirmed
      An Unconfirmed route cannot be used for forwarding packets.  When
      adjacency with the next hop router is confirmed, the route will
      transition to Idle.



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   If the time since the route's last sequence number update exceeds
   MAX_SEQNUM_LIFETIME, the sequence number must be removed from the
   route.  If the route is Invalid at this time, it MUST be expunged.
   Active and Idle routes can continue to be used to forward packets.
   The removal of the sequence number is required to ensure that any
   AODVv2 routers following the initialization procedure can safely
   begin routing functions using a new sequence number.

   Appendix D.1.1 contains an algorithmic representation of this timeout
   behavior.

   Routes can become Invalid before a timeout occurs:

   o  If a link breaks, all routes using that link as the next hop MUST
      immediately be marked as Invalid.

   o  If a Route Error (RERR) message containing the route is received
      from the route's next hop, the route MUST immediately be marked as
      Invalid.

   Memory constrained devices MAY choose to expunge routes from the
   AODVv2 route table before their expiration time, but MUST adhere to
   the following rules:

   o  An Active route MUST NOT be expunged.

   o  An Idle route SHOULD NOT be expunged.

   o  Any Invalid route MAY be expunged; least recently used Invalid
      routes SHOULD be expunged first.

   o  An Unconfirmed route MUST NOT be expunged, if it was installed
      within the last RREQ_WAIT_TIME.  Otherwise, it MAY be expunged.

6.7.2.  Reporting Invalid Routes

   When an Active route becomes Invalid as a result of a broken link or
   a received Route Error (RERR) message, other routers should be
   informed by sending a RERR message containing details of the
   invalidated route.

   A RERR message should also be sent when an AODVv2 router receives a
   packet to forward on behalf of another router but does not have a
   valid route for the destination of the packet.  This packet may be a
   data packet or, in rare cases, a RREP message, if the route to the
   request originator has been lost.  The packet or message triggering
   the RERR MUST be discarded.




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   Generation of a RERR message is described in Section 7.4.1.

7.  AODVv2 Protocol Messages

   AODVv2 defines four message types: Route Request (RREQ), Route Reply
   (RREP), Route Reply Acknowledgement (RREP_Ack), and Route Error
   (RERR).

   Each AODVv2 message is defined as a set of data elements.  Rules for
   the generation, reception and regeneration of each message type are
   described in the following sections.  Section 8 discusses how the
   data elements map to RFC 5444 Message TLVs, Address Blocks, and
   Address TLVs.

7.1.  Route Request (RREQ) Message

   Route Request messages are used in route discovery operations to
   request a route to a specified target address.  RREQ messages have
   the following general structure:

    +-----------------------------------------------------------------+
    |             msg_hop_limit, (optional) msg_hop_count             |
    +-----------------------------------------------------------------+
    |                           AddressList                           |
    +-----------------------------------------------------------------+
    |                   PrefixLengthList (optional)                   |
    +-----------------------------------------------------------------+
    |                OrigSeqNum, (optional) TargSeqNum                |
    +-----------------------------------------------------------------+
    |                      MetricType (optional)                      |
    +-----------------------------------------------------------------+
    |                           OrigMetric                            |
    +-----------------------------------------------------------------+
    |                     ValidityTime (optional)                     |
    +-----------------------------------------------------------------+

                     Figure 1: RREQ message structure

   RREQ Data Elements

      msg_hop_limit
         The remaining number of hops allowed for dissemination of the
         RREQ message.

      msg_hop_count
         The number of hops already traversed during dissemination of
         the RREQ message.




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      AddressList
         Contains OrigAddr and TargAddr, the source and destination
         addresses of the packet for which a route is requested.
         OrigAddr and TargAddr MUST be routable unicast addresses.

      PrefixLengthList
         Contains the length, in bits, of the prefix associated with
         OrigAddr.  If omitted, the prefix length is equal to OrigAddr's
         address length in bits.  If OrigAddr resides on a subnet
         configured as a Router Client, the prefix length represents the
         number of bits in the subnet mask.

      OrigSeqNum
         The sequence number associated with OrigAddr.

      TargSeqNum
         A sequence number associated with TargAddr.  This may be
         included if an Invalid route exists to the target.  This is
         useful for the optional Intermediate RREP feature (see
         Section 10.3).

      MetricType
         The type of metric associated with OrigMetric.  This element
         can be omitted if the default metric type is used.

      OrigMetric
         The metric associated with the route to OrigAddr, as measured
         by the sender of the message.

      ValidityTime
         The length of time that the message sender is willing to offer
         a route toward OrigAddr.  Omitted if no time limit is imposed.

   The OrigSeqNum data element in a RteMsg MUST apply only to OrigAddr.
   Therefore the other address in the AddressList is TargAddr.  If the
   TargSeqNum data element is included, then it MUST apply only to
   TargAddr.

7.1.1.  RREQ Generation

   A RREQ is generated when a packet needs to be forwarded for a Router
   Client, and no valid route currently exists for the packet's
   destination.

   Before creating a RREQ, the router should check if a RREQ has
   recently been sent for the requested destination.  If so, and the
   wait time for a reply has not yet been reached, the router should
   continue to await a response without generating a new RREQ.  If the



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   timeout has been reached, a new RREQ may be generated.  If buffering
   is configured, the incoming packet SHOULD be buffered until the route
   discovery is completed.

   If the limit for the rate of AODVv2 control message generation has
   been reached, no message should be generated.

   To generate the RREQ, the router (referred to as RREQ_Gen) follows
   this procedure:

   1.  Set msg_hop_limit := MAX_HOPCOUNT

   2.  Set msg_hop_count := 0, if including it

   3.  Set AddressList := {OrigAddr, TargAddr}

   4.  For the PrefixLengthList:

       *  If OrigAddr resides on a Router Client subnet, set
          PrefixLengthList := {OrigAddr's prefix length in bits, null}.

       *  Otherwise, omit PrefixLengthList.

   5.  For OrigSeqNum:

       *  Increment the SeqNum associated with OrigAddr as specified in
          Section 4.4.

       *  Set OrigSeqNum := SeqNum.

   6.  For TargSeqNum:

       *  If an Invalid route exists matching TargAddr using longest
          prefix matching and has a valid sequence number, set
          TargSeqNum := route's sequence number.

       *  If no Invalid route exists matching TargAddr, or the route
          doesn't have a sequence number, omit TargSeqNum.

   7.  Include the MetricType data element if requesting a route for a
       non-default metric type, and set the type accordingly

   8.  Set OrigMetric := Route[OrigAddr].Metric

   9.  Include the ValidityTime data element if advertising that the
       route to OrigAddr via this router is offered for a limited time,
       and set ValidityTime accordingly




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   This AODVv2 message is used to create a corresponding RFC 5444
   message (see Section 8) which is multicast, by default, to LL-MANET-
   Routers on all interfaces configured for AODVv2 operation.

7.1.2.  RREQ Reception

   Upon receiving a RREQ, an AODVv2 router performs the following steps:

   1.  If the sender is blacklisted (Section 4.3), check the entry's
       reset time

       *  If CurrentTime < Remove Time, ignore this RREQ for further
          processing.

       *  If CurrentTime >= Remove Time, reset the neighbor state to
          Unknown and continue to Step 2.

   2.  Verify that the message hop count, if included, hasn't exceeded
       MAX_HOPCOUNT

       *  If so, ignore this RREQ for further processing.

   3.  Verify that the message contains the required data elements:
       msg_hop_limit, OrigAddr, TargAddr, OrigSeqNum, and a OrigMetric,
       and that OrigAddr and TargAddr are valid addresses (routable and
       unicast)

       *  If not, ignore this RREQ for further processing.

   4.  If the MetricType data element is present, check that the metric
       type is known

       *  If not, ignore this RREQ for further processing.

   5.  Verify that the cost of the advertised route will not exceed the
       maximum allowed metric value for the metric type (Metric <=
       MAX_METRIC[MetricType] - Cost(L))

       *  If it will, ignore this RREQ for further processing.

   6.  Process the route to OrigAddr as specified in Section 6.5.1

   7.  Check if the message is redundant by comparing to entries in the
       RteMsg table (Section 6.6)

       *  If redundant, ignore this RREQ for further processing.





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       *  If not redundant, save the information in the RteMsg table to
          identify future duplicates and continue processing.

   8.  Check if the TargAddr belongs to one of the Router Clients

       *  If so, generate a RREP as specified in Section 7.2.1.

       *  If not, continue to RREQ regeneration.

7.1.3.  RREQ Regeneration

   By regenerating a RREQ, a router advertises that it will forward
   packets to the OrigAddr contained in the RREQ according to the
   information enclosed.  The router MAY choose not to regenerate the
   RREQ, though this could decrease connectivity in the network or
   result in non-optimal paths.  The full set of circumstances under
   which a router may avoid regenerating a RREQ are not declared in this
   document, though examples include the router being heavily loaded or
   low on energy and therefore unwilling to advertise routing capability
   for more traffic.

   The RREQ should not be regenerated if the limit for the rate of
   AODVv2 control message generation has been reached.

   The procedure for RREQ regeneration is as follows:

   1.  Set msg_hop_limit := received msg_hop_limit - 1

   2.  If msg_hop_limit is now zero, do not continue with the
       regeneration process

   3.  Set msg_hop_count := received msg_hop_count + 1, if included,
       otherwise omit msg_hop_count

   4.  Set AddressList, PrefixLengthList, sequence numbers and
       MetricType to the values in the received RREQ

   5.  Set OrigMetric := Route[OrigAddr].Metric

   6.  If the received RREQ contains a ValidityTime, or if the
       regenerating router wishes to limit the time that it offers a
       route to OrigAddr, the regenerated RREQ MUST include a
       ValidityTime data element

       *  The ValidityTime is either the ValidityTime the previous
          AODVv2 router specified, or the ValidityTime this router
          wishes to impose, whichever is lower.




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   This AODVv2 message is used to create a corresponding RFC 5444
   message (see Section 8) which is multicast, by default, to LL-MANET-
   Routers on all interfaces configured for AODVv2 operation.  However,
   the regenerated RREQ can be unicast to the next hop address of the
   route toward TargAddr, if known.

7.2.  Route Reply (RREP) Message

   A Route Reply message is sent in response to a Route Request message
   and offers a route to the Target Address in the RREQ.  RREP messages
   have the following general structure:

    +-----------------------------------------------------------------+
    |             msg_hop_limit, (optional) msg_hop_count             |
    +-----------------------------------------------------------------+
    |                        AckReq (optional)                        |
    +-----------------------------------------------------------------+
    |                           AddressList                           |
    +-----------------------------------------------------------------+
    |                   PrefixLengthList (optional)                   |
    +-----------------------------------------------------------------+
    |                           TargSeqNum                            |
    +-----------------------------------------------------------------+
    |                      MetricType (optional)                      |
    +-----------------------------------------------------------------+
    |                           TargMetric                            |
    +-----------------------------------------------------------------+
    |                     ValidityTime (optional)                     |
    +-----------------------------------------------------------------+

                     Figure 2: RREP message structure

   RREP Data Elements

      msg_hop_limit
         The remaining number of hops allowed for dissemination of the
         RREP message.

      msg_hop_count
         The number of hops already traversed during dissemination of
         the RREP message.

      AckReq
         Indicates that an acknowledgement to the RREP is requested by
         the sender (see Section 6.2).

      AddressList




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         Contains OrigAddr and TargAddr, the source and destination
         addresses of the packet for which a route is requested.
         OrigAddr and TargAddr MUST be routable unicast addresses.

      PrefixLengthList
         Contains the length, in bits, of the prefix associated with
         TargAddr.  If omitted, the prefix length is equal to TargAddr's
         address length, in bits.  If TargAddr resides on a subnet
         configured as a Router Client, the prefix length represents the
         number of bits in the subnet mask.

      TargSeqNum
         The sequence number associated with TargAddr.

      MetricType
         The type of metric associated with TargMetric.  This element
         can be omitted if the default metric type is used.

      TargMetric
         The metric associated with the route to TargAddr, as seen from
         the sender of the message.

      ValidityTime
         The length of time that the message sender is willing to offer
         a route toward TargAddr.  Omitted if no time limit is imposed.

   The TargSeqNum data element in a RteMsg MUST apply only to TargAddr.
   Therefore the other address in the AddressList is OrigAddr.

7.2.1.  RREP Generation

   A RREP is generated when a RREQ arrives for one of the AODVv2
   router's Router Clients.

   Before creating a RREP, the router should check if the corresponding
   RREQ is redundant, i.e., a response has already been generated, or if
   the limit for the rate of AODVv2 control message generation has been
   reached.  If so, the RREP should not be created.

   The RREP SHOULD include an AckReq data element in order to achieve
   adjacency monitoring as described in Section 6.2.  If adjacency is
   already confirmed, it can be omitted.  The AckReq data element
   indicates that an acknowledgement to the RREP is requested in the
   form of a Route Reply Acknowledgement (RREP_Ack).  Implementations
   SHOULD resend the RREP if an acknowledgement is not received within
   RREP_Ack_SENT_TIMEOUT, doubling the timeout with each retry, up to a
   maximum number of retries RREP_RETRIES, using the same exponential
   backoff described in Section 6.4 for RREQ retries.



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   Adjacency confirmation SHOULD be considered to have failed after
   RREP_RETRIES and the corresponding wait time for a RREP_Ack response
   to the final RREP.  The next hop router MUST be marked as blacklisted
   (Section 4.3), and any installed routes with next hop set to the
   newly blacklisted router should be invalidated.

   To generate the RREP, the router (also referred to as RREP_Gen)
   follows this procedure:

   1.  Set msg_hop_limit := msg_hop_count from the received RREQ
       message, if it was included, or MAX_HOPCOUNT if it was not
       included

   2.  Set msg_hop_count := 0, if including it

   3.  If adjacency with the next hop toward OrigAddr is not already
       confirmed, include the AckReq data element

   4.  Set Address List := {OrigAddr, TargAddr}

   5.  For the PrefixLengthList:

       *  If TargAddr resides on a Router Client subnet, set
          PrefixLengthList := {null, TargAddr subnet's prefix length, in
          bits}.

       *  Otherwise, omit PrefixLengthList.

   6.  For the TargSeqNum:

       *  Increment the SeqNum associated with TargAddr as specified in
          Section 4.4.

       *  Set TargSeqNum := SeqNum.

   7.  Include the MetricType data element if the route requested is for
       a non-default metric type, and set the type accordingly

   8.  Set TargMetric := Route[TargAddr].Metric

   9.  Include the ValidityTime data element if advertising that the
       route to TargAddr via this router is offered for a limited time,
       and set ValidityTime accordingly

   This AODVv2 message is used to create a corresponding RFC 5444
   message (see Section 8) which is unicast, by default, to the IP
   address of the next hop of RREP_Gen's route to OrigAddr.




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7.2.2.  RREP Reception

   Upon receiving a RREP, an AODVv2 router performs the following steps:

   1.   If the sender is blacklisted (Section 4.3), but the RREP answers
        a recently sent RREQ, the sender state should be set to
        Confirmed since a RREP is an indication of adjacency

   2.   Verify that the message hop count, if included, hasn't exceeded
        MAX_HOPCOUNT

        *  If so, ignore this RREQ for further processing.

   3.   Verify that the message contains the required data elements:
        msg_hop_limit, OrigAddr, TargAddr, TargSeqNum, and TargMetric,
        and that OrigAddr and TargAddr are valid addresses (routable and
        unicast)

        *  If not, ignore this RREP for further processing.

   4.   If the MetricType data element is present, check that the metric
        type is known

        *  If not, ignore this RREP for further processing.

   5.   Verify that the cost of the advertised route will not exceed the
        maximum allowed metric value for the metric type (Metric <=
        MAX_METRIC[MetricType] - Cost(L))

        *  If it will, ignore this RREP for further processing.

   6.   Process the route to TargAddr as specified in Section 6.5.1

        *  If the route to TargAddr fulfills a previously sent RREQ, any
           associated timeouts will be cancelled and buffered packets
           will be forwarded to TargAddr, but processing continues to
           Step 7.

   7.   If the AckReq data element is present, send an acknowledgement
        as specified in Section 7.3

   8.   Check if the message is redundant by comparing to entries in the
        RteMsg table (Section 6.6)

        *  If redundant, ignore this RREP for further processing.






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        *  If not redundant, save the information in the RteMsg table to
           identify future redundant RREP messages and continue
           processing.

   9.   Check if the OrigAddr belongs to one of the Router Clients

        *  If so, no further processing is necessary.

   10.  Check if a valid route exists to OrigAddr

        *  If so, continue to RREP regeneration.

        *  If not, a Route Error message SHOULD be transmitted to
           TargAddr according to Section 7.4.1 and the RREP should be
           discarded and not regenerated.

7.2.3.  RREP Regeneration

   Unless the router is prepared to advertise the route contained within
   the RREP, it halts processing.  By regenerating a RREP, a router
   advertises that it will forward packets to TargAddr according to the
   information enclosed.  The router MAY choose not to regenerate the
   RREP, in the same way it may choose not to regenerate a RREQ (see
   Section 7.1.3), though this could decrease connectivity in the
   network or result in non-optimal paths.

   The RREP should not be regenerated if the limit for the rate of
   AODVv2 control message generation has been reached.

   The procedure for RREP regeneration is as follows:

   1.  Set msg_hop_limit := received msg_hop_limit - 1

   2.  If msg_hop_limit is now zero, do not continue with the
       regeneration process

   3.  Set msg_hop_count := received msg_hop_count + 1, if it was
       included, otherwise omit msg_hop_count

   4.  If an adjacency with the next hop toward OrigAddr is not already
       confirmed, include the AckReq data element

   5.  Set AddressList, PrefixLengthList, TargSeqNum and MetricType to
       the values in the received RREP

   6.  Set TargMetric := Route[TargAddr].Metric





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   7.  If the received RREP contains a ValidityTime, or if the
       regenerating router wishes to limit the time that it will offer a
       route to TargAddr, the regenerated RREP MUST include a
       ValidityTime data element

       *  The ValidityTime is either the ValidityTime the previous
          AODVv2 router specified, or the ValidityTime this router
          wishes to impose, whichever is lower.

   This AODVv2 message is used to create a corresponding RFC 5444
   message (see Section 8) which is unicast, by default, to the IP
   address of the next hop on the route to OrigAddr.

7.3.  Route Reply Acknowledgement (RREP_Ack) Message

   The Route Reply Acknowledgement is sent in response to a received
   Route Reply which includes an AckReq data element.  When the RREP_Ack
   is received, it confirms the adjacency between the two routers.  The
   RREP_Ack has no data elements.

7.3.1.  RREP_Ack Generation

   A RREP_Ack is generated when the AckReq data element is included in a
   received RREP.  The RREP_Ack should not be generated if the limit for
   the rate of AODVv2 control message generation has been reached.

   There are no data elements in a RREP_Ack.  The RFC 5444
   representation is discussed in Section 8.  The RREP_Ack is unicast,
   by default, to the IP address of the router that requested it.

7.3.2.  RREP_Ack Reception

   Upon receiving a RREP_Ack, an AODVv2 router performs the following
   steps:

   1.  If a RREP_Ack message was expected from the IP source address of
       the RREP_Ack, the router cancels any associated timeouts

   2.  If the RREP_Ack was expected, ensure the router sending the
       RREP_Ack is marked with state Confirmed in the neighbor list
       (Section 4.3)

7.4.  Route Error (RERR) Message

   A Route Error message is generated by an AODVv2 router to notify
   other AODVv2 routers of routes that are no longer available.  A RERR
   message has the following general structure:




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    +-----------------------------------------------------------------+
    |                          msg_hop_limit                          |
    +-----------------------------------------------------------------+
    |                       PktSource (optional)                      |
    +-----------------------------------------------------------------+
    |                           AddressList                           |
    +-----------------------------------------------------------------+
    |                   PrefixLengthList (optional)                   |
    +-----------------------------------------------------------------+
    |                       SeqNumList (optional)                     |
    +-----------------------------------------------------------------+
    |                     MetricTypeList (optional)                   |
    +-----------------------------------------------------------------+

                     Figure 3: RERR message structure

   RERR Data Elements

      msg_hop_limit
         The remaining number of hops allowed for dissemination of the
         RERR message.

      PktSource
         The source IP address of the packet triggering the RERR.  If
         the RERR is triggered by a broken link, the PktSource data
         element is not required.

      AddressList
         The addresses of the routes no longer available through
         RERR_Gen.

      PrefixLengthList
         The prefix lengths, in bits, associated with the routes no
         longer available through RERR_Gen, indicating whether a route
         represents a single device or a subnet.

      SeqNumList
         The sequence numbers of the routes no longer available through
         RERR_Gen (where known).

      MetricTypeList
         The types of metric associated with the routes no longer
         available through RERR_Gen.  This element can be omitted if all
         routes use the default metric type.







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7.4.1.  RERR Generation

   A RERR is generated when an AODVv2 router (also referred to as
   RERR_Gen) needs to report that a destination is no longer reachable.
   There are two events that cause this response:

   o  If a packet arrives that cannot be forwarded because no valid
      route exists for its destination, the RERR generated MUST contain
      the PktSource data element and will contain only one unreachable
      address.  The contents of PktSource and AddressList depend on the
      packet that triggered the RERR:

      *  If the packet is a data packet forwarded by another AODVv2
         router, PktSource is set to the source IP address of the
         packet, and the AddressList contains the destination IP address
         of the packet.

      *  If the packet contains a RREP message and the route to OrigAddr
         has been lost, PktSource is set to the TargAddr of the RREP,
         and the AddressList contains the OrigAddr from the RREP.

      The prefix length and sequence number MAY be included if known
      from an Invalid route entry to the destination of the packet.  The
      MetricTypeList MAY also be included if a MetricType can be
      determined from the packet itself, or if an Invalid route exists
      for the packet's destination and the metric type is not
      DEFAULT_METRIC_TYPE.

      RERR_Gen MUST discard the packet or message that triggered
      generation of the RERR.

      In order to avoid flooding the network with RERR messages when a
      stream of packets to an unreachable address arrives, an AODVv2
      router SHOULD determine whether a RERR has recently been sent with
      the same unreachable address and PktSource, and SHOULD avoid
      creating duplicate RERR messages.

   o  When a link breaks, multiple routes may become Invalid, and the
      RERR generated MAY contain multiple unreachable addresses.  If the
      message contents would cause the MTU to be exceeded, multiple RERR
      messages must be sent.  The RERR MUST include the MetricTypeList
      data element when it contains routes which do not use the
      DEFAULT_METRIC_TYPE.  The PktSource data element is omitted.

      All previously Active routes that used the broken link MUST be
      reported.  The AddressList, PrefixLengthList, SeqNumList, and
      MetricTypeList will contain entries for each invalidated route.




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      A RERR message is only sent if an Active route becomes Invalid,
      though an AODVv2 router can also include Idle routes that become
      Invalid if the configuration parameter ENABLE_IDLE_IN_RERR is set
      (see Section 11.3).

   Incidentally, if an AODVv2 router receives an ICMP error packet to or
   from the address of one of its Router Clients, it simply forwards the
   ICMP packet in the same way as any other data packet, and will not
   generate any RERR message based on the contents of the ICMP packet.

   The RERR should not be generated if the limit for the rate of AODVv2
   control message generation has been reached.

   To generate the RERR, the router follows this procedure:

   1.  Set msg_hop_limit := MAX_HOPCOUNT

   2.  If necessary, include the PktSource data element and set the
       value to the source address of the packet triggering the RERR

   3.  For each route that needs to be reported, while respecting the
       interface MTU:

       *  Insert the route address into the AddressList.

       *  Insert the prefix length into PrefixLengthList, if known and
          not equal to the address length.

       *  Insert the sequence number into SeqNumList, if known.

       *  Insert the metric type into MetricTypeList, if known and not
          equal to DEFAULT_METRIC_TYPE.

   4.  If interface MTU would be exceeded, create additional RERR
       messages

   The AODVv2 message is used to create a corresponding RFC 5444 message
   (see Section 8).

   If the RERR is sent in response to an undeliverable packet or
   message, it SHOULD be sent unicast to the next hop on the route to
   PktSource, or alternatively it MUST be multicast to LL-MANET-Routers.

   If the RERR is sent in response to a broken link, the RERR is, by
   default, multicast to LL-MANET-Routers.






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   If the optional precursor lists feature (see Section 10.2) is
   enabled, the RERR is unicast to the precursors of the routes being
   reported.

7.4.2.  RERR Reception

   Upon receiving a RERR, an AODVv2 router performs the following steps:

   1.  Verify that the message contains the required data elements:
       msg_hop_limit and at least one unreachable address

       *  If not, ignore this RREP for further processing.

   2.  For each address in the AddressList, check that:

       *  The address is valid (routable and unicast)

       *  The MetricType, if present, is known (assume
          DEFAULT_METRIC_TYPE if not present)

       *  There is a valid route with the same MetricType matching the
          address using longest prefix matching

       *  Either the route's next hop is the sender of the RERR and
          route's next hop interface is the interface on which the RERR
          was received, or PktSource is present in the RERR and is a
          Router Client address

       *  The unreachable address' sequence number is either unknown, or
          is greater than the route's sequence number

       If any of the above are false, the route does not need to be
       invalidated and the unreachable address does not need to be
       advertised in a regenerated RERR.

       If all of the above are true:

       *  If the route's prefix length is the same as the unreachable
          address' prefix length, set the route state to Invalid, and
          note that the route should be advertised in a regenerated
          RERR.

       *  If the prefix length is shorter than the original route, the
          route MUST be expunged from the routing table, since it is a
          sub-route of the larger route which is reported to be Invalid.

       *  If the prefix length is different, create a new route with the
          unreachable address, and its prefix and sequence number, set



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          the state to Invalid, and note that the route should be
          advertised in a regenerated RERR.

       *  Update the sequence number on the stored route, if the
          reported sequence number is greater.

   3.  If PktSource is included and is a Router Client, do not
       regenerate the RERR.

   4.  Check if there are unreachable addresses which need to be
       advertised in a regenerated RERR

       *  If so, regenerate the RERR as detailed in Section 7.4.3.

       *  If not, take no further action.

7.4.3.  RERR Regeneration

   The RERR should not be generated if the limit for the rate of AODVv2
   control message generation has been reached.

   The procedure for RERR regeneration is as follows:

   1.  Set msg_hop_limit := received msg_hop_limit - 1

   2.  If msg_hop_limit is now zero, do not continue with the
       regeneration process

   3.  If the PktSource data element was included in the original RERR,
       copy it into the regenerated RERR

   4.  For each route that needs to be reported, while respecting the
       interface MTU:

       *  Insert the unreachable address into the AddressList.

       *  Insert the prefix length into PrefixLengthList, if known and
          not equal to the address length.

       *  Insert the sequence number into SeqNumList, if known.

       *  Insert the MetricType into MetricTypeList if known, and not
          equal to DEFAULT_METRIC_TYPE.

   5.  If interface MTU would be exceeded, create additional RERR
       messages





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   The AODVv2 message is used to create a corresponding RFC 5444 message
   (see Section 8).  If the RERR contains the PktSource data element,
   the regenerated RERR SHOULD be sent unicast to the next hop on the
   route to PktSource, or alternatively it MUST be multicast to LL-
   MANET-Routers.  If the RERR is sent in response to a broken link, the
   RERR is, by default, multicast to LL-MANET-Routers.

8.  RFC 5444 Representation

   AODVv2 specifies that all control plane messages between routers
   SHOULD use the Generalized Mobile Ad Hoc Network Packet/Message
   Format [RFC5444], and therefore AODVv2 defines route messages
   comprising data elements that map to message elements in RFC 5444.

   RFC 5444 provides a multiplexed transport for multiple protocols.  An
   RFC 5444 multiplexer may choose to optimize the content of certain
   message elements to reduce control plane overhead.

   A brief summary of the RFC 5444 format:

   1.  A packet contains zero or more messages

   2.  A message contains a Message Header, one Message TLV Block, zero
       or more Address Blocks, and one Address Block TLV Block per
       Address Block

   3.  The Message TLV Block MAY contain zero or more Message TLVs

   4.  An Address Block TLV Block MAY include zero or more Address Block
       TLVs

   5.  Each TLV value in an Address Block TLV Block can be associated
       with all of the addresses, a contiguous set of addresses, or a
       single address in the Address Block

   AODVv2 does not require access to the RFC 5444 packet header.

   In the message header, AODVv2 uses <msg-hop-limit>, <msg-hop-count>,
   <msg-type> and <msg-addr-length>.  <msg-addr-length> indicates the
   length of any addresses in the message (using <msg-addr-length> :=
   address length in octets - 1, i.e. 3 for IPv4 and 15 for IPv6).

   The addresses in an Address Block may appear in any order, and values
   in an Address Block TLV must be associated with the correct address
   in the Address Block.  To indicate which address each value is
   associated with, the AODVv2 message representation uses lists where
   the order of the addresses in the AddressList matches the order of
   values in the other lists, e.g., SeqNumList in a RERR.



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   The following sections show how AODVv2 data elements are represented
   in RFC 5444 messages.  See Section 12 for more information about the
   Message TLVs and Address Block TLVs AODVv2 defines, and the type
   numbers allocated.

   Where the extension type of a TLV is set to zero, this is the default
   RFC 5444 value and the extension type will not be included in the
   message.

8.1.  RREQ

8.1.1.  Message Header

   +---------------+-----------------+---------------------------------+
   | Data Element  | Header Field    | Value                           |
   +---------------+-----------------+---------------------------------+
   | None          | <msg-type>      | RREQ                            |
   | msg_hop_limit | <msg-hop-limit> | MAX_HOPCOUNT                    |
   | msg_hop_count | <msg-hop-count> | Number of hops traversed so far |
   |               |                 | by the message.                 |
   +---------------+-----------------+---------------------------------+

8.1.2.  Message TLV Block

   A RREQ contains no Message TLVs.

8.1.3.  Address Block

   A RREQ contains two Addresses, OrigAddr and TargAddr, and each
   address has an associated prefix length.

        +-------------------------+------------------------------+
        | Data Elements           | Address Block                |
        +-------------------------+------------------------------+
        | OrigAddr/OrigPrefixLen  | <address> + <prefix-length>  |
        | TargAddr/TargPrefixLen  | <address> + <prefix-length>  |
        +-------------------------+------------------------------+

8.1.4.  Address Block TLV Block

   Address Block TLVs are always associated with addresses in the
   Address Block.  The following sections show the TLVs that apply to
   each address.








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8.1.4.1.  Address Block TLVs for OrigAddr

   +--------------+---------------+------------+-----------------------+
   | Data Element | TLV Type      | Extension  | Value                 |
   |              |               | Type       |                       |
   +--------------+---------------+------------+-----------------------+
   | OrigSeqNum   | ORIG_SEQ_NUM  | 0          | Sequence Number of    |
   |              |               |            | RREQ_Gen, the router  |
   |              |               |            | which initiated route |
   |              |               |            | discovery.            |
   | OrigMetric   | PATH_METRIC   | MetricType | Metric for the route  |
   | /MetricType  |               | (optional) | to OrigAddr, using    |
   |              |               |            | MetricType.           |
   | ValidityTime | VALIDITY_TIME | 0          | ValidityTime for      |
   | (optional)   |               |            | route to OrigAddr.    |
   +--------------+---------------+------------+-----------------------+

   In the AODVv2 representation, if the message relates to
   DEFAULT_METRIC_TYPE, MetricType is not included in the message.  The
   RFC 5444 representation will set the extension type in the
   PATH_METRIC TLV to 0.  AODVv2 interprets a MetricType of 0 as
   DEFAULT_METRIC_TYPE.

8.1.4.2.  Address Block TLVs for TargAddr

   +----------------+--------------+------------+----------------------+
   | Data Element   | TLV Type     | Extension  | Value                |
   |                |              | Type       |                      |
   +----------------+--------------+------------+----------------------+
   | TargSeqNum     | TARG_SEQ_NUM | 0          | The last known       |
   | (optional)     |              |            | TargSeqNum for       |
   |                |              |            | TargAddr.            |
   +----------------+--------------+------------+----------------------+

8.2.  RREP

8.2.1.  Message Header

   +---------------+-----------------+---------------------------------+
   | Data Element  | Header Field    | Value                           |
   +---------------+-----------------+---------------------------------+
   | None          | <msg-type>      | RREP                            |
   | msg_hop_limit | <msg-hop-limit> | <msg-hop-count> from            |
   |               |                 | corresponding RREQ.             |
   | msg_hop_count | <msg-hop-count> | Number of hops traversed so far |
   |               |                 | by the message.                 |
   +---------------+-----------------+---------------------------------+




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8.2.2.  Message TLV Block

   A RREP may contain the AAckReq data element in order to monitor
   adjacency, as described in Section 6.2.

       +--------------------+-----------+-----------------+--------+
       | Data Element       | TLV Type  | Extension Type  | Value  |
       +--------------------+-----------+-----------------+--------+
       | AckReq (optional)  | ACK_REQ   | 0               | None   |
       +--------------------+-----------+-----------------+--------+

8.2.3.  Address Block

   A RREP contains two Addresses, OrigAddr and TargAddr, and each
   address has an associated prefix length.

        +-------------------------+------------------------------+
        | Data Elements           | Address Block                |
        +-------------------------+------------------------------+
        | OrigAddr/OrigPrefixLen  | <address> + <prefix-length>  |
        | TargAddr/TargPrefixLen  | <address> + <prefix-length>  |
        +-------------------------+------------------------------+

8.2.4.  Address Block TLV Block

   Address Block TLVs are always associated with addresses in the
   Address Block.  The following sections show the TLVs that apply to
   each address.

8.2.4.1.  Address Block TLVs for OrigAddr

   No Address Block TLVs apply to OrigAddr in a RREP.

8.2.4.2.  Address Block TLVs for TargAddr

















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   +--------------+---------------+------------+-----------------------+
   | Data Element | TLV Type      | Extension  | Value                 |
   |              |               | Type       |                       |
   +--------------+---------------+------------+-----------------------+
   | TargSeqNum   | TARG_SEQ_NUM  | 0          | Sequence number of    |
   |              |               |            | RREP_Gen, the router  |
   |              |               |            | which created the     |
   |              |               |            | RREP.                 |
   | TargMetric   | PATH_METRIC   | MetricType | Metric for the route  |
   | /MetricType  |               | (optional) | to TargAddr, using    |
   |              |               |            | MetricType.           |
   | ValidityTime | VALIDITY_TIME | 0          | ValidityTime for      |
   | (optional)   |               |            | route to TargAddr.    |
   +--------------+---------------+------------+-----------------------+

   In the AODVv2 representation, if the message relates to
   DEFAULT_METRIC_TYPE, MetricType is not included in the message.  The
   RFC 5444 representation will set the extension type in the
   PATH_METRIC TLV to 0.  AODVv2 interprets a MetricType of 0 as
   DEFAULT_METRIC_TYPE.

8.3.  RREP_Ack

8.3.1.  Message Header

               +---------------+---------------+-----------+
               | Data Element  | Header Field  | Value     |
               +---------------+---------------+-----------+
               | None          | <msg-type>    | RREP_Ack  |
               +---------------+---------------+-----------+

8.3.2.  Message TLV Block

   A RREP_Ack contains no Message TLVs.

8.3.3.  Address Block

   A RREP_Ack contains no Address Block.

8.3.4.  Address Block TLV Block

   A RREP_Ack contains no Address Block TLV Block.

8.4.  RERR







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8.4.1.  Message Header

           +----------------+------------------+---------------+
           | Data Element   | Header Field     | Value         |
           +----------------+------------------+---------------+
           | None           | <msg-type>       | RERR          |
           | msg_hop_limit  | <msg-hop-limit>  | MAX_HOPCOUNT  |
           +----------------+------------------+---------------+

8.4.2.  Message TLV Block

   A RERR contains no Message TLVs.

8.4.3.  Address Block

   The Address Block in a RERR may contain PktSource, the source IP
   address of the packet triggering RERR generation, as detailed in
   Section 7.4.  Prefix Length associated with PktSource is equal to the
   address length in bits.

   Address Block always contains one Address per route that is no longer
   valid, and each address has an associated prefix length.

   +------------------------------+------------------------------------+
   | Data Element                 | Address Block                      |
   +------------------------------+------------------------------------+
   | PktSource (optional)         | <address> + <prefix-length> for    |
   |                              | PktSource                          |
   | AddressList/PrefixLengthList | <address> + <prefix-length> for    |
   |                              | each unreachable address in        |
   |                              | AddressList                        |
   +------------------------------+------------------------------------+

8.4.4.  Address Block TLV Block

   Address Block TLVs are always associated with addresses in the
   Address Block.  The following sections show the TLVs that apply to
   each type of address in the RERR.

8.4.4.1.  Address Block TLVs for PktSource











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   +----------------------------------+------------+-----------+-------+
   | Data Element                     | TLV Type   | Extension | Value |
   |                                  |            | Type      |       |
   +----------------------------------+------------+-----------+-------+
   | PktSource (MUST be used when     | PKT_SOURCE | 0         | None. |
   | PktSource is included in Address |            |           |       |
   | Block)                           |            |           |       |
   +----------------------------------+------------+-----------+-------+

8.4.4.2.  Address Block TLVs for Unreachable Addresses

   +----------------+-------------+------------+-----------------------+
   | Data Element   | TLV Type    | Extension  | Value                 |
   |                |             | Type       |                       |
   +----------------+-------------+------------+-----------------------+
   | SeqNumList     | SEQ_NUM     | 0          | Sequence Number       |
   | (optional)     |             |            | associated with       |
   |                |             |            | invalid route to the  |
   |                |             |            | unreachable address.  |
   | MetricTypeList | PATH_METRIC | MetricType | None. Extension Type  |
   | (optional)     |             |            | set to MetricType of  |
   |                |             |            | the route to the      |
   |                |             |            | unreachable address.  |
   +----------------+-------------+------------+-----------------------+

   Multiple PATH_METRIC TLVs may be necessary if routes with multiple
   MetricTypes are included in the RERR.

   In the AODVv2 representation, if the message relates to
   DEFAULT_METRIC_TYPE, MetricType is not included in the message.  The
   RFC 5444 representation will set the extension type in the
   PATH_METRIC TLV to 0.  AODVv2 interprets a MetricType of 0 as
   DEFAULT_METRIC_TYPE.

9.  Simple Internet Attachment

   Figure 4 shows a stub (i.e., non-transit) network of AODVv2 routers
   which is attached to the Internet via a single Internet AODVv2 Router
   (abbreviated IAR).

   As in any Internet-attached network, AODVv2 routers and clients that
   wish to be reachable from hosts on the Internet MUST have IP
   addresses within the IAR's routable and topologically correct prefix
   (i.e., 191.0.2.0/24).  This AODVv2 network and subnets within it will
   be advertised to the internet using procedures which are out of scope
   for this specification.





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       /-------------------------\
      / +----------------+        \
     /  |  AODVv2 Router |         \
     |  |  191.0.2.2/32  |         |
     |  +----------------+         |            Routable
     |                       +-----+--------+   Prefix
     |                       |   Internet   |  /191.0.2.0/24
     |                       | AODVv2 Router| /
     |                       |  191.0.2.1   |/      /---------------\
     |                       | serving net  +------+    Internet     \
     |                       | 191.0.2.0/24 |      \                 /
     |                       +-----+--------+       \---------------/
     |         +----------------+  |
     |         |  AODVv2 Router |  |
     |         |  191.0.2.3/32  |  |
     \         +----------------+  /
      \                           /
       \-------------------------/

               Figure 4: 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, i.e., destinations not
   on the configured 191.0.2.0/24 subnet.

   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 exact destination it will perform normal AODVv2 route discovery
   for that destination.

10.  Optional Features

   A number of optional features for AODVv2, associated initially with
   AODV, MAY be useful in networks with greater mobility or larger node
   populations, or networks requiring reduced latency for application
   launches.  These features are not required by minimal
   implementations.

10.1.  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.





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10.2.  Precursor Lists

   This section specifies an interoperable enhancement to AODVv2
   enabling more economical RERR notifications.

   There can be several sources of traffic for a certain destination.
   Each source of traffic and each upstream router between the
   forwarding AODVv2 router and the traffic source is known as a
   "precursor" for the destination.  For each destination, an AODVv2
   router MAY choose to keep track of precursors that have provided
   traffic for that destination.  Route Error messages about that
   destination can be sent unicast to these precursors instead of
   multicast to all AODVv2 routers.

   Since a RERR will be regenerated if it comes from a next hop on a
   valid route, the RERR should ideally be sent backwards along the
   route that the source of the traffic uses, to ensure it is
   regenerated at each hop and reaches the traffic source.  If the
   reverse path is unknown, the RERR should be sent toward the source
   along some other route.  Therefore, the options for saving precursor
   information are as follows:

   o  Save the next hop on an existing route to the packet's source
      address as the precursor.  In this case, it is not guaranteed that
      a RERR that is sent will follow the reverse of the source's route.
      In rare situations, this may prevent the route from being
      invalidated at the source of the data traffic.

   o  Save the packet's source address as the precursor.  In this case,
      the RERR can be sent along any existing route to the source of the
      data traffic, and should include the PktSource data element to
      ensure that the route will be invalidated at the source of the
      traffic, in case the RERR does not follow the reverse of the
      source's route.

   o  By inspecting the MAC address of each forwarded packet, determine
      which router forwarded the packet, and save the router address as
      a precursor.  This ensures that when a RERR is sent to the
      precursor router, the route will be invalidated at that router,
      and the RERR will be regenerated toward the source of the packet.

   During normal operation, each AODVv2 router maintaining precursor
   lists for a route must update the precursor list whenever it uses
   this route to forward traffic to the destination.  Precursors are
   classified as Active if traffic has recently been forwarded by the
   precursor.  The precursor is marked with a timestamp to indicate the
   time it last forwarded traffic on this route.




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   When an AODVv2 router detects that one or more routes are broken, it
   MAY notify each Active precursor using a unicast Route Error message
   instead of creating multicast traffic.  Unicast is applicable when
   there are few Active precursors compared to the number of neighboring
   AODVv2 routers.  However, the default multicast behavior is still
   preferable when there are many precursors, since fewer message
   transmissions are required.

   When an AODVv2 router supporting precursor lists receives a RERR
   message, it MAY identify the list of its own affected Active
   precursors for the routes in the RERR, and choose to send a unicast
   RERR to those, rather than send a multicast RERR.

   When a route is expunged, any precursor list associated with it must
   also be expunged.

10.3.  Intermediate RREP

   Without iRREP, only the AODVv2 router responsible for the target
   address can respond to a RREQ.  Using iRREP, route discoveries can be
   faster and create less control traffic.  This specification has been
   published as a separate Internet Draft [I-D.perkins-irrep].

10.4.  Message Aggregation Delay

   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].

11.  Configuration

   AODVv2 uses various parameters which can be grouped into the
   following categories:

   o  Timers

   o  Protocol constants

   o  Administrative parameters and controls

   This section show the parameters along with their definitions and
   default values (if any).






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   Note that several fields have limited size (bits or bytes).  These
   sizes and their encoding may place specific limitations on the values
   that can be set.

11.1.  Timers

   AODVv2 requires certain timing information to be associated with
   route table entries and message replies.  The default values are as
   follows:

                +------------------------+----------------+
                | Name                   | Default Value  |
                +------------------------+----------------+
                | ACTIVE_INTERVAL        | 5 second       |
                | MAX_IDLETIME           | 200 seconds    |
                | MAX_BLACKLIST_TIME     | 200 seconds    |
                | MAX_SEQNUM_LIFETIME    | 300 seconds    |
                | RteMsg_ENTRY_TIME      | 12 seconds     |
                | RREQ_WAIT_TIME         | 2 seconds      |
                | RREP_Ack_SENT_TIMEOUT  | 1 second       |
                | RREQ_HOLDDOWN_TIME     | 10 seconds     |
                +------------------------+----------------+

                     Table 3: 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.  Ideally,
   for networks with frequent topology changes the AODVv2 parameters
   should be adjusted using experimentally determined values or dynamic
   adaptation.  For example, in networks with infrequent topology
   changes MAX_IDLETIME may be set to a much larger value.

11.2.  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 section describing their use.













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   +------------------------+---------+--------------------------------+
   | Name                   | Default | Description                    |
   +------------------------+---------+--------------------------------+
   | DISCOVERY_ATTEMPTS_MAX | 3       | Section 6.4                    |
   | RREP_RETRIES           | 2       | Section 7.2.1                  |
   | MAX_METRIC[MetricType] | [TBD]   | Section 5                      |
   | MAX_METRIC[HopCount]   | 20 hops | Section 5 and Section 7        |
   | MAX_HOPCOUNT           | 20      | Same as MAX_METRIC[HopCount]   |
   | MAX_TIME               | [TBD]   | Maximum expressible clock time |
   |                        |         | (Section 6.5.2)                |
   +------------------------+---------+--------------------------------+

                         Table 4: AODVv2 Constants

   Note that <msg-hop-count> is an 8-bit field in the RFC 5444 message
   header and therefore MAX_HOPCOUNT cannot be larger than 255.  Field
   lengths associated with metrics are to be found in Section 12.4.

   MAX_METRIC[MetricType] MUST always be the maximum expressible metric
   of type MetricType.

   These protocol constants MUST have the same values for all AODVv2
   routers in the ad hoc network.  If the values were configured
   differently, the following consequences may be observed:

   o  DISCOVERY_ATTEMPTS_MAX: Nodes with higher values are likely to be
      more successful at finding routes, at the cost of additional
      control traffic.

   o  RREP_RETRIES: Nodes with lower values are more likely to blacklist
      neighbors when there is a temporary fluctuation in link quality.

   o  MAX_HOPCOUNT: Nodes with a value too small would not be able to
      discover routes to distant addresses.

   o  MAX_METRIC[MetricType]: No interoperability problems due to
      variations on different nodes, but nodes with lower values may
      exhibit overly restrictive behavior during route comparisons.

   o  MAX_TIME: No interoperability problems due to variations on
      different nodes, but if a lower value is used, route state
      management may exhibit overly restrictive behavior.

11.3.  Local Settings

   The following table lists AODVv2 parameters which should be
   administratively configured for each node:




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    +------------------------+------------------------+--------------+
    | Name                   | Default Value          | Description  |
    +------------------------+------------------------+--------------+
    | AODVv2_INTERFACES      |                        | Section 3    |
    | BUFFER_SIZE_PACKETS    | 2                      | Section 6.4  |
    | BUFFER_SIZE_BYTES      | MAX_PACKET_SIZE [TBD]  | Section 6.4  |
    | CLIENT_ADDRESSES       | AODVv2_INTERFACES      | Section 4.2  |
    | CONTROL_TRAFFIC_LIMIT  | [TBD - 50 pkts/sec?]   | Section 7    |
    +------------------------+------------------------+--------------+

                 Table 5: Configuration for Local Settings

11.4.  Network-Wide Settings

   The following administrative controls may be used to change the
   operation of the network.  The same settings should be used across
   the network.  Inconsistent settings at different nodes in the network
   will not result in protocol errors, but poor performance may result,
   especially if metrics are misinterpreted because DEFAULT_METRIC_TYPE
   is configured differently at different nodes.

     +----------------------+----------------------+----------------+
     | Name                 | Default              | Description    |
     +----------------------+----------------------+----------------+
     | DEFAULT_METRIC_TYPE  | 3 (i.e., Hop Count)  | [RFC6551]      |
     | ENABLE_IDLE_IN_RERR  | Disabled             | Section 7.4.1  |
     +----------------------+----------------------+----------------+

             Table 6: Configuration for Network-Wide Settings

11.5.  Optional Feature Settings

   These options are not required for correct routing behavior, although
   they may reduce AODVv2 protocol overhead in certain situations.  The
   default behavior is to leave these options disabled.

   +---------------------------+-----------+---------------------------+
   | Name                      | Default   | Description               |
   +---------------------------+-----------+---------------------------+
   | PRECURSOR_LISTS           | Disabled  | Local (Section 10.2)      |
   | MSG_AGGREGATION           | Disabled  | Local (Section 10.4)      |
   | ENABLE_IRREP              | Disabled  | Network-wide (Section     |
   |                           |           | 10.3)                     |
   | EXPANDING_RINGS_MULTICAST | Disabled  | Network-wide (Section     |
   |                           |           | 10.1)                     |
   +---------------------------+-----------+---------------------------+

               Table 7: Configuration for Optional Features



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12.  IANA Considerations

   This section specifies several RFC 5444 message types, message tlv-
   types, and address tlv-types required for AODVv2.  Also, a new
   registry of 16-bit metric types is specified.

12.1.  RFC 5444 Message Types

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

                       Table 8: AODVv2 Message Types

12.2.  RFC 5444 Message TLV Types

   +--------------------------+----------+---------------+-------------+
   | Name of TLV              | Type     | Length        | Reference   |
   |                          |          | (octets)      |             |
   +--------------------------+----------+---------------+-------------+
   | ACK_REQ (Acknowledgment  | 10 (TBD) | 0             | Section 6.2 |
   | Request)                 |          |               |             |
   +--------------------------+----------+---------------+-------------+

                     Table 9: AODVv2 Message TLV Types

12.3.  RFC 5444 Address Block TLV Types

   +------------------------+----------+---------------+---------------+
   | Name of TLV            | Type     | Length        | Reference     |
   +------------------------+----------+---------------+---------------+
   | PATH_METRIC            | 10 (TBD) | depends on    | Section 7     |
   |                        |          | MetricType    |               |
   | SEQ_NUM                | 11 (TBD) | 2 octets      | Section 7     |
   | ORIG_SEQ_NUM           | 12 (TBD) | 2 octets      | Section 7     |
   | TARG_SEQ_NUM           | 13 (TBD) | 2 octets      | Section 7     |
   | PKT_SOURCE             | 14 (TBD) | 0             | Section 7.4   |
   |                        |          |               | and Section 8 |
   | VALIDITY_TIME          | 1        | 1 octet       | [RFC5497]     |
   +------------------------+----------+---------------+---------------+

                 Table 10: AODVv2 Address Block TLV Types




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12.4.  MetricType Allocation

   Metric types are identified according to the assignments in
   [RFC6551].

           +------------------------+----------+--------------+
           | Name of MetricType     | Type     | Metric Size  |
           +------------------------+----------+--------------+
           | Unassigned             | 0        | Undefined    |
           | Currently Unsupported  | 1 - 2    | TBD          |
           | Hop Count              | 3 [TBD]  | 1 octet      |
           | Currently Unsupported  | 4 - 8    | TBD          |
           | Unallocated            | 9 - 254  | TBD          |
           | Reserved               | 255      | Undefined    |
           +------------------------+----------+--------------+

                       Table 11: AODVv2 Metric Types

   When creating AODVv2 messages which relate to the
   DEFAULT_METRIC_TYPE, MetricType is not reported in the message.  In
   the RFC 5444 message representation, the PATH_METRIC TLV will not
   include an extension type.  While RFC 5444 would interpret the lack
   of an extension type to mean extension type is zero, AODVv2 will
   interpret an extension type of zero to mean the DEFAULT_METRIC_TYPE
   configured on the router.  This is possible because zero is not
   assigned to any metric type ([RFC6551]).

13.  Security Considerations

   This section describes various security considerations and potential
   avenues to secure AODVv2 routing.  The objective of the AODVv2
   protocol is for each router to communicate reachability information
   about addresses for which it is responsible, and for routes it has
   learned from other AODVv2 routers.  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 RERR messages.  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.

   Networks using AODVv2 to maintain connectivity and establish routes
   on demand may be vulnerable to certain well-known types of threats.
   Flooding attacks using RREQ amount to a denial of service for route
   discovery.  Valid route table entries can be replaced by maliciously
   constructed RREQ and RREP messages.  Links could be erroneously
   treated as bidirectional if malicious unsolicited RREP or RREP_Ack
   messages were to be accepted.  Replay attacks using RERR messages



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   could, in some circumstances, be used to disrupt active routes.
   Passive inspection of AODVv2 control messages could enable
   unauthorized devices to gain information about the network topology,
   since exchanging such information is the main purpose of AODVv2.

   The on-demand nature of AODVv2 route discovery reduces the
   vulnerability to route disruption.  Since control traffic for
   updating route tables is diminished, there is less opportunity for
   failure.  Processing requirements for AODVv2 are typically quite
   small, and would typically be dominated by calculations to verify
   integrity.  This has the effect of reducing (but by no means
   eliminating) AODVv2's vulnerability to denial of service attacks.

   Encryption MAY be used for AODVv2 messages.  If the routers share a
   packet-level security association, the message data can be encrypted
   prior to message transmission.  The establishment of such security
   associations is outside the scope of this specification.  Encryption
   will not only protect against unauthorized devices obtaining
   information about network topology but will ensure that only trusted
   routers participate in routing operations.

   Message integrity checking is enabled by the Integrity Check Value
   mechanisms defined in [RFC7182].  The data contained in AODVv2
   routing protocol messages SHOULD be verified using ICV values, to
   avoid the use of message data if the message has been tampered with
   or replayed.  Otherwise, it would be possible to disrupt
   communications by injecting nonexistent or malicious routes into the
   route tables of nodes within the ad hoc network.  This can result in
   loss of data or message processing by unauthorized devices.

   The remainder of this section provides specific recommendations for
   the use of the integrity checking and timestamp functions defined in
   [RFC7182] to ensure the integrity of each AODVv2 message.  The
   calculation used for the Integrity Check Value will depend on the
   message type.  Sequence numbers can be used as timestamps to protect
   against replay, since they are known to be strictly increasing.

   RREQ messages advertise a route to OrigAddr, and impose very little
   processing requirement for receivers.  The main threat presented by
   sending a RREQ message with false information is that traffic to
   OrigAddr could be disrupted.  Since RREQ is multicast and likely to
   be received by all nodes in the ad hoc network, this threat could
   have serious impact on applications communicating by way of OrigAddr.
   The actual threat to disrupt routes to OrigAddr is reduced by the
   AODVv2 mechanism of marking RREQ-derived routes as "Unconfirmed"
   until adjacency with the next hop is confirmed.  If AODVv2 routers
   always verify the integrity of the RREQ message data, then the threat
   of disruption is minimized.  The ICV mechanisms offered in [RFC7182]



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   are sufficient for this purpose.  Since OrigAddr is included as a
   data element of the RREQ, the ICV can be calculated and verified
   using message contents.  The ICV should be verified at every step
   along the dispersal path of the RREQ to mitigate the threat.  Since
   RREQ_Gen's sequence number is incremented for each new RREQ, replay
   protection is already afforded and no extra timestamp mechanism is
   required.

   RREP messages advertise a route to TargAddr, and impose very little
   processing requirement for receivers.  The main threat presented by
   sending a RREP message with false information is that traffic to
   TargAddr could be disrupted.  Since RREP is unicast, this threat is
   restricted to receivers along the path from OrigAddr to TargAddr.  If
   AODVv2 routers always verify the integrity of the RREP message data,
   then this threat is minimized.  This facility is offered by the ICV
   mechanisms in [RFC7182].  Since TargAddr is included as a data
   element of the RREP, the ICV can be calculated and verified using
   message contents.  The ICV should be verified at every step along the
   unicast path of the RREP.  Since RREP_Gen's sequence number is
   incremented for each new RREP, replay protection is afforded and no
   extra timestamp mechanism is required.

   RREP_Ack messages are intended to verify bidirectional neighbor
   connectivity, and impose very little processing requirement for
   receivers.  The main threat presented by sending a RREP_Ack message
   with false information is that the route advertised to a target node
   in a RREP might be erroneously accepted even though the route would
   contain a unidirectional link and thus not be suitable for most
   traffic.  Since RREP_Ack is unicast, this threat is strictly local to
   the RREP transmitter expecting the acknowledgement.  A malicious
   router could also attempt to send an unsolicited RREP_Ack to convince
   another router that a bidirectional link exists and subsequently use
   further messages to divert traffic along a route which is not valid.
   If AODVv2 routers always verify the integrity of the RREP_Ack message
   data, then this threat is minimized.  This facility is offered by the
   ICV mechanisms in [RFC7182].  The RREP_Gen SHOULD use the source IP
   address of the RREP_Ack to identify the sender, and so the ICV should
   be calculated using the message contents and the IP source address.
   The message must also include the Timestamp defined in [RFC7182] to
   protect against replay attacks, using TargSeqNum from the RREP as the
   value in the TIMESTAMP TLV.

   RERR messages remove routes, and impose very little processing
   requirement for receivers.  The main threat presented by sending a
   RERR message with false information is that traffic to the advertised
   destinations could be disrupted.  Since RERR is multicast and can be
   received by many routers in the ad hoc network, this threat could
   have serious impact on applications communicating by way of the



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   sender of the RERR message.  However, since the sender of the RERR
   message with erroneous information may be presumed to be either
   malicious or broken, it is better that such routes not be used
   anyway.  Another threat is that a malicious RERR message may be sent
   with a PktSource data element included, to disrupt PktSource's
   ability to send to the addresses contained in the RERR.  If AODVv2
   routers always verify the integrity of the RERR message data, then
   this threat is reduced.  This facility is offered by the ICV
   mechanisms in [RFC7182].  The receiver of the RERR SHOULD use the
   source IP address of the RERR to identify the sender.  The message
   must also include the Timestamp defined in [RFC7182] to protect
   against replay attacks, using SeqNum from RERR_Gen as the value in
   the TIMESTAMP TLV.

14.  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 and Ian
   Chakeres for their 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, Romain Thouvenin, Richard Trefler,
   Jiazi Yi, Seung Yi, and Cong Yuan, for their reviews AODVv2 and DYMO,
   as well as numerous specification suggestions.

15.  References

15.1.  Normative References

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

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

   [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.





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   [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.

15.2.  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.

   [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.






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   [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.

   [RFC7182]  Herberg, U., Clausen, T., and C. Dearlove, "Integrity
              Check Value and Timestamp TLV Definitions for Mobile Ad
              Hoc Networks (MANETs)", RFC 7182, April 2014.

Appendix A.  Features Required of IP

   AODVv2 needs the following:

   o  information that IP routes are requested

   o  information that packets are flowing

   o  the ability to queue packets

   A reactive protocol reacts when a route is needed.  A route is
   requested when an application tries to send a packet.  The
   fundamental concept of reactive routing is to avoid creating routes
   that are not needed.  The trigger for route discovery is an
   application trying to send a packet.  If a route is not available to
   forward the packet, the packet is queued while the route is
   requested.

Appendix B.  Multi-homing Considerations

   Multi-homing is not supported by the AODVv2 specification.  The
   coordination between multiple AODVv2 routers to distribute routing
   information correctly for a shared address is not defined.

   Previous work indicates 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.  Without this, comparing sequence
   numbers would not work to evaluate freshness.  Even when the IP
   address is included, there is no good way to compare sequence numbers



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   from different IP addresses, but 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
   necessary for reactive protocol operation.

Appendix C.  Router Client Relocation

   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, i.e., it must wait at
   least MAX_SEQNUM_LIFETIME after the previous AODVv2 router's last
   SeqNum update for this network prefix.

Appendix D.  Example Algorithms for AODVv2 Operations

   The following subsections show example algorithms for protocol
   operations required by AODVv2.  AODVv2 requires general algorithms
   for manipulating and comparing table entries, and algorithms specific
   to each message type.

   Processing for 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.

   The following table indicates the field names used in subsequent
   sections to describe the AODVv2 algorithms.

   +-------------------------+-----------------------------------------+



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   | Parameter               | Description                             |
   +-------------------------+-----------------------------------------+
   | RteMsg                  | A route message                         |
   |                         | (inRREQ/outRREQ/inRREP/outRREP)         |
   | RteMsg.HopLimit         | Hop limit for the message               |
   | RteMsg.HopCount         | Hop count for the message               |
   | RteMsg.AckReq           | True/False, optional in RREP            |
   | RteMsg.MetricType       | The type of metric included, optional   |
   | RteMsg.OrigAddr         | Address of source of queued data        |
   | RteMsg.TargAddr         | Address route is requested for          |
   | RteMsg.OrigPrefixLen    | Prefix length of OrigAddr, optional     |
   | RteMsg.TargPrefixLen    | Prefix length of TargAddr, optional     |
   | RteMsg.OrigSeqNum       | SeqNum of OrigAddr, in RREQ only        |
   | RteMsg.TargSeqNum       | SeqNum of TargAddr, in RREP, optional   |
   |                         | in RREQ                                 |
   | RteMsg.OrigMetric       | Metric to OrigAddr, in RREQ only        |
   | RteMsg.TargMetric       | Metric to TargAddr, in RREP only        |
   | RteMsg.ValidityTime     | Time limit for route advertised         |
   | RteMsg.NbrIP            | Sender of the RteMsg                    |
   | RteMsg.Netif            | Interface on which the RteMsg arrived   |
   | AdvRte                  | Derived from a RteMsg (see Section 6.5) |
   | AdvRte.Address          | Route destination address               |
   | AdvRte.PrefixLength     | Route destination prefix length         |
   | AdvRte.SeqNum           | SeqNum associated with route            |
   | AdvRte.MetricType       | MetricType associated with route        |
   | AdvRte.Metric           | Advertised metric of route              |
   | AdvRte.Cost             | Cost from receiving router              |
   | AdvRte.ValidityTime     | Time limit for route advertised         |
   | AdvRte.NextHopIP        | Sender of the RteMsg                    |
   | AdvRte.NextHopIntf      | Interface on which the RteMsg arrived   |
   | AdvRte.HopCount         | Number of hops traversed                |
   | AdvRte.HopLimit         | Allowed number of hops remaining        |
   | Route                   | A route table entry (see Section 4.6)   |
   | Route.Address           | Route destination address               |
   | Route.PrefixLength      | Route destination prefix length         |
   | Route.SeqNum            | SeqNum associated with route            |
   | Route.NextHop           | Address of router which advertised the  |
   |                         | route                                   |
   | Route.NextHopInterface  | Interface on which next hop is          |
   |                         | reachable                               |
   | Route.LastUsed          | Time this route was last used for       |
   |                         | packet forwarding                       |
   | Route.LastSeqNumUpdate  | Time the SeqNum of the route was last   |
   |                         | updated                                 |
   | Route.ExpirationTime    | Time at which the route will expire     |
   | Route.MetricType        | MetricType associated with route        |
   | Route.Metric            | Cost from receiving router              |
   | Route.State             | Active/Idle/Invalid                     |



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   | Route.Precursors        | Optional (see Section 10.2)             |
   | RERR                    | Route Error message (inRERR/outRERR)    |
   | RERR.HopLimit           | Hop limit for the message               |
   | RERR.PktSource          | Source address of packet which          |
   |                         | triggered RERR                          |
   | RERR.AddressList[]      | List of unreachable route addresses     |
   | RERR.PrefixLengthList[] | List of PrefixLengths for AddressList   |
   | RERR.SeqNumList[]       | List of SeqNums for AddressList         |
   | RERR.MetricTypeList[]   | MetricType for the invalid routes       |
   | RERR.Netif              | Interface on which the RERR arrived     |
   +-------------------------+-----------------------------------------+

                    Table 12: Notation used in Appendix

D.1.  General Operations

D.1.1.  Check_Route_State

    /*  Update the state of the route entry based on timeouts. Return
        whether the route can be used for forwarding a packet. */

    Check_Route_State(route)
    {
        if (CurrentTime > route.ExpirationTime)
            route.State := Invalid;
        if ((CurrentTime - route.LastUsed > ACTIVE_INTERVAL + MAX_IDLETIME)
            AND (route.State != Unconfirmed)
            AND (route.ExpirationTime == MAX_TIME)) //not a timed route
            route.State := Invalid;
        if ((CurrentTime - route.LastUsed > ACTIVE_INTERVAL)
            AND (route.State != Unconfirmed)
            AND (route.ExpirationTime == MAX_TIME)) //not a timed route
            route.State := Idle;
        if ((CurrentTime - route.LastSeqNumUpdate > MAX_SEQNUM_LIFETIME)
            AND (route.State == Invalid OR route.State == Unconfirmed))
            /* remove route from route table */
        if ((CurrentTime - route.LastSeqNumUpdate > MAX_SEQNUM_LIFETIME)
            AND (route.State != Invalid)
            route.SeqNum := 0;

        if (route still exists AND route.State != Invalid
            AND Route.State != Unconfirmed)
            return TRUE;
        else
            return FALSE;
    }





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D.1.2.  Process_Routing_Info

   (See Section 6.5.1)

 /* Compare incoming route information to stored route, and if better,
 use to update stored route.  */

 Process_Routing_Info (advRte)
 {
     rte := Fetch_Route_Table_Entry (advRte);
     if (!rte exists)
     {
         rte := Create_Route_Table_Entry(advRte);
         return rte;
     }

     if (AdvRte.SeqNum > Route.SeqNum        /* stored route is stale */
         OR
         (AdvRte.SeqNum == Route.SeqNum                /* same SeqNum */
          AND
          ((Route.State == Invalid AND LoopFree(advRte, rte))
                                          /* advRte can repair stored */
           OR AdvRte.Cost < Route.Metric)))       /* advRte is better */
     {
         if (advRte is from a RREQ)
             rte := Create_Route_Table_Entry(advRte);
         else
             Update_Route_Table_Entry (rte, advRte);
     }
     return rte;
 }

D.1.3.  Fetch_Route_Table_Entry


















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   /* Lookup a route table entry matching an advertised route */

   Fetch_Route_Table_Entry (advRte)
   {
       foreach (rteTableEntry in rteTable)
       {
           if (rteTableEntry.Address == advRte.Address
               AND rteTableEntry.MetricType == advRte.MetricType)
               return rteTableEntry;
       }
       return null;
   }

   /* Lookup a route table entry matching address and metric type */

   Fetch_Route_Table_Entry (destination, metricType)
   {
       foreach (rteTableEntry in rteTable)
       {
           if (rteTableEntry.Address == destination
               AND rteTableEntry.MetricType == metricType)
               return rteTableEntry;
       }
       return null;
   }

D.1.4.  Update_Route_Table_Entry

   /* Update a route table entry using AdvRte in received RteMsg */

   Update_Route_Table_Entry (rte, advRte);
   {
       rte.SeqNum := advRte.SeqNum;
       rte.NextHop := advRte.NextHopIp;
       rte.NextHopInterface := advRte.NextHopIntf;
       rte.LastUsed := CurrentTime;
       rte.LastSeqNumUpdate := CurrentTime;
       if (validityTime)
           rte.ExpirationTime := CurrentTime + advRte.ValidityTime;
       else
           rte.ExpirationTime := MAX_TIME;

       rte.Metric := advRte.Cost;
       if (rte.State == Invalid)
           rte.State := Idle (if advRte is from RREP);
                        or Unconfirmed (if advRte is from RREQ);
   }




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D.1.5.  Create_Route_Table_Entry

   /* Create a route table entry from address and prefix length */

   Create_Route_Table_Entry (address, prefixLength, seqNum, metricType)
   {
       rte := allocate_memory();
       rte.Address := address;
       rte.PrefixLength := prefixLength;
       rte.SeqNum := seqNum;
       rte.MetricType := metricType;
   }


   /* Create a route table entry from the advertised route */

   Create_Route_Table_Entry(advRte)
   {
       rte := allocate_memory();

       rte.Address := advRte.Address;
       if (advRte.PrefixLength)
           rte.PrefixLength := advRte.PrefixLength;
       else
           rte.PrefixLength := maxPrefixLenForAddressFamily;

       rte.SeqNum := advRte.SeqNum;
       rte.NextHop := advRte.NextHopIp;
       rte.NextHopInterface := advRte.NextHopIntf;
       rte.LastUsed := CurrentTime;
       rte.LastSeqNumUpdate := CurrentTime;
       if (validityTime)
           rte.ExpirationTime := CurrentTime + advRte.ValidityTime;
       else
           rte.ExpirationTime := MAX_TIME;
       rte.MetricType := advRte.MetricType;
       rte.Metric := advRte.Metric;
       rte.State := Idle (if advRte is from RREP);
                    or Unconfirmed (if advRte is from RREQ);
   }

D.1.6.  LoopFree









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   /* Return TRUE if the route advRte is LoopFree compared to rte */

   LoopFree(advRte, rte)
   {
       if (advRte.Cost <= rte.Cost)
           return TRUE;
       else
           return FALSE;
   }

D.1.7.  Fetch_Rte_Msg_Table_Entry

   /* Find an entry in the RteMsg table matching the given
      message's msg-type, OrigAddr, TargAddr, MetricType   */

   Fetch_Rte_Msg_Table_Entry (rteMsg)
   {
       foreach (entry in RteMsgTable)
       {
           if (entry.msg-type == rteMsg.msg-type
               AND entry.OrigAddr == rteMsg.OrigAddr
               AND entry.TargAddr == rteMsg.TargAddr
               AND entry.MetricType == rteMsg.MetricType)
                   return entry;
       }
       return NULL;
   }

D.1.8.  Update_Rte_Msg_Table

   (See Section 4.5)

 /* Update the multicast route message suppression table based on the
    received RteMsg, return true if it was created or the SeqNum was
    updated (i.e. it needs to be regenerated) */

 Update_Rte_Msg_Table(rteMsg)
 {
     /* search for a comparable entry */
     entry := Fetch_Rte_Msg_Table_Entry(rteMsg);

     /* if there is none, create one */
     if (entry does not exist)
     {
         entry.MessageType := rteMsg.msg_type;
         entry.OrigAddr := rteMsg.OrigAddr;
         entry.TargAddr := rteMsg.TargAddr;
         entry.OrigSeqNum := rteMsg.origSeqNum; // (if present)



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         entry.TargSeqNum := rteMsg.targSeqNum; // (if present)
         entry.MetricType := rteMsg.MetricType;
         entry.Metric := rteMsg.OrigMetric; // (for RREQ)
                      or rteMsg.TargMetric; // (for RREP)
         entry.Timestamp := CurrentTime;
         return TRUE;
     }

     /* if current entry is stale */
     if (
     (rteMsg.msg-type == RREQ AND entry.OrigSeqNum < rteMsg.OrigSeqNum)
     OR
     (rteMsg.msg-type == RREP AND entry.TargSeqNum < rteMsg.TargSeqNum))
     {
         entry.OrigSeqNum := rteMsg.OrigSeqNum; // (if present)
         entry.TargSeqNum := rteMsg.TargSeqNum; // (if present)
         entry.Timestamp := CurrentTime;
         return TRUE;
     }

     /* if received rteMsg is stale */
     if (
     (rteMsg.msg-type == RREQ AND entry.OrigSeqNum > rteMsg.OrigSeqNum)
     OR
     (rteMsg.msg-type == RREP AND entry.TargSeqNum > rteMsg.TargSeqNum))
     {
         entry.Timestamp := CurrentTime;
         return FALSE;
     }

     /* if same SeqNum but rteMsg has lower metric */
     if (entry.Metric > rteMsg.Metric)
         entry.Metric := rteMsg.Metric;

     entry.Timestamp := CurrentTime;
     return FALSE;
 }

D.1.9.  Build_RFC_5444_Message_Header












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   /*  This pseudocode shows possible RFC 5444 actions, and would not
       be performed by the AODVv2 implementation. It is shown only to
       provide more understanding about the AODVv2 message that will be
       constructed by RFC 5444.
       MAL := Message Address Length
       MF  := Message Flags
       Size := number of octets in MsgHdr, AddrBlk, AddrTLVs  */

   Build_RFC_5444_Message_Header (msgType, Flags, AddrFamily, Size,
       hopLimit, hopCount, tlvLength)
   {
       /* Build RFC 5444 message header fields */
       msg-type := msgType;
       MF := Flags;
       MAL := 3 or 15;  // for IPv4 or IPv6
       msg-size := Size;
       msg-hop-limit := hopLimit;
       if (hopCount != 0)  /* if hopCount is 0, do not include */
           msg-hop-count := hopCount;
       msg.tlvs-length := tlvLength;
   }

D.2.  RREQ Operations

D.2.1.  Generate_RREQ

/*  Generate a route request message to find a route from OrigAddr
    to TargAddr using the given MetricType
    origAddr   := IP address of Router Client which generated the
                  packet to be forwarded
    origPrefix := prefix length associated with the Router Client
    targAddr   := destination IP address in the packet to be forwarded
    targSeqNum := sequence number in existing route to targAddr
    mType      := metric type for the requested route   */

Generate_RREQ(origAddr, origPrefix, targAddr, targSeqNum, mType)
{
    /* Increment sequence number in nonvolatile storage */
    mySeqNum := (1 + mySeqNum);

    /* Marshall parameters */
    outRREQ.HopLimit := MAX_HOPCOUNT;
    outRREQ.HopCount := 0;                              // if included
    outRREQ.MetricType := mType;   //include if not DEFAULT_METRIC_TYPE
    outRREQ.OrigAddr := origAddr;
    outRREQ.TargAddr := targAddr;
    outRREQ.OrigPrefixLen := origPrefix; //include if not address length
    outRREQ.OrigSeqNum := mySeqNum;



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    outRREQ.TargSeqNum := targSeqNum;            //included if available
    outRREQ.OrigMetric := Route[OrigAddr].Metric;       //zero by default
    outRREQ.ValidityTime := limit for route to OrigAddr;   //if required

    /* Build Address Blk using prefix length information from
       outRREQ.OrigPrefixLen if necessary */
    AddrBlk := {outRREQ.OrigAddr, outRREQ.TargAddr};

    /* Include sequence numbers in appropriate Address Block TLVs */
    /* OrigSeqNum Address Block TLV */
    origSeqNumAddrBlkTlv.value := outRREQ.OrigSeqNum;
    /* TargSeqNum Address Block TLV */
    if (outRREQ.TargSeqNum is known)
        targSeqNumAddrBlkTlv.value := outRREQ.TargSeqNum;

    /* Build Metric Address Block TLV, include Metric AddrBlkTlv
       Extension type if a non-default metric */
    metricAddrBlkTlv.value := outRREQ.OrigMetric;
    if (outRREQ.MetricType != DEFAULT_METRIC_TYPE)
        metricAddrBlkTlv.typeExtension := outRREQ.MetricType;

    if (outRREQ.ValidityTime is required)
    {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value := outRREQ.ValidityTime;
    }

    Build_RFC_5444_Message_Header (RREQ, 4, IPv4 or IPv6, NN,
        outRREQ.HopLimit, outRREQ.HopCount, tlvLength);

    /* multicast RFC 5444 message to LL-MANET-Routers */
}

D.2.2.  Receive_RREQ

















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 /*  Process a RREQ received on link L */

 Receive_RREQ (inRREQ, L)
 {
     if (inRREQ.NbrIP present in blacklist)
     {
         if (blacklist_expiration_time < CurrentTime)
             return; // don't process or regenerate RREQ
         else
             remove nbrIP from blacklist;
     }
     if (inRREQ does not contain msg_hop_limit, OrigAddr,
         TargAddr, OrigSeqNum, OrigMetric)
         return;
     if (inRREQ.OrigAddr and inRREQ.TargAddr are not valid routable
         and unicast addresses)
         return;
     if (inRREQ.MetricType is present but an unknown value)
         return;
     if (inRREQ.OrigMetric > MAX_METRIC[inRREQ.MetricType] - Cost(L))
         return;

     /* Extract inRREQ values */
     advRte.Address := inRREQ.OrigAddr;
     advRte.PrefixLength := inRREQ.OrigPrefixLen; (if present)
                         or the address length of advRte.Address;
     advRte.SeqNum := inRREQ.OrigSeqNum;
     advRte.MetricType := inRREQ.MetricType;
     advRte.Metric := inRREQ.OrigMetric;
     advRte.Cost := inRREQ.OrigMetric + Cost(L);
                                 //according to the indicated MetricType
     advRte.ValidityTime := inRREQ.ValidityTime; //if present
     advRte.NextHopIP := inRREQ.NbrIP;
     advRte.NextHopIntf := inRREQ.Netif;
     advRte.HopCount := inRREQ.HopCount;
     advRte.HopLimit := inRREQ.HopLimit;

     rte := Process_Routing_Info (advRte);

     /*  Update the RteMsgTable and determine if the RREQ needs
         to be regenerated */
     regenerate := Update_Rte_Msg_Table(inRREQ);

     if (inRREQ.TargAddr is in Router Client list)
         Generate_RREP(inRREQ, rte);
     else if (regenerate)
         Regenerate_RREQ(inRREQ, rte);
 }



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D.2.3.  Regenerate_RREQ

 /*  Called from receive_RREQ()
     rte := the route to OrigAddr */

 Regenerate_RREQ (inRREQ, rte)
 {
     outRREQ.HopLimit := inRREQ.HopLimit - 1;
     if (outRREQ.HopLimit == 0)
         return; // don't regenerate

     if (inRREQ.HopCount exists)
     {
         if (inRREQ.HopCount >= MAX_HOPCOUNT)
             return; // don't regenerate
         outRREQ.HopCount := inRREQ.HopCount + 1;
     }

     /* Marshall parameters */
     outRREQ.MetricType := rte.MetricType;
     outRREQ.OrigAddr := rte.Address;
     outRREQ.TargAddr := inRREQ.TargAddr;
     /* include prefix length if not equal to address length */
     outRREQ.OrigPrefixLen := rte.PrefixLength;
     outRREQ.OrigSeqNum := rte.SeqNum;
     outRREQ.TargSeqNum := inRREQ.TargSeqNum; // if present
     outRREQ.OrigMetric := rte.Metric;
     outRREQ.ValidityTime := rte.ValidityTime;
                          or the time limit this router wishes to put on
                          route to OrigAddr

     /*  Build Address Block using prefix length information from
         outRREQ.OrigPrefixLen if necessary */
     AddrBlk := {outRREQ.OrigAddr, outRREQ.TargAddr};

     /* Include sequence numbers in appropriate Address Block TLVs */
     /* OrigSeqNum Address Block TLV */
     origSeqNumAddrBlkTlv.value := outRREQ.OrigSeqNum;
     /* TargSeqNum Address Block TLV */
     if (outRREQ.TargSeqNum is known)
         targSeqNumAddrBlkTlv.value := outRREQ.TargSeqNum;

     /* Build Metric Address Block TLV, include Metric AddrBlkTlv
        Extension type if a non-default metric */
     metricAddrBlkTlv.value := outRREQ.OrigMetric;
     if (outRREQ.MetricType != DEFAULT_METRIC_TYPE)
         metricAddrBlkTlv.typeExtension := outRREQ.MetricType;




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     if (outRREQ.ValidityTime is required)
     {
         /* Build VALIDITY_TIME Address Block TLV */
         VALIDITY_TIMEAddrBlkTlv.value := outRREQ.ValidityTime;
     }
     Build_RFC_5444_Message_Header (RREQ, 4, IPv4 or IPv6, NN,
         outRREQ.HopLimit, outRREQ.HopCount, tlvLength);

     /*  Multicast RFC 5444 message to LL-MANET-Routers, or if
         inRREQ was unicast, the message can be unicast to the next
         hop on the route to TargAddr, if known */
 }

D.3.  RREP Operations

D.3.1.  Generate_RREP

Generate_RREP(inRREQ, rte)
{
    /* Increment sequence number in nonvolatile storage */
    mySeqNum := (1 + mySeqNum);

    /* Marshall parameters */
    outRREP.HopLimit := inRREQ.HopCount;
    outRREP.HopCount := 0;
    /* Include the AckReq when:
       - previous RREP does not seem to enable any data flow, OR
       - when RREQ is received from same OrigAddr after RREP was
         unicast to rte.NextHop     */
    outRREP.AckReq := TRUE or FALSE; //TRUE if acknowledgement required
    /* if included, set timeout RREP_Ack_SENT_TIMEOUT */

    if (rte.MetricType != DEFAULT_METRIC_TYPE)
        outRREP.MetricType := rte.MetricType;
    outRREP.OrigAddr := rte.Address;
    outRREP.TargAddr := inRREQ.TargAddr;
    outRREP.TargPrefixLen := rte.PrefixLength; //if not address length
    outRREP.TargSeqNum := mySeqNum;
    outRREP.TargMetric := Route[TargAddr].Metric;
                                  //zero by default
    outRREP.ValidityTime := limit for route to TargAddr;   //if required

    if (outRREP.AckReq == TRUE)
        /* include AckReq Message TLV */

    /*  Build Address Block using prefix length information from
        outRREP.TargPrefixLen if necessary */
    AddrBlk := {outRREP.OrigAddr, outRREP.TargAddr};



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    /* TargSeqNum Address Block TLV */
    targSeqNumAddrBlkTlv.value := outRREP.TargSeqNum;

    /* Build Metric Address Block TLV include Metric AddrBlkTlv
       Extension type if a non-default metric */
    metricAddrBlkTlv.value := outRREP.TargMetric;
    if (outRREP.MetricType != DEFAULT_METRIC_TYPE)
        metricAddrBlkTlv.typeExtension := outRREP.MetricType;

    if (outRREP.ValidityTime is required)
    {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value := outRREP.ValidityTime;
    }

    Build_RFC_5444_Message_Header (RREP, 4, IPv4 or IPv6, NN,
        outRREP.HopLimit, outRREQ.HopCount, tlvLength);

    /* unicast RFC 5444 message to rte[OrigAddr].NextHop */
}

D.3.2.  Receive_RREP

 /*  Process a RREP received on link L */

 Receive_RREP (inRREP, L)
 {
     if (inRREP.NbrIP present in blacklist)
     {
         if (blacklist_expiration_time < CurrentTime)
             return;   // don't process or regenerate RREP
         else
             remove NbrIP from blacklist;
     }

     if (inRREP does not contain msg_hop_limit, OrigAddr,
             TargAddr, TargSeqNum, TargMetric)
         return;
     if (inRREP.OrigAddr and inRREQ.TargAddr are not
         valid routable and unicast addresses)
         return;
     if (inRREP.MetricType is present but an unknown value)
         return;
     if (inRREP.TargMetric > MAX_METRIC[inRREP.MetricType] - Cost(L))
         return;

     /* Extract inRREP values */
     advRte.Address := inRREP.TargAddr;



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     advRte.PrefixLength := inRREP.TargPrefixLen; //if present
                         or the address length of advRte.Address;
     advRte.SeqNum := inRREP.TargSeqNum;
     advRte.MetricType := inRREP.MetricType;
     advRte.Metric := inRREP.TargMetric;
     advRte.Cost := inRREP.TargMetric + Cost(L);
                                 //according to the indicated MetricType
     advRte.ValidityTime := inRREP.ValidityTime; //if present
     advRte.NextHopIP := inRREP.NbrIP;
     advRte.NextHopIntf := inRREP.Netif;
     advRte.HopCount := inRREP.HopCount;
     advRte.HopLimit := inRREP.HopLimit; //if included

     rte := Process_Routing_Info (advRte);

 `   if (inRREP includes AckReq data element)
         Generate_RREP_Ack(inRREP);

     /*  Update the RteMsgTable and determine if the RREP needs
         to be regenerated */
     regenerate := Update_Rte_Msg_Table(inRREP);

     if (inRREP.TargAddr is in the Router Client list)
         send_buffered_packets(rte);    /* start to use the route */
     else if (regenerate)
         Regenerate_RREP(inRREP, rte);
 }

D.3.3.  Regenerate_RREP

Regenerate_RREP(inRREP, rte)
{
    if (rte does not exist)
    {
        Generate_RERR(inRREP);
        return;
    }

    outRREP.HopLimit := inRREP.HopLimit - 1;
    if (outRREP.HopLimit == 0) /* don't regenerate */
        return;

    if (inRREP.HopCount exists)
    {
        if (inRREP.HopCount >= MAX_HOPCOUNT)
            return; // don't regenerate the RREP
        outRREP.HopCount := inRREP.HopCount + 1;
    }



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    /* Marshall parameters */
    /* Include the AckReq when:
       - previous unicast RREP seems not to enable data flow, OR
       - when RREQ is received from same OrigAddr after RREP
         was unicast to rte.NextHop     */
    outRREP.AckReq := TRUE or FALSE; //TRUE if acknowledgement required
    /* if included, set timeout RREP_Ack_SENT_TIMEOUT */

    if (rte.MetricType != DEFAULT_METRIC_TYPE)
        outRREP.MetricType := rte.MetricType;
    outRREP.OrigAddr := inRREP.OrigAddr;
    outRREP.TargAddr := rte.Address;
    outRREP.TargPrefixLen := rte.PrefixLength; //if not address length
    outRREP.TargSeqNum := rte.SeqNum;
    outRREP.TargMetric := rte.Metric;
    outRREP.ValidityTime := limit for route to TargAddr;   //if required
    outRREP.NextHop := rte.NextHop

    if (outRREP.AckReq == TRUE)
        /* include AckReq Message TLV */

    /*  Build Address Block using prefix length information from
        outRREP.TargPrefixLen if necessary */
    AddrBlk := {outRREP.OrigAddr, outRREP.TargAddr};

    /* TargSeqNum Address Block TLV */
    targSeqNumAddrBlkTlv.value := outRREP.TargSeqNum;

    /* Build Metric Address Block TLV include Metric AddrBlkTlv
       Extension type if a non-default metric */
    metricAddrBlkTlv.value := outRREP.TargMetric;
    if (outRREP.MetricType != DEFAULT_METRIC_TYPE)
        metricAddrBlkTlv.typeExtension := outRREP.MetricType;

    if (outRREP.ValidityTime is required)
    {
        /* Build VALIDITY_TIME Address Block TLV */
        VALIDITY_TIMEAddrBlkTlv.value := outRREP.ValidityTime;
    }

    Build_RFC_5444_Message_Header (RREP, 4, IPv4 or IPv6, NN,
        outRREP.HopLimit, 0, tlvLength);

    /* unicast RFC 5444 message to rte[OrigAddr].NextHop */
}






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D.4.  RREP_Ack Operations

D.4.1.  Generate_RREP_Ack

  /* To be sent when a received RREP includes the AckReq data element */

  Generate_RREP_Ack(inRREP)
  {
      Build_RFC_5444_Message_Header (RREP_Ack, 4, IPv4 or IPv6, NN,
          1, 0, 0);
      /* unicast RFC 5444 message to inRREP.NbrIP */
  }

D.4.2.  Receive_RREP_Ack

   Receive_RREP_Ack(inRREP_Ack)
   {
       /* cancel timeout event for the node sending RREP_Ack */
   }

D.4.3.  Timeout_RREP_Ack

   Timeout_RREP_Ack(outRREP)
   {
       if (numRetries < RREP_RETRIES)
           /* resend RREP and double the previous timeout */
       else
           /* insert unresponsive node into blacklist */
   }

D.5.  RERR Operations

D.5.1.  Generate_RERR

   There are two parts to this function, based on whether it was
   triggered by an undeliverable packet or a broken link to neighboring
   AODVv2 router.

/*  Generate a Route Error message.
    errorType := undeliverablePacket or brokenLink  */

Generate_RERR(errorType, triggerPkt, brokenLinkNbrIp)
{
    switch (errorType)
    {
    case (brokenLink):
        doGenerate := FALSE;
        num-broken-addr := 0;



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        precursors[] := new empty precursor list;
        outRERR.HopLimit := MAX_HOPCOUNT;
        /* find routes which are now Invalid */
        foreach (rte in route table)
        {
            if (brokenLinkNbrIp == rte.NextHop
                AND (rte.State == Active
                     OR
                     (rte.State == Idle AND ENABLE_IDLE_IN_RERR)))
             {
                if (rte.State == Active)
                    doGenerate := TRUE;
                rte.State := Invalid;
                precursors += rte.Precursors (if any);
                outRERR.AddressList[num-broken-addr] := rte.Address;
                outRERR.PrefixLengthList[num-broken-addr] :=
                                                 rte.PrefixLength;
                outRERR.SeqNumList[num-broken-addr] := rte.SeqNum;
                outRERR.MetricTypeList[num-broken-addr] := rte.MetricType
                num-broken-addr := num-broken-addr + 1;
            }
        }
    }
    case (undeliverablePacket):
        doGenerate := TRUE;
        num-broken-addr := 1;
        outRERR.HopLimit := MAX_HOPCOUNT;
        outRERR.PktSource := triggerPkt.SrcIP;
                          or triggerPkt.TargAddr; //if pkt was a RREP
        outRERR.AddressList[0] := triggerPkt.DestIP;
                               or triggerPkt.OrigAddr; //if pkt was RREP
        /* optional to include outRERR.PrefixLengthList, outRERR.SeqNumList
           and outRERR.MetricTypeList */
    }

    if (doGenerate == FALSE)
        return;

    if (triggerPkt exists)
    {
        /* Build PktSource Message TLV */
        pktSourceMessageTlv.value := outRERR.PktSource;
    }

    /*  The remaining steps add address, prefix length, sequence
        number and metric type information for each unreachable address,
        while conforming to the allowed MTU. If the MTU is reached, a new
        message MUST be created. */



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    /*  Build Address Block using prefix length information from
        outRERR.PrefixLengthList[] if necessary */
    AddrBlk := outRERR.AddressList[];

    /*  Optionally, add SeqNum Address Block TLV, including index values */
    seqNumAddrBlkTLV := outRERR.SeqNumList[];

    if (outRERR.MetricTypeList contains non-default MetricTypes)
        /* include Metric Address Block TLVs with Type Extension set to
           MetricType, including index values if necessary */
        metricAddrBlkTlv.typeExtension := outRERR.MetricTypeList[];

    Build_RFC_5444_Message_Header (RERR, 4, IPv4 or IPv6, NN,
        outRERR.HopLimit, 0, tlvLength);

    if (undeliverablePacket)
        /* unicast outRERR to rte[outRERR.PktSource].NextHop */
    else if (brokenLink)
        /* unicast to precursors, or multicast to LL-MANET-Routers */
}

D.5.2.  Receive_RERR

Receive_RERR (inRERR)
{
    if (inRERR does not contain msg_hop_limit and at least
        one unreachable address)
        return;

    /*  Extract inRERR values, copy relevant unreachable addresses,
        their prefix lengths, and sequence numbers to outRERR */
    num-broken-addr := 0;
    precursors[] := new empty precursor list;
    foreach (unreachableAddress in inRERR.AddressList)
    {
        if (unreachableAddress is not valid routable and unicast)
            continue;
        if (unreachableAddress MetricType is present but an unknown value)
            return;

        /*  Find a matching route table entry, assume
            DEFAULT_METRIC_TYPE if no MetricType included */
        rte := Fetch_Route_Table_Entry (unreachableAddress,
                                        unreachableAddress MetricType)
        if (rte does not exist)
            continue;
        if (rte.State == Invalid)/* ignore already invalid routes */
            continue;



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        if ((rte.NextHop != inRERR.NbrIP
            OR
            rte.NextHopInterface != inRERR.Netif)
            AND (PktSource is not present OR is not a Router Client))
            continue;
        if (unreachableAddress SeqNum (if known) < rte.SeqNum)
            continue;

        /* keep a note of all precursors of newly Invalid routes */
        precursors += rte.Precursors; //if any

        /* assume prefix length is address length if not included */
        if (rte.PrefixLength != unreachableAddress prefixLength)
        {
            /* create new route with unreachableAddress information */
            invalidRte := Create_Route_Table_Entry(unreachableAddress,
                                        unreachableAddress PrefixLength,
                                        unreachableAddress SeqNum,
                                        unreachableAddress MetricType);
            invalidRte.State := Invalid;

            if (rte.PrefixLength > unreachableAddress prefixLength)
                expunge_route(rte);
            rte := invalidRte;
        }
        else if (rte.PrefixLength == unreachableAddress prefixLength)
            rte.State := Invalid;

        outRERR.AddressList[num-broken-addr] := rte.Address;
        outRERR.PrefixLengthList[num-broken-addr] := rte.PrefixLength;
        outRERR.SeqNumList[num-broken-addr] := rte.SeqNum;
        outRERR.MetricTypeList[num-broken-addr] := rte.MetricType;
        num-broken-addr := num-broken-addr + 1;
    }

    if (num-broken-addr AND (PktSource is not present OR PktSource is not
        a Router Client))
        Regenerate_RERR(outRERR, inRERR, precursors);
}

D.5.3.  Regenerate_RERR










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Regenerate_RERR (outRERR, inRERR, precursors)
{
    /* Marshal parameters */
    outRERR.HopLimit := inRERR.HopLimit - 1;
    if (outRERR.HopLimit == 0) // don't regenerate
        return;

    outRERR.PktSource := inRERR.PktSource; //if included
    /*  AddressList[], SeqNumList[], and PrefixLengthList[] are
        already up-to-date */

    if (outRERR.PktSource exists)
    {
        /* Build PktSource Message TLV */
        pktSourceMessageTlv.value := outRERR.PktSource;
    }

    /*  Build Address Block using prefix length information from
        outRERR.PrefixLengthList[] if necessary */
    AddrBlk := outRERR.AddressList[];

    /*  Optionally, add SeqNum Address Block TLV, including index values */
    seqNumAddrBlkTLV := outRERR.SeqNumList[];

    if (outRERR.MetricTypeList contains non-default MetricTypes)
        /* include Metric Address Block TLVs with Type Extension set to
           MetricType, including index values if necessary */
        metricAddrBlkTlv.typeExtension := outRERR.MetricTypeList[];

    Build_RFC_5444_Message_Header (RERR, 4, IPv4 or IPv6, NN,
        outRERR.HopLimit, 0, tlvLength);

    if (outRERR.PktSource exists)
        /*  unicast RFC 5444 message to next hop towards
            outRERR.PktSource */
    else if (number of precursors == 1)
        /*  unicast RFC 5444 message to precursors[0] */
    else if (number of precursors > 1)
        /*  unicast RFC 5444 message to all precursors, or multicast
            RFC 5444 message to RERR_PRECURSORS if preferable */
    else
        /* multicast RFC 5444 message to LL-MANET-Routers */
}








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Appendix E.  AODVv2 Draft Updates

E.1.  Changes between revisions 8 and 9

   This section lists the changes between AODVv2 revisions ...-08.txt
   and ...-09.txt.

   o  Numerous editorial improvements were made, including
      relocation/removal/renaming/adding of some sections and text,
      collection and tidying of scattered text on same topic, formatting
      made more consistent to improve readability.

   o  Removed mentions of precursors from main text, except one mention
      in Route Table Entry.

   o  Removed use of MIN_METRIC which was not defined.

   o  Changed Current_Time to CurrentTime for consistency.

   o  Changed OrigAddrMetric and TargAddrMetric to OrigMetric and
      TargMetric respectively.

   o  Updated Overview to simplify and provide a broader summary.

   o  Updated Terminology definitions, Data Elements tables and combined
      sections.

   o  Updated Applicability Statement to move some of the non-
      applicability text and to simplify what remains.

   o  Updated TLV names to conform to existing naming style.

   o  Updated Blacklist to be a NeighborList to include neighbors that
      have confirmed bidirectional connectivity.

   o  Updated messages processed if router on blacklist and which are
      indicators of bidirectional links.

   o  Added RemoveTime to RteMsg Table section.

   o  Added short description of timed route to Route Table Entry
      section but removed Route.Timed flag.  Route is timed if its
      expiration time is not MAX_TIME.

   o  Added Unconfirmed route state for route to OrigAddr learned from
      RREQ.





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   o  Updated AODVv2 Protocol Operations section and subsections,
      including Initialization, Adjacency Monitoring, making algorithms
      easier to read and making notation consistent, general
      improvements to the text.

   o  Updated Route Discovery, Retries and Buffering to include a more
      complete description of the route discovery process.

   o  Updated wording relating to different metric types.

   o  Added text regarding control message limit in Message Transmission
      section.

   o  Added short explanation of positive/negative effects of buffering.

   o  Simplified the packet diagrams, since some of their contents was
      already explained in the text below and then again as part of
      generation, reception and regeneration processes.

   o  Clarified some elements of the message content descriptions.

   o  Moved MetricType above MetricList in message sections, for
      consistency.

   o  Mirrored structure throughout AODVv2 Protocol Messages.

   o  Changed RREQ and RREP's use of Lists when only one entry is
      necessary.

   o  Added some pre-message-generation checks.

   o  Ensured consistency in regeneration (if msg-hop-limit is reduced
      to zero, do not regenerate).

   o  Removed statements about neighbors but added blacklist checks
      where necessary.

   o  Noted that RREQ retries should increase the SeqNum.

   o  Added statement that implementations SHOULD retry sending RREP.

   o  Added text explaining what happens if RREP is lost, regarding
      blacklisting and RREQ retries.

   o  Removed hop limit from RREP_Ack.  Changed order of blacklist
      check.





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   o  Updated RERR so that multiple metric types can be reported in the
      same message.

   o  Updated RERR reception processing to ensure PktSource deletes the
      contained route.

   o  Added text to show that if a router is the destination of a RERR,
      the RERR is not regenerated.

   o  Added text that RERRs should not be created if the same RERR has
      recently been sent.

   o  Updated RFC 5444 overview and simplified/rearranged text in this
      section.

   o  Major update to RFC 5444 representation section

   o  Updated RERR's RFC 5444 representation so that PktSource is placed
      in Address Block, and updated IANA section to make PktSource an
      Address Block TLV to indicate which address is PktSource.

   o  Described use of extension type in Metric TLV to represent
      MetricType, and the interpretation when using the default metric
      type.

   o  Removed Multicast RREP as an optional feature.

   o  Updated Precursor Lists section to include options for precursor
      information to store.

   o  Updated Security Considerations.

E.2.  Changes between revisions 7 and 8

   This section lists the changes between AODVv2 revisions ...-07.txt
   and ...-08.txt.

   o  MetricType is now an Address Block TLV.  Minor changes to the
      text.  By using an extension type in the Metric TLV we can
      represent MetricType more elegantly in the RFC 5444 message.

   o  Updated Overview to be slightly more concise.

   o  Moved MetricType next to Metric when mentioned for better flow.

   o  Added text to Applicability to address comments on mailing list
      regarding gateway behavior and NHDP HELLO messages.




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   o  Removed paragraph in AODVv2 Message Transmission section regarding
      TTL.

   o  Added reference where precursors are mentioned in route table
      entry.

   o  Added text to bidirectionality explanation regarding NHDP HELLO
      messages and lower layer triggers.

   o  Clarified blacklist removal with SHOULD rather than MAY.

   o  Removed pseudo-code from section on evaluating incoming routing
      information.

   o  Clarified rules for expunging route entries on memory-constrained
      devices.

   o  Clarified the use of exponential backoff for route discovery
      attempts.

   o  Small updates to message sections.  Removed steps about checking
      if neighbors.

   o  Renamed RFC 5444 parser to multiplexer in Section 10.

   o  Removed "optional feature" to include multiple addresses in RERR.

   o  Removed MetricType from the Message TLV Type Specification.

   o  Updated Security Considerations.

   o  Added reference to RFC 7182.

   o  Small updates to message algorithms, including moving MetricType
      from Message TLV to the Metric TLV in the Address Block TLV Block,
      and only generating RERR if an Active route was made Invalid.

E.3.  Changes between revisions 6 and 7

   This section lists the changes since AODVv2 revision ...-06.txt

   o  Added Victoria Mercieca as co-author.

   o  Reorganized protocol message descriptions into major subsections
      for each protocol message.  For protocol messages, organized
      processing into Generation, Reception, and Regeneration
      subsections.




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   o  Separated RREQ and RREP message processing description into
      separate major subsection which had previously been combined into
      RteMsg description.

   o  Enlarged RREQ Table function to include similar processing for
      optional flooded RREP messages.  The table name has been
      correspondingly been changed to be the Table for Multicast
      RteMsgs.

   o  Moved sections for Multiple Interfaces and AODVv2 Control Message
      Generation Limits to be major subsections of the AODVv2 Protocol
      Operations section.

   o  Reorganized the protocol message processing steps into the
      subsections as previously described, adopting a more step-by-step
      presentation.

   o  Coalesced the router states Broken and Expired into a new combined
      state named the Invalid state.  No changes in processing are
      required for this.

   o  Merged the sections describing Next-hop Router Adjacency
      Monitoring and Blacklists.

   o  Specified that routes created during Route Discovery are marked as
      Idle routes.  If they are used for carrying data they become
      Active routes.

   o  Added Route.LastSeqNumUpdate information to route table, so that
      route activity and sequence number validity can be tracked
      separately.  An active route can still forward traffic even if the
      sequence number has not been refreshed within MAX_SEQNUM_LIFETIME.

   o  Mandated implementation of RREP_Ack as response to AckReq Message
      TLV in RREP messages.
      Added field to RREP_Ack to ensure correspondence to the correct
      AckReq message.

   o  Added explanations for what happens if protocol constants are
      given different values on different AODVv2 routers.

   o  Specified that AODVv2 implementations are free to choose their own
      heuristics for reducing multicast overhead, including RFC 6621.

   o  Added appendix to identify AODVv2 requirements from OS
      implementation of IP and ICMP.

   o  Deleted appendix showing example RFC 5444 packet formats.



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   o  Clarification on the use of RFC 5497 VALIDITY_TIME.

   o  In Terminology, deleted superfluous definitions, added missing
      definitions.

   o  Numerous editorial improvements and clarifications.

E.4.  Changes between revisions 5 and 6

   This section lists the changes between AODVv2 revisions ...-05.txt
   and ...-06.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
      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.





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   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.

E.5.  Changes between revisions 4 and 5

   This section lists the changes between AODVv2 revisions ...-04.txt
   and ...-05.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



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      (i.e., RteMsg) versus the route advertised by the RteMsg (i.e.,
      AdvRte).

E.6.  Changes between revisions 3 and 4

   This section lists the changes between AODVv2 revisions ...-03.txt
   and ...-04.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 MetricType TLV to allow for omission when
      MetricType == 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.

E.7.  Changes between revisions 2 and 3

   This section lists the changes between AODVv2 revisions ...-02.txt
   and ...-03.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



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      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.

   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.

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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Internet-Draft                   AODVv2                         May 2015


   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.dowdell@airbus.com


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

   Email: lotte.steenbrink@haw-hamburg.de


   Victoria Mercieca
   Airbus Defence and Space
   Celtic Springs
   Newport, Wales  NP10 8FZ
   United Kingdom

   Email: victoria.mercieca@airbus.com

















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