Mobile Ad Hoc Networking Working Group                   Charles Perkins
INTERNET DRAFT                                          Sun Microsystems
20 November 1997

            Ad Hoc On Demand Distance Vector (AODV) Routing
                      draft-ietf-manet-aodv-00.txt


Status of This Memo

   This document is a submission by the Mobile Ad Hoc Networking Working
   Group of the Internet Engineering Task Force (IETF).  Comments should
   be submitted to the manet@itd.nrl.navy.mil mailing list.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
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Abstract

   The Ad Hoc On-Demand Distance Vector (AODV) routing protocol is
   intended for use by mobile nodes in an ad hoc network characterized
   by frequent changes in link connectivity to each other caused
   by relative movement.  It offers quick adaptation to dynamic
   link conditions, low processing and memory overhead, low network
   utilization, and establishment of routes between sources and
   destination which are loop free at all times.  It makes use of
   destination sequence numbers, which are a novel means of ensuring
   loop freedom even in the face of anomalous delivery of routing
   control messages, and which solve classical problems associated with
   distance vector protocols, including the problem of ''counting to
   infinity''.








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                                Contents


Status of This Memo                                                    i

Abstract                                                               i

 1. Introduction                                                       1

 2. Overview                                                           2

 3. AODV Terminology                                                   3

 4. Route Request Message Format                                       4

 5. Route Reply Message Format                                         5

 6. Node Operation                                                     5
     6.1. Maintaining Route Utilization Records . . . . . . . . . .    5
     6.2. Generating Route Requests . . . . . . . . . . . . . . . .    6
     6.3. Forwarding Route Requests . . . . . . . . . . . . . . . .    6
     6.4. Generating Route Replies  . . . . . . . . . . . . . . . .    7
     6.5. Generating Hello Messages . . . . . . . . . . . . . . . .    8
     6.6. Initiating Triggered Route Replies  . . . . . . . . . . .    8
     6.7. Detecting Link Breakage . . . . . . . . . . . . . . . . .    9

 7. Configuration Parameters                                           9

 8. Extensions                                                        10

 9. Security Considerations                                           10


1. Introduction

   The Ad-Hoc On-Demand Distance Vector (AODV) algorithm enables
   dynamic, self-starting, multihop routing between participating mobile
   nodes wishing to establish and maintain an ad-hoc network.  AODV
   allows mobile nodes to obtain routes quickly for new destinations,
   and does not require nodes to maintain routes to destinations that
   are not in active communication.  AODV also defines timely responses
   to link breakages.  The operation of AODV is loop free, and by
   avoiding the Bellman-Ford "counting to infinity" problem offers quick
   convergence when the ad-hoc network topology changes (typically, when
   a node moves in the network).





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   One distinguishing feature of AODV is its use of a destination
   sequence number for each route entry.  The destination sequence
   number is created by the destination itself for any usable route
   information it sends to requesting nodes.  Using destination sequence
   numbers ensures loop freedom, and is simple to program.  Given the
   choice between two routes to a destination, a requesting node always
   selects one with the greatest sequence number.

   Another feature of AODV is that link breakages cause immediate
   notifications to be sent to the affected set of nodes, but only that
   set.


2. Overview

   Route Requests (RREQs) and Route Replies (RREPs) are the two message
   types defined by AODV. These message types are handled by UDP,
   and normal IP header processing applies.  So, for instance, the
   requesting node is expected to use its IP address as the source IP
   address for the messages.  The range of dissemination of broadcast
   RREQs can be indicated by the TTL in the IP header.  Fragmentation is
   typically not required.

   As long as the endpoints of a communication connection have valid
   routes to each other, AODV does not play any role.  When a route to a
   new destination is needed, the node uses a broadcast RREQ to find a
   route to the destination.  A route can be determined when the request
   reaches either the destination itself, or an intermediate node with a
   fresh enough route to the destination.  The route is made available
   by unicasting a RREP back to the source of the RREQ. Since each node
   receiving the request keeps track of a route back to the source of
   the request, the RREP Reply can be unicast back from the destination
   to the source, or from any intermediate node that is able to satisfy
   the request back to the source.

   If a RREP is broadcast to the limited broadcast address
   (255.255.255.255), and has a TTL of one, and a destination address of
   the node itself with metric 0, then it is received by all the node's
   neighbors, and treated by them as a "hello" message.  This hello
   message is a local advertisement for the continued presence of the
   node.  Neighbors that are using routes through the broadcasting node
   will continue to mark the routes as valid.  If hello messages from a
   particular node stop coming, the neighbor can assume that the node
   has moved away.  When that happens, the neighbor will mark the link
   to the node as broken, and may trigger a notification to some of its
   other neighbors that the link has broken.






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   Since AODV is a routing protocol, it deals with route table
   management.  AODV assumes the following fields exist in each route
   table entry:

      - Destination IP Address
      - Destination Sequence Number
      - Hop Count
      - Next Hop
      - Lifetime


   This information must be kept even for ephemeral routes, such as are
   created to temporarily keep track of reverse paths towards nodes
   originating RREQs.


3. AODV Terminology

   This section defines terminology used with AODV that is not already
   defined in [2].

      route table

         The table where ad-hoc nodes keep routing (including next hop)
         information for various destinations.  For IPv6, this can be
         associated with the Destination Cache.

      triggered update

         An unsolicited route update transmitted by an intermediate node
         along the path to the destination.

   This protocol specification uses conventional meanings [1] for
   capitalized words such as MUST, SHOULD, etc., to indicate requirement
   levels for various protocol features.

















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4. Route Request Message Format

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |            Reserved           |   Hop Count   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Broadcast ID                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination IP address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Sequence Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source IP address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Sequence Number                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the Route Request message is illustrated above, and
   contains the following fields:

      Type     xx

      Reserved Sent as 0; ignored on reception.

      Hop Count The number of hops from the Source IP Address to the
               node handling the request.

      Broadcast ID
               A sequence number identifying the particular RREQ
               uniquely when taken in conjunction with the source node's
               IP address.

      Destination IP Address
               The IP address of the destination for which a route is
               desired

      Destination Sequence Number
               The last sequence number received in the past by the
               source for any route towards the destination.

      Source IP Address
               The IP address of the node which originated the Route
               Request

      Source Sequence Number
               The current sequence number for route information
               generated by the source of the route request.




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5. Route Reply Message Format

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |L|          Reserved           |   Hop Count   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination IP address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Sequence Number                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Lifetime                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The format of the Route Reply message is illustrated above, and
   contains the following fields:

      Type     xx

      Reserved Sent as 0; ignored on reception.

      Hop Count The number of hops from the Source IP Address to the
               Destination IP Address.

      L        If the 'L' bit is set, the message is a "hello" message
               and contains a list of the node's neighbors.

      Destination IP Address
               The IP address of the destination for which a route is
               supplied

      Destination Sequence Number
               The destination sequence number associated to the route

      Lifetime
               The time for which nodes receiving the RREP consider the
               route to be valid.


6. Node Operation

   This section describes the scenarios under which nodes generate RREQs
   and RREPs, and how the fields in the message are handled.


6.1. Maintaining Route Utilization Records

   For each valid route maintained by a node (containing a finite
   metric), the node also maintains a list of those neighbors that are



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