


Mobile Ad hoc Networks Working                               I. Chakeres
Group                                                   E. Belding-Royer
Internet-Draft                                          UC Santa Barbara
Expires: November 9, 2005                                     C. Perkins
                                                                   Nokia
                                                             May 8, 2005


                 Dynamic MANET On-demand (DYMO) Routing
                        draft-ietf-manet-dymo-01

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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   This Internet-Draft will expire on November 9, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The Dynamic MANET On-demand (DYMO) routing protocol is intended for
   use by mobile nodes in wireless multihop networks.  It offers
   adaptation to changing network topology and determines unicast routes
   between nodes within the network.




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Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4

   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5

   3.  Data Structures  . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1   Route Table Entry  . . . . . . . . . . . . . . . . . . . .  6
     3.2   DYMO Message Elements  . . . . . . . . . . . . . . . . . .  7
       3.2.1   Generic DYMO Element Structure . . . . . . . . . . . .  7
       3.2.2   Routing Element (RE) . . . . . . . . . . . . . . . . .  9
       3.2.3   Route Error (RERR) . . . . . . . . . . . . . . . . . . 11
       3.2.4   Unsupported-element Error (UERR) . . . . . . . . . . . 12

   4.  Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 13
     4.1   Sequence Numbers . . . . . . . . . . . . . . . . . . . . . 13
       4.1.1   Maintaining a Sequence Number  . . . . . . . . . . . . 13
       4.1.2   Incrementing a Sequence Number . . . . . . . . . . . . 13
       4.1.3   Sequence Number Rollover . . . . . . . . . . . . . . . 13
       4.1.4   Actions After Sequence Number Loss . . . . . . . . . . 13
     4.2   DYMO Routing Table Operations  . . . . . . . . . . . . . . 13
       4.2.1   Creating or Updating a Route Table Entry from a
               Routing Element Block  . . . . . . . . . . . . . . . . 13
       4.2.2   Route Table Entry Timeouts . . . . . . . . . . . . . . 14
     4.3   General DYMO Processing  . . . . . . . . . . . . . . . . . 15
       4.3.1   DYMO Control Packet Processing . . . . . . . . . . . . 15
       4.3.2   Generic Element Pre-processing . . . . . . . . . . . . 15
       4.3.3   Processing Unsupported DYMO Element Types  . . . . . . 15
         4.3.3.1   Generating an Unsupported-element Error  . . . . . 16
       4.3.4   Generic Element Post-processing  . . . . . . . . . . . 16
       4.3.5   DYMO Control Packet Transmission . . . . . . . . . . . 16
     4.4   Routing Element  . . . . . . . . . . . . . . . . . . . . . 17
       4.4.1   Routing Element Creation . . . . . . . . . . . . . . . 17
       4.4.2   Routing Element Processing . . . . . . . . . . . . . . 17
       4.4.3   Appending Additional Routing Information to an
               Existing Routing Element . . . . . . . . . . . . . . . 18
     4.5   Route Discovery  . . . . . . . . . . . . . . . . . . . . . 18
     4.6   Route Maintenance  . . . . . . . . . . . . . . . . . . . . 19
       4.6.1   Active Link Monitoring . . . . . . . . . . . . . . . . 19
       4.6.2   Updating Route Lifetimes . . . . . . . . . . . . . . . 19
       4.6.3   Route Error Generation . . . . . . . . . . . . . . . . 19
       4.6.4   Route Error Processing . . . . . . . . . . . . . . . . 20
     4.7   Routing Prefix . . . . . . . . . . . . . . . . . . . . . . 20
     4.8   Internet Attachment  . . . . . . . . . . . . . . . . . . . 21
     4.9   Multiple Interfaces  . . . . . . . . . . . . . . . . . . . 21
     4.10  Packet Generation Limits . . . . . . . . . . . . . . . . . 22

   5.  Configuration Parameters . . . . . . . . . . . . . . . . . . . 23



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   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25

   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26

   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     9.1   Normative References . . . . . . . . . . . . . . . . . . . 27
     9.2   Informative References . . . . . . . . . . . . . . . . . . 27

       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 27

       Intellectual Property and Copyright Statements . . . . . . . . 29






































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1.  Overview

   The Dynamic MANET On-demand (DYMO) routing protocol enables reactive,
   multihop routing between participating nodes that wish to
   communicate.  The basic operations of the DYMO protocol are route
   discovery and management.  During route discovery the originating
   node initiates dissemination of a Route Request (RREQ) throughout the
   network to find the target node.  During this dissemination process,
   each intermediate node records a route to the originating node.  When
   the target node receives the RREQ, it responds with a Route Reply
   (RREP), unicast toward the originating node.  Each node that receives
   the RREP records a route to the target node, and then the RREP is
   unicast toward the originating node.  When the originating node
   receives the RREP, routes have then been established between the
   originating node and the target node in both directions.

   In order to react to changes in the network topology nodes maintain
   their routes and monitor their links.  When a packet is received for
   a route that is no longer available the source of the packet is
   notified.  A Route Error (RERR) is sent to the packet source to
   indicate the current route is broken.  Once the source receives the
   RERR, it re-initiates route discovery if it still has packets to
   deliver.

   In order to enable extension of the base specification, DYMO defines
   a generic element structure and handling of future extensions.  By
   defining a fixed structure and default handling, future extensions
   are handled in a predetermined fashion.

   DYMO uses sequence numbers as they have been proven to ensure loop
   freedom [3].  Sequence numbers enable nodes to determine the order of
   DYMO route discovery packets, thereby avoiding use of stale routing
   information.

   All DYMO packets are transmitted via UDP on port TBD.
















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2.  Terminology

      IP Destination Address (IPDestinationAddress)
         The destination of a packet, indicated by examining the IP
         header.

      IP Source Address (IPSourceAddress)
         The source of a packet, indicated by examining the IP header.

      DYMOcast
         Packet transmission to all MANET routers within reception
         range.  DYMOcast packets should be sent with an
         IPDestinationAddress of IPv4 TBD (IPv6 TBD), the
         DYMOcastAddress.

      Routing Element (RE)
         A DYMO message element that is used to distribute routing
         information.

      Route Invalidation
         Disabling the use of a route, causing it to be unavailable for
         forwarding data.

      Route Reply (RREP)
         Upon receiving a RREQ, the target node generates a Route Reply
         (RREP).  A RREP is a RE with a unicast IPDestinationAddress,
         indicating that this RE is to be unicast hop-by-hop toward the
         TargetAddress.

      Route Request (RREQ)
         A node generates a Route Request (RREQ) to discover a valid
         route to a particular destination (TargetAddress).  A RREQ is
         simply a RE with the DYMOcastAddress in the
         IPDestinationAddress field of the IP packet.  Also, the A-bit
         is set to one (A=1) to indicate that the TargetNode must
         respond with a RREP.

      Valid Route
         A known route where the Route.ValidTimeout is greater than the
         current time.











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3.  Data Structures

3.1  Route Table Entry

   The route table entry is a conceptual data structure.
   Implementations may use any internal representation that conforms to
   the semantics of a route as specified in this document.
   o  Route.DestAddress
   o  Route.DeleteTimeout
   o  Route.HopCnt
   o  Route.IsGateway
   o  Route.NextHopAddress
   o  Route.NextHopInterface
   o  Route.Prefix
   o  Route.SeqNum
   o  Route.ValidTimeout
      These fields are defined as follows:
      Route Node Address (Route.DestAddress)
         The IP address of the node associated with the routing table
         entry.

      Route Delete Timeout (Route.DeleteTimeout)
         If the time current is after Route.DeleteTimeout the
         corresponding routing table entry MUST be deleted.

      Route Hop Count (Route.HopCnt)
         The number of intermediate node hops before reaching the
         Route.DestAddress.

      Route Is Gateway (Route.IsGateway)
         1-bit selector indicating whether the Route.DestAddress is a
         gateway.

      Route Next Hop Address (Route.NextHopAddress)
         The IP address of the next node on the path toward the
         Route.DestAddress.

      Route Next Hop Interface (Route.NextHopInterface)
         The interface used to send packets toward the
         Route.DestAddress.

      Route Prefix (Route.Prefix)
         6-bit field that specifies the size of the subnet reachable
         through the Route.DestAddress, see Section 4.7.  The definition
         of the Prefix field is different for gateways; entries with
         Route.IsGateway set to one (1).





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      Route Sequence Number (Route.SeqNum)
         The sequence number of the Route.DestAddress.

      Route.ValidTimeout
         The time at which a route table entry is scheduled to be
         invalidated.  The routing table entry is no longer considered
         valid if the current time is after Route.ValidTimeout.

3.2  DYMO Message Elements

3.2.1  Generic DYMO Element Structure

   All DYMO message elements MUST conform to the fixed data structure
   below.


   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      |          Len          |    TTL    |I|Reserved |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .          NotifyAddress (Only Types with M-bit set)            .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   . TargetAddress (for non-DYMOcastAddress IPDestinationAddresses).
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                             Data                              .
   .                     Type-Specific Payload                     .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                Figure 1


      Element Type (Type)


                  0                          0
                  0 1 2 3 4 5 6 7 8          0 1 2 3 4 5 6 7 8
                  +-+-+-+-+-+-+-+-+          +-+-+-+-+-+-+-+-+
                  |     Type      |     =    |M| H |         |
                  +-+-+-+-+-+-+-+-+          +-+-+-+-+-+-+-+-+

                                Figure 2


         The Type field identifies the element as well as the handling
         by nodes that do not implement or understand the element.  The



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         most significant bit, the M-bit, denotes whether the element
         requires notification via an Unsupported-element Error (UERR)
         when the element is not understood or handled by a particular
         node.  The next two bits, H-bits, identify how the Type is to
         be handled by nodes not implementing the Type, regardless of
         UERR delivery.  Section 4.3.3 describes the handling behavior
         based on the Type.

      I-bit (I)
         1-bit selector indicating whether the element has been ignored
         by some node that has relayed this element.  If I=1 the element
         has been ignored.

      Reserved (Reserved, Reservd, Res, R)
         Reserved bits.  These bits are set to zero (0) during element
         creation and ignored during processing.

      Element Time to Live (TTL)
         6-bit field that identifies the maximum number of times the
         element is to be retransmitted.  The TTL field operates similar
         to IPTTL (MaxCount) and is decremented at each hop.  When TTL
         reaches zero (0) the element is dropped.

      Element Length (Len)
         12-bit field that indicates the size of the element in bytes,
         including the fixed portion.

      Element Notify Address (NotifyAddress)
         The node to send a UERR if the Element Type is unsupported or
         not handled by the processing node.  The NotifyAddress field is
         only present if the Type field has the M-bit is set to one (1).

      Element Target Address (TargetAddress)
         The node that is the ultimate destination of the element.  This
         field is only required if the IPDestinationAddress is not the
         DYMOcastAddress.  During hop-by-hop transmission of a DYMO
         packet the IPDestinationAddress is filled with the
         Route.NextHopAddress of the route table entry associated with
         the TargetAddress.

      Element Data (Data)
         Type-specific payload.









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3.2.2  Routing Element (RE)


   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      |          Len          |    TTL    |I|A|  Res  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                          TargetAddress                        .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          TargetSeqNum                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  THopCnt  |Res|                                               .
   +-+-+-+-+-+-+-+-+                                               .
   .                                                               .
   .                Routing Element Blocks (1 or more)             .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                Figure 3


      A-bit (A)
         1-bit selector indicating whether this RE requires a RREP by
         the TargetAddress.  If A=1 a RREP is required.  The
         instructions for generating a RREP are described in
         Section 4.4.2.

      Element Target Address (TargetAddress)
         The node that is the ultimate destination of the Routing
         Element.

      Target Sequence Number (TargetSeqNum)
         The sequence number of the ultimate destination of this Routing
         Element.  If the Sequence Number is unknown for this particular
         Route.DestAddress then TargetSeqNum is set to zero (0).

      Target Hop Count (THopCnt)
         6-bit field that identifies the number of intermediate nodes
         through which a packet traversed on the route to this
         particular TargetAddress the last time a route was available.
         The THopCnt is the Route.HopCnt of the TargetAddress, stored in
         the routing table of the RREQ originator.  If the hop count
         information is not available at the originating node then the
         THopCnt is set to zero (0).

      Routing Element Block (REBlock)




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         Data structure that describes routing information related to a
         particular IP address, RENodeAddress.

      Routing Element Block (REBlock)

   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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |G| Prefix  |Reservd| REHopCnt  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                          RENodeAddress                        .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          RENodeSeqNum                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                Figure 4


         G-bit (G)
            1-bit selector to indicate whether the RENodeAddress is a
            gateway.  If G=1 RENodeAddress is a gateway.  For more
            information on gateway operation see Section 4.8.

         Prefix Size (Prefix)
            6-bit field that specifies the size of the subnet reachable
            through the associated node, see Section 4.7.  The
            definition of Prefix is different for gateways.

         Routing Element Block Hop Count (REHopCnt)
            6-bit field that identifies the number of intermediate nodes
            through which the associated REBlock has passed.

         Routing Element Node Address (RENodeAddress)
            The IP address of the node associated with this REBlock.

         Routing Element Node Sequence Number (RENodeSeqNum)
            The sequence number of the node associated with this
            REBlock.













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3.2.3  Route Error (RERR)


   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      |          Len          |    TTL    |I|Reserved |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                          UNodeAddress1                        .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          UNodeSeqNum1                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .               Additional UNodeAddressN (if needed)            .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Additional UNodeSeqNumN (if needed)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                Figure 5


      Unreachable Node Address (UNodeAddress)
         The IP address of the unreachable node.

      Unreachable Node Sequence Number (UNodeSeqNum)
         The sequence number of the unreachable node, if known;
         otherwise, zero (0).  RERR generation is described in
         Section 4.6.3.
























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3.2.4  Unsupported-element Error (UERR)


   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      |          Len          |    TTL    |I|Reserved |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                          TargetAddress                        .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                       UElemTargetAddress                      .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                        UERRNodeAddress                        .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   UElemType   |
   +-+-+-+-+-+-+-+-+

                                Figure 6


      Element Target Address (TargetAddress)
         The node that is the ultimate destination of the element,
         NotifyAddress.

      Unsupported-element Target Address (UElemTargetAddress)
         Address of the destination of the element that caused
         generation of this UERR; TargetAddress from the offending fixed
         DYMO element.

      Unsupported-element Node Address (UERRNodeAddress)
         The IP address of the node that created the UERR.

      Unsupported-element Type (UElemType)
         The Type that required generation of the UERR.

















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4.  Detailed Operation

4.1  Sequence Numbers

4.1.1  Maintaining a Sequence Number

   DYMO requires each node in the network to maintain its own sequence
   number (OwnSeqNum).  The circumstances for a node to change its
   OwnSeqNum are described in Section 4.4.1.

4.1.2  Incrementing a Sequence Number

   When a node increments its OwnSeqNum (as described in Section 4.4.1
   and Section 4.4.2) it MUST do so by treating the sequence number
   value as if it was an unsigned number.  The sequence number zero (0)
   is reserved and is used in several DYMO data structures to represent
   an unknown sequence number.

4.1.3  Sequence Number Rollover

   If the sequence number has been assigned to be the largest possible
   number representable as a 32-bit unsigned integer (i.e., 4294967295),
   then the sequence number MUST be set to one (1) when incremented.

4.1.4  Actions After Sequence Number Loss

   If a node's OwnSeqNum is lost, it must take certain actions to avoid
   creating routing loops.  To prevent this possibility after sequence
   number loss a node MUST wait for at least ROUTE_DELETE_PERIOD before
   transmitting any DYMO packet other than RERR generated by this node.
   If a DYMO control packet is received during this period, the node
   SHOULD process it normally but MUST not retransmit any DYMO control
   packets.  If a data packet is received during this waiting period the
   node MUST send a RERR message to the IPSourceAddress with the
   UNodeSeqNum set to zero (0) and restart its waiting period before
   transmitting any DYMO control packets except RERR generated by this
   node.

4.2  DYMO Routing Table Operations

4.2.1  Creating or Updating a Route Table Entry from a Routing Element
      Block

   While processing a RE, as described in Section 4.4.2, a node checks
   its routing table for an entry to the RENodeAddress using
   longest-prefix matching.  In the event that no matching entry is
   found, an entry is created.




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   If a matching entry is found, the routing information about
   RENodeAddress contained in this REBlock is considered stale if:
   o  the result of subtracting the Route.SeqNum from RENodeSeqNum is
      less than zero (0) using signed 32-bit arithmetic, OR
   o  the result of subtracting the Route.SeqNum from RENodeSeqNum is
      equal to zero (0) using signed 32-bit arithmetic AND the REHopCnt
      is greater than Route.HopCnt.

   If there exists a valid route AND the result of subtracting the
   Route.SeqNum from RENodeSeqNum is equal to zero (0) using signed
   32-bit arithmetic AND the REHopCnt is equal to the Route.HopCnt in
   this REBLock the information is not stale, but the routing
   information SHOULD be disregarded and no routing update should occur.

   If the information in this REBLock is stale or disregarded and this
   REBlock is the first node in the RE this DYMO packet MUST be dropped.
   For other REBlocks containing stale or disregarded routing
   information, the REBlock is simply removed from this RE and the RELen
   adjusted.  Removing stale and disregarded REBlocks ensures that
   unused information is not propagated further.

   If the route information for RENodeAddress is not stale or
   disregarded, then the following actions occur to the route table
   entry for RENodeAddress:
   1.  the Route.HopCnt is set to the REHopCnt,
   2.  the Route.IsGateway is set to the G-bit,
   3.  the Route.DeleteTimeout is set to the current time +
       ROUTE_DELETE_TIMEOUT,
   4.  the Route.NextHopAddress is set to the node that transmitted this
       DYMO packet (IPSourceAddress),
   5.  the Route.NextHopInterface is set to the interface that this DYMO
       packet was received on,
   6.  the Route.Prefix is set to Prefix,
   7.  the Route.SeqNum is set to the RENodeSeqNum,
   8.  and the Route.ValidTimeout is set to the current time +
       ROUTE_TIMEOUT.

   If a valid route exists to RENodeAddress, the route can be used to
   send any queued data packets and to fulfill any outstanding route
   requests.

4.2.2  Route Table Entry Timeouts

   If the current time is later than a routing entry's
   Route.ValidTimeout, the route is stale and it is not be used to route
   packets.  The information in invalid entries may still be useful for
   generating RREQ messages.




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   If the current time is after Route.DeleteTimeout the corresponding
   routing table entry MUST be deleted.

4.3  General DYMO Processing

4.3.1  DYMO Control Packet Processing

   A DYMO packet may consist of multiple DYMO elements.  Each element is
   processed individually and in sequence, from first to last.  An
   incoming DYMO packet MUST be completely processed prior to any DYMO
   packet transmissions.

   The length of IP addresses (32-bits for IPv4 and 128-bits for IPv6)
   inside DYMO elements is dependent on the IP packet header.  For
   example, if the IP header is IPv6 then all DYMO elements contained in
   the payload use IPv6 addresses.

   Unless specific element processing requires dropping the DYMO packet,
   it is retransmitted after processing, according to the method
   described in Section 4.3.5.

4.3.2  Generic Element Pre-processing

   Each element in a DYMO packet undergoes pre-processing before the
   element specific processing occurs.  During pre-processing, the TTL
   is decremented by one (1).

4.3.3  Processing Unsupported DYMO Element Types

   This section describes the processing for unsupported DYMO element
   Types.  The Type field identifies the handling by nodes that do not
   implement, support or understand a particular Element Type.  The most
   significant bit (M-bit) indicates whether an Unsupported-element
   Error (UERR) SHOULD be sent to the NotifyAddress.  The next two bits
   (H-bits) identify how the element should be handled.

                  0                          0
                  0 1 2 3 4 5 6 7 8          0 1 2 3 4 5 6 7 8
                  +-+-+-+-+-+-+-+-+          +-+-+-+-+-+-+-+-+
                  |     Type      |     =    |M| H |         |
                  +-+-+-+-+-+-+-+-+          +-+-+-+-+-+-+-+-+

   If the M-bit is set in a DYMO element being processed by a node that
   does not support this Element Type a UERR SHOULD be sent to the
   NotifyAddress.  This is accomplished by following the instructions in
   Section 4.3.3.1.

   Regardless of whether or not a UERR is sent in response to this



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   unsupported Element Type, the processing node MUST also examine the
   H-bits to determine how this unsupported element is handled.  The
   unsupported element Type MUST be handled as follows:
   o  If H == 00 skip the element and continue as if the packet did not
      contain this element.
   o  If H == 01 remove the unsupported element (using the Len field)
      from the packet and continue as if the packet did not include this
      element.
   o  If H == 10 set the ignored bit (I-bit) skip this element and
      continue, as if the packet did not contain this element.
   o  If H == 11 drop the packet without processing any other DYMO
      elements.

4.3.3.1  Generating an Unsupported-element Error

   When an unsupported element type is received with the M-bit set, the
   processing node SHOULD generate an Unsupported-element Error (UERR).
   The TargetAddress is set to the NotifyAddress.  The
   IPDestinationAddress is set to the Route.NextHopAddress toward the
   NotifyAddress.  The UElemTargetAddress is set to the TargetAddress
   from the unsupported element.  The UERRNodeAddress is set to the node
   address generating this UERR.  The UElemType is the Type from the
   unsupported element.  The TTL SHOULD be set to NET_DIAMETER, but MAY
   be set smaller.  The Len is set to the total number of bytes in this
   UERR.  The element is then processed as described in Section 4.3.4.

4.3.4  Generic Element Post-processing

   If the first element TTL is zero (0) the DYMO packet is dropped after
   processing of all elements.  If the TTL of the first element is
   greater than zero the DYMO packet is re-transmitted after processing
   of all elements.  If the TTL of any element is zero (0) after
   processing it MUST be removed from the DYMO packet prior to
   transmission.

4.3.5  DYMO Control Packet Transmission

   DYMO packet transmission and re-transmission is controlled by the
   IPDestinationAddress.  If the IPDestinationAddress is a unicast
   address, the packet IPDestinationAddress is replaced by the
   Route.NextHopAddress from a route table lookup for the TargetAddress.
   If a route for the TargetAddress is unknown or invalid the packet is
   dropped and a RERR SHOULD be generated.

   For all currently defined DYMO packets the IPTTL (IPMaxCount) SHOULD
   be set to 1 (IPTTL=1), since all DYMO packet communications are
   between direct neighbors.




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4.4  Routing Element

4.4.1  Routing Element Creation

   When a node creates a RE it MUST increment its OwnSeqNum by one
   according to the rules specified in Section 4.1.2, except under the
   following conditions: The RE being created is a RREP AND either the
   o  TargetSeqNum is less than OwnSeqNum OR
   o  TargetSeqNum is equal to OwnSeqNum AND the and THopCnt is less
      than or equal to HopCnt.
   Then the node sets the RENodeAddress1 to its own address.  The
   RENodeSeqNum1 is the node's OwnSeqNum.  The node may advertise a
   prefix using the Prefix field, as described in Section 4.7.
   Otherwise, the Prefix field is set to zero (0).  The node may
   advertise it is a gateway by setting the G-bit if it is a gateway, as
   described in Section 4.8.  Otherwise, the G-bit is set to zero (0).
   The TTL SHOULD be set to NET_DIAMETER, but MAY be set smaller.  For
   the case of RREQ, the TTL MAY be set in accordance with an expanding
   ring search as described in [2].

4.4.2  Routing Element Processing

   After general DYMO element pre-processing (Section 4.3.2), the
   REHopCnt for the first REBlock is incremented by one (1).  A route to
   the first REBlock is then created or updated, as described in
   Section 4.2.1.  If this REBlock does not result in a valid route the
   packet MUST be dropped.

   Each additional REBlock SHOULD be processed.  For each REBlock the
   REHopCnt is incremented by one (1), then a route is created or
   updated as defined in Section 4.2.1.  Each REBlock resulting in a
   valid route entry may alleviate a future route discovery.  Any
   REBlocks that do not result in a valid route update or that are not
   processed MUST be removed from the RE.

   If this node is the TargetAddress AND the A-bit is set (A=1), this
   node MUST respond with a RREP.  The target node creates a new RE as
   described in Section 4.4.1.  The TargetAddress in the new RE is set
   to the RENodeAddress1 from the RE currently being processed.  The
   THopCnt is the hop count for the TargetAddress.  The A-bit is set to
   (A=0).  The IPDestinationAddress is set to the Route.NextHopAddress
   for the TargetAddress.  The TargetSeqNum is set to Route.SeqNum for
   the TargetAddress.  Then the new RE undergoes post-processing,
   according to Section 4.3.4.

   After processing a RE, a node MAY append its routing information to
   the RE, according to the process described in Section 4.4.3.  The
   additional routing information will reduce route discoveries to this



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   node.

   If this node is not the TargetAddress, the current RE SHOULD be
   handled according to Section 4.3.4.

   If this node is the TargetAddress, the current packet and any
   additional elements are processed, but this packet is not
   retransmitted.

4.4.3  Appending Additional Routing Information to an Existing Routing
      Element

   Appending routing information will alleviate route discovery attempts
   to this node from other nodes that process the resultant RE.  Nodes
   SHOULD append a REBlock to RE processed.

   Prior to appending a REBlock to a RE, a node MUST increment its
   OwnSeqNum as defined in Section 4.1.2.  Then it appends its IP
   address, OwnSeqNum, Prefix and G-bit to the RE in a REBlock.  The
   REHopCnt is set to zero (0).  The RE Len is also adjusted according
   to the number of REBlocks in the RE.

4.5  Route Discovery

   A node generates a Route Request (RREQ) to discover a valid route to
   a particular destination (TargetAddress).  A RREQ is a RE with the
   A-bit is set to one (A=1) to indicate that the TargetNode must
   respond with a RREP.  If a sequence number is known for the
   TargetAddress it is placed in the TargetSeqNum field.  Otherwise,
   TargetSeqNum is set to zero (0).  Similarly, if a hop count is known
   for the TargetAddress it is placed in the THopCnt field.  Otherwise,
   the THopCnt is set to zero (o).  The IPDestinationAddress is set to
   the DYMOcastAddress.  Then the RE is then transmitted according to
   the procedure defined in Section 4.3.5.

   After issuing a RREQ, the originating node waits for a route to be
   created to the TargetNode.  If a route is not received within
   RREQ_WAIT_TIME milliseconds, this node MAY again try to discover a
   route by issuing another RREQ.

   To reduce congestion in a network, repeated attempts at route
   discovery for a particular TargetNode SHOULD utilize a binary
   exponential backoff.  The first time a node issues a RREQ, it waits
   RREQ_WAIT_TIME milliseconds for a route to the TargetNode.  If a
   route is not found within that time, the node MAY send another RREQ.
   If a route is not found within two (2) times the current waiting
   time, another RREQ may be sent, up to a total of RREQ_TRIES.  For
   each additional attempt, the waiting time for the previous RREQ is



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   multiplied by two (2) so that the waiting time conforms to a binary
   exponential backoff.

   Data packets awaiting for a route SHOULD be buffered.

   If a route discovery has been attempted RREQ_TRIES times without
   receiving a route to the TargetNode, all data packets destined for
   the corresponding TargetNode SHOULD be dropped from the buffer and a
   Destination Unreachable ICMP message SHOULD be delivered to the
   application.

4.6  Route Maintenance

4.6.1  Active Link Monitoring

   Nodes MUST monitor links on active routes.  This may be accomplished
   by one or several mechanisms.  Including:
   o  Link layer feedback
   o  Hello messages
   o  Neighbor discovery
   o  Route timeout
   Upon detecting a link break the detecting node MUST set the
   Route.ValidTimeout to the current time for all routes active routes
   utilizing the broken link.

   A RERR MUST be issued if a data packet is received and it cannot be
   delivered to the next hop.  RERR generation is described in
   Section 4.6.3.  A RERR SHOULD be issued after detecting a broken link
   of an active route to quickly notify nodes that a link break occurred
   and a route or routes are no longer available.

4.6.2  Updating Route Lifetimes

   To avoid route timeouts for active routes, a node MUST update the
   Route.ValidTimeout to the IPSourceAddress to be the current time +
   ROUTE_TIMEOUT upon receiving a data packet.  The Route.DeleteTimeout
   MUST also be updated to the current time + ROUTE_DELETE_TIMEOUT.

   To avoid route timeouts for active routes, a node SHOULD update the
   Route.ValidTimeout to the IPDestinationAddress to be the current time
   + ROUTE_TIMEOUT upon successfully transmitting a packet to the next
   hop.  The Route.DeleteTimeout SHOULD also be updated to the current
   time + ROUTE_DELETE_TIMEOUT.

4.6.3  Route Error Generation

   When a data packet is received for a destination without a valid
   routing table entry, a Route Error (RERR) MUST be generated by this



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   node.  A RERR informs the source that the current route is no longer
   available.

   In the RERR, the UNodeAddress1 field is the address of the
   unreachable node (IPDestinationAddress) from the data packet.  If the
   UNodeSeqNum is known, it is placed in the RERR; otherwise, zero (0)
   is placed in the UNodeSeqNum field of the RERR.  The TTL SHOULD be
   set to NET_DIAMETER, but may be set smaller.  The
   IPDestinationAddress is set to the DYMOcastAddress.

   Additional unreachable nodes that required the same unavailable link
   (routes with the same Route.NextHopAddress and
   Route.NextHopInterface) as the UNodeAddress1 SHOULD be appended to
   the RERR.  For each unreachable node the UNodeAddress and UNodeSeqNum
   are appended.  The Len is set accordingly.

   The RERR is then processed as described in Section 4.3.5.

4.6.4  Route Error Processing

   When a node processes a RERR after generic element pre-processing
   (Section 4.3.2), it SHOULD set the Route.ValidTimeout to the current
   time for each route to a UNodeAddress that meets all of the following
   conditions:
   1.  The Route.NextHopAddress is the same as the RERR IPSourceAddress.
   2.  The Route.NextHopInterface is the same as the interface on which
       the RERR was received.
   3.  The UNodeSeqNum is zero (0) OR the result of subtracting
       Route.SeqNum from UNodeSeqNum is less than or equal to zero using
       signed 32-bit arithmetic.

   Each UNodeAddress that did not result in a change to
   Route.ValidTimeout SHOULD be removed from the RERR.

   Prior to generic post processing a node MAY remove any UNodeAddressN,
   UNodeSeqNumN pairs except UNodeAddress1 to decrease the element size.

   If at least one UNodeAddress remains and at least one route remains
   in the RERR it SHOULD be handled as described in Section 4.3.4 to
   continue notification of nodes effected by the broken link.
   Otherwise, the RERR is dropped.

4.7  Routing Prefix

   Any node can advertise connectivity to a subset of other nodes within
   its address space by using the prefix field in RE.  The nodes within
   the advertised prefix SHOULD NOT participate in the MANET and MUST be
   reachable by forwarding packets to the node advertising connectivity.



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   For example, 192.168.1.1 with a prefix of 16 indicates all nodes with
   the prefix 192.168.X.X are reachable through 192.168.1.1.

   The meaning of the prefix field is altered for routes to the gateway;
   Route.IsGateway is one (1).  If the G-bit is set the prefix in
   association with the IP address indicates that all nodes outside the
   subnet are reachable via the gateway node.  For example, a route to a
   gateway with IP address 192.168.1.1 and a prefix of 16 indicates that
   all nodes with an IP address NOT matching 192.168.X.X are reachable
   via this route.

4.8  Internet Attachment

   Internet attachment consists of a network of MANET nodes connected to
   the Internet via a gateway node.  The gateway is responsible for
   responding to RREQs for TargetNodes outside its configured MANET
   subnet, as well as delivering packets to destinations outside the
   MANET subnet.

   MANET nodes wishing to be reachable from nodes in the Internet MUST
   have IP addresses within the gateway's configured MANET subnet.
   Given a node with a globally routeable address or care-of address
   handled by the gateway, the gateway is responsible for routing and
   forwarding packets received from the Internet destined for nodes
   inside its MANET subnet.

   Since many nodes may commonly wish to communicate with the gateway,
   the gateway SHOULD indicate to nodes that it is a gateway by setting
   the gateway bit (G-bit) in any RE created or processed.  The G-bit
   flag indicates to nodes in the MANET that the RENodeAddress is
   attached to the Internet and is capable of routing data packets to
   all nodes outside of the configured MANET subnet, described by the
   RENodeAddress and Prefix fields.

4.9  Multiple Interfaces

   It is likely that DYMO will be used with multiple wireless
   interfaces; therefore, the particular interface over which packets
   arrive must be known whenever a packet is received.  Whenever a new
   route is created, the interface through which the Route.DestAddress
   can be reached is also recorded into the route table entry.

   When multiple interfaces are available, a node transmitting a
   DYMOcast packet SHOULD send the packet on all interfaces that have
   been configured for operation in the MANET.






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4.10  Packet Generation Limits

   To avoid congestion, a node SHOULD NOT transmit more than RATE_LIMIT
   control messages per second.  RREQ packets SHOULD be discarded before
   RREP or RERR packets.














































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5.  Configuration Parameters

   Here are some default parameter values for DYMO:
      Parameter Name                  Suggested Value
      ---------------------------     ---------------
      NET_DIAMETER                    10
      RATE_LIMIT                      10
      ROUTE_TIMEOUT                   3000 milliseconds
      ROUTE_DELETE_TIMEOUT            5*ROUTE_TIMEOUT
      RREQ_WAIT_TIME                  1000 milliseconds
      RREQ_TRIES                      3

   For large networks or networks with frequent topology changes the
   default DYMO parameters should be adjusted using either
   experimentally determined values or dynamic adaptation.  For example,
   in networks with infrequent topology changes ROUTE_TIMEOUT may be set
   to a much larger value.

   It is assumed that all nodes in the network share the same parameter
   settings.  Different parameter values for ROUTE_TIMEOUT or
   ROUTE_DELETE_TIMEOUT in addition to arbitrary packet delays may
   result in frequent route breaks or routing loops.





























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6.  IANA Considerations

   DYMO defines a Type field for each element within a packet sent to
   port TBD.  A new registry will be created for the values for this
   Type field, and the following values will be assigned:
      Type                                 Value
      --------------------------------     -----
      Routing Element (RE)                 1
      Route Error (RERR)                   2
      Unsupported-element Error (UERR)     3

   Future values of the Type will be allocated using standard actions as
   described in [1].  For future Types with the M-bit set NotifyAddress
   MUST be included.  Similarly for future Types that are unicast
   hop-by-hop (packets not sent to the DYMOcastAddress), these Types
   MUST include the TargetAddress field.



































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7.  Security Considerations

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

   In particular, RE messages SHOULD be authenticated to avoid creation
   of spurious routes to a destination.  Otherwise, an attacker could
   masquerade as that destination and maliciously deny service to the
   destination and/or maliciously inspect and consume traffic intended
   for delivery to the destination.  RERR messages, while slightly less
   dangerous, SHOULD be authenticated in order to prevent malicious
   nodes from disrupting active routes between communicating nodes.

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





















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8.  Acknowledgments

   DYMO is a descendant of the design of previous MANET reactive
   protocols, especially AODV [2] and DSR [4].  Changes to previous
   MANET reactive protocols stem from research and implementation
   experiences.  Thanks to Luke Klein-Berndt for reviewing of DYMO, as
   well as several specification suggestions.












































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9.  References

9.1  Normative References

   [1]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", RFC 2434, BCP 26, October 1998.

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

9.2  Informative References

   [3]  Perkins, C. and E. Belding-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.

   [4]  Johnson, D. and D. Maltz, "Dynamic Source Routing (DSR) in Ad
        hoc Networks", In Mobile Computing, Chapter 5, pp. 153-181,
        1996.


Authors' Addresses

   Ian Chakeres
   University of California Santa Barbara
   Dept. of Electrical and Computer Engineering
   Santa Barbara, CA  93106
   USA

   Phone: +1-805-893-8981
   Fax:   +1-805-893-8553
   Email: idc@engineering.ucsb.edu


   Elizabeth Belding-Royer
   University of California Santa Barbara
   Dept. of Computer Science
   Santa Barbara, CA  93106-5110
   USA

   Phone: +1-805-893-3411
   Fax:   +1-805-893-8553
   Email: ebelding@cs.ucsb.edu







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   Charlie Perkins
   Nokia Research Center
   313 Fairchild Drive
   Mountain View, CA  94043
   USA

   Phone: +1-650-625-2986
   Fax:   +1-650-625-2502
   Email: charlie.perkins@nokia.com










































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