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Copyright Notice

Copyright © The Internet Society (2006).

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 on-demand.

Table of Contents

1.  Overview
2.  Applicability
3.  Terminology
4.  Data Structures
    4.1.  Route Table Entry
    4.2.  DYMO Messages
        4.2.1.  Generalized MANET Packet and Message Structure
        4.2.2.  Routing Message (RM)
        4.2.3.  Route Error (RERR)
5.  Detailed Operation
    5.1.  DYMO Sequence Numbers
        5.1.1.  Maintaining A Node's Own Sequence Number
        5.1.2.  Incrementing a Sequence Number
        5.1.3.  Sequence Number Rollover
        5.1.4.  Actions After Sequence Number Loss
    5.2.  DYMO Routing Table Operations
        5.2.1.  Judging New Routing Information's Usefulness
        5.2.2.  Updating a Route Table Entry with Fresh Routing Information
        5.2.3.  Route Table Entry Timeouts
    5.3.  Routing Message
        5.3.1.  RREQ Creation
        5.3.2.  RREP Creation
        5.3.3.  RM Processing
        5.3.4.  Adding Additional Routing Information to a RM
    5.4.  Route Discovery
    5.5.  Route Maintenance
        5.5.1.  Active Link Monitoring
        5.5.2.  Updating Route Lifetimes during Packet Forwarding
        5.5.3.  Route Error Generation
        5.5.4.  Route Error Processing
    5.6.  General DYMO Packet and Message Processing
        5.6.1.  Processing Unknown Message and TLV Types
    5.7.  Network Addresses
    5.8.  Simple Internet Attachment and Gatewaying
    5.9.  Multiple Interfaces
    5.10.  Packet Generation Limits
6.  Configuration Parameters
7.  IANA Considerations
    7.1.  DYMO Message Type Specification
    7.2.  DYMO Message TLV Type Specification
    7.3.  Address Block TLV Specification
8.  Security Considerations
9.  Acknowledgments
10.  References
    10.1.  Normative References
    10.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

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 route 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 data packet is received for a route or link 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 can perform route discovery if it still has packets to deliver.

DYMO uses sequence numbers as they have been proven to ensure loop freedom [Perkins99] (Perkins, C. and E. Belding-Royer, “Ad hoc On-Demand Distance Vector (AODV) Routing,” February 1999.). Sequence numbers enable nodes to determine the order of DYMO route discovery messages, thereby avoiding use of stale routing information.

2. Applicability

The DYMO routing protocol is designed for mobile ad hoc networks in small, medium, and large node populations. DYMO handles all mobility ranges. DYMO can handle various traffic patterns, but is most suited for sparse traffic sources and destinations. DYMO is designed for network where trust is assumed, since it depends on nodes properly forwarding traffic to the next hop toward the destination on behalf of the source.

DYMO is applicable to memory constrained devices, since little routing state needs to be maintained. Only routing information related to active destinations must be maintained, as opposed to other routing protocols where routing information to all destinations or a large population destinations must be maintained.

The routing algorithm in DYMO may be operated at layers other than the network layer, using layer-appropriate addresses. Only modification of the packet format is required. The routing algorithm need not change.

3. Terminology

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

This document defines the following terminology:

DYMO Sequence Number (SeqNum)

A DYMO Sequence Number is maintained by each node. This sequence number is used to identify the freshness of related routing information and to ensure loop-free routes.

Hop Count (HopCnt)

The number of IP hops a message or piece of information must traverse to reach the node holding this information.

Originator (Orig)

The originator is the node that created a DYMO Message in an effort to disseminate information.

Route Error (RERR)

A node generates a RERR to disseminate that it does not have valid route to a particular destination, or set of destinations.

Route Reply (RREP)

Upon receiving a RREQ during route discovery, the target node generates a Route Reply (RREP). A RREP is used to disseminate routing information, on how to reach the target, to nodes between the target and the RREQ originator.

Route Request (RREQ)

A node generates a RREQ to discover a valid route to a particular destination, called the target. A RREQ also disseminates routing information on how to reach the originator of the RREQ.

Target

The Target node is the ultimate destination of a message. For RREQ the target is the desired destination. For RREP the target is the originator of the RREQ.

Valid Route

A valid route is a known route where the Route.ValidTimeout is greater than the current time. Valid routes may be used to forward data.

When describing DYMO messages, information found in the:

IP header

is proceeded with 'IP.'

UDP header

is proceeded with 'UDP.'

packetbb message header

is proceeded with 'MsgHdr.'

packetbb message TLVs

is proceeded with 'MsgTLV.'

packetbb address blocks

is proceeded with 'AddBlk.'

packetbb address block TLVs

is proceeded with 'AddTLV.'

4. Data Structures

4.1. 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. The number zero (0) is reserved and can be used to indicate that the field value for this routing entry is unknown or invalid.

A routing table entry has the following fields:

Route.Address

The IP destination address of the node associated with the routing table entry.

Route.SeqNum

The DYMO SeqNum associated with this routing information.

Route.NextHopAddress

The IP address of the next node on the path toward the Route.Address.

Route.NextHopInterface

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

Route.ValidTimeout

The time at which a route table entry is no longer valid.

Route.DeleteTimeout

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

The following fields are optional:

Route.HopCnt

The number of intermediate node hops traversed before reaching the Route.Address node.

Route.IsInternetGateway

1-bit selector indicating whether the Route.Address is a an Internet gateway, see Section 5.8 (Simple Internet Attachment and Gatewaying).

Route.Prefix

Indicates that the associated address is a network address, rather than a host address. The value is the length of the netmask/prefix. If prefix is set to zero (0), unknown, or equal to the address length in bits, this address is a host address. The definition of Route.Prefix is different for gateways; entries with Route.IsInternetGateway set to one (1), seeSection 5.8 (Simple Internet Attachment and Gatewaying).

Route.Used

1-bit selector indicating whether this Route has been used to forward data toward the destination.

Not including this optional information may result in sub-optimal performance, but it is not required for correct protocol operation.

4.2. DYMO Messages

4.2.1. Generalized MANET Packet and Message Structure

All DYMO messages conform to the generalized packet and message format as described in[I-D.ietf-manet-packetbb] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” June 2006.).

All DYMO messages are sent using UDP to the destination port TBD.

All DYMO messages are sent with the IP destination address set to the link local multicast address LL_ALL_MANET_ROUTER unless otherwise stated.

The IP TTL (IP Hop Limit) field for all DYMO messages is set to one (1).

The length of IP addresses (32-bits for IPv4 and 128-bits for IPv6) inside DYMO messages are dependent on the IP packet header. For example, if the IP header uses IPv6 addresses then all messages and addresses contained in the payload use IPv6 addresses. In the case of mixed IPv6 and IPv4 addresses, IPv4 addresses are carried in IPv6 as specified in [RFC3513] (Hinden, R. and S. Deering, “Internet Protocol Version 6 (IPv6) Addressing Architecture,” April 2003.).

4.2.2. Routing Message (RM)

Routing Messages (RM) are used to disseminate routing information. There are two DYMO message types that are RM, RREQ and RREP. They contain the same information, but have slightly different processing rules. The fundamental difference between the two messages are that RREQ messages require a response; while a RREP is the response to RREQ.

RM creation and processing are described in Section 5.3 (Routing Message).

A RM requires the following information:

IP.DestinationAddress

The IP address of the packet destination.

MsgHdr.HopLimit

The remaining number of hops this message may traverse.

AddBlk.Target.Address

The IP address of the message target. In RREQ the target is the unknown destination. In RREP the Target is the RREQ originator.

AddBlk.Orig.Address

The IP address of the message originator.

AddTLV.Orig.SeqNum

The DYMO sequence number of the message originator.

A RM may optionally include the following information:

AddTLV.Target.SeqNum

The last known DYMO sequence number of the Target. If the AddTLV.Target.SeqNum is set to zero (0), then only the destination may respond to this RREQ.

AddBlk.AdditionalNode.Address

The IP address of an additional node that can be reached via the node adding this information. Each AdditionalNode.Address must have an associated SeqNum in the message.

AddTLV.AdditionalNode.SeqNum

The DYMO sequence number of the additional node's routing information.

AddTLV.Node.HopCnt

The number of IP hops to reach the associated Node.Address.

AddTLV.Node.Prefix

The Node.Address is a network address ([I-D.ietf-manet-packetbb] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” June 2006.)).

AddTLV.Node.IsGateway

This AddTLV indicates that the Internet is reachable via this node. That is, all nodes outside this Node's prefix are reachable via the advertising Node.

AddTLV.Node.IsTarget

If the target is not the first address in the address blocks, this AddTLV may be used to indicate the target.

AddTLV.Node.IsOriginator

In the event that the originator is not the second address in the address blocks, this AddTLV may be used to indicate the originator.

AddTLV.AdditionalNode.IsOffPath

This AddTLV is used to indicate that a node is not on the path between the originator and the target.

AddTLV.Node.Ignore

If the information associated with Node.Address should not be used create or update a route, this flag is set.

Not including this optional information may result in sub-optimal performance, but it is not required for correct protocol operation.

Example IPv4 RREQ

     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

IP Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         IP.DestinationAddress=LL_ALL_MANET_ROUTERS            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...

UDP Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Destination Port=TBD      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Message Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   RREQ-type   |  Resv   |0|0|1|         msg-size=24           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | msg-hoplimit  |  msg-hopcnt   |      msg-tlv-block-size=0     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Address Block
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Number Addrs=2 |0|HeadLength=24|             Head              :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :  Head (cont)  |  Target.Tail  |   Orig.Tail   |  TLV-blk-size :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    : size=7 (cont) |
    +-+-+-+-+-+-+-+-+
...
Address TLVs
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |DYMOSeqNum-type| Resv  |1|0|0|0| Index Start=1 | Index Stop=1  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | tlv-length=16 |          Orig.SeqNum          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.3. Route Error (RERR)

RERR are used to disseminate that a valid route is not available for a particular destination, or set of destinations.

RERR creation and processing are described in Section 5.5.3 (Route Error Generation) and Section 5.5.4 (Route Error Processing).

A RERR requires the following information:

IP.DestinationAddress

The IP address of the packet destination.

MsgHdr.HopLimit

The remaining number of hops this message may traverse.

AddBlk.Unreachable.Address

The IP address of an Unreachable Node. Multiple Unreachable Addresses may be included. If a SeqNum for this address is not included, it is assumed to be unknown.

A Route Error may optionally include the following information:

AddTLV.Unreachable.SeqNum

The DYMO sequence number of the Unreachable Node.

AddTLV.Node.Ignore

If the information associated with Node.Address should not be used to invalidate routes, this flag is set.

Example IPv4 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

IP Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         IP.DestinationAddress=LL_ALL_MANET_ROUTERS            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...

UDP Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Destination Port=TBD      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Message Header
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   RERR-type   |  Resv   |0|0|1|         msg-size=16           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | msg-hoplimit  |  msg-hopcnt   |      msg-tlv-block-size=0     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Address Block
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Number Addrs=1 |0|HeadLength=0 |       Unreachable.Addr        :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :    Unreachable.Addr (cont)    |        TLV-blk-size=0         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5. Detailed Operation

5.1. DYMO Sequence Numbers

DYMO sequence numbers allow nodes to judge the freshness of routing information, and ensure loop freedom.

5.1.1. Maintaining A Node's Own Sequence Number

DYMO requires a each node in the network to maintain its own DYMO sequence number (OwnSeqNum), a 16-bit unsigned integer. The circumstances for a node to incrementing its OwnSeqNum are described in Section 5.3 (Routing Message).

5.1.2. Incrementing a Sequence Number

When a node increments its OwnSeqNum (as described in Section 5.3 (Routing Message)) 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.

5.1.3. Sequence Number Rollover

If the sequence number has been assigned to be the largest possible number representable as a 16-bit unsigned integer (i.e., 65535), then the sequence number MUST be set to 256 when incremented. Setting the sequence number to 256 allows other nodes to detect that the number has rolled over and the node has not lost its sequence number.

5.1.4. Actions After Sequence Number Loss

A node can maintain its sequence number in persistent storage, between reboots.

If a node's OwnSeqNum is lost, it must take certain actions to avoid creating routing loops. To prevent this possibility after OwnSeqNum loss a node MUST wait for at least ROUTE_DELETE_PERIOD before fully participating in the DYMO routing protocol. If a DYMO control message is received during this waiting period, the node SHOULD process it normally but MUST not transmit or retransmit any DYMO messages. If a data packet is received for forwarding to another destination during this waiting period, the node MUST generate a RERR message indicating that this route is not available and reset its waiting period. RERR generation is described in Section 5.5.3 (Route Error Generation). At the end of the waiting period a node sets its OwnSeqNum to one (1).

5.2. DYMO Routing Table Operations

5.2.1. Judging New Routing Information's Usefulness

Given a routing table entry (Route.SeqNum, Route.HopCnt, and Route.ValidTimeout) and new routing information for a particular node in a RM (Node.SeqNum, Node.HopCnt, and RM message type - RREQ/RREP), the quality of the new routing information is evaluated to determine its usefulness. The following comparisons are performed in order:

1. Stale

If Node.SeqNum - Route.SeqNum > 0 (using signed 16-bit arithmetic) the information is stale. Using stale routing information is not allowed, since doing so might result in routing loops.

2. Loop-prone

If Node.SeqNum = Route.SeqNum the information maybe loop-prone, additional information must be examined. If Route.HopCnt is unknown or set to zero (0), then the routing information is loop-prone. Likewise, if Node.HopCnt is unknown or set to zero (0), then the routing information is loop-prone. If Node.HopCnt > Route.HopCnt + 1, then the routing information is loop-prone. Using loop-prone routing information is not allowed, since doing so might result in routing loops.

3. Inferior

If Node.SeqNum == Route.SeqNum the information may be inferior, additional information must be examined. If the route is valid (by examining Route.ValidTimeout and the current time), then the new information is inferior if Node.HopCnt > Route.HopCnt. Additionally, if the route is valid, then the new information is inferior if Node.HopCnt == Route.HopCnt and the Message containing the new information is a RREQ.

4. Fresh

Routing information that does not match any of the above criteria is loop-free and better than the information existing in the routing table. This information should be used to update the routing table.

5.2.2. Updating a Route Table Entry with Fresh Routing Information

If fresh routing information is received, the routing table entry is populated with the following information:

1. the Route.Address is set to Node.Address,
2. the Route.SeqNum is set to the Node.SeqNum,
3. the Route.NextHopAddress is set to the node that transmitted this DYMO packet (IP.SourceAddress),
4. the Route.NextHopInterface is set to the interface that this DYMO packet was received on,
5. the Route.ValidTimeout is set to the current time + ROUTE_VALID_TIMEOUT,
6. the Route.HopCnt is set to the Node.HopCnt,
7. the Route.IsInternetGateway is set if address is an Internet Gateway,
8. the Route.Prefix is set to the Node.Prefix

Unknown values are set to zero (0).

If a valid route exists to Node.Address at this point, the route can be used to send any queued data packets and to fulfill any outstanding RREQ.

5.2.3. Route Table Entry Timeouts

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

If the current time is later than a routing entry's Route.ValidTimeout, the route is stale and cannot be used to route packets. The information in invalid entries is still used for filling fields in outgoing RM with last known values.

5.3. Routing Message

5.3.1. RREQ Creation

When a node creates a RREQ it SHOULD increment its OwnSeqNum by one (1) according to the rules specified in (Incrementing a Sequence Number).

Fist, the node adds the Target.Address to the RM address block.

If a previous value of the Target.SeqNum is known, it SHOULD be placed in a corresponding add-tlv. If a Target.SeqNum is not included, it is assumed to be unknown by processing nodes and only the target s allowed to respond. A Target.SeqNum of zero (0) MAY be set to indicate that any node with valid routing information about this destination may respond to this RREQ if the node is so enabled, though the process for doing so is not described in this document.

Similarly, if a previous value of the Target.HopCnt is known, it SHOULD be placed in a corresponding add-tlv HopCnt. Otherwise, the HopCnt is not included and assumed unknown by processing nodes.

These address-block-TLVs associated with the target SHOULD be set to maximum protocol efficiency, but they may be omitted to reduce message size.

Next, the node adds the Orig.Address to the RM address block and the Orig.SeqNum (OwnSeqNum) in an address block TLV. The Orig.Address is this node's primary addresses/identifier.

Other address-block-TLVs for the Originator SHOULD be set to maximum protocol efficiency, but they may be omitted to reduce message size.

The msg-hopcnt is set to zero (0). The msg-ttl SHOULD be set to NET_DIAMETER, but MAY be set smaller. For RREQ, the msg-ttl MAY be set in accordance with an expanding ring search as described in (Perkins, C., Belding-Royer, E., and S. Das, “Ad hoc On-Demand Distance Vector (AODV) Routing,” July 2003.) [RFC3561] to limit the RREQ propagation to a subset of the network and possibly reduce route discovery overhead.

5.3.2. RREP Creation

When a node creates a RREP in response to a RREQ, it MUST increment its OwnSeqNum under the following conditions:

• Target.SeqNum is not included in the message, OR
• Target.SeqNum is zero (0), OR
• Target.SeqNum > OwnSeqNum (using 16-bit signed arithmetic), OR
• Target.SeqNum == OwnSeqNum AND Target.HopCnt is unknown, OR
• Target.SeqNum == OwnSeqNum AND Orig.HopCnt is unknown, OR
• Target.SeqNum == OwnSeqNum AND Target.HopCnt (the last know hop count value) < Orig.HopCnt (the number of hops traversed by this RREQ to reach the target).

First, the node adds the Target.Address to the RM address block. The Target.Address is copied from the incoming RREQ Orig.Address.

Next, the node adds the Orig.Address to the RM address block and the Orig.SeqNum (OwnSeqNum) in an address block TLV. The Orig.Address is copied from the incoming RREQ Target.Address.

Other address-block-TLVs for the Originator and Target SHOULD be set to maximum protocol efficiency, but they may be omitted to reduce message size.

The msg-hopcnt is set to zero (0). The msg-ttl SHOULD be set to NET_DIAMETER, but MAY be set to the Route.HopCnt for the outgoing Target.Address if known.

5.3.3. RM Processing

When a RM is received the msg-ttl is decremented by one (1) and msg-hopcnt is incremented by one (1).

For each address that includes HopCnt information except the target and those addresses tagged with the Ignore address-block-TLV, the HopCnt information incremented by one (1).

Next, this node checks whether its routing table has an entry to the Orig.Address using longest-prefix matching (Baker, F., “Requirements for IP Version 4 Routers,” June 1995.) [RFC1812]. If a route does not exist, the new routing information is considered fresh and a new route table entry is created and updated as described in Section 5.2.2 (Updating a Route Table Entry with Fresh Routing Information). If a routing table entry exists, the new information is compared with the route table entry following the procedure described in Section 5.2.1 (Judging New Routing Information's Usefulness). If the new routing information is considered fresh, the route table entry is updated as described in Section 5.2.2 (Updating a Route Table Entry with Fresh Routing Information).

If the routing information for the originator is not fresh then this RM must be discarded and no further processing of this message is performed.

If the originator's routing information was considered fresh, then each address that is not the target and is not flagged with the Ignore address-block-tlv SHOULD considered for creating and updating routes. If routing table space is limited, only the routing information about the originator is required. Creating and updating routes for other locations can reduce routing overhead, in the even that data needs to be forwarded to these destinations in the near future.

For each of these addresses, if the routing table does not have a matching route using longest-prefix matching, then a route is created and updated as described in Section 5.2.2 (Updating a Route Table Entry with Fresh Routing Information). If a routing table entry exists, the new information is compared with the route table entry following the procedure described in Section 5.2.1 (Judging New Routing Information's Usefulness). If the new routing information is considered fresh, the route table entry is updated as described in Section 5.2.2 (Updating a Route Table Entry with Fresh Routing Information).

If the routing information for an Node.Address is not considered fresh, then if MUST be removed from the RM. Removing this information ensures that non-fresh information is not propagated.

If this node is the target AND this RM is a RREQ, this node responds with a RREP. This node creates a new RREP as described in Section 5.3.2 (RREP Creation).

After processing a RM or creating a new RM, a node MAY append routing information to the RM, according to the process described in Section 5.3.4 (Adding Additional Routing Information to a RM). The additional routing information will help reduce route discoveries at the expense of increased message size.

If this RM's msg-ttl is greater than one (1), this node is not the target, and this RM is a RREQ the current RM (altered by the process defined above) SHOULD be sent to the LL_ALL_MANET_ROUTERS IP.Destination.

If this RM's msg-ttl is greater than one (1), this node is not the target, and this RM is a RREP the new RM SHOULD be sent to the Route.NextHopAddress for the Target.Address.

If this node is the target, the current RM's information is not retransmitted.

5.3.4. Adding Additional Routing Information to a RM

Appending routing information will alleviate route discovery attempts to the nodes whose information is included, if other nodes use this information to update their routing tables.

Nodes MAY append routing information to a RM, if the node believe that this additional routing information will alleviate future RREQ. This option should be administratively controlled.

Prior to appending their address to a RM, a node MUST increment its OwnSeqNum as defined in Section 5.1.2 (Incrementing a Sequence Number). Then it appends its IP address and OwnSeqNum. It MAY also append other information to its address, such as prefix length and/or that it is an Internet Gateway. If included, the Node.HopCnt is set to one (1).

Routing information about other nodes MAY also be added. If this information is included, it must be flagged with the IsOffPath address-block-tlv.

5.4. Route Discovery

A node creates a RREQ (described in Section 5.3.1 (RREQ Creation)) to discover a route to a particular destination (target). The IP.DestinationAddress for this RREQ is set to the LL_ALL_MANET_ROUTERS. Then the RM is transmitted.

After issuing a RREQ, the originating node waits for a route to be created to the Target. If a route is not found 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 Target 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 Target. 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 multiplied by two (2) so that the waiting time conforms to a binary exponential backoff.

Data packets awaiting a route SHOULD be buffered. This buffer SHOULD have a fixed limited size and discard older data packets first.

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

5.5. Route Maintenance

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 (Route Error Generation). A RERR MAY be issued immediately after detecting a broken link of an active route to quickly notify nodes that a link break occurred and certain routes are no longer available. If a route has not been used, a RERR SHOULD NOT be generated unless generation is expected to reduce future traffic.

5.5.1. Active Link Monitoring

Nodes MUST monitor links on active routes. This may be accomplished by one or several mechanisms. Including:

• Link layer feedback
• Neighborhood discovery (Clausen, T., Dearlove, C., and J. Dean, “MANET Neighborhood Discovery Protocol,” June 2006.) [I-D.ietf-manet-nhdp]
• Route timeout
• Other monitoring mechanisms or heuristics

Upon detecting a link break the detecting node MUST set the Route.ValidTimeout to the current time for all active routes utilizing the broken link.

5.5.2. Updating Route Lifetimes during Packet Forwarding

To avoid route timeouts for active routes, a node SHOULD update the Route.ValidTimeout for the IP.SourceAddress to be the current time + ROUTE_VALID_TIMEOUT upon receiving a data packet. This route's Route.Used bit is also set, if implemented.

To avoid route timeouts for active routes, a node SHOULD update the Route.ValidTimeout for the IP.DestinationAddress to be the current time + ROUTE_VALID_TIMEOUT upon successfully transmitting a packet to the next hop. This route's Route.Used bit is also set.

5.5.3. Route Error Generation

When a data packet is received for a destination without a valid routing table entry, a RERR MUST be generated. A RERR informs the IP.SourceAddress that the route does not exist, is no longer available, or is now invalid.

In a new RERR, the address of first unreachable node (IP.DestinationAddress from the data packet) is inserted. If a value for the unreachable node's SeqNum is known, it SHOULD be placed in the RERR. The msg-ttl is set to NET_DIAMETER. The msg-hopcnt is set to one (1).

Additional unreachable nodes that required the same unavailable link (routes with the same Route.NextHopAddress and Route.NextHopInterface) MAY be added to the RERR. For each unreachable node the Node.Address is included. The SeqNum if know should also be included. Appending additional routing information notifies each processing node of additional routes that are no longer available.

If SeqNum information is not known or not included all nodes processing the routing information will assume their routing information associated with the unreachable node is no longer valid.

The RERR is sent to the IP.DestinationAddress LL_ALL_MANET_ROUTERS. Sending the RERR to the LL_ALL_MANET_ROUTERS address will notify the maximum number of nodes of the broken link.

5.5.4. Route Error Processing

When a node processes a RERR, it processes each unreachable node address. It sets the Route.ValidTimeout to the current time for each Address found using longest prefix matching that meet all of the following conditions:

1. The Route.NextHopAddress is the same as the RERR IP.SourceAddress.
2. The Route.NextHopInterface is the same as the interface on which the RERR was received.
3. The Node.SeqNum is zero (0), unknown, OR Node.SeqNum - Route.SeqNum <= 0 (using signed 16-bit arithmetic).

Each unreachable node that did not result in a change to Route.ValidTimeout is removed from the RERR, since propagation of this information will not result in any benefit. Any information associated with the removed addresses is also removed.

If this RERR's msg-ttl is greater than one (1) and at least one unreachable node address remains in the RERR, then the RERR is sent to the IP.DestinationAddress LL_ALL_MANET_ROUTERS.

If no unreachable node addresses remain, no further processing is necessary.

5.6. General DYMO Packet and Message Processing

5.6.1. Processing Unknown Message and TLV Types

We expect the next version of the generalized MANET packet and message format [I-D.ietf-manet-packetbb] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” June 2006.) to include message semantic bits and tlv semantic bits to control the behavior of unknown types.

For addresses marked with the NoDefaultProcess, the default processing associated with addresses of RREQ, RREP, and RERR should not be performed. The addresses and associated TLVs should be ignored and retransmitted in resulting DYMO messages of the same type. The addresses and associated TLVs MAY be discarded, if space becomes a consideration. Removal of this additional information may result in lower performance of any future extensions.

5.7. Network Addresses

Any node MAY advertise a network address by using a Prefix tlv [I-D.ietf-manet-packetbb] (Clausen, T., Dearlove, C., Dean, J., and C. Adjih, “Generalized MANET Packet/Message Format,” June 2006.). Any nodes (other than the advertising node) within the advertised Prefix SHOULD NOT participate in the MANET and these nodes MUST be reachable by forwarding packets to the node advertising connectivity. For example, A.B.C.1 with a prefix length of 24 indicates all nodes with the matching A.B.C.X are reachable through the node with address A.B.C.1.

The meaning of the Prefix field is altered for theroute to an Internet gateway; Route.IsInternetGateway is one (1). If the route refers to an Internet gateway, its Prefix in association with the IP address indicates that all nodes outside that subnet are reachable via the Internet gateway node. For example, a route to a Internet gateway with IP address A.B.C.1 and a prefix of 24 indicates that all nodes with an IP address NOT matching A.B.C.X are reachable via this node.

5.8. Simple Internet Attachment and Gatewaying

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

      /--------------------------\
     /          Internet          \
     \                            /
      \------------+-------------/
      MANET Subnet | A.B.C.X
             +-----+-----+
             |   MANET   |
      /------|  Internet |------\
     /       |  Gateway  |       \
    /        |  A.B.C.1  |        \
    |        +-----------+        |
    |            MANET            |
    |                             |
    | +------------+              |
    | | MANET Node |              |
    | |  A.B.C.2   |              |
    | +------------+              |
    |              +------------+ |
    |              | MANET Node | |
    |              |   A.B.C.3  | |
    \              +------------+ /
     \                           /
      \-------------------------/

MANET nodes wishing to be reachable from nodes in the Internet MUST have IP addresses within the gateway's configured and advertised 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 using the gateway tlv in any RM transmitted. The Internet Gateway tlv indicates to nodes in the MANET that the Node.Address is attached to the Internet and is capable of routing data packets to all nodes outside of the configured MANET subnet, defined by the Node.Address and Node.Prefix fields.

5.9. 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.Address can be reached is also recorded in the route table entry.

When multiple interfaces are available, a node transmitting a packet with IP.DestinationAddress set to LL_ALL_MANET_ROUTERS SHOULD send the packet on all interfaces that have been configured for DYMO operation.

5.10. 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.

6. Configuration Parameters

Suggested Parameter Values

These suggested values work well for small and medium well connected networks with infrequence topology changes. For larger 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_VALID_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_VALID_TIMEOUT or ROUTE_DELETE_TIMEOUT in addition to arbitrary packet delays may result in frequent route breaks or in extreme cases routing loops.

7. IANA Considerations

This section specifies several messages types, message tlv-types, and address tlv-types.

Future types will be allocated using standard actions as described in (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.) [RFC2434].

7.1. DYMO Message Type Specification

The following address block TLV.

DYMO Message Types

7.2. DYMO Message TLV Type Specification

DYMO Message TLV Types

7.3. Address Block TLV Specification

Address Block TLV Specification Overview

8. 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 messages must be protected by the use of authentication techniques, such as those involving generation of unforgeable and cryptographically strong message digests or digital signatures. While DYMO does not place restrictions on the authentication mechanism used for this purpose, IPsec Authentication Message (AH) is an appropriate choice for cases where the nodes share an appropriate security association that enables the use of AH.

In particular, RM 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.

9. Acknowledgments

DYMO is a descendant of the design of previous MANET reactive protocols, especially AODV [RFC3561] (Perkins, C., Belding-Royer, E., and S. Das, “Ad hoc On-Demand Distance Vector (AODV) Routing,” July 2003.) and DSR [Johnson96] (Johnson, D. and D. Maltz, “Dynamic Source Routing (DSR) in Ad hoc Networks,” 1996.). Changes to previous MANET reactive protocols stem from research and implementation experiences. Thanks to Elizabeth Belding-Royer for her long time authorship of DYMO. Additional thanks to Luke Klein-Berndt, Pedro Ruiz, Fransisco Ros and Koojana Kuladinithi for reviewing of DYMO, as well as several specification suggestions.

10. References

10.1. Normative References

10.2. Informative References

Authors' Addresses

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