Mobile Ad hoc Networks Working I. Chakeres
Group Boeing
Internet-Draft C. Perkins
Expires: December 22, 2006 Nokia
June 20, 2006
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-05
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Copyright Notice
Copyright (C) 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.
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Route Table Entry . . . . . . . . . . . . . . . . . . . . 6
4.2. DYMO Messages . . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Generalized MANET Packet and Message Structure . . . . 7
4.2.2. Routing Message (RM) . . . . . . . . . . . . . . . . . 8
4.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 10
5. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 12
5.1. DYMO Sequence Numbers . . . . . . . . . . . . . . . . . . 12
5.1.1. Maintaining A Node's Own Sequence Number . . . . . . . 12
5.1.2. Incrementing a Sequence Number . . . . . . . . . . . . 13
5.1.3. Sequence Number Rollover . . . . . . . . . . . . . . . 13
5.1.4. Actions After Sequence Number Loss . . . . . . . . . . 13
5.2. DYMO Routing Table Operations . . . . . . . . . . . . . . 13
5.2.1. Judging New Routing Information's Usefulness . . . . . 13
5.2.2. Updating a Route Table Entry with Fresh Routing
Information . . . . . . . . . . . . . . . . . . . . . 14
5.2.3. Route Table Entry Timeouts . . . . . . . . . . . . . . 15
5.3. Routing Message . . . . . . . . . . . . . . . . . . . . . 15
5.3.1. RREQ Creation . . . . . . . . . . . . . . . . . . . . 15
5.3.2. RREP Creation . . . . . . . . . . . . . . . . . . . . 16
5.3.3. RM Processing . . . . . . . . . . . . . . . . . . . . 16
5.3.4. Adding Additional Routing Information to a RM . . . . 18
5.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 18
5.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 19
5.5.1. Active Link Monitoring . . . . . . . . . . . . . . . . 19
5.5.2. Updating Route Lifetimes during Packet Forwarding . . 20
5.5.3. Route Error Generation . . . . . . . . . . . . . . . . 20
5.5.4. Route Error Processing . . . . . . . . . . . . . . . . 21
5.6. General DYMO Packet and Message Processing . . . . . . . . 21
5.6.1. Receiving Packets . . . . . . . . . . . . . . . . . . 21
5.6.2. Processing Unknown Message and TLV Types . . . . . . . 21
5.7. Network Addresses . . . . . . . . . . . . . . . . . . . . 22
5.8. Simple Internet Attachment and Gatewaying . . . . . . . . 22
5.9. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 23
5.10. Packet Generation Limits . . . . . . . . . . . . . . . . . 24
6. Configuration Parameters . . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
7.1. DYMO Message Type Specification . . . . . . . . . . . . . 25
7.2. Packet TLV Type Specification . . . . . . . . . . . . . . 25
7.3. Address Block TLV Specification . . . . . . . . . . . . . 26
8. Security Considerations . . . . . . . . . . . . . . . . . . . 26
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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10.1. Normative References . . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . . . 30
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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 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]. 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
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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
[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.
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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.
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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.
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.
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].
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).
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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].
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.
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.
Only one address can be marked as the target.
AddBlk.Orig.Address
The IP address of the message originator. This address is in an
address block and not in the message header to allow for address
compression and additional AddTLVs.
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.
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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]).
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 is 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 is 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 this 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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
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 and
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Section 5.5.4.
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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
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.
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5.1.2. Incrementing a Sequence Number
When a node increments its OwnSeqNum (as described in Section 5.3) 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. 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.
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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. If the
route is valid, then the new information is also inferior if
Node.HopCnt == Route.HopCnt AND this RM 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. Only this type of information is 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.Prefix is set to the Node.Prefix,
8. the Route.IsInternetGateway is set if address is an Internet
Gateway.
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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
Before using a routing table entry its timeouts must be examined.
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 (Section 5.1.2).
Fist, the node adds the AddBlk.Target.Address to the RM.
If a previous value of the Target.SeqNum is known (from an existing
routing table entry), it SHOULD be placed in AddTLV.Target.SeqNum.
If a Target.SeqNum is not included, it is assumed to be unknown by
processing nodes and only the target is allowed to respond. A
Target.SeqNum of zero (0) MAY be set to indicate that any node with
valid routing information about this destination can 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 AddTLV.Target.HopCnt. Otherwise, the HopCnt is
not included and assumed unknown by processing nodes.
These AddTLVs associated with the target SHOULD be set to maximum
protocol efficiency, but they may be omitted to reduce message size.
Next, the node adds AddBlk.Orig.Address to the RM and the
AddTLV.Orig.SeqNum (OwnSeqNum) in an address block TLV. The
Orig.Address is this node's primary addresses/identifier. The
Orig.Address must be a routable IP address.
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Other AddTLVs for the originator SHOULD be set to maximum protocol
efficiency, but they may be omitted to reduce message size.
The MsgHdr.HopCnt is set to zero (0). The MsgHdr.HopLimit SHOULD be
set to NET_DIAMETER, but MAY be set smaller. For RREQ, the
MsgHdr.HopLimit MAY be set in accordance with an expanding ring
search as described in [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:
o Target.SeqNum is not included in the message, OR
o Target.SeqNum is zero (0), OR
o Target.SeqNum - OwnSeqNum > 0 (using 16-bit signed arithmetic), OR
o Target.SeqNum == OwnSeqNum AND Target.HopCnt is unknown, OR
o Target.SeqNum == OwnSeqNum AND Orig.HopCnt is unknown, OR
o 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 AddBlk.Target.Address to the RM. The
Target.Address is copied from the incoming RREQ AddBlk.Orig.Address.
Next, the node adds the AddBlk.Orig.Address to the RM and the
AddTLV.Orig.SeqNum (OwnSeqNum) in an address block TLV. The
Orig.Address is copied from the incoming RREQ AddBlk.Target.Address.
Other AddTLVs for the originator and target SHOULD be set to maximum
protocol efficiency, but they may be omitted to reduce message size.
The MsgHdr.HopCnt is set to zero (0). The MsgHdr.HopLimit is set to
NET_DIAMETER.
5.3.3. RM Processing
When a RM is received the MsgHdr.HopLimit is decremented by one (1)
and MsgHdr.HopCnt is incremented by one (1).
For each address in the RM that includes AddTLV-HopCnt information
except the target and those addresses tagged with the AddTLV-Ignore,
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the AddTLV-HopCnt information is incremented by one (1).
Next, this node checks whether its routing table has an entry to the
AddBlk.Orig.Address using longest-prefix matching [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. If a routing table entry exists, the new node's
information is compared with the route table entry following the
procedure described in Section 5.2.1. If the new node's routing
information is considered fresh, the route table entry is updated as
described in Section 5.2.2.
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 eliminate RREQ for those destination,
in the event that data needs to be forwarded to these destinations in
the near future.
For each of these addresses considered, 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. If a routing
table entry exists, the new node's information is compared with the
route table entry following the procedure described in Section 5.2.1.
If the new node's routing information is considered fresh, the route
table entry is updated as described in Section 5.2.2.
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.
After processing a RM or creating a new RM, a node MAY append
additional routing information to the RM, according to the process
described in Section 5.3.4. The additional routing information will
help reduce route discoveries at the expense of increased message
size.
If this RM's MsgHdr.HopLimit is greater than one (1), this node is
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not the target, AND this RM is a RREQ, then the current RM (altered
by the process defined above) SHOULD be sent to the
LL_ALL_MANET_ROUTERS IP.DestinationAddress.
If this RM's MsgHdr.HopLimit is greater than one (1), this node is
not the target, AND this RM is a RREP, then the new RM SHOULD be sent
to the Route.NextHopAddress for the RREP's 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 own address to a RM, a node MUST increment
its OwnSeqNum as defined in Section 5.1.2. Then the node appends its
IP address (AddBlk-Address) and OwnSeqNum (AddTLV-SeqNum). It MAY
also append other information to its address, such as prefix 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
AddTLV.AdditionalNode.IsOffPath.
Note an address may appear only once in a message's address blocks.
Prior to adding any address, the message is searched for existing
entries. If an existing entry exists, this entry will have the
information as this node's routing table information (created or
updated while processing the RM) and therefore no update is
necessary.
In the event a newly appended address already has an AddTLV-Ignore
flag set, it is removed.
5.4. Route Discovery
A node creates a RREQ (described in Section 5.3.1) 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.
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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
Section 5.5.3. 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 that are being used. This
may be accomplished by one or several mechanisms. Including:
o Link layer feedback
o Neighborhood discovery [I-D.ietf-manet-nhdp]
o Route timeout
o Other monitoring mechanisms or heuristics
Upon detecting a link break the detecting node MUST set the
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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. When a RREP is being
transmitted and no active route to the target exists, 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 (AddTLV-SeqNum) is known, it SHOULD
be placed in the RERR. The MsgHdr.HopLimit is set to NET_DIAMETER.
The MsgHdr.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. The SeqNum if know
SHOULD also be included. Appending unreachable node 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 notifies the
maximum number of nodes of the broken link.
The packet or message that forced generation of this RERR is
discarded.
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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 Route.SeqNum is zero (0), unknown, OR 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 no unreachable node addresses remain, no further processing is
performed.
If this RERR's MsgHdr.HopLimit 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.
Addresses marked with AddTLV-Ignore should remain in the RERR.
5.6. General DYMO Packet and Message Processing
5.6.1. Receiving Packets
When a packet is received, its PktTLV are first examined. Next each
message is examined and processed in order.
Each message's headers are first examined. Next, the MsgTLV are
examined. Finally, each message is processed according to its
MsgHdr.type.
5.6.2. Processing Unknown Message and TLV Types
To allow future extensions, DYMO uses bits from the semantics fields
of PktTLV, Message, MsgTLV, and AddTLV [I-D.ietf-manet-packetbb].
Note [I-D.ietf-manet-packetbb] does not currently support this
functionality.
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The semantic bits have the following names and characteristics for
nodes that do not understand the type.
Remove
If the Semantics.Remove-bit is set, this information SHOULD be
removed from the message.
Discard
If the Semantics.Discard-bit is set, this message SHOULD not be
processed further and it should not be propagated. In the case of
PktTLVs if the Semantics.Discard-bit is set, no messages from the
packet should be processed or propagated.
5.7. Network Addresses
Any node MAY advertise a network address by using a Prefix tlv
[I-D.ietf-manet-packetbb]. 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.
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/--------------------------\
/ 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 | |
\ +------------+ /
\ /
\-------------------------/
Figure 3: Simple Internet Attachament Example
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.
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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
+------------------------+-------------------------+
| Name | Value |
+------------------------+-------------------------+
| NET_DIAMETER | 10 |
| RATE_LIMIT | 10 |
| ROUTE_VALID_TIMEOUT | 5000 milliseconds |
| ROUTE_DELETE_TIMEOUT | 5 * ROUTE_VALID_TIMEOUT |
| ROUTE_DELETE_PERIOD | 6 * ROUTE_VALID_TIMEOUT |
| ROUTE_RREQ_WAIT_TIME | 1000 milliseconds |
| RREQ_TRIES | 3 |
+------------------------+-------------------------+
Table 1
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
DYMO requires a UDP port number to carry protocol packets - TBD.
DYMO also requires the link-local multicast address
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LL_ALL_MANET_ROUTERS; IPv4 TBD, IPv6 TBD.
This section also specifies several messages types, message tlv-
types, and address tlv-types.
Future types will be allocated using standard actions as described in
[RFC2434].
7.1. DYMO Message Type Specification
The following address block TLV.
DYMO Message Types
+------------------------+----------+
| Name | Type |
+------------------------+----------+
| Route Request (RREQ) | 10 - TBD |
| Route Reply (RREP) | 11 - TBD |
| Route Error (RERR) | 12 - TBD |
+------------------------+----------+
Table 2
7.2. Packet TLV Type Specification
Packet TLV Types
+-------------------+------+--------+-------------------------------+
| Name | Type | Length | Value |
+-------------------+------+--------+-------------------------------+
| Unicast Response | TBD | 10 - | Indicates to the processing |
| Request | | TBD | node that the previous hop |
| | | | (IP.SourceAddress) expects a |
| | | | unicast message within |
| | | | UNICAST_MESSAGE_SENT_TIMEOUT. |
| | | | Any unicast packet will serve |
| | | | this purpose, and it MAY be |
| | | | an ICMP REPLY message. If a |
| | | | message is not sent, then the |
| | | | previous hop may assume that |
| | | | the link is unidirectional |
| | | | and may blacklist this node. |
+-------------------+------+--------+-------------------------------+
Table 3
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7.3. Address Block TLV Specification
Address Block TLV Specification Overview
+----------------------+------+--------+----------------------------+
| Name | Type | Length | Value |
+----------------------+------+--------+----------------------------+
| DYMOSeqNum | 10 - | 16 | The DYMO sequence num |
| | TBD | bits | associated with this |
| | | | address. The sequence |
| | | | number may be the last |
| | | | known sequence number. |
| HopCount | 11 - | 8 bits | The number of hops |
| | TBD | | traversed by the |
| | | | information associated |
| | | | with this address. |
| IsInternetGateway | 12 - | 0 bits | Usde to indicate that this |
| | TBD | | node is an Internet |
| | | | Gateway |
| IsOriginator | 13 - | 0 bits | Used to indicate that this |
| | TBD | | node is the Originator of |
| | | | the RM. |
| IsTarget | 14 - | 0 bits | Used to indicate this node |
| | TBD | | is the target of the DYMO |
| | | | message |
| Ignore | 15 - | 0 | Used to indicate that this |
| | TBD | | addresses should not be |
| | | | processed normally; |
| | | | instead it should be |
| | | | ignored. |
+----------------------+------+--------+----------------------------+
Table 4
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
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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] and DSR [Johnson96]. 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, Koojana Kuladinithi, Ramon
Caceres, and Thomas Clausen for reviewing of DYMO, as well as several
specification suggestions.
10. References
10.1. Normative References
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
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[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
July 2003.
10.2. Informative References
[I-D.ietf-manet-nhdp]
Clausen, T., Dearlove, C., and J. Dean, "MANET
Neighborhood Discovery Protocol", draft-ietf-manet-nhdp-00
(work in progress), June 2006.
[I-D.ietf-manet-packetbb]
Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized MANET Packet/Message Format",
draft-ietf-manet-packetbb-01 (work in progress),
June 2006.
[Johnson96]
Johnson, D. and D. Maltz, "Dynamic Source Routing (DSR) in
Ad hoc Networks", In Mobile Computing, Chapter 5, pp. 153-
181, 1996.
[Perkins99]
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.
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Authors' Addresses
Ian Chakeres
Boeing Phantom Works
The Boeing Company
P.O. Box 3707 Mailcode 7L-49
Seattle, WA 98124-2207
USA
Email: ian.chakeres@gmail.com
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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