Mobile Ad hoc Networks Working I. Chakeres
Group E. Belding-Royer
Internet-Draft UC Santa Barbara
Expires: July 5, 2005 C. Perkins
Nokia
January 2005
Dynamic MANET On-demand Routing Protocol (DYMO)
draft-ietf-manet-dymo-00
Status of this Memo
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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 quick
adaptation to dynamic conditions, low processing and memory overhead,
low network utilization, 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 Conceptual Data Structures . . . . . . . . . . . . . . . . 6
3.1.1 Route Table Entry . . . . . . . . . . . . . . . . . . 6
3.2 DYMO Message Elements . . . . . . . . . . . . . . . . . . 6
3.2.1 Fixed Portion of DYMO Elements . . . . . . . . . . . . 6
3.2.2 Routing Element (RE) . . . . . . . . . . . . . . . . . 7
3.2.3 Route Error (RERR) . . . . . . . . . . . . . . . . . . 8
3.2.4 Unsupported-element Error (UERR) . . . . . . . . . . . 8
3.3 Field Descriptions . . . . . . . . . . . . . . . . . . . . 8
4. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 12
4.1 Sequence Numbers . . . . . . . . . . . . . . . . . . . . . 12
4.1.1 Maintaining a Sequence Number . . . . . . . . . . . . 12
4.1.2 Incrementing a Sequence Number . . . . . . . . . . . . 12
4.1.3 Sequence Number Rollover . . . . . . . . . . . . . . . 12
4.1.4 Actions After Sequence Number Loss . . . . . . . . . . 12
4.2 DYMO Routing Table Operations . . . . . . . . . . . . . . 12
4.2.1 Creating or Updating a Route Table Entry from
Routing Element Information . . . . . . . . . . . . . 12
4.2.2 Route Table Entry Timeouts . . . . . . . . . . . . . . 13
4.3 DYMO General Processing . . . . . . . . . . . . . . . . . 13
4.3.1 DYMO Control Packet Processing . . . . . . . . . . . . 13
4.3.2 Generic Element Pre-processing . . . . . . . . . . . . 14
4.3.3 Processing Unsupported DYMO Elements . . . . . . . . . 14
4.3.3.1 Generating an Unsupported-element Error . . . . . 14
4.3.4 Generic Element Post-processing . . . . . . . . . . . 15
4.3.5 DYMO Control Packet Transmission . . . . . . . . . . . 15
4.4 Routing Element . . . . . . . . . . . . . . . . . . . . . 15
4.4.1 Routing Element Creation . . . . . . . . . . . . . . . 15
4.4.2 Appending Additional Routing Information to an
Existing Routing Element . . . . . . . . . . . . . . . 15
4.4.3 Routing Element Processing . . . . . . . . . . . . . . 16
4.5 Route Discovery . . . . . . . . . . . . . . . . . . . . . 16
4.6 Route Maintenance . . . . . . . . . . . . . . . . . . . . 17
4.6.1 Link Breaks . . . . . . . . . . . . . . . . . . . . . 17
4.6.2 Updating Route Lifetimes . . . . . . . . . . . . . . . 17
4.6.3 Extending Route Lifetimes . . . . . . . . . . . . . . 17
4.6.4 Route Error Generation . . . . . . . . . . . . . . . . 18
4.6.5 Route Error Processing . . . . . . . . . . . . . . . . 18
4.7 Routing Prefix . . . . . . . . . . . . . . . . . . . . . . 19
4.8 Internet Attachment . . . . . . . . . . . . . . . . . . . 19
4.9 Multiple Interfaces . . . . . . . . . . . . . . . . . . . 19
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4.10 Packet Generation Limits . . . . . . . . . . . . . . . . . 20
5. Configuration Parameters . . . . . . . . . . . . . . . . . . . 21
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1 Normative References . . . . . . . . . . . . . . . . . . . 25
9.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . 27
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1. Overview
The Dynamic MANET On-demand (DYMO) routing protocol enables dynamic,
reactive, multihop routing between participating nodes wishing to
communicate. The basic operations of the protocol are route
discovery and management. During route discovery the originating
node causes dissemination of a Routing Element (RE) throughout the
network to find the target node. During dissemination each
intermediate node creates a route to the originating node. When the
target node receives the RE it responds with RE unicast toward
originating node. During propagation each node creates a route to
the target node. When the originating node is reached routes have
been established between the originating node and the target node in
both directions.
In order to react quickly to changes in the network topology nodes
should 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 should be 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 will re-initiate route discovery if it
still has packets to deliver.
In order to enable extension of the base specification, DYMO defines
the handling of unsupported extensions. By defining default
handling, future extensions are handled in a predetermined understood
fashion.
DYMO uses sequence numbers to ensure loop freedom [3].
All DYMO packets are transmitted via UDP on port TBD.
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2. Terminology
IPBroadcastAddress
Transmit the packet to the IP Limited Broadcast address,
255.255.255.255 (IPv4) or FF:FF:FF:FF:FF:FF (IPv6).
IPDestinationAddress
The destination of a packet, indicated by examining the IP
header.
IPSourceAddress
The source of a packet, indicated by examining the IP header.
MANETcast
Transmit the packet to all MANET nodes within reception range.
In a simple implementation MANETcast packets are sent to the
IPBroadcastAddress. MANETcast SHOULD preform duplicate
suppression.
Valid Route
A known route where the RouteValidTimeout is larger than the
current time.
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3. Data Structures
3.1 Conceptual Data Structures
3.1.1 Route Table Entry
o RouteAddress
o RouteDeleteTimeout
o RouteHopCnt
o RouteIsGateway
o RouteNextHopAddress
o RouteNextHopInterface
o RoutePrefix
o RouteSeqNum
o RouteValidTimeout
3.2 DYMO Message Elements
3.2.1 Fixed Portion of DYMO Elements
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ElemType |T|I| Res | ElemTTL | ElemLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ElemNotifyAddress (Only ElemTypes with M-bit set) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. ElemData .
. ElemType-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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ElemType |T|I| Res | ElemTTL | ElemLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ElemTargetSeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|G| Prefix1 | Res | REHopCnt1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. RENodeAddress1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RENodeSeqNum1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|G| PrefixN | Res | REHopCntN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Additional RENodeAddressN (if needed) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional RENodeSeqNumN (if needed) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ElemType: 1. Nodes MUST implement the Routing Element.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ElemType |T|I| Res | ElemTTL | ElemLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UNodeAddress1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UNodeSeqNum1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Additional UNodeAddress (if needed) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional UNodeSeqNum (if needed) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ElemType: 2. Nodes not implementing RERR will ignore the element
and continue.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ElemType |T|I| Res | ElemTTL | ElemLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UERRNodeAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UElemType |
+-+-+-+-+-+-+-+-+
ElemType: 3. Nodes not implementing UERR will ignore the element
and continue.
3.3 Field Descriptions
A-bit (A)
1-bit selector indicating whether this RE requires an answer RE
by the ElemTargetAddress. If A=1 an answer is required. The
instructions for generating an answer RE are described in
Section 4.4.3.
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Element Data (ElemData)
ElemType-specific payload.
Element Length (ElemLen)
12-bit field that indicates the size of the element in bytes,
including the fixed portion.
Element Notify Address (ElemNotifyAddress)
The node to send a UERR if the ElemType is unsupported. The
ElemNotifyAddress field is only present if the ElemType has the
M-bit is set to one (1).
Element Target Address (ElemTargetAddress)
The node that is the ultimate destination of the element.
Element Time to Live (ElemTTL)
6-bit field that identifies the maximum number of times the
element is to be retransmitted. The ElemTTL field operates
similar to IPTTL (MaxCount) and is decremented at each hop.
When ElemTTL reaches zero (0) the element is dropped.
Element Type (ElemType)
0 0
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| ElemType | = |M| H | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
The ElemType field identifies the element as well as the
handling by nodes that do not implement or understand the
element. The MSB bit, 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 ElemType
MUST be handled by nodes not implementing the ElemType,
regardless of UERR delivery. Section 4.3.3 describes the
handling behavior based on the ElemType.
G-bit (G)
1-bit selector to indicate whether the RENodeAddress1 is a
gateway. If G=1 RENodeAddress1 is a gateway. For more
information on gateway operation see Section 4.8.
I-bit (I)
1-bit selector indicating whether the element has been ignored.
If I=1 the element has been ignored. For a description of
processing for unsupported elements by ElemType see
Section 4.3.3.
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.
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Routing Element Block Hop Count (REHopCnt)
6-bit field that identifies the number of intermediate nodes
the associated RE block has passed through.
Routing Element Node Address (RENodeAddress)
The IP address of the node that appending its RENodeAddress.
Routing Element Node Sequence Number (RENodeSeqNum)
The sequence number of the node appending its RENodeSeqNum.
Reserved (Res, R)
Reserved bits. These bits are set to zero (0) during element
creation and ignored during processing.
Route Node Address (RouteNodeAddress)
The IP address of the node associated with the routing table
entry.
Route Delete Timeout (RouteDeleteTimeout)
The corresponding routing table entry MUST be deleted if the
current time is after RouteDeleteTimeout.
Route Hop Count (RouteHopCnt)
The number of intermediate node hops before reaching the
RouteNodeAddress.
Route Is Gateway (RouteIsGateway)
1-bit selector indicating whether the RouteNodeAddress is a
gateway.
Route Next Hop Address (RouteNextHopAddress)
The IP address of the next node on the path toward the
RouteNodeAddress.
Route Next Hop Interface (RouteNextHopInterface)
The interface to send packets toward the RouteNodeAddress.
Route Prefix (RoutePrefix)
6-bit field that specifies the size of the subnet reachable
through the RouteNodeAddress, see Section 4.7. The definition
of the Prefix field is different for gateways.
Route Sequence Number (RouteSeqNum)
The sequence number of the RouteNodeAddress.
RouteValidTimeout
The routing table entry is no longer considered valid if the
current time is after RouteValidTimeout.
T-bit (T)
1-bit selector indicating how the element must be transmitted.
If T=0 the element is unicast toward the ElemTargetAddress.
Otherwise, if T=1 the element is MANETcast.
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).
Unsupported-element Node Address (UERRNodeAddress)
The IP address of the node that generated the UERR.
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Unsupported-element Target Address (UElemTargetAddress)
Address of the destination of the element that caused delivery
of the UERR.
Unsupported-element Type (UElemType)
The ElemType 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 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 proscribed in Section 4.4.1
and Section 4.4.3) it MUST do so by treating the sequence number
value as if it were 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
To accomplish 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
when incremented MUST be set to one (1).
4.1.4 Actions After Sequence Number Loss
If a node's OwnSeqNum is lost it MUST NOT participate in the MANET
network (forward any data or issue any DYMO control packets) until it
is sure that all other nodes have deleted any sequence number
information about it. If RouteDeleteTimeout is set to
ROUTE_DELETE_TIMEOUT + the current time (as described in
Section 4.2.1), nodes should avoid participation for at least
ROUTE_DELETE_TIMEOUT after sequence number loss.
4.2 DYMO Routing Table Operations
4.2.1 Creating or Updating a Route Table Entry from Routing Element
Information
While processing a RE, as described in Section 4.4.3, a node checks
its routing table for an entry to the RENodeAddress using
longest-prefix matching. In the event that there is no corresponding
entry for the node, an entry is created.
The routing information about RENodeAddress contained in the RE block
is considered stale if:
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o the result of subtracting the RouteSeqNum from RENodeSeqNum is
less than zero (0) using signed 32-bit arithmetic, OR
o the result of subtracting the RouteSeqNum from RENodeSeqNum is
equal to zero (0) using signed 32-bit arithmetic AND the REHopCnt
is greater than RouteHopCnt.
If the information is stale and this RE block is the first node in
the RE (RENodeAddress1) this DYMO packet dropped. Otherwise, the
RENodeAddress and RENodeSeqNum are removed from this RE.
If the route information for RENodeAddress is not stale, then the
following actions occur to the route table entry for RENodeAddress:
o the RouteDeleteTimeout is set to the current time +
ROUTE_DELETE_TIMEOUT,
o the RouteNextHopAddress is set to the node that transmitted this
DYMO packet (IPSourceAddress),
o the RouteNextHopInterface is set to the interface that this DYMO
packet was received on,
o the RoutePrefix is set to Prefix,
o and the RouteSeqNum is set to the RENodeSeqNum.
o the RouteValidTimeout 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
RouteValidTimeout, the route is stale and it is not be used to route
packets.
If the current time is later than a routing entry's
RouteDeleteTimeout, the route MUST be deleted.
4.3 DYMO General 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, resulting from the contained DYMO elements.
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.
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Unless specific element processing requires dropping the DYMO packet,
it is retransmitted after processing.
4.3.2 Generic Element Pre-processing
Each element in a DYMO packet undergoes pre-processing before the
element specific processing occurs. The ElemTTL is decremented by
one (1).
4.3.3 Processing Unsupported DYMO Elements
This section describe the processing for unsupported DYMO ElemTypes.
For unsupported DYMO elements, the ElemType field identifies the
handling by nodes that do not implement or understand the element.
The most significant bit (M-bit) indicates whether an
Unsupported-element Error (UERR) SHOULD be sent to the
ElemNotifyAddress. 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
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| ElemType | = |M| H | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
If the M-bit is set is this DYMO element, a UERR is sent to the
ElemNotifyAddress. 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
unsupported ElemType, the processing node MUST also examine the
H-bits to determine how this unsupported element is handled. If :
o H == 00: Processing for this ElemType MUST skip the element and
continue, as if the packet did not contain this element.
o H == 01: Processing for this ElemType MUST remove the element
(using the ElemLen) from the packet and continue, as if the packet
did not include this element.
o H == 10: Processing for this ElemType MUST set the ignored bit
(I-bit), skip this element and continue, as if the packet did not
contain this element.
o H == 11: Processing for this ElemType dictates that the packet
MUST be dropped.
4.3.3.1 Generating an Unsupported-element Error
The ElemTargetAddress in the UERR is set to the ElemNotifyAddress
from the unsupported element. The UElemTargetAddress is set to the
ElemTargetAddress from the unsupported element. The UERRNodeAddress
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is set to the generating nodes IP address. The UElemType is the
ElemType from the unsupported element. The ElemTTL is set to
NET_DIAMETER. The UERRNodeAddress is set to the address of the node
generating this UERR. The ElemLen is set to the total number of
bytes in this UERR. The T-bit is set to zero (T=0). The element is
then processed as described in Section 4.3.4.
4.3.4 Generic Element Post-processing
If the ElemTTL is zero (0) AND this element is the first element this
DYMO packet is dropped after processing of all elements in the DYMO
packet. If the ElemTTL is zero (0) AND this is NOT the first
element, this element is removed from the packet. If the ElemTTL is
larger than zero (0), this element is re-transmitted in a DYMO packet
after all elements have been processed.
4.3.5 DYMO Control Packet Transmission
DYMO packet transmission is controlled by the T-bit in the first
element. If T=0 the element is unicast toward the ElemTargetAddress
via a routing table lookup. If the RouteNextHopAddress for the
ElemTargetAddress is not known the packet is dropped. If T=1 the
element is MANETcast.
For all DYMO packets the IPTTL (IPMaxCount) SHOULD be set to 1
(IPTTL=1).
4.4 Routing Element
4.4.1 Routing Element Creation
When a node creates a RE, it first increments its OwnSeqNum by one
according to the rules specified in Section 4.1.2. Then it 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). This node may advertise it is a gateway by setting the
G-bit, as described in Section 4.8. Otherwise, the G-bit is set to
zero (0). The ElemTTL is set to NET_DIAMETER.
4.4.2 Appending Additional Routing Information to an Existing Routing
Element
After processing a RE, a node MAY append its IP address and OwnSeqNum
to the RE. Appending its own routing information may alleviate some
route discovery procedures to this node from other nodes that process
this RE.
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If this node plans to append its IP address to the RE, it first
increments its OwnSeqNum as defined in Section 4.1.2. Then this node
appends its IP address and OwnSeqNum to the RE. The ElemLen is also
adjusted accordingly.
4.4.3 Routing Element Processing
After general DYMO element pre-processing, the ElemHopCnt is
incremented by one. A route to RENodeAddress1 is then created or
updated using the associated RENodeSeqNum, G-bit, Prefix, and
REHopCnt, as defined in Section 4.2.1.
Each RENodeAddress, RENodeSeqNum, G-bit, Prefix, and REHopCnt block
MAY be processed. First the REHopCnt is incremented, then a route is
created or updated as defined in Section 4.2.1. Each RENodeAddress
block resulting in a valid route entry may alleviate a future route
discovery. Any unprocessed RENodeAddress blocks MUST be removed from
the RE.
If this node is the ElemTargetAddress AND the A-bit is set (A=1),
this node MUST reciprocate with a RE. This node creates a new RE as
described in Section 4.4.1. The ElemTargetAddress in the new RE is
set to the RENodeAddress1 from the RE currently being processed. The
T-bit is set to zero (T=0) and the A-bit is set to (A=0). Then the
new RE undergoes post-processing, according to Section 4.3.5.
If this node is not the ElemTargetAddress the current RE SHOULD be
handled according to Section 4.3.4.
If this node is the ElemTargetAddress the current packet and any
additional elements are processed, but this packet is not
retransmitted.
4.5 Route Discovery
A node generates a Route Request (RREQ) to discover a valid route to
a particular destination (ElemTargetAddress), other than itself. A
RREQ is simply a RE with the T-bit set (T=1) to indicate that this RE
is to be MANETcast. Also, the A-bit is set to one (A=1) to indicate
that the TargetNode must respond with a RE. If a sequence number is
known for the ElemTargetAddress it is placed in the ElemTargetSeqNum
field. Otherwise, ElemTargetSeqNum is set to zero (0).
Before sending the RREQ, the generating node buffers its
RENodeAddress and RENodeSeqNum in its RE Table. The RE is then
transmitted according to the procedure defined in Section 4.3.5.
After issuing the RREQ, the node waits for a route to be created to
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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 an 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 2*RREQ_WAIT_TIME, another RREQ may be
sent, up to a total of RREQ_TRIES. For each additional attempt, the
waiting time for the previous RREP is multiplied by 2 so that the
waiting time conforms to a binary exponential backoff.
Data packets waiting 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 Link Breaks
Nodes SHOULD monitor links to active neighbors. This may be
accomplished by one or several mechanisms. Such as:
o Link layer feedback
o Hello messages
o Neighbor discovery
o Route timeout
Upon detecting a link break the valid routes utilizing the broken
link MUST set their RouteValidTimeout to the current time.
A RERR MAY be issued after detecting a broken link of an active
route. RERR Generation is described in Section 4.6.4.
4.6.2 Updating Route Lifetimes
To avoid route timeouts for active sources, after receiving a packet
a node MAY update the RouteValidTimeout to the IPSourceAddress to be
the current time + ROUTE_TIMEOUT.
4.6.3 Extending Route Lifetimes
To avoid route timeouts for active routes, an originating node MAY
periodically send a RE with the T-bit set to zero (0), the A-bit set
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to one (A=1) and the ElemTargetAddress set to the target node's
address (RouteAddress). The resultant DYMO packet transmissions and
RE processing (Section 4.2.1) will update the lifetime of routes to
the originating node and target node (RouteAddress) at all
intermediate nodes, if a valid route still exists.
4.6.4 Route Error Generation
When a non-DYMO packet is received for a destination without a valid
routing table entry, a Route Error (RERR) SHOULD be generated by this
node. A RERR informs the source that the current route is no longer
available in a more timely manner than RouteValidTimeout.
In the RERR, the ElemTargetAddress is the node that sent the non-DYMO
packet, the IPSourceAddress. The UNodeAddress1 field is the address
of the unreachable node (IPDestinationAddress) from the non-DYMO
packet. If the UNodeSeqNum is known, it is placed in the RERR;
otherwise zero (0) is placed in the this field of the RERR. The
ElemTTL is set to NET_DIAMETER. The T-bit is set to one (T=1).
Additional unreachable nodes utilizing the same invalid link (routes
with the same RouteNextHopAddress and RouteNextHopInterface) as the
UNodeAddress1 MAY be appended to the RERR. For each unreachable node
their UNodeAddress and UNodeSeqNum are appended. The ElemLen is set
accordingly.
The RERR is then processed as described in Section 4.3.5.
4.6.5 Route Error Processing
When a node processes a RERR after generic element pre-processing, it
SHOULD set the RouteValidTimeout to the current time for each route
to a UNodeAddress that meet all of the following conditions:
The RouteNextHopAddress is the same as the RERR IPSourceAddress.
The RouteNextHopInterface is the same as the interface this RERR
was received.
The UNodeSeqNum is zero (0) OR if the result of subtracting
RouteSeqNum from UNodeSeqNum is less than or equal to zero using
signed 32-bit arithmetic
If any route's RouteValidTimeout is set to the current time, this
RERR MAY be handled as described in Section 4.3.4. Otherwise, the
RERR is dropped.
Prior to RERR element post processing a node MAY remove UNodeAddress,
UNodeSeqNum pairs to decrease the element size.
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4.7 Routing Prefix
Any node can advertise connectivity to a subset of 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.
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.
If the G-bit is set the meaning of the prefix field is altered. For
a gateway the prefix in association with the IP address indicates
that nodes outside the subnet are reachable via the gateway node.
For example, a gateway with IP address 192.168.1.1 and a prefix of 16
indicates all nodes with the IP address NOT matching 192.168.X.X are
reachable through 192.168.1.1.
4.8 Internet Attachment
Basic Internet attachment consists of a stub network of MANET nodes
connected to the Internet via a single 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 route-able address or care-of address
handled by the gateway, the gateway is responsible for performing
route discovery for 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 the RE. 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 RouteAddress can be
reached is also recorded into the route table entry.
When multiple interfaces are available, a node transmitting a
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MANETcast packet SHOULD send the packet on all interfaces that have
been configured for operation in the MANET.
4.10 Packet Generation Limits
To avoid congestion, a node SHOULD NOT transmit more than RATE_LIMIT
control messages per second.
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5. Configuration Parameters
Here are some suggested 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
These parameters work well for small well-connected networks with
moderate network topology changes.
For other networks these DYMO parameters SHOULD be adjusted using
either dynamic adaptation or experimentally determined values. For
example in static networks, ROUTE_TIMEOUT may be set to a much larger
value.
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6. IANA Considerations
DYMO defines a ElemType field for each element within a packet sent
to port TBD. A new registry will be created for the values for this
ElemType field, and the following values will be assigned:
ElemType Value
-------------------------------- -----
Routing Element (RE) 1
Route Error (RERR) 2
Unsupported-element Error (UERR) 3
Future values of the ElemType and ErrType will be allocated using
standard actions as described in [1].
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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 less
dangerous, SHOULD be authenticated in order to prevent malicious
nodes from disrupting active routes between communicating nodes.
DYMO does not make any assumption about the method by which addresses
are assigned to the mobile nodes except that they are presumed to
have unique IP addresses. Therefore, no special consideration, other
than what is natural because of the general protocol specifications,
can be made about the applicability of IPsec authentication elements
or key exchange mechanisms. However, if the mobile nodes in the ad
hoc network have pre-established security associations, it is
presumed that the purposes for which the security associations are
created 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 an decedent of the design of previous MANET reactive
protocols. Special thanks to the authors of AODV [2] and DSR [4].
The authors of AODV and DSR include Charlie Perkins, Elizabeth
Belding-Royer, Samir Das, David Johnson, David Maltz, Yih-Chun Hu and
Jorjeta Jetcheva. Much of the DYMO protocol also stems from research
and implementation of MANET reactive-routing protocols. To mention a
few major contributors Sung-Ju Lee, Mahesh Marina, Erik Nordstrom,
Yves Prelot, J.J. Garcia-Luna-Aceves, Marc Mosko, Manel Guerrero
Zapata, Philippe Jacquet, and Chris Shiflet. Also, special thanks to
Luke Klein-Berndt for extensive implementation and testing of AODV,
early reviewing of DYMO, as well as several technical discussions.
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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", February 1999.
[4] Johnson, D. and D. Maltz, "Dynamic Source Routing in Ad-hoc
Wireless Networks", August 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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