Mobile Ad hoc Networks Working I. Chakeres
Group Boeing
Internet-Draft E. Belding-Royer
Expires: April 26, 2006 UC Santa Barbara
C. Perkins
Nokia
October 23, 2005
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-03
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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
adaptation to changing network topology and determines unicast routes
between nodes within the network.
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Route Table Entry . . . . . . . . . . . . . . . . . . . . 7
3.2 DYMO Message Elements . . . . . . . . . . . . . . . . . . 8
3.2.1 Generic DYMO Element Structure . . . . . . . . . . . . 9
3.2.2 Routing Element (RE) . . . . . . . . . . . . . . . . . 11
3.2.3 Route Error (RERR) . . . . . . . . . . . . . . . . . . 14
3.2.4 Unsupported-element Error (UERR) . . . . . . . . . . . 15
4. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 16
4.1 Sequence Numbers . . . . . . . . . . . . . . . . . . . . . 16
4.1.1 Maintaining a Sequence Number . . . . . . . . . . . . 16
4.1.2 Incrementing a Sequence Number . . . . . . . . . . . . 16
4.1.3 Sequence Number Rollover . . . . . . . . . . . . . . . 16
4.1.4 Actions After Sequence Number Loss . . . . . . . . . . 16
4.2 DYMO Routing Table Operations . . . . . . . . . . . . . . 16
4.2.1 Creating or Updating a Route Table Entry from a
Routing Block . . . . . . . . . . . . . . . . . . . . 16
4.2.2 Route Table Entry Timeouts . . . . . . . . . . . . . . 18
4.3 Routing Element . . . . . . . . . . . . . . . . . . . . . 18
4.3.1 Routing Element Creation . . . . . . . . . . . . . . . 18
4.3.2 Routing Element Processing . . . . . . . . . . . . . . 18
4.3.3 Appending Additional Routing Information to an
Existing Routing Element . . . . . . . . . . . . . . . 19
4.4 Route Discovery . . . . . . . . . . . . . . . . . . . . . 19
4.5 Route Maintenance . . . . . . . . . . . . . . . . . . . . 20
4.5.1 Active Link Monitoring . . . . . . . . . . . . . . . . 20
4.5.2 Updating Route Lifetimes . . . . . . . . . . . . . . . 21
4.5.3 Route Error Generation . . . . . . . . . . . . . . . . 21
4.5.4 Route Error Processing . . . . . . . . . . . . . . . . 22
4.6 General DYMO Processing . . . . . . . . . . . . . . . . . 22
4.6.1 DYMO Control Packet Processing . . . . . . . . . . . . 22
4.6.2 Generic Element Pre-processing . . . . . . . . . . . . 23
4.6.3 Processing Unsupported DYMO Element Types . . . . . . 23
4.6.3.1 Generating an Unsupported-element Error . . . . . 24
4.6.4 Generic Element Post-processing . . . . . . . . . . . 24
4.6.5 DYMO Control Packet Transmission . . . . . . . . . . . 24
4.7 Routing Prefix . . . . . . . . . . . . . . . . . . . . . . 24
4.8 Internet Attachment . . . . . . . . . . . . . . . . . . . 25
4.9 Multiple Interfaces . . . . . . . . . . . . . . . . . . . 25
4.10 Packet Generation Limits . . . . . . . . . . . . . . . . . 25
5. Configuration Parameters . . . . . . . . . . . . . . . . . . . 26
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6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 Normative References . . . . . . . . . . . . . . . . . . . 30
9.2 Informative References . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . 32
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1. Overview
The Dynamic MANET On-demand (DYMO) routing protocol enables reactive,
multihop routing between participating nodes that wish to
communicate. The basic operations of the DYMO protocol are route
discovery and management. During route discovery the originating
node initiates dissemination of a Route Request (RREQ) throughout the
network to find the target node. During this dissemination process,
each intermediate node records a route to the originating node. When
the target node receives the RREQ, it responds with a Route Reply
(RREP) unicast toward the originating node. Each node that receives
the RREP records a route to the target node, and then the RREP is
unicast toward the originating node. When the originating node
receives the RREP, routes have then been established between the
originating node and the target node in both directions.
In order to react to changes in the network topology nodes maintain
their routes and monitor their links. When a packet is received for
a route that is no longer available the source of the packet is
notified. A Route Error (RERR) is sent to the packet source to
indicate the current route is broken. Once the source receives the
RERR, it re-initiates route discovery if it still has packets to
deliver.
In order to enable extension of the base specification, DYMO defines
a generic element structure and handling of future extensions. By
defining a fixed structure and default handling, future extensions
are handled in a predetermined fashion.
DYMO uses sequence numbers as they have been proven to ensure loop
freedom [3]. Sequence numbers enable nodes to determine the order of
DYMO route discovery packets, thereby avoiding use of stale routing
information.
All DYMO packets are transmitted via UDP on port TBD.
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2. Terminology
IP Destination Address (IPDestinationAddress)
The destination of a packet, indicated by examining the IP
header.
IP Source Address (IPSourceAddress)
The source of a packet, indicated by examining the IP header.
DYMOcast
Packet transmission to all DYMO routers. DYMOcast packets
should be sent with an IPDestinationAddress of IPv4 TBD (IPv6
TBD), the DYMOcastAddress.
Routing Element (RE)
A DYMO message element that is used to distribute routing
information.
Route Invalidation
Disabling the use of a route, causing it to be unavailable for
forwarding data.
Route Reply (RREP)
Upon receiving a RREQ, the target node generates a Route Reply
(RREP). A RREP is a RE with a unicast IPDestinationAddress,
indicating that this RE is to be unicast hop-by-hop toward the
TargetAddress.
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Route Request (RREQ)
A node generates a Route Request (RREQ) to discover a valid
route to a particular destination (TargetAddress). A RREQ is
simply a RE with the DYMOcastAddress in the
IPDestinationAddress field of the IP packet. Also, the A-bit
is set to one (A=1) to indicate that the TargetNode must
respond with a RREP.
Valid Route
A known route where the Route.ValidTimeout is greater than the
current time.
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3. Data Structures
3.1 Route Table Entry
The route table entry is a conceptual data structure.
Implementations may use any internal representation that conforms to
the semantics of a route as specified in this document.
o Route.DestAddress
o Route.DeleteTimeout
o Route.HopCnt
o Route.IsGateway
o Route.NextHopAddress
o Route.NextHopInterface
o Route.Prefix
o Route.SeqNum
o Route.ValidTimeout
These fields are defined as follows:
Route Node Address (Route.DestAddress)
The IP address of the node associated with the routing table
entry.
Route Delete Timeout (Route.DeleteTimeout)
If the time current is after Route.DeleteTimeout the
corresponding routing table entry MUST be deleted.
Route Hop Count (Route.HopCnt)
The number of intermediate node hops before reaching the
Route.DestAddress.
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Route Is Gateway (Route.IsGateway)
1-bit selector indicating whether the Route.DestAddress is a
gateway.
Route Next Hop Address (Route.NextHopAddress)
The IP address of the next node on the path toward the
Route.DestAddress.
Route Next Hop Interface (Route.NextHopInterface)
The interface used to send packets toward the
Route.DestAddress.
Route Prefix (Route.Prefix)
6-bit field that specifies the size of the subnet reachable
through the Route.DestAddress, see Section 4.7. The definition
of the Prefix field is different for gateways; entries with
Route.IsGateway set to one (1).
Route Sequence Number (Route.SeqNum)
The sequence number of the Route.DestAddress.
Route.ValidTimeout
The time at which a route table entry is scheduled to be
invalidated. The routing table entry is no longer considered
valid if the current time is after Route.ValidTimeout.
3.2 DYMO Message Elements
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3.2.1 Generic DYMO Element Structure
All DYMO message elements MUST conform to the fixed data structure
below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Len | TTL |I|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. NotifyAddress (Only Types with M-bit set) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. TargetAddress (for non-DYMOcastAddress IPDestinationAddresses).
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Data .
. Type-Specific Payload .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
Element Type (Type)
0 0
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Type | = |M| H | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Figure 2
The Type field identifies the element as well as the handling
by nodes that do not implement or understand the element. The
most significant bit, the M-bit, denotes whether the element
requires notification via an Unsupported-element Error (UERR)
when the element is not understood or handled by a particular
node. The next two bits, H-bits, identify how the Type is to
be handled by nodes not implementing the Type, regardless of
UERR delivery. Section 4.6.3 describes the handling behavior
based on the Type.
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I-bit (I)
1-bit selector indicating whether the element has been ignored
by some node that has relayed this element. If I=1 the element
has been ignored.
Reserved (Reserved, Reservd, Res, R)
Reserved bits. These bits are set to zero (0) during element
creation and ignored during processing.
Element Time to Live (TTL)
6-bit field that identifies the maximum number of times the
element is to be retransmitted. The TTL field operates similar
to IPTTL (MaxCount) and is decremented at each hop. When TTL
reaches zero (0) the element is dropped.
Element Length (Len)
12-bit field that indicates the size of the element in bytes,
including the fixed portion.
Element Notify Address (NotifyAddress)
The node to send a UERR if the Element Type is unsupported or
not handled by the processing node. The NotifyAddress field is
only present if the Type field has the M-bit is set to one (1).
Element Target Address (TargetAddress)
The node that is the ultimate destination of the element. This
field is only required if the IPDestinationAddress is not the
DYMOcastAddress. During hop-by-hop transmission of a DYMO
packet the IPDestinationAddress is filled with the
Route.NextHopAddress of the route table entry associated with
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the TargetAddress.
Element Data (Data)
Type-specific payload.
3.2.2 Routing Element (RE)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Len | TTL |I|A|S| Res |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. TargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TargetSeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| THopCnt |Res| .
+-+-+-+-+-+-+-+-+ .
. .
. Routing Block 1 (RBlock1) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Additional Routing Blocks .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
A-bit (A)
1-bit selector indicating whether this RE requires a RREP by
the TargetAddress. If A=1 a RREP is required. The
instructions for generating a RREP are described in
Section 4.3.2.
S-bit (S)
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1-bit selector indicating whether this RE requires a unicast
message be sent to the previous hop address. This message MAY
used by the previous hop to ensure that the link traversed is
not unidirectional. The handling instructions for the S-bit is
explained in Section 4.3.2.
Element Target Address (TargetAddress)
The node that is the ultimate destination of the Routing
Element.
Target Sequence Number (TargetSeqNum)
The sequence number of the ultimate destination of this Routing
Element. If the Sequence Number is unknown for this particular
Route.DestAddress then TargetSeqNum is set to zero (0).
Target Hop Count (THopCnt)
6-bit field that identifies the number of intermediate nodes
through which a packet traversed on the route to this
particular TargetAddress the last time a route was available.
The THopCnt is the Route.HopCnt of the TargetAddress, stored in
the routing table of the RREQ originator. If the hop count
information is not available at the originating node then the
THopCnt is set to zero (0).
Routing Block (RBlock)
Data structure that describes routing information related to a
particular IP address, RBNodeAddress.
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Routing Block (RBlock)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G| RBPrefix |Res| RBHopCnt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. RBNodeAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RBNodeSeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4
G-bit (G)
1-bit selector to indicate whether the RBNodeAddress is a
gateway. If G=1 RBNodeAddress is a gateway. For more
information on gateway operation see Section 4.8.
Prefix Size (Prefix)
7-bit field that specifies the size of the subnet reachable
through the associated node, see Section 4.7. The
definition of Prefix is different for gateways.
Routing Block Hop Count (RBHopCnt)
6-bit field that identifies the number of intermediate nodes
through which the associated RBlock has passed.
Routing Block Node Address (RBNodeAddress)
The IP address of the node associated with this RBlock.
Routing Block Node Sequence Number (RBNodeSeqNum)
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The sequence number of the node associated with this RBlock.
3.2.3 Route Error (RERR)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Len | TTL |I|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UNodeAddress1 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UNodeSeqNum1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Additional UNodeAddressN (if needed) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional UNodeSeqNumN (if needed) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
Unreachable Node Address (UNodeAddress)
The IP address of the unreachable node.
Unreachable Node Sequence Number (UNodeSeqNum)
The sequence number of the unreachable node, if known;
otherwise, zero (0). RERR generation is described in
Section 4.5.3.
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3.2.4 Unsupported-element Error (UERR)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Len | TTL |I|Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. TargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UElemTargetAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. UERRNodeAddress .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UElemType |
+-+-+-+-+-+-+-+-+
Figure 6
Element Target Address (TargetAddress)
The node that is the ultimate destination of the element,
NotifyAddress.
Unsupported-element Target Address (UElemTargetAddress)
Address of the destination of the element that caused
generation of this UERR; TargetAddress from the offending fixed
DYMO element.
Unsupported-element Node Address (UERRNodeAddress)
The IP address of the node that created the UERR.
Unsupported-element Type (UElemType)
The Type that required generation of the UERR.
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4. Detailed Operation
4.1 Sequence Numbers
4.1.1 Maintaining a Sequence Number
DYMO requires each node in the network to maintain its own sequence
number (OwnSeqNum). The circumstances for a node to change its
OwnSeqNum are described in Section 4.3.1.
4.1.2 Incrementing a Sequence Number
When a node increments its OwnSeqNum (as described in Section 4.3.1
and Section 4.3.2) it MUST do so by treating the sequence number
value as if it was an unsigned number. The sequence number zero (0)
is reserved and is used in several DYMO data structures to represent
an unknown sequence number.
4.1.3 Sequence Number Rollover
If the sequence number has been assigned to be the largest possible
number representable as a 32-bit unsigned integer (i.e., 4294967295),
then the sequence number MUST be set to one (1) when incremented.
4.1.4 Actions After Sequence Number Loss
If a node's OwnSeqNum is lost, it must take certain actions to avoid
creating routing loops. To prevent this possibility after sequence
number loss a node MUST wait for at least ROUTE_DELETE_PERIOD before
transmitting any DYMO packet other than RERR generated by this node.
If a DYMO control packet is received during this period, the node
SHOULD process it normally but MUST not retransmit any DYMO control
packets. If a data packet is received during this waiting period the
node MUST send a RERR message to the IPSourceAddress with the
UNodeSeqNum set to zero (0) and restart its waiting period before
transmitting any DYMO control packets except RERR generated by this
node.
4.2 DYMO Routing Table Operations
4.2.1 Creating or Updating a Route Table Entry from a Routing Block
While processing a RE, as described in Section 4.3.2, a node checks
its routing table for an entry to the RBNodeAddress using longest-
prefix matching. In the event that no matching entry is found, an
entry is created.
If a matching entry is found, the routing information about
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RBNodeAddress contained in this RBlock is NOT stale if the result of
subtracting the Route.SeqNum from RBNodeSeqNum is greater than zero
(0) using signed 32-bit arithmetic.
If a matching entry is found, the routing information about
RBNodeAddress contained in this RBlock is NOT stale if the result of
subtracting the Route.SeqNum from RBNodeSeqNum is equal to zero (0)
using signed 32-bit arithmetic but it SHOULD be disregarded if:
o the Route.ValidTimeout has not passed and RBHopCnt is greater than
or equal to Route.HopCnt, OR
o the Route.ValidTimeout has passed and RBHopCnt is greater than
Route.HopCnt plus one (1).
If the information in this RBlock is stale or disregarded and this
RBlock is the first RBlock in a RREQ this DYMO packet MUST be
dropped. For other RBlocks containing stale or disregarded routing
information, the RBlock is simply removed from this RE and the RELen
adjusted. Removing stale and disregarded RBlocks ensures that unused
information is not propagated further.
If the route information for RBNodeAddress is not stale, disregarded
or a disregarded RREP, then the following actions occur to the route
table entry for RBNodeAddress:
1. the Route.HopCnt is set to the RBHopCnt,
2. the Route.IsGateway is set to the G-bit,
3. the Route.NextHopAddress is set to the node that transmitted this
DYMO packet (IPSourceAddress),
4. the Route.NextHopInterface is set to the interface that this DYMO
packet was received on,
5. the Route.Prefix is set to RBPrefix,
6. the Route.SeqNum is set to the RBNodeSeqNum,
7. and the Route.ValidTimeout is set to the current time +
ROUTE_TIMEOUT.
If a valid route exists to RBNodeAddress, the route can be used to
send any queued data packets and to fulfill any outstanding route
requests.
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4.2.2 Route Table Entry Timeouts
If the current time is later than a routing entry's
Route.ValidTimeout, the route is stale and it is not be used to route
packets. The information in invalid entries is still used for
generating RREQ messages.
If the current time is after Route.DeleteTimeout the corresponding
routing table entry MUST be deleted.
4.3 Routing Element
4.3.1 Routing Element Creation
When a node creates a RREQ it SHOULD increment its OwnSeqNum by one
according to the rules specified in Section 4.1.2. When a node
creates a RREP, then it increments its OwnSeqNum under the following
conditions:
o TargetSeqNum is greater than OwnSeqNum OR
o TargetSeqNum is equal to OwnSeqNum AND THopCnt is less than to
RBHopCnt.
In either case (for RREQ or RREP), the node MUST create the first
RBlock. It sets the RBNodeAddress to its own address. The
RBNodeSeqNum is the node's OwnSeqNum. The node may advertise a
prefix using the Prefix field, as described in Section 4.7.
Otherwise, the Prefix field is set to zero (0). The node may
advertise it is a gateway by setting the G-bit if it is a gateway, as
described in Section 4.8. Otherwise, the G-bit is set to zero (0).
The TTL SHOULD be set to NET_DIAMETER, but MAY be set smaller. For
the case of RREQ, the TTL MAY be set in accordance with an expanding
ring search as described in [2].
4.3.2 Routing Element Processing
After general DYMO element pre-processing (Section 4.6.2), the
RBHopCnt for the first RBlock is incremented by one (1). A route to
the first RBlock is then created or updated, as described in
Section 4.2.1. If this RBlock does not result in a valid route the
packet MUST be dropped.
Each additional RBlock SHOULD be processed. For each RBlock the
RBHopCnt is incremented by one (1), then a route is created or
updated as defined in Section 4.2.1. Each RBlock resulting in a
valid route entry may alleviate a future route discovery. Any
RBlocks that do not result in a valid route update or that are not
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processed MUST be removed from the RE.
If this node is the TargetAddress AND the A-bit is set (A=1), this
node MUST respond with a RREP. The target node creates a new RE as
described in Section 4.3.1. The TargetAddress in the new RE is set
to the RBNodeAddress1 from the RE currently being processed. The
THopCnt is the hop count for the TargetAddress. The A-bit is set to
(A=0). The IPDestinationAddress is set to the Route.NextHopAddress
for the TargetAddress. The TargetSeqNum is set to Route.SeqNum for
the TargetAddress. Then the new RE undergoes post-processing,
according to Section 4.6.4.
After processing a RE, a node MAY append its routing information to
the RE, according to the process described in Section 4.3.3. The
additional routing information will reduce route discoveries to this
node.
If this node is not the TargetAddress, the current RE SHOULD be
handled according to Section 4.6.4.
If this node is the TargetAddress, the current packet and any
additional elements are processed, but this packet is not
retransmitted.
If the S-bit is set to one (1) in the RE, then a unicast message
SHOULD be sent or have been sent to the previous hop within
UNICAST_MESSAGE_SENT_TIMEOUT. Any unicast packet will serve this
purpose, but 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.
4.3.3 Appending Additional Routing Information to an Existing Routing
Element
Appending routing information will alleviate route discovery attempts
to this node from other nodes that process the resultant RE. Nodes
MAY append a RBlock to RE processed if the believes that this
additional routing information will alleviate future RREQ.
Prior to appending a RBlock to a RE, a node MUST increment its
OwnSeqNum as defined in Section 4.1.2. Then it appends its IP
address, OwnSeqNum, Prefix and G-bit to the RE in a RBlock. The
RBHopCnt is set to zero (0). The RE Len is also adjusted according
to the number of RBlocks in the RE.
4.4 Route Discovery
A node generates a Route Request (RREQ) to discover a valid route to
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a particular destination (TargetAddress). A RREQ is a RE with the
A-bit is set to one (A=1) to indicate that the TargetNode must
respond with a RREP. If a sequence number is known for the
TargetAddress it is placed in the TargetSeqNum field. Otherwise,
TargetSeqNum is set to zero (0). A TargetSeqNum of zero MAY be set
to indicate that only the destination may respond to this RREQ. If a
hop count is known for the TargetAddress it is placed in the THopCnt
field. Otherwise, the THopCnt is set to zero (0). The
IPDestinationAddress is set to the DYMOcastAddress. Then the RE is
then transmitted according to the procedure defined in Section 4.6.5.
After issuing a RREQ, the originating node waits for a route to be
created to the TargetNode. If a route is not received within
RREQ_WAIT_TIME milliseconds, this node MAY again try to discover a
route by issuing another RREQ.
To reduce congestion in a network, repeated attempts at route
discovery for a particular TargetNode SHOULD utilize a binary
exponential backoff. The first time a node issues a RREQ, it waits
RREQ_WAIT_TIME milliseconds for a route to the TargetNode. If a
route is not found within that time, the node MAY send another RREQ.
If a route is not found within two (2) times the current waiting
time, another RREQ may be sent, up to a total of RREQ_TRIES. For
each additional attempt, the waiting time for the previous RREQ is
multiplied by two (2) so that the waiting time conforms to a binary
exponential backoff.
Data packets awaiting for a route SHOULD be buffered.
If a route discovery has been attempted RREQ_TRIES times without
receiving a route to the TargetNode, all data packets destined for
the corresponding TargetNode SHOULD be dropped from the buffer and a
Destination Unreachable ICMP message SHOULD be delivered to the
application.
4.5 Route Maintenance
4.5.1 Active Link Monitoring
Before a route can be used for forwarding a packet, it MUST be
checked to make sure that the route is still valid. If the
Route.ValidTimeout is earlier than the current time, the packet
cannot be forwarded, and a RERR message MUST be generated (see
section Section 4.5.3). In this case, the Route.DeleteTimeout is set
to Route.ValidTimeout + ROUTE_DELETE_TIMEOUT.
If the current time is after Route.DeleteTimeout, then the route
SHOULD be deleted, though a route MAY be deleted at any time.
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Nodes MUST monitor links on active routes. This may be accomplished
by one or several mechanisms. Including:
o Link layer feedback
o Hello messages
o Neighbor discovery
o Route timeout
Upon detecting a link break the detecting node MUST set the
Route.ValidTimeout to the current time for all routes active routes
utilizing the broken link.
A RERR MUST be issued if a data packet is received and it cannot be
delivered to the next hop. RERR generation is described in
Section 4.5.3. A RERR SHOULD be issued after detecting a broken link
of an active route to quickly notify nodes that a link break occurred
and a route or routes are no longer available. If a route has not
been used, a RERR SHOULD NOT be generated.
4.5.2 Updating Route Lifetimes
To avoid route timeouts for active routes, a node MUST update the
Route.ValidTimeout to the IPSourceAddress to be the current time +
ROUTE_TIMEOUT upon receiving a data packet.
To avoid route timeouts for active routes, a node SHOULD update the
Route.ValidTimeout to the IPDestinationAddress to be the current time
+ ROUTE_TIMEOUT upon successfully transmitting a packet to the next
hop.
4.5.3 Route Error Generation
When a data packet is received for a destination without a valid
routing table entry, a Route Error (RERR) MUST be generated by this
node. A RERR informs the source that the current route is no longer
available.
In the RERR, the UNodeAddress1 field is the address of the
unreachable node (IPDestinationAddress) from the data packet. If the
UNodeSeqNum is known, it is placed in the RERR; otherwise, zero (0)
is placed in the UNodeSeqNum field of the RERR. The TTL SHOULD be
set to NET_DIAMETER, but may be set smaller. The
IPDestinationAddress is set to the DYMOcastAddress.
Additional unreachable nodes that required the same unavailable link
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(routes with the same Route.NextHopAddress and
Route.NextHopInterface) as the UNodeAddress1 SHOULD be appended to
the RERR. For each unreachable node the UNodeAddress and UNodeSeqNum
are appended. The Len is set accordingly.
The RERR is then processed as described in Section 4.6.5.
4.5.4 Route Error Processing
When a node processes a RERR after generic element pre-processing
(Section 4.6.2), it SHOULD set the Route.ValidTimeout to the current
time for each route to a UNodeAddress that meets all of the following
conditions:
1. The Route.NextHopAddress is the same as the RERR IPSourceAddress.
2. The Route.NextHopInterface is the same as the interface on which
the RERR was received.
3. The UNodeSeqNum is zero (0) OR the result of subtracting
Route.SeqNum from UNodeSeqNum is less than or equal to zero using
signed 32-bit arithmetic.
Each UNodeAddress that did not result in a change to
Route.ValidTimeout SHOULD be removed from the RERR.
Prior to generic post processing a node MAY remove any UNodeAddressN,
UNodeSeqNumN pairs except UNodeAddress1 to decrease the element size.
If at least one UNodeAddress remains and at least one route remains
in the RERR it SHOULD be handled as described in Section 4.6.4 to
continue notification of nodes effected by the broken link.
Otherwise, the RERR is dropped.
4.6 General DYMO Processing
4.6.1 DYMO Control Packet Processing
A DYMO packet may consist of multiple DYMO elements. Each element is
processed individually and in sequence, from first to last. An
incoming DYMO packet MUST be completely processed prior to any DYMO
packet transmissions.
The length of IP addresses (32-bits for IPv4 and 128-bits for IPv6)
inside DYMO elements is dependent on the IP packet header. For
example, if the IP header is IPv6 then all DYMO elements contained in
the payload use IPv6 addresses.
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Unless specific element processing requires dropping the DYMO packet,
it is retransmitted after processing, according to the method
described in Section 4.6.5.
4.6.2 Generic Element Pre-processing
Each element in a DYMO packet undergoes pre-processing before the
element specific processing occurs. During pre-processing, the TTL
is decremented by one (1).
4.6.3 Processing Unsupported DYMO Element Types
This section describes the processing for unsupported DYMO element
Types. The Type field identifies the handling by nodes that do not
implement, support or understand a particular Element Type. The most
significant bit (M-bit) indicates whether an Unsupported-element
Error (UERR) SHOULD be sent to the NotifyAddress. The next two bits
(H-bits) identify how the element should be handled.
0 0
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Type | = |M| H | |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
If the M-bit is set in a DYMO element being processed by a node that
does not support this Element Type a UERR SHOULD be sent to the
NotifyAddress. This is accomplished by following the instructions in
Section 4.6.3.1.
Regardless of whether or not a UERR is sent in response to this
unsupported Element Type, the processing node MUST also examine the
H-bits to determine how this unsupported element is handled. The
unsupported element Type MUST be handled as follows:
o If H == 00 skip the element and continue as if the packet did not
contain this element.
o If H == 01 remove the unsupported element (using the Len field)
from the packet and continue as if the packet did not include this
element.
o If H == 10 set the ignored bit (I-bit) skip this element and
continue, as if the packet did not contain this element.
o If H == 11 drop the packet without processing any other DYMO
elements.
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4.6.3.1 Generating an Unsupported-element Error
When an unsupported element type is received with the M-bit set, the
processing node SHOULD generate an Unsupported-element Error (UERR).
The TargetAddress is set to the NotifyAddress. The
IPDestinationAddress is set to the Route.NextHopAddress toward the
NotifyAddress. The UElemTargetAddress is set to the TargetAddress
from the unsupported element. The UERRNodeAddress is set to the node
address generating this UERR. The UElemType is the Type from the
unsupported element. The TTL SHOULD be set to NET_DIAMETER, but MAY
be set smaller. The Len is set to the total number of bytes in this
UERR. The element is then processed as described in Section 4.6.4.
4.6.4 Generic Element Post-processing
If the first element TTL is zero (0) the DYMO packet is dropped after
processing of all elements. If the TTL of the first element is
greater than zero the DYMO packet is re-transmitted after processing
of all elements. If the TTL of any element is zero (0) after
processing it MUST be removed from the DYMO packet prior to
transmission.
4.6.5 DYMO Control Packet Transmission
DYMO packet transmission and re-transmission is controlled by the
IPDestinationAddress. If the IPDestinationAddress is a unicast
address, the packet IPDestinationAddress is replaced by the
Route.NextHopAddress from a route table lookup for the TargetAddress.
If a route for the TargetAddress is unknown or invalid the packet is
dropped and a RERR SHOULD be generated.
For all currently defined DYMO packets the IPTTL (IPMaxCount) SHOULD
be set to 1 (IPTTL=1), since all DYMO packet communications are
between direct neighbors.
4.7 Routing Prefix
Any node can advertise connectivity to a subset of other nodes within
its address space by using the prefix field in RE. The nodes within
the advertised prefix SHOULD NOT participate in the MANET and MUST be
reachable by forwarding packets to the node advertising connectivity.
For example, 192.168.1.1 with a prefix of 16 indicates all nodes with
the prefix 192.168.X.X are reachable through 192.168.1.1.
The meaning of the prefix field is altered for routes to the gateway;
Route.IsGateway is one (1). If the G-bit is set the prefix in
association with the IP address indicates that all nodes outside the
subnet are reachable via the gateway node. For example, a route to a
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gateway with IP address 192.168.1.1 and a prefix of 16 indicates that
all nodes with an IP address NOT matching 192.168.X.X are reachable
via this route.
4.8 Internet Attachment
Internet attachment consists of a network of MANET nodes connected to
the Internet via a gateway node. The gateway is responsible for
responding to RREQs for TargetNodes outside its configured MANET
subnet, as well as delivering packets to destinations outside the
MANET subnet.
MANET nodes wishing to be reachable from nodes in the Internet MUST
have IP addresses within the gateway's configured MANET subnet.
Given a node with a globally routeable address or care-of address
handled by the gateway, the gateway is responsible for routing and
forwarding packets received from the Internet destined for nodes
inside its MANET subnet.
Since many nodes may commonly wish to communicate with the gateway,
the gateway SHOULD indicate to nodes that it is a gateway by setting
the gateway bit (G-bit) in any RE created or processed. The G-bit
flag indicates to nodes in the MANET that the RBNodeAddress is
attached to the Internet and is capable of routing data packets to
all nodes outside of the configured MANET subnet, described by the
RBNodeAddress and RBPrefix fields.
4.9 Multiple Interfaces
It is likely that DYMO will be used with multiple wireless
interfaces; therefore, the particular interface over which packets
arrive must be known whenever a packet is received. Whenever a new
route is created, the interface through which the Route.DestAddress
can be reached is also recorded into the route table entry.
When multiple interfaces are available, a node transmitting a
DYMOcast packet SHOULD send the packet on all interfaces that have
been configured for operation in the MANET.
4.10 Packet Generation Limits
To avoid congestion, a node SHOULD NOT transmit more than RATE_LIMIT
control messages per second. RREQ packets SHOULD be discarded before
RREP or RERR packets.
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5. Configuration Parameters
Here are some default parameter values for DYMO:
Parameter Name Suggested Value
--------------------------- ---------------
NET_DIAMETER 10
RATE_LIMIT 10
ROUTE_TIMEOUT 3000 milliseconds
ROUTE_DELETE_TIMEOUT 5*ROUTE_TIMEOUT
RREQ_WAIT_TIME 1000 milliseconds
RREQ_TRIES 3
For large networks or networks with frequent topology changes the
default DYMO parameters should be adjusted using either
experimentally determined values or dynamic adaptation. For example,
in networks with infrequent topology changes ROUTE_TIMEOUT may be set
to a much larger value.
It is assumed that all nodes in the network share the same parameter
settings. Different parameter values for ROUTE_TIMEOUT or
ROUTE_DELETE_TIMEOUT in addition to arbitrary packet delays may
result in frequent route breaks or routing loops.
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6. IANA Considerations
DYMO defines a Type field for each element within a packet sent to
port TBD. A new registry will be created for the values for this
Type field, and the following values will be assigned:
Type Value
-------------------------------- -----
Routing Element (RE) 1
Route Error (RERR) 2
Unsupported-element Error (UERR) 3
Future values of the Type will be allocated using standard actions as
described in [1]. For future Types with the M-bit set NotifyAddress
MUST be included. Similarly for future Types that are unicast hop-
by-hop (packets not sent to the DYMOcastAddress), these Types MUST
include the TargetAddress field.
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7. Security Considerations
Currently, DYMO does not specify any special security measures.
Routing protocols, however, are prime targets for impersonation
attacks. In networks where the node membership is not known, it is
difficult to determine the occurrence of impersonation attacks, and
security prevention techniques are difficult at best. However, when
the network membership is known and there is a danger of such
attacks, DYMO elements must be protected by the use of authentication
techniques, such as those involving generation of unforgeable and
cryptographically strong message digests or digital signatures.
While DYMO does not place restrictions on the authentication
mechanism used for this purpose, IPsec Authentication Element (AH) is
an appropriate choice for cases where the nodes share an appropriate
security association that enables the use of AH.
In particular, RE messages SHOULD be authenticated to avoid creation
of spurious routes to a destination. Otherwise, an attacker could
masquerade as that destination and maliciously deny service to the
destination and/or maliciously inspect and consume traffic intended
for delivery to the destination. RERR messages, while slightly less
dangerous, SHOULD be authenticated in order to prevent malicious
nodes from disrupting active routes between communicating nodes.
If the mobile nodes in the ad hoc network have pre-established
security associations, the purposes for which the security
associations are created should include that of authorizing the
processing of DYMO control packets. Given this understanding, the
mobile nodes should be able to use the same authentication mechanisms
based on their IP addresses as they would have used otherwise.
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8. Acknowledgments
DYMO is a descendant of the design of previous MANET reactive
protocols, especially AODV [2] and DSR [4]. Changes to previous
MANET reactive protocols stem from research and implementation
experiences. Thanks to Luke Klein-Berndt, Pedro Ruiz, Fransisco Ros
and Koojana Kuladinithi for reviewing of DYMO, as well as several
specification suggestions.
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9. References
9.1 Normative References
[1] T. Narten and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, BCP 26, October 1998.
[2] C. Perkins, E. Belding-Royer, and S. Das, "Ad hoc On-demand
Distance Vector (AODV) Routing", RFC 3561, July 2003.
9.2 Informative References
[3] C. Perkins and E. Belding-Royer, "Ad hoc On-Demand Distance
Vector (AODV) Routing", Proceedings of the 2nd IEEE Workshop on
Mobile Computing Systems and Applications, New Orleans, LA, pp.
90-100, February 1999.
[4] D. Johnson and D. Maltz, "Dynamic Source Routing (DSR) in Ad hoc
Networks", In Mobile Computing, Chapter 5, pp. 153-181, 1996.
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
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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