Mobile Ad hoc Networks Working I. Chakeres
Group Boeing
Internet-Draft C. Perkins
Expires: September 6, 2006 Nokia
March 5, 2006
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-04
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Route Table Entry . . . . . . . . . . . . . . . . . . . . 8
3.2. DYMO Messages . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Generalized MANET Packet and Message Structure . . . . 10
3.2.2. Routing Message (RM) . . . . . . . . . . . . . . . . . 10
3.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 12
4. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 14
4.1. Sequence Numbers . . . . . . . . . . . . . . . . . . . . . 14
4.1.1. Maintaining a Sequence Number . . . . . . . . . . . . 14
4.1.2. Incrementing a Sequence Number . . . . . . . . . . . . 14
4.1.3. Sequence Number Rollover . . . . . . . . . . . . . . . 14
4.1.4. Actions After Sequence Number Loss . . . . . . . . . . 14
4.2. DYMO Routing Table Operations . . . . . . . . . . . . . . 14
4.2.1. Creating or Updating a Route Table Entry from
Routing Message Information . . . . . . . . . . . . . 14
4.2.2. Route Table Entry Timeouts . . . . . . . . . . . . . . 16
4.3. Routing Message . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. Routing Message Creation . . . . . . . . . . . . . . . 16
4.3.2. Routing Message Processing . . . . . . . . . . . . . . 16
4.3.3. Appending Additional Routing Information to an
Existing Routing Message . . . . . . . . . . . . . . . 17
4.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 18
4.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 18
4.5.1. Active Link Monitoring . . . . . . . . . . . . . . . . 18
4.5.2. Updating Route Lifetimes . . . . . . . . . . . . . . . 19
4.5.3. Route Error Generation . . . . . . . . . . . . . . . . 19
4.5.4. Route Error Processing . . . . . . . . . . . . . . . . 20
4.6. General DYMO Packet and Message Processing . . . . . . . . 21
4.6.1. Packet Processing . . . . . . . . . . . . . . . . . . 21
4.6.2. Generic Message Pre-processing . . . . . . . . . . . . 21
4.6.3. Processing Unknown Message and TLV Types . . . . . . . 21
4.6.4. Generic Message Post-processing . . . . . . . . . . . 21
4.6.5. DYMO Control Packet Transmission . . . . . . . . . . . 21
4.7. Routing Prefix . . . . . . . . . . . . . . . . . . . . . . 21
4.8. Simple Internet Attachment and Gatewaying . . . . . . . . 22
4.9. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 22
4.10. Packet Generation Limits . . . . . . . . . . . . . . . . . 23
5. Configuration Parameters . . . . . . . . . . . . . . . . . . . 24
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative References . . . . . . . . . . . . . . . . . . . 28
9.2. 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.
In order to enable extension of the base specification, DYMO uses the
generalized MANET packet and message format [5]. Additionally, by
following the defined default behavior for nodes not understanding a
particular type of information, future enhancements are handled in an
understood and 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 messages, thereby avoiding use of stale routing
information.
All DYMO messages conform to the generalized MANET message and packet
format [5] and are transmitted via UDP on port TBD.
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2. Terminology
DYMO Sequence Number (SeqNum)
A DYMO Sequence Number is 16-bit number maintained by each
node, and it is used to ensure loop-free routes.
Hop Count (HopCnt)
The number of hops a particular message or piece of information
has traversed.
IP Destination Address (IPDestinationAddress)
The destination of a packet, determined by examining the IP
header.
IP Source Address (IPSourceAddress)
The source of a packet, determined by examining the IP header.
MANETcast
Packet transmission to all neighboring MANET routers.
MANETcast packets should be sent with an IPDestinationAddress
of IPv4 TBD (IPv6 TBD), the MANETcastAddress.
Originator (Orig)
The Originator is the node that created a Routing Message in an
effort to disseminate and possibly learn new routing
information.
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Prefix
A Prefix indicates that an address is a network address, rather
than a host address. If a Prefix is omitted, the address is
assumed to be a host address.
Routing Message (RM)
A DYMO message 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 during route discovery, the target node
generates a Route Reply (RREP). A RREP is used to disseeminate
routing information on how to reach the Target. A RREP is a RM
with a unicast IPDestinationAddress, indicating that this RM is
to be unicast hop-by-hop toward the Target.
Route Error (RERR)
A node generates a Route Error (RERR) to disseminate that it
does not have correct routing information about a particular
destination, or set of destinations. A RERR is most often
generated in response to a request to forward a data packet for
which the current node does not have a valid route.
Route Request (RREQ)
A node generates a Route Request (RREQ) to discover a valid
route to a particular destination (Target). A RREQ is used to
disseminate routing information on how to reach the Originator
of the RREQ. A RREQ is simply a RM with the MANETcastAddress
in the IPDestinationAddress field of the IP packet, causing
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distribution to all neighboring DYMO routers.
Target
The Target is the ultimate destination of a message. For RREQ
this will be the desired destination. For RREP this will be
the Originator of the RREQ.
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, see Section 4.8.
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)
8-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), see Section 4.8.
Route Sequence Number (Route.SeqNum)
The sequence number of the Route.DestAddress, zero (0) if
unknown.
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.
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3.2. DYMO Messages
3.2.1. Generalized MANET Packet and Message Structure
All DYMO messages conform to the generalized packet and message
format as described in [5].
3.2.2. Routing Message (RM)
Routing messages are used to disseminate routing information. The
two message types are RREQ and RREP and they have the same general
format. RREQ messages require a response, while RREP are responses
to RREQ.
Routing message creation and processing are described in Section 4.3.
Example Simple RREQ/RREP Routing Message
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | RSRV |U|N|0|1| msg-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-ttl | msg-hopcnt | msg-tlv-block-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head Length | Head |Number Tails=2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TailOrig | TailTarget | tlv-block-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|DYMOSEQNUM-type| TLV Length | Orig.SeqNum.:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
:.Orig.SeqNum | Target.SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
o RM conform to the generalized message format.
o msg-type = DYMO-RREQ or DYMO-RREP
o msg-semantics
* RM indicate inclusion of msg-ttl and msg-hop-count in msg-
header-info, by setting bit 1
o msg-header-info
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* RM contains msg-ttl
* RM contains msg-hop-count
o add-block entries
* RM contain 1 and only 1 address marked as Originator - If no
address is marked as the originator the first address is
assumed to be the Originator
* if the RM is unicast (the IPDestinationAddress is a unicast
address), RM contain 1 and only 1 address marked as Target
(Target) - if no address is marked the second address is
assumed to be the Target
o add-tlv
* RM contain the DYMO Sequence Number of the Originator
(Orig.SeqNum) in a DYMO Sequence Number tlv
* RM should contain the SeqNum for each address. If the SeqNum
is not included a value of Zero (0) is assumed. For the Target
the SeqNum will be the Last Known SeqNum (Target.SeqNum) or
Zero (0) to indicate that only the Target can reply
* RM should contain the HopCnt for each address. If HopCnt is
not included, it is assumed to be zero (unknown). For the
Target the HopCnt should be the Last Known HopCnt
(Target.HopCnt)
* RM should contain a Prefix for each address that is not a host
address. If a prefix is not included in conjunction with an
address, it is assumed zero (host address only). For more
information on advertising a Prefix see Section 4.7.
* RM should contain a Gateway tlv for an address that is a
gateway. If gateway indicator is not included in association
with an address, the address is assumed to not be a gateway.
For more information on gateway operation see Section 4.8.
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3.2.3. Route Error (RERR)
Example Simple RERR Message
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| rerr-msg-type | RSRV |U|N|0|1| msg-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-ttl | msg-hopcnt | msg-tlv-block-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head Length | Head |Number Tails=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tail1 | tlv-block-size |dymo-seqnum-typ|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Length | Tail1.SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
o RERR conform to the generalized message format.
o msg-type = DYMO-RERR
o msg-semantics
* RERR indicates inclusion of msg-ttl and msg-hop-count in msg-
header-info, using bit 1
o msg-header-info
* RERR contain msg-ttl
* RERR contain msg-hop-count
o add-block entries
* All addresses are considered unreachable unless marked
otherwise
o add-tlvs
* RERR should contain SeqNum for each unreachable node. If the
SeqNum is not included in the message it is assumed to be zero
(unknown)
* RERR should contain the Last Known HopCnt for each unreachable
node. If the HopCnt is not included in the message it is
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assumed to be zero (unknown)
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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 DYMO
sequence number (OwnSeqNum), a 16-bit unsigned integer. 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 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.
4.1.4. Actions After Sequence Number Loss
A node SHOULD maintain its sequence number in persistent storage.
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
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 RM. 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 4.5.3. At the end of the waiting
period a node sets its sequence number to one (1).
4.2. DYMO Routing Table Operations
4.2.1. Creating or Updating a Route Table Entry from Routing Message
Information
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While processing a RM, as described in Section 4.3.2, a node checks
its routing table for an entry to the Node.Address using longest-
prefix matching [6]. In the event that no matching entry is found,
an entry is created.
If a matching entry is found, the routing information about
Node.Address contained in this RM is NOT stale if the result of
subtracting the Route.SeqNum from Node.SeqNum is equal to zero (0)
using signed 16-bit arithmetic but it SHOULD be disregarded if:
o the Route.ValidTimeout has not passed and Node.HopCnt is greater
than or equal to Route.HopCnt, OR
o the Route.ValidTimeout has passed and Node.HopCnt is greater than
Route.HopCnt plus one (1).
If the information associated with this Node.Address is stale or
disregarded and this Node.Address is the Originator then this DYMO
message MUST be dropped. For other Node.Addresses that are stale or
disregarded, the information is simply removed from the RM. Removing
stale and disregarded routing informations ensures that unused
information is not propagated further.
If the route information for Node.Address is not stale or
disregarded, then the following actions occur to the route table
entry for Node.Address:
1. the Route.HopCnt is set to the Node.HopCnt,
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 Node.Prefix,,
6. the Route.SeqNum is set to the Node.SeqNum,
7. and the Route.ValidTimeout is set to the current time +
ROUTE_TIMEOUT.
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 route requests.
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4.2.2. Route Table Entry Timeouts
If the current time is after Route.DeleteTimeout the corresponding
routing table entry MUST be deleted.
If the current time is later than a routing entry's
Route.ValidTimeout, the route is stale and it is not be used to route
packets. The information in invalid entries can still be used for
filling fields in outgoing RM with last known values.
4.3. Routing Message
4.3.1. Routing Message 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 in response to a RREQ, it MUST increment its OwnSeqNum
under the following conditions:
o Target.SeqNum is greater than OwnSeqNum OR
o Target.SeqNum is equal to OwnSeqNum AND Target.HopCnt is unknown
OR
o Target.SeqNum is equal to OwnSeqNum AND Orig.HopCnt is unknown OR
o Target.SeqNum is equal to OwnSeqNum AND Target.HopCnt (the last
know hop count value) is less than to Orig.HopCnt (the number of
hops traversed by this RREQ to reach the target).
In either case (both RREQ and RREP), the node MUST add the
Orig.Address to the add-block and the Orig.SeqNum to the add-tlv-
block. It sets the Orig.Address to its own address. The Orig.SeqNum
is the node's OwnSeqNum. The node MAY advertise a prefix using the
Prefix add-tlv, as described in Section 4.7. Otherwise, the Prefix
add-tlv is not included. The node MAY advertise it is a gateway by
using a gateway add-tlv, as described in Section 4.8. Otherwise, the
gateway add-tlv is not included. The msg-ttl SHOULD be set to
NET_DIAMETER, but MAY be set smaller. The msg-hopcnt is set to zero
(0). the case of RREQ, the msg-ttl MAY be set in accordance with an
expanding ring search as described in [2] to limit the RREQ
propagation to a subset of the network and possibly reduce route
discovery overhead.
4.3.2. Routing Message Processing
After general message pre-processing (Section 4.6.2), a route to the
Originator is then created or updated, as described in Section 4.2.1.
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If a valid route to the Originator is not created or updated then the
message MUST be dropped.
Each additional address in the address block(s) SHOULD be processed
except the Target. For each of these addresses the Node.HopCnt
associated with the address is incremented by one (1) if it exists
and is not zero, then a route is created or updated as defined in
Section 4.2.1. The updating of the HopCnt occurs after processing.
Each address resulting in a valid route entry may alleviate a future
route discovery. Any addresses that do not yield a valid route or
that are not processed MUST be removed from the RM. Only valid
routing information is propagated within RM messages.
If this node is the Target AND this is a RREQ, this node responds
with a RREP. The Target creates a new RREP as described in
Section 4.3.1. The Target.Address in the new RM is set to the
Orig.Address from the RM currently being processed. The
Target.HopCnt is the hop count for the Orig.Address. The
IPDestinationAddress is set to the Route.NextHopAddress for the
Orig.Address of the current RM being processed. The Target.SeqNum is
set to Route.SeqNum for Orig.Address from the current RM being
processed. Then the new RM undergoes post-processing, according to
Section 4.6.4.
After processing a RM, a node MAY append its routing information to
the RM, according to the process described in Section 4.3.3. The
additional routing information will reduce route discoveries to this
node. If all nodes along the path append their information path
information will also be available.
If this node is not the Target.Address and this is a RREQ the current
RM SHOULD be MANETcast. If this node is not the Target Address and
this is a RREP the current RM SHOULD be unicast to the next hop
address on the route to the Target.
If this node is the Target.Address, the current message is processed,
but this message is not forwarded or retransmitted.
4.3.3. Appending Additional Routing Information to an Existing Routing
Message
Appending routing information will alleviate route discovery attempts
to this node from other nodes that process the resultant RM
information. Nodes MAY append a their routing information to a RM
processed if they believe that this additional routing information
will alleviate future RREQ.
Prior to appending their address to a RM, a node MUST increment its
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OwnSeqNum as defined in Section 4.1.2. Then it appends its IP
address and OwnSeqNum. It MAY also append its Prefix and G-bit to
the RM. This Node.HopCnt is set to one (1) if included. Several
length fields MUST also be adjusted to include the newly inserted
information.
4.4. Route Discovery
A node generates a Route Request (RREQ) to discover a route to a
particular destination (Target). If a sequence number is known for
the Target it is placed in the RREQ. Otherwise, Target.SeqNum
assumed to be unknown by processing nodes. A Target.SeqNum of zero
(0) MAY be set to indicate that only the destination may respond to
this RREQ. If a previous value of the HopCnt is known for the Target
it is placed in a corresponding add-tlv HopCnt. Otherwise, the
HopCnt is not included. The IPDestinationAddress is set to the
MANETcastAddress. Then the RM is 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 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.
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 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
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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 MUST
be deleted, though a route MAY be deleted at any time.
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
o Other monitoring mechanisms or heuristics
Upon detecting a link break the detecting node MUST set the
Route.ValidTimeout to the current time for all active routes
utilizing the broken link.
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 MAY 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 unless generation is
expected to reduce future control traffic.
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
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routing table entry, a Route Error (RERR) MUST be generated by this
node. A RERR informs the source that the route does not exist, is no
longer available, or is now invalid.
In a new RERR, the address of unreachable node (IPDestinationAddress)
from the data packet is inserted. If a value for the unreachable
node's SeqNum is known, it is placed in the RERR; otherwise, if
unknown it will be assumed to be zero (0). The msg-ttl SHOULD be set
to NET_DIAMETER, but may be set smaller to limit the scope of the
RERR. The msg-hopcnt is set to zero (0). The IPDestinationAddress
is set to the MANETcastAddress. This option will notify the maximum
number of nodes of the broken link.
Additional unreachable nodes that required the same unavailable link
(routes with the same Route.NextHopAddress and
Route.NextHopInterface) MAY be added to the RERR. For each
unreachable node the Address is appended. The SeqNum if know should
also be included. Appending additional routing information notifies
each processing node of additional routes that are no longer
available.
The RERR is then processed as described in Section 4.6.5.
4.5.4. Route Error Processing
When a node processes a RERR, it SHOULD set the Route.ValidTimeout to
the current time for each Address 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 Node.SeqNum is zero (0), unknown, OR the result of
subtracting Route.SeqNum from Node.SeqNum is less than or equal
to zero using signed 16-bit arithmetic.
Each Node.Address that did not result in a change to
Route.ValidTimeout SHOULD be removed from the RERR, since propagation
of this information should not result in any benefit.
Prior to post processing a node MAY remove any unreachable node
address and its associated information to decrease the message size.
If this node is the Target and the IPDestinationAddress is its own
Address then it may stop processing.
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If at least one unreachable node address 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 Packet and Message Processing
4.6.1. Packet Processing
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.
4.6.2. Generic Message Pre-processing
Each message undergoes pre-processing before the message specific
processing occurs. During pre-processing, the msg-ttl is decremented
by one (1) and the msg-hopcnt is incremented by one (1).
4.6.3. Processing Unknown Message and TLV Types
We expect the next version of the generalized MANET packet and
message format [5] to include message semantic bits and tlv semantic
bits to control the behavior of unknown types.
4.6.4. Generic Message Post-processing
If the msg-ttl of any message is zero (0) after processing it MUST be
dropped.
4.6.5. DYMO Control Packet Transmission
Packet transmission and re-transmission are 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 Target. If a
route for the Target 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
exchanged between direct neighbors only.
4.7. Routing Prefix
Any node MAY advertise connectivity to a subset of node addresses
within its address space by using a Prefix tlv [5]. The nodes (other
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than the advertising node) 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
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 node.
4.8. Simple Internet Attachment and Gatewaying
Simple Internet attachment consists of a network of MANET nodes
connected to the Internet via a single 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.
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 created or processed. The 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.
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.Address can
be reached is also recorded in the route table entry.
When multiple interfaces are available, a node transmitting a
MANETcast packet SHOULD send the packet on all interfaces that have
been configured for DYMO operation.
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4.10. Packet Generation Limits
To avoid congestion, a node SHOULD NOT transmit more than RATE_LIMIT
control messages per second. RREQ packets SHOULD be discarded before
RREP or RERR packets.
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5. Configuration Parameters
Here are some default parameter values for DYMO:
Parameter Name Suggested Value
--------------------------- ---------------
NET_DIAMETER 10
RATE_LIMIT 10
ROUTE_TIMEOUT 5000 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 several message-types and tlv-types. A new registry
will be created for the values for the various type fields, and the
following values will be assigned:
msg-type Value
-------------------------------- -------
Route Request (DYMO-RREQ) 8 - TBD
Route Reply (DYMO-RREP) 9 - TBD
Route Error (DYMO-RERR) 10 - TBD
address-tlv Value
-------------------------------- -----
DYMO SeqNum (multivalue) 20 - TBD
HopCnt (multivalue) 21 - TBD
Prefix (multivalue) 0 [5]
Gateway (zero length) 22 - TBD
Originator 23 - TBD
Target 24 - TBD
Future values of the Type will be allocated using standard actions as
described in [1]. For future Types that are unicast hop-by-hop
(packets not sent to the MANETcastAddress), these Types MUST include
the Target.Address 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 messages must be protected by the use of authentication
techniques, such as those involving generation of unforgeable and
cryptographically strong message digests or digital signatures.
While DYMO does not place restrictions on the authentication
mechanism used for this purpose, IPsec Authentication Message (AH) is
an appropriate choice for cases where the nodes share an appropriate
security association that enables the use of AH.
In particular, RM messages SHOULD be authenticated to avoid creation
of spurious routes to a destination. Otherwise, an attacker could
masquerade as that destination and maliciously deny service to the
destination and/or maliciously inspect and consume traffic intended
for delivery to the destination. RERR messages, while slightly less
dangerous, SHOULD be authenticated in order to prevent malicious
nodes from disrupting active routes between communicating nodes.
If the mobile nodes in the ad hoc network have pre-established
security associations, the purposes for which the security
associations are created should include that of authorizing the
processing of DYMO control packets. Given this understanding, the
mobile nodes should be able to use the same authentication mechanisms
based on their IP addresses as they would have used otherwise.
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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 Elizabeth Belding-Royer for her long time
authorship of DYMO. Additional thanks to Luke Klein-Berndt, Pedro
Ruiz, Fransisco Ros and Koojana Kuladinithi for reviewing of DYMO, as
well as several specification suggestions.
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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.
[6] Baker, R., "Requirements for IP Version 4 Routers", RFC 1812,
June 1995.
9.2. Informative References
[3] Perkins, C. and E. Belding-Royer, "Ad hoc On-Demand Distance
Vector (AODV) Routing", Proceedings of the 2nd IEEE Workshop on
Mobile Computing Systems and Applications, New Orleans, LA, pp.
90-100, February 1999.
[4] Johnson, D. and D. Maltz, "Dynamic Source Routing (DSR) in Ad
hoc Networks", In Mobile Computing, Chapter 5, pp. 153-181,
1996.
[5] Clausen, T., Dearlove, C., and J. Dean, "Generalized MANET
Packet/Message Format", February 2006.
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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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