Mobile Ad hoc Networks Working I. Chakeres
Group Motorola
Internet-Draft C. Perkins
Intended status: Standards Track Nokia
Expires: May 21, 2008 November 18, 2007
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-11
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
The Dynamic MANET On-demand (DYMO) routing protocol is intended for
use by mobile modes in wireless, multihop networks. It offers
adaptation to changing network topology and determines unicast routes
between DYMO routers within the network in an on-demand fashion.
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Route Table Entry . . . . . . . . . . . . . . . . . . . . 7
4.2. DYMO Messages . . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Generalized MANET Packet and Message Structure . . . . 8
4.2.2. Routing Messages (RM) - RREQ & RREP . . . . . . . . . 9
4.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 13
5. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 14
5.1. DYMO Sequence Numbers . . . . . . . . . . . . . . . . . . 14
5.1.1. Maintaining A Node's Own Sequence Number . . . . . . . 15
5.1.2. Numerical Operations on OwnSeqNum . . . . . . . . . . 15
5.1.3. OwnSeqNum Rollover . . . . . . . . . . . . . . . . . . 15
5.1.4. Actions After OwnSeqNum Loss . . . . . . . . . . . . . 15
5.2. DYMO Routing Table Operations . . . . . . . . . . . . . . 15
5.2.1. Judging Routing Information's Usefulness . . . . . . . 16
5.2.2. Creating or Updating a Route Table Entry with New
Routing Information . . . . . . . . . . . . . . . . . 17
5.2.3. Route Table Entry Timeouts . . . . . . . . . . . . . . 18
5.3. Routing Messages . . . . . . . . . . . . . . . . . . . . . 19
5.3.1. RREQ Creation . . . . . . . . . . . . . . . . . . . . 19
5.3.2. RREP Creation . . . . . . . . . . . . . . . . . . . . 20
5.3.3. Intermediate DYMO Router RREP Creation . . . . . . . . 21
5.3.4. RM Processing . . . . . . . . . . . . . . . . . . . . 21
5.3.5. Adding Additional Routing Information to a RM . . . . 24
5.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 24
5.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 25
5.5.1. Active Link Monitoring . . . . . . . . . . . . . . . . 26
5.5.2. Updating Route Lifetimes During Packet Forwarding . . 26
5.5.3. Route Error Generation . . . . . . . . . . . . . . . . 26
5.5.4. RERR Processing . . . . . . . . . . . . . . . . . . . 27
5.6. Unknown Message & TLV Types . . . . . . . . . . . . . . . 28
5.7. Advertising Network Addresses . . . . . . . . . . . . . . 28
5.8. Simple Internet Attachment and Gatewaying . . . . . . . . 28
5.9. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 30
5.10. Packet/Message Generation Limits . . . . . . . . . . . . . 30
6. Configuration Parameters and Other Administrative Options . . 30
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
7.1. DYMO Message Type Specification . . . . . . . . . . . . . 32
7.2. Packet and Message TLV Type Specification . . . . . . . . 32
7.3. Address Block TLV Specification . . . . . . . . . . . . . 33
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1. Normative References . . . . . . . . . . . . . . . . . . . 34
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10.2. Informative References . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
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1. Overview
The Dynamic MANET On-demand (DYMO) routing protocol enables reactive,
multihop unicast routing between participating DYMO routers. The
basic operations of the DYMO protocol are route discovery and route
management. During route discovery, the originator's DYMO router
initiates dissemination of a Route Request (RREQ) throughout the
network to find a route to the target's DYMO router. During this
hop-by-hop dissemination process, each intermediate DYMO router
records a route to the originator. When the target's DYMO router
receives the RREQ, it responds with a Route Reply (RREP) sent hop-by-
hop toward the originator. Each intermediate DYMO router that
receives the RREP records a route to the target, and then the RREP is
unicast hop-by-hop toward the originator. When the originator's DYMO
router receives the RREP, routes have then been established between
the originating DYMO router and the target DYMO router in both
directions.
In order to preserve routes in use, DYMO routers extend route
lifetimes upon successfully forwarding a packet. In order to react
to changes in the network topology, DYMO routers monitor links over
which traffic is moving. When a data packet is received for
forwarding if a route for the destination is not known or the route
is broken, then the DYMO router of source of the packet is notified.
A Route Error (RERR) is sent toward the packet source to indicate the
current route to a particular destination is broken. When the
source's DYMO router receives the RERR, it deletes the route. If the
DYMO router later receives a packet for forwarding to the same
destination, it must perform route discovery again.
DYMO uses sequence numbers to ensure loop freedom [Perkins99].
Sequence numbers enable DYMO routers to determine the order of DYMO
route discovery messages, thereby avoiding use of stale routing
information.
2. Applicability Statement
The DYMO routing protocol is designed for stub or disconnected mobile
ad hoc networks. DYMO handles a wide variety of mobility patterns by
dynamically determining routes on-demand. DYMO also handles a wide
variety of traffic patterns. In large networks DYMO is best suited
for traffic scenarios where nodes communicate with only a portion of
the other nodes.
DYMO is applicable to memory constrained devices, since little
routing state must be maintained in each DYMO router. Only routing
information related to active sources and destinations must be
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maintained, in contrast to other routing protocols that require
routing information to all routers within the routing region be
maintained.
DYMO supports routers which have multiple interfaces participating in
the MANET. DYMO also supports nodes which have non-MANET interfaces
to which hosts can attach.
DYMO routers perform route discovery to find a route to a particular
destination. Therefore, DYMO routers must be configured to initiate
route discovery for certain destinations. When DYMO is the only
protocol interacting with the forwarding table, DYMO should be
configured to perform route discovery for all unknown unicast
destinations.
DYMO should only utilizes bidirectional links. In the case of
possible unidirectional links, either blacklists (see Section 7.2) or
other means (e.g. only accepting RM from bidirectional links as
indicated by NHDP [I-D.ietf-manet-nhdp]) of ensuring bi-
directionality should be used. Otherwise, persistent packet loss may
occur.
The routing algorithm in DYMO may be operated at layers other than
the network layer, using layer-appropriate addresses. Only
modification of the packet format is required. The routing algorithm
need not change. Note that, using the DYMO algorithm with message
formats other than those specified in this document will not be
interoperable.
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Additionally, this document uses some terminology from
[I-D.ietf-manet-packetbb].
This document defines the following terminology:
Distance (Dist)
A metric of the distance a message or piece of information has
traversed. The minimum value of distance is the number of IP hops
traversed. The maximum value is 65,535.
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DYMO Sequence Number (SeqNum)
A DYMO Sequence Number is maintained by each DYMO router. This
sequence number is used by other DYMO routers to identify the
order of routing information generated and ensure loop-free
routes.
Forwarding Route
A route that is used to forward data packets. Forwarding routes
are generally maintained in a forwarding information base (FIB) or
the kernel forwarding/routing table.
Originating Node (OrigNode)
The originating node is the DYMO router that creates a DYMO
Message in an effort to disseminate some information. The
originating node is also referred to as a particular message's
originator.
Route Error (RERR)
A RERR message is used indicate that a DYMO router does not have
forwarding route to one or more particular addresses.
Route Reply (RREP)
A RREP message is used to disseminate routing information about
the RREP OrigNode to the RREP TargetNode and the DYMO routers
between them.
Route Request (RREQ)
A RREQ message is issued to discover a valid route to a particular
destination address, called the RREQ TargetNode. When a DYMO
router processes a RREQ, it learns routing information on how to
reach the RREQ OrigNode.
Target Node (TargetNode)
The TargetNode is the ultimate destination of a message.
This Node (ThisNode)
ThisNode corresponds to the DYMO router currently performing a
calculation or processing a message.
Type-Length-Value structure (TLV)
A generic way to represent information, please see
[I-D.ietf-manet-packetbb] for additional information.
Unreachable Node (UnreachableNode)
An UnreachableNode is a node for which a forwarding route does not
exist.
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4. Data Structures
4.1. Route Table Entry
The route table entry is a conceptual data structure.
Implementations may use any internal representation that conforms to
the semantics of a route as specified in this document.
Conceptually, a route table entry has the following fields:
Route.Address
The IP (host or network) destination address of the node(s)
associated with the routing table entry.
Route.SeqNum
The DYMO SeqNum associated with this routing information.
Route.NextHopAddress
The IP address of the next DYMO router on the path toward the
Route.Address.
Route.NextHopInterface
The interface used to send packets toward the Route.Address.
Route.Broken
A flag indicating whether this Route is broken. This flag is set
if the next hop becomes unreachable or in response to processing a
RERR (see Section 5.5.4).
The following fields are optional:
Route.Dist
A metric indicating the distance traversed before reaching the
Route.Address node.
Route.Prefix
Indicates that the associated address is a network address, rather
than a host address. The value is the length of the netmask/
prefix. If an address block does not have an associated
PREFIX_LENGTH TLV [I-D.ietf-manet-packetbb], the prefix may be
considered to have a prefix length equal to the address length in
bits.
Not including optional information may cause performance degradation,
but it will not cause the protocol to operate incorrectly.
In addition to a route table data structure, each route table entry
may have several timers associated with the information. These
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timers/timeouts are discussed in Section 5.2.3.
4.2. DYMO Messages
When describing DYMO protocol messages, it is necessary to refer to
fields in several distinct parts of the overall packet. These
locations include the IP or IPv6 header, the UDP header, and fields
from [I-D.ietf-manet-packetbb]. This document uses the following
notation conventions. Information found in the table.
+----------------------------+-------------------+
| Information Location | Notational Prefix |
+----------------------------+-------------------+
| IP header | IP. |
| UDP header | UDP. |
| packetbb message header | MsgHdr. |
| packetbb message TLV | MsgTLV. |
| packetbb address blocks | AddBlk. |
| packetbb address block TLV | AddTLV. |
+----------------------------+-------------------+
Table 1
4.2.1. Generalized MANET Packet and Message Structure
DYMO messages conform to the generalized packet and message format as
described in [I-D.ietf-manet-packetbb]. Here is a brief description
of the format. A packet is made up of messages. A message is made
up of a message header, message TLV block, and zero or more address
blocks. Each of the address blocks may also have an associated
address TLV block.
All DYMO messages specified in this document are sent using UDP to
the destination port MANET [I-D.ietf-manet-iana].
Most DYMO messages are sent with the IP destination address set to
the link-local multicast address LL MANET ROUTERS unless otherwise
stated. Therefore, all DYMO routers SHOULD subscribe to LL MANET
ROUTERS for receiving control packets.
Unicast DYMO messages specified in this document are sent with the IP
destination set to the Route.NextHopAddress of the route to the
TargetNode.
The IPv4 TTL (IPv6 Hop Limit) field for DYMO messages is set to one
(1) for all messages specified in this document.
The length of an IP address (32 bits for IPv4 and 128 bits for IPv6)
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inside a DYMO message depends on the IP packet header containing the
DYMO message/packet. For example, if the IP header uses IPv6
addresses then all messages and addresses contained in the payload
use IPv6 addresses. In the case of mixed IPv6 and IPv4 addresses,
please see [I-D.ietf-manet-packetbb].
If a packet contains only a single DYMO message and no packet TLVs,
it need not include a packet-header [I-D.ietf-manet-packetbb].
The aggregation of multiple messages into a packet is not specified
in this document, but the IP.SourceAddress and IP.DestinationAddress
of all contained messages must be the same.
Implementations may choose to temporarily delay transmission of
messages for the purpose of aggregation (into a single packet) or to
improve performance by introducing jitter [I-D.ietf-manet-jitter].
4.2.2. Routing Messages (RM) - RREQ & RREP
Routing Messages (RMs) are used to disseminate routing information.
There are two DYMO message types that are considered to be routing
messages (RMs): RREQ and RREP. They contain very similar information
and function, but have slightly different processing rules. The main
difference between the two messages is that RREQ messages generally
solicit a RREP, whereas a RREP is the response to RREQ.
RM creation and processing are described in Section 5.3.
A RM requires the following information:
IP.SourceAddress
The IP address of the node currently sending this packet. This
field is generally filled automatically by the operating system
and should not require special handling.
IP.DestinationAddress
The IP address of the packet destination. For RREQ the
IP.DestinationAddress is set to LL MANET ROUTERS. For RREP the
IP.DestinationAddress is set to the NextHopAddress toward the RREP
TargetNode.
UDP.DestinationPort
The UDP destination port is set to MANET [I-D.ietf-manet-iana].
MsgHdr.HopLimit
The remaining number of hops this message is allowed to traverse.
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AddBlk.TargetNode.Address
The IP address of the message TargetNode. In a RREQ the
TargetNode is the destination for which a forwarding route does
not exist and route discovery is being performed. In a RREP the
TargetNode is the RREQ OrigNode DYMO router. The TargetNode
address is the first address in a routing message.
AddBlk.OrigNode.Address
The IP address of the originator. In a RREQ the OrigNode is the
source's DYMO router for which a route discovery is being
performed. In a RREP the OrigNode is the RREQ TargetNode's DYMO
router for which a RREP is being generated. This address is the
second address in the message for RREQ.
OrigNode.AddTLV.SeqNum
The DYMO sequence number of the originator's DYMO router.
A RM may optionally include the following information:
TargetNode.AddTLV.SeqNum
The last known DYMO sequence number of the TargetNode.
TargetNode.AddTLV.Dist
The last known distance to the TargetNode.
AddBlk.AdditionalNode.Address
The IP address of an additional node that can be reached via the
DYMO router adding this information. Each AdditionalNode.Address
must have an associated Node.SeqNum in the address TLV block.
AdditionalNode.AddTLV.SeqNum
The DYMO sequence number associated with this routing information.
OrigNode.AddTLV.Dist
A metric of the distance to reach the associated OrigNode.Address.
This field is incremented by at least one at each intermediate
DYMO router.
AdditionalNode.AddTLV.Dist
A metric of the distance to reach the associated
AdditionalNode.Address. This field is incremented by at least one
at each intermediate DYMO router.
OrigNode.AddTLV.Prefix
The OrigNode.Address is a network address with a particular prefix
length.
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AdditionalNode.AddTLV.Prefix
The AdditionalNode.Address is a network address with a particular
prefix length.
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Example IPv4 RREQ
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
IP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.SourceAddress |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.DestinationAddress = LL MANET ROUTERS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = MANET |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RREQ-type | Rsv |N|1|1|0|1| msg-size=23 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-hoplimit |
+-+-+-+-+-+-+-+-+
...
Message Body - Message TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-tlv-block-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Number Addrs=2 | Resv |0|1|0| HeadLength=3 | Head :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Head (cont) | Target.Tail | Orig.Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| tlv-block-size=6 |DYMOSeqNum-type|Rsv|0|1|0|0|0|0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=1 | tlv-length=2 | Orig.SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
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4.2.3. Route Error (RERR)
A RERR message is used to disseminate the information that a route is
not available for one or more particular IP addresses.
RERR creation and processing are described in Section 5.5.
A RERR requires the following information:
IP.SourceAddress
The IP address of the node currently sending this packet. This
field is generally filled automatically by the operating system
and should not require special handling.
IP.DestinationAddress
The IP address is set to LL MANET ROUTERS.
UDP.DestinationPort
The UDP destination port is set to MANET [I-D.ietf-manet-iana].
MsgHdr.HopLimit
The remaining number of hops this message is allowed to traverse.
AddBlk.UnreachableNode.Address
The IP address of an UnreachableNode. Multiple unreachable
addresses may be included in a RERR.
A Route Error may optionally include the following information:
UnreachableNode.AddTLV.SeqNum
The last known DYMO sequence number of the unreachable node. If a
SeqNum for an address is not included, it is assumed to be
unknown. This case occurs when a node receives a message to
forward to a destination for which it does not have any
information in its routing table.
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Example IPv4 RERR
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
IP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.SourceAddress |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.DestinationAddress = LL MANET ROUTERS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = MANET |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RERR-type |Resv |0|1|1|0|1| msg-size=15 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-hoplimit |
+-+-+-+-+-+-+-+-+
...
Message Body
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-tlv-block-size=0 |Number Addrs=1 | Resv |0|1|1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unreachable.Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV-blk-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
5. Detailed Operation
5.1. DYMO Sequence Numbers
DYMO sequence numbers allow nodes to judge the freshness of routing
information and ensure loop freedom.
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5.1.1. Maintaining A Node's Own Sequence Number
DYMO requires that each DYMO router in the network to maintain its
own DYMO sequence number (OwnSeqNum), a 16-bit unsigned integer. The
circumstances for ThisNode to incrementing its OwnSeqNum are
described in Section 5.3.
5.1.2. Numerical Operations on OwnSeqNum
When ThisNode increments its OwnSeqNum (as described in Section 5.3)
it MUST do so by treating the sequence number value as an unsigned
number.
Note: The sequence number zero (0) is reserved.
5.1.3. OwnSeqNum Rollover
If the sequence number has been assigned to be the largest possible
number representable as a 16-bit unsigned integer (i.e., 65,535),
then the sequence number is set to 256 when incremented. Setting the
sequence number to 256 allows other nodes to detect that the number
has rolled over and the node has not lost its sequence number.
5.1.4. Actions After OwnSeqNum Loss
A node should maintain its sequence number in persistent storage,
between reboots.
If a node's OwnSeqNum is lost, it must take certain actions to avoid
creating routing loops. To prevent this possibility after OwnSeqNum
loss a node MUST wait for at least ROUTE_DELETE_TIMEOUT before fully
participating in the DYMO routing protocol. If a DYMO control
message is received during this waiting period, the node SHOULD
process it normally but MUST NOT transmit or retransmit any DYMO
messages. If a data packet is received for forwarding to another
destination during this waiting period, the node MUST generate a RERR
message indicating that this route is not available and reset its
waiting timeout. At the end of the waiting period a node sets its
OwnSeqNum to one (1).
The longest a node must wait is ROUTE_AGE_MAX_TIMEOUT. At the end of
the maximum waiting period a node sets its OwnSeqNum to one (1) and
begins participating.
5.2. DYMO Routing Table Operations
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5.2.1. Judging Routing Information's Usefulness
Given a route table entry (Route.SeqNum, Route.Dist, and
Route.Broken) and new incoming routing information for a particular
node in a RM (Node.SeqNum, Node.Dist, and RM message type - RREQ/
RREP), the quality of the new routing information is evaluated to
determine its usefulness. Incoming routing information is classified
as follows:
1. Stale
If Node.SeqNum - Route.SeqNum < 0 (using signed 16-bit arithmetic)
the incoming information is stale. Using stale routing
information is not allowed, since doing so might result in routing
loops.
(Node.SeqNum - Route.SeqNum < 0)
2. Loop-possible
If Node.SeqNum == Route.SeqNum the incoming information may cause
loops if used; in this case additional information must be
examined. If Route.Dist or Node.Dist is unknown or zero (0), then
the routing information is loop-possible. If Node.Dist >
Route.Dist + 1, then the routing information is loop-possible.
Using loop-possible routing information is not allowed, otherwise
routing loops may be formed.
(Node.SeqNum == Route.SeqNum) AND
((Node.Dist is unknown) OR
(Route.Dist is unknown) OR
(Node.Dist > Route.Dist + 1))
3. Inferior
In case of known equal SeqNum, the information is inferior in
multiple cases: (case i) if Node.Dist == Route.Dist + 1 (it is a
greater distance route) AND Route.Broken == false; (case ii) if
Node.Dist == Route.Dist (equal distance route) AND Route.Broken ==
false AND this RM is a RREQ. The inferior condition stops
forwarding of RREQ with equivalent distance.
((Node.SeqNum == Route.SeqNum) AND
(((Node.Dist == Route.Dist + 1) AND (Route.Broken == false)) OR
((Node.Dist == Route.Dist) AND
(RM is RREQ) AND (Route.Broken == false))))
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4. Superior
Incoming routing information that does not match any of the above
criteria is loop-free and better than the information existing in
the routing table. Information is always superior if Node.SeqNum
- Route.SeqNum > 0 (using 16-bit signed arithmetic). In the case
of equal sequence numbers, the information is superior in multiple
cases: (case i) if Node.Dist < Route.Dist; (case ii) if Node.Dist
== Route.Dist + 1 AND Route.Broken == true (a broken route is
being repaired); (case iii) if Node.Dist == Route.Dist AND it is a
RREP (RREP with equal distance are forwarded) OR Route.Broken ==
true (a broken route is being repaired). For completeness, we
provide the following (optimized) pseudo-code.
(Node.SeqNum - Route.SeqNum > 0) OR
((Node.SeqNum == Route.SeqNum) AND
((Node.Dist < Route.Dist) OR
((Node.Dist == Route.Dist + 1) AND (Route.Broken == true)) OR
((Node.Dist == Route.Dist) AND
((RM is RREP) OR (Route.Broken == true)))))
5.2.2. Creating or Updating a Route Table Entry with New Routing
Information
The route table entry is populated with the following information:
1. the Route.Address is set to Node.Address,
2. the Route.SeqNum is set to the Node.SeqNum,
3. the Route.NextHopAddress is set to the node that transmitted this
DYMO RM packet (i.e., the IP.SourceAddress),
4. the Route.NextHopInterface is set to the interface that this DYMO
packet was received on,
5. if known, the Route.Dist is set to the Node.Dist,
6. if known, the Route.Prefix is set to the Node.Prefix.
Fields without known values are not populated with any value.
Previous timers for this route table entry are removed. A timer for
the minimum delete timeout (ROUTE_AGE_MIN) is set to
ROUTE_AGE_MIN_TIMEOUT. A timer to indicate a recently learned route
(ROUTE_NEW) is set to ROUTE_NEW_TIMEOUT. A timer for the maximum
delete timeout (ROUTE_AGE_MAX). ROUTE_AGE_MAX is set to
Node.AddTLV.MaxAge if included; otherwise, ROUTE_AGE_MAX is set to
ROUTE_AGE_MAX_TIMEOUT. The usage of these timers and others are
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described in Section 5.2.3.
At this point, a forwarding route should be installed. Afterward,
the route can be used to send any queued data packets and forward any
incoming data packets for Route.Address. This route also fulfills
any outstanding route discovery attempts for Node.Address.
5.2.3. Route Table Entry Timeouts
5.2.3.1. Minimum Delete Timeout (ROUTE_AGE_MIN)
When a DYMO router transmits a RM, other DYMO routers expect the
transmitting DYMO router to have a forwarding route to the RM
originator. After updating a route table entry, it should be
maintained for at least ROUTE_AGE_MIN. Failure to maintain the
information might result in lost messages/packets, or in the worst
case scenario several duplicate messages.
After the ROUTE_AGE_MIN timeout a route can safely be deleted.
5.2.3.2. Maximum Delete Timeout (ROUTE_AGE_MAX)
Sequence number information is time sensitive, and must be deleted
after a time in order to avoid conflicts due to reboots and
rollovers. When a DYMO router has lost its sequence number (e.g, due
to daemon reboot or node replacement) the DYMO router must wait until
routing information associated with that IP address and sequence
number are no longer maintained by other DYMO routers in the network
to ensure loop-free routing.
After the ROUTE_AGE_MAX timeout a route must be deleted. All
information about the route is deleted upon ROUTE_AGE_MAX timeout.
If a forwarding route exists it is also removed.
5.2.3.3. New Information Timeout (ROUTE_NEW)
As time progresses the likelihood that a route remains intact
decreases, if the network nodes are mobile. Maintaining and using
old routing information can lead to many DYMO messages and excess
route discovery delay.
After the ROUTE_NEW timeout if the route has not been used, a timer
for deleting the route (ROUTE_DELETE) is set to ROUTE_DELETE_TIMEOUT.
5.2.3.4. Recently Used Timeout (ROUTE_USED)
When a route is used to forward data packets, this timer is set to
expire after ROUTE_USED_TIMEOUT. This operation is also discussed in
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Section 5.5.2.
If a route has not been used recently, then a timer for ROUTE_DELETE
is set to ROUTE_DELETE_TIMEOUT.
5.2.3.5. Delete Information Timeout (ROUTE_DELETE)
As time progresses the likelihood that old routing information is
useful decreases, especially if the network nodes are mobile.
Therefore, old information should be deleted.
After the ROUTE_DELETE timeout, the routing table entry should be
deleted. If a forwarding route exists, it should also be removed.
5.3. Routing Messages
5.3.1. RREQ Creation
When a DYMO router creates a RREQ it SHOULD increment its OwnSeqNum
by one (1) according to the rules specified in Section 5.1.2.
Incrementing OwnSeqNum will ensure that all nodes with existing
routing information to consider this new information fresh. If the
sequence number is not incremented, certain DYMO routers might not
consider this information useful if they have superior information
already.
First, ThisNode adds the AddBlk.TargetNode.Address to the RREQ; the
IP.DestinationAddress for which a forwarding route does not exist.
If a previous value of the TargetNode.SeqNum is known (from a routing
table entry using longest-prefix matching), it SHOULD be placed in
TargetNode.AddTLV.SeqNum in all but the last RREQ attempt. If a
TargetNode.SeqNum is not included, it is assumed to be unknown by
processing nodes. This operation ensures that no intermediate DYMO
routers reply, and ensures that the TargetNode's DYMO router
increments its sequence number.
Similarly, if a previous value of the TargetNode.Dist is known, it
SHOULD be placed in TargetNode.AddTLV.Dist. Otherwise, the
TargetNode.AddTLV.Dist is not included and assumed unknown by
processing nodes.
Next, the node adds AddBlk.OrigNode.Address to the RM and the
OrigNode.AddTLV.SeqNum (OwnSeqNum) in an address block TLV.
The OrigNode.Address is the address of the DYMO router that is
initiating this route discovery. The OrigNode.Address must be a
routable IP address. If this DYMO router is performing route
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discovery on behalf of an attached node (i.e. the source of the data
packet causing this route discovery), the DYMO router MUST advertise
it's address and prefix that contain the source's address. This
information will be used by nodes to create a route toward the
OrigNode, enable delivery of a RREP, and eventually for data packets.
If OrigNode.Dist is included it is set to a number greater than zero
(0).
The MsgHdr.HopLimit should be set to MAX_HOPLIMIT, but may be set
smaller.
For RREQ, the MsgHdr.HopLimit may be set in accordance with an
expanding ring search as described in [RFC3561] to limit the RREQ
propagation to a subset of the network and possibly reduce route
discovery overhead.
The IP.DestinationAddress for RREQ is set to LL MANET ROUTERS.
5.3.2. RREP Creation
When the TargetNode's DYMO router creates a RREP, if the
TargetNode.SeqNum was not included in the RREQ it MUST increment its
OwnSeqNum by one (1) according to the rules specified in
Section 5.1.2.
If TargetNode.SeqNum is included in the RM and TargetNode.SeqNum -
OwnSeqNum < 0 (using signed 16-bit arithmetic), OwnSeqNum SHOULD be
incremented by one (1) according to the rules specified in
Section 5.1.2.
If TargetNode.SeqNum is included in the RM and TargetNode.SeqNum ==
OwnSeqNum (using signed 16-bit arithmetic) and Dist will not be
included in the RREP being generated, OwnSeqNum SHOULD be incremented
by one (1) according to the rules specified in Section 5.1.2.
If OwnSeqNum is not incremented the routing information might be
considered stale. In this case, the RREP would not reach the RREP
Target.
First, the AddBlk.TargetNode.Address is added to the RREP. The
TargetNode is the ultimate destination of this RREP; the RREQ
OrigNode.Address.
Next, AddBlk.OrigNode.Address is added to the RREP. The
AddBlk.OrigNode.Address must be a routable IP address. If the RREQ
TargetNode is this DYMO router, its address added to the RREP as the
OrigNode.Address. If the RREQ TargetNode is attached to this DYMO
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router, it MUST advertise its address and prefix that contain the
RREQ TargetNode.Address. The RREP OrigNode.AddTLV.SeqNum (OwnSeqNum)
must also added to the RREP.
Other AddTLVs in the RREP for the OrigNode and TargetNode SHOULD be
included and set accordingly. If OrigNode.Dist is included it is set
to a number greater than zero (0).
The MsgHdr.HopLimit is set to MAX_HOPLIMIT.
The IP.DestinationAddress for RREP is set to the IP address of the
Route.NextHopAddress for the route to the RREP TargetNode.
5.3.3. Intermediate DYMO Router RREP Creation
Sometimes a DYMO router other than the TargetNode's DYMO router (call
it an "intermediate DYMO router") has routing information that can
satisfy an incoming RREQ. An intermediate DYMO router can issue a
intermediate DYMO router RREP on behalf of the TargetNode's DYMO
router.
Before creating a intermediate DYMO router RREP, OwnSeqNum SHOULD be
incremented by one (1) according to the rules specified in
Section 5.1.2.
If OwnSeqNum is not incremented the routing information might be
considered stale by a processing DYMO router. In this case, the RREP
would not reach the RREP Target.
When an intermediate DYMO router originates a RREP in response to a
RREQ on behalf of the TargetNode's DYMO router, it sends the RREP to
the RREQ OrigNode with additional routing information (Address,
SeqNum, Prefix, Dist, etc.) about the RREQ TargetNode. Appending
additional routing information is described in Section 5.3.5.
The Intermediate DYMO router SHOULD also issue a RREP to the RREQ
TargetNode, so that the RREQ TargetNode receives routing information
on how to reach the RREQ OrigNode.
When an intermediate DYMO router creates this RREP, it sends a RREP
to the RREQ TargetNode with additional routing information (Address,
SeqNum, Dist, Prefix, etc.) about the RREQ OrigNode.
5.3.4. RM Processing
Before processing a RM, the DYMO router checks the IP.Destination to
ensure that it was sent to LL MANET ROUTERS.
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When a RM is received the MsgHdr.HopLimit is decremented by one (1).
For each address (except the TargetNode) in the RM that includes
AddTLV.Dist information, the AddTLV.Dist information is incremented
by at lease one (1).
Next, ThisNode checks whether AddBlk.OrigNode.Address is an address
handled by this DYMO router. If this node is the originating DYMO
router, the RM is dropped.
Next, ThisNode checks whether its routing table has an entry to the
AddBlk.OrigNode.Address using longest-prefix matching [RFC1812]. If
a route does not exist and the address is a unicast address, then the
new routing information is considered fresh and a new route table
entry is created and updated as described in Section 5.2.2. If a
route table entry does exists, the incoming routing information is
compared with the route table entry following the procedure described
in Section 5.2.1. If the incoming routing information is considered
superior, the route table entry is updated as described in
Section 5.2.2.
After processing the OrigNode's routing information, then each
address that is not the TargetNode should be considered for creating
and updating routes. Creating and updating routes to other nodes can
eliminate RREQ for those IP destinations, in the event that data
needs to be forwarded to the IP destination(s) in the near future.
For each of the additional addresses considered, if the address is a
unicast address and the routing table does not have a matching route
using longest-prefix matching, then a route is created and updated as
described in Section 5.2.2. If a route table entry exists, the
incoming routing information is compared with the route table entry
following the procedure described in Section 5.2.1. If the incoming
routing information is considered superior, the route table entry is
updated as described in Section 5.2.2.
If the routing information for an AdditionalNode.Address is not a
unicast address and considered superior, then it is removed from the
RM. Removing this information ensures that the information is not
propagated.
At this point, if the routing information for the OrigNode was not
superior then this RM should be discarded and no further processing
of this message is performed.
If the ThisNode is the DYMO router for the TargetNode and this RM is
a RREQ, then ThisNode responds with a RREP to the RREQ OrigNode (the
new RREP's TargetNode). Alternatively, to distribute routing
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information about ThisNode (the RREQ TargetNode) more widely,
ThisNode may optionally perform a RREQ; by issuing a RREQ with
ThisNode listed as the TargetNode, using the procedure in
Section 5.3.1. The procedure for issuing a new RREP is described in
Section 5.3.2. Note: it is important that when creating the RREP,
the RREP OrigNode.Address be the same as the RREQ TargetNode.Address,
if ThisNode is responsible for several addresses. At this point,
ThisNode need not perform any more operations for this RM.
If ThisNode is not the TargetNode, this RM is a RREQ, the RREQ
contains the TargetNode.AddTLV.SeqNum, and ThisNode has a forwarding
route to the TargetNode with a SeqNum where Route.TargetNode.SeqNum -
RREQ.TargetNode.AddTLV.SeqNum >= 0 (using signed 16-bit arithmetic);
then this node MAY respond with an intermediate DYMO router RREP.
The procedure for performing intermediate DYMO router RREP is
described in Section 5.3.3. At this point, ThisNode need not perform
any more operations for this RM.
After processing a RM or creating a new RM, a node can append
additional routing information to the RM, according to the procedure
described in Section 5.3.5. The additional routing information can
help reduce route discoveries at the expense of increased message
size.
For each address (except the TargetNode) in the RM that includes
AddTLV.Dist information, the AddTLV.Dist information is incremented
by a cost value. Advice regarding the cost value is not included in
this specification, it is left up to the implementation.
The updated distance value will be an measure in determining whether
the routing information is inferior or superior to known information
at other DYMO routers that process this RM.
If the resulting distance value for the OrigNode is greater than
65,535, the message is discarded. If the resulting distance value
for another node is greater than 65,535, the associated address and
its information are removed from the RM.
If this RM's MsgHdr.HopLimit is greater than or equal to one (1),
ThisNode is not the TargetNode, AND this RM is a RREQ, then the
current RM (altered by the procedure defined above) SHOULD be sent to
the LL MANET ROUTERS IP.DestinationAddress.
By sending the RM ThisNode is advertising that it will provide
routing for IP addresses contained in the outgoing RM based on the
information enclosed. ThisNode MAY choose not to send the RM, though
not resending this RM could decrease connectivity in the network or
result in a non-shortest distance path.
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Some examples of why ThisNode might choose to not send the RM are: if
ThisNode does not want to advertise routing for the contained IP
addresses because it is already congested; if ThisNode has already
issued nearly identical routing information (e.g. ThisNode had
recently issued a RM with nearly the same distance); or if ThisNode
is low on energy and does not want to expend energy for control
message sending or packet forwarding. This type of advanced behavior
is not defined in this specification.
If this RM's MsgHdr.HopLimit is greater than or equal to one (1),
ThisNode is not the TargetNode, AND this RM is a RREP, then the
current RM is sent to the Route.NextHopAddress for the RREP's
TargetNode.Address. If no forwarding route exists to Target.Address,
then a RERR is issued to the OrigNode of the RREP.
5.3.5. Adding Additional Routing Information to a RM
Appending routing information can alleviate route discovery attempts
to the nodes whose information is included, if other DYMO routers use
this information to update their routing tables.
DYMO routers can append routing information to a RM. This option
should be administratively configurable.
Prior to appending an address controlled by this DYMO router to a RM,
ThisNode MAY increment its OwnSeqNum as defined in Section 5.1.2. If
OwnSeqNum is not incremented the appended routing information might
not be considered fresh, when received by nodes with existing routing
information. Incrementation of the sequence number when appending
information to an RM in transit should be administratively
configurable.
If an address controlled by this DYMO router includes ThisNode.Dist,
it is set to a number greater than zero (0).
For added addresses not controlled by this DYMO router, Route.Dist
can be included if known. If Route.Dist is not known, it cannot be
included.
Additional information about the appended address(es) can also be
included (e.g. Prefix).
5.4. Route Discovery
When a source's DYMO router needs to forward a data packet and it
does not have a forwarding route to the IP.DestinationAddress, it
sends a RREQ (described in Section 5.3.1) to discover a route to the
particular destination (TargetNode).
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After issuing a RREQ, the OrigNode DYMO router waits for a route to
be created to the TargetNode. If a route is not created within
RREQ_WAIT_TIME, ThisNode may again try to discover a route by issuing
another RREQ using the procedure defined in Section 5.3.1.
To reduce congestion in a network, repeated attempts at route
discovery for a particular TargetNode should utilize an exponential
backoff.
For example, the first time a DYMO router issues a RREQ, it waits
RREQ_WAIT_TIME for a route to the TargetNode. If a route is not
found within that time, the DYMO router 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 by the source's DYMO
router. This buffer should have a fixed limited size
(BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES) and older data packets
SHOULD be discarded first.
Buffering of data packets may have positive or negative impact, and
therefore must be administratively configurable.
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 are dropped from the buffer and a
Destination Unreachable ICMP message should be delivered to the
source.
5.5. Route Maintenance
A RERR MUST be issued if a data packet is to be forwarded and it
cannot be delivered to the next hop because no forwarding route for
the IP.Destination exists; RERR generation is described in
Section 5.5.3.
Upon this condition, an ICMP Destination Unreachable message SHOULD
NOT be generated unless this router is responsible for the
IP.Destination and that IP.Destination is known to be unreachable.
In addition to inability to forward a data packet, a RERR SHOULD be
issued immediately after detecting a broken link of an forwarding
route to quickly notify DYMO routers that a link break occurred and
that certain routes are no longer available. If the route with the
broken link has not been used recently (indicated by ROUTE_USED), the
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RERR SHOULD NOT be generated.
5.5.1. Active Link Monitoring
Nodes MUST monitor next hop links on forwarding routes. This
monitoring can be accomplished by one or several mechanisms,
including:
o Link layer feedback
o Neighborhood discovery [I-D.ietf-manet-nhdp]
o Route timeout
o Other monitoring mechanisms or heuristics
Upon detecting a link break (or an unreachable next hop) ThisNode
must remove the affected forwarding routes (those with an unreachable
next hop). ThisNode also flags these routes as Broken. For each
broken route a timer for ROUTE_DELETE is set to ROUTE_DELETE_TIMEOUT.
5.5.2. Updating Route Lifetimes During Packet Forwarding
To avoid removing the forwarding route to reach the IP.SourceAddress,
a node SHOULD set a timeout (ROUTE_USED) to ROUTE_USED_TIMEOUT for
the route to the IP.SourceAddress upon receiving a data packet. If a
timer for ROUTE_DELETE is set, it is removed.
To avoid removing the forwarding route to the IP.DestinationAddress
that is being used, a node SHOULD set a timeout (ROUTE_USED) to
ROUTE_USED_TIMEOUT for the route to the IP.DestinationAddress upon
sending a data packet. If a timer for ROUTE_DELETE is set, it is
removed.
5.5.3. Route Error Generation
A RERR informs DYMO routers that a route to certain destinations is
not available through this node.
When creating a new RERR, the address of first UnreachableNode
(IP.DestinationAddress from a data packet or RREP.TargetNode.Address)
is inserted into an Address Block AddBlk.UnreachableNode.Address. If
a value for the UnreachableNode's SeqNum
(UnreachableNode.AddTLV.SeqNum) is known, it SHOULD be placed in the
RERR. The MsgHdr.HopLimit is set to MAX_HOPLIMIT.
Additional UnreachableNodes that require the same unavailable link
(routes with the same Route.NextHopAddress and
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Route.NextHopInterface) SHOULD be added to the RERR, as additional
AddBlk.UnreachableNode.Address. The SeqNum if known SHOULD also be
included. Appending UnreachableNode information notifies each
processing node of additional routes that are no longer available.
This option SHOULD be administratively configurable.
If SeqNum information is not known or not included in the RERR, all
nodes processing the RERR will assume their routing information
associated with the UnreachableNode is no longer valid and flags
those routes as broken.
The RERR is sent to the IP.DestinationAddress LL MANET ROUTERS.
Sending the RERR to the LL MANET ROUTERS address notifies nearby
nodes that might depend on the now broken link.
The packet or message that forced generation of this RERR is
discarded.
5.5.4. RERR Processing
Before processing a RERR, the DYMO router checks the IP.Destination
to ensure that it is addressed to LL MANET ROUTERS.
Upon reception of a RERR the MsgHdr.HopLimit is decremented by one
(1).
When a DYMO router processes a RERR, it processes each
UnreachableNode's information. The processing DYMO router removes
the forwarding route, sets the broken flag, and a timer for
ROUTE_DELETE is set to ROUTE_DELETE_TIMEOUT for each
UnreachableNode.Address found using longest prefix matching that meet
all of the following conditions:
1. The UnreachableNode.Address is a unicast address.
2. The Route.NextHopAddress is the same as the RERR
IP.SourceAddress.
3. The Route.NextHopInterface is the same as the interface on which
the RERR was received.
4. The Route.SeqNum is zero (0), unknown, OR the
UnreachableNode.SeqNum is zero (0), unknown, OR Route.SeqNum -
UnreachableNode.SeqNum <= 0 (using signed 16-bit arithmetic).
During processing if Route.SeqNum is zero (0) or unknown and
Unreachable.SeqNum exists in the RERR, then Route.SeqNum can be set
to Unreachable.SeqNum. Setting Route.SeqNum can reduce future RRER
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processing and forwarding.
Each UnreachableNode that did not result in a broken route is removed
from the RERR, since propagation of this information will not result
in any benefit. Any other information (AddTLVs) associated with the
removed address(es) is also removed.
After processing if Route.SeqNum is known and an Unreachable.SeqNum
is not included in the RERR, then Route.SeqNum (i.e.
Unreachable.SeqNum) can be added to the RERR. Including
Unreachable.SeqNum can reduce future RRER processing and forwarding.
If no UnreachableNode addresses remain in the RERR, no other
processing is required and the RERR is discarded.
If this RERR's MsgHdr.HopLimit is greater than one (1) and at least
one unreachable node address remains in the RERR, then the updated
RERR is sent to the IP.DestinationAddress LL MANET ROUTERS.
5.6. Unknown Message & TLV Types
If a message with an unknown type is received, the message is
discarded.
If a message contains TLVs of an unknown type, a node ignores these
during processing. The processing node can remove these TLVs from
any resulting transmitted messages. The behavior for unknown TLV
types should be administratively configurable.
5.7. Advertising Network Addresses
Any DYMO router advertises a network address by using a PREFIX_LENGTH
TLV [I-D.ietf-manet-packetbb]. Any nodes (other than the advertising
DYMO router) within the advertised prefix SHOULD NOT participate in
the DYMO protocol directly and these nodes MUST be reachable by
forwarding packets to the DYMO router advertising connectivity.
Nodes other than the advertising DYMO router that do participate in
DYMO must forward the DYMO control packets to the advertising DYMO
router. For example, A.B.C.1 with a prefix length of 24 indicates
all nodes with the matching A.B.C.X are reachable through the DYMO
router with address A.B.C.1.
5.8. Simple Internet Attachment and Gatewaying
Simple Internet attachment consists of a stub network of MANET
routers connected to the Internet via a single Internet gateway node.
DYMO can operate with multiple gateways, but such behavior is not
specified in this document.
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The gateway is responsible for responding to RREQs for TargetNodes
outside its configured DYMO prefix, as well as delivering packets to
destinations outside the MANET.
/--------------------------\
/ Internet \
\ /
\------------+-------------/
Gateway's |
Advertised | A.B.C.X/24
Prefix |
+-----+-----+
| DYMO |
/------| Internet |--------\
/ | Gateway | \
/ | A.B.C.1 | \
| +-----------+ |
| DYMO Region |
| |
| +--------------+ |
| | DYMO Router | |
| | A.B.C.2 | |
| +--------------+ |
| +--------------+ |
| | DYMO Router | |
| | A.B.C.3 | |
\ +--------------+ /
\ /
\---------------------------/
Figure 7: Simple Internet Attachment Example
DYMO routers wishing to be reachable from nodes in the Internet MUST
have IP addresses within the gateway's configured and advertised
prefix. 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.
When DYMO router within the MANET want to send messages to nodes in
the Internet, they simply issue RREQ for those
IP.DestinationAddresses. The gateway is responsible for responding
to RREQ on behalf of the Internet destinations and maintaining their
associated sequence number.
For an Internet gateway and other DYMO routers that maintain the
sequence number on behalf of other nodes, these routers must be
administratively configurable to know the IP addresses for which they
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must generate DYMO messages and maintain OwnSeqNum.
5.9. Multiple Interfaces
DYMO may be used with multiple interfaces; therefore, the particular
interface over which packets arrive must be known whenever a packet
is received. Whenever a new route is created, the interface through
which the Route.Address can be reached is also recorded in the route
table entry.
When multiple interfaces are available, a node transmitting a packet
with IP.DestinationAddress set to LL MANET ROUTERS SHOULD send the
packet on all interfaces that have been configured for DYMO
operation.
Similarly, DYMO routers should subscribe to LL MANET ROUTERS on all
their DYMO interfaces.
5.10. Packet/Message Generation Limits
To avoid congestion, a node's rate of packet/message generation
should be limited. The rate and algorithm for limiting messages is
left to the implementor and should be administratively configurable.
Messages should be discarded in the following order of preferences
RREQ, RREP, and finally RERR.
6. Configuration Parameters and Other Administrative Options
Suggested Parameter Values
+------------------------------+------------------------+
| Name | Value |
+------------------------------+------------------------+
| MAX_HOPLIMIT | 10 hops |
| NET_TRAVERSAL_TIME | 1000 milliseconds |
| ROUTE_TIMEOUT | 5 seconds |
| ROUTE_AGE_MIN_TIMEOUT | NET_TRAVERSAL_TIME |
| ROUTE_AGE_MAX_TIMEOUT | 60 seconds |
| ROUTE_NEW_TIMEOUT | ROUTE_TIMEOUT |
| ROUTE_USED_TIMEOUT | ROUTE_TIMEOUT |
| ROUTE_DELETE_TIMEOUT | 2 * ROUTE_TIMEOUT |
| ROUTE_RREQ_WAIT_TIME | 2 * NET_TRAVERSAL_TIME |
| RREQ_TRIES | 3 tries |
| UNICAST_MESSAGE_SENT_TIMEOUT | 1 second |
+------------------------------+------------------------+
Table 2
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These suggested values work well for small and medium well connected
networks with infrequent topology changes. These parameters should
be administratively configurable for the network where DYMO is used.
Ideally, for networks with frequent topology changes the DYMO
parameters should be adjusted using either experimentally determined
values or dynamic adaptation. For example, in networks with
infrequent topology changes ROUTE_USED_TIMEOUT may be set to a much
larger value.
In addition to the parameters above several administrative options
exist. The following table enumerates several of the options and
suggested values.
Suggested Options Settings
+-------------------------------------+----------------------------+
| Name | Value |
+-------------------------------------+----------------------------+
| RESPONSIBLE_ADDRESSES | Self or Prefix |
| DYMO_INTERFACES | User Specified |
| INCLUDE_INFORMATION | Yes-SeqNum,Dist,Prefix |
| APPEND_ADDRESS | Yes - RREQ & RREP |
| APPEND_OWN_ADDRESS_INCREMENT_SEQNUM | Yes for RREQ |
| GENERATE_RERR_IMMEDIATELY | No |
| RERR_INCLUDE_ALL_UNREACHABLES | Yes |
| UNKNOWN_TYPE_HANDLING | Ignore |
| BUFFER_SIZE_PACKETS | 50 packets |
| BUFFER_SIZE_BYTES | 1500 * BUFFER_SIZE_PACKETS |
+-------------------------------------+----------------------------+
Table 3
7. IANA Considerations
DYMO requires a UDP port number to carry protocol packets - MANET
[I-D.ietf-manet-iana]. DYMO also requires the link-local multicast
address LL MANET ROUTERS [I-D.ietf-manet-iana].
This section specifies several messages types, message tlv-types, and
address tlv-types.
Future types will be allocated using standard actions as described in
[RFC2434].
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7.1. DYMO Message Type Specification
DYMO Message Types
+------------------------+----------+
| Name | Type |
+------------------------+----------+
| Route Request (RREQ) | 10 - TBD |
| Route Reply (RREP) | 11 - TBD |
| Route Error (RERR) | 12 - TBD |
+------------------------+----------+
Table 4
7.2. Packet and Message TLV Type Specification
Packet TLV Types
+-------------------+------+--------+-------------------------------+
| Name | Type | Length | Value |
+-------------------+------+--------+-------------------------------+
| Unicast Response | 10 - | 0 | Indicates to the processing |
| Request | TBD | | node that the previous hop |
| | | | (IP.SourceAddress) expects a |
| | | | unicast message within |
| | | | UNICAST_MESSAGE_SENT_TIMEOUT. |
| | | | Any unicast packet will serve |
| | | | this purpose, and it MAY be |
| | | | an ICMP REPLY message. If a |
| | | | message is not sent, then the |
| | | | previous hop may assume that |
| | | | the link is unidirectional |
| | | | and may blacklist the link to |
| | | | this node. |
+-------------------+------+--------+-------------------------------+
Table 5
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7.3. Address Block TLV Specification
Address Block TLV Types
+----------------+------+---------+---------------------------------+
| Name | Type | Length | Value |
+----------------+------+---------+---------------------------------+
| DYMOSeqNum | 10 - | 16 bits | The DYMO sequence num |
| | TBD | (2 | associated with this address. |
| | | bytes) | The sequence number may be the |
| | | | last known sequence number. |
| Distance | 11 - | up to | A metric of the distance |
| | TBD | 16 bits | traversed by the information |
| | | (2 | associated with this address. |
| | | bytes) | |
| MaxAge | 12 - | | The maximum amount of time that |
| | TBD | | information can be maintained |
| | | | before being deleted. This TLV |
| | | | conforms to |
| | | | [I-D.ietf-manet-timetlv] |
| | | | VALIDITY_TIME TLV, except that |
| | | | the TLV is attached to |
| | | | addresses. |
+----------------+------+---------+---------------------------------+
Table 6
8. Security Considerations
Currently, DYMO does not specify any special security measures.
In situations where confidentiality o DYMO messages is important,
traditional cryptographic techniques can be applied.
Securing routing information integrity will likely require DYMO
routers to authenticate DYMO messages upon reception. Also, since
routing information is distributed hop-by-hop, DYMO routers will also
likely need to authenticate the source of the routing information,
the source's DYMO router.
Note that is important that any confidentiality and integrity
algorithms used permit multiple receivers to process the message,
since all DYMO messaging is multicast.
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9. Acknowledgments
DYMO is a descendant of the design of previous MANET reactive
protocols, especially AODV [RFC3561] and DSR [RFC4728]. Changes to
previous MANET reactive protocols stem from research and
implementation experiences. Thanks to Elizabeth Belding-Royer for
her long time authorship of DYMO. Additional thanks to Luke Klein-
Berndt, Pedro Ruiz, Fransisco Ros, Koojana Kuladinithi, Ramon
Caceres, Thomas Clausen, Christopher Dearlove, Seung Yi, Romain
Thouvenin, Tronje Krop, Henner Jakob, Alexandru Petrescu, Christoph
Sommer, Cong Yuan, and Lars Kristensen for reviewing of DYMO, as well
as several specification suggestions.
10. References
10.1. Normative References
[I-D.ietf-manet-iana]
Chakeres, I., "IANA Allocations for Mobile Ad hoc Network
(MANET) Protocols", draft-ietf-manet-iana-06 (work in
progress), October 2007.
[I-D.ietf-manet-packetbb]
Clausen, T., "Generalized MANET Packet/Message Format",
draft-ietf-manet-packetbb-10 (work in progress),
October 2007.
[I-D.ietf-manet-timetlv]
Clausen, T. and C. Dearlove, "Representing multi-value
time in MANETs", draft-ietf-manet-timetlv-02 (work in
progress), August 2007.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
10.2. Informative References
[I-D.ietf-manet-jitter]
Clausen, T., "Jitter considerations in MANETs",
draft-ietf-manet-jitter-02 (work in progress),
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Internet-Draft DYMO November 2007
August 2007.
[I-D.ietf-manet-nhdp]
Clausen, T., "MANET Neighborhood Discovery Protocol
(NHDP)", draft-ietf-manet-nhdp-04 (work in progress),
July 2007.
[Perkins99]
Perkins, C. and E. Belding-Royer, "Ad hoc On-Demand
Distance Vector (AODV) Routing", Proceedings of the 2nd
IEEE Workshop on Mobile Computing Systems and
Applications, New Orleans, LA, pp. 90-100,
February 1999.
[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
July 2003.
[RFC4728] Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source
Routing Protocol (DSR) for Mobile Ad Hoc Networks for
IPv4", RFC 4728, February 2007.
Authors' Addresses
Ian D Chakeres
Motorola
Bangalore
India
Email: ian.chakeres@gmail.com
URI: http://www.ianchak.com/
Charles E. Perkins
Palo Alto Systems Research Center
975 Page Mill Road, Suite 200
Palo Alto, CA 94304-1003
USA
Phone: +1-650-496-4402
Fax: +1-650-739-0779
Email: charles.perkins@nokia.com
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