Mobile Ad hoc Networks Working I. Chakeres
Group CenGen
Internet-Draft C. Perkins
Intended status: Standards Track WiChorus
Expires: September 9, 2009 March 8, 2009
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-17
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Abstract
The Dynamic MANET On-demand (DYMO) routing protocol is intended for
use by mobile routers in wireless, multihop networks. DYMO
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determines unicast routes among DYMO routers within the network in an
on-demand fashion, offering improved convergence in dynamic
topologies.
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 Packet and Message Structure . . . . . . . 9
4.2.2. Routing Messages (RM) - RREQ & RREP . . . . . . . . . 10
4.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 12
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 . . . . . . . 15
5.2.2. Creating or Updating a Route Table Entry with
Received Superior Routing Information . . . . . . . . 17
5.2.3. Route Table Entry Timeouts . . . . . . . . . . . . . . 18
5.3. Routing Messages . . . . . . . . . . . . . . . . . . . . . 18
5.3.1. RREQ Creation . . . . . . . . . . . . . . . . . . . . 18
5.3.2. RREP Creation . . . . . . . . . . . . . . . . . . . . 19
5.3.3. Intermediate DYMO Router RREP Creation . . . . . . . . 20
5.3.4. RM Processing . . . . . . . . . . . . . . . . . . . . 21
5.3.5. Adding Additional Routing Information to a RM . . . . 24
5.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 25
5.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 26
5.5.1. Active Link Monitoring . . . . . . . . . . . . . . . . 26
5.5.2. Updating Route Lifetimes During Packet Forwarding . . 26
5.5.3. RERR Generation . . . . . . . . . . . . . . . . . . . 27
5.5.4. RERR Processing . . . . . . . . . . . . . . . . . . . 28
5.6. DYMO Identifier (DID) . . . . . . . . . . . . . . . . . . 29
5.7. Unknown Message & TLV Types . . . . . . . . . . . . . . . 29
5.8. Advertising Network Addresses . . . . . . . . . . . . . . 30
5.9. Simple Internet Attachment . . . . . . . . . . . . . . . . 30
5.10. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 31
5.11. DYMO Control Packet/Message Generation Limits . . . . . . 31
6. Configuration Parameters and Other Administrative Options . . 32
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
7.1. DYMO Message Type Specification . . . . . . . . . . . . . 33
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7.2. Packet and Message TLV Type Specification . . . . . . . . 33
7.3. Address Block TLV Specification . . . . . . . . . . . . . 34
8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.1. Normative References . . . . . . . . . . . . . . . . . . . 36
10.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
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1. Overview
The Dynamic MANET On-demand (DYMO) routing protocol enables reactive,
multihop unicast routing among participating DYMO routers. The basic
operations of the DYMO protocol are route discovery and route
maintenance.
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
creates 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.
Route maintenance consists of two operations. 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 routers over which traffic is flowing.
When a data packet is received for forwarding and 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 route to that particular
destination is invalid or missing. When the source's DYMO router
receives the RERR, it deletes the route. If the source's DYMO router
later receives a packet for forwarding to the same destination, it
will need to perform route discovery again for that destination.
DYMO uses sequence numbers to ensure loop freedom [Perkins99].
Sequence numbers enable DYMO routers to determine the temporal 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 (MANETs). DYMO handles a wide variety of mobility
patterns by dynamically determining routes on-demand. DYMO also
handles a wide variety of traffic patterns. In networks with a large
number of routers, DYMO is best suited for sparse traffic scenarios
where routers forward packets to with only a small portion of the
other DYMO routers, due to the reactive nature of route discovery and
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route maintenance.
DYMO is applicable to memory constrained devices, since very little
routing state is maintained in each DYMO router. Only routing
information related to active sources and destinations is maintained,
in contrast to most other more proactive routing protocols that
require routing information to all routers within the routing region
be maintained.
DYMO supports routers with multiple interfaces participating in the
MANET. DYMO routers can also perform routing on behalf of other
nodes, attached via participating or non-participating interfaces.
DYMO routers perform route discovery to find a route to a particular
destination. Therefore, DYMO routers MUST be configured to initiate
route discovery on behalf of certain sources and find routes to
certain destinations. When DYMO is the only protocol interacting
with the forwarding table, DYMO MAY be configured to perform route
discovery for all unknown unicast destinations.
DYMO MUST only utilizes bidirectional links. In the case of possible
unidirectional links, either blacklists ( see Section 7.2) or other
means (e.g. adjacency establishment with only neighboring routers
that have bidirectional communication 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. For operation
at other layers DYMO's routing algorithm likely will not need to
change. Although, modification of the packet/message format may be
required.
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 [RFC2119].
Additionally, this document uses some terminology from
[I-D.ietf-manet-packetbb].
This document defines the following terminology:
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Adjacency
A relationship formed between selected bi-directional neighboring
routers for the purpose of exchanging routing information. Not
every pair of neighboring routers become adjacent. Neighboring
routers may form an adjacency based several different pieces of
information or protocols; for example, exchange of DYMO routing
messages, other protocols (e.g. NDP [RFC4861] or NHDP
[I-D.ietf-manet-nhdp]), or manual configuration.
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.
DYMO Identifier (DID)
A DID is maintained by each DYMO routing protocol instance
(ThisNode.DID), and the default value is zero (0). Each routing
message is tagged with its associated DID (MsgTLV.DID), unless
zero (0). Upon receipt of DYMO protocol message a DYMO routing
protocol instance SHOULD only process messages with a matching DID
value.
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
temporal 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.
Multihop-capable Unicast IP Address
A multihop-capable unicast IP address is a unicast IP address that
when put into the IP.SoureAddress or IP.DestinationAddress field
is scoped sufficiently to be forwarded by a router. For example,
site-scoped or globally-scoped unicast IP addresses.
Originating Node (OrigNode)
The originating node is the source, its DYMO router creates a DYMO
control message on its behalf in an effort to disseminate some
routing information. The originating node is also referred to as
a particular message's originator.
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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.
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.
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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.
Route.SeqNum
The DYMO SeqNum associated with this routing information.
Route.NextHopAddress
The IP address of the adjacent DYMO router on the path toward the
Route.Address.
Route.NextHopInterface
The interface used to send packets toward the Route.Address.
Route.Forwarding
A flag indicating whether this Route can be used for forwarding
data packets. This flag MAY be provided for management and
monitoring.
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 field is optional:
Route.Dist
A metric indicating the distance traversed before reaching the
Route.Address node.
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
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.
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+----------------------------+-------------------+
| 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 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
[I-D.ietf-manet-iana] unless otherwise stated. Therefore, all DYMO
routers SHOULD subscribe to LL-MANET-ROUTERS [I-D.ietf-manet-iana]
for receiving control packets. Note that multicast packets may be
sent via unicast. For example, this may occur for certain link-types
(non broadcast mediums), improved robustness, or manually configured
router adjacency.
Unicast DYMO messages (e.g. RREP) unless otherwise 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 all packets containing DYMO
messages is set to 255. If a packet is received with a value other
than 255, it is discarded. This mechanism helps to ensures packets
have not passed through any intermediate routers, and it is known as
GTSM [RFC5082].
The length of an IP address (32 bits for IPv4 and 128 bits for IPv6)
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 addresses contained in the payload use IPv6
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addresses of the same length. In the case of mixed IPv6 and IPv4
addresses, please use the methods specified in
[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 if aggregation does occur 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 using jitter [RFC5148].
DYMO control packets SHOULD be given priority queue and channel
access.
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 multicast RREQ the
IP.DestinationAddress is set to LL-MANET ROUTERS
[I-D.ietf-manet-iana]. For unicast RREQ and RREP the
IP.DestinationAddress is set to the NextHopAddress toward the RREP
TargetNode.
UDP.DestinationPort
By default, the UDP destination port is set to MANET
[I-D.ietf-manet-iana].
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MsgHdr.HopLimit
The remaining number of hops this message is allowed to traverse.
AddBlk.TargetNode.Address
The IP address of the message TargetNode. In a RREQ the
TargetNode is the destination address for which route discovery is
being performed. In a RREP the TargetNode is the RREQ OrigNode
address. The TargetNode address is the first address in a routing
message.
AddBlk.OrigNode.Address
The IP address of the originator and its associated prefix length.
In a RREQ the OrigNode is the source's address and prefix. In a
RREP the OrigNode is the RREQ TargetNode's address and prefix 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 include its prefix. Each AdditionalNode.Address MUST also
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.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP TTL/HopLimit = 255 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = MANET |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RREQ-type |0|1|0|0|0|0|0|0| msg-size=23 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-hoplimit |
+-+-+-+-+-+-+-+-+
Message TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-tlv-block-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Number Addrs=2 |1|0|0|0|0| Rsv | HeadLength=3 | Head :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Head (cont) | Target.Tail | Orig.Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| tlv-block-size=6 |DYMOSeqNum-type|0|1|0|1|0|0|Rsv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=1 | tlv-length=2 | Orig.SeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
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.
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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
For multicast RERR messages, The IP address is set to LL-MANET-
ROUTERS [I-D.ietf-manet-iana]. For unicast RERR messages, The IP
address is set to the NextHopAddress.
UDP.DestinationPort
By default, 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 and its associated prefix
length. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.TTL/HopLimit = 255 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = MANET |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RERR-type |0|1|0|0|0|0|0|0| msg-size=15 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-hoplimit |
+-+-+-+-+-+-+-+-+
Message TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-tlv-block-size=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Number Addrs=1 |0|0|0|0|0| Rsv |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UnreachableNode.Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Body - Address Block TLV Block
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
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 SHOULD be set to one (1) incremented.
5.1.4. Actions After OwnSeqNum Loss
A DYMO router SHOULD maintain its sequence number in persistent
storage.
If a DYMO router's OwnSeqNum is lost, it MUST take certain actions to
avoid creating routing loops. To prevent this possibility after
OwnSeqNum loss a DYMO router 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 DYMO router 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 DYMO router MUST generate a RERR message indicating that
this route is not available and reset its waiting timeout. At the
end of the waiting period the DYMO router sets its OwnSeqNum to one
(1) and begins participating.
The longest a node need wait is ROUTE_SEQNUM_AGE_MAX_TIMEOUT. At the
end of the maximum waiting period a node SHOULD set its OwnSeqNum to
one (1) and begins participating.
5.2. DYMO Routing Table Operations
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/
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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)
using signed 16-bit arithmetic
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))))
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 signed 16-bit 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
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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
using signed 16-bit arithmetic
((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 Received Superior
Routing Information
The route table entry is populated with the following information:
1. the Route.Address is set to Node.Address,
2. the Route.Prefix is set to the Node.Prefix.
3. the Route.SeqNum is set to the Node.SeqNum,
4. the Route.NextHopAddress is set to the node that transmitted this
DYMO RM packet (i.e., the IP.SourceAddress),
5. the Route.NextHopInterface is set to the interface that this DYMO
packet was received on,
6. if known, the Route.Dist is set to the Node.Dist,
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 for the maximum delete timeout
(ROUTE_SEQNUM_AGE_MAX). ROUTE_SEQNUM_AGE_MAX is set to
Node.AddTLV.VALIDITY_TIME [I-D.ietf-manet-timetlv] if included;
otherwise, ROUTE_SEQNUM_AGE_MAX is set to
ROUTE_SEQNUM_AGE_MAX_TIMEOUT. The usage of these timers and others
are described in Section 5.2.3.
At this point, a forwarding route should be created and the
Route.Forwarding flag set. 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.
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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 Sequence Number Delete Timeout (ROUTE_SEQNUM_AGE_MAX)
Sequence number information is time sensitive, and MUST be deleted
after a time in order to ensure loop-free routing.
After the ROUTE_AGE_MAX timeout a route's sequence number information
MUST be discarded.
5.2.3.3. 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
Section 5.5.2.
If a route has not been used recently, then a timer for ROUTE_DELETE
is set to ROUTE_DELETE_TIMEOUT.
5.2.3.4. 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 be removed and the
Route.Forwarding flag unset.
5.3. Routing Messages
5.3.1. RREQ Creation
Before 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 will consider this new information superior to
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existing routing table information. If the sequence number is not
incremented, certain DYMO routers might not consider this information
superior, if they have existing better routing information already.
First, ThisNode adds the AddBlk.TargetNode.Address to the RREQ; the
unicast IP Destination Address 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.
Next, the node adds AddBlk.OrigNode.Address, its prefix, and the
OrigNode.AddTLV.SeqNum (OwnSeqNum) to the RM.
The OrigNode.Address is the address of the source for which this DYMO
router is initiating this route discovery. The OrigNode.Address MUST
be a unicast IP address. This information will be used by nodes to
create a route toward the OrigNode, enabling delivery of a RREP, and
eventually used for proper forwarding of data packets.
If OrigNode.Dist is included it is set to a number greater than zero
(0).
The MsgHdr.HopLimit SHOULD be set to MSG_HOPLIMIT.
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 local network and possibly reduce
route discovery overhead.
The IP.DestinationAddress for multicast RREQ is set to LL-MANET-
ROUTERS. The IP.DestinationAddress for unicast RREQ is set to the
NextHopAddress.
Each DYMO routing protocol message SHOULD contain ThisNode.DID's
value in a message TLV (MsgTLV.DID). If ThisNode.DID value is zero
(0) it MAY be omitted.
5.3.2. RREP Creation
First, the AddBlk.TargetNode.Address is added to the RREP. The
TargetNode is the ultimate destination of this RREP; the RREQ
OrigNode.Address.
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Next, AddBlk.OrigNode.Address and prefix are added to the RREP. The
AddBlk.OrigNode.Address is the RREQ TargetNode.Address. The
AddBlk.OrigNode.Address MUST be a unicast IP address. ThisNode
SHOULD advertise the largest known prefix containing
AddBlk.OrigNode.Address.
When the TargetNode's DYMO router creates a RREP, if the
TargetNode.SeqNum was not included in the RREQ, ThisNode 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 might not reach the RREP
Target.
After any of the sequence number operations above, 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) and less than 65,535. The Distance
value will influence judgment of the routing information
(Section 5.2.1) against known information at other DYMO routers that
process this RM.
The MsgHdr.HopLimit is set to MSG_HOPLIMIT.
The IP.DestinationAddress for RREP is set to the IP address of the
Route.NextHopAddress for the route to the RREP TargetNode.
Each DYMO routing protocol message SHOULD contain ThisNode.DID's
value in a message TLV (MsgTLV.DID). If ThisNode.DID value is zero
(0) it MAY be omitted.
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
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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 about
ThisNode might be considered stale by a processing DYMO router. In
this case, the RREP would not reach the RREP TargetNode.
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,
Prefix, SeqNum, 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,
Prefix, SeqNum, Dist, etc.) about the RREQ OrigNode.
5.3.4. RM Processing
First, ThisNode decides whether to process this message. If the
message contains a MsgTLV.DID it SHOULD match ThisNode.DID's value.
If the message does not contain a MsgTLV.DID it is assumed to be zero
(0) and SHOULD be discarded if ThisNode.DID's value is not zero (0).
Next, ThisNode MAY selectively process messages based upon
information in the message. ThisNode SHOULD only process messages
from adjacent DYMO routers. If ThisNode chooses not to process this
message, the message is discarded and further processing stopped.
ThisNode checks if the AddBlk.OrigNode.Address is a valid multihop-
capable (e.g. site or global scope) unicast IP address. If the
address is not a valid unicast IP address, the messages is discarded
and further processing stopped.
ThisNode also 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.
ThisNode checks if the AddBlk.TargetNode.Address is a valid multihop-
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capable unicast IP address. If the address is not a valid unicast IP
address, the messages is discarded and further processing stopped.
Next, ThisNode checks whether its routing table has an entry to the
AddBlk.OrigNode.Address using longest-prefix matching [RFC1812]. If
a route with a valid Route.SeqNum does not exist, 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 and it has a valid Route.SeqNum, 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.
For each address (except the TargetNode) in the RM that includes
AddTLV.Dist information, the AddTLV.Dist information MAY be
incremented. The updated Distance value will influence judgment of
the routing information (Section 5.2.1).
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.
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) now or in the near
future.
For each of the additional addresses considered, ThisNode first
checks the that the address is a multihop-capable unicast IP address.
If the address is not a unicast IP address, the address and all
related information MUST be removed.
If the routing table does not have a matching route with a valid
Route.SeqNum for this additional address using longest-prefix
matching exists, then a route is created and updated as described in
Section 5.2.2. If a route table entry exists with a valid
Route.SeqNum, 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
considered superior, then it is removed from the RM. Removing this
information ensures that the information is not propagated.
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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 SHOULD be performed.
If the ThisNode is the DYMO router responsible for the TargetNode and
this RM is a RREQ, then ThisNode responds with a RREP to the RREQ
OrigNode (the new RREP's TargetNode). The procedure for issuing a
new RREP is described in Section 5.3.2. At this point, ThisNode need
not perform any more operations for this RM.
Alternatively, ThisNode MAY choose to distribute routing information
about ThisNode (the RREQ TargetNode) more widely, ThisNode MAY
optionally perform a route discovery; by issuing a RREQ with ThisNode
listed as the TargetNode, using the procedure in Section 5.3.1. At
this point, ThisNode need not perform any more operations for the
original 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. If an intermediate DYMO router RREP is
sent, ThisNode need not perform any more operations for the original
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 at least one (1). The updated Distance value will influence
judgment of the routing information (Section 5.2.1) against 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.
Next, the MsgHdr.HopLimit is decremented by one (1). 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
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IP.DestinationAddress LL-MANET-ROUTERS [I-D.ietf-manet-iana]. If the
RREQ is unicast, the IP.DestinationAddress is set to the
NextHopAddress.
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 SHOULD be issued to the OrigNode of the RREP.
By sending the updated 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.
Some examples of why ThisNode might choose to not re-issue a RM are:
if ThisNode does not want to advertise routing for the contained IP
addresses because it is already heavily loaded; 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.
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 or intelligently controlled.o
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 superior, 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 or intelligently controlled.
If an address controlled by this DYMO router includes ThisNode.Dist,
it is set to a number greater than zero (0).
For added addresses (and their prefixes) not controlled by this DYMO
router, Route.Dist can be included if known. If Route.Dist is not
known, it MUST NOT be included.
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MaxAge information about the appended address(es) MUST be included.
Additional information (e.g. SeqNum and Dist) about any appended
address(es) SHOULD be included.
Note that, the routing information about the TargetNode MUST NOT be
added. Also, duplicate address entries SHOULD NOT be added.
Instead, only the best routing information (Section 5.2.1) for a
particular address SHOULD be included.
5.4. Route Discovery
When a source's DYMO router needs to forward a data packet on behalf
of an attached node and it does not have a forwarding route to the
data packet's unicast IP destination address, ThisNode sends a RREQ
(described in Section 5.3.1) to discover a route to the particular
destination (TargetNode).
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 again.
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 can have both positive and negative
effects, and therefore buffer settings SHOULD be administratively
configurable or intelligently controlled.
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
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Destination Unreachable ICMP message should be delivered to the
source.
5.5. Route Maintenance
A RERR SHOULD 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.DestinationAddress 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.DestinationAddress and that IP.DestinationAddress 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
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 determining that a link is broken or the next-hop is
unreachable, ThisNode MUST remove the affected forwarding routes
(those with an unreachable next-hop) and unset the Route.Forwarding
flag. ThisNode also flags the associated routes in DYMO's routing
table 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,
ThisNode SHOULD set a timeout (ROUTE_USED) to ROUTE_USED_TIMEOUT for
the route to the IP.SourceAddress upon receiving a data packet. If a
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timer for ROUTE_DELETE is set, it is removed.
To avoid removing the forwarding route to the IP.DestinationAddress
that is being used, ThisNode 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. RERR Generation
A RERR informs DYMO routers that a route to certain destinations is
not available through ThisNode.
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 prefix is known for the UnreachableNode.Address, it SHOULD be
included. Otherwise, the UnreachableNode.Address assumed to be a
host address with a full length prefix. 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
MSG_HOPLIMIT.
Additional UnreachableNodes that require the same unavailable link
(routes with the same Route.NextHopAddress and
Route.NextHopInterface) SHOULD be added to the RERR, as additional
AddBlk.UnreachableNode.Address entries with their associated prefix.
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 or intelligently controlled.
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 flag those
routes as broken.
Each DYMO routing protocol message SHOULD contain ThisNode.DID's
value in a message TLV (MsgTLV.DID). If ThisNode.DID value is zero
(0) it MAY be omitted.
A multicast RERR is sent to the IP.DestinationAddress LL-MANET-
ROUTERS [I-D.ietf-manet-iana]. Sending the RERR to the LL-MANET-
ROUTERS address notifies all nearby DYMO routers that might depend on
the now broken link. If the RERR is unicast, the
IP.DestinationAddress is set to the NextHopAddress.
At this point, the packet or message that forced generation of this
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RERR SHOULD be discarded.
5.5.4. RERR Processing
First, ThisNode decides whether to process this message. If the
message contains a MsgTLV.DID it SHOULD match ThisNode.DID's value.
If the message does not contain a MsgTLV.DID it is assumed to be zero
(0) and SHOULD be discarded if ThisNode.DID's value is not zero (0).
Next, ThisNode MAY selectively process messages based upon
information in the message. ThisNode MAY choose to only process
messages from adjacent DYMO routers. If ThisNode chooses not to
process this message, the message is discarded and further processing
stopped.
When a DYMO router processes a RERR, it processes each
UnreachableNode's information. The processing DYMO router removes
the forwarding route, unsets the Route.Forwarding flag, sets the
Route.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 multihop-capable unicast IP
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
UnreachableNode.SeqNum exists in the RERR, then Route.SeqNum MAY be
set to UnreachableNode.SeqNum. Setting Route.SeqNum can reduce
future RRER 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.
Each UnreachableNode that did result in a broken route SHOULD remain
in the RERR.
If any UnreachableNode was removed, all other information (AddTLVs)
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associated with the removed address(es) MUST also removed.
After processing if Route.SeqNum is known and an
UnreachableNode.SeqNum is not included in the RERR, then Route.SeqNum
(i.e. UnreachableNode.SeqNum) MAY be added to the RERR. Including
UnreachableNode.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 processing continues, the MsgHdr.HopLimit is decremented by one
(1). Further, if this RERR's new MsgHdr.HopLimit is greater than one
(1) and at least one unreachable node address remains in the RERR,
then the updated RERR SHOULD be sent.
A multicast RERR is sent to the IP.DestinationAddress LL-MANET-
ROUTERS [I-D.ietf-manet-iana]. If the RERR is unicast, the
IP.DestinationAddress is set to the NextHopAddress.
5.6. DYMO Identifier (DID)
Each DYMO routing protocol instance MUST have an associated DYMO
Identifier (DID). The default value is zero (0). The DID value
should be administratively configured.
Each DYMO routing protocol message sent SHOULD contain its associated
DID in a message TLV. If the DID value is zero (0) it MAY be
omitted.
Upon receipt of DYMO protocol message a DYMO routing protocol
instance SHOULD only process messages with a DID (MsgTLV.DID) value
matching its own DID (ThisNode.DID).
The DID allows multiple DYMO routing protocol instances to operate
over the same links and same node independently.
The DID fulfills a function similar to OSPF Instance ID [RFC2740]
[I-D.ietf-ospf-multi-instance], OSPF Area ID [RFC2328] [RFC2740],
and/or the MANET_ID TLV [I-D.chakeres-manet-manetid].
5.7. Unknown Message & TLV Types
If a message with an unknown type is received, the message is
discarded.
For processing of messages that contain unknown TLV types, operation
should be administratively controlled.
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5.8. Advertising Network Addresses
DYMO routers advertise specify the prefix length for each advertised
address. Any nodes (other than the advertising DYMO router) within
the advertised prefix MUST NOT participate in the DYMO protocol
directly. 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.
5.9. Simple Internet Attachment
Simple Internet attachment consists of a stub network of MANET
routers connected to the Internet via a single Internet DYMO router
(IDR). The Internet may be connected via multiple DYMO routers, but
such behavior is not specified in this document.
The IDR is responsible for responding to RREQs for DYMO routers on
behalf of TargetNodes on the Internet, as well as delivering packets
to destinations on the Internet.
/--------------------------\
/ Internet \
\ /
\------------+-------------/
|
Routable & |
Topologically | A.B.C.X/24
Correct |
Prefix |
+-----+-----+
| Internet |
/------| DYMO |--------\
/ | Router | \
/ | A.B.C.1 | \
| +-----------+ |
| DYMO Region |
| |
| +--------------+ |
| | DYMO Router | |
| | A.B.C.2 | |
| +--------------+ |
| +--------------+ |
| | DYMO Router | |
| | A.B.C.3 | |
\ +--------------+ /
\ /
\---------------------------/
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Figure 3: Simple Internet Attachment Example
DYMO routers wishing to be reachable from nodes in the Internet MUST
have IP addresses within the IDR's routable and topologically correct
prefix. Given a node with a routeable address or care-of address
handled by the IDR, the IDR 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 packets to a node on
the Internet, they simply issue RREQ for those IP Destination
Addresses; using normal DYMO route discovery. The IDR is responsible
for properly responding to RREQ on behalf of the Internet
destinations, and maintaining their associated sequence number(s).
For an IDR and other DYMO routers that maintain the sequence number
on behalf of other nodes, these routers MUST know the IP addresses
for which they MUST generate DYMO messages and maintain OwnSeqNum.
Likewise, they MUST be capable of advertising an address within the
same prefix as these IP addresses. Alternatively, they may behave as
a proxy on behalf of Internet destinations.
5.10. 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
multicast 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.
5.11. DYMO Control Packet/Message Generation Limits
To ensure predictable control overhead, DYMO router'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 or intelligently controlled. DYMO
control messages SHOULD be discarded in the following order of
preferences RREQ, RREP, and finally RERR.
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6. Configuration Parameters and Other Administrative Options
Suggested Parameter Values
+------------------------------+-------------------+
| Name | Value |
+------------------------------+-------------------+
| MSG_HOPLIMIT | 10 hops |
| ROUTE_TIMEOUT | 5 seconds |
| ROUTE_AGE_MIN_TIMEOUT | 1 second |
| ROUTE_SEQNUM_AGE_MAX_TIMEOUT | 60 seconds |
| ROUTE_USED_TIMEOUT | ROUTE_TIMEOUT |
| ROUTE_DELETE_TIMEOUT | 2 * ROUTE_TIMEOUT |
| ROUTE_RREQ_WAIT_TIME | 2 seconds |
| RREQ_TRIES | 3 tries |
| UNICAST_MESSAGE_SENT_TIMEOUT | 1 second |
+------------------------------+-------------------+
Table 2
These suggested values work well for small and medium well connected
networks with moderate 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. Many of these options can be administratively controlled, but
they may be better served by intelligent control. The following
table enumerates several of the options.
Important Settings
+------------------------+------------------------------------------+
| Name | Description |
+------------------------+------------------------------------------+
| RESPONSIBLE_ADDRESSES | List of addresses, and their associated |
| | prefix, for which this DYMO router is |
| | responsible. |
| DYMO_INTERFACES | List of the interfaces participating in |
| | DYMO routing protocol. |
+------------------------+------------------------------------------+
Table 3
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Note: several fields have limited size (bits or bytes) these sizes
and their encoding may place specific limitations on the values that
can be set. For example, MsgHdr.HopLimit is a 8-bit field and
therefore MSG_HOPLIMIT cannot be larger than 255.
7. IANA Considerations
In its default mode of operation, DYMO uses the UDP port MANET
[I-D.ietf-manet-iana] to carry protocol packets. DYMO also uses 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.
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
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+-------------------+------+--------+-------------------------------+
| Name | Type | Length | Value |
+-------------------+------+--------+-------------------------------+
| Unicast Response | 10 - | 0 | Indicates to the processing |
| Request | TBD | octets | 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 can assume that |
| | | | the link is unidirectional |
| | | | and MAY blacklist the link to |
| | | | this node. |
+-------------------+------+--------+-------------------------------+
Table 5
7.3. Address Block TLV Specification
Address Block TLV Types
+---------------+--------------+--------+---------------------------+
| Name | Type | Length | Value |
+---------------+--------------+--------+---------------------------+
| DYMO | 9 - TBD | DID | ThisNode.DID's value. |
| Identifier | | length | More information can be |
| (DID) | | | found in Section 5.6 |
| DYMO Sequence | 10 - TBD | up to | The DYMO sequence num |
| Number | | 2 | associated with this |
| (DYMOSeqNum) | | octets | address. The sequence |
| | | | number may be the last |
| | | | known sequence number. |
| Distance | 11 - TBD | up to | A metric of the distance |
| | | 2 | traversed by the |
| | | octets | information associated |
| | | | with this address. |
| VALIDITY_TIME | TBD | | The maximum amount of |
| - AKA MaxAge | [I-D.ietf-ma | | time that information can |
| | n et-timetlv | | be maintained before |
| | ] | | being deleted. The |
| | | | VALIDITY_TIME TLV is |
| | | | defined in |
| | | | [I-D.ietf-manet-timetlv]. |
+---------------+--------------+--------+---------------------------+
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Table 6
8. Security Considerations
This document does not mandate any specific security measures.
Instead, this section describes various security considerations and
potential avenues to secure DYMO routing.
The most important security mechanisms for DYMO routing are
integrity/authentication and confidentiality.
In situations where routing information or router identity are
suspect, integrity and authentication techniques SHOULD be applied to
DYMO messages. In these situations, routing information that is
distributed over multiple hops SHOULD also verify the integrity and
identity of information based on originator of the routing
information.
A digital signature could be used to identify the source of DYMO
messages and information, along with its authenticity. A nonce or
timestamp SHOULD also be used to protect against replay attacks.
S/MIME and OpenPGP are two authentication/integrity protocols that
could be adapted for this purpose.
In situations where confidentiality of DYMO messages is important,
cryptographic techniques SHOULD be applied.
In certain situations, like sending a RREP or RERR, a DYMO router
could include proof that it has previously received valid routing
information to reach the destination, at one point of time in the
past. In situations where routers are suspected of transmitting
maliciously erroneous information, the original routing information
along with its security credentials SHOULD be included.
Note that if multicast is used, any confidentiality and integrity
algorithms used must permit multiple receivers to process the
message.
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
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Caceres, Thomas Clausen, Christopher Dearlove, Seung Yi, Romain
Thouvenin, Tronje Krop, Henner Jakob, Alexandru Petrescu, Christoph
Sommer, Cong Yuan, Lars Kristensen, and Derek Atkins 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 MANET Protocols",
draft-ietf-manet-iana-07 (work in progress),
November 2007.
[I-D.ietf-manet-packetbb]
Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized MANET Packet/Message Format",
draft-ietf-manet-packetbb-17 (work in progress),
November 2008.
[I-D.ietf-manet-timetlv]
Clausen, T. and C. Dearlove, "Representing multi-value
time in MANETs", draft-ietf-manet-timetlv-08 (work in
progress), September 2008.
[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.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
10.2. Informative References
[I-D.chakeres-manet-manetid]
Chakeres, I., "MANET_ID TLV",
draft-chakeres-manet-manetid-03 (work in progress),
February 2008.
[I-D.ietf-manet-nhdp]
Clausen, T., Dearlove, C., and J. Dean, "MANET
Neighborhood Discovery Protocol (NHDP)",
draft-ietf-manet-nhdp-07 (work in progress), July 2008.
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[I-D.ietf-ospf-multi-instance]
Lindem, A., Roy, A., and S. Mirtorabi, "OSPF Multi-
Instance Extensions", draft-ietf-ospf-multi-instance-00
(work in progress), February 2009.
[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.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2740] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 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.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC5148] Clausen, T., Dearlove, C., and B. Adamson, "Jitter
Considerations in Mobile Ad Hoc Networks (MANETs)",
RFC 5148, February 2008.
Authors' Addresses
Ian D Chakeres
CenGen
9250 Bendix Road North
Columbia, Maryland 21045
USA
Email: ian.chakeres@gmail.com
URI: http://www.ianchak.com/
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Charles E. Perkins
WiChorus Inc.
3590 North First Street, Suite 300
San Jose, CA 95134
USA
Phone: +1-408-421-1172
Email: charliep@computer.org
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