Mobile Ad hoc Networks Working I. Chakeres
Group CenGen
Internet-Draft C. Perkins
Intended status: Standards Track WiChorus
Expires: January 27, 2011 July 26, 2010
Dynamic MANET On-demand (DYMO) Routing
draft-ietf-manet-dymo-21
Abstract
The Dynamic MANET On-demand (DYMO) routing protocol is intended for
use by mobile routers in wireless, multihop networks. DYMO
determines unicast routes among DYMO routers within the network in an
on-demand fashion, offering improved convergence in dynamic
topologies.
Status of this Memo
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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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 Packet and Message Structure . . . . . . . 9
4.2.2. Routing Messages (RM) - RREQ & RREP . . . . . . . . . 10
4.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 13
5. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 15
5.1. DYMO Sequence Numbers . . . . . . . . . . . . . . . . . . 15
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 . . . . . . . . . . . . . . 16
5.2.1. Judging Routing Information's Usefulness . . . . . . . 16
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 . . . . . . . . . . . . . . . . . . . . . 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 Handling . . . . . . . . . . . . . . . . . . . . . 21
5.3.5. Adding Additional Routing Information to a RM . . . . 25
5.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 25
5.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 26
5.5.1. Active Next-hop Router Adjacency Monitoring . . . . . 27
5.5.2. Updating Route Lifetimes During Packet Forwarding . . 27
5.5.3. RERR Generation . . . . . . . . . . . . . . . . . . . 27
5.5.4. RERR Handling . . . . . . . . . . . . . . . . . . . . 28
5.6. DYMO Identifier (DID) . . . . . . . . . . . . . . . . . . 30
5.7. Unknown Message & TLV Types . . . . . . . . . . . . . . . 30
5.8. Advertising Network Addresses . . . . . . . . . . . . . . 31
5.9. Simple Internet Attachment . . . . . . . . . . . . . . . . 31
5.10. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 32
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5.11. DYMO Control Packet/Message Generation Limits . . . . . . 33
6. Administratively Configured Parameters and Timer Values . . . 33
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
7.1. DYMO Message Types Specification . . . . . . . . . . . . . 36
7.2. Message and Address Block TLV Type Specification . . . . . 36
7.3. Address Block TLV Specification . . . . . . . . . . . . . 37
8. Security Considerations . . . . . . . . . . . . . . . . . . . 37
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . . 39
Appendix A. Shifting Responsibility for an Address Between
DYMO Routers . . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
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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 routes 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 the 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 this 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 only a small portion of the other
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DYMO routers, due to the reactive nature of route discovery and route
maintenance.
DYMO is applicable to memory constrained devices, since little
routing state is maintained in each DYMO router. Only routing
information related to active sources and destinations is maintained,
in contrast to most 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
and respond to route discovery on behalf of certain nodes, identified
by address. When DYMO is the only protocol interacting with the
forwarding table, DYMO MAY be configured to perform route discovery
for all unknown unicast destinations.
At any time within a DYMO routing region only one DYMO router SHOULD
be responsible for, i.e. "own", a particular address. Coordination
among multiple DYMO routers to distribute routing information
correctly for a shared address (i.e. an address that is advertised
and can be reached via multiple DYMO routers) is not described in
this document. The router behavior for shifting responsibility for
an address from one DYMO router to another are described in
Appendix A.
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 and monitoring 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].
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Additionally, this document uses some terminology from [RFC5444].
This document defines the following terminology:
Adjacency
A relationship 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. Similarly, loss of a routing adjacency may
also be based upon several pieces of information, and monitoring
of adjacencies where packets are being forwarded is required (see
Section 5.5.1).
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 for each DYMO routing process (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 process
SHOULD only attend to messages with a matching DID value.
DYMO Sequence Number (SeqNum)
A DYMO Sequence Number is maintained by each DYMO router process.
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.SourceAddress or IP.DestinationAddress field
is scoped sufficiently to be forwarded by a router. For example,
site-scoped or globally-scoped unicast IP addresses.
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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.
Route Error (RERR)
A RERR message is used to indicate that a DYMO router does not
have a 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 process currently
performing a calculation or attending to a message.
Type-Length-Value structure (TLV)
A generic way to represent information, please see [RFC5444] 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:
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Route.Address
The (host or network) destination address of the node(s)
associated with the routing table entry.
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
to true if the next-hop becomes unreachable or in response to
attending to a RERR (see Section 5.5.4).
The following field is optional:
Route.Dist
A dimensionless 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 header, the UDP header, and fields from
[RFC5444]. This document uses the following notation conventions.
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Information found in the table.
+---------------------------+-------------------+
| Information Location | Notational Prefix |
+---------------------------+-------------------+
| IP header | IP. |
| UDP header | UDP. |
| RFC5444 message header | MsgHdr. |
| RFC5444 message TLV | MsgTLV. |
| RFC5444 address blocks | AddBlk. |
| RFC5444 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 [RFC5444]. 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.
For interoperability with other DYMO routers, all DYMO messages
specified in this document SHOULD sent using the IP protocol number
(138) reserved for manet protocols [RFC5498]; or the UDP destination
port (269) reserved for manet protocols [RFC5498] and IP protocol
number for UDP.
Most DYMO messages are sent with the IP destination address set to
the link-local multicast address LL-MANET-Routers [RFC5498] unless
otherwise stated. Therefore, all DYMO routers SHOULD subscribe to
LL-MANET-Routers [RFC5498] 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 adjacencies.
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 that
packets have not passed through any intermediate routers, and it is
known as GTSM [RFC5082].
The length of an address (32 bits for IPv4 and 128 bits for IPv6)
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inside a DYMO message depends on the msg-addr-length (MAL) in the
msg-header, as specified in [RFC5444].
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 queuing 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 handling 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 handling 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 [RFC5498]. For
unicast RREP the IP.DestinationAddress is set to the
NextHopAddress toward the RREP TargetNode.
IP.ProtocolNumber and UDP.DestinationPort
The IP Protocol Number 138 (manet) has been reserved for MANET
protocols [RFC5498]. In addition to using this IP protocol
number, DYMO may use the UDP port 269 (manet) [RFC5498] in
conjunction with the IP Protocol Number 17 (UDP).
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 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.
Example IPv4 RREQ
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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.Proto = UDP|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.SourceAddress |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.DestinationAddress = LL-MANET-Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP TTL/HopLimit = 255 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = manet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Packet Header
+-+-+-+-+-+-+-+-+
| ver= 0|0|0|0|0|
+-+-+-+-+-+-+-+-+
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RREQ-type |0|1|0|0| MAL=3 | 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
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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 addresses.
RERR creation and handling are described in Section 5.5.
A RERR requires the following information:
IP.SourceAddress
The IP address of the DYMO router that sent 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 [RFC5498]. For unicast RERR messages, the IP address is
set to the NextHopAddress.
IP.ProtocolNumber and UDP.DestinationPort
The IP Protocol Number 138 (manet) has been reserved for MANET
protocols [RFC5498]. In addition to using this IP protocol
number, DYMO may use the UDP port 269 (manet) [RFC5498] in
conjunction with the IP Protocol Number 17 (UDP).
MsgHdr.HopLimit
The remaining number of hops this message is allowed to traverse.
AddBlk.UnreachableNode.Address
The 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 zero (0) or 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.Proto = UDP|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.SourceAddress |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.DestinationAddress = LL-MANET-Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP.TTL/HopLimit = 255 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port = manet |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Packet Header
+-+-+-+-+-+-+-+-+
| ver= 0|0|0|0|0|
+-+-+-+-+-+-+-+-+
Message Header
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RERR-type |0|1|0|0| MAL=3 | 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
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5. Detailed Operation
5.1. DYMO Sequence Numbers
DYMO sequence numbers allow DYMO routers to judge the freshness of
routing information and ensure loop freedom.
5.1.1. Maintaining A Node's Own Sequence Number
DYMO requires that each DYMO router in the network maintain its own
DYMO sequence number (OwnSeqNum) on behalf of the addresses for which
it is responsible. OwnSeqNum a 16-bit unsigned integer. The
circumstances for ThisNode to increment its OwnSeqNum are described
in Section 5.3.
5.1.2. Numerical Operations on OwnSeqNum
When ThisNode increments its OwnSeqNum it MUST do so by treating the
sequence number value as an unsigned number.
5.1.3. OwnSeqNum Rollover
Incrementing an OwnSeqNum whose value is the largest largest possible
number representable as a 16-bit unsigned integer (i.e., 65,535),
SHOULD be set to one (1). In other words, the sequence number after
65,535 is 1.
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 handle 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.
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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/
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 or equivalent
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. This condition reduces the number of
RREQ flooded by stopping 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 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
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. the Route.Broken flag is set to false,
7. if known, the Route.Dist is set to the Node.Dist,
Fields without known values are not populated with any value.
The timer for the minimum delete timeout (ROUTE_AGE_MIN) is set to
ROUTE_AGE_MIN_TIMEOUT. The timer for the maximum delete timeout
(ROUTE_SEQNUM_AGE_MAX) is set to Node.AddTLV.VALIDITY_TIME [RFC5497]
if included; otherwise, ROUTE_SEQNUM_AGE_MAX is set to
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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 has been 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.
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_SEQNUM_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 if a forwarding route exists it SHOULD
be removed, and the routing table entry SHOULD also be deleted.
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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.
Incrementing OwnSeqNum will ensure that all nodes with existing
routing information will consider this new information superior to
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.
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
handling 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 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).
Additional routing information can be added to this RM using the
procedure described in Section 5.3.5.
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. For links that do not support multicast or situations in
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which unicast messaging is preferred, 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.
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 RM 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.
If TargetNode.SeqNum was 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.
If TargetNode.SeqNum is included in the RM and TargetNode.SeqNum ==
OwnSeqNum (using signed 16-bit arithmetic) and OrigNode.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.
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 be 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 or equal to 65,535.
The Distance value will influence judgment of the routing information
(Section 5.2.1) against known information at other DYMO routers that
handle this RM.
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Additional routing information can be added to this RM using the
procedure described in Section 5.3.5.
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
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.
If OwnSeqNum is not incremented the routing information about
ThisNode might be considered stale by a handling 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 Handling
First, ThisNode examines the RM to ensure that it contains the
required information: MsgHdr.HopLimit, AddBlk.TargetNode.Address,
AddBlk.OrigNode.Address, and OrigNode.AddTLV.SeqNum. If the required
information do not exist, the message is discarded and further
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processing stopped.
Next, ThisNode decides whether to attend to 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 attend to messages based upon
information in the message. ThisNode SHOULD only handle messages
from adjacent DYMO routers. If ThisNode chooses not to handle 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 address. If the address
is not a valid unicast address, the message 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-
capable unicast address. If the address is not a valid unicast
address, the message 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 superior 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 known 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. 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. The
updated Distance value will influence judgment of the routing
information (Section 5.2.1).
After handling the OrigNode's routing information, then each address
that is not the TargetNode MAY be considered for creating and
updating routes. Creating and updating routes to other nodes can
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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 address.
If the address is not a unicast address, the address and all related
information MUST be removed.
If the routing table does not have a matching route with a known
Route.SeqNum for this additional address using longest-prefix
matching, then a route is created and updated as described in
Section 5.2.2. If a route table entry exists with a known
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.
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 the RM being processed.
As an alternative to issuing a RREP, ThisNode MAY choose to
distribute routing information about ThisNode (the RREQ TargetNode)
more widely. That is, 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 RM being processed.
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 ThisNode 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 RM being
processed.
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After handling a RM or creating a new RM, ThisNode MAY append
additional routing information to the RM prior to redistributing this
information, 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 handle 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
IP.DestinationAddress LL-MANET-Routers [RFC5498]. 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
TargetNode.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 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
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. These types of
advanced behavior are not defined in this specification.
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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
(APPEND_INFORMATION) SHOULD be administratively configurable or
intelligently controlled.
Prior to appending an address controlled by this DYMO router to a RM,
ThisNode MAY increment its OwnSeqNum as defined in Section 5.1. 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 a RM in transit (APPEND_INFORMATION_SEQNUM)
SHOULD be administratively configurable or intelligently controlled.
Note that, during handling of this RM OwnSeqNum may have already been
incremented; and in this case OwnSeqNum need not be incremented
again.
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.
The VALIDITY_TIME of routing information for appended address(es)
MUST be included, to inform routers about when to delete this
information. The VALIDITY_TIME TLV is defined in Section 7.3.
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).
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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 again.
Route discovery SHOULD be considered failed after
DISCOVERY_ATTEMPTS_MAX and the final RREQ's corresponding
RREQ_WAIT_TIME.
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. No more than DISCOVERY_ATTEMPTS_MAX route
discovery attempts SHOULD be made before considering route discovery
for this destination to have failed. 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 (BUFFER_DURING_DISCOVERY)
SHOULD be administratively configurable or intelligently controlled.
If a route discovery attempt has failed (i.e. an attempt or multiple
attempts have been made without receiving a RREP) to find a route to
the TargetNode, any data packets buffered for the corresponding
TargetNode are dropped and a 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.
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In addition to inability to forward a data packet, a RERR SHOULD be
issued immediately after detecting a broken link (see Section 5.5.1)
of a forwarding route to quickly notify DYMO routers that certain
routes are no longer available. If a newly unavailable route has not
been used recently (indicated by ROUTE_USED), the RERR SHOULD NOT be
generated.
5.5.1. Active Next-hop Router Adjacency Monitoring
Nodes MUST monitor connectivity to adjacent next-hop DYMO routers on
forwarding routes. This monitoring can be accomplished by one or
several mechanisms, including:
o Neighborhood discovery [I-D.ietf-manet-nhdp]
o Route timeout
o Lower layer feedback that a particular adjacent router is no
longer reachable
o Other monitoring mechanisms or heuristics
Upon determining that a next-hop DYMO router 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 the 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
the 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 the 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 the first UnreachableNode
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(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 is 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 node that handles this
message of additional routes that are no longer available. This
option (APPEND_EXTRA_UNREACHABLE) SHOULD be administratively
configurable or intelligently controlled.
If SeqNum information is not known or not included in the RERR, all
nodes handling 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 [RFC5498]. 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
RERR SHOULD be discarded.
5.5.4. RERR Handling
First, ThisNode examines the RM to ensure that it contains the
required information: MsgHdr.HopLimit and
AddBlk.UnreachableNode.Address. If the required information do not
exist, the message is discarded and further processing stopped.
Next, ThisNode decides whether to handle 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).
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Next, ThisNode MAY selectively handle messages based upon information
in the message. ThisNode MAY choose to only handle messages from
adjacent DYMO routers. If ThisNode chooses not to handle this
message, the message is discarded and further processing stopped.
When a DYMO router handles a RERR, it examines each UnreachableNode's
information. The attending DYMO router removes the forwarding route,
unsets the Route.Forwarding flag, sets the Route.Broken flag, and the
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
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 handling if Route.SeqNum is zero (0) or unknown and
UnreachableNode.SeqNum exists in the RERR and is not zero (0), then
Route.SeqNum MAY be set to UnreachableNode.SeqNum. Setting
Route.SeqNum can reduce future RERR handling 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)
associated with the removed address(es) MUST also be removed.
After handling 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 RERR handling and
forwarding.
If no UnreachableNode addresses remain in the RERR, no other handling
is required and the RERR is discarded.
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If handling 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 [RFC5498]. If the RERR is unicast, the IP.DestinationAddress
is set to the NextHopAddress.
5.6. DYMO Identifier (DID)
Each DYMO routing protocol process MUST have an associated DYMO
Identifier (DID). The DID allows multiple DYMO routing protocol
processes to operate over the same links and on the same device
independently. This function may also be used to administratively
separate DYMO processes with incompatible options, timers, or
extensions.
The DID is similar in function to OSPF Instance ID [RFC5340]
[I-D.ietf-ospf-multi-instance], OSPF Area ID [RFC2328] [RFC5340],
and/or the MANET_ID TLV [I-D.chakeres-manet-manetid].
All DYMO routers with the same DID that come in contact with each
other MUST operate with a compatible set of configuration options,
timing parameters (see Section 6), and protocol extensions. In cases
with non-default options, the DID value SHOULD be administratively
chosen.
The default DID value is zero (0), and using this value requires that
the implementation utilize options and timing parameters compatible
with those defined in Section 6.
Each DYMO routing protocol message sent MUST contain its associated
DID in a message TLV; unless the DID value is zero (0), in which case
it MAY be omitted.
Upon receipt of DYMO protocol message a DYMO routing protocol process
SHOULD only process messages with a DID (MsgTLV.DID) value matching
its own DID (ThisNode.DID).
5.7. Unknown Message & TLV Types
If a message with an unknown type is received, the message is
discarded.
For handling of messages that contain unknown TLV types, the default
behavior is to leave the information in control messages unmodified.
Although, this behavior (UNKNOWN_TYPES) MAY be administratively
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controlled.
5.8. Advertising Network Addresses
DYMO routers 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, advertising 192.0.2.1 with a prefix length of 24
indicates that all nodes with the matching 192.0.2.X are reachable
through this DYMO router.
5.9. Simple Internet Attachment
Simple Internet attachment consists of a stub network of DYMO routers
connected to the Internet via a single Internet DYMO router (IDR).
DYMO routers, and hosts behind these routers, wishing to be reachable
from hosts on the Internet MUST have IP addresses within the IDR's
routable and topologically correct prefix (e.g. 192.0.2.0/24).
The IDR is responsible for generating RREQ to find nodes within the
DYMO Region on behalf of nodes on the Internet, as well as responding
to route requests from the DYMO region on behalf of the nodes on the
Internet.
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/--------------------------\
/ Internet \
\ /
\------------+-------------/
|
Routable & |
Topologically |
Correct |
Prefix |
+-----+------+
| Internet |
/------| DYMO |-------\
/ | Router | \
/ |192.0.2.1/32| \
| |Responsible | |
| | for | |
| |DYMO Region | |
| |192.0.2.0/24| |
| +------------+ |
| +--------------+ |
| | DYMO Router | |
| | 192.0.2.2/32 | |
| +--------------+ |
| +--------------+ |
| | DYMO Router | |
| | 192.0.2.3/32 | |
\ +--------------+ /
\ /
\---------------------------/
Figure 3: Simple Internet Attachment Example
When a DYMO router within the DYMO Region wants to discover a route
to a node on the Internet, it uses the normal DYMO route discovery
for that IP Destination Address. The IDR is responsible for properly
responding to RREQ on behalf of the Internet destination.
When a packet from a node on the Internet destine for a node in the
DYMO region reaches the IDR, if the IDR does not have a route to that
destination it will perform normal DYMO route discovery for that
destination.
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
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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 (CONTROL_TRAFFIC_LIMITS) 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.
6. Administratively Configured Parameters and Timer Values
DYMO contains several parameters which MUST be administratively
configured. The list of these follows:
Required Administratively Configured Parameters
+------------------------+------------------------------------------+
| Name | Description |
+------------------------+------------------------------------------+
| DID | All DYMO routers with the same DID that |
| | come in contact with each other MUST |
| | operate with a compatible set of |
| | configuration options, timing |
| | parameters, and protocol extensions. If |
| | non-default potentially incompatible |
| | options, timing parameters or protocol |
| | extensions are utilized the DID MUST be |
| | set to a non-zero value. |
| 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 2
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DYMO contains a number of timers. The default timing parameter
values follow:
Default Timing Parameter Values
+------------------------------+-------------------+
| Name | Value |
+------------------------------+-------------------+
| 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 |
| UNICAST_MESSAGE_SENT_TIMEOUT | 1 second |
+------------------------------+-------------------+
Table 3
The above timing parameter values work well for small and medium
well-connected networks with moderate topology changes.
The timing 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.
Default Parameter Values
+------------------------+-------+----------------------------------+
| Name | Value | Description |
+------------------------+-------+----------------------------------+
| MSG_HOPLIMIT | 10 | This value MUST be larger than |
| | hops | the DYMO network diameter. |
| | | Otherwise, routing messages may |
| | | not reach their intended |
| | | destinations. |
| DISCOVERY_ATTEMPTS_MAX | 3 | The number of route discovery |
| | | attempts to make before |
| | | indicating that a particular |
| | | address is not reachable. |
+------------------------+-------+----------------------------------+
Table 4
In addition to the above parameters and timing values, several
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administrative options exist. These options have no influence on
correct routing behavior, although they may potentially reduce DYMO
routing control messaging in certain situations. The default
behavior is to NOT enable any of these options; and although many of
these options can be administratively controlled, they may be better
served by intelligent control. The following table enumerates
several of the options.
Administratively Controlled Options
+---------------------------+---------------------------------------+
| Name | Description |
+---------------------------+---------------------------------------+
| APPEND_INFORMATION | Whether to append ThisNode's routing |
| | information to a RM. |
| APPEND_INFORMATION_SEQNUM | Whether to increment ThisNode's |
| | OwnSeqNum when append ThisNode's |
| | routing information to a RM. |
| BUFFER_DURING_DISCOVERY | Whether and how much data to buffer |
| | during route discovery. |
| APPEND_EXTRA_UNREACHABLE | Whether to append additional |
| | Unreachable information to RERR. |
| UNKNOWN_TYPES | What action to take when an unknown |
| | TLV type is received. The default |
| | action is to forward this information |
| | unmodified. Another action would be |
| | to remove this information. |
| CONTROL_TRAFFIC_LIMITS | DYMO control messaging SHOULD be |
| | limited to avoid consuming all the |
| | network bandwidth. |
+---------------------------+---------------------------------------+
Table 5
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
[RFC5498] to carry protocol packets. DYMO also uses the link-local
multicast address LL-MANET-Routers [RFC5498].
This section specifies several message types, message tlv-types, and
address tlv-types.
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7.1. DYMO Message Types Specification
DYMO Message Types
+------------------------+----------+
| Name | Type |
+------------------------+----------+
| Route Request (RREQ) | 10 - TBD |
| Route Reply (RREP) | 11 - TBD |
| Route Error (RERR) | 12 - TBD |
+------------------------+----------+
Table 6
7.2. Message and Address Block TLV Type Specification
Message TLV Types
+-------------------+------+--------+-------------------------------+
| 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 7
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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 2 | The DYMO sequence num |
| Number | | octets | associated with this |
| (DYMOSeqNum) | | | address. The sequence |
| | | | number may be the last |
| | | | known sequence number. |
| Distance | 11 - TBD | up to 2 | A metric of the distance |
| | | octets | traversed by the |
| | | | information associated |
| | | | with this address. |
| VALIDITY_TIME | 1[RFC5497] | | The maximum amount of |
| | | | time that information can |
| | | | be maintained before |
| | | | being deleted. The |
| | | | VALIDITY_TIME TLV is |
| | | | defined in [RFC5497]. |
+---------------+------------+----------+---------------------------+
Table 8
8. Security Considerations
The objective of the DYMO protocol is for each router to communicate
reachability information to addresses for which it is responsible.
Positive routing information (i.e. a route exists) is distributed via
RMs and negative routing information (i.e. a route does not exist)
via RERRs. DYMO routers that handle these messages store the
contained information to properly forward data packets, and they
generally provide this information to other DYMO routers.
This section 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
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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 can 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 handle 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
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
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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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.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497,
March 2009.
[RFC5498] Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network
(MANET) Protocols", RFC 5498, March 2009.
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, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
draft-ietf-manet-nhdp-14 (work in progress), July 2010.
[I-D.ietf-ospf-multi-instance]
Lindem, A., Roy, A., and S. Mirtorabi, "OSPF Multi-
Instance Extensions", draft-ietf-ospf-multi-instance-02
(work in progress), April 2010.
[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.
[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
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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.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
Appendix A. Shifting Responsibility for an Address Between DYMO Routers
Only one DYMO router within a routing region SHOULD be responsible
for a particular address at any time. If two DYMO routers
dynamically pass responsibility of an address correct DYMO routing
behavior must be observed. The DYMO router adding the new address
must wait for any exiting routing information about this address to
be purged from the network. Therefore, it must wait at least
ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous DYMO router for this
address stopped participating and advertising routing information on
its behalf.
Authors' Addresses
Ian D Chakeres
CenGen
9250 Bendix Road North
Columbia, Maryland 21045
USA
Email: ian.chakeres@gmail.com
URI: http://www.ianchak.com/
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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