Subject: [manet] DYMO review

From: Ulrich Herberg <[email-masked]>
Date: Wed, 28 Jul 2010 23:28:01 +0200

Hi,

First, I'd like to apologize that until now I never had the time to
review DYMO in detail. Here is my review of the -21 draft.

Overall comments:
 - The draft is very hard/complicated to read; I would have a hard time
implementing it.
 - There are many things which should be cleared and checked for
consistency in the spec (for details see below)
 - The protocol seems to be difficult to secure for end-to-end messages.
 - I have doubts about the correct usage of RFC5444 in the draft

Detailed comments: (starting with "UH> ", always immediately following
the concerned sentence or paragraph)
============

<SNIP>

2.  Applicability Statement

  The DYMO routing protocol is designed for stub or disconnected mobile

UH> ================
UH> What is a "disconnected MANET"? Disconnected from what? Are these
UH> terms (stub / disconnected) defined anywhere?
UH> ================

  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.

UH> ================
UH> Is "routing region" for the context of a MANET defined somewhere?
UH> ================

  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.

UH> ================
UH> 1) The document mixes up node / router. Is there a difference? I
UH> would prefer to talk about routers only.
UH> 2) What is a participating vs. non-participating interface? Is
UH> that defined somewhere?
UH> ================

  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.

UH> ================
UH> A router may have several interfaces, each of which may have
UH> several IP(v6) addresses. Which is the address that identifies a
UH> router? (that applies at many places within the draft)
UH> ================

  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.

UH> ================
UH> Which address is that? Of the interface? Or is it a prefix that
UH> this router may delegate to attached hosts? What does it mean, to
UH> "own" an address? (any citation to an RFC?)
UH> ================

  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.

UH> ================
UH> This whole previous section is unclear. Not sure it belongs in the spec
UH> ================

  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.

UH> ================
UH> Not clear how NHDP interoperates with DYMO (in particular using
UH> several DYMO processes on the same router)
UH> ================

  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.

UH> ================
UH> I did not understand this previous section. It seems that
UH> the whole draft is based on IP/UDP only.
UH> ================

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].

UH> ================
UH> Which terminology of RFC5444 is used? "some" is imprecise.
UH> ================

  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).

UH> ================
UH> This is only used in section 5.5.1. Seems to be unnecessary to
UH> define it for the whole document.
UH> ================

  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.

UH> ================
UH> What metrics is the distance based on? Only Hop count? Can that
UH> be more than 255 (in IP networks)?
UH> ================

  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.

UH> ================
UH> Using DID is unclear to me. How does a router process know which
UH> DID it runs? Often, in the spec. it is unclear whether the "DYMO
UH> router" or the "DYMO routing process" does something (see later in my
UH> comments for examples). How do the different routing processes
UH> interact? If NHDP is used, is there a single NHDP instance per process
UH> or per router?
UH> ================

  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.

UH> ================
UH> Sometimes confusing whether the seqnum is used per router or per
UH> router process. That's not consistent in the spec.
UH> ================

  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.

UH> ================
UH> Site-scoped is deprecated. Unclear previous section. Is that term
UH> defined in some other RFC? IP.SourceAddress and
UH> IP.DestinationAddress have not been defined until this
UH> point in the spec (comes only later)
UH> ================

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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.

UH> ================
UH> What is the difference to ThisNode?
UH> ================

  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.

UH> ================
UH> TargetNode not yet defined
UH> ================

  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.

UH> ================
UH> Interface address? Originator address? Including prefix notation
UH> or just the address(es)?
UH> ================

  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.

UH> ================
UH> So what is the value for a host entry? (32 or 128)?
UH> ================

  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.

UH> ================
UH> Purpose of the Forwarding flag is unclear
UH> ================

  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.

UH> ================
UH> Having optional fields sounds dangerous in a database.
UH> ================

  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].

UH> ================
UH> Until now, no mentioning whether the protocol runs on UDP/IP
UH> (which version of IP? The spec never says that it both supports IPv4
UH> and IPv6 (or I haven't seen it)). Is DYMO limited to run on IP?
UH> ================

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

UH> ================
UH> This table and the hierarchical notation which is used in the
UH> following section is unclear
UH> ================

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.
UH> ================
UH> Imprecise (and no a scientific language style, "made up of
UH> messages").  Rather something like "A packet formatted according to
UH> RFC5444 contains zero or more messages"
UH> ================

  A message is made up of a message
  header, message TLV block, and zero or more address blocks.
UH> ================
UH> Same comment as the previous one
UH> ================

  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.

UH> ================
UH> I would not include the protocol/port numbers here. Citation is enough.
UH> ================

  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.

UH> ================
UH> How would a router send a unicast RREQ? It would need to know at
UH> least one IP address per adjacent neighbor. This assumption is never
UH> specified.
UH> ================

  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

UH> ================
UH> 1) That sounds wrong (mixing RFC5444 packet and IP datagram in the
UH> first sentence). The (RFC5444) packet does not contain an IPv4
UH> TTL/IPv6 Hop Limit.
UH> 2) You cannot discard a (RFC5444) packet (maybe "ignore it"). It
UH> may contain messages intended for other processes (like NHDP/OLSRv2).
UH> ================

 , 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.

UH> ================
UH> I don't understand. The contained messages do not have any IP
UH> header fields. Also, isn't the IP.SourceAddress always the originator
UH> address of the router or one IP address of the interface the packet is
UH> sent from? (unclear from the spec)
UH> ================

  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].

UH> ================
UH> Unclear how jitter is applied in the whole spec.
UH> ================

  DYMO control packets SHOULD be given priority queuing and channel
  access.

UH> ================
UH> Does that apply to "packet" as in RFC5444 or in IP datagram?
UH> ================

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.
UH> ================
UH> Which IP address?
UH> ================

    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).

UH> ================
UH> Mentioning IP fields here seems to be mixing up RFC5444-layer and IP-layer
UH> ================

  MsgHdr.HopLimit
     The remaining number of hops this message is allowed to traverse.

UH> ================
UH> What about the other msg headers? MUST/SHOULD/MAY they be contained?
UH> ================

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  AddBlk.TargetNode.Address
UH> ================
UH> This hierarchical notation has never been defined.
UH> ================

     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.

UH> ================
UH> The first address? So my (imaginary) routing protocol extension
UH> cannot add addresses at will (at any position), as it is possible in
UH> RFC5444? I would associate a TLV with it to guarantee extensibility of
UH> the protocol.
UH> What if there are several address blocks? First address if the
UH> first address block?
UH> ================

  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.
UH> ================
UH> Unclear.. prefix or address seems to be mixed here and throughout the spec
UH> ================

     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.
UH> ================
UH> DYMO router or router process?
UH> ================

  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.
UH> ================
UH> Never defined before what an AdditionalNode is. Which address is that?
UH> ================

  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
UH> ================
UH> I don't know which fields are mandatory, which are optional. The
UH> example could be moved into the appendix.
UH> ================

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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    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

UH> ================
UH> 1) Seems to be a short UDP header, only one octet...
UH> 2) I would not include IP and UDP headers here
UH> 3) Why is the figure not aligned to 4 bytes per row (as it is done later)?
UH> ================

  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   |

UH> ================
UH> I almost did not see the vertical dots for omission of some lines
UH> By the way, is it really necessary to include the Orig. address in
UH> an address block? Couldn't one use the msg originator header (and use
UH> message TLVs)?
UH> ================

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  Message Body - Address Block TLV Block
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       tlv-block-size=6        |DYMOSeqNum-type|0|1|0|1|0|0|Rsv|

UH> ================
UH> Where is DYMOSeqNum-type defined?
UH> ================

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | 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.
UH> ================
UH> Unclear sentence. For which addresses?
UH> ================

  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.
UH> ================
UH> Which address? Interface address (if so, which address if several
UH> iface addresses are used?)
UH> ================

     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.
UH> ================
UH> Which address? Originator?
UH> ================

     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
UH> ================
UH> This whole section is unclear. Why start with the sequence
numbers? There is no motivation why sequence numbers are important in
the beginning of the section.
UH> ================

  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.

UH> ================
UH> Sequence number per router or router process? The "on behalf of
UH> the addresses" part is unclear.
UH> ================

  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.
UH> ================
UH> This sentence is redundant with the second sentence of section 5.1.1
UH> ================

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
UH> ================
UH> How can a sequence number be lost?
UH> ================

  , 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
UH> ================
UH> What does that mean, "fully participate"? What is the opposite then?
UH> ================

  in the DYMO routing
  protocol.  If a DYMO control message is received during this waiting
  period, the DYMO router SHOULD handle it normally
UH> ================
UH> What does "handle it normally" mean?
UH> ================

  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

UH> ================
UH> "using signed 16-bit arithmetic" is unclear. Better cite RFC or
UH> explain wrap-around of sequence numbers.
UH> ================

  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))
UH> ================
UH> What is this pseudocode for? Unclear when and where to use it.
UH> ================

  3. Inferior or equivalent
     In case of known equal SeqNum, the information is inferior in
     multiple cases:
UH> ================
UH> That sentence sounds strange: "inferior/superior information". How
UH> can information (=data with semantics) be inferior?
UH> ================

    (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.
UH> ================
UH> Why "optimized" pseudo-code? What is optimized?
UH> ================

     (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)))))

<SNIP>

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
UH> ================
UH> Which node? "the"...
UH> ================

  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).

UH> ================
UH> Which exact value does the router put into that field?
UH> ================

  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.
UH> ================
UH> Where does the router (or router process?) get the NextHopAddress
UH> from in an initial RREQ? From NHDP?
UH> ================

  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.

UH> ================
UH> Unclear what datatype (i.e. how many octets long) the DID is. (in
UH> C syntax: "uint8_t", "uint16_t",...)
UH> ================

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.
UH> ================
UH> "advertise" where?
UH> ================

  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.
UH> ================
UH> That makes any end-to-end security of control messages tricky.
UH> ================

  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
UH> ================
UH> This whole section 5.3.4. is extremely long and complicate to
UH> read. I suggest to better structure in a pseudo-code manner:
UH>   e.g.    1) If BLA then
UH>                    doFoo
UH>              2) otherwise....
UH> ================

  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).
UH> ================
UH> Can the distance be > 255?
UH> ================

  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.
UH> ================
UH> Makes end-to-end security impossible
UH> ================

  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.
UH> ================
UH> What is the default value of VALIDITY_TIME?
UH> ================

  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.
UH> ================
UH> Is there any jitter involved? The exp. backoff is not exactly
UH> specified, just explained with an example.
UH> ================

  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.
UH> ================
UH> What parameters are set in the ICMP message (e.g. which code?) On
UH> which interface(s) is the ICMP sent?
UH> ================

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.
UH> ================
UH> Which assumptions are made of the underlying L2? (ACKs, timeout, NUD, etc.)
UH> ================

  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.
UH> ================
UH> Is that known terminology "a router is responsible for an address?"
UH> ================

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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.

<SNIP>

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].
UH> ================
UH> The MANET_ID draft is expired. Anyways, I have strong doubts about
UH> the concept of MANET_IDs (but this is another discussion...)
UH> ================

  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.
UH> ================
UH> That is unclear. That may be very complicated. What does "come in
UH> contact with each other" mean?
UH> ================

  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.
UH> ================
UH> I think it should be ignored, not discarded. It may be an
UH> NHDP/OLSRv2 messages for example.
UH> ================

  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
UH> ================
UH> I don't understand this section. Of course, any hosts attached to
UH> the router (on it's non-MANET interface) are unaware of the routing
UH> protocol. That's true for any routing protocol, it does not run on the
UH> hosts.
UH> ================

  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
UH> ================
UH> Unclear why this section is needed. Is this an example deployment?
UH> ================

  Simple Internet attachment consists of a stub network of DYMO routers
  connected to the Internet via a single Internet DYMO router (IDR).
UH> ================
UH> What does "connected to the Internet" mean? How the routers know?
UH> Why introducing another acronym (IDR), just for an example?
UH> ================

  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).
UH> ================
UH> That's true for routing in general, not just for DYMO
UH> ================

  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.

UH> ================
UH> How would that work for multi-homing?
UH> ================

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.

UH> ================
UH> It seems to be more complicated than just a small section like
UH> this. A large part of the complexity of, e.g., NHDP is due to multiple
UH> interfaces.
UH> Just some thoughts: On which interfaces are RM sent to? Which
UH> addresses are used as originator of a message? Is loop-detection more
UH> difficult with several interfaces?
UH> ================

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.
UH> ================
UH> I think that this is too vague. I would prefer to have a basic
UH> mechanism explained how to do that (e.g. having MIN_INTERVAL
UH> parameters)
UH> ================

<SNIP>

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.

UH> ================
UH> That seems impossible in DYMO, since intermediate routers can (i)
UH> cache target destinations and (ii) modify forwarded messages.
UH> ================

  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.

<SNIP>

Appendix A.  Shifting Responsibility for an Address Between DYMO Routers
UH> ================
UH> Section is unclear to me.
UH> ================

  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.

<SNIP>