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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7787

Homenet Working Group                                        M. Stenberg
Internet-Draft
Intended status: Standards Track                                S. Barth
Expires: July 9, 2015
                                                         January 5, 2015


                  Distributed Node Consensus Protocol
                       draft-ietf-homenet-dncp-00

Abstract

   This document describes the Distributed Node Consensus Protocol
   (DNCP), a generic state synchronization protocol which uses Trickle
   and Merkle trees.  DNCP is transport agnostic and leaves some of the
   details to be specified in profiles, which define actual
   implementable DNCP based protocols.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 9, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Trickle-Driven Status Update Messages . . . . . . . . . .   6
     5.2.  Processing of Received Messages . . . . . . . . . . . . .   7
     5.3.  Adding and Removing Peers . . . . . . . . . . . . . . . .   8
     5.4.  Purging Unreachable Nodes . . . . . . . . . . . . . . . .   8
   6.  Keep-Alive Extension  . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Data Model Additions  . . . . . . . . . . . . . . . . . .   9
     6.2.  Periodic Keep-Alive Messages  . . . . . . . . . . . . . .   9
     6.3.  Received Message Processing Additions . . . . . . . . . .  10
     6.4.  Neighbor Removal  . . . . . . . . . . . . . . . . . . . .  10
   7.  Protocol Messages . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Short Network State Update Message  . . . . . . . . . . .  11
     7.2.  Long Network State Update Message . . . . . . . . . . . .  11
     7.3.  Network State Request Message . . . . . . . . . . . . . .  11
     7.4.  Node Data Request Message . . . . . . . . . . . . . . . .  12
     7.5.  Node Data Reply Message . . . . . . . . . . . . . . . . .  12
   8.  Type-Length-Value Objects . . . . . . . . . . . . . . . . . .  12
     8.1.  Request TLVs  . . . . . . . . . . . . . . . . . . . . . .  13
       8.1.1.  Request Network State TLV . . . . . . . . . . . . . .  13
       8.1.2.  Request Node Data TLV . . . . . . . . . . . . . . . .  13
     8.2.  Data TLVs . . . . . . . . . . . . . . . . . . . . . . . .  14
       8.2.1.  Node Connection TLV . . . . . . . . . . . . . . . . .  14
       8.2.2.  Network State TLV . . . . . . . . . . . . . . . . . .  14
       8.2.3.  Node State TLV  . . . . . . . . . . . . . . . . . . .  14
       8.2.4.  Node Data TLV . . . . . . . . . . . . . . . . . . . .  15
       8.2.5.  Neighbor TLV (within Node Data TLV) . . . . . . . . .  16
       8.2.6.  Keep-Alive Interval TLV (within Node Data TLV)  . . .  16
     8.3.  Custom TLV (within/without Node Data TLV) . . . . . . . .  17
   9.  Security and Trust Management . . . . . . . . . . . . . . . .  17
     9.1.  Pre-Shared Key Based Trust Method . . . . . . . . . . . .  17
     9.2.  PKI Based Trust Method  . . . . . . . . . . . . . . . . .  17
     9.3.  Certificate Based Trust Consensus Method  . . . . . . . .  18
       9.3.1.  Trust Verdicts  . . . . . . . . . . . . . . . . . . .  18
       9.3.2.  Trust Cache . . . . . . . . . . . . . . . . . . . . .  19
       9.3.3.  Announcement of Verdicts  . . . . . . . . . . . . . .  19
       9.3.4.  Bootstrap Ceremonies  . . . . . . . . . . . . . . . .  20
   10. DNCP Profile-Specific Definitions . . . . . . . . . . . . . .  21
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  23
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23



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   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     13.1.  Normative references . . . . . . . . . . . . . . . . . .  24
     13.2.  Informative references . . . . . . . . . . . . . . . . .  24
   Appendix A.  Some Outstanding Issues  . . . . . . . . . . . . . .  25
   Appendix B.  Some Obvious Questions and Answers . . . . . . . . .  25
   Appendix C.  Changelog  . . . . . . . . . . . . . . . . . . . . .  25
   Appendix D.  Draft Source . . . . . . . . . . . . . . . . . . . .  26
   Appendix E.  Acknowledgements . . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   DNCP is designed to provide a way for nodes to publish data
   consisting of an ordered set of TLV (Type-Length-Value) tuples, and
   to receive the data published by all other reachable DNCP nodes.

   DNCP has relatively few requirements for the underlying transport; it
   requires some way of transmitting either unicast datagram or stream
   data to a DNCP peer, and if used in multicast mode, a way of sending
   multicast datagrams.  If security is desired and one of the built-in
   security methods is to be used, support for some TLS-derived
   transport scheme, such as TLS [RFC5246] on top of TCP, or DTLS
   [RFC6347] on top of UDP, is also required.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Terminology

   DNCP profile is a definition of a set of rules and values listed in
   Section 10 specifying the behavior of a DNCP based protocol, such as
   the used transport method.  For readability, any DNCP profile
   specific parameters with a profile-specific fixed value are prefixed
   with DNCP_.

   DNCP node is a single node which runs a protocol based on a DNCP
   profile.

   DNCP network is a set of DNCP nodes running the same DNCP profile
   that can reach each other, either via learned shared connections in
   the underlying network, or using each other's addresses learned via
   other means.  As DNCP exchanges are bidirectional, DNCP nodes
   connected via only unidirectional links are not considered connected.





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   Node identifier is an opaque fixed-length identifier of
   DNCP_NODE_IDENTIFIER_LENGTH bytes which uniquely identifies a DNCP
   node within a DNCP network.

   Link indicates a link-layer media over which directly connected nodes
   can communicate.

   Interface indicates a port of a node that is connected to a
   particular link.

   Connection denotes a locally configured use of DNCP on a DNCP node,
   that is attached either to an interface, to a specific remote unicast
   address to be contacted, or to a range of remote unicast addresses
   that are allowed to contact.

   Connection identifier is a 32-bit opaque value, which identifies a
   particular connection of that particular DNCP node.  The value 0 is
   reserved for DNCP and sub-protocol purposes in the TLVs, and MUST NOT
   be used to identify an actual connection.  This definition is in sync
   with [RFC3493], as the non-zero small positive integers should
   comfortably fit within 32 bits.

   (DNCP) peer refers to another DNCP node with which a DNCP node
   communicates directly on a particular connection.

   Node data is a set of TLVs published by a node in the DNCP network.

   Node state is a set of metadata attributes for node data.  It
   includes a sequence number for versioning, a hash value for comparing
   and a timestamp indicating the time passed since its last
   publication.  The hash function and the number of bits used are
   defined in the DNCP profile.

   Network state (hash) is a hash value which represents the current
   state of the network.  The hash function and the number of bits used
   are defined in the DNCP profile.  Whenever any node is added, removed
   or changes its published node data this hash value changes as well.
   It is calculated over the hash values of each reachable nodes' node
   data in ascending order of the respective node identifier.

   Effective (trust) verdict for a certificate is defined as the verdict
   with the highest priority within the set of verdicts announced for
   the certificate in the DNCP network.








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4.  Data Model

   A DNCP node has:

   o  A timestamp indicating the most recent neighbor graph traversal
      described in Section 5.4.

   A DNCP node has for every DNCP node in the DNCP network:

   o  A node identifier, which uniquely identifies the node.

   o  The node data, an ordered set of TLV tuples published by that
      particular node.  This set of TLVs has a well-defined order based
      on ascending binary content (including TLV type and length).  This
      facilitates linear time state delta processing.

   o  The latest update sequence number, a 32 bit number that is
      incremented any time the TLV set is published.  For comparison
      purposes, a looping comparison should be used to avoid problems in
      case of overflow.  An example would be: a < b <=> (a - b) % 2^32 &
      2^31 != 0.

   o  The relative time (in milliseconds) since the current TLV data set
      with the current update sequence number was published.  It is also
      a 32 bit number on the wire.  If this number is close to overflow
      (greater than 2^32-2^16), a node MUST re-publish its TLVs even if
      there is no change to avoid overflow of the value.  In other
      words, absent any other changes, the TLV set MUST be re-published
      roughly every 49 days.

   o  A timestamp identifying the time it was last reachable based on
      neighbor graph traversal described in Section 5.4.

   Additionally, a DNCP node has a set of connections for which DNCP is
   configured to be used.  For each such connection, a node has:

   o  A connection identifier.

   o  An interface, a unicast address of a DNCP peer it should connect
      with, or a range of addresses from which DNCP peers are allowed to
      connect.

   o  A Trickle [RFC6206] instance with parameters I, T, and c.

   For each DNCP peer detected on a connection, a DNCP node has:

   o  The node identifier of the DNCP peer.




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   o  The connection identifier of the DNCP peer.

   o  The most recent address used by the DNCP peer (in an authenticated
      message, if security is enabled).

5.  Operation

   The DNCP protocol consists of Trickle [RFC6206] driven unicast or
   multicast status messages which indicate the current status of shared
   TLV data, and additional unicast message exchanges which ensure DNCP
   peer reachability and synchronize the data when necessary.

   If DNCP is to be used on a multicast-capable interface, as opposed to
   only point-to-point using unicast, a datagram-based transport which
   supports multicast SHOULD be defined in the DNCP profile to be used
   for the messages to be sent to the whole link.  As this is used only
   to identify potential new DNCP nodes, and to notify that an unicast
   exchange should be triggered, the multicast transport does not have
   to be particularly secure.

5.1.  Trickle-Driven Status Update Messages

   Each node MUST send either a Long Network State Update message
   (Section 7.2) or a Short Network State Update message (Section 7.1)
   every time the connection-specific Trickle algorithm [RFC6206]
   instance indicates that an update should be sent.  The destination
   address of the message should be multicast in case of an interface
   which is multicast-capable, or the unicast address of the remote
   party in case of a point-to-point connection.  By default, Long
   Network State Update messages SHOULD be used, but if it is defined as
   undesirable for some case by the DNCP profile, Short Network State
   Update message MUST be sent instead.  This may be useful to avoid
   fragmenting packets to multicast destinations, or for security
   reasons.

   A Trickle state MUST be maintained separately for each connection.
   The Trickle state for all connections is considered inconsistent and
   reset if and only if the locally calculated network state hash
   changes.  This occurs either due to a change in the local node's own
   node data, or due to receipt of more recent data from another node.

   The Trickle algorithm has 3 parameters; Imin, Imax and k.  Imin and
   Imax represent the minimum and maximum values for I, which is the
   time interval during which at least k Trickle updates must be seen on
   a connection to prevent local state transmission.  The actual
   suggested Trickle algorithm parameters are DNCP profile specific, as
   described in Section 10.




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5.2.  Processing of Received Messages

   This section describes how received messages are processed.  The DNCP
   profile may specify criteria based on which received messages are
   ignored.  Any 'reply' mentioned in the steps below denotes sending of
   the specified message via unicast to the originator of the message
   being processed.  If the reply was caused by a multicast message and
   sent to a link with shared bandwidth it SHOULD be delayed by a random
   timespan in [0, Imin/2].

   Upon receipt of:

      Short Network State Update (Section 7.1): If the network state
      hash within the message differs from the locally calculated
      network state hash, the receiver MUST reply with a Network State
      Request message (Section 7.3).

      Long Network State Update (Section 7.2):

      *  If the network state hash within the message matches the
         locally calculated network state hash, stop processing.

      *  Otherwise the receiver MUST identify nodes for which local
         information is outdated (local update sequence number is lower
         than that within the message), potentially incorrect (local
         update sequence number matches but the hash of the node data
         TLV differs) or missing.

      *  If any such nodes are identified, the receiver MUST reply with
         one or more Node Data Request message(s) (Section 7.4)
         containing Request Node Data TLV(s) (Section 8.1.2) for the
         corresponding nodes.

      Network State Request (Section 7.3): the receiver MUST reply with
      a Long Network State Update (Section 7.2).

      Node Data Request (Section 7.4): the receiver MUST reply with the
      requested data in a Node Data Reply message (Section 7.5).
      Optionally - if specified by the DNCP profile - multiple replies
      MAY be sent in order to e.g. keep size of each datagram within the
      PMTU to the destination.  However these replies must be valid
      stand-alone Node Data Reply messages, with the full state for the
      particular nodes.

      Node Data Reply (Section 7.5): If the message contains Node State
      TLVs that are more recent than the local state (the received TLV
      has a higher update sequence number, the node data TLV hash
      differs from the local one, or local data is missing altogether),



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      and if the message also contains corresponding Node Data TLVs, the
      receiver MUST update its locally stored state.

   If a message containing Node State TLVs (Section 8.2.3) is received
   with the node identifier matching the local node identifier and a
   higher update sequence number than its current local value, or the
   same update sequence number and a different hash, the node SHOULD re-
   publish its own node data with an update sequence number 1000 higher
   than the received one.  This may occur normally once due to the local
   node restarting, and not storing the most recently used update
   sequence number.  If this occurs more than once, the DNCP profile
   should provide guidance on how to handle these situations as it
   indicates the existence of a second active node on the network with
   the same node identifier.

5.3.  Adding and Removing Peers

   When receiving a message on a connection from an unknown peer:

      If it is a unicast message, the remote node MUST be added as a
      peer on the connection and a Neighbor TLV (Section 8.2.5) MUST be
      created for it.

      If it is a multicast message, the remote node SHOULD be sent a
      (possibly rate-limited) unicast Network State Request Message
      (Section 7.3).

   If keep-alives are NOT sent by the peer (either DNCP profile does not
   specify the use of keep-alives, or the particular peer chooses not to
   send keep-alive messages), some other means MUST be employed to
   ensure a DNCP peer is present, and when the peer is no longer
   present, the Neighbor TLV and the local DNCP peer state MUST be
   removed.

5.4.  Purging Unreachable Nodes

   When a Neighbor TLV or a whole node is added or removed, the neighbor
   graph SHOULD be traversed for each node following the bidirectional
   neighbor relationships.  These are identified by looking for Neighbor
   TLVs on both nodes, that have the other node's identifier in the
   neighbor node identifier, and local and neighbor connection
   identifiers swapped.  Each node reached should be marked currently
   reachable.

   DNCP nodes MUST be either purged immediately when not marked
   reachable in a particular graph traversal, or eventually after they
   have not been marked reachable within DNCP_GRACE_INTERVAL.  During
   the grace period, the nodes that were not marked reachable in the



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   most recent graph traversal MUST NOT be used for calculation of the
   network state hash, be provided to any applications that need to use
   the whole TLV graph, or be provided to remote nodes.

6.  Keep-Alive Extension

   The Trickle-driven messages provide a mechanism for handling of new
   peer detection (if applicable) on a connection, as well as state
   change notifications.  Another mechanism may be needed to get rid of
   old, no longer valid DNCP peers if the transport or lower layers do
   not provide one.

   If keep-alives are not specified in the DNCP profile, the rest of
   this section MUST be ignored.

   A DNCP profile MAY specify either per-connection or per-peer keep-
   alive support.  This document specifies only per-connection keep-
   alive, thus if per-peer support is required either a lower layer
   mechanism or a definition within the profile is required.

6.1.  Data Model Additions

   The following additions to the Data Model (Section 4) are needed to
   support keep-alive:

   Each node MUST have a timestamp which indicates the last time a
   Network State TLV (Section 8.2.2) was sent for each connection, i.e.
   on an interface or to the point-to-point peer(s).

   Each node MUST have for each peer:

   o  Last consistent state timestamp: a timestamp which indicates the
      last time a consistent Network State TLV (Section 8.2.2) was
      received from the peer.  When adding a new peer, it should be
      initialized to the current time.

6.2.  Periodic Keep-Alive Messages

   For every connection that a keep-alive is specified for in the DNCP
   profile, the connection-specific keep-alive interval MUST be
   maintained.  By default, it is DNCP_KEEPALIVE_INTERVAL.  If there is
   a local value that is preferred for that for any reason
   (configuration, energy conservation, media type, ..), it should be
   substituted instead.  If non-default keep-alive interval is used on
   any connection, a DNCP node MUST publish appropriate Keep-Alive
   Interval TLV(s) (Section 8.2.6).





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   If no traffic containing a Network State TLV (Section 8.2.2) has been
   sent to a particular connection within the connection-specific keep-
   alive interval, a Long Network State Update message (Section 7.2) or
   a Short Network State Update message (Section 7.1) MUST be sent on
   that connection.  The type of message should be chosen based on the
   considerations in Section 5.1.  When such a message is sent, a new
   Trickle transmission time 't' in [I/2, I] MUST be randomly chosen.

6.3.  Received Message Processing Additions

   If the received message contains a Network State TLV (Section 8.2.2)
   which is consistent with the locally calculated network state hash,
   the Last consistent state timestamp for the peer MUST be updated.

6.4.  Neighbor Removal

   For every peer on every connection, the connection-specific keep-
   alive interval must be calculated by looking for Keep-Alive Interval
   TLVs (Section 8.2.6) published by the node, and if none exist, using
   the default value of DNCP_KEEPALIVE_INTERVAL.  If the peer's last
   consistent state timestamp has not been updated for at least
   DNCP_KEEPALIVE_MULTIPLIER times the peer's connection-specific keep-
   alive interval, the Neighbor TLV for that peer and the local DNCP
   peer state MUST be removed.

7.  Protocol Messages

   For point-to-point exchanges, DNCP can run across datagram-based or
   reliable ordered stream-based transports.  If a stream-based
   transport is used, a 32-bit length-value in network byte order is
   sent before each message to indicate the number of bytes the
   following message consists of.

   DNCP messages are encoded as a concatenated sequence of Type-Length-
   Value objects (Section 8).  In order to facilitate fast comparing of
   local state with that in a received message update, all TLVs in every
   encoding scope (either within the message itself, or within a
   container TLV) MUST be placed in ascending order based on the binary
   comparison of both TLV header and value.  By design, the TLVs which
   MUST be present have the lowest available type values, ensuring they
   will naturally occur at the start of the Protocol Message, resembling
   a fixed format header.

   DNCP profiles MAY add additional TLVs to the message specified here,
   or even define additional messages as needed.






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7.1.  Short Network State Update Message

   The Short Network State Update Message is used to announce the
   sender's view of the network state using multicast.

   The following TLVs MUST be present:

   o  One Node Connection TLV (Section 8.2.1) identifying the
      originating node and connection.

   o  One Network State TLV (Section 8.2.2) containing the network state
      hash as calculated by the sender.

   The Short Network Status update message MUST NOT contain any Node
   State TLV(s) (Section 8.2.3).

7.2.  Long Network State Update Message

   The Long Network State Update Message is used to announce the
   sender's view of the network state and all node states using
   multicast or unicast.

   The following TLVs MUST be present:

   o  One Node Connection TLV (Section 8.2.1) identifying the
      originating node and connection.

   o  One Network State TLV (Section 8.2.2) containing the network state
      hash as calculated by the sender.

   o  One or more Node State TLVs (Section 8.2.3) containing the node
      state of DNCP nodes as currently known to the sender.

   The Long Network State Update message MUST include the corresponding
   Node State TLV (Section 8.2.3) for each Node Data TLV used to
   calculate the network state hash.

7.3.  Network State Request Message

   The Network State Request message is used to request the recipient's
   view of the network state and all node states currently known to it.

   The following TLVs MUST be present:

   o  One Node Connection TLV (Section 8.2.1) identifying the
      originating node and connection.





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   o  One Request Network State TLV (Section 8.1.1) indicating the type
      of request.

7.4.  Node Data Request Message

   The Node Data Request message is used to request the node state and
   data of one or more DNCP nodes in the network.

   The following TLVs MUST be present:

   o  One Node Connection TLV (Section 8.2.1) identifying the
      originating node and connection.

   o  One or more Request Node Data TLVs (Section 8.1.2) indicating the
      nodes for which state and data is requested.

7.5.  Node Data Reply Message

   The Node Data Request message is used to provide the node data of one
   or more DNCP nodes in the network.

   The following TLVs MUST be present:

   o  One Node Connection TLV (Section 8.2.1) identifying the
      originating node and connection.

   o  One or more Node State TLV (Section 8.2.3) and Node Data TLV
      (Section 8.2.4) pairs with matching node identifiers for each node
      previously requested in a Node Data Request message (Section 7.4).

8.  Type-Length-Value Objects

   Each TLV is encoded as a 2 byte type field, followed by a 2 byte
   length field (of the value, excluding header; 0 means no value)
   followed by the value itself (if any).  Both type and length fields
   in the header as well as all integer fields inside the value - unless
   explicitly stated otherwise - are represented in network byte order.
   Zero padding bytes MUST be added up to the next 4 byte boundary if
   the length is not divisible by 4.  These padding bytes MUST NOT be
   included in the length field.











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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Type               |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Value                             |
   |                     (variable # of bytes)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For example, type=123 (0x7b) TLV with value 'x' (120 = 0x78) is
   encoded as: 007B 0001 7800 0000.

   Notation:

      .. = octet string concatenation operation.

      H(x) = non-cryptographic hash function specified by DNCP profile.

8.1.  Request TLVs

8.1.1.  Request Network State TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type: REQ-NETWORK-STATE (2)  |           Length: 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV is used to identify a Network State Request message
   (Section 7.3).

8.1.2.  Request Node Data TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: REQ-NODE-DATA (3)    |          Length: >0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV is used within a Node Data Request message (Section 7.4) to
   request node state and node data for the node with matching node
   identifier, if any, to be included in a subsequent Node Data Reply
   message (Section 7.5).



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8.2.  Data TLVs

8.2.1.  Node Connection TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type: NODE-CONNECTION (1)   |          Length: > 4          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Connection Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV identifies both the local node's node identifier, as well as
   the particular connection identifier.  It MUST be sent in all
   messages.

8.2.2.  Network State TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Type: NETWORK-STATE (10)   |          Length: > 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     H(H(node data TLV 1) .. [...] .. H(node data TLV N))      |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV contains the current locally calculated network state hash.
   The network state hash is derived by calculating the hash value for
   each currently reachable node's Node Data TLV, concatenating said
   hash values based on the ascending order of their corresponding node
   identifiers, and hashing the resulting concatenated hash values.

8.2.3.  Node State TLV












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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type: NODE-STATE (11)    |          Length: > 8          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Update Sequence Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Milliseconds since Origination                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        H(node data TLV)                       |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV represents the local node's knowledge about the published
   state of a node in the DNCP network identified by the node identifier
   field in the TLV.

   The whole network should have roughly same idea about the time since
   origination of any particular published state.  Therefore every node,
   including the originating one, MUST increment the time whenever it
   needs to send a Node State TLV for an already published Node Data
   TLV.  This age value is not included within the Node Data TLV,
   however, as that is immutable and used to detect changes in the
   network state.

8.2.4.  Node Data TLV

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type: NODE-DATA (12)     |         Length: > 4           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        node identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Update Sequence Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Nested TLVs containing node information            |







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8.2.5.  Neighbor TLV (within Node Data TLV)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Type: NEIGHBOR (13)     |          Length: > 8          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    neighbor node identifier                   |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Neighbor Connection Identifier                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Local Connection Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV indicates that the node in question vouches that the
   specified neighbor is reachable by it on the specified local
   connection.  The presence of this TLV at least guarantees that the
   node publishing it has received traffic from the neighbor recently.
   For guaranteed up-to-date bidirectional reachability, the existence
   of both nodes' matching Neighbor TLVs should be checked.

8.2.6.  Keep-Alive Interval TLV (within Node Data TLV)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type: KEEP-ALIVE-INTERVAL (14)|          Length: 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Connection Identifier                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Interval                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV indicates a non-default interval being used to send keep-
   alive messages specified in Section 6.

   Connection identifier is used to identify the particular connection
   for which the interval applies.  If 0, it applies for ALL connections
   for which no specific TLV exists.

   Interval specifies the interval in milliseconds at which the node
   sends keep-alives.  A value of zero means no keep-alives are sent at
   all; in that case, some lower layer mechanism that ensures presence
   of nodes MUST be available and used.





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8.3.  Custom TLV (within/without Node Data TLV)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type: CUSTOM-DATA (15)    |         Length: > 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            H(URI)                             |
   |                  (length fixed in DNCP profile)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Opaque Data                          |

   This TLV can be used to contain anything; the URI used should be
   under control of the author of that specification.  For example:

   V = H('http://example.com/author/json-for-dncp') .. '{"cool": "json
   extension!"}'

   or

   V = H('mailto:author@example.com') .. '{"cool": "json extension!"}'

9.  Security and Trust Management

   If specified in the DNCP profile, either DTLS [RFC6347] or TLS
   [RFC5246] may be used to authenticate and encrypt either some (if
   specified optional in the profile), or all unicast traffic.  The
   following methods for establishing trust are defined, but it is up to
   the DNCP profile to specify which ones may, should or must be
   supported.

9.1.  Pre-Shared Key Based Trust Method

   A PSK-based trust model is a simple security management mechanism
   that allows an administrator to deploy devices to an existing network
   by configuring them with a pre-defined key, similar to the
   configuration of an administrator password or WPA-key.  Although
   limited in nature it is useful to provide a user-friendly security
   mechanism for smaller networks.

9.2.  PKI Based Trust Method

   A PKI-based trust-model enables more advanced management capabilities
   at the cost of increased complexity and bootstrapping effort.  It
   however allows trust to be managed in a centralized manner and is
   therefore useful for larger networks with a need for an authoritative
   trust management.




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9.3.  Certificate Based Trust Consensus Method

   The certificate-based consensus model is designed to be a compromise
   between trust management effort and flexibility.  It is based on
   X.509-certificates and allows each DNCP node to provide a verdict on
   any other certificate and a consensus is found to determine whether a
   node using this certificate or any certificate signed by it is to be
   trusted.

   The current effective trust verdict for any certificate is defined as
   the one with the highest priority from all verdicts announced for
   said certificate at the time.

9.3.1.  Trust Verdicts

   Trust Verdicts are statements of DNCP nodes about the trustworthiness
   of X.509-certificates.  There are 5 possible verdicts in order of
   ascending priority:

   0 Neutral  : no verdict exists but the DNCP network should determine
      one.

   1 Cached Trust  : the last known effective verdict was Configured or
      Cached Trust.

   2 Cached Distrust  : the last known effective verdict was Configured
      or Cached Distrust.

   3 Configured Trust  : trustworthy based upon an external ceremony or
      configuration.

   4 Configured Distrust  : not trustworthy based upon an external
      ceremony or configuration.

   Verdicts are differentiated in 3 groups:

   o  Configured verdicts are used to announce explicit verdicts a node
      has based on any external trust bootstrap or predefined relation a
      node has formed with a given certificate.

   o  Cached verdicts are used to retain the last known trust state in
      case all nodes with configured verdicts about a given certificate
      have been disconnected or turned off.

   o  The Neutral verdict is used to announce a new node intending to
      join the network so a final verdict for it can be found.





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   The current effective trust verdict for any certificate is defined as
   the one with the highest priority within the set of verdicts +
   announced for the certificate in the DNCP network.  A node MUST be
   trusted for participating in the DNCP network if and only if the
   current effective verdict for its own certificate or any one in its
   certificate hierarchy is (Cached or Configured) Trust and none of the
   certificates in its hierarchy have an effective verdict of (Cached or
   Configured) Distrust.  In case a node has a configured verdict, which
   is different from the current effective verdict for a certificate,
   the current effective verdict takes precedence in deciding
   trustworthiness.  Despite that, the node still retains and announces
   its configured verdict.

9.3.2.  Trust Cache

   Each node SHOULD maintain a trust cache containing the current
   effective trust verdicts for all certificates currently announced in
   the DNCP network.  This cache is used as a backup of the last known
   state in case there is no node announcing a configured verdict for a
   known certificate.  It SHOULD be saved to a non-volatile memory at
   reasonable time intervals to survive a reboot or power outage.

   Every time a node (re)joins the network or detects the change of an
   effective trust verdict for any certificate, it will synchronize its
   cache, i.e. store new effective verdicts overwriting any previously
   cached verdicts.  Configured verdicts are stored in the cache as
   their respective cached counterparts.  Neutral verdicts are never
   stored and do not override existing cached verdicts.

9.3.3.  Announcement of Verdicts

   A node SHOULD always announce any configured trust verdicts it has
   established by itself, and it MUST do so if announcing the configured
   trust verdict leads to a change in the current effective verdict for
   the respective certificate.  In absence of configured verdicts, it
   MUST announce cached trust verdicts it has stored in its trust cache,
   if one of the following conditions applies:

   o  The stored verdict is Cached Trust and the current effective
      verdict for the certificate is Neutral or does not exist.

   o  The stored verdict is Cached Distrust and the current effective
      verdict for the certificate is Cached Trust.

   A node rechecks these conditions whenever it detects changes of
   announced trust verdicts anywhere in the network.





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   Upon encountering a node with a hierarchy of certificates for which
   there is no effective verdict, a node adds a Neutral Trust-Verdict-
   TLV to its node data for all certificates found in the hierarchy, and
   publishes it until an effective verdict different from Neutral can be
   found for any of the certificates, or a reasonable amount of time (10
   minutes is suggested) with no reaction and no further authentication
   attempts has passed.  Such verdicts SHOULD also be limited in rate
   and number to prevent denial-of-service attacks.

   Trust verdicts are announced using Trust-Verdict TLVs:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type: Trust-Verdict (16)    |        Length: 37-100         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Verdict    |                 (reserved)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                                                               |
   |                      SHA-256 Fingerprint                      |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Common Name                          |

      Verdict represents the numerical index of the verdict.

      (reserved) is reserved for future additions and MUST be set to 0
      when creating TLVs and ignored when parsing them.

      SHA-256 Fingerprint contains the SHA-256 [RFC6234] hash value of
      the certificate in DER-format.

      Common Name contains the variable-length (1-64 bytes) common name
      of the certificate.  Final byte MUST have value of 0.

9.3.4.  Bootstrap Ceremonies

   The following non-exhaustive list of methods describes possible ways
   to establish trust relationships between DNCP nodes and node
   certificates.  Trust establishment is a two-way process in which the
   existing network must trust the newly added node and the newly added
   node must trust at least one of its neighboring nodes.  It is
   therefore necessary that both the newly added node and an already



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   trusted node perform such a ceremony to successfully introduce a node
   into the DNCP network.  In all cases an administrator MUST be
   provided with external means to identify the node belonging to a
   certificate based on its fingerprint and a meaningful common name.

9.3.4.1.  Trust by Identification

   A node implementing certificate-based trust MUST provide an interface
   to retrieve the current set of effective trust verdicts, fingerprints
   and names of all certificates currently known and set configured
   trust verdicts to be announced.  Alternatively it MAY provide a
   companion DNCP node or application with these capabilities with which
   it has a pre-established trust relationship.

9.3.4.2.  Preconfigured Trust

   A node MAY be preconfigured to trust a certain set of node or CA
   certificates.  However such trust relationships MUST NOT result in
   unwanted or unrelated trust for nodes not intended to be run inside
   the same network (e.g. all other devices by the same manufacturer).

9.3.4.3.  Trust on Button Press

   A node MAY provide a physical or virtual interface to put one or more
   of its internal network interfaces temporarily into a mode in which
   it trusts the certificate of the first DNCP node it can successfully
   establish a connection with.

9.3.4.4.  Trust on First Use

   A node which is not associated with any other DNCP node MAY trust the
   certificate of the first DNCP node it can successfully establish a
   connection with.  This method MUST NOT be used when the node has
   already associated with any other DNCP node.

10.  DNCP Profile-Specific Definitions

   Each DNCP profile MUST define following:

   o  How the messages are secured:

      *  Not at all,

      *  optionally or always with the TLS scheme defined here using one
         or more of the methods, or

      *  with something else.




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      Given that links with DNCP nodes can be sufficiently secured or
      isolated it is possible to run DNCP in a secure manner without
      using any form of authentication or encryption.

   o  Unicast and optionally multicast transport protocol(s) to be used.
      If TLS scheme within this document is to be used security, TLS or
      DTLS support for at least the unicast transport protocol is
      mandatory.

   o  Transport protocols' parameters such as port numbers to be used,
      or multicast address to be used.  Unicast, multicast, and secure
      unicast may each require different parameters, if applicable.

   o  When receiving messages, what sort of messages are dropped, as
      specified in Section 5.2.

   o  What is the criteria for sending Trickle-based Long Network State
      Update message (Section 7.2) on an interface or to a DNCP peer.

   o  How to deal with node identifier collision as described in
      Section 5.2.  Main options are either for one or both nodes to
      assign new node identifiers to themselves, or to notify someone
      about a fatal error condition in the DNCP network.

   o  Imin, Imax and k ranges to be suggested for implementations to be
      used in the Trickle algorithm.  The Trickle algorithm does not
      require these to be same across all implementations for it to
      work, but similar orders of magnitude helps implementations of a
      DNCP profile to behave more consistently and to facilitate
      estimation of lower and upper bounds for behavior of the network.

   o  Hash function H(x) to be used, and how many bits of the input are
      actually used.  The chosen hash function is used to handle both
      hashing of node specific data, and network state hash, which is a
      hash of node specific data hashes.  SHA-256 defined in [RFC6234]
      is the recommended default choice.

   o  DNCP_NODE_IDENTIFIER_LENGTH: The fixed length of a node identifier
      (in bytes).

   o  DNCP_GRACE_INTERVAL: How long node data for unreachable nodes is
      kept.

   o  Whether to send keep-alives, and if so, on an interface, using
      multicast, or directly using unicast to peers.  Keep-alive has
      also associated parameters:





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      *  DNCP_KEEPALIVE_INTERVAL: How often keep-alive messages are to
         be sent by default (if enabled).

      *  DNCP_KEEPALIVE_MULTIPLIER: How many times the
         DNCP_KEEPALIVE_INTERVAL (or peer-supplied keep-alive interval
         value) a node may not be heard from to be considered still
         valid.

11.  Security Considerations

   DNCP profiles may use multicast to indicate DNCP state changes and
   for keep-alive purposes.  However, no actual data TLVs will be sent
   across that channel.  Therefore an attacker may only learn hash
   values of the state within DNCP and may be able to trigger unicast
   synchronization attempts between nodes on a local link this way.  A
   DNCP node should therefore rate-limit its reactions to multicast
   packets.

   When using DNCP to bootstrap a network, PKI based solutions may have
   issues when validating certificates due to potentially unavailable
   accurate time, or due to inability to use the network to either check
   Certifcate Revocation Lists or perform on-line validation.

   The Certificate-based trust consensus mechanism defined in this
   document allows for a consenting revocation, however in case of a
   compromised device the trust cache may be poisoned before the actual
   revocation happens allowing the distrusted device to rejoin the
   network using a different identity.  Stopping such an attack might
   require physical intervention and flushing of the trust caches.

12.  IANA Considerations

   IANA should set up a registry for DNCP TLV types, with the following
   initial contents:

   0: Reserved (should not happen on wire)

   1: Node connection

   2: Request network state

   3: Request node data

   4-9: Reserved for DNCP profile use

   10: Network state

   11: Node state



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   12: Node data

   13: Neighbor

   14: Keep-alive interval

   15: Custom

   16: Trust-Verdict

   17-31: Reserved for future DNCP versions.

   192-255: Reserved for per-implementation experimentation.  The nodes
   using TLV types in this range SHOULD use e.g.  Custom TLV to identify
   each other and therefore eliminate potential conflict caused by
   potential different use of same TLV numbers.

   For the rest of the values (32-191, 256-65535), policy of 'standards
   action' should be used.

13.  References

13.1.  Normative references

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6206]  Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
              "The Trickle Algorithm", RFC 6206, March 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

13.2.  Informative references

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6", RFC
              3493, February 2003.

   [RFC6234]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234, May 2011.







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Appendix A.  Some Outstanding Issues

   Should per-peer keep-alives be specified here?  They are essentially
   constant unicast keep-alives, as opposed to unicast OR multicast per-
   connection ones are.

Appendix B.  Some Obvious Questions and Answers

   Q: Should there be nested container syntax that is actually self-
   describing? (i.e. type flag that indicates container, no body except
   sub-TLVs?)

   A: Not for now, but perhaps valid design.. TBD.

   Q: Add third case for multicast - 'medium' network state, which is
   'long' one, but partial?

   A: Drops typical convergence on large networks 5->3 packets, at
   expense of some specification/implementation complexity.  However, as
   anything else than short network state leaks information via
   multicast, it does not seem worth it as secure protocols probably
   want to prevent multicast sending of anything else than short network
   state in any case.

   Q: 32-bit connection id?

   A: Here, it would save 32 bits per neighbor if it was 16 bits (and
   less is not realistic).  However, TLVs defined elsewhere would not
   seem to even gain that much on average.  32 bits is also used for
   ifindex in various operating systems, making for simpler
   implementation.

   Q: Why not doing (performance thing X, Y or Z)?

   A: This is designed mostly to be minimal (only timers Trickle ones;
   everything triggered by Trickle-driven messages or local state
   changes).  However, feel free to suggest better (even more minimal)
   design which works.

Appendix C.  Changelog

   draft-stenberg-homenet-dncp-00: Split from pre-version of draft-ietf-
   homenet-hncp-03 generic parts.  Changes that affect implementations:

   o  TLVs were renumbered.

   o  TLV length does not include header (=-4).  This facilitates e.g.
      use of DHCPv6 option parsing libraries (same encoding), and



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      reduces complexity (no need to handle error values of length less
      than 4).

   o  Trickle is reset only when locally calculated network state hash
      is changes, not as remote different network state hash is seen.
      This prevents e.g. attacks by multicast with one multicast packet
      to force Trickle reset on every interface of every node on a link.

   o  Instead of 'ping', use 'keep-alive' (optional) for dead peer
      detection.  Different message used!

Appendix D.  Draft Source

   As usual, this draft is available at https://github.com/fingon/ietf-
   drafts/ in source format (with nice Makefile too).  Feel free to send
   comments and/or pull requests if and when you have changes to it!

Appendix E.  Acknowledgements

   Thanks to Ole Troan, Pierre Pfister, Mark Baugher, Mark Townsley,
   Juliusz Chroboczek and Jiazi Yi for their contributions to the draft.

Authors' Addresses

   Markus Stenberg
   Helsinki  00930
   Finland

   Email: markus.stenberg@iki.fi


   Steven Barth
   Halle  06114
   Germany

   Email: cyrus@openwrt.org















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