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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: October 26, 2015
                                                          April 24, 2015


                  Distributed Node Consensus Protocol
                       draft-ietf-homenet-dncp-03

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 October 26, 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 Updates . . . . . . . . . . . . . .   7
     5.2.  Processing of Received TLVs . . . . . . . . . . . . . . .   7
     5.3.  Adding and Removing Peers . . . . . . . . . . . . . . . .   9
     5.4.  Purging Unreachable Nodes . . . . . . . . . . . . . . . .   9
   6.  Optional Extensions . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Keep-Alives . . . . . . . . . . . . . . . . . . . . . . .   9
       6.1.1.  Data Model Additions  . . . . . . . . . . . . . . . .  10
       6.1.2.  Per-Endpoint Periodic Keep-Alives . . . . . . . . . .  10
       6.1.3.  Per-Peer Periodic Keep-Alives . . . . . . . . . . . .  10
       6.1.4.  Received TLV Processing Additions . . . . . . . . . .  11
       6.1.5.  Neighbor Removal  . . . . . . . . . . . . . . . . . .  11
     6.2.  Support For Dense Broadcast Links . . . . . . . . . . . .  11
     6.3.  Node Data Fragmentation . . . . . . . . . . . . . . . . .  12
   7.  Type-Length-Value Objects . . . . . . . . . . . . . . . . . .  12
     7.1.  Request TLVs  . . . . . . . . . . . . . . . . . . . . . .  13
       7.1.1.  Request Network State TLV . . . . . . . . . . . . . .  13
       7.1.2.  Request Node State TLV  . . . . . . . . . . . . . . .  13
     7.2.  Data TLVs . . . . . . . . . . . . . . . . . . . . . . . .  14
       7.2.1.  Node Endpoint TLV . . . . . . . . . . . . . . . . . .  14
       7.2.2.  Network State TLV . . . . . . . . . . . . . . . . . .  14
       7.2.3.  Node State TLV  . . . . . . . . . . . . . . . . . . .  14
       7.2.4.  Custom TLV  . . . . . . . . . . . . . . . . . . . . .  15
     7.3.  Data TLVs within Node State TLV . . . . . . . . . . . . .  16
       7.3.1.  Fragment Count TLV  . . . . . . . . . . . . . . . . .  16
       7.3.2.  Neighbor TLV  . . . . . . . . . . . . . . . . . . . .  16
       7.3.3.  Keep-Alive Interval TLV . . . . . . . . . . . . . . .  17
   8.  Security and Trust Management . . . . . . . . . . . . . . . .  18
     8.1.  Pre-Shared Key Based Trust Method . . . . . . . . . . . .  18
     8.2.  PKI Based Trust Method  . . . . . . . . . . . . . . . . .  18
     8.3.  Certificate Based Trust Consensus Method  . . . . . . . .  18
       8.3.1.  Trust Verdicts  . . . . . . . . . . . . . . . . . . .  18
       8.3.2.  Trust Cache . . . . . . . . . . . . . . . . . . . . .  19
       8.3.3.  Announcement of Verdicts  . . . . . . . . . . . . . .  20
       8.3.4.  Bootstrap Ceremonies  . . . . . . . . . . . . . . . .  21
   9.  DNCP Profile-Specific Definitions . . . . . . . . . . . . . .  22
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  23
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25



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     12.1.  Normative references . . . . . . . . . . . . . . . . . .  25
     12.2.  Informative references . . . . . . . . . . . . . . . . .  25
   Appendix A.  Some Questions and Answers [RFC Editor: please
                remove]  . . . . . . . . . . . . . . . . . . . . . .  25
   Appendix B.  Changelog [RFC Editor: please remove]  . . . . . . .  25
   Appendix C.  Draft Source [RFC Editor: please remove] . . . . . .  27
   Appendix D.  Acknowledgements . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

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 validates the set of data within it by ensuring that it is
   reachable via nodes that are currently accounted for; therefore,
   unlike Time-To-Live (TTL) based solutions, it does not require
   periodic re-publishing of the data by the nodes.  On the other hand,
   it does require the topology to be visible to every node that wants
   to be able to identify unreachable nodes and therefore remove old,
   stale data.  Another notable feature is the use of Trickle to send
   status updates as it makes the DNCP network very thrifty when there
   are no updates.  DNCP is most suitable for data that changes only
   gradually to gain the maximum benefit from using Trickle, and if more
   rapid state exchanges are needed, something point-to-point is
   recommended and just e.g. publishing of addresses of the services
   within DNCP.

   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

   A DNCP profile is a definition of a set of rules and values listed in
   Section 9 specifying the behavior of a DNCP based protocol, such as
   the used transport method.  For readability, any DNCP profile



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   specific parameters with a profile-specific fixed value are prefixed
   with DNCP_.

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

   The DNCP network is a set of DNCP nodes running the same DNCP profile
   that can reach each other, either via discovered connectivity 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.

   A DNCP message is an abstract concept: when using a reliable stream
   transport, the whole stream of TLVs can be considered a single
   message, with new TLVs becoming one by one available once they have
   been fully received.  On a datagram transport, each individual
   datagram is considered a separate message.

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

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

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

   An endpoint 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.

   The endpoint identifier is a 32-bit opaque value, which identifies a
   particular endpoint 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 endpoint.  This definition is in sync
   with the interface index definition in [RFC3493], as the non-zero
   small positive integers should comfortably fit within 32 bits.

   A (DNCP) peer refers to another DNCP node with which a DNCP node
   communicates directly using a particular local and remote endpoint
   pair.

   The node data is a set of TLVs published by a node in the DNCP
   network.  The whole node data is owned by the node that publishes it,
   and it MUST be passed along as-is, including TLVs unknown to the
   forwarder.



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   The 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.

   The 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 updates its published node data this hash value changes as well.
   It is calculated over each reachable nodes' update number
   concatenated with the hash value of its node data in ascending order
   of the respective node identifier.

   The 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.

   The neighbor graph is the undirected graph of DNCP nodes produced by
   retaining only bidirectional peer relationships between nodes.

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 MUST use 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



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      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 endpoints for which DNCP is
   configured to be used.  For each such endpoint, a node has:

   o  An endpoint identifier, a 32-bit opaque value.

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

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

   For each remote (DNCP node, endpoint) pair detected on a local
   endpoint, a DNCP node has:

   o  The node identifier of the DNCP peer.

   o  The endpoint identifier of the DNCP peer.

   o  The most recent address used by the DNCP peer (authenticated and
      authorized, if security is enabled).

5.  Operation

   The DNCP protocol consists of Trickle [RFC6206] driven unicast or
   multicast status payloads which indicate the current status of shared
   TLV data and additional unicast 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 TLVs 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.

   To form bidirectional peer relationships DNCP requires identification
   of the endpoints used for communication.  A DNCP node therefore MUST
   include an Endpoint TLV (Section 7.2.1) in each message intended to
   maintain a DNCP peer relationship.





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5.1.  Trickle-Driven Status Updates

   When employing unreliable transport, each node MUST send a Network
   State TLV (Section 7.2.2) every time the endpoint-specific Trickle
   algorithm [RFC6206] instance indicates that an update should be sent.
   Multicast MUST be employed on a multicast-capable interface;
   otherwise, unicast can be used as well.  If possible, most recent,
   recently changed, or best of all, all known Node State TLVs
   (Section 7.2.3) SHOULD be also included, unless it is defined as
   undesirable for some reason by the DNCP profile.  Avoiding sending
   some or all Node State TLVs may make sense to avoid fragmenting
   packets to multicast destinations, or for security reasons.

   A Trickle state MUST be maintained separately for each endpoint which
   employs unreliable transport.  The Trickle state for all endpoints 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
   an endpoint to prevent local state transmission.  The actual
   suggested Trickle algorithm parameters are DNCP profile specific, as
   described in Section 9.

5.2.  Processing of Received TLVs

   This section describes how received TLVs are processed.  The DNCP
   profile may specify criteria based on which particular TLVs are
   ignored.  Any 'reply' mentioned in the steps below denotes sending of
   the specified TLV(s) via unicast to the originator of the TLV being
   processed.  If the TLV being replied to was received via multicast
   and it was sent to a link with shared bandwidth, the reply SHOULD be
   delayed by a random timespan in [0, Imin/2].  Sending of replies
   SHOULD be rate-limited by the implementation, and in case of excess
   load (or some other reason), a reply MAY be omitted altogether.

   Upon receipt of:

   o  Request Network State TLV (Section 7.1.1): The receiver MUST reply
      with a Network State TLV (Section 7.2.2) and a Node State TLV
      (Section 7.2.3) for each node data used to calculate the network
      state hash.  The Node State TLVs SHOULD NOT contain the optional
      node data part.





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   o  Request Node State TLV (Section 7.1.2): If the receiver has node
      data for the corresponding node, it MUST reply with a Node State
      TLV (Section 7.2.3) for the corresponding node.  The optional node
      data part MUST be included in the TLV.

   o  Network State TLV (Section 7.2.2): If the network state hash
      differs from the locally calculated network state hash, and the
      receiver is unaware of any particular node state differences with
      the sender, the receiver MUST reply with a Request Network State
      TLV (Section 7.1.1).  The receiver MAY omit this, if there are
      already recent pending requests for network or node state.

   o  Node State TLV (Section 7.2.3):

      *  If the node identifier matches the local node identifier and
         the TLV has 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 another active node with the same node identifier.

      *  If the node identifier does not match the local node
         identifier, and the local information is outdated for the
         corresponding node (local update sequence number is lower than
         that within the TLV), potentially incorrect (local update
         sequence number matches but the node data hash differs), or the
         data is altogether missing:

         +  If the TLV does not contain node data, and the hash of the
            node data differs, the receiver MUST reply with a Request
            Node State TLV (Section 7.1.2) for the corresponding node.

         +  Otherwise the receiver MUST update its locally stored state
            for that node (node data if present, update sequence number,
            relative time) to match the received TLV.

   o  Any other TLV: TLVs not recognized by the receiver MUST be
      silently ignored.

   If secure unicast transport is configured for an endpoint, any Node
   State TLVs received via insecure multicast MUST be silently ignored.






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5.3.  Adding and Removing Peers

   When receiving a Node Endpoint TLV (Section 7.2.1) on an endpoint
   from an unknown peer:

   o  If it comes via unicast, the remote node MUST be added as a peer
      on the endpoint and a Neighbor TLV (Section 7.3.2) MUST be created
      for it.

   o  If it comes via multicast, the node SHOULD be sent a (possibly
      rate-limited) unicast Request Network State TLV (Section 7.1.1).

   If keep-alives specified in Section 6.1 are NOT sent by the peer
   (either the DNCP profile does not specify the use of keep-alives or
   the particular peer chooses not to send keep-alives), some other
   means MUST be employed to ensure a DNCP peer is present.  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, starting from the local node.  The edges
   to be traversed 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 endpoint 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
   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.  Optional Extensions

   This section specifies extensions to the core protocol that a DNCP
   profile may want to use.

6.1.  Keep-Alives

   Trickle-driven status updates (Section 5.1) provide a mechanism for
   handling of new peer detection (if applicable) on an endpoint, 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.



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

   A DNCP profile MAY specify either per-endpoint or per-peer keep-alive
   support.

   For every endpoint that a keep-alive is specified for in the DNCP
   profile, the endpoint-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 a non-default keep-alive interval is used on
   any endpoint, a DNCP node MUST publish appropriate Keep-Alive
   Interval TLV(s) (Section 7.3.3) within its node data.

6.1.1.  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 7.2.2) was sent for each endpoint, i.e. on
   an interface or to the point-to-point peer(s).

   Each node MUST have for each peer:

   o  Last contact timestamp: a timestamp which indicates the last time
      a consistent Network State TLV (Section 7.2.2) was received from
      the peer via multicast, or anything was received via unicast.
      When adding a new peer, it should be initialized to the current
      time.

6.1.2.  Per-Endpoint Periodic Keep-Alives

   If per-endpoint keep-alives are enabled on an endpoint with a
   multicast-enabled link, and if no traffic containing a Network State
   TLV (Section 7.2.2) has been sent to a particular endpoint within the
   endpoint-specific keep-alive interval, a Network State TLV
   (Section 7.2.2) MUST be sent on that endpoint, and a new Trickle
   transmission time 't' in [I/2, I] MUST be randomly chosen.  The
   actual sending time SHOULD be further delayed by a random timespan in
   [0, Imin/2].

6.1.3.  Per-Peer Periodic Keep-Alives

   If per-peer keep-alives are enabled on a unicast-only endpoint, and
   if no traffic containing a Network State TLV (Section 7.2.2) has been
   sent to a particular peer within the endpoint-specific keep-alive



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   interval, a Network State TLV (Section 7.2.2) MUST be sent to the
   peer and a new Trickle transmission time 't' in [I/2, I] MUST be
   randomly chosen.

6.1.4.  Received TLV Processing Additions

   If a TLV is received via unicast from the peer, the Last contact
   timestamp for the peer MUST be updated.

   On receipt of a Network State TLV (Section 7.2.2) which is consistent
   with the locally calculated network state hash, the Last contact
   timestamp for the peer MUST be updated.

6.1.5.  Neighbor Removal

   For every peer on every endpoint, the endpoint-specific keep-alive
   interval must be calculated by looking for Keep-Alive Interval TLVs
   (Section 7.3.3) published by the node, and if none exist, using the
   default value of DNCP_KEEPALIVE_INTERVAL.  If the peer's last contact
   state timestamp has not been updated for at least
   DNCP_KEEPALIVE_MULTIPLIER times the peer's endpoint-specific keep-
   alive interval, the Neighbor TLV for that peer and the local DNCP
   peer state MUST be removed.

6.2.  Support For Dense Broadcast Links

   An upper bound for the number of neighbors that are allowed for a
   (particular type of) link that an endpoint runs on SHOULD be provided
   by a DNCP profile, user configuration, or some hardcoded default in
   the implementation.  If an implementation does not support this, the
   rest of this subsection MUST be ignored.

   If the specified limit is exceeded, nodes without the highest Node
   Identifier on the link SHOULD treat the endpoint as a unicast
   endpoint connected to the node that has the highest Node Identifier
   detected on the link.  The nodes MUST also keep listening to
   multicast traffic to both detect the presence of that node, and to
   react to nodes with a higher Node Identifier appearing.  If the
   highest Node Identifier present on the link changes, the remote
   unicast address of unicast endpoints MUST be changed.  If the Node
   Identifier of the local node is the highest one, the node MUST keep
   the endpoint in multicast mode, and the node MUST allow others to
   peer with it over the link via unicast as well.








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6.3.  Node Data Fragmentation

   A DNCP profile may be required to support node data which would not
   the fit maximum size of a single Node State TLV (Section 7.2.3)
   (roughly 64KB of payload), or use a datagram-only transport with a
   limited MTU and no reliable support for fragmentation.  To handle
   such cases, a DNCP profile MAY specify a fixed number of trailing
   bytes in the Node Identifier to represent a fragment number
   indicating a part of a node's node data.  The profile MAY also
   specify an upper bound for the size of a single fragment to
   accommodate limitations of links in the network.

   The data within Node State TLVs of fragments with non-zero fragment
   number must be treated as opaque (as they may not contain even a
   single full TLV).  However, the concatenated node data for a
   particular node MUST be produced by concatenating all node data for
   each fragment, in ascending fragment number order.  The concatenated
   node data MUST follow the ordering described in Section 4.

   Any Node Identifiers on the wire used to identify the own or any
   other node MUST have the fragment number 0.  For algorithm purposes,
   the relative time since the most recent fragment change MUST be used,
   regardless of fragment number.  Therefore, even if just part of the
   node data fragments change, they all are considered refreshed if one
   of them is.

   If using fragmentation, the unreachable node purging defined in
   Section 5.4 is extended so that if a Fragment Count TLV
   (Section 7.3.1) is present within the fragment number 0, all
   fragments up to fragment number specified in the Count field are also
   considered reachable if the fragment number 0 itself is reachable
   based on graph traversal.

7.  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.

7.1.  Request TLVs

7.1.1.  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 (1)  |           Length: 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV is used to request response with a Network State TLV
   (Section 7.2.2) and all Node State TLVs (Section 7.2.3).

7.1.2.  Request Node 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-NODE-STATE (2)    |          Length: >0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV is used to request response with a Node State TLV
   (Section 7.2.3) for the node with matching node identifier which also
   includes the node data.




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7.2.  Data TLVs

7.2.1.  Node Endpoint 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-ENDPOINT (3)     |          Length: > 4          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Endpoint Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV identifies both the local node's node identifier, as well as
   the particular endpoint's endpoint identifier.  It MUST be sent in
   every message if bidirectional peer relationship is desired with
   remote nodes on that endpoint.  Bidirectional peer relationship is
   not necessary for read-only access to the DNCP state, but it is
   required to be able to publish something.

7.2.2.  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 (4)    |          Length: > 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     H(H(update number of node 1) .. H(node data of node 1) .. |
   |    .. H(update number of node N) .. H(node data of node N))   |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV contains the current locally calculated network state hash.
   It is calculated over each reachable nodes' update number
   concatenated with the hash value of its node data in ascending order
   of the respective node identifier.

7.2.3.  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 (5)     |          Length: > 8          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Node Identifier                        |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Update Sequence Number                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Milliseconds since Origination                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         H(node data)                          |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |(optionally) Nested TLVs containing node information           |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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 already published node data.

   The actual node data of the node may be included within the TLV as
   well; see Section 5.2 for the cases where it MUST or MUST NOT be
   included.  In a DNCP profile which supports fragmentation, described
   in Section 6.3, the TLV data may be only partial and not really
   usable without other fragments.

7.2.4.  Custom 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 (6)     |         Length: > 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            H(URI)                             |
   |                  (length fixed in DNCP profile)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Opaque Data                          |




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   This TLV can be used to contain anything; the URI used should be
   under control of the author of that specification.  The TLV may
   appear within protocol exchanges, or within Node State TLV
   (Section 7.2.3).  For example:

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

   or

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

7.3.  Data TLVs within Node State TLV

   These TLVs are DNCP-specific parts of node-specific node data, and
   are encoded within the Node State TLVs.  If encountered outside Node
   State TLV, they MUST be silently ignored.

7.3.1.  Fragment Count 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: FRAGMENT-COUNT (7)     |         Length: > 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Count                             |
   |                  (length fixed in DNCP profile)               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   If the DNCP profile supports node data fragmentation as specified in
   Section 6.3, this TLV indicates that the node data is encoded as a
   sequence of Node State TLVs.  Following Node State TLVs with Node
   Identifiers up to Count higher than the current one MUST be
   considered reachable and part of the same logical set of node data
   that this TLV is within.  The fragment portion of the Node Identifier
   of the Node State TLV this is TLV appears in MUST be zeros.

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

   This TLV indicates that the node in question vouches that the
   specified neighbor is reachable by it on the specified local
   endpoint.  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.

7.3.3.  Keep-Alive Interval 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 (9) |          Length: 8            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Endpoint Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Interval                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This TLV indicates a non-default interval being used to send keep-
   alives specified in Section 6.1.

   Endpoint identifier is used to identify the particular endpoint for
   which the interval applies.  If 0, it applies for ALL endpoints 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.  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.

8.1.  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.

8.2.  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.

8.3.  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.

8.3.1.  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.




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   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.

   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.

8.3.2.  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.





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   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.

8.3.3.  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.

   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:
















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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: Trust-Verdict (10)    |        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.

8.3.4.  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
   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.

8.3.4.1.  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



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   companion DNCP node or application with these capabilities with which
   it has a pre-established trust relationship.

8.3.4.2.  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).

8.3.4.3.  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.

8.3.4.4.  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.

9.  DNCP Profile-Specific Definitions

   Each DNCP profile MUST define following:

   o  How the transport is secured: Not at all, optionally or always
      with the TLS scheme defined here using one or more of the methods,
      or with something else.  If the 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.





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   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:

      *  DNCP_KEEPALIVE_INTERVAL: How often keep-alives 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.

   o  Whether to support fragmentation, and if so, the number of bytes
      reserved for fragment count in the node identifier.

10.  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.



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   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.

11.  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: Request network state

   2: Request node state

   3: Node endpoint

   4: Network state

   5: Node state

   6: Custom

   7: Fragment count

   8: Neighbor

   9: Keep-alive interval

   10: Trust-Verdict

   32-191: Reserved for per-DNCP profile use

   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 (11-31, 256-65535), policy of 'standards
   action' should be used.



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12.  References

12.1.  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.

12.2.  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.

Appendix A.  Some Questions and Answers [RFC Editor: please remove]

   Q: 32-bit endpoint 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 have topology information at all?

   A: It is an alternative to the more traditional seq#/TTL-based
   flooding schemes.  In steady state, there is no need to e.g. re-
   publish every now and then.

Appendix B.  Changelog [RFC Editor: please remove]

   draft-ietf-homenet-dncp-03:

   o  Renamed connection -> endpoint.





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   o  !!! Backwards incompatible change: Renumbered TLVs, and got rid of
      node data TLV; instead, node data TLV's contents are optionally
      within node state TLV.

   draft-ietf-homenet-dncp-02:

   o  Changed DNCP "messages" into series of TLV streams, allowing
      optimized round-trip saving synchronization.

   o  Added fragmentation support for bigger node data and for chunking
      in absence of reliable L2 and L3 fragmentation.

   draft-ietf-homenet-dncp-01:

   o  Fixed keep-alive semantics to consider unicast requests also
      updates of most recently consistent, and added proactive unicast
      request to ensure even inconsistent keep-alive messages eventually
      triggering consistency timestamp update.

   o  Facilitated (simple) read-only clients by making Node Connection
      TLV optional if just using DNCP for read-only purposes.

   o  Added text describing how to deal with "dense" networks, but left
      actual numbers and mechanics up to DNCP profiles and (local)
      configurations.

   draft-ietf-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
      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!








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Internet-Draft     Distributed Node Consensus Protocol        April 2015


Appendix C.  Draft Source [RFC Editor: please remove]

   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 D.  Acknowledgements

   Thanks to Ole Troan, Pierre Pfister, Mark Baugher, Mark Townsley,
   Juliusz Chroboczek, Jiazi Yi, Mikael Abrahamsson and Brian Carpenter
   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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