One document matched: draft-ietf-homenet-dncp-05.xml
<?xml version='1.0' ?>
<!--
Created: Mon Nov 18 17:55:22 2013 mstenber
split from draft-ietf-homenet-hncp-03-pre - generic parts
TBD: Where should we note that DNCP is fundamentally about individual TLVs,
and they can be queued (and jittered) freely?
-->
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<?rfc autobreaks="yes"?>
<?rfc compact="yes"?>
<?rfc strict='yes'?>
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<?rfc symrefs="yes"?>
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<rfc
ipr='trust200902'
docName='draft-ietf-homenet-dncp-05'
category='std'
>
<front>
<title abbrev="Distributed Node Consensus Protocol">
Distributed Node Consensus Protocol
</title>
<author initials="M" surname="Stenberg" fullname="Markus Stenberg">
<address>
<postal>
<street/>
<city>Helsinki</city>
<code>00930</code>
<country>Finland</country>
</postal>
<email>markus.stenberg@iki.fi</email>
</address>
</author>
<author initials="S" surname="Barth" fullname="Steven Barth">
<address>
<postal>
<street/>
<city>Halle</city>
<code>06114</code>
<country>Germany</country>
</postal>
<email>cyrus@openwrt.org</email>
</address>
</author>
<date month="June" year="2015" />
<area>Internet</area>
<workgroup>Homenet Working Group</workgroup>
<keyword>Homenet</keyword>
<abstract>
<t>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. </t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>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.</t>
<t>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. </t>
<t>DNCP has relatively few requirements for the underlying transport;
it requires some way of transmitting either unicast datagram or
stream data to a 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 <xref target="RFC5246">TLS</xref> on top of
TCP or <xref target="RFC6347">DTLS</xref> on top of UDP - is also
required. </t>
</section>
<section anchor="kwd" title='Requirements Language'>
<t>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
<xref target='RFC2119'>RFC 2119</xref>.</t>
</section>
<section title="Terminology">
<texttable suppress-title="true" style="none" align="left">
<ttcol width="25%" /><ttcol width="75%" />
<c>DNCP profile</c>
<c>a definition of the set of rules and values listed in
<xref target="profile-bits"/> 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_.</c>
<c /><c />
<c>DNCP node</c>
<c>a single node which runs a protocol based on a DNCP
profile.</c>
<c /><c />
<c>DNCP network</c>
<c>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.</c>
<c /><c />
<c>DNCP message</c>
<c>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.</c>
<c /><c />
<c>Node identifier</c>
<c>an opaque fixed-length identifier consisting of
DNCP_NODE_IDENTIFIER_LENGTH bytes which uniquely identifies a DNCP
node within a DNCP network.</c>
<c /><c />
<c>Link</c>
<c>a link-layer media over which directly connected nodes can
communicate.</c>
<c /><c />
<c>Interface</c>
<c>a port of a node that is connected to a particular link.</c>
<c /><c />
<c>Endpoint</c>
<c>a locally configured use of DNCP on a DNCP node. It is
attached either to an interface, a specific remote unicast address to
be contacted, or a range of remote unicast addresses that are allowed
to contact.</c>
<c /><c />
<c>Endpoint identifier</c>
<c>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 and MUST NOT be used to
identify an actual endpoint. This definition is in sync with the
interface index definition in <xref target="RFC3493"/>, as the
non-zero small positive integers should comfortably fit within 32
bits.</c>
<c /><c />
<c>Peer</c>
<c>another DNCP node with which a DNCP node communicates
directly using a particular local and remote endpoint pair.</c>
<c /><c />
<c>Node data</c>
<c>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.</c>
<c /><c />
<c>Node state</c>
<c>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. </c>
<c /><c />
<c>Network state hash</c>
<c>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 a 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. For calculation these tuples are sorted in
ascending order of the respective node's node identifier.</c>
<c /><c />
<c>Trust verdict</c>
<c>a statement about the trustworthiness of a
certificate announced by a node participating in the certificate
based trust consensus mechanism.</c>
<c /><c />
<c>Effective trust verdict</c>
<c>the trust verdict with the highest
priority within the set of trust verdicts announced for the
certificate in the DNCP network.</c>
<c /><c />
<c>Neighbor graph</c>
<c>the undirected graph of DNCP nodes produced by
retaining only bidirectional peer relationships between nodes.</c>
</texttable>
</section>
<section anchor="dm" title="Data Model">
<t>A DNCP node has:
<list style="symbols">
<t>A timestamp indicating the most recent neighbor graph traversal
described in <xref target="purge" />.</t>
<t>A data structure containing data about the most recently sent
<xref target="req-net-state">Request Network State TLVs</xref>.
The simplest option is keeping a timestamp of the most recent request
(see <xref target="reception" />).</t>
</list>
</t>
<t>A DNCP node has for every DNCP node in the DNCP network:
<list style="symbols">
<t>Node identifier:
the unique identifier of the node.</t>
<t>Node data: the ordered set of TLV tuples published by that
particular node. This set of TLVs MUST be strictly ordered based on
ascending binary content (including TLV type and length). This
facilitates linear time state delta processing.</t>
<t>Latest update sequence number: the 32-bit sequence 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.</t>
<t>Relative time delta: the 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. In other words,
absent any other changes, the TLV set MUST be re-published roughly
every 49 days.</t>
<t>Timestamp: the time it was last reachable based on
neighbor graph traversal described in <xref target="purge" />.</t>
</list>
</t>
<t>Additionally, a DNCP node has a set of endpoints for which DNCP
is configured to be used. For each such endpoint, a node has:
<list style="symbols">
<t>Endpoint identifier: the 32-bit opaque value uniquely
identifying it.</t>
<t><xref target="RFC6206">Trickle</xref> instance: the endpoint's
individual trickle instance with parameters I, T, and c.</t>
</list>
</t>
<t>and one (or more) of the following:
<list style="symbols">
<t>Interface: the assigned local network interface.</t>
<t>Unicast address: the DNCP node it should connect with.</t>
<t>Range of addresses: the DNCP nodes that are allowed to connect.</t>
</list>
</t>
<t>For each remote (peer, endpoint) pair detected on a
local endpoint, a DNCP node has:
<list style="symbols">
<t>Node identifier: the unique identifier of the peer.</t>
<t>Endpoint identifier: the unique endpoint identifier used by the
peer.</t>
<t>Peer address: the most recently used address of the peer
(authenticated and authorized, if security is enabled).</t>
</list>
</t>
</section>
<section title="Operation">
<t>The DNCP protocol consists of <xref target="RFC6206">Trickle</xref>
driven unicast or multicast status payloads which indicate the current
status of shared TLV data and additional unicast exchanges
which ensure peer reachability and synchronize the data when
necessary. </t>
<t>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 a
unicast exchange should be triggered, the multicast transport does
not have to be particularly secure.</t>
<t>To form bidirectional peer relationships DNCP requires identification
of the endpoints used for communication. A DNCP node therefore MUST
include an <xref target="endpoint">Endpoint TLV</xref> in each message
intended to maintain a DNCP peer relationship.</t>
<section title="Trickle-Driven Status Updates"
anchor="trickle-updates">
<t>When employing unreliable transport, each node MUST send a <xref
target="net-state">Network State TLV</xref> every time the
endpoint-specific <xref target="RFC6206">Trickle algorithm</xref>
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 <xref target="node-state">Node State TLVs</xref> 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.
If the DNCP profile supports <xref target="broadcast">dense
broadcast link optimization</xref>, and if a node does not have the
highest node identifier on a link, the endpoint may be in a unicast
mode in which multicast traffic is only listened to. In that mode,
multicast updates MUST NOT be sent.</t>
<t>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.</t>
<t>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 <xref target="profile-bits"/>.</t>
</section>
<section title="Processing of Received TLVs" anchor="reception">
<t>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. </t>
<t>A DNCP node MUST reply to a request from any valid address, as
specified by a given DNCP profile, whether this address is known to
be the address of a neighbour or not. (This provision satisfies
the needs of monitoring or other host software that needs to
discover the DNCP topology without adding to the state in the
network.)</t>
<t>Upon receipt of:
<list style="symbols">
<t><xref target="req-net-state">Request Network State TLV</xref>:
The receiver MUST reply with a <xref target="net-state">Network
State TLV</xref> and a <xref target="node-state">Node State
TLV</xref> for each node data used to calculate the network state
hash. The Node State TLVs SHOULD NOT contain the optional node
data part.</t>
<t><xref target="req-node-state">Request Node State TLV</xref>:
If the receiver has node data for the corresponding node, it MUST
reply with a <xref target="node-state">Node State TLV</xref> for
the corresponding node. The optional node data part MUST be
included in the TLV.</t>
<t><xref target="net-state">Network State TLV</xref>:
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 <xref target="req-net-state">Request Network State
TLV</xref>. These replies MUST be rate limited to only at most
one reply per link per unique network state hash within Imin. The
simplest way to ensure this rate limit is a timestamp indicating
requests, and sending at most one <xref target="req-net-state">
Request Network State TLV</xref> per Imin.
To facilitate faster state synchronization, if a Request Network
State TLV is sent in a reply, a local, current Network State TLV
SHOULD be also sent.</t>
<t><xref target="node-state">Node State TLV</xref>:
<list style="symbols">
<t>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.</t>
<t>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:
<list style="symbols">
<t>If the TLV does not contain node data, and the hash of the
node data differs, the receiver MUST reply with a <xref
target="req-node-state">Request Node State TLV</xref> for the
corresponding node.</t>
<t>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.</t>
</list>
</t>
</list>
</t>
<t>Any other TLV:
TLVs not recognized by the receiver MUST be silently ignored.</t>
</list>
</t>
<t>If secure unicast transport is configured for an endpoint, any
Node State TLVs received via insecure multicast MUST be silently
ignored.</t>
</section>
<section title="Adding and Removing Peers">
<t>When receiving a <xref target="endpoint">Node Endpoint
TLV</xref> on an endpoint from an unknown peer:
<list style="symbols">
<t>If it comes via unicast, the remote node MUST be added as a
peer on the endpoint and a <xref target="neighbor">Neighbor
TLV</xref> MUST be created for it.
</t>
<t>If it comes via multicast, the node SHOULD be sent a (possibly
rate-limited) unicast <xref target="req-net-state">Request
Network State TLV</xref>.</t>
</list>
</t>
<t>If keep-alives specified in <xref target="ka" /> 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 its
presence. When the peer is no longer present, the Neighbor
TLV and the local DNCP peer state MUST be removed.</t>
<t>If the DNCP profile supports <xref target="broadcast">dense
broadcast link optimization</xref>, and if a node does not have the
highest node identifier on a link, the endpoint may be in a unicast
mode in which multicast traffic is only listened to. In that mode,
all peers except the one with the highest node identifier MUST NOT
have <xref target="neighbor">Neighbor TLV</xref> published nor any
local state.</t>
</section>
<section anchor="purge" title="Purging Unreachable Nodes">
<t>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. </t>
<t>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.</t>
<t>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. </t>
</section>
</section>
<section anchor="ext" title="Optional Extensions">
<t>This section specifies extensions to the core protocol that a DNCP
profile may want to use.</t>
<section anchor="ka" title="Keep-Alives">
<t><xref target="trickle-updates">Trickle-driven status
updates</xref> 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 peers if the transport or lower layers do not
provide one.</t>
<t>If keep-alives are not specified in the DNCP profile, the rest
of this subsection MUST be ignored.</t>
<t>A DNCP profile MAY specify either per-endpoint or per-peer
keep-alive support. </t>
<t>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 <xref
target="ka-interval">Keep-Alive Interval TLV(s)</xref> within its
node data.</t>
<section title="Data Model Additions">
<t>The following additions to the <xref target="dm">Data
Model</xref> are needed to support keep-alive:</t>
<t>Each node MUST have a timestamp which indicates the last time a
<xref target="net-state">Network State TLV</xref> was sent for each
endpoint, i.e. on an interface or to the point-to-point
peer(s).</t>
<t>Each node MUST have for each peer:
<list style="symbols">
<t>Last contact timestamp: a timestamp which indicates the last
time a consistent <xref target="net-state">Network State
TLV</xref> 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.</t>
</list>
</t>
</section>
<section title="Per-Endpoint Periodic Keep-Alives">
<t>If per-endpoint keep-alives are enabled on an endpoint with
a multicast-enabled link, and if no traffic containing a <xref
target="net-state">Network State TLV</xref> has been sent to a
particular endpoint within the endpoint-specific keep-alive
interval, a <xref target="net-state">Network State TLV</xref> 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].</t>
</section>
<section title="Per-Peer Periodic Keep-Alives">
<t>If per-peer keep-alives are enabled on a unicast-only
endpoint, and if no traffic containing a <xref
target="net-state">Network State TLV</xref> has been sent to a
particular peer within the endpoint-specific keep-alive interval,
a <xref target="net-state">Network State TLV</xref> MUST be sent to
the peer and a new Trickle transmission time 't' in [I/2, I] MUST
be randomly chosen.</t>
</section>
<section title="Received TLV Processing Additions">
<t>If a TLV is received via unicast from the peer, the Last
contact timestamp for the peer MUST be updated.</t>
<t>On receipt of a <xref target="net-state">Network State TLV</xref>
which is consistent with the locally calculated network state hash,
the Last contact timestamp for the peer MUST be updated.</t>
</section>
<section title="Neighbor Removal">
<t>For every peer on every endpoint, the endpoint-specific
keep-alive interval must be calculated by looking for <xref
target="ka-interval">Keep-Alive Interval TLVs</xref> 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.</t>
</section>
</section>
<section anchor="broadcast" title="Support For Dense Broadcast Links">
<t>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.</t>
<t>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.</t>
</section>
<section anchor="fragmentation" title="Node Data Fragmentation">
<t>A DNCP profile may be required to support node data which
would not fit the maximum size of a single <xref
target="node-state">Node State TLV</xref> (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.</t>
<t>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 <xref target="dm"
/>.</t>
<t>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.</t>
<t>If using fragmentation, the unreachable node purging defined in
<xref target="purge" /> is extended so that if a <xref
target="fragment-count">Fragment Count TLV</xref> 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. </t>
</section>
</section>
<section anchor="tlvs" title="Type-Length-Value Objects">
<t>
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. Padding bytes with value zero 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 number stored in the length
field.
</t>
<figure>
<artwork>
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
For example, type=123 (0x7b) TLV with value 'x' (120 =
0x78) is encoded as: 007B 0001 7800 0000.
</t>
<t>In this section, the following special notation is used:
<list>
<t>.. = octet string concatenation operation.</t>
<t>H(x) = non-cryptographic hash function specified by DNCP
profile. </t>
</list>
</t>
<section title="Request TLVs">
<section anchor="req-net-state" title="Request Network State TLV">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>This TLV is used to request response with a <xref
target="net-state">Network State TLV</xref> and all <xref
target="node-state">Node State TLVs</xref>.</t>
</section>
<section anchor="req-node-state" title="Request Node State TLV">
<figure>
<artwork>
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) |
...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>This TLV is used to request a <xref target="node-state">
Node State TLV</xref> (including node data) for the node
matching the node identifier.</t>
</section>
</section>
<section title="Data TLVs">
<section anchor="endpoint" title="Node Endpoint TLV">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>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 data.</t>
</section>
<section anchor="net-state" title="Network State TLV">
<figure>
<artwork>
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) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>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 identifiers.</t>
</section>
<section anchor="node-state" title="Node State TLV">
<figure>
<artwork>
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 |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>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.</t>
<t>The whole network should have roughly the 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.</t>
<t>The actual node data of the node may be included within the
TLV as well; see <xref target="reception" /> for the cases where
it MUST or MUST NOT be included. In a DNCP profile which supports
fragmentation, described in <xref target="fragmentation" />, the
TLV data may be only partial and not really usable without other
fragments.</t>
</section>
<section anchor="custom" title="Custom TLV">
<figure>
<artwork>
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 |
</artwork>
</figure>
<t>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 <xref
target="node-state">Node State TLV</xref>. For example:</t>
<t>V = H('http://example.com/author/json-for-dncp') .. '{"cool":
"json extension!"}'</t>
<t>or</t>
<t>V = H('mailto:author@example.com') .. '{"cool": "json
extension!"}'</t>
</section>
</section>
<section title="Data TLVs within Node State TLV">
<t>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.</t>
<section anchor="fragment-count"
title="Fragment Count TLV">
<figure>
<artwork>
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) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>If the DNCP profile supports node data fragmentation as
specified in <xref target="fragmentation" />, 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 TLV appears in MUST be zero.</t>
</section>
<section anchor="neighbor"
title="Neighbor TLV">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>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. </t>
</section>
<section anchor="ka-interval"
title="Keep-Alive Interval TLV">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>This TLV indicates a non-default interval being used to send
keep-alives specified in <xref target="ka" />.</t>
<t>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.</t>
<t>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. </t>
</section>
</section>
</section>
<section title="Security and Trust Management">
<t>If specified in the DNCP profile, either <xref
target="RFC6347">DTLS</xref> or <xref target="RFC5246">TLS</xref> 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.</t>
<section title="Pre-Shared Key Based Trust Method">
<t>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. </t>
</section>
<section title="PKI Based Trust Method">
<t>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.</t>
</section>
<section title="Certificate Based Trust Consensus Method">
<t>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
trust 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. </t>
<t>The current effective trust verdict for any certificate is
defined as the one with the highest priority from all trust
verdicts announced for said certificate at the time.</t>
<section title="Trust Verdicts">
<t>Trust verdicts are statements of DNCP nodes about the
trustworthiness of X.509-certificates. There are 5 possible
trust verdicts in order of ascending priority:
<list>
<t>0 (Neutral): no trust verdict exists but the DNCP network
should determine one.</t>
<t>1 (Cached Trust): the last known effective trust verdict was
Configured or Cached Trust.</t>
<t>2 (Cached Distrust): the last known effective trust verdict
was Configured or Cached Distrust.</t>
<t>3 (Configured Trust): trustworthy based upon an external
ceremony or configuration.</t>
<t>4 (Configured Distrust): not trustworthy based upon an
external ceremony or configuration.</t>
</list>
</t>
<t>
Trust verdicts are differentiated in 3 groups:
<list style="symbols">
<t>Configured verdicts are used to announce explicit
trust verdicts a node has based on any external trust
bootstrap or predefined relation a node has formed with a
given certificate.</t>
<t>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.</t>
<t>The Neutral verdict is used to announce a new node
intending to join the network so a final verdict for it can
be found.</t>
</list>
</t>
<t>
The current effective trust verdict for any certificate is
defined as the one with the highest priority within the set of
trust 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 trust 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 trust verdict of (Cached or
Configured) Distrust.
In case a node has a configured verdict, which is different
from the current effective trust verdict for a certificate, the
current effective trust verdict takes precedence in deciding
trustworthiness. Despite that, the node still retains and
announces its configured verdict.
</t>
</section>
<section title="Trust Cache">
<t>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.</t>
<t>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 trust 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.</t>
</section>
<section title="Announcement of Verdicts">
<t>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 trust 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:
<list style="symbols">
<t>The stored trust verdict is Cached Trust and the current
effective trust verdict for the certificate is Neutral or does
not exist.</t>
<t>The stored trust verdict is Cached Distrust and the current
effective trust verdict for the certificate is Cached
Trust.</t>
</list>
A node rechecks these conditions whenever it detects changes of
announced trust verdicts anywhere in the network.
</t>
<t>Upon encountering a node with a hierarchy of certificates for
which there is no effective trust 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 trust 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
trust verdicts SHOULD also be limited in rate and number to
prevent denial-of-service attacks.</t>
<t>Trust verdicts are announced using Trust-Verdict TLVs:
<figure>
<artwork>
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 |
</artwork>
</figure>
<list>
<t>Verdict represents the numerical index of the trust
verdict.</t>
<t>(reserved) is reserved for future additions and MUST be set
to 0 when creating TLVs and ignored when parsing them.</t>
<t>SHA-256 Fingerprint contains the <xref
target="RFC6234">SHA-256</xref> hash value of the certificate
in DER-format.</t>
<t>Common Name contains the variable-length (1-64 bytes) common
name of the certificate. Final byte MUST have value of 0.</t>
</list>
</t>
</section>
<section title="Bootstrap Ceremonies">
<t>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.</t>
<section title="Trust by Identification">
<t>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.</t>
</section>
<section title="Preconfigured Trust">
<t>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).</t>
</section>
<section title="Trust on Button Press">
<t>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.</t>
</section>
<section title="Trust on First Use">
<t>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.</t>
</section>
</section>
</section>
</section>
<section anchor="profile-bits" title="DNCP Profile-Specific Definitions">
<!-- TBD - Pierre has a point - should define guidance on these,
perhaps -->
<t>Each DNCP profile MUST specify the following aspects:
<list style="symbols">
<t>Unicast and optionally multicast transport protocol(s) to be
used.</t>
<t>How the chosen transport(s) 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. 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.</t>
<t>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. </t>
<t>When receiving messages, what sort of messages are dropped, as
specified in <xref target="reception" />.</t>
<t>How to deal with node identifier collision as described in <xref
target="reception" />. 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.</t>
<t>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 the 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 convergence behavior of the network.</t>
<t>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 <xref
target="RFC6234" /> is the recommended default choice.</t>
<t>DNCP_NODE_IDENTIFIER_LENGTH: The fixed length of a node
identifier (in bytes).</t>
<t>DNCP_GRACE_INTERVAL: How long node data for unreachable nodes is
kept.</t>
<t>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:
<list style="symbols">
<t>DNCP_KEEPALIVE_INTERVAL: How often keep-alives are to be
sent by default (if enabled).</t>
<t>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.</t>
</list>
</t>
<t>Whether to support fragmentation, and if so, the number of bytes
reserved for fragment count in the node identifier.</t>
</list>
</t>
</section>
<section title="Security Considerations">
<t>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.</t>
<t>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.</t>
<t>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. </t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>IANA should set up a registry for DNCP TLV types,
with the following initial contents:</t>
<t>0: Reserved (should not happen on wire)</t>
<t>1: Request network state</t>
<t>2: Request node state</t>
<t>3: Node endpoint</t>
<t>4: Network state</t>
<t>5: Node state</t>
<t>6: Custom</t>
<t>7: Fragment count</t>
<t>8: Neighbor</t>
<t>9: Keep-alive interval</t>
<t>10: Trust-Verdict</t>
<t>32-191: Reserved for per-DNCP profile use</t>
<t>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. </t>
<t>For the rest of the values (11-31, 256-65535), policy of 'standards
action' should be used.</t>
</section>
</middle>
<back>
<references title="Normative references">
<?rfc include="reference.RFC.2119.xml"?>
<?rfc include="reference.RFC.6206.xml"?>
<?rfc include="reference.RFC.6347.xml"?>
<?rfc include="reference.RFC.5246.xml"?>
</references>
<references title="Informative references">
<?rfc include="reference.RFC.3493.xml"?>
<?rfc include="reference.RFC.6234.xml"?>
</references>
<section title="Some Questions and Answers [RFC Editor: please remove]">
<t>Q: 32-bit endpoint id?</t>
<t>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.</t>
<t>Q: Why have topology information at all?</t>
<t>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.</t>
</section>
<section title="Changelog [RFC Editor: please remove]">
<t>draft-ietf-homenet-dncp-04:
<list style="symbols">
<t>Added mandatory rate limiting for network state requests, and
optional slightly faster convergence mechanism by including current
local network state in the remote network state requests.</t>
</list>
</t>
<t>draft-ietf-homenet-dncp-03:
<list style="symbols">
<t>Renamed connection -> endpoint.</t>
<t>!!! Backwards incompatible change: Renumbered TLVs, and got rid
of node data TLV; instead, node data TLV's contents are optionally
within node state TLV.</t>
</list>
</t>
<t>draft-ietf-homenet-dncp-02:
<list style="symbols">
<t>Changed DNCP "messages" into series of TLV streams, allowing
optimized round-trip saving synchronization.</t>
<t>Added fragmentation support for bigger node data and for chunking
in absence of reliable L2 and L3 fragmentation.</t>
</list>
</t>
<t>draft-ietf-homenet-dncp-01:
<list style="symbols">
<t>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.</t>
<t>Facilitated (simple) read-only clients by making Node Connection
TLV optional if just using DNCP for read-only purposes.</t>
<t>Added text describing how to deal with "dense" networks, but left
actual numbers and mechanics up to DNCP profiles and (local)
configurations.</t>
</list>
</t>
<t>draft-ietf-homenet-dncp-00: Split from pre-version of
draft-ietf-homenet-hncp-03 generic parts. Changes that affect
implementations:
<list style="symbols">
<t>TLVs were renumbered.</t>
<t>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).</t>
<t>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.</t>
<t>Instead of 'ping', use 'keep-alive' (optional) for dead peer
detection. Different message used!</t>
</list>
</t>
</section>
<section title="Draft Source [RFC Editor: please remove]">
<t>As usual, this draft is available at <eref
target="https://github.com/fingon/ietf-drafts/">
https://github.com/fingon/ietf-drafts/</eref>
in source format (with nice Makefile too). Feel free to send comments
and/or pull requests if and when you have changes to it! </t>
</section>
<section title="Acknowledgements">
<t>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.</t>
</section>
</back>
</rfc>
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