Distributed Node Consensus Protocol
draft-ietf-homenet-dncp-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7787.
|
|
|---|---|---|---|
| Authors | Markus Stenberg , Steven Barth | ||
| Last updated | 2015-03-05 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7787 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-homenet-dncp-01
Homenet Working Group M. Stenberg
Internet-Draft
Intended status: Standards Track S. Barth
Expires: September 6, 2015
March 5, 2015
Distributed Node Consensus Protocol
draft-ietf-homenet-dncp-01
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 September 6, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Trickle-Driven Status Update Messages . . . . . . . . . . 6
5.2. Processing of Received Messages . . . . . . . . . . . . . 7
5.3. Adding and Removing Peers . . . . . . . . . . . . . . . . 8
5.4. Purging Unreachable Nodes . . . . . . . . . . . . . . . . 9
6. Keep-Alive Extension . . . . . . . . . . . . . . . . . . . . 9
6.1. Data Model Additions . . . . . . . . . . . . . . . . . . 10
6.2. Per-Connection Periodic Keep-Alive Messages . . . . . . . 10
6.3. Per-Peer Periodic Keep-Alive Messages . . . . . . . . . . 10
6.4. Received Message Processing Additions . . . . . . . . . . 10
6.5. Neighbor Removal . . . . . . . . . . . . . . . . . . . . 11
7. Support For Dense Broadcast Links . . . . . . . . . . . . . . 11
8. Protocol Messages . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Short Network State Update Message . . . . . . . . . . . 12
8.2. Long Network State Update Message . . . . . . . . . . . . 12
8.3. Network State Request Message . . . . . . . . . . . . . . 13
8.4. Node Data Request Message . . . . . . . . . . . . . . . . 13
8.5. Node Data Reply Message . . . . . . . . . . . . . . . . . 13
9. Type-Length-Value Objects . . . . . . . . . . . . . . . . . . 13
9.1. Request TLVs . . . . . . . . . . . . . . . . . . . . . . 14
9.1.1. Request Network State TLV . . . . . . . . . . . . . . 14
9.1.2. Request Node Data TLV . . . . . . . . . . . . . . . . 14
9.2. Data TLVs . . . . . . . . . . . . . . . . . . . . . . . . 15
9.2.1. Node Connection TLV . . . . . . . . . . . . . . . . . 15
9.2.2. Network State TLV . . . . . . . . . . . . . . . . . . 15
9.2.3. Node State TLV . . . . . . . . . . . . . . . . . . . 15
9.2.4. Node Data TLV . . . . . . . . . . . . . . . . . . . . 16
9.2.5. Neighbor TLV (within Node Data TLV) . . . . . . . . . 17
9.2.6. Keep-Alive Interval TLV (within Node Data TLV) . . . 17
9.3. Custom TLV (within/without Node Data TLV) . . . . . . . . 18
10. Security and Trust Management . . . . . . . . . . . . . . . . 18
10.1. Pre-Shared Key Based Trust Method . . . . . . . . . . . 18
10.2. PKI Based Trust Method . . . . . . . . . . . . . . . . . 18
10.3. Certificate Based Trust Consensus Method . . . . . . . . 19
10.3.1. Trust Verdicts . . . . . . . . . . . . . . . . . . . 19
10.3.2. Trust Cache . . . . . . . . . . . . . . . . . . . . 20
10.3.3. Announcement of Verdicts . . . . . . . . . . . . . . 20
10.3.4. Bootstrap Ceremonies . . . . . . . . . . . . . . . . 21
11. DNCP Profile-Specific Definitions . . . . . . . . . . . . . . 22
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12. Security Considerations . . . . . . . . . . . . . . . . . . . 24
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
14.1. Normative references . . . . . . . . . . . . . . . . . . 25
14.2. Informative references . . . . . . . . . . . . . . . . . 25
Appendix A. Some Outstanding Issues . . . . . . . . . . . . . . 25
Appendix B. Some Obvious Questions and Answers . . . . . . . . . 26
Appendix C. Changelog . . . . . . . . . . . . . . . . . . . . . 26
Appendix D. Draft Source . . . . . . . . . . . . . . . . . . . . 27
Appendix E. 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].
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3. Terminology
A DNCP profile is a definition of a set of rules and values listed in
Section 11 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_.
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.
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.
A connection denotes a locally configured use of DNCP on a DNCP node,
that is attached either to an interface, to a specific remote unicast
address to be contacted, or to a range of remote unicast addresses
that are allowed to contact.
The connection identifier is a 32-bit opaque value, which identifies
a particular connection of that particular DNCP node. The value 0 is
reserved for DNCP and sub-protocol purposes in the TLVs, and MUST NOT
be used to identify an actual connection. This definition is in sync
with [RFC3493], as the non-zero small positive integers should
comfortably fit within 32 bits.
A (DNCP) peer refers to another DNCP node with which a DNCP node
communicates directly on a particular connection.
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 changes its published node data this hash value changes as well.
It is calculated over the hash values of each reachable nodes' node
data in ascending order of the respective node identifier.
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 has a well-defined order based
on ascending binary content (including TLV type and length). This
facilitates linear time state delta processing.
o The latest update sequence number, a 32 bit number that is
incremented any time the TLV set is published. For comparison
purposes, a looping comparison should be used to avoid problems in
case of overflow. An example would be: a < b <=> (a - b) % 2^32 &
2^31 != 0.
o The relative time (in milliseconds) since the current TLV data set
with the current update sequence number was published. It is also
a 32 bit number on the wire. If this number is close to overflow
(greater than 2^32-2^16), a node MUST re-publish its TLVs even if
there is no change to avoid overflow of the value. In other
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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 connections for which DNCP is
configured to be used. For each such connection, a node has:
o A connection identifier.
o An interface, a unicast address of a DNCP peer it should connect
with, or a range of addresses from which DNCP peers are allowed to
connect.
o A Trickle [RFC6206] instance with parameters I, T, and c.
For each DNCP peer detected on a connection, a DNCP node has:
o The node identifier of the DNCP peer.
o The connection identifier of the DNCP peer.
o The most recent address used by the DNCP peer (in an authenticated
message, if security is enabled).
5. Operation
The DNCP protocol consists of Trickle [RFC6206] driven unicast or
multicast status messages which indicate the current status of shared
TLV data and additional unicast message exchanges which ensure DNCP
peer reachability and synchronize the data when necessary.
If DNCP is to be used on a multicast-capable interface, as opposed to
only point-to-point using unicast, a datagram-based transport which
supports multicast SHOULD be defined in the DNCP profile to be used
for the messages to be sent to the whole link. As this is used only
to identify potential new DNCP nodes and to notify that an unicast
exchange should be triggered, the multicast transport does not have
to be particularly secure.
5.1. Trickle-Driven Status Update Messages
Each node MUST send either a Long Network State Update message
(Section 8.2) or a Short Network State Update message (Section 8.1)
every time the connection-specific Trickle algorithm [RFC6206]
instance indicates that an update should be sent. The destination
address of the message should be multicast in case of an interface
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which is multicast-capable, or the unicast address of the remote
party in case of a point-to-point connection. By default, Long
Network State Update messages SHOULD be used, but if it is defined as
undesirable for some case by the DNCP profile, Short Network State
Update message MUST be sent instead. This may be useful to avoid
fragmenting packets to multicast destinations, or for security
reasons.
A Trickle state MUST be maintained separately for each connection.
The Trickle state for all connections is considered inconsistent and
reset if and only if the locally calculated network state hash
changes. This occurs either due to a change in the local node's own
node data, or due to receipt of more recent data from another node.
The Trickle algorithm has 3 parameters: Imin, Imax and k. Imin and
Imax represent the minimum and maximum values for I, which is the
time interval during which at least k Trickle updates must be seen on
a connection to prevent local state transmission. The actual
suggested Trickle algorithm parameters are DNCP profile specific, as
described in Section 11.
5.2. Processing of Received Messages
This section describes how received messages are processed. The DNCP
profile may specify criteria based on which received messages are
ignored. Any 'reply' mentioned in the steps below denotes sending of
the specified message via unicast to the originator of the message
being processed. If the reply was caused by a multicast message and
sent to a link with shared bandwidth it SHOULD be delayed by a random
timespan in [0, Imin/2]. 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:
Short Network State Update (Section 8.1): If the network state
hash within the message differs from the locally calculated
network state hash, the receiver MUST reply with a Network State
Request message (Section 8.3).
Long Network State Update (Section 8.2):
* If the network state hash within the message matches the
locally calculated network state hash, stop processing.
* Otherwise the receiver MUST identify all nodes for which local
information is outdated (local update sequence number is lower
than that within the message), potentially incorrect (local
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update sequence number matches but the hash of the node data
TLV differs) or missing.
* If any such nodes are identified, the receiver MUST reply with
one or more Node Data Request message(s) (Section 8.4)
containing Request Node Data TLV(s) (Section 9.1.2) for the
corresponding nodes.
Network State Request (Section 8.3): the receiver MUST reply with
a Long Network State Update (Section 8.2).
Node Data Request (Section 8.4): the receiver MUST reply with the
requested data in a Node Data Reply message (Section 8.5).
Optionally - if specified by the DNCP profile - multiple replies
MAY be sent in order to e.g. keep size of each datagram within the
PMTU to the destination. However these replies must be valid
stand-alone Node Data Reply messages, with the full state for the
particular nodes.
Node Data Reply (Section 8.5): If the message contains Node State
TLVs that are more recent than the local state (the received TLV
has a higher update sequence number, the node data TLV hash
differs from the local one, or local data is missing altogether)
and if the message also contains corresponding Node Data TLVs, the
receiver MUST update its locally stored state.
If a message containing Node State TLVs (Section 9.2.3) is received
with the node identifier matching the local node identifier and a
higher update sequence number than its current local value, or the
same update sequence number and a different hash, the node SHOULD re-
publish its own node data with an update sequence number 1000 higher
than the received one. This may occur normally once due to the local
node restarting and not storing the most recently used update
sequence number. If this occurs more than once, the DNCP profile
should provide guidance on how to handle these situations as it
indicates the existence of another active node with the same node
identifier.
5.3. Adding and Removing Peers
When receiving a message on a connection from an unknown peer:
If it is a unicast message, and the message contains a Node
Connection TLV (Section 9.2.1), the remote node MUST be added as a
peer on the connection and a Neighbor TLV (Section 9.2.5) MUST be
created for it.
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If it is a multicast message, and the message contains a Node
Connection TLV (Section 9.2.1), the remote node SHOULD be sent a
(possibly rate-limited) unicast Network State Request Message
(Section 8.3).
If keep-alives 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-alive messages), 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 connection identifiers swapped.
Each node reached should be marked currently reachable.
DNCP nodes MUST be either purged immediately when not marked
reachable in a particular graph traversal, or eventually after they
have not been marked reachable within DNCP_GRACE_INTERVAL. During
the grace period, the nodes that were not marked reachable in the
most recent graph traversal MUST NOT be used for calculation of the
network state hash, be provided to any applications that need to use
the whole TLV graph, or be provided to remote nodes.
6. Keep-Alive Extension
The Trickle-driven messages provide a mechanism for handling of new
peer detection (if applicable) on a connection, as well as state
change notifications. Another mechanism may be needed to get rid of
old, no longer valid DNCP peers if the transport or lower layers do
not provide one.
If keep-alives are not specified in the DNCP profile, the rest of
this section MUST be ignored.
A DNCP profile MAY specify either per-connection or per-peer keep-
alive support.
For every connection that a keep-alive is specified for in the DNCP
profile, the connection-specific keep-alive interval MUST be
maintained. By default, it is DNCP_KEEPALIVE_INTERVAL. If there is
a local value that is preferred for that for any reason
(configuration, energy conservation, media type, ..), it should be
substituted instead. If a non-default keep-alive interval is used on
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any connection, a DNCP node MUST publish appropriate Keep-Alive
Interval TLV(s) (Section 9.2.6).
6.1. Data Model Additions
The following additions to the Data Model (Section 4) are needed to
support keep-alive:
Each node MUST have a timestamp which indicates the last time a
Network State TLV (Section 9.2.2) was sent for each connection, i.e.
on an interface or to the point-to-point peer(s).
Each node MUST have for each peer:
o Last consistent state timestamp: a timestamp which indicates the
last time a consistent Network State TLV (Section 9.2.2) was
received from the peer. When adding a new peer, it should be
initialized to the current time.
6.2. Per-Connection Periodic Keep-Alive Messages
If per-connection keep-alives are enabled on connection with a
multicast-enabled link, and if no traffic containing a Network State
TLV (Section 9.2.2) has been sent to a particular connection within
the connection-specific keep-alive interval, a Long Network State
Update message (Section 8.2) or a Short Network State Update message
(Section 8.1) MUST be sent on that connection. The type of message
should be chosen based on the considerations in Section 5.1. The
actual sending time SHOULD be further delayed by a random timespan in
[0, Imin/2]. When such a message is sent, a new Trickle transmission
time 't' in [I/2, I] MUST be randomly chosen.
6.3. Per-Peer Periodic Keep-Alive Messages
If per-peer keep-alives are enabled on a unicast-only connection, and
if no traffic containing a Network State TLV (Section 9.2.2) has been
sent to a particular peer within the connection-specific keep-alive
interval, a Long Network State Update message (Section 8.2) or a
Short Network State Update message (Section 8.1) MUST be sent to the
peer. The type of message should be chosen based on the
considerations in Section 5.1. When such a message is sent, a new
Trickle transmission time 't' in [I/2, I] MUST be randomly chosen.
6.4. Received Message Processing Additions
If a message is received via unicast from the peer, the Last
consistent state timestamp for the peer MUST be updated.
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If the received multicast message contains a Network State TLV
(Section 9.2.2) which is consistent with the locally calculated
network state hash, the Last consistent state timestamp for the peer
MUST be updated. If the TLV is inconsistent, and would not cause any
unicast exchange, Network State Request (Section 8.3) SHOULD be sent
via unicast.
6.5. Neighbor Removal
For every peer on every connection, the connection-specific keep-
alive interval must be calculated by looking for Keep-Alive Interval
TLVs (Section 9.2.6) published by the node, and if none exist, using
the default value of DNCP_KEEPALIVE_INTERVAL. If the peer's last
consistent state timestamp has not been updated for at least
DNCP_KEEPALIVE_MULTIPLIER times the peer's connection-specific keep-
alive interval, the Neighbor TLV for that peer and the local DNCP
peer state MUST be removed.
7. Support For Dense Broadcast Links
The DNCP profile or a user configuration should limit the number of
neighbors that are allowed for a (particular type of) link that a
connection runs on. If that limit is exceeded, nodes without the
highest Node Identifier on the link SHOULD treat the connection as an
unicast connection 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 connection
endpoint MUST be changed. If the Node Identifier of the local node
is the highest one, the node MUST keep the connection in normal
multicast mode, and the node MUST allow others to peer with it over
the link.
8. Protocol Messages
For point-to-point exchanges, DNCP can run across datagram-based or
reliable ordered stream-based transports. If a stream-based
transport is used, a 32-bit length-value in network byte order is
sent before each message to indicate the number of bytes the
following message consists of.
DNCP messages are encoded as a concatenated sequence of Type-Length-
Value objects (Section 9). In order to facilitate fast comparing of
local state with that in a received message update, all TLVs in every
encoding scope (either within the message itself, or within a
container TLV) MUST be placed in ascending order based on the binary
comparison of both TLV header and value. By design, the TLVs which
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MUST be present have the lowest available type values, ensuring they
will naturally occur at the start of the Protocol Message, resembling
a fixed format header.
DNCP profiles MAY add additional TLVs to the message specified here,
or even define additional messages as needed. TLVs not recognized by
the receiver MUST be ignored.
8.1. Short Network State Update Message
The Short Network State Update Message is used to announce the
sender's view of the network state using multicast.
The following TLVs MUST be present:
o One Node Connection TLV (Section 9.2.1) identifying the
originating node and connection.
o One Network State TLV (Section 9.2.2) containing the network state
hash as calculated by the sender.
The Short Network Status update message MUST NOT contain any Node
State TLV(s) (Section 9.2.3).
8.2. Long Network State Update Message
The Long Network State Update Message is used to announce the
sender's view of the network state and all node states using
multicast or unicast.
The following TLVs MUST be present:
o One Node Connection TLV (Section 9.2.1) identifying the
originating node and connection.
o One Network State TLV (Section 9.2.2) containing the network state
hash as calculated by the sender.
o One or more Node State TLVs (Section 9.2.3) containing the node
state of DNCP nodes as currently known to the sender.
The Long Network State Update message MUST include the corresponding
Node State TLV (Section 9.2.3) for each Node Data TLV used to
calculate the network state hash.
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8.3. Network State Request Message
The Network State Request message is used to request the recipient's
view of the network state and all node states currently known to it.
The following TLVs MUST be present:
o One Request Network State TLV (Section 9.1.1) indicating the type
of request.
8.4. Node Data Request Message
The Node Data Request message is used to request the node state and
data of one or more DNCP nodes in the network.
The following TLVs MUST be present:
o One or more Request Node Data TLVs (Section 9.1.2) indicating the
nodes for which state and data is requested.
8.5. Node Data Reply Message
The Node Data Request message is used to provide the node data of one
or more DNCP nodes in the network.
The following TLVs MUST be present:
o One Node Connection TLV (Section 9.2.1) identifying the
originating node and connection.
o One or more Node State TLV (Section 9.2.3) and Node Data TLV
(Section 9.2.4) pairs with matching node identifiers for each node
previously requested in a Node Data Request message (Section 8.4).
9. 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.
9.1. Request TLVs
9.1.1. Request Network State TLV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: REQ-NETWORK-STATE (2) | Length: 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV is used to identify a Network State Request message
(Section 8.3).
9.1.2. Request Node Data TLV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: REQ-NODE-DATA (3) | Length: >0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Identifier |
| (length fixed in DNCP profile) |
...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV is used within a Node Data Request message (Section 8.4) to
request node state and node data for the node with matching node
identifier, if any, to be included in a subsequent Node Data Reply
message (Section 8.5).
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9.2. Data TLVs
9.2.1. Node Connection TLV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: NODE-CONNECTION (1) | Length: > 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Identifier |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Connection Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV identifies both the local node's node identifier, as well as
the particular connection identifier. It MUST be sent in all
messages if bidirectional peer relationship is desired with remote
nodes. Bidirectional peer relationship is not necessary for read-
only access to the DNCP state, but it is required to be able to
publish something.
9.2.2. Network State TLV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: NETWORK-STATE (10) | Length: > 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H(H(node data TLV 1) .. [...] .. H(node data TLV N)) |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV contains the current locally calculated network state hash.
The network state hash is derived by calculating the hash value for
each currently reachable node's Node Data TLV, concatenating said
hash values based on the ascending order of their corresponding node
identifiers, and hashing the resulting concatenated hash values.
9.2.3. Node State TLV
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: NODE-STATE (11) | Length: > 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Identifier |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Milliseconds since Origination |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H(node data TLV) |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV represents the local node's knowledge about the published
state of a node in the DNCP network identified by the node identifier
field in the TLV.
The whole network should have roughly same idea about the time since
origination of any particular published state. Therefore every node,
including the originating one, MUST increment the time whenever it
needs to send a Node State TLV for an already published Node Data
TLV. This age value is not included within the Node Data TLV,
however, as that is immutable and used to detect changes in the
network state.
9.2.4. Node Data TLV
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: NODE-DATA (12) | Length: > 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| node identifier |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nested TLVs containing node information |
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9.2.5. Neighbor TLV (within Node Data TLV)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: NEIGHBOR (13) | Length: > 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| neighbor node identifier |
| (length fixed in DNCP profile) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor Connection Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Connection Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV indicates that the node in question vouches that the
specified neighbor is reachable by it on the specified local
connection. The presence of this TLV at least guarantees that the
node publishing it has received traffic from the neighbor recently.
For guaranteed up-to-date bidirectional reachability, the existence
of both nodes' matching Neighbor TLVs should be checked.
9.2.6. Keep-Alive Interval TLV (within Node Data TLV)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: KEEP-ALIVE-INTERVAL (14)| Length: 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Connection Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This TLV indicates a non-default interval being used to send keep-
alive messages specified in Section 6.
Connection identifier is used to identify the particular connection
for which the interval applies. If 0, it applies for ALL connections
for which no specific TLV exists.
Interval specifies the interval in milliseconds at which the node
sends keep-alives. A value of zero means no keep-alives are sent at
all; in that case, some lower layer mechanism that ensures presence
of nodes MUST be available and used.
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9.3. Custom TLV (within/without Node Data TLV)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: CUSTOM-DATA (15) | Length: > 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H(URI) |
| (length fixed in DNCP profile) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Data |
This TLV can be used to contain anything; the URI used should be
under control of the author of that specification. For example:
V = H('http://example.com/author/json-for-dncp') .. '{"cool": "json
extension!"}'
or
V = H('mailto:author@example.com') .. '{"cool": "json extension!"}'
10. 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.
10.1. 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.
10.2. PKI Based Trust Method
A PKI-based trust-model enables more advanced management capabilities
at the cost of increased complexity and bootstrapping effort. It
however allows trust to be managed in a centralized manner and is
therefore useful for larger networks with a need for an authoritative
trust management.
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10.3. 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.
10.3.1. Trust Verdicts
Trust Verdicts are statements of DNCP nodes about the trustworthiness
of X.509-certificates. There are 5 possible verdicts in order of
ascending priority:
0 Neutral : no verdict exists but the DNCP network should determine
one.
1 Cached Trust : the last known effective verdict was Configured or
Cached Trust.
2 Cached Distrust : the last known effective verdict was Configured
or Cached Distrust.
3 Configured Trust : trustworthy based upon an external ceremony or
configuration.
4 Configured Distrust : not trustworthy based upon an external
ceremony or configuration.
Verdicts are differentiated in 3 groups:
o Configured verdicts are used to announce explicit verdicts a node
has based on any external trust bootstrap or predefined relation a
node has formed with a given certificate.
o Cached verdicts are used to retain the last known trust state in
case all nodes with configured verdicts about a given certificate
have been disconnected or turned off.
o The Neutral verdict is used to announce a new node intending to
join the network so a final verdict for it can be found.
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The current effective trust verdict for any certificate is defined as
the one with the highest priority within the set of verdicts +
announced for the certificate in the DNCP network. A node MUST be
trusted for participating in the DNCP network if and only if the
current effective verdict for its own certificate or any one in its
certificate hierarchy is (Cached or Configured) Trust and none of the
certificates in its hierarchy have an effective verdict of (Cached or
Configured) Distrust. In case a node has a configured verdict, which
is different from the current effective verdict for a certificate,
the current effective verdict takes precedence in deciding
trustworthiness. Despite that, the node still retains and announces
its configured verdict.
10.3.2. Trust Cache
Each node SHOULD maintain a trust cache containing the current
effective trust verdicts for all certificates currently announced in
the DNCP network. This cache is used as a backup of the last known
state in case there is no node announcing a configured verdict for a
known certificate. It SHOULD be saved to a non-volatile memory at
reasonable time intervals to survive a reboot or power outage.
Every time a node (re)joins the network or detects the change of an
effective trust verdict for any certificate, it will synchronize its
cache, i.e. store new effective verdicts overwriting any previously
cached verdicts. Configured verdicts are stored in the cache as
their respective cached counterparts. Neutral verdicts are never
stored and do not override existing cached verdicts.
10.3.3. Announcement of Verdicts
A node SHOULD always announce any configured trust verdicts it has
established by itself, and it MUST do so if announcing the configured
trust verdict leads to a change in the current effective verdict for
the respective certificate. In absence of configured verdicts, it
MUST announce cached trust verdicts it has stored in its trust cache,
if one of the following conditions applies:
o The stored verdict is Cached Trust and the current effective
verdict for the certificate is Neutral or does not exist.
o The stored verdict is Cached Distrust and the current effective
verdict for the certificate is Cached Trust.
A node rechecks these conditions whenever it detects changes of
announced trust verdicts anywhere in the network.
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Upon encountering a node with a hierarchy of certificates for which
there is no effective verdict, a node adds a Neutral Trust-Verdict-
TLV to its node data for all certificates found in the hierarchy, and
publishes it until an effective verdict different from Neutral can be
found for any of the certificates, or a reasonable amount of time (10
minutes is suggested) with no reaction and no further authentication
attempts has passed. Such verdicts SHOULD also be limited in rate
and number to prevent denial-of-service attacks.
Trust verdicts are announced using Trust-Verdict TLVs:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type: Trust-Verdict (16) | Length: 37-100 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Verdict | (reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
| SHA-256 Fingerprint |
| |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Name |
Verdict represents the numerical index of the verdict.
(reserved) is reserved for future additions and MUST be set to 0
when creating TLVs and ignored when parsing them.
SHA-256 Fingerprint contains the SHA-256 [RFC6234] hash value of
the certificate in DER-format.
Common Name contains the variable-length (1-64 bytes) common name
of the certificate. Final byte MUST have value of 0.
10.3.4. Bootstrap Ceremonies
The following non-exhaustive list of methods describes possible ways
to establish trust relationships between DNCP nodes and node
certificates. Trust establishment is a two-way process in which the
existing network must trust the newly added node and the newly added
node must trust at least one of its neighboring nodes. It is
therefore necessary that both the newly added node and an already
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trusted node perform such a ceremony to successfully introduce a node
into the DNCP network. In all cases an administrator MUST be
provided with external means to identify the node belonging to a
certificate based on its fingerprint and a meaningful common name.
10.3.4.1. Trust by Identification
A node implementing certificate-based trust MUST provide an interface
to retrieve the current set of effective trust verdicts, fingerprints
and names of all certificates currently known and set configured
trust verdicts to be announced. Alternatively it MAY provide a
companion DNCP node or application with these capabilities with which
it has a pre-established trust relationship.
10.3.4.2. 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).
10.3.4.3. 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.
10.3.4.4. 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.
11. DNCP Profile-Specific Definitions
Each DNCP profile MUST define following:
o How the messages are secured: Not at all, optionally or always
with the TLS scheme defined here using one or more of the methods,
or with something else. 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
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DTLS support for at least the unicast transport protocol is
mandatory.
o Transport protocols' parameters such as port numbers to be used,
or multicast address to be used. Unicast, multicast, and secure
unicast may each require different parameters, if applicable.
o When receiving messages, what sort of messages are dropped, as
specified in Section 5.2.
o What is the criteria for sending Trickle-based Long Network State
Update message (Section 8.2) on an interface or to a DNCP peer.
o How to deal with node identifier collision as described in
Section 5.2. Main options are either for one or both nodes to
assign new node identifiers to themselves, or to notify someone
about a fatal error condition in the DNCP network.
o Imin, Imax and k ranges to be suggested for implementations to be
used in the Trickle algorithm. The Trickle algorithm does not
require these to be same across all implementations for it to
work, but similar orders of magnitude helps implementations of a
DNCP profile to behave more consistently and to facilitate
estimation of lower and upper bounds for behavior of the network.
o Hash function H(x) to be used, and how many bits of the input are
actually used. The chosen hash function is used to handle both
hashing of node specific data, and network state hash, which is a
hash of node specific data hashes. SHA-256 defined in [RFC6234]
is the recommended default choice.
o DNCP_NODE_IDENTIFIER_LENGTH: The fixed length of a node identifier
(in bytes).
o DNCP_GRACE_INTERVAL: How long node data for unreachable nodes is
kept.
o Whether to send keep-alives, and if so, on an interface, using
multicast, or directly using unicast to peers. Keep-alive has
also associated parameters:
* DNCP_KEEPALIVE_INTERVAL: How often keep-alive messages are to
be sent by default (if enabled).
* DNCP_KEEPALIVE_MULTIPLIER: How many times the
DNCP_KEEPALIVE_INTERVAL (or peer-supplied keep-alive interval
value) a node may not be heard from to be considered still
valid.
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12. Security Considerations
DNCP profiles may use multicast to indicate DNCP state changes and
for keep-alive purposes. However, no actual data TLVs will be sent
across that channel. Therefore an attacker may only learn hash
values of the state within DNCP and may be able to trigger unicast
synchronization attempts between nodes on a local link this way. A
DNCP node should therefore rate-limit its reactions to multicast
packets.
When using DNCP to bootstrap a network, PKI based solutions may have
issues when validating certificates due to potentially unavailable
accurate time, or due to inability to use the network to either check
Certifcate Revocation Lists or perform on-line validation.
The Certificate-based trust consensus mechanism defined in this
document allows for a consenting revocation, however in case of a
compromised device the trust cache may be poisoned before the actual
revocation happens allowing the distrusted device to rejoin the
network using a different identity. Stopping such an attack might
require physical intervention and flushing of the trust caches.
13. IANA Considerations
IANA should set up a registry for DNCP TLV types, with the following
initial contents:
0: Reserved (should not happen on wire)
1: Node connection
2: Request network state
3: Request node data
4-9: Reserved for DNCP profile use
10: Network state
11: Node state
12: Node data
13: Neighbor
14: Keep-alive interval
15: Custom
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16: Trust-Verdict
17-31: Reserved for future DNCP versions.
192-255: Reserved for per-implementation experimentation. The nodes
using TLV types in this range SHOULD use e.g. Custom TLV to identify
each other and therefore eliminate potential conflict caused by
potential different use of same TLV numbers.
For the rest of the values (32-191, 256-65535), policy of 'standards
action' should be used.
14. References
14.1. 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.
14.2. 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 Outstanding Issues
Should better forms of combined messages be defined? e.g. allow
sending both request-network-state, and currently set of known local
state at same time in one message.
Should some sort of fragmentation scheme be defined for the data?
Currently, DNCP uses Merkle tree of depth 2 (node data -> node hash
-> network hash). However, it essentially treats all TLVs published
by a single node as a single chunk on the protocol level. Is that a
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scalability problem? Adding one more level to the tree might address
this.
Appendix B. Some Obvious Questions and Answers
Q: Should there be nested container syntax that is actually self-
describing? (i.e. type flag that indicates container, no body except
sub-TLVs?)
A: Not for now, but perhaps valid design.. TBD.
Q: Add third case for multicast - 'medium' network state, which is
'long' one, but partial?
A: Drops typical convergence on large networks 5->3 packets, at
expense of some specification/implementation complexity. However, as
anything else than short network state leaks information via
multicast, it does not seem worth it as secure protocols probably
want to prevent multicast sending of anything else than short network
state in any case. Additionally, the long network state being
complete set of nodes actually facilitates light-weight nodes that do
not want to do graph-based pruning. So all in all, perhaps not worth
it.
Q: 32-bit connection id?
A: Here, it would save 32 bits per neighbor if it was 16 bits (and
less is not realistic). However, TLVs defined elsewhere would not
seem to even gain that much on average. 32 bits is also used for
ifindex in various operating systems, making for simpler
implementation.
Q: Why 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 C. Changelog
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.
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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!
Appendix D. Draft Source
As usual, this draft is available at https://github.com/fingon/ietf-
drafts/ in source format (with nice Makefile too). Feel free to send
comments and/or pull requests if and when you have changes to it!
Appendix E. Acknowledgements
Thanks to Ole Troan, Pierre Pfister, Mark Baugher, Mark Townsley,
Juliusz Chroboczek and Jiazi Yi for their contributions to the draft.
Authors' Addresses
Markus Stenberg
Helsinki 00930
Finland
Email: markus.stenberg@iki.fi
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Steven Barth
Halle 06114
Germany
Email: cyrus@openwrt.org
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