One document matched: draft-ietf-homenet-hncp-02.xml
<?xml version='1.0' ?>
<!--
Created: Mon Nov 18 17:55:22 2013 mstenber
-->
<!DOCTYPE rfc SYSTEM 'rfc2629.dtd'>
<?rfc autobreaks="yes"?>
<?rfc compact="yes"?>
<?rfc strict='yes'?>
<?rfc subcompact="no"?>
<?rfc symrefs="yes"?>
<?rfc toc="yes"?>
<?rfc tocindent="yes"?>
<rfc
ipr='trust200902'
docName='draft-ietf-homenet-hncp-02'
category='std'
>
<front>
<title abbrev="Home Networking Control Protocol">
Home Networking Control 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></city>
<code></code>
<country></country>
</postal>
<email>cyrus@openwrt.org</email>
</address>
</author>
<date month="October" year="2014" />
<area>Internet</area>
<workgroup>Homenet Working Group</workgroup>
<keyword>IPv6</keyword>
<keyword>Homenet</keyword>
<abstract>
<t>This document describes the Home Networking Control Protocol
(HNCP), a minimalist state synchronization protocol for homenet
routers. </t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>HNCP is designed to synchronize state across a homenet (or other
small site) in order to facilitate automated configuration within the
site. The design supports border discovery, IP prefix distribution
<xref target="I-D.ietf-homenet-prefix-assignment" />, and service
discovery across multiple links<xref
target="I-D.stenberg-homenet-dnssd-hybrid-proxy-zeroconf" />.</t>
<t>HNCP is designed to provide enough information for
a routing protocol to operate without homenet-specific
extensions. In homenet environments where multiple IPv6 prefixes are
present, routing based on source and destination address is
necessary <xref target="I-D.troan-homenet-sadr"/>. Routing protocol
requirements for source and destination routing are described in
section 3 of <xref
target="I-D.baker-rtgwg-src-dst-routing-use-cases" />. </t>
<t>A GPLv2-licensed implementation of the HNCP protocol is
currently under development at <eref target="https://github.com/sbyx/hnetd/">https://github.com/sbyx/hnetd/</eref>
and the binaries are available in the routing feed of <eref
target="http://www.openwrt.org">OpenWrt</eref> trunk release.
Some information how to get started with it is available at <eref
target="http://www.homewrt.org/doku.php?id=run-conf" />.
Comments and/or pull requests are welcome.</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="Data model">
<t>The data model of the HNCP protocol is simple: Every participating
node has (and also knows for every other participating node):
<list>
<t>A unique node identifier. It may be a public key, unique
hardware ID, or some other unique blob of binary data which HNCP
can run a hash upon to obtain a node identifier that is very likely
unique among the set of routers in the homenet.</t>
<t>A set of Type-Length-Value (TLV) data it wants to share with
other routers. The set of TLVs have a well-defined order based on
ascending binary content that is used to quickly identify changes
in the set as they occur. </t>
<t>Latest update sequence number. A 32 bit number that is
incremented anytime TLV data changes are detected.</t>
<t>Relative time, in milliseconds, since last publishing of the
current TLV data set. It is also 32 bit number on the wire.</t>
</list>
</t>
</section>
<section title="Operation">
<t>HNCP is designed to run on UDP port IANA-UDP-PORT, using
both link-local scoped IPv6 unicast and link-local scoped IPv6
multicast messages to address IANA-MULTICAST-ADDRESS for
transport. The protocol consists of <xref target="RFC6206">Trickle</xref>
driven multicast status messages to indicate changes in shared TLV
data, and unicast state synchronization message exchanges when the
Trickle state is found to be inconsistent.</t>
<section title="Trickle-Driven Status Updates" anchor="trickle-updates">
<t>Each node MUST send link-local multicast <xref
target="net-message">NetState Messages</xref> each time the <xref
target="RFC6206">Trickle algorithm</xref> indicates they should on
each link the protocol is active on. When the locally stored
network state hash changes (either by a local node event that
affects the TLV data, or upon receipt of more recent data from
another node), all Trickle instances MUST be reset. Trickle state
MUST be maintained separately for each link.</t>
<t>Trickle algorithm has 3 parameters; Imin, Imax and k. Imin and
Imax represent minimum and maximum values for I, which is the time
interval during which at least k Trickle updates must be seen on a
link to prevent local state transmission. Bounds for recommended
Trickle values are described below.
<list>
<t>k=1 SHOULD be used, as given the timer reset on data updates,
retransmissions should handle packet loss.</t>
<t>Imax MUST be at least one minute.</t>
<t>Imin MUST be at least 200 milliseconds (earliest transmissions
may occur at Imin/2 = 100 milliseconds given minimum values as
per the Trickle algorithm).</t>
</list>
</t>
</section>
<section title="Protocol Messages">
<t>Protocol messages are encoded as purely as a sequence of <xref
target="tlvs">TLV objects</xref>. This section describes which set
of TLVs MUST or MAY be present in a given message. </t>
<t>In order to facilitate fast comparing of local
state with that in a received message update, all TLVs in every
encoding scope (either root level, within the message
itself, or within a container TLV) MUST be placed
in ascending order based on the binary comparison of both
TLV header and value. By design, the
TLVs which MUST be present have the lowest available type values,
ensuring they will naturally occur at the start of the
Protocol Message, resembling a fixed format preamble.
</t>
<section title="Network State Update (NetState)"
anchor="net-message">
<t>This Message SHOULD be sent as a multicast message.</t>
<t>The following TLVs MUST be present at the start of the message:
<list>
<t><xref target="node-id">Node Link TLV</xref>.</t>
<t><xref target="net-hash">Network State TLV</xref>.</t>
</list>
</t>
<t>The NetState Message MAY contain <xref
target="node-state">Node State TLV(s)</xref>. If so, either all
Node State TLVs are included (referred to as a "long" NetState
Message), or none are included (referred to as a "short" NetState
Message). The NetState Message MUST NOT contain only a portion of
Node State TLVs as this could cause problems with the <xref
target="reception"> Protocol Message Processing</xref>
algorithm. Finally, if the long version of the NetState message
would exceed the minimum IPv6 MTU when sent, the short version of
the NetState message MUST be used instead.</t>
</section>
<section title="Network State Request, (NetState-Req)"
anchor="req-net-message">
<t>This Message MUST be sent as a unicast message.</t>
<t>The following TLVs MUST be present at the start of the message:
<list>
<t><xref target="node-id">Node Link TLV</xref>.</t>
<t><xref target="req-net-hash">Request Network State TLV</xref>.</t>
</list>
</t>
</section>
<section title="Node Data Request (Node-Req)"
anchor="req-node-message">
<t>This Message MUST be sent as a unicast message.</t>
<t>MUST be present:
<list>
<t><xref target="node-id">Node Link TLV</xref>.</t>
<t>one or more <xref
target="req-node-data">Request Node Data TLVs</xref>.</t>
</list>
</t>
</section>
<section title="Network and Node State Reply (NetNode-Reply)"
anchor="reply-message">
<t>This Message MUST be sent as a unicast message.</t>
<t>MUST be present:
<list>
<t><xref target="node-id">Node Link TLV</xref>.</t>
<t><xref target="net-hash">Network State TLV</xref>
and <xref target="node-state">Node State TLV</xref> for
every known node by the sender, or</t>
<t>one or more combinations of Node State and <xref
target="node-data">Node Data TLVs</xref>.</t>
</list>
</t>
</section>
</section>
<section title="HNCP Protocol Message Processing" anchor="reception">
<t>The majority of status updates among known nodes are handled via
the <xref target="trickle-updates">Trickle-driven updates
</xref>. This section describes processing of messages as received,
along with associated actions or responses.</t>
<t>HNCP is designed to operate between directly connected neighbors on
a shared link using link-local IPv6 addresses. If the source address
of a received HNCP packet is not an IPv6 link-local unicast address, the
packet SHOULD be dropped. Similarly, if the destination address is not
IPv6 link-local unicast or IPv6 link-local multicast address,
packet SHOULD be dropped.</t>
<t>Upon receipt of:
<list>
<t><xref target="net-message">NetState Message</xref>: If the
network state hash within the message matches the hash of the
locally stored network state, consider Trickle state as
consistent with no further processing required. If the hashes do
not match, consider Trickle state as inconsistent. In this case,
if the message is "short" (contains zero Node State TLVs), reply
with a <xref target="req-net-message">NetState-Req
Message</xref>. If the message was in long format (contained all
Node State TLVs), reply with <xref
target="req-node-message">NodeState-Req</xref> for any nodes for
which local information is outdated (local update number is lower
than that within the message), potentially incorrect (local
update number is same and the hash of node data TLV differs) or
missing. Note that if local information is more recent than that
of the neighbor, there is no need to send a message.</t>
<t><xref target="req-net-message">NetState-Req</xref>: Provide
requested data in a NetNode-Reply Message containing Network
State TLV and all Node State TLVs.</t>
<t><xref target="req-node-message">NodeState-Req</xref>: Provide
requested data in a NetNode-Reply containing Node State and Node
Data TLVs. </t>
<t><xref target="reply-message">State-Reply</xref>: If the
message contains Node State TLVs that are more recent than local
state (higher update number, different node data TLV hash, or we
lack the node data altogether), and if the message also contains
corresponding Node Data TLVs, update local state and reset
Trickle. If the message is lacking Node Data TLVs for some Node
State TLVs which are more recent than local state, reply with a
<xref target="req-node-message">NodeState-Req</xref> for the
corresponding nodes. </t>
</list>
</t>
<t>Each node is responsible for publishing a valid set of data
TLVs. When there is a change in a node's set of
data TLVs, the update number MUST be incremented accordingly.</t>
<t>If a message containing <xref target="node-state">Node State
TLVs</xref> is received via unicast or multicast with the node's
own node identifier and a higher update number than current local
value, or the same update number and different hash, there is an
error somewhere. A recommended default way to handle this is to
attempt to assert local state by increasing the local update number
to a value higher than that received and republish node data using
the same node identifier. If this happens more than 3 times in 60
seconds and the local node identifier is not globally unique, there
may be more than one router with the same node identifier on the
network. If there is no global guarantee of unique node identifier,
a new node identifier SHOULD be generated and node data republished
accordingly. </t>
<t>In all cases, if node data for any node changes, all Trickle
instances MUST be considered inconsistent (I=Imin + timer
reset).</t>
</section>
<section title="Adding and Removing Neighbors" anchor="neighbor">
<t>Whenever multicast message or unicast reply is received on a
link from another node, the node should be added as <xref
target="neighbor-tlv">Neighbor TLV</xref> for current node. If
nothing (for example - no router advertisements, no HNCP traffic)
is received from that neighbor in Imax seconds and the neighbor is
not in neighbor discovery cache, and no layer 2 indication of
presence is available, at least 3 attempts to ping it with <xref
target="req-net-message">request network state message</xref>
SHOULD be sent with increasing timeouts (e.g. 1, 2, 4 seconds). If
even after suitable period after the last message nothing is
received, the Neighbor TLV MUST be removed so that there are no
dangling neighbors. As an alternative, if there is a layer 2
unreachability notification of some sort available for either whole
link or for individual neighbor, it MAY be used to immediately
trigger removal of corresponding Neighbor TLV(s).</t>
</section>
<section title="Purging Unreachable Nodes">
<t>When node data has changed, the neighbor graph SHOULD be
traversed for each node following the bidirectional neighbor
relationships. These are identified by looking for neighbor TLVs on
both nodes, that have the remote node's identifier hash as
h(neighbor node identifier), and local and neighbor link
identifiers swapped. After the traverse, unreachable nodes SHOULD
be purged after some grace period. During the grace period, the
unreachable nodes MUST NOT be used for calculation of network state
hash, or even be provided to any applications that need to use the
whole TLV graph. </t>
</section>
</section>
<section anchor="tlvs" title="Type-Length-Value objects">
<t>
Every TLV is encoded as 2 octet type, followed by 2 octet length
(of the whole TLV, including header; 4 means no value),
and then the value itself (if any).
The actual length of TLV MUST be always divisible by 4; if the
length of the value is not, zeroed padding bytes MUST be inserted
at the end of TLV. The padding bytes MUST NOT be included 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>
Encoding of type=123 (0x7b) TLV with value 'x' (120 = 0x78):
007B 0005 7800 0000
</t>
<t>Notation:
<list>
<t>.. = octet string concatenation operation</t>
<t>H(x) = MD5 hash of x</t>
<t>H-64(x) = H(x) truncated by taking just first 64 bits of the result.</t>
</list>
</t>
<section title="Request TLVs (for use within unicast requests)">
<section anchor="req-net-hash" 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 (2) | Length: 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="req-node-data" title="Request Node Data 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-DATA (3) | Length: 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(node identifier) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
<section title="Data TLVs (for use in both multi- and unicast data)">
<section anchor="node-id" title="Node Link 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-LINK (1) | Length: 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(node identifier) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="net-hash" 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: 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(H(node data TLV 1) .. H(node data TLV N)) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The Node Data TLVs are ordered for hashing by octet comparison of
the corresponding node identifier hashes in ascending order.</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: 44 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(node identifier) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Milliseconds since Origination |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(node data TLV) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>The whole network should have roughly the same idea about the
time since origination, i.e. even the originating router should
increment the time whenever it needs to send a new Node State TLV
regarding itself without changing the corresponding Node Data
TLV. This age value is not included within the Node Data TLV,
however, as that is immutable and potentially signed by the
originating node at the time of origination.</t>
</section>
<section anchor="node-data" title="Node Data 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-DATA (6) | Length: >= 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(node identifier) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nested TLVs containing node information |
</artwork>
</figure>
</section>
<section anchor="neighbor-tlv" title="Neighbor TLV (within Node Data 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: 28 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| H(neighbor node identifier) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Neighbor Link Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Link Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>This TLV indicates that the node in question vouches that the
specified neighbor is reachable by it on the local link id
given. This reachability may be unidirectional (if no unicast
exchanges have been performed with the neighbor).
The presence of this TLV at least
guarantees that the node publishing it has received traffic
from the neighbor recently. For guaranteed bidirectional
reachability, existence of both nodes' matching Neighbor TLVs
should be checked. </t>
</section>
</section>
<section anchor="user-tlv" title="Custom TLV (within/without Node Data 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 (9) | Length: >= 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| H-64(URI) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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.
For example:</t>
<t>V=H-64('http://example.com/author/json-for-hncp') .. '{"cool": "json
extension!"}'</t>
<t>or</t>
<t>V=H-64('mailto:author@example.com') .. '{"cool": "json
extension!"}'</t>
</section>
<section anchor="version-tlv" title="Version TLV (within Node Data 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: VERSION (10) | Length: >= 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User-agent |
</artwork>
</figure>
<t>This TLV indicates which version of HNCP TLV binary structures
is in use by this particular node. All TLVs within node data from
nodes that do not publish version TLV, or with different Version
value than locally supported one MUST be ignored (but forwarded).
The user-agent is an optional human-readable UTF-8 string that can
describe e.g. current HNCP implementation version. This draft
describes Version=1 TLVs.</t>
</section>
</section>
<section title="Border Discovery and Prefix Assignment">
<t>This section defines border discovery algorithm derived from the
edge router interactions described in the <xref
target="RFC7084">Basic Requirements for IPv6 Customer Edge
Routers</xref>. The algorithm is designed to work for both IPv4 and
IPv6 (single or dual-stack). </t>
<t>In order to avoid conflicts between border discovery and homenet
routers running <xref target="RFC2131">DHCP</xref> or <xref
target="RFC3633">DHCPv6-PD</xref> servers each router MUST implement
the following mechanism based on <xref target="RFC3004">The User
Class Option for DHCP</xref> or its <xref target="RFC3315">DHCPv6
counterpart</xref> respectively into its DHCP and DHCPv6-logic:
<list>
<t>A homenet router running a DHCP-client on a homenet-interface
MUST include a DHCP User-Class consisting of the ASCII-String
"HOMENET".</t>
<t>A homenet router running a DHCP-server on a homenet-interface
MUST ignore or reject DHCP-Requests containing a DHCP User-Class
consisting of the ASCII-String "HOMENET".</t>
</list>
</t>
<t>The border discovery auto-detection algorithm works as follows,
with evaluation stopping at first match:
<list style="numbers">
<t>If a fixed category is set for an interface, it MUST be used.</t>
<t>Any of the following conditions indicate an interface MUST
be considered external:
<list style="numbers">
<t>A delegated prefix could be acquired by running a DHCPv6-client
on the interface.</t>
<t>An IPv4-address could be acquired by running a DHCP-client on
the interface.</t>
<!-- perhaps once we define HNCP security
<t>HNCP security is enabled and there are routers on the interface
which could not be authenticated.</t>
-->
</list>
</t>
<t>As default fallback, interface MUST be considered internal.</t>
</list>
</t>
<t>A router MUST allow setting a category of either auto-detected,
internal or external for each interface which is suitable for both
internal and external connections. In addition the following
specializations of the internal category are defined to modify the local router behavior:
<list>
<t>Leaf category: This declares an interface used by clients only.
A router SHOULD implement this category and MUST NOT send
nor accept HNCP messages on these interfaces.</t>
<t>Guest category: This declares an interface used by untrusted
clients only. In addition to the restrictions of the leaf
category, clients connected to these interfaces MUST NOT be able
to reach devices inside the home network by default and instead
SHOULD only be able to reach the internet. This category SHOULD be
also supported.</t>
<t>Ad-hoc category: This declares an interface to be in ad-hoc mode. This
indicates to HNCP applications such as prefix assignment that links
on this interface are potentially non-transitive. This category MAY
be implemented.</t>
<t>Hybrid category: This allows the router to still accepts external connections but
does not do border discovery. It is assumed that the link is under
control of a legacy, trustworthy non-HNCP router, still within the
same home network. Detection of this category automatically in
addition to manual configuration is out
of scope for this document. This category MAY be implemented.</t>
</list>
</t>
<t>A homenet router SHOULD provide basic connectivity to <xref
target="RFC7084">legacy CERs</xref> connected to internal interfaces
in order to allow coexistence with existing devices.</t>
<t>Each router MUST continuously scan each active interface that does
not have a fixed category in order to dynamically reclassify it if
necessary. The router therefore runs an appropriately configured
DHCP and DHCPv6-client as long as the interface is active including
states where it considers the interface to be internal. The router
SHOULD wait for a reasonable time period (5 seconds as a possible
default) in which the DHCP-clients can acquire a lease before
treating a newly activated or previously external interface as
internal. Once it treats a certain interface as internal it MUST
start forwarding traffic with appropriate source addresses between
its internal interfaces and allow internal traffic to reach external
networks. Once a router detects an interface to be external it MUST
stop any previously enabled internal forwarding. In addition it
SHOULD announce the acquired information for use in the homenet as
described in later sections of this draft if the interface appears to
be connected to an external network.</t>
<t>To distribute an external connection in the homenet an edge router
announces one or more delegated prefixes and associated
DHCP(v6)-encoded auxiliary information like recursive
DNS-servers. Each external connection is announced using one
container-TLV as follows:</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: EXTERNAL-CONNECTION (41)| Length: > 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nested TLVs |
</artwork>
</figure>
<t>Auxiliary connectivity information is encoded as a stream of
DHCPv6-attributes or DHCP-attributes placed inside a TLV of type
EXTERNAL-CONNECTION or DELEGATED-PREFIX (for IPv6 prefix-specific
information). There MUST NOT be more than one instance of this TLV
inside a container and the order of the DHCP(v6)-attributes contained
within it MUST be preserved as long as the information contained does
not change. The TLVs are encoded as follows:</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: DHCPV6-DATA (45) | Length: > 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCPv6 attribute stream |
</artwork>
</figure>
<t>and</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: DHCP-DATA (44) | Length: > 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DHCP attribute stream |
</artwork>
</figure>
<t>Each delegated prefix is encoded using one TLV inside an
EXTERNAL-CONNECTION TLV. For external IPv4 connections the prefix is
encoded in the form of an <xref target="RFC4291">IPv4-mapped
address</xref> and is usually from a <xref target="RFC1918">private
address range</xref>. The related TLV is defined as follows.</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: DELEGATED-PREFIX (42) | Length: >= 13 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid until (milliseconds) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred until (milliseconds) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | |
+-+-+-+-+-+-+-+-+ Prefix Address [+ nested TLVs] +
| |
</artwork>
</figure>
<t>
<list>
<t>Valid until is the time in milliseconds the delegated prefix
is valid. The value is relative to the point in time the TLV is
first announced.</t>
<t>Preferred until is the time in milliseconds the delegated
prefix is preferred. The value is relative to the point in time
the TLV is first announced.</t>
<t>Prefix length specifies the number of significant bits in the
prefix.</t>
<t>Prefix address is of variable length and contains the
significant bits of the prefix padded with zeroes up to the next
byte boundary.</t>
<t>Nested TLVs might contain prefix-specific information like
DHCPv6-options.</t>
</list>
</t>
<t>In order for routers to use the distributed information, prefixes
and addresses have to be assigned to the interior links of the
homenet. A router MUST therefore implement the algorithm defined in
<xref target="I-D.ietf-homenet-prefix-assignment">Prefix and
Address Assignment in a Home Network</xref>. In order to announce
the assigned prefixes the following TLVs are defined.</t>
<t>Each assigned prefix is given to an interior link and is encoded
using one TLVs. Assigned IPv4 prefixes are stored as mapped
IPv4-addresses. The TLV is defined as follows:</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: ASSIGNED-PREFIX (43) | Length: >= 9 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R. |A| Pref. | Prefix Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Prefix Address +
| |
</artwork>
</figure>
<t>
<list>
<t>Link Identifier is the local HNCP identifier of the link the
prefix is assigned to.</t>
<t>R. is reserved for future additions and MUST be set to 0 when
creating TLVs and ignored when parsing them.</t>
<t>A is the authoritative flag which indicates that an assignment
is enforced and ignores usual collision detection rules.</t>
<t>Pref. describes the preference of the assignment and can be
used to differentiate the importance of a given assignment over
others.</t>
<t>Prefix length specifies the number of significant bits in the
prefix.</t>
<t>Prefix address is of variable length and contains the
significant bits of the prefix padded with zeroes up to the next
byte boundary.</t>
</list>
</t>
<t>In some cases (e.g. IPv4) the set of addresses is very limited and
stateless mechanisms are not really suitable for address assignment.
Therefore HNCP can manage router address in these cases by itself.
Each router assigning an address to one of its interfaces announces
one TLV of the following kind:</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: ROUTER-ADDRESS (46) | Length: 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Router Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list>
<t>Link Identifier is the local HNCP identifier of the link the
address is assigned to.</t>
<t>Router Address is the address assigned to one of the router
interfaces.</t>
</list>
</t>
</section>
<section anchor="how" title="DNS-based Service Discovery">
<t>Service discovery is generally limited to a local link. <xref
target="I-D.stenberg-homenet-dnssd-hybrid-proxy-zeroconf" /> defines
a mechanism to automatically extended DNS-based service discovery
across multiple links within the home automatically. Following TLVs
MAY be used to provide transport for that specification. </t>
<section anchor="delegated-zone-tlv" title="DNS Delegated Zone 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: DNS-DELEGATED-ZONE (50) | Length: >= 21 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|B| |
+-+-+-+-+-+-+-+-+ Zone (DNS label sequence - variable length) |
| |
</artwork>
</figure>
</section>
<section anchor="domain-name-tlv" title="Domain Name 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: DOMAIN-NAME (51) | Length: >= 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Domain (DNS label sequence - variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section anchor="router-name-tlv" title="Router Name 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: ROUTER-NAME (52) | Length: >= 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Name (not null-terminated - variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
<section title="Routing support">
<section title="Protocol Requirements">
<t>In order to be advertised for use within the homenet, a routing protocol MUST:
<list>
<t>Comply with <xref target="I-D.baker-rtgwg-src-dst-routing-use-cases">Requirements and Use Cases for Source/Destination Routing</xref>.</t>
<t>Be configured with suitable defaults or have an auto-configuration mechanism (e.g. <xref target="I-D.acee-ospf-ospfv3-autoconfig" />) such that it will run in a homenet without requiring specific configuration from the home user. </t>
</list>
</t>
<t>A router MUST NOT announce that it supports a certain routing protocol if its implementation of the routing protocol does not meet these requirements,
e.g. it does not implement extensions that are necessary for compliance.</t>
</section>
<section title="Announcement">
<t>Each router SHOULD announce all routing protocols that it is capable of supporting in the homenet.
It MUST announce at least one protocol or the fallback mechanism to be considered for protocol selection and MAY omit announcing
the fallback mechanism if it announces at least one other routing protocol.
It SHOULD assign a preference value for each protocol that indicates its desire to use said protocol over other protocols it supports and SHOULD
make these values configurable.</t>
<t>Each router includes one HNCP TLV of type ROUTING-PROTOCOL for every such routing protocol. This TLV is defined as follows:</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: ROUTING-PROTOCOL (60) | Length: 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list>
<t>Protocol ID is one of:
<list>
<t>0 = Fallback (explicit announcement)</t>
<t>1 = Babel (dual-stack)</t>
<t>2 = OSPFv3 (dual-stack)</t>
<t>3 = IS-IS (dual-stack)</t>
<t>4 = RIP (dual-stack)</t>
</list>
</t>
<t>Preference is a value from 0 to 255. If a router is neutral
about a routing protocol it SHOULD use the value 128,
otherwise a lower value indicating lower preference
or a higher value indicating higher preference respectively.</t>
</list>
</t>
</section>
<section title="Protocol Selection">
<t>When HNCP detects that a device has joined or left the homenet it MUST examine all advertised
routing protocols and preference values from all devices announcing at least one ROUTING-PROTOCOL-TLV
in order to find the one routing protocol which:
<list style="numbers">
<t>Is understood by all routers in the homenet</t>
<t>Has the highest preference value among
all routers (calculated as sum of preference
values)</t>
<t>Has the highest protocol ID among those with the
highest preference </t>
</list>
</t>
<t>If the router protocol selection results in the need to change from one routing protocol
to another on the homenet, the router MUST stop the previously running protocol, remove
associated routes, and start the new protocol in a graceful manner. If there is no common routing
protocol available among all homenet routers, routers MUST utilize the
<xref target="fallback">Fallback Mechanism</xref>.</t>
</section>
<section anchor="fallback" title="Fallback Mechanism">
<t>In cases where there is no commonly supported routing protocol available the following fallback algorithm is run to setup routing and preserve interoperability among the homenet.
While not intended to replace a routing protocol, this mechanism provides a valid - but not necessarily optimal - routing topology.
This algorithm uses the node and neighbor state already synchronized by HNCP,
and therefore does not require any additional protocol message exchange.
<list style="numbers">
<t>Interpret the neighbor information received via HNCP as a graph of connected routers.</t>
<t>Use breadth-first traversal to determine the next-hop and hop-count in the path to each router in the homenet:
<list>
<t>Start the traversal with the immediate neighbors of the router running the algorithm.</t>
<t>Always visit the immediate neighbors of a router in ascending order of their router ID.</t>
<t>Never visit a router more often than once.</t>
</list>
</t>
<t>For each delegated prefix P of any router R in the homenet: Create a default route via the next-hop for R acquired in #2.
Each such route MUST be source-restricted to only apply to traffic with a source address within P and its metric MUST reflect the hop-count to R.</t>
<t>For each assigned prefix A of a router R:
Create a route to A via the next-hop for R acquired in #2. Each such route MUST NOT be source-restricted.</t>
<t>For the first router R visited in the traversal announcing an IPv4-uplink: Create a default IPv4-route via the next-hop for R acquired in #2.</t>
<t>For each assigned IPv4-prefix A of a router R: Create an IPv4-route to A via the next-hop for R acquired in #2.</t>
</list>
</t>
</section>
</section>
<section title="Security Considerations">
<t>General security issues for home networks are discussed at length
in <xref target="RFC7368" />. The protocols used to
set up IP in home networks today have rarely security enabled
within the control protocol itself. For example, DHCP has defined
<xref target="RFC3118" /> to authenticate DHCP messages, but this is
very rarely implemented in large or small networks. Further, while
PPP can provide secure authentication of both sides of a point to
point link, it is most often deployed with one-way authentication of
the subscriber to the ISP, not the ISP to the subscriber. </t>
<t>HNCP itself sends messages as clear text which is as secure, or
insecure, as the security of the link it runs on. As HNCP messages
are sent over IPv6 UDP, IPsec may be used for confidentiality or
message authentication. This requires manually keyed IPsec per-port
granularity for port IANA-UDP-PORT UDP traffic, and a pre-shared key
has to be utilized in this case given IKE cannot be used with
multicast traffic. This seems acceptable, though, as most routing
protocols also operate based on pre-shared keys, and the homenet
architecture draft explicitly allows their use for securing them<xref
target="RFC7368" />. Other traffic security mechanisms
are out of scope for this specification. There is <xref
target="I-D.barth-homenet-hncp-security-trust">ongoing work</xref>
to define a mechanism that can be used with HNCP and be more
user-friendly than pre-shared keys.</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>IANA should set up a registry (policy TBD) for HNCP TLV types, with following
initial contents:</t>
<t>0: Reserved (should not happen on wire)</t>
<t>1: Node link</t>
<t>2: Request network state</t>
<t>3: Request node data</t>
<t>4: Network state</t>
<t>5: Node state</t>
<t>6: Node data</t>
<t>7: (unused - was node public key, but never implemented)</t>
<t>8: Neighbor</t>
<t>9: Custom</t>
<t>10: Version</t>
<t>41: External connection</t>
<t>42: Delegated prefix</t>
<t>43: Assigned prefix</t>
<t>44: DHCP-data</t>
<t>45: DHCPv6-data</t>
<t>46: Router-address</t>
<t>50: DNS Delegated Zone</t>
<t>51: Domain name</t>
<t>52: Node name</t>
<t>60: Routing protocol</t>
<t>65535: Signature</t>
<t>HNCP will also require allocation of a UDP port number
IANA-UDP-PORT, as well as IPv6 link-local multicast address
IANA-MULTICAST-ADDRESS.</t>
</section>
</middle>
<back>
<references title="Normative references">
<?rfc include="reference.RFC.2119.xml"?>
<?rfc include="reference.RFC.6206.xml"?>
<?rfc include="reference.I-D.draft-ietf-homenet-prefix-assignment-01"?>
<?rfc include="reference.I-D.draft-stenberg-homenet-dnssd-hybrid-proxy-zeroconf-01"?>
</references>
<references title="Informative references">
<?rfc include="reference.RFC.7084.xml"?>
<?rfc include="reference.RFC.3004.xml"?>
<?rfc include="reference.RFC.3118.xml"?>
<?rfc include="reference.RFC.2131.xml"?>
<?rfc include="reference.RFC.3315.xml"?>
<?rfc include="reference.RFC.3633.xml"?>
<?rfc include="reference.RFC.1918.xml"?>
<?rfc include="reference.RFC.4291.xml"?>
<?rfc include="reference.RFC.7368.xml"?>
<?rfc include="reference.I-D.draft-troan-homenet-sadr-01.xml"?>
<?rfc include="reference.I-D.draft-baker-rtgwg-src-dst-routing-use-cases-01.xml"?>
<?rfc include="reference.I-D.draft-acee-ospf-ospfv3-autoconfig-03.xml"?>
<?rfc include="reference.I-D.draft-barth-homenet-hncp-security-trust-01.xml"?>
</references>
<section title="Some Outstanding Issues">
<t>Should we use MD5 hashes, or EUI-64 node identifier to identify
nodes?</t>
<t>Is there a case for non-link-local unicast? Currently explicitly
stating this is link-local only protocol. </t>
<t>Consider if using Trickle with k=1 really pays off, as we need to
do reachability checks if layer 2 does not provide them periodically
in any case. Using Trickle with k=inf would remove the need for
unicast reachability checks, but at cost of extra multicast
traffic. On the other hand, N*(N-1)/2 unicast reachability checks
when lot of routers share a link is not appealing either.</t>
<t>Valid and preferred are now 32 bit millisecond and you cannot even
represent a month in them; is this enough? Or should we switch to 32
bit seconds (or 64 bit milliseconds)?</t>
</section>
<section title="Some Obvious Questions and Answers">
<t>Q: Why not use TCP?</t>
<t>A: It does not address the node discovery problem. It also leads to
N*(N-1)/2 connections when N nodes share a link, which is
awkward. </t>
<t>Q: Why not multicast-only?</t>
<t>A: It would require defining application level fragmentation
scheme. Hopefully the data amounts used will stay small so we just
trust unicast UDP to handle 'big enough' packets to contain single
node's TLV data. On some link layers unicast is also much more
reliable than multicast, especially for large packets. Also on
wireless, multicast is much more power expensive than unicast.</t>
<t>Q: Why so long IDs?</t>
<t>A: Scalability of protocol is not really affected by using real
(=cryptographic) hash function.</t>
<t>Q: Why trust IPv6 fragmentation in unicast case? Why not do L7
fragmentation?</t>
<t>A: Because it will be there for a while at least. And while PMTU
et al may be problems on open internet, in a home network
environment UDP fragmentation should NOT be broken in the foreseeable
future. </t>
<t>Q: Should there be nested container syntax that is actually
self-describing? (i.e. type flag that indicates container, no body
except sub-TLVs?)</t>
<t>A: Not for now, but perhaps valid design.. TBD.</t>
<t>Q: Why not doing (performance thing X, Y or Z)?</t>
<t>A: This is designed mostly to be minimal (only timers Trickle
ones; everything triggered by Trickle-driven messages or local state
changes). However, feel free to suggest better (even more minimal)
design which works. </t>
</section>
<section title="Changelog">
<t>draft-ietf-homenet-hncp-02: Removed any built-in security. Relying
on IPsec. Reorganized interface categories, added requirements languages,
made manual border configuration a MUST-support. Redesigned routing
protocol election to consider non-router devices.</t>
<t>draft-ietf-homenet-hncp-01: Added (MAY) guest, ad-hoc, hybrid
categories for interfaces. Removed old hnetv2 reference, and now
pointing just to OpenWrt + github. Fixed synchronization algorithm to
spread also same update number, but different data hash case. Made
purge step require bidirectional connectivity between nodes when
traversing the graph. Edited few other things to be hopefully
slightly clearer without changing their meaning. </t>
<t>draft-ietf-homenet-hncp-00: Added version TLV to allow for TLV content
changes pre-RFC without changing IDs. Added link id to assigned
address TLV. </t>
</section>
<section title="Draft source">
<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
and Juliusz Chroboczek for their contributions to the draft.</t>
<t>Thanks to Eric Kline for the original border discovery work.</t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 09:03:54 |