One document matched: draft-ietf-6lowpan-nd-09.xml
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<rfc category="std" ipr="trust200902" updates="4944" docName="draft-ietf-6lowpan-nd-09">
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<front>
<title abbrev="ND Optimization for LLNs">
Neighbor Discovery Optimization for Low-power and Lossy Networks</title>
<author initials="Z" surname="Shelby" fullname="Zach Shelby" role="editor">
<organization>
Sensinode
</organization>
<address>
<postal>
<street>Hallituskatu 13-17D</street>
<city>Oulu</city>
<code>90100</code>
<country>FINLAND</country>
</postal>
<phone>+358407796297</phone>
<email>zach@sensinode.com</email>
</address>
</author>
<author initials="S" surname="Chakrabarti" fullname="Samita Chakrabarti">
<organization>IP Infusion</organization>
<address>
<postal>
<street> 1188 Arquest Street</street>
<city>Sunnyvale, CA</city>
<country>USA</country>
</postal>
<email>samitac@ipinfusion.com</email>
</address>
</author>
<author initials="E" surname="Nordmark" fullname="Erik Nordmark">
<organization>Oracle, Inc.</organization>
<address>
<postal>
<street>17 Network Circle</street>
<city>Menlo Park, CA 94025</city>
<country>USA</country>
</postal>
<email>Erik.Nordmark@Oracle.COM</email>
</address>
</author>
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Cisco Systems
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<author fullname="Jonathan W. Hui" initials="J.H." surname="Hui">
<organization abbrev="Arch Rock">Arch Rock Corporation</organization>
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<street>501 2nd St. Ste. 410</street>
<city>San Francisco</city>
<region>California</region>
<code>94107</code>
<country>USA</country>
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<phone>+415 692 0828</phone>
<email>jhui@archrock.com</email>
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</author>
<author initials="C." surname="Bormann" fullname="Carsten Bormann">
<organization>Universität Bremen TZI</organization>
<address>
<postal>
<street>Postfach 330440</street>
<city>Bremen</city>
<code>D-28359</code>
<country>Germany</country>
</postal>
<phone>+49-421-218-63921</phone>
<facsimile>+49-421-218-7000</facsimile>
<email>cabo@tzi.org</email>
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<date year="2010"/>
<area>Internet</area>
<workgroup>6lowpan Working Group</workgroup>
<abstract>
<t>
The IETF 6LoWPAN working group defines IPv6 for low-power and lossy networks (LLNs) such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non-transitive wireless links. The traditional IPv6 link concept and heavy use of multicast make the protocol inefficient and sometimes impractical in a low power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, addressing mechanisms and duplicate address detection for 6LoWPAN and similar networks.
</t>
</abstract>
</front>
<middle>
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<section anchor='introduction' title="Introduction">
<t>
The IPv6-over-IEEE 802.15.4 <xref target="RFC4944"/> document specifies how IPv6 is carried over an IEEE 802.15.4 network with the help of an adaptation layer which sits between the MAC layer and the IP network layer.
A link in a LoWPAN is characterized as lossy, low-power, low bit-rate, short range, with many nodes saving energy with long sleep periods. Multicast as used in IPv6 Neighbor Discovery <xref target="RFC4861"/> is not desirable in such a wireless low-power and lossy network. Moreover, LoWPAN links are asymmetric and non-transitive in nature. A LoWPAN is potentially composed of a large number of overlapping radio ranges. Although a given radio range has broadcast capabilities, the aggregation of these is a complex Non-Broadcast MultiAccess (NBMA, <xref target="RFC2491"/>) structure with generally no LoWPAN-wide multicast capabilities. Link-local scope is in reality defined by reachability and radio strength. Thus we can consider a LoWPAN to be made up of links with undetermined connectivity properties as in <xref target="I-D.ietf-autoconf-adhoc-addr-model"/>, along with the corresponding address model assumptions defined therein.</t>
<t>This specification introduces the following optimizations to IPv6 Neighbor Discovery <xref target="RFC4861"/> specifically aimed at low-power and lossy networks such as LoWPANs:
<list style="symbols">
<t>Host-initiated interactions to allow for sleeping hosts.</t>
<t>Elimination of multicast-based address resolution.</t>
<t>Elimination of redirects since they are problematic on links with non-transitive connectivity.</t>
<t>A host address registration feature using a new option
in unicast Neighbor Solicitation and Neighbor Advertisement messages.</t>
<t>A new Neighbor Discovery option to distribute 6LoWPAN header compression context to hosts.</t>
<t>Optional multihop distribution of prefix and 6LoWPAN header compression context.</t>
<t>Optional multihop duplicate address detection.</t>
</list>
</t>
<t>The document defines three new ICMPv6 message options: the required Address Registration option and the optional Authoritative Border Router and 6LoWPAN Context options.</t>
<section anchor='nd_problems' title="The Shortcomings of IPv6 Neighbor Discovery">
<t>IPv6 Neighbor Discovery <xref target="RFC4861"/> provides several
important mechanisms used for Router Discovery, Address Resolution, Duplicate
Address Detection, Redirect, along with Prefix and Parameter Discovery.</t>
<t>Following power-on and initialization of the network in IPv6 Ethernet
networks, a node joins the solicited-node multicast address on the interface
and then performs Duplicate Address Detection (DAD) for the acquired
link-local address by sending a solicited-node multicast message to the link.
After that it sends multicast messages to the all-router address to solicit
router advertisements. If the host receives a valid Router Advertisement
with the "A" flag, it autoconfigures the IPv6 address with the advertised
prefix in the Router Advertisement (RA) message. Besides this, the IPv6 routers
usually send router advertisements periodically on the network. RAs are sent to the all-node multicast address. Nodes send Neighbor Solicitation/Neighbor
Advertisement messages to resolve the IPv6 address of the destination
on the link. The Neighbor Solicitation messages used for address resolution are multicast. The Duplicate Address Detection procedure and the use of periodic Router Advertisement messages assumes that the nodes are powered on
and reachable most of the time.</t>
<t>In Neighbor Discovery the routers find the hosts by assuming that a subnet
prefix maps to one broadcast domain, and then multicast Neighbor Solicitation
messages to find the host and its link-layer address.
Furthermore, the DAD of use multicast assumes that all hosts that autoconfigure
IPv6 addresses from the same prefix can be used using link-local multicast
messages.</t>
<t>Note that the 'L' (on-link) bit in the Prefix Information option can
be set to zero in Neighbor Discovery, which makes the host not use
multicast Neighbor Solicitation (NS) messages for address resolution of other hosts, but routers still
use multicast NS messages to find the hosts.</t>
<t>
In a LoWPAN, primarily two types of network topologies are found - star networks and mesh networks. A star network is similar to a regular IPv6 subnet with a router and a set of nodes connected to it via the same non-transitive link. But in Mesh networks, the nodes are capable of routing and forwarding packets. Due to the lossy nature of wireless communication and a changing radio environment, the IPv6-link node-set may change due to external physical factors. Thus the link is often unstable and the nodes appear to be moving without moving physically.
</t>
<t>
A LoWPAN can use two types of link-layer addresses; 16-bit short addresses and 64-bit unique addresses as defined in <xref target="RFC4944"/>. Moreover, the available link-layer payload size is on the order of less than 100 bytes thus header compression is very useful.</t>
<t>Considering the above characteristics in a LoWPAN, and the IPv6 Neighbor Discovery <xref target="RFC4861"/> protocol design center, some optimizations and extensions to Neighbor Discovery are useful for the wide deployment of IPv6 over low-powered and lossy networks such as 6LoWPANs.
</t>
</section>
<section anchor='mu_ro' title="Mesh-under and Route-over Concepts">
<t>
In the 6LoWPAN context, often a link-layer mesh routing mechanism is referred to as "mesh-under" while routing/forwarding packets using IP-layer addresses is referred to as "route-over". The difference between mesh-under and route-over is similar to a bridged-network versus IP-routing using Ethernet. In a mesh-under network all nodes are on the same link which is served by one or more routers, which we call 6LoWPAN Border Routers (6LBR).
In a route-over network, there are multiple links in the 6LoWPAN. Unlike fixed IP links, these link's members may be changing due to the nature of the low-power and lossy behavior of wireless technology. Thus a route-over network is made up of a flexible set of links interconnected by interior routers, which we call 6LoWPAN Routers (6LR).
</t>
<t>
This specification is applicable to both mesh-under and route-over networks. However, in route-over networks, we have two types of routers - 6LBRs and 6LRs. 6LoWPAN Border Routers sit at the boundary of the 6LoWPAN and the rest of the network while 6LoWPAN Routers are inside the LoWPAN. 6LoWPAN Routers are assumed to be running a routing protocol.
</t>
<t>
In a mesh-under configuration a 6LBR is acting as the IPv6 router where all the hosts in the LoWPAN are on the same link, thus they are only one IP hop away. No 6LoWPAN Routers exist in this topology as forwarding is handled by a link-layer mesh routing protocol.
</t>
<t>
In a route-over configuration, Neighbor Discovery operations take place between hosts and 6LRs or 6LBRs. The 6LR nodes are able to send and receive Router Advertisements, Router Solicitations as well as forward and route IPv6 packets. Here packet forwarding happens at the routing layer.
</t>
<t>In both types of configurations, hosts do not take part in routing and forwarding packets and they act as simple IPv6 hosts.</t>
</section>
<section anchor='goals' title="Applicability, Goals and Assumptions">
<t>
The optimizations described in this document are most useful for route-over and mesh-under configurations in Mesh topologies. However, Star topology configurations will also benefit from the optimizations due to minimized signaling, robust handling of the non-transitive link, and header compression context information. </t>
<t>The document has the following main goals and assumptions
</t>
<t>Goals:
<list style="symbols">
<t>Optimize Neighbor Discovery with a mechanism that is minimal yet sufficient for the operation in both mesh-under and route-over configurations.</t>
<t>Make the host to router interaction the same whether mesh-under or
route-over is used.</t>
<t>Minimize signaling by avoiding the use of multicast flooding and reducing the use of link-scope multicast messages.</t>
<t>Optimize the interfaces between hosts and their default routers.</t>
<t>Support for sleeping hosts.</t>
<t>Minimize the complexity of nodes.</t>
<t>Disseminate context information to hosts as needed by <xref target="I-D.ietf-6lowpan-hc"/>.</t>
<t>Optionally disseminate context information and prefix information from the border to all routers in a LoWPAN.</t>
<t>Optional duplicate address detection mechanism suitable for route-over LoWPANs.</t>
</list>
</t>
<t>Assumptions:
<list style="symbols">
<t>EUI-64s are globally unique.</t>
<t>All nodes in the LLN have an EUI-64 interface identifier in order to do address auto-configuration and detect duplicate addresses.</t>
<t>If IEEE 802.15.4 16-bit short addresses are used, then some technique is
used to ensure uniqueness of those link-layer addresses. That could be done using
DHCPv6 or other techniques outside of the scope of this document. Optionally
it can be done using the Address Registration Option based duplicate address detection (Specified in <xref target="optional_dad"/>).
</t>
<t>The link layer technology is assumed to be low-power and lossy, exhibiting undetermined connectivity, such as IEEE 802.15.4 <xref target="RFC4944"/>. However, the Address Registration mechanism might be useful
for other link layer technologies.</t>
<t>A 6LoWPAN is configured with one or more global IPv6 address prefixes
to enable hosts to move between routers in the 6LoWPAN without changing their
IPv6 addresses.</t>
</list>
</t>
</section>
</section>
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<section anchor='terminology' title="Terminology">
<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"/>.
</t>
<t>
This specification requires readers to be familiar with all the terms and concepts that are discussed in <xref target="RFC4861">"Neighbor Discovery for IP version 6"</xref> <xref target="RFC4862">"IPv6 Stateless Address Autoconfiguration"</xref>, <xref target="RFC4919">"IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals"</xref>, <xref target="RFC4944"> "Transmission of IPv6 Packets over IEEE 802.15.4 Networks"</xref> and <xref target="I-D.ietf-autoconf-adhoc-addr-model">"IP Addressing Model in Ad Hoc Networks"</xref>.
</t>
<t>
This specification makes extensive use of the same terminology defined in
<xref target="RFC4861"/> unless otherwise defined below.
</t>
<t>
<list style="hanging">
<t hangText="6LoWPAN link:"><vspace />
A wireless link determined by single hop reachability of neighboring nodes. These are considered links with undetermined connectivity properties as in <xref target="I-D.ietf-autoconf-adhoc-addr-model"/>
</t>
<t hangText="Low-Power and Lossy Network (LLN):"><vspace />
A network made up of low-power links, often with a high probability of packet loss and undetermined connectivity properties. A LoWPAN is such a network for example.
</t>
<t hangText="6LoWPAN Router (6LR):"><vspace />
An intermediate router in the LoWPAN who can communicate with other 6LoWPAN routers in the same LoWPAN. 6LoWPAN routers are present only in route-over topologies.
</t>
<t hangText="6LoWPAN Border Router (6LBR):"><vspace />
A border router located at the junction of separate 6LoWPAN networks or between a 6LoWPAN network and another IP network. There may be one or more 6LBRs at the 6LoWPAN network boundary. A 6LBR is the responsible authority for IPv6 Prefix propagation for the 6LoWPAN network it is serving. An isolated LoWPAN also contains a 6LBR in the network, which provides the prefix(es) for the isolated network.
</t>
<t hangText="Router:"><vspace/>Either a 6LR or a 6LBR. Note that
nothing in this document precludes a node bring a router on some interfaces
and a host on other interfaces as allowed by <xref target="RFC2460"/>.</t>
<t hangText="Mesh-under:"><vspace />
A topology where hosts are connected to a 6LBR through a mesh using link-layer forwarding. Thus in a mesh-under configuration all IPv6 hosts in a LoWPAN are only one IP hop away from the 6LBR. This topology simulates the typical IP-subnet topology with one router with multiple nodes in the same subnet.
</t>
<t hangText="Route-over:"><vspace />
A configuration topology where hosts are connected to the 6LBR through the use of intermediate layer-3 (IP) routing. Here hosts are typically multiple IP hops away from a 6LBR. The route-over topology typically consists of a 6LBR, a set of 6LRs and hosts.
</t>
<t hangText="Registration:"><vspace />
The process during which a LoWPAN node sends an Neighbor Solicitation message with an Address Registration option to a Router creating a Neighbor Cache entry for the LoWPAN node with a specific timeout.
</t>
</list>
</t>
</section>
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<section anchor='overview' title="Protocol Overview">
<t>The Neighbor Discovery optimizations for LLNs are applicable to both
mesh-under and route-over configurations. In a mesh-under configuration
only 6LoWPAN Border Routers and hosts exist; there are no 6LoWPAN routers in
mesh-under topologies.</t>
<t>The most important part of the optizations is the evolved host-to-router
interaction that allows for sleeping nodes and avoids using multicast Neighbor
Discovery messages except
for the case of a host finding an initial set of default routers, and
redoing such determination when those set of routers have become unreachable.
</t>
<t>The protocol also provides for header compression
<xref target="I-D.ietf-6lowpan-hc"/> by carrying header compression information
in a new option in Router Advertisement messages.</t>
<t>In addition, there are optional and separate mechanisms that can be used between 6LRs and
6LBRs to perform multihop Duplicate Address Detection and distribution
of the Prefix and compression Context information from the 6LBRs to all the
6LRs, which in turn use normal Neighbor Discovery mechanisms to convey this information
to the hosts.</t>
<t>The protocol is designed so that the host-to-router interaction is
not affected by the configuration of the 6LoWPAN; the host-to-router
interaction is the same in a mesh-under and route-over configuration.</t>
<section anchor="Optimization" title="Extensions to RFC4861">
<t>This document specifies the following optimizations and extensions
to IPv6 Neighbor Discovery <xref target="RFC4861"/>:
<list style="symbols">
<t>Host initiated refresh of Router Advertisement information. This
removes the need for periodic or unsolicited Router Advertisements from
routers to hosts.</t>
<t>No Duplicate Address Detection (DAD) is required if EUI-64 based
IPv6 addresses are used.</t>
<t>DAD is optional if DHCPv6 is used to assign addresses.</t>
<t>A New Address Registration mechanism using new Address Registration
option between hosts and routers. This removes the need for Routers to
use multicast Neighbor Solicitations to find hosts, and supports sleeping
hosts. This also enables the same IPv6 address prefix(es) to be
used across a route-over 6LoWPAN. It provides the host-to-router interface
for Duplicate Address Detection. </t>
<t>A new optional Router Advertisement option for Context information used by
6LoWPAN header compression.</t>
<t>A new optional mechanism to perform Duplicate Address Detection
across a route-over 6LoWPAN reusing the above Address Registration option.</t>
<t>New optional mechanisms to distribute Prefixes and Context
information across a route-over network which uses a new Authoritative Border
Router option to control the flooding of configuration changes.</t>
<t>A few new default protocol constants are introduced and some
existing Neighbor Discovery protocol constants are tuned for LLN usage.</t>
</list>
</t>
</section>
<section anchor="Addr-assign" title="Address Assignment">
<t>Hosts in a 6LoWPAN configure their IPv6 address as specified in
<xref target="RFC4861"/> and <xref target="RFC4862"/> based on the information
received in Router Advertisement messages.</t>
<t>Optionally, 6LRs can use the same mechanisms to configure their IPv6
addresses.</t>
<t>The 6LBRs are responsible for managing the prefix(es) assigned to the
6LoWPAN, using manual configuration, DHCPv6 Prefix Delegation
<xref target="RFC3633"/>, or other mechanisms.
In an isolated LoWPAN a ULA <xref target="RFC4193"/> prefix SHOULD
be generated by the 6LBR.</t>
</section>
<section anchor='overview_hr' title="Host-to-Router Interaction">
<t>A host sends Router Solicitation messages at startup and
also when it suspects that one of its default routers have become
unreachable (after Neighbor Unreachability Detection towards the router fails).
</t>
<t>Hosts receive Router Advertisement messages typically containing the Authoritative Border Router option
(ABRO) and may optionally contain one or more 6LoWPAN Context options (6CO)
in addition to the existing Prefix Information options (PIO) as described
in <xref target="RFC4861"/>.</t>
<t>When a host has configured a non-link-local IPv6 address, it registers
that address with one or more of its default routers using the Address
Registration option (ARO). The host chooses a lifetime of the registration
and repeats the ARO option to maintain the registration, even while the host
is sleeping.</t>
<t>The registration can fail (an ARO option returned to the host with a non-zero
Status) if the router determines that the IPv6 address is already used
by another hosts, that is, is used by a host with a different EUI-64.
This can be used to support non-EUI-64 based addresses such as temporary
IPv6 addresses <xref target="RFC4941"/> or addresses based on an Interface ID
that is a IEEE 802.15.4 16-bit short addresses.</t>
<t>The re-registration of a address can be combined with Neighbor
Unreachability Detection (NUD) of the router since both use unicast Neighbor
Solicitation messages. This makes things efficient when a host wakes up
to send a packet and both need to perform NUD to check that the router
is still reachable, and refresh its registration with the router.</t>
<t>The response to an address registration might not be immediate since
in route-over configurations the 6LR might perform Duplicate Address Detection
against the 6LBR. A host retransmits the Address Registration option
until it is
acknowledged by the receipt of a Address Registration option.</t>
<t>As part of the optimizations, Address Resolution is not performed by
multicasting Neighbor Solicitation messages as in <xref target="RFC4861"/>.
Instead, the routers maintain Neighbor Cache entries for all registered
IPv6 addresses. If the address is not in the Neighbor Cache in the router, then
the address either doesn't exist, or is assigned a host attached to some other router
in the 6LoWPAN, or is external to the 6LoWPAN. In a route-over configuration
the routing protocol is used to route such packets toward the destination.</t>
</section>
<section anchor='overview_rr' title="Router-to-Router Interaction">
<t>The optional new router-to-router interaction is only for the route-over
configuration where 6LRs are present. It is optional in this protocol since the
functions it provides might be better provided by other protocol mechanisms,
be it DHCPv6, link-layer mechanisms, the routing protocol, or something else.
Some mechanisms from this protocol might be used for router-to-router, while
others are provided by other protocols. For instance, context information
and/or prefix information might be disseminated using this protocol, while
Duplicate Address Detection is done using some other protocol.</t>
<t>6LRs can act like a host during system startup and prefix configuration
by sending Router Solicitation messages and autoconfiguring their IPv6
addresses unlike routers in <xref target="RFC4861"/>.</t>
<t>When multihop prefix or context dissemination is used then the 6LRs
store the ABRO, 6CO and Prefix Information received (directly or indirectly)
from the 6LBRs
and redistribute this information in the Router
Advertisements they send to other 6LRs or send to hosts in response to a
Router Solicitations. There is a version number field in the ABRO which
is used to limit the flooding of updated information between the 6LRs.</t>
<t>Optionally the 6LRs can perform Duplicate Address Detection
against one or more 6LBRs using a special form of the Address Registration
option. In this case, the Neighbor Solicitation and Advertisement messages will be forwarded between the 6LR and
6LBRs and the <xref target="RFC4861"/> rule for checking hop-limit=255
is relaxed. Such multihop DAD messages MUST NOT modify any Neighbor Cache
entries on the routers since we do not have the security benefits provided
by the hop-limit=255 check.</t>
</section>
</section>
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<section anchor='message_options' title="New Neighbor Discovery Options">
<t>This section defines new Neighbor Discovery message options used by this specification. The Address Registration Option is mandatory, whereas the Authoritative Border Router Option and 6LoWPAN Context Option are optional.</t>
<section anchor="ARO" title="Address Registration Option">
<t>
The routers need to know the set of host IP addresses that are directly reachable and their corresponding link-layer addresses. This
needs to be maintained as the radio reachability changes. For this purpose an Address Registration Option (ARO) is introduced, which can be included in unicast Neighbor Solicitation (NS) messages sent by
hosts. Thus it can be included in the unicast NS messages that a host
sends as part of Neighbor Unreachability Detection to determine that it can still reach a default router.
The ARO is used by the receiving router to reliably maintain its Neighbor Cache. The same option is included in corresponding Neighbor Advertisement (NA) messages with a Status field indicating the success or failure of the registration. This option is always host initiated.</t>
<t>The ARO is reused for the optional multihop Duplicate Address Detection
from 6LRs to 6LBRs, in which case it has a different Length. In that case one
or more AROs can be included in an NS.
</t>
<t>
The ARO is required for reliability and power saving. The lifetime field provides flexibility to the host to register an address which should be usable (continue to be advertised by the 6LR in the routing protocol etc.) during its intended sleep schedule.
</t>
<t>
The sender of the NS also includes the EUI-64 of the interface it is registering an address from. This is used as a unique ID for the detection of duplicate addresses. It is used to tell the difference between the same node re-registering its address and a different node (with a different EUI-64) registering an address that is already in use by someone else.
</t>
<t>
When the ARO is used by hosts the address that is registered MUST be the IPv6 source
address for the Neighbor Solicitation message. Thus the Registered Address field
is omitted and the Length field MUST be two. When the ARO is used for the optional multihop DAD
between a 6LR and a 6LBR then the Registered Address field is included and the Length field MUST be four.
</t>
<figure>
<artwork><![CDATA[
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 | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| EUI-64 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Registered Address (Optional) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Fields:
<list style='hanging' hangIndent='15'>
<t hangText="Type:"> TBD1</t>
<t hangText="Length:"> 8-bit unsigned integer.
The length of the option in units of 8 octets. 2 without or 4 with the Registered Address.</t>
<t hangText="Status:"> 8-bit unsigned integer.
Indicates the status of a registration in the NA response. MUST be set to 0 in NS messages. See below.</t>
<t hangText="Reserved:"> 8-bits. This field is unused.
It MUST be initialized to zero by the sender and MUST be ignored by the
receiver.</t>
<t hangText="Registration Lifetime:"> 32-bit unsigned integer.
The amount of time in seconds that the router should retain the Neighbor Cache
entry for the sender of the NS that includes this option.</t>
<t hangText="EUI-64:">64 bits. This field is used to uniquely identify the
interface of the registered address.</t>
<t hangText="Registered Address:">128-bit optional field. MUST NOT be sent by a host. Used for the optional router-router registrations on behalf of a host. Carries the host address, which was contained in the IPv6 Source field in the original NS that contained the option sent by the host.</t>
</list>
</t>
<t>The Status values used in Neighbor Advertisements are:
</t>
<texttable anchor='status codes'>
<ttcol align='center'> Status </ttcol>
<ttcol align='center'> Description</ttcol>
<c>0</c> <c>Success</c>
<c>1</c> <c>Duplicate Address</c>
<c>2-255</c> <c>Allocated using Standards Action <xref target="RFC2434"/></c>
</texttable>
</section>
<section anchor='6CO' title="6LoWPAN Context Option">
<t>
The optional 6LoWPAN Context Option (6CO) carries prefix information for
LoWPAN header compression, and is similar
to the Prefix Information Option of <xref target="RFC4861"/>.
However, the prefixes can be remote as well as local to the LoWPAN since header compression potentially applies to all IPv6 addresses. This option allows for the dissemination of multiple contexts
identified by a Context Identifier (CID) for use as specified in <xref target="I-D.ietf-6lowpan-hc"/>. A context may be a prefix of any length or an address (/128), and up to 16 6LoWPAN Context options may be carried in an Router Advertisement message.
</t>
<figure anchor='6co_format' title="6LoWPAN Context Option format">
<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 |Context Length | Res |C| CID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Context Prefix .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list style="hanging">
<t hangText="Type:">
TBD2
</t>
<t hangText="Length:">
8-bit unsigned integer. The length of the option
(including the type and length fields) in units
of 8 octets. May be 2 or 3 depending on the
length of the Context Prefix field.
</t>
<t hangText="Context Length:">
8-bit unsigned integer. The number of leading bits
in the Context Prefix field that are valid. The value ranges from 0 to 128. If it is more than 64 then the Length MUST be 3.
</t>
<t hangText="C:">
1-bit context compression flag. This flag indicates if the context is valid for use in compression. A context that is not valid MUST NOT be used for compression, but SHOULD be used in decompression in case another compressor has not yet received the updated context information.
</t>
<t hangText="CID:">
4-bit Context Identifier for this prefix information. CID is used
by context based header compression specified in <xref target="I-D.ietf-6lowpan-hc"/>. The
list of CIDs for a LoWPAN is configured by on the 6LBR that originates the context information for the 6LoWPAN.
</t>
<t hangText="Res:">
3-bit reserved field. This field is unused. It MUST be initialized to
zero by the sender and MUST be ignored by the
receiver.
</t>
<t hangText="Valid Lifetime:">
32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is received)
that the context is valid for the purpose of header compression or decompression. A value of all one bits (0xffffffff) represents infinity. A value of all zero bits (0x0) indicates that this context entry MUST be removed immediately.
</t>
<t hangText="Context Prefix:">
The IPv6 prefix or address corresponding to the Context ID (CID) field. The valid length of this field is included in the Context Length field. This field is padded with zeros in order to make the option a multiple of 8-bytes.
</t>
</list>
</t>
</section>
<section anchor='ABRO' title="Authoritative Border Router Option">
<t>The optional Authoritative Border Router Option (ABRO) is needed when Router
Advertisement (RA) messages are used to disseminate prefixes and context information across
a route-over topology.
In this case 6LRs receive Prefix Information options from other 6LRs.
This implies that a 6LR can't just let the most recently received RA win.
In order to be able to reliably add and remove prefixes from the 6LoWPAN we
need to carry information from the authoritative 6LBR.
This is done by introducing a version number which the 6LBR sets and 6LRs propagate as they propagate the prefix and context information with this Authoritative Border Router Option. When there are multiple 6LBRs they would have
separate version number spaces. Thus this option needs to carry the IP address of
the 6LBR that originated that set of information.
</t>
<t>
The Authoritative Border Router option MUST be included in all Router Advertisement
messages in the case when Router Advertisements are used to propagate
information between routers (as described in <xref target="optional_dad"/>.
</t>
<figure>
<artwork><![CDATA[
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 = 3 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ 6LBR Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>Fields:
<list style='hanging' hangIndent='15'>
<t hangText="Type:"> TBD3</t>
<t hangText="Length:"> 8-bit unsigned integer.
The length of the option in units of 8 octets. Always 3.</t>
<t hangText="Reserved:"> 16-bits. This field is unused.
It MUST be initialized to zero by the sender and MUST be ignored by the
receiver.</t>
<t hangText="Version Number:"> 32-bit unsigned integer.
The version number corresponding to this set of information contained in the RA message. The authoritative 6LBR originating the prefix increases this version number each time its set of prefix or context information changes.</t>
<t hangText="6LBR Address:"> IPv6 address of the 6LBR that is the origin of the included version number.</t>
</list>
</t>
</section>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='host' title="Host Behavior">
<t>Hosts in a LoWPAN use the Address Registration option in the Neighbor Solicitation messages they send as a way to maintain the Neighbor Cache in the routers
thereby removing the need for multicast Neighbor Solicitations to do address resolution. Unlike in <xref target="RFC4861"/> the hosts initiate updating
the information they receive in Router Advertisements by sending Router
Solicitations before the information expires. Finally, when Neighbor Unreachability
Detection indicates that one or all default routers have become unreachable, then
the host uses Router Solicitations to find a new set of default routers.</t>
<section title="Forbidden Actions">
<t>A host in a 6LoWPAN MUST NOT accept a Redirect message. Redirect
messages are problematic on a link with non-transitive reachability.</t>
<t>A host would never multicast a Neighbor Solicitation message.</t>
</section>
<section anchor='host_interface' title="Interface Initialization">
<t>When the interface on a host is initialized it follows the specification in
<xref target="RFC4861"/>. A link-local address is formed based on the EUI-64 assigned
to the interface, and then the host sends Router Solicitation messages as described in <xref target="RFC4861"/> Section 6.3.7.</t>
<t>There is no need to join the Solicited-Node multicast address since nobody
multicasts Neighbor Solicitations in this type of network.</t>
<!-- TODO: Erik: Should we say something about joining or not joining the
all-nodes multicast address? -->
</section>
<section title="Sending a Router Solicitation">
<t>The Router Solicitation is formatted as specified in <xref target="RFC4861"/> and
sent to the IPv6 All-Routers multicast address (see <xref target="RFC4861"/> Section 6.3.7 for details). If the link layer supports a way
to send packets to some kind of all-routers anycast link-layer address, then that MAY be
used to convey theses packets to a router.</t>
</section>
<section title="Processing a Router Advertisement">
<t>The processing of Router Advertisements is as in <xref target="RFC4861"/> with
the addition of handling the 6LoWPAN Context option and triggering address registration when a new address has been configured.</t>
<t>Should the host erroneously receive a Prefix Information option with the 'L'
(on-link) flag set, then that Prefix Information Option (PIO) MUST be ignored.</t>
<section title="Address configuration">
<t>Address configuration follows <xref target="RFC4862"/>. Once an address has been
configured it will be registered by unicasting a Neighbor Solicitation with the Address
Registration option to the router.</t>
</section>
<section title="Storing Contexts">
<t>The host maintains a conceptual data structure for the context information
it receives from the routers, which is called the Context Table.
This includes the Context ID, the prefix (from the
Context Prefix field in the 6CO), the Compression bit, and the Valid Lifetime.
A Context Table entry
that has the Compression bit clear is used for decompression when receiving
packets, but MUST NOT be used for compression when sending packets.</t>
<t>When a 6CO option is received in a Router Advertisement it is used to add or
update the information in the Context Table. If the Context ID field in the
6CO matches an existing Context Table entry, then that entry is updated with the
information in the 6CO. If the Valid Lifetime field in the 6CO is zero, then the
entry is immediately deleted.</t>
<t>If there is no matching entry in the Context Table, and the Valid Lifetime
field is non-zero, then a new context is added to the Context Table. The 6CO is used
to update the created entry.</t>
<t>
When the 6LBR changes the context information a host might not immediately
notice. And in the worst case a host might have stale context information. For this reason 6LBRs use the recommendations in <xref target="context_management"/> for carefully managing the context lifecycle.
</t>
<!-- No longer needed as now changed to match on CID rather than the Context Prefix...
<t>The above matching of Context Table entries MUST only compare the first Context
Length bits in the Context Prefix field. Subsequent bits MUST be ignored in
the comparison.</t>
-->
<!-- <t> If a host
discovers that changes to the Context Table result in the same CID being specified
in multiple Context Table entries, then the host should discard the oldest entry.
The host can determine which entry is the oldest by inspecting the Version number
field in the Authoritative Border Router option, which is included in the Router Advertisement
message.</t>
-->
</section>
<section title="Maintaining Prefix and Context Information">
<t>The prefix information is timed out as specified in <xref target="RFC4861"/>.
When the Valid Lifetime for a Context Table entry expires the entry is deleted.</t>
<t>A host should inspect the various lifetimes to determine when it should next initiate sending a Router Solicitation to ask for any updates to the information. The
lifetimes that matter are the Default Router lifetime, the Valid Lifetime in the
Prefix Information options, and the Valid Lifetime in the 6CO. The host SHOULD unicast
an Router Solicitation to the router well before the minimum of those lifetimes (across all the prefixes
and all the contexts) expire.</t>
</section>
</section>
<section anchor='host_registration'
title="Registration and Neighbor Unreachability Detection">
<t>Unicast Neighbor Solicitation (NS) messages are send by hosts to register their
IPv6 addresses, and also to do NUD to verify that its default routers
are still reachable. The registration is performed by the host including
an ARO in the Neighbor Solicitation it sends. Even if the host doesn't have
data to send, but is
expecting others to try to send packets to the host, the host needs to maintain
its Neighbor Cache entries in the routers. This is done by sending NS messages with the ARO to the router well in advance of the registration lifetime expiring. NS messages are retransmitted up to MAX_UNICAST_SOLICIT times using a minimum timeout of RETRANS_TIMER until the host receives an Neighbor Advertisement message with an ARO option. </t>
<t>Hosts that receive Router Advertisement messages from multiple default routers
SHOULD attempt to register with more than one of them in order to increase the robustness
of the network.</t>
<!-- TODO: Zach: We should consider making this a MAY as it is a lot of overhead to register with all possible routers in a mesh network... Erik: changed from "all" to "more than one". -->
<t>Note that Neighbor Unreachability Detection probes can be suppressed if
by Reachability Confirmations from transport protocols or applications
as specified in <xref target="RFC4861"/>.</t>
<section anchor='host_ns' title="Sending a Neighbor Solicitation">
<t>The host triggers sending Neighbor Solicitation (NS) messages containing an ARO when a new address is configured, when it discovers a new default router, or well before
the Registration Lifetime expires. Such an NS MUST include a Source Link-Layer Address (SLLA) option, since
the router needs to record the link-layer address of the host.</t>
</section>
<section title="Processing a Neighbor Advertisement">
<t>A host handles Neighbor Advertisement messages as specified in <xref target="RFC4861"/>, with added logic described in this section for handling the Address Registration option.</t>
<t>
In addition to the normal validation of a Neighbor Advertisement and its options, the Address Registration option is verified as follows (if present). If the Length field is not two, the option is silently ignored. If the EUI-64 field does not match the EUI-64 of the interface, the option is silently ignored.
</t>
<t>
If the status field is zero, then the address registration was successful. The host saves the Registration Lifetime from the Address Registration option for use to trigger a new NS well before the lifetime expires. If the Status field is not equal to zero, the address registration has failed.
</t>
</section>
<section title="Recovering from Failures">
<t>The procedure for maintaining reachability information about a neighbor is the same as in <xref target="RFC4861"/> Section 7.3 with the exception that address resolution is not performed. </t>
<t>The address registration procedure may fail for two reasons: no response to Neighbor Solicitations is received (NUD failure), or an Address Registration option with a failure Status (Status > 0) is received. In the case of NUD failure the entry for that router will be removed thus address registration is no longer of importance. When an Address Registration option with a non-zero Status field is received this indicates that registration for that address has failed. A failure Status of one indicates that a duplicate address was detected and the procedure described in <xref target="RFC4862"/> Section 5.4.5 is followed. Other failure codes may be defined in future documents. For all
non-zero Status values the host MUST NOT use the address it tried to register.
</t>
</section>
</section>
<section title="Next-hop Determination">
<t>
The IP address of the next-hop for a destination is determined as follows. Destinations to the link-local prefix (FE80::) are always sent on the link to that destination. All other prefixes are assumed to be off-link <xref target="I-D.ietf-autoconf-adhoc-addr-model"/>. Anycast addresses are always considered to be off-link.
They are therefore sent to one of the routers in the Default Router List.
</t>
<t>
Multicast addresses are considered to be on-link and are resolved as specified in <xref target="RFC4944"/> or the appropriate IP-over-foo document.</t>
<t>A LoWPAN Node is not required to maintain a minimum of one buffer per
neighbor as specified in <xref target="RFC4861"/>, since packets are never queued while waiting for address resolution.
</t>
</section>
<section title="Address Resolution">
<t>
The address registration mechanism and the SLLA option in Router Advertisement message provide sufficient a priori state in routers and hosts to resolve an IPv6 address to its associated link-layer address. As all prefixes but the link-local prefix are always assumed to be off-link, multicast-based address resolution between neighbors is not needed.
</t>
<t>
Link-layer addresses for neighbors are stored in Neighbor Cache entries <xref target="RFC4861"/>
In order to achieve LoWPAN compression, most global addresses are formed using
a link-layer address. Thus a host can minimize memory usage by optimizing
for this case and only storing link-layer address information if it differs
from the link-layer address corresponding to the Interface ID of the
IPv6 address (i.e., differs in more than the on-link/global bit being inverted).
</t>
</section>
<section title="Sleeping">
<t>It is often advantageous for battery-powered hosts in LoWPANs to keep a low duty cycle. The optimizations described in this document enable hosts to sleep as described further in this section. Routers may want to cache traffic destined to a host which is sleeping, but such functionality is out of the scope of this document.</t>
<section title="Picking an Appropriate Registration Lifetime">
<t>As all Neighbor Discovery messages are initiated by the hosts, this allows a host to sleep or otherwise be unreachable between NS messages. The Address Registration option attached to NS messages indicates to a router to keep the Neighbor Cache entry for that address valid for the period in the Registration Lifetime field. A host should choose a sleep time appropriate for its energy characteristics, and set a registration lifetime larger than the sleep time to ensure the registration is renewed successfully (considering e.g. clock drift). A host should also consider the stability of the network (how quickly the topology changes) when choosing its sleep time (and thus registration lifetime). A dynamic network may require a shorter sleep time. </t>
</section>
<section title="Behavior on Wakeup">
<t>When a host wakes up from a sleep period it SHOULD maintain its current address registrations that will timeout before the next wakeup. This is done by sending Neighbor Solicitation messages with the Address Registration option as described in <xref target="host_ns"/>. The host may also need to refresh its prefix and context information by sending new unicast Router Solicitation. If after wakeup the host (using NUD) determines that some or all previous default routers have become unreachable, then the host will restart doing multicast Router Solicitations to discover new default router(s) and restart the address registration process.</t>
</section>
</section>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='router' title="Router Behavior for 6LR and 6LBR">
<t>Both 6LRs and 6LBRs maintain the Neighbor Cache <xref target="RFC4861"/>
based on the Address Registration Options they receive in Neighbor Advertisement
messages from hosts. Note that the handling of ARO from other routers (with Length=4)
is specified in <xref target="optional"/>.</t>
<t>The routers SHOULD NOT garbage collect the Neighbor Cache entries since
they need to retain them until the Registration Lifetime expires. Similarly,
if Neighbor Unreachability Detection on the router determines that the
a host is UNREACHABLE (based on the logic in <xref target="RFC4861"/>), the
Neighbor Cache entry SHOULD NOT be deleted but be retained until the
Registration Lifetime expires. A renewed ARO should mark the cache entry as
STALE.</t>
<t>Routers MAY implement the Default Router Preferences <xref target="RFC4191"/> and
use that to indicate to the host whether the router is a 6LBR or a 6LR. If this is
implemented then 6LRs with no route to a border router MUST set Prf to (11) for
low preference, other 6LRs MUST set Prf to (00) for normal preference, and 6LBRs MUST
set Prf to (01) for high preference.</t>
<section title="Forbidden Actions">
<t>A router SHOULD NOT send Redirect messages. Since the link has non-transitive
reachability the router has no way to determine that the recipient of a Redirect
message can reach the link-layer address.</t>
<t>A router MUST NOT set the 'L' (on-link) flag in the Prefix Information options,
since that might trigger hosts to send multicast Neighbor Solicitations.</t>
</section>
<section title="Interface Initialization">
<t>A router initializes its interface more or less as in <xref target="RFC4861"/>.
However, a 6LR might want to wait to make its interfaces advertising (implicitly
keeping the AdvSendAdvertisements flag clear) until it has received the prefix(es)
and context information from its 6LBR. That is independent of whether prefixes and
context information is disseminated using the methods specified in this document,
or using some other method.</t>
</section>
<section title="Processing a Router Solicitation">
<t>A router processes Router Solicitation messages as specified in
<xref target="RFC4861"/>. The differences relate to the inclusion of Authoritative
Border Router options in the Router Advertisement (RA) messages.
If a 6LR has received an ABRO
from a 6LBR, then it will include that option unmodified in the Router Advertisement
messages it sends. And if the 6LR has received RAs, whether with the same prefixes
and context information or different, from different 6LBR, then it will need to
keep those prefixes and context information separately so that the RAs the 6LR sends
will maintain the association between the ABRO and the prefixes and context
information. The router can tell which 6LBR originated the prefixes and context
information from the 6LBR Address field in the ABRO.
<!-- TODO: Zach: I propose adding the following text below (pointed out in a comment from Daniel). In other words, we can't force 6LRs to store info from all 6LBRs if it becomes a memory issue. So this should be a MAY rather than an implied MUST. Erik: Such a network will be very suboptimal, because the 6LRs can't terminate the flooding unless they have the ABRO version numbers for all the 6LBRs. Much better to not have more than one or two 6LBRs in the network and
require the 6LRs to store at least two.-->
</t>
<t>A 6LR or 6LBR MUST include a Source Link-layer address option in the Router
Advertisements it sends. That is required so that the hosts will know the
link-layer address of the router.</t>
</section>
<section title="Periodic Router Advertisements">
<t>A router does not need to send any periodic Router Advertisement messages
since the hosts will solicit updated information by sending Router Solicitations
before the lifetimes expire.</t>
<t>However, if the routers use Router Advertisements to optionally
distribute prefix and/or context information across a route-over topology,
that might require periodic Router Advertisement messages.</t>
<!-- TODO: We could require that such RAs be sent to the all-routers
address instead of all-nodes. Is this worth-while? -->
</section>
<section anchor='router_ns' title="Processing a Neighbor Solicitation">
<t>A router handles Neighbor Solicitation messages as specified in
<xref target="RFC4861"/>, with added logic described in this section for handling
the Address Registration option.</t>
<t>In addition to the normal validation of a Neighbor Solicitation and its options,
the Address Registration option is verified as follows (if present). If the Length field is not
two, or if the Status field is not zero, then the Neighbor Solicitation is silently ignored. Note that
<xref target="optional_dad"/> specify optional behavior for a 6LBR for other Length field
values.</t>
<t>If the source address of the NS is the unspecified address, or if no SLLA option is included, then any included ARO
is ignored, that is, the NS is processed as if it did not contain an ARO.</t>
<section title="Checking for Duplicates">
<t>If the NS contains a valid ARO, then the router inspects its Neighbor Cache
on the arriving interface to see if it is a duplicate. If there is no Neighbor Cache
entry for the IPv6 source address of the NS, then it isn't a duplicate. If there is such a Neighbor Cache entry
and the EUI-64 is the same, then it isn't a duplicate either. Otherwise it is a duplicate address.</t>
<t>In the case it is a duplicate address then the router responds with a unicast
Neighbor Advertisement (NA) message sent to the source link-layer address (from the Source Link-Layer Address (SLLA) option) of the NS. The NA is formatted with a copy of the ARO from the NS, but with the Status
field set to one to indicate it was a duplicate. In this case there is no modification
to the Neighbor Cache.</t>
</section>
<section title="Updating the Neighbor Cache">
<t>If ARO did not result in a duplicate address being detected as above, then
if the Registration Lifetime is non-zero
the router creates (if it didn't exist) or updates (otherwise) a Neighbor Cache entry
for the IPv6 source address of the NS. The Registration Lifetime and the EUI-64 are
recorded in the Neighbor Cache entry. A unicast Neighbor Advertisement (NA) is then sent
in response to the NS. This NA SHOULD include a copy of the ARO, with the Status
field set to zero.</t>
<t>If the ARO contains a zero Registration Lifetime then any existing Neighbor
Cache entry for the IPv6 source address of the NS MUST be deleted, and a NA sent as above.</t>
<t>Should the Registration Lifetime in a Neighbor Cache entry expire, then the router
MUST delete the cache entry. This might result in notifying the routing protocol.
</t>
</section>
<section title="Address Resolution between Routers">
<t>There needs to be a mechanism somewhere for the routers to discover
each other's link-layer addresses. If the routing protocol used between the routers provides this, then there is no need for the routers to use the Address Registration option between each other. Otherwise, the routers MAY use the ARO. When routers use ARO to register with each other and the optional DAD to the 6LBR <xref target="optional_dad"/> is in use, then care should be taken to ensure that
there isn't a flood of ARO-carrying messages send to the 6LBR as each router
hears an ARO from their neighboring routers. The details for this is out of
scope of this document.</t>
</section>
<section title="Neighbor Unreachability Detection">
<t>Just like in <xref target="RFC4861"/> the use of NUD from routers to hosts
is required. NUD may
also be used between routers, but is not required if an equivalent
mechanism is available, for example, as part of the routing
protocols.</t>
</section>
</section>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='border_router' title="Border Router Behavior">
<t>A 6LBR handles sending of Router Advertisements and processing of
Neighbor Solicitations from hosts as specified above in section
<xref target="router"/>. A 6LBR SHOULD always include an Authoritative Border
Router option in the Router Advertisements it sends, listing itself as the 6LBR
Address. That requires that the 6LBR maintain the version number in stable storage,
and increases the version number when some information in its Router Advertisements
change.</t>
<t>In addition, a 6LBR is somehow configured with the prefix or
prefixes that are assigned to the LoWPAN, and advertises those in Router Advertisements as in <xref target="RFC4861"/>.
Optionally, in the case of route-over, those prefixes can be disseminated
to all the 6LRs using the technique in <xref target="optional_dist"/>. However,
there might be mechanisms outside of the scope of this document that can be used instead
for prefix dissemination with route-over.</t>
<t>If the 6LoWPAN uses Header Compression <xref target="I-D.ietf-6lowpan-hc"/>
then the 6LBR needs to manage the context IDs, and advertise those in Router
Advertisements by including 6CO options in its Router Advertisements so that
directly attached hosts are informed about the context IDs. Below we specify things
to consider when the 6LBR needs to add, remove, or change the context information.
Optionally, in the case of route-over, the context information can be disseminated
to all the 6LRs using the technique in <xref target="optional"/>. However,
there might be mechanisms outside of the scope of this document that can be used instead
for disseminating context information with route-over.</t>
<section anchor='border_router_prefix' title="Prefix Determination">
<t>
The prefix or prefixes used in a LoWPAN can be manually configured, or can be
acquired using DHCPv6 Prefix Delegation <xref target="RFC3633"/>. For a LoWPAN
that is isolated from the network, either permanently or occasionally, the 6LBR
can assign a ULA prefix using <xref target="RFC4193"/>. The ULA prefix should be
stored in stable storage so that the same prefix is used after a failure of the 6LBR.
If the LoWPAN has multiple 6LBRs, then they should be configured with the same
set of prefixes. The set of prefixes are included in the Router Advertisement
messages as specified in <xref target="RFC4861"/>.
</t>
</section>
<section anchor='context_management' title="Context Configuration and Management">
<t>If the LoWPAN uses Header Compression <xref target="I-D.ietf-6lowpan-hc"/>
then the 6LBR may be configured with context information and related context
IDs. If the LoWPAN has multiple 6LBRs, then they MUST be configured with the same
context information and context IDs.</t>
<t>The context information carried in Router
Advertisement (RA) messages originate at 6LBRs and must be
disseminated to all the routers and hosts within the
LoWPAN. RAs include one 6CO for each context. </t>
<t>
For the dissemination of context information using the 6CO, a
strict lifecycle SHOULD be used in order to ensure
the context information stays synchronized throughout
the LoWPAN. New context information SHOULD be
introduced into the LoWPAN with C=0, to
ensure it is known by all nodes that may have to
decompress based on this context information. Only
when it is reasonable to assume that this information was
successfully disseminated SHOULD an option with
C=1 be sent, enabling the actual use of the
context information for compression.
</t>
<t>
Conversely, to avoid that nodes send packets making use
of previous values of contexts, resulting in
ambiguity when receiving a packet that uses a
recently changed context, old values of a context
SHOULD be taken out of use for a while before new
values are assigned to this specific context. That is,
in preparation for a change of context information,
its dissemination SHOULD continue for at least MIN_CONTEXT_CHANGE_DELAY with
C=0. Only when it is reasonable to assume
that the fact that the context is now invalid was
successfully disseminated, should the context ID be
taken out of dissemination or reused with a different
Context Prefix field. In the latter case, dissemination of
the new value again SHOULD start with C=0, as above.
</t>
</section>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='optional' title="Optional Behavior">
<t>Optionally the Router Advertisement messages can be used to disseminate prefixes
to all the 6LRs in a route-over topology. This is optional because there are likely
to be other mechanisms for such information distribution.</t>
<t>There is also the option to reuse the Address Registration option as a way for
a 6LR to perform DAD (for non-EUI-64 derived IPv6 addresses) against a 6LBR in a
route-over topology. This is optional because there might be other ways to either
allocate unique address, such as DHCPv6 <xref target="RFC3315"/>, or other future
mechanisms for DAD.</t>
<section anchor='optional_dist' title="Multihop Prefix and Context Distribution">
<t>The multihop distribution relies on Router Solicitation messages and Router
Advertisement (RA) messages sent between routers, and using the ABRO version number to control
the propagation of the information (prefixes and context information) that is
being sent in the RAs.</t>
<section title="Routers Sending Router Solicitations">
<t>If multihop distribution is done using Router Advertisement (RA) messages, then on interface initialization
a router SHOULD send some Router Solicitation messages similarly to how hosts do this in
<xref target="RFC4861"/>. That will cause the routers to respond with RA messages
which then can be used to initially seed the prefix and context information.
</t>
</section>
<section title="Routers Processing Router Advertisements">
<t>If multihop distribution is not done using RA messages, then the routers
follow <xref target="RFC4861"/> which states that they merely do some consistency
checks. Otherwise the routers will check and record the prefix and context information
from the receive RAs, and use that information as follows.</t>
<t>If a received RA does not contain a Authoritative Border Router option, then
the RA MUST be silently ignored.</t>
<t>The router uses the 6LBR Address field in the ABRO to check if it has previously
received information from the 6LBR. If it finds no such information, then it just
records the 6LBR Address and Version and the associated prefixes and context
information. If the 6LBR is previously known, then the Version number field MUST be compared
against the recorded version number for that 6LBR. The comparison MUST be done the
same way as TCP sequence number comparisons to handle the case when the version
number wraps around. If the received version number is older or the same as the
recorded version, then the information in the RA is silently ignored. Otherwise
the recorded information and version number are updated.</t>
</section>
<section title="Storing the Information">
<t>The router keeps state for each 6LBR that it sees with an ABRO.
<!-- TODO: Zach: I think this should be changed to a MAY keep state (not forcing routers to overextend their memory). Erik: See TODO earlier in document.-->
This includes the
version number, and the complete set of Prefix Information options and 6LoWPAN Context
options. The prefixes are timed out based on the Valid lifetime in the
Prefix Information Option. The Context Prefix is timed out based on the Valid
lifetime in the 6LoWPAN Context option.</t>
<t>While the prefixes and context information are stored in the router their valid
and preferred lifetimes are decremented as time passes. This ensures that when
the router is in turn later advertising that information in the Router Advertisements
it sends the 'expiry time' doesn't accidentally move further into the future. For
example, if a 6CO with a Valid lifetime of 10 minutes is receive at time T, and
the router includes this in a RA it sends at time T+5 minutes, the Valid lifetime
in the 6CO it sends will be only 5 minutes.</t>
</section>
<section title="Sending Router Advertisements">
<t>If multihop distribution is performed using RA messages, then the routers MUST
ensure that the ABRO always stay together with the prefixes and context
information received with that ABRO. Thus if the router has received prefix P1 with
ABRO saying it is from one 6LBR, and prefix P2 from another 6LBR, then the router
MUST NOT include the two prefixes in the same RA message. Prefix P1 MUST be in a RA
that include a ABRO from the first 6LBR etc.</t>
<t>The routers periodically send Router Advertisements as in <xref target="RFC4861"/>.
This is for the benefit of the other routers receiving the prefixes and context
information. And the routers also respond to Router Solicitations by unicasting RA
messages. In both cases the above constraint of keeping the ABRO together with 'its'
prefixes and context information apply.</t>
<t>When a router receives new information from a 6LBR, that is, either it hears from
a new 6LBR (a new 6LBR Address in the ABRO) or the ABRO version number of an existing 6LBR has increased, then
it is useful to send out a few triggered updates. The recommendation is to behave the
same as when an interface has become an advertising interface in
<xref target="RFC4861"/>, that is, send up to three RA messages. This ensures
rapid propagation of new information to all the 6LRs.</t>
</section>
</section>
<section anchor='optional_dad' title="Duplicate Address Detection">
<!-- TODO Zach: The ARO is used? -->
<t>The ARO can be used, in addition to register an address
in a 6LR, to have the 6LR verify that the address isn't used by some other host.
However, that isn't sufficient in a route-over topology since some host attached to
another 6LR could be using the same address. There might be different ways for the 6LRs
to coordinate such Duplicate Address Detection in the future, or addresses
could be assigned using a DHCPv6 server that verifies uniqueness as part of the
assignment. This specification offers an optional and simple technique for 6LRs and
6LBRs to perform Duplicate Address Detection that reuses the Address Registration
option. This technique is not needed when the Interface ID in the address
is based on an EUI-64, since those are assumed to be globally unique.</t>
<t>When a 6LR receives a Neighbor Solicitation containing an Address Registration
option with a non-zero Registration Lifetime and there was no existing
Neighbor Cache entry, then with this mechanism the 6LR will unicast a new Neighbor Solicitation message to one or more 6LBRs, where the NS
contains an ARO with the host's address in the Registered Address field.
This NS will be forwarded by 6LRs until it reaches the 6LBR, hence its IPv6 hop
limit field might be less than 255 when received by the 6LBR. The 6LBR will respond
with a Neighbor Advertisement message containing an ARO, which might have a hop limit
less than 255 when it reaches the 6LR.</t>
<t>When the 6LR receives the NS from the 6LBR it will respond to the host,
copying the Status field from the ARO it received from the 6LBR.</t>
<section title="Special Message Validation">
<t>Due to the forwarding of the above special NS/NA between the 6LR and 6LBR the
hop limit check on receipt MUST be bypassed for such messages that contain a ARO
with a Length field of 4. The receipt of such messages MUST NOT modify any state
on the router with the exception of the DAD table below.</t>
</section>
<section title="Conceptual Data Structures">
<t>A 6LBR implementing the optional multi-hop DAD needs to maintain some state
separate from the Neighbor Cache. We call this conceptual data structure the DAD
table. It is indexed by the IPv6 address - the Registered Address in the ARO - and
contains the EUI-64 of the host that is using that address.</t>
</section>
<section title="6LR Sending a special Neighbor Solicitation">
<t>When a 6LR that implements the optional multihop DAD receives an NS from a host
(the ARO has Length = 2) and the 6LR does not already have a Neighbor Cache entry
for the host's IPv6 address, then the 6LR forms and sends an NS to at least one 6LBR.
The NS contains the following information:
<list style="symbols">
<t>In the IPv6 source address, a global address of the 6LR.</t>
<t>In the IPv6 destination address, the address of the 6LBR.</t>
<t>In the IPv6 hop limit, 255 or a smaller number.</t>
<t>In the NS Target Address, the address of the 6LBR.</t>
<t>No SLLA option - just an Address Registration option with Length 4</t>
<t>In the ARO the Status field MUST be set to zero</t>
<t>In the ARO the EUI-64 and Registration lifetime are copied from the ARO
received from the host.</t>
<t>In the ARO and the Registered Address set to the IPv6 address of the host,
that is, the sender of the triggering NS.</t>
</list>
</t>
<t>When a 6LR receives an NS from a host with a zero Registration Lifetime then,
in addition to removing the Neighbor Cache entry for the host as specified in
section <xref target="router"/>, an NS is sent to the 6LBRs as above.</t>
<t>A router MUST NOT modify the Neighbor Cache as a result of receiving
a Neighbor Solicitation with an ARO of Length=4.</t>
</section>
<section title="6LBR Receiving a special Neighbor Solicitation">
<t>When a 6LBR that implements the optional multihop DAD receives an NS from a 6LR,
that is an NS that contains an ARO with Length = 4, then it MUST NOT verify that the
hop limit is 255 as specified above. The it proceeds to look for the Registration
Address in the DAD Table. If an entry is found and the recorded EUI-64 is different
than the EUI-64 in the ARO, then it returns an NA with the ARO Status set to 1 ('Duplicate
Address'). Otherwise it returns an NA with ARO Status set to zero.</t>
<t>If no entry is found in the DAD Table and the Registration Lifetime is non-zero,
then an entry is created and the EUI-64 and Registered Address from the ARO are stored
in that entry.</t>
<t>If an entry is found in the DAD Table and the Registration Lifetime is zero
then the entry is deleted from the table.</t>
<t>A router MUST NOT modify the Neighbor Cache as a result of receiving
a Neighbor Advertisement with an ARO of Length=4.</t>
<t>In both of the above cases the 6LBR forms an NA with the ARO Status set to
zero and sends it back to the 6LR.</t>
</section>
<section title="Processing a special Neighbor Advertisement">
<t>When a 6LR that implements the optional multihop DAD receives an NA from a 6LBR,
that is an NS that contains an ARO with Length = 4, then it MUST NOT verify that the
hop limit is 255 as specified above. If there is no pending ARO from a host for
the Registered Address, then NA is silently ignored. Otherwise,
the information from the 6LBR is used to form an NA to
send to the host. The Status code is copied from the ARO received from the 6LBR to
the ARO that is sent to the host.</t>
<t>If the Status is non-zero indicating an error, then the Neighbor Cache entry
for the Registration Address is removed.</t>
</section>
<section title="Recovering from Failures">
<t>If there is no response from a 6LBR after RETRANS_TIMER <xref target="RFC4861"/>
then the 6LR would retransmit the NS to the 6LBR up to MAX_UNICAST_SOLICIT
<xref target="RFC4861"/> times. After this the 6LR SHOULD respond to the host with
an ARO Status of zero.</t>
</section>
</section>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='constants' title="Protocol Constants">
<t>
This section defines the relevant protocol constants used in this document based
on a subset of <xref target="RFC4861"/> constants. (*) indicates constants
modified from <xref target="RFC4861"/> and (+) indicates new constants.
</t>
<t>
Additional protocol constants are defined in Section <xref target="message_options"/>.
</t>
<t>6LBR Constants:
<list style="hanging" hangIndent="40">
<t hangText="MIN_CONTEXT_CHANGE_DELAY+">60 seconds</t>
</list>
</t>
<t>6LR Constants:
<list style="hanging" hangIndent="40">
<!-- <t hangText="MAX_INITIAL_RTR_ADVERT_INTERVAL*">60 seconds</t> -->
<t hangText="MAX_RTR_ADVERTISEMENTS">3 transmissions</t>
<t hangText="MIN_DELAY_BETWEEN_RAS*">10 seconds</t>
<t hangText="MAX_RA_DELAY_TIME*">2 seconds</t>
</list>
</t>
<t>Host Constants:
<list style="hanging" hangIndent="40">
<t hangText="MAX_RTR_SOLICITATION_DELAY*">2 second</t>
<t hangText="RTR_SOLICITATION_INTERVAL*">10 seconds</t>
<t hangText="MAX_RTR_SOLICITATIONS">3 transmissions</t>
</list>
</t>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section anchor='messex' title="Message Examples">
<t>
The following diagrams show the two-step process of the optimized
Neighbor Discovery mechanisms for bootstrapping and Address Registration.
</t>
<figure anchor='figmessrsra'
title="Basic Router Solicitation/Router Advertisement exchange between a node and 6LR or 6LBR">
<artwork><![CDATA[
Node Router
| |
| ---------- Router Solicitation --------> |
| |
| <-------- Router Advertisement --------- |
| [PIO + ABRO + SLLAO] |
]]></artwork>
</figure>
<figure anchor='figmessbasic'
title="Neighbor Discovery Address Registration ">
<artwork><![CDATA[
Node Router
| |
| ------- NS with Address Registration -----> |
| [NS + ARO + SLLAO] |
| <-----NA with Address Registration --------- |
| [NA + ARO with Status + SLLAO] |
]]></artwork>
</figure>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section title="Security Considerations">
<t>
The security considerations of IPv6 Neighbor Discovery <xref target="RFC4861"/>
apply. Additional considerations can be found in <xref target="RFC3756"/>.
</t>
<t>
This specification expects that the link layer is sufficiently
protected, for instance using MAC sublayer cryptography. In other words, model
1 from <xref target="RFC3756"/> applies. In particular, it is expected that the
LoWPAN MAC provides secure unicast to/from Routers and secure
broadcast from the Routers in a way that prevents tampering with or
replaying the Router Advertisement messages. However, any future 6LoWPAN security
protocol that applies to Neighbor Discovery for 6LoWPAN protocol,
is out of scope of this document.
</t>
<t>The multihop DAD mechanisms rely on Neighbor Solicitation and Neighbor
Advertisement messages that are forwarded by 6LRs, and as a result the
hop_limit=255 check on the receiver is disabled for such messages. This implies
that any node on the Internet could successfully send such messages. We avoid
any additional security issues due to this by requiring that the routers
never modify the Neighbor Cache entry due to such messages, and that they
reject them unless they are received on an interface that has been explicitly
configured to use these LLN optimizations.</t>
<t>In some future deployments one might want to use SEcure Neighbor Discovery
<xref target="RFC3971"/> <xref target="RFC3972"/>. This is possible with the Address
Registration option as sent between hosts and routers, since the address that
is being registered is the IPv6 source address of the Neighbor Solicitation and
SeND verifies the IPv6 source address of the packet. Applying SeND to the optional
router-to-router communication in this document is out of scope.</t>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section title="IANA Considerations">
<t>
The document requires three new Neighbor Discovery option types under the
subregistry "IPv6 Neighbor Discovery Option Formats":
<list style="symbols">
<t>Address Registration Option (TBD1)</t>
<t>6LoWPAN Context Option (TBD2)</t>
<t>Authoritative Border Router Option (TBD3)</t>
</list>
</t>
<t>
[TO BE REMOVED: This registration should take place at the following location:
http://www.iana.org/assignments/icmpv6-parameters]
</t>
</section>
<!--==================================================-->
<!-- SECTION: ACKNOWLEDGMENTS -->
<!--==================================================-->
<section title="Acknowledgments">
<t>The authors thank Pascal Thubert, Jonathan Hui, Carsten Bormann, Richard Kelsey, Geoff Mulligan, Julien Abeille, Alexandru Petrescu, Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs, Phil Roberts, Daniel Gavelle and Joakim Eriksson for useful discussions and comments that have helped shaped and improve this document.</t>
<t>
Additionally, the authors would like to recognize Carsten Bormann for the suggestions on the Context Prefix Option and contribution to earlier version of the draft, Pascal Thubert for contribution of the original registration idea and contribution to earlier version of the draft, Jonathan Hui for contribution to earlier versions of the draft, and Geoff Mulligan for suggesting the use of Address Registration as part of existing IPv6 Neighbor Discovery messages.
</t>
</section>
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<!-- **************************************************************** -->
<section title="Changelog">
<t>Changes from -08 to -09:
<list>
<t>o Clean re-write of the draft (re-use of some introductory material)</t>
<t>o Merged in draft-chakrabarti-6lowpan-ipv6-nd-simple-00</t>
<t>o Changed address registration to an option piggybacked on NS/NA</t>
<t>o New Authoritative Border Router option</t>
<t>o New Address Registration Option</t>
<t>o Separated Prefix Information and Content Information</t>
<t>o Optional DAD to the edge</t>
</list>
</t>
<t>Changes from -07 to -08:
<list>
<t>o Removed Extended LoWPAN and Whiteboard related sections.</t>
<t>o Included reference to the autoconf addressing model.</t>
<t>o Added Optimistic Flag to 6AO.</t>
<t>o Added guidelines on routers performing DAD.</t>
<t>o Removed the NR/NC Advertising Interval.</t>
<t>o Added assumption of uniform IID formation and DAD throughout a LoWPAN.</t>
</list>
</t>
<t>Changes from -06 to -07:
<list>
<t>o Updated addressing and address resolution (#60).</t>
<t>o Changed the Address Option to 6LoWPAN Address Option, fixed S values (#61).</t>
<t>o Added support for classic RFC4861 RA Prefix Information messages to be processed (#62).</t>
<t>o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861 stack (#63).</t>
<t>o Updated the NR/NC message with a new Router flag, combined the Code and Status fields into one byte, and added the capability to carry 6IOs (#64).</t>
<t>o Made co-existence with other ND mechanisms clear (#59).</t>
<t>o Added a new Protocol Specification section with all mechanisms specified there (#59).</t>
<t>o Removed dependencies and conflicts with RFC4861 wherever possible (#59).</t>
<t>o Some editorial cleanup.</t>
</list>
</t>
<t>Changes from -05 to -06:
<list>
<t>o Fixed the Prf codes (#52).</t>
<t>o Corrected the OIIO TID field to 8-bits. Changed the Nonce/OII order in both the OIIO and the NR/NC. (#53)</t>
<t>o Corrected an error in Table 1 (#54).</t>
<t>o Fixed asymmetric and a misplaced transient in the 6LoWPAN terminology section.</t>
<t>o Added Updates RFC4861 to header</t>
</list>
</t>
<t>Changes from -04 to -05:
<list>
<t>o Meaning of the RA's M-bit changed to original <xref target="RFC4861"/> meaning (#46).</t>
<t>o Terms "on-link" and "off-link" used in place of "on-link" and "off-link".</t>
<t>o Next-hop determination text simplified (#49).</t>
<t>o Neighbor cache and destination cache removed.</t>
<t>o IID to link-layer address requirement relaxed. </t>
<t>o NR/NC changes to enable on-link refresh with routers (#48).</t>
<t>o Modified 6LoWPAN Information Option (#47).</t>
<t>o Added a Protocol Constants section (#24)</t>
<t>o Added the NR processing table (#51)</t>
<t>o Considered the use of SeND on backbone NS/NA messages (#50)</t>
</list>
</t>
<t>Changes from -03 to -04:
<list>
<t>o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix generation a features useful also in Simple and Extended LoWPANs. (#41)</t>
<t>o Added a 32-bit Owner Nonce to the NR/NC messages and the Whiteboard, removed the TID history. (#39)</t>
<t>o Improved the duplicate OII detection algorithm using the Owner Nonce. (#39)</t>
<t>o Clarified the use of Source and Target link-layer options in NR/NC. (#43)</t>
<t>o Included text on the use of alternative methods to acquire addresses. (#38)</t>
<t>o Removed S=2 from Address Option (not needed). (#36)</t>
<t>o Added a section on router dissemination consistency. (#44)</t>
<t>o Small improvements and extensive editing. (#42, #37, #35)</t>
</list>
</t>
<t>Changes from -02 to -03:
<list>
<t>o Updated terminology, with RFC4861 non-transitive link model.</t>
<t>o 6LoWPAN and ND terminology separated.</t>
<t>o Protocol overview explains RFC4861 diff in detail.</t>
<t>o RR/RC is now Node Registration/Confirmation (NR/NC).</t>
<t>o Added NR failure codes.</t>
<t>o ER Metric now included in 6LoWPAN Summary Option for use in default router determination by hosts.</t>
<t>o Examples of host data structures, and the Whiteboard given.</t>
<t>o Whiteboard is supported by all Edge Routers for option simplicity.</t>
<t>o Edge Router Specification chapter re-structured, clarifying optional Extended LoWPAN operation.</t>
<t>o NS/NA now completely optional for nodes. No address resolution or NS/NA NUD required.</t>
<t>o link-local operation now compatible with oDAD (was broken).</t>
<t>o Exception to hop limit = 255 for NR/NC messages.</t>
<t>o Security considerations improved.</t>
<t>o ICMPv6 destination unreachable supported.</t>
</list>
</t>
<t>Changes from -01 to -02:
<list>
<t>o Fixed 16 != 0xff bug (ticket closed).</t>
<t>o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket closed).</t>
<t>o Terminology cleanup based on Alex's comments.</t>
<t>o General editing improvements.</t>
</list>
</t>
<t>Changes from -00 to -01:
<list>
<t>o Specified the duplicate owner interface identifier procedures. A TID lollipop algorithm was sufficient (nonce unnecessary).</t>
<t>o Defined fault tolerance using secondary bindings.</t>
<t>o Defined ad-hoc network operation.</t>
<t>o Removed the E flag from RA and the X flag from RR/RC.</t>
<t>o Completed message examples.</t>
<t>o Lots of improvements in text quality and consistency were made. </t>
</list>
</t>
</section>
</middle>
<back>
<references title='Normative References'>
&I-D.ietf-autoconf-adhoc-addr-model;
&RFC2119;
&RFC2434;
&RFC2460;
&RFC2491;
&RFC4191;
&RFC4193;
&RFC4861;
&RFC4862;
&RFC4944;
</references>
<references title='Informative References'>
&RFC3315;
&RFC3633;
&RFC3756;
&RFC3971;
&RFC3972;
&RFC4919;
&RFC4941;
&I-D.ietf-6lowpan-hc;
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-22 12:59:25 |