6lowpan Working Group Z. Shelby, Ed.
Internet-Draft Sensinode
Intended status: Standards Track P. Thubert
Expires: November 29, 2009 Cisco
J. Hui
Arch Rock
S. Chakrabarti
IP Infusion
E. Nordmark
Sun
May 28, 2009
Neighbor Discovery for 6LoWPAN
draft-ietf-6lowpan-nd-03
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 29, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
Shelby, et al. Expires November 29, 2009 [Page 1]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
and restrictions with respect to this document.
Abstract
This document specifies Neighbor Discovery optimized for 6LoWPAN.
The 6LoWPAN format allows IPv6 to be used over energy and bandwidth
constrained wireless networks often making use of multihop
topologies. However, the use of standard IPv6 Neighbor Discovery
with 6LoWPAN has several problems. Standard Neighbor Discovery was
not designed for non-transitive wireless links, and the standard IPv6
link concept and heavy use of multicast makes it inefficient. This
document specifies a new ND mechanism allowing for the efficient
detection of duplicate addresses over entire LoWPANs while avoiding
or simplifying other ND operations. In addition it specifies context
dissemination for use with router advertisements, claim and defend
address generation, and the support of Extended LoWPANs over backbone
links.
Shelby, et al. Expires November 29, 2009 [Page 2]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Goals & Assumptions . . . . . . . . . . . . . . . . . . . 6
1.2. Why not standard IPv6 ND? . . . . . . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. 6LoWPAN Terminology . . . . . . . . . . . . . . . . . . . 8
2.2. ND Terminology . . . . . . . . . . . . . . . . . . . . . . 10
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 13
3.1. Topology . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2. Links . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3. Bootstrapping . . . . . . . . . . . . . . . . . . . . . . 15
3.4. Basic operation . . . . . . . . . . . . . . . . . . . . . 17
3.5. Optional features . . . . . . . . . . . . . . . . . . . . 17
4. 6LoWPAN ND Messages . . . . . . . . . . . . . . . . . . . . . 18
4.1. Node Registration/Confirmation Message . . . . . . . . . . 19
4.2. Router Solicitation Message . . . . . . . . . . . . . . . 21
4.3. Router Advertisement Message . . . . . . . . . . . . . . . 21
4.4. NS/NA Messages . . . . . . . . . . . . . . . . . . . . . . 22
4.5. 6LoWPAN ND Message Options . . . . . . . . . . . . . . . . 23
4.5.1. Address Option . . . . . . . . . . . . . . . . . . . . 23
4.5.2. 6LoWPAN Prefix Information Option . . . . . . . . . . 24
4.5.3. 6LoWPAN Prefix Summary Option . . . . . . . . . . . . 26
4.5.4. Owner Interface Identifier Option . . . . . . . . . . 27
5. LoWPAN Node Specification . . . . . . . . . . . . . . . . . . 27
5.1. Conceptual structures and variables . . . . . . . . . . . 28
5.2. Interface initialization . . . . . . . . . . . . . . . . . 29
5.3. Registration process . . . . . . . . . . . . . . . . . . . 30
5.4. Next-hop determination . . . . . . . . . . . . . . . . . . 31
5.5. Destination unreachability detection . . . . . . . . . . . 32
6. LoWPAN Router Specification . . . . . . . . . . . . . . . . . 32
6.1. Router Configuration Variables . . . . . . . . . . . . . . 33
6.2. Becoming an Advertising Interface . . . . . . . . . . . . 33
6.3. Router Advertisement Message Content . . . . . . . . . . . 33
6.4. Sending Unsolicited Router Advertisements . . . . . . . . 34
6.5. Ceasing To Be an Advertising Interface . . . . . . . . . . 34
6.6. Processing Router Solicitations . . . . . . . . . . . . . 34
6.7. Relaying a Node Registration Message . . . . . . . . . . . 34
6.8. Relaying a Node Confirmation Message . . . . . . . . . . . 35
7. LoWPAN Edge Router Specification . . . . . . . . . . . . . . . 35
7.1. The Whiteboard . . . . . . . . . . . . . . . . . . . . . . 36
7.2. Simple LoWPAN . . . . . . . . . . . . . . . . . . . . . . 37
7.3. Extended LoWPAN . . . . . . . . . . . . . . . . . . . . . 37
7.4. Registration process . . . . . . . . . . . . . . . . . . . 38
7.5. Forwarding packets between a LoWPAN and an IPv6
infrastructure . . . . . . . . . . . . . . . . . . . . . . 40
7.6. Address collision detection and resolution . . . . . . . . 40
7.7. Duplicate OII detection . . . . . . . . . . . . . . . . . 43
Shelby, et al. Expires November 29, 2009 [Page 3]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
7.8. Fault tolerance . . . . . . . . . . . . . . . . . . . . . 44
8. Ad-hoc LoWPAN Operation . . . . . . . . . . . . . . . . . . . 44
9. Message Examples . . . . . . . . . . . . . . . . . . . . . . . 45
9.1. Basic NR/NC message exchange . . . . . . . . . . . . . . . 45
9.2. Relaying an NR message . . . . . . . . . . . . . . . . . . 46
9.3. Router advertisement . . . . . . . . . . . . . . . . . . . 47
10. Security Considerations . . . . . . . . . . . . . . . . . . . 48
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 49
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 49
13.1. Normative References . . . . . . . . . . . . . . . . . . . 49
13.2. Informative References . . . . . . . . . . . . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51
Shelby, et al. Expires November 29, 2009 [Page 4]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
1. Introduction
The IPv6 over IEEE 802.15.4 [RFC4944] document has specified how to
carry IPv6 packets over IEEE 802.15.4 and similar networks with the
help of an adaptation header which comes before the IP header. A
link in 6LoWPAN is characterized as lossy, low-power, low bit-rate,
short range, with many nodes saving energy with long deep sleep
periods. Multicast as used in IPv6 Neighbor Discovery [RFC4861] is
not desirable in such a wireless low-power, lossy network.
Moreover, LoWPAN links are non-symmetric and transient in nature;
they are not always considered to be in a fixed network nor are they
bounded by our standard definition of a wired-link. A LoWPAN is
potentially composed of a potentially large amount of overlapping
radio ranges, eventually federated by a backbone or a backhaul link.
Although a given radio range has broadcast capabilities, the
aggregation of these is a complex Non-Broadcast MultiAccess (NBMA,
[RFC2491]) structure with no multicast capabilities. Link-local
scope is in reality defined by reachability and radio strength. The
standard IPv6 Neighbor Discovery [RFC4861] control messages, the use
of multicast and their default frequency also attribute to
unnecessary waste of energy in LoWPANs.
Neighbor discovery for 6LoWPAN provides for basic bootstrapping and
network operation, along with advanced features such as claim and
defend address generation and Extended LoWPANs over backbone links,
while avoiding the use of multicast flooding. The solution supports
the use of both link-layer or LoWPAN mesh (Mesh Under) and IP routing
(Route Over) multihop solutions. Unlike standard IPv6 ND [RFC4861],
this document specifically takes the characteristics of low-power,
lossy wireless links into account.
This specification introduces a registration mechanism over the radio
edge of the NBMA network and proxy operation over the federating
backbone or backhaul. That registration mechanism provides a service
somewhat similar to the Multicast Address Resolution Server (MARS)
[RFC2022] for a limited purpose, and in a lot simpler and less
generic fashion. For those link scope multicasts that could not be
avoided, such as for Router Advertisements, optimizations like the
Trickle algorithm may be used to optimize the dissemination of the
information in the Low Power network.
The concept of a LoWPAN Whiteboard located at Edge Routers (ERs) is
introduced, which allows for duplicate address detection and claim
and defend addressing for the entire LoWPAN. Address resolution is
not needed, and thus makes LoWPAN operation power efficient and to
reduces LoWPAN Node complexity. A new registration/confirmation
message sequence is specified, allowing nodes to register their IPv6
Shelby, et al. Expires November 29, 2009 [Page 5]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
addresses with an Edge Router.
The Whiteboard makes use of soft bindings, thus nodes send periodic
registration messages in order to maintain their bindings. Changes
in network topology, and mobility between ERs and LoWPANs are
supported. The dissemination of RA information between LoWPAN
Routers in multihop IP LoWPANs is also discussed.
This document also specifies the seamless integration of an Extended
LoWPAN with multiple edge routers on a shared backbone link (e.g.
Ethernet) to form a single IPv6 subnet. This allows nodes to keep
the same IPv6 address throughout a large network, and allows for easy
communications with nodes over the backbone link and with other IPv6
hosts.
The document defines two new ICMPv6 messages: Node Registration and
Node Confirmation. In addition a new 6LOWPAN_ER anycast address is
introduced, used by LoWPAN Routers in order to relay a registration
message to any Edge Router.
1.1. Goals & Assumptions
This document has the following main goals and makes several
assumptions.
Goals:
o Enable ND operations over an entire LoWPAN, even with non-
transitive links and over multihop IP hops.
o Minimize signalling by avoiding the use of multicast flooding
and reducing the frequency of link scope multicast for ND messages
inside the LoWPANs.
o Disseminate context information throughout the LoWPAN.
o Minimize the complexity of LoWPAN Nodes.
o Interconnect LoWPANs with backbone links seamlessly.
o Provide a mechanism for claim and defend addressing.
Assumptions:
o Link layer technology may be e.g. IEEE 802.15.4 as in
[RFC4944], or any other suitable link-layer.
Shelby, et al. Expires November 29, 2009 [Page 6]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
o Link-local IPv6 addresses are derived from a unique identifier
(e.g. EUI-64).
o There is a direct mapping between the IPv6 address IID and the
link-layer address (as in e.g. [RFC4944]), thus address
resolution is not required.
o A subnet includes all the LoWPAN Nodes, Edge Router(s) and
optionally their backbone link sharing the same IPv6 prefix.
1.2. Why not standard IPv6 ND?
IPv6 Neighbor Discovery [RFC4861] provides several important
functions such as Router Discovery, Address Resolution, Duplicate
Address Detection, Redirect, Prefix and Parameter Discovery.
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. Once 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). 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. These NS/NA messages are also often
multicast messages and it is assumed that the node is on the same
link and relies on the fact that the destination node is always
powered and generally reliable.
A LoWPAN network typically uses two types of L2 addresses - for
example 16-bit short addresses and 64-bit unique addresses as defined
in [RFC4944]. Moreover, the available L2 payload size on the order
of less than 100 bytes where we often might need to use header
compression and use a minimum payload. The network is lossy and low-
powered, and it does not provide multicast capability at the link-
layer, thus simulating multicast behavior by both using broadcast or
sending a number of unicast messages, both expensive for the low-
powered network and the low-processing capable nodes. Often these
low-powered nodes conserve energy by using sleep schedules; waking
them up to receive IPv6 signaling messages such as multicast messages
for NS or periodic RAs is not practical. Also they are not capable
of processing address-resolution for their neighbors effectively.
Due to the radio strength of its neighboring router or its own
strength, a node may often move from one router to another without
Shelby, et al. Expires November 29, 2009 [Page 7]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
physically moving from one place to another. Considering the above
characteristics in a LoWPAN, and the IPv6 Neighbor Discovery
[RFC4861] base protocol requirements, it was concluded that standard
Neighbor Discovery is not suitable as it is and a 6LoWPAN-specific ND
definition would be useful and efficient for the wide deployment of
IPv6 over low-powered wireless networks of embedded devices.
2. Terminology
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 [RFC2119].
This specification requires readers to be familiar with all the terms
and concepts that are discussed in "IPv6 Stateless Address
Autoconfiguration" [RFC4862], "IPv6 over Low-Power Wireless Personal
Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement,
and Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE
802.15.4 Networks" [RFC4944].
Readers would benefit from reading "Mobility Support in IPv6"
[RFC3775], "Neighbor Discovery Proxies (ND Proxy)" [RFC4389] and
"Optimistic Duplicate Address Detection" [RFC4429] prior to this
specification for a clear understanding of state of the art in ND
proxy and binding.
This specification makes extensive use of the same terminology
defined in [RFC4861] unless otherwise redefined below.
2.1. 6LoWPAN Terminology
This section defines additional general terms related to the 6LoWPAN
architecture used in this specification:
IP Routing
The forwarding of datagrams at the IP layer between arbitrary
source-destination pairs, during which the hop limit is
decremented. In the LoWPAN context, IP routing is performed by
LoWPAN Routers on a single interface within the same link to
overcome the non-transient nature of the link. Exact match search
is performed on the destination address of the IP packet to find
the next-hop to the destination. Referred to as routing in this
document.
Shelby, et al. Expires November 29, 2009 [Page 8]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Link
The link is a communication facility or medium over which nodes
can communicate at the link-layer, i.e., the layer directly below
IP ([RFC4861]). 6LoWPAN assumes the use of low-power and lossy
wireless links such as IEEE 802.15.4, which is a special type of
link as described in [RFC4861] exhibiting severe asymmetric
reachability with both non-symmetric (A can reach B, but B can't
reach A) and non-transitive (A can reach B, and B can reach C, but
A can't reach C) qualities. Furthermore complex Non-broadcast
Multi-Access (NBMA) behaviour is exhibited as these links do not
support native multicast, and broadcast reaches only a subset of
nodes on the link. Such a wireless link may consist of multiple
overlapping link-local scopes. Link-local scope multicast on such
a link is realized as a broadcast.
The use of link-layer mesh technology (see Mesh Under) emulates
transitivity across the link but still has problems with non-
symmetricity. Multicast on a link-layer mesh is usually
implemented as a broadcast flood.
Link-local
Standard IPv6 link-local scope as defined in [RFC4291] and
[RFC4861] is supported by the 6LoWPAN link and subnet model.
Link-local scope is achieved by setting the hop limit to 1, using
a link-local prefix (FE80::) or link-local multicast scope
(FFx2::). If a link is non-transitive then link-local scope may
include only a subset of nodes on the link (the set of nodes
within symmetric radio range of a node). Nodes in the link-local
scope of a node are its neighbors, and this link-local scope may
differ from the perspective of each node.
On-link
The set of nodes reachable using link-local scope are said to be
on-link. All other destinations are assumed to be off-link.
LoWPAN Host
A node that only sources or sinks IPv6 datagrams. Referred to as
a host in this document.
LoWPAN Node
Shelby, et al. Expires November 29, 2009 [Page 9]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
A node that composes a LoWPAN, referring to both hosts and
routers. Simply called a node in this document.
LoWPAN Router
A node that forwards datagrams between arbitrary source-
destination pairs using a single 6LoWPAN interface performing IP
routing on that interface.
Mesh Under
A term referring to a configuration where the link-local scope is
defined by the boundaries of the LoWPAN and includes all the
6LoWPAN interfaces within it. There are forwarding and multihop
routing functions at L2 to achieve transitivity on the link. In
this configuration the link may still exhibit lossy, asymmetric
behaviour.
Route Over
A term referring to a configuration where the link is non-
transitive and the link-local scope reaches only a subset of the
LoWPAN nodes. IP routing is performed by LoWPAN Routers to
overcome the non-transitive nature of the link. A LoWPAN with
this configuration may consist of both routers and hosts. Route
Over and Mesh Under are not mutually exclusive, and IP routing may
be used between links that perform Mesh Under.
Subnet
A subnet is the collection of interfaces having the same IPv6
subnet prefix on a link, as defined in [RFC4291]. A LoWPAN is
made up of the interfaces of LoWPAN Nodes and Edge Routers sharing
the same subnet prefix. Due to the non-transitive nature of
LoWPAN links, IP routing may be used on the link to provide
transitivity. This Route Over configuration exhibits a multi-hop
subnet feature with regard to hop limit as discussed in [RFC4903],
and thus 6LoWPAN applications should be careful when making
assumptions about the hop limit as it may be decremented in a
LoWPAN.
2.2. ND Terminology
This section defines Neighbor Discovery specific terminology used in
this specification:
Shelby, et al. Expires November 29, 2009 [Page 10]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Ad-hoc LoWPAN
An isolated LoWPAN, not connected to any other IP networks. Ad-
Hoc LoWPANs make use of Unique Local IPv6 Unicast Addresses (ULAs)
[RFC4193].
Backbone Link
This is an IPv6 link that interconnects two or more edge routers
in an Extended LoWPAN topology. It is expected to be deployed as
a high speed backbone in order to federate a potentially large set
of LoWPANs.
Binding
The association of the LoWPAN node IPv6 address and Owner
Interface ID with associated Whiteboard and ND states including
the remaining lifetime of that association.
Extended LoWPAN
This is the aggregation of multiple LoWPANs as defined in
[RFC4919] interconnected by a backbone link via Edge Routers and
forming a single subnet, shown in Figure 2.
LoWPAN Edge Router
An IPv6 router that interconnects the LoWPAN to another IP
network. Referred to as an Edge Router in this document.
Simple LoWPAN
A Simple LoWPAN consists of a single Edge Router and the set of
LoWPAN nodes on the same LoWPAN Subnet, shown in Figure 1. If the
Edge Router has a Whiteboard, all nodes belonging to its LoWPAN
have a whiteboard entry.
Registration
The process during which a LoWPAN node sends a Node Registration
ND message to an Edge Router causing a binding for the LoWPAN node
to be registered.
Whiteboard
Shelby, et al. Expires November 29, 2009 [Page 11]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
A conceptual data structure similar to a MIPv6 binding cache which
may be supported by Edge Routers. The Whiteboard is used for
performing DAD and NUD across the entire LoWPAN. The Whiteboard
contains bindings for LoWPAN nodes consisting of Owner Interface
Identifier, IPv6 address, timeout, along with Transaction ID
history.
Infrastructure Cloud
|
|
|
+-----+
| | Edge
| | router
+-----+
o o
o o o
o o o o o o: LoWPAN Node
o o o o
o o o
Simple LoWPAN
Figure 1: A simple LoWPAN topology
Shelby, et al. Expires November 29, 2009 [Page 12]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Infrastucture Cloud
|
|
+-----+ +-----+
| | Router | | Host
| | | |
+-----+ +-----+
| |
| Backbone link |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Edge | | Edge | | Edge
| | Router | | Router | | Router
+-----+ +-----+ +-----+
o o o o o o o o
o o o o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o o
o o o o o o o o o o o o
o o o o o o o o o
Extended LoWPAN
Figure 2: Extended LoWPAN with a backbone link and edge routers
3. Protocol Overview
Neighbor discovery for 6LoWPAN provides additions and optimizations
to IPv6 ND [RFC4861] specifically supporting 6LoWPAN. Basic Neighbor
Discovery mechanisms are optimized, avoiding the use of multicast
flooding and minimizing link-local multicast (broadcast) frequency.
The detection of duplicate addresses is performed across the entire
LoWPAN. This is achieved using a Whiteboard located on the Edge
Routers of the LoWPAN network. An Extended LoWPAN topology over a
shared backbone link is optionally supported.
The following list summarizes ND for 6LoWPAN operations and the
differences with [RFC4861]:
Router Discovery: As in [RFC4861] with the addition of new 6LoWPAN
specific options to Router Advertisements.
Prefix Discovery: The discovery of 6LoWPAN prefixes with context
identifiers. Destinations are assumed to be off-link unless
explicitly known to be a neighbor.
Shelby, et al. Expires November 29, 2009 [Page 13]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Address Autoconfiguration: Stateless address autoconfiguration is
supported as in [RFC4861]. Additionally a claim and defend
address generation method is supported using the Whiteboard.
Address Resolution: Not performed as there is a direct mapping
between the IID and the link-layer address.
Next-hop Determination: Next-hop determination is performed
considering LoWPAN routing and link specifics, and is simplified
compared to [RFC4861].
Neighbor Unreachability Detection: An algorithm is specified that
makes use of ND messages and link-layer reachability information,
without the use of NS/NA exchanges. In addition, ICMP destination
unreachable messages are supported.
Duplicate Address Detection: The detection of duplicate addresses is
performed across the entire LoWPAN using a lookup on the
Whiteboard using a new registration method. Edge routers in an
Extended LoWPAN formation perform standard [RFC4861] DAD on the
backbone link.
Redirect: Redirect messages are not required.
Node Registration (new): Method in which nodes in the LoWPAN
register with Edge Routers, creating Whiteboard state about all
IPv6 addresses in the LoWPAN.
Whiteboard Conflict Resolution (new): This method is used in the
Extended LoWPAN topology, using the backbone link to resolve
conflicts between the Whiteboards of Edge Routers.
This specification makes use of RS/RA message exchanges along with
standard NS/NA on the backbone link. The use of NS/NA message
exchanges in the LoWPAN are not required by this document. In
addition ND for 6LoWPAN defines two new ICMP packet types:
Node Registration: Sent by a node to an Edge Router to register a
binding for an IPv6 address in the Whiteboard. Is relayed by an
intermediate router if there is no Edge Router on-link.
Node Confirmation: The reponse sent by an Edge Router or router back
to the registering node. May be relayed by an intermediate
router.
Shelby, et al. Expires November 29, 2009 [Page 14]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
3.1. Topology
ND for 6LoWPAN is designed to work with a wide variety of 6LoWPAN
topologies, including isolated Ad-hoc LoWPANs, Simple LoWPANs and
Extended LoWPANs. A Simple LoWPAN topology is assumed by default in
the text. The special case of Ad-hoc LoWPAN operation is described
in Section 8. Edge Router operation and Extended LoWPAN
functionality are described in Section 7. Edge Routers which will
operate only in Simple LoWPANs do not need to support Extended LoWPAN
functionality, such as Edge Routers which do not have a backbone link
(but instead e.g. an ADSL interface).
3.2. Links
The use of IEEE 802.15.4 or any other similar link-layer technology
which exhibits the characteristics defined for a 6LoWPAN link such as
low data-rates, packet loss, limited range, asymmetricity and long
sleep-cycles. This specification is able to deal with the non-
symmetric, non-transitive nature of these links.
ND for 6LoWPAN is agnostic to the use of link-layer mesh or [RFC4944]
mesh techniques, which alleviate the otherwise non-transitive nature
of wireless links. This so-called Mesh Under topology thus makes the
entire link to appear to the IP layer as having a link-local scope
covering all the 6LoWPAN interfaces in the LoWPAN. This kind of
LoWPAN is made up of hosts and Edge Routers. This link still
exhibits lossy, low-rate, asymmetric behaviour along with sleep
cycles.
The non-transitive nature of the link can also be overcome using IP
routing within the LoWPAN, also called a Route Over topology. LoWPAN
Routers are used in the LoWPAN to provide routing between all nodes
in the LoWPAN. LoWPAN Router operations are specified in Section 6.
Link-local scope includes the neighbors of each node within symmetric
wireless range. Mesh Under and Route Over techniques are not
mutually exclusive, and it is possible to combine IP routing and mesh
link-layers within a LoWPAN.
3.3. Bootstrapping
1. A Host first performs stateless autoconfiguration of its link-
local unicast address for each LoWPAN interface from its EUI-64 as in
[RFC4944]. When a LoWPAN Node wants to join a LoWPAN, it does so by
listening for Route Advertisements from Edge Routers or LoWPAN
Routers, or by broadcasting a Router Solicitation (RS) and receiving
RA responses from on-link routers (see Figure 3). If a valid prefix
is advertised in the RA, the host will also form an optimistic global
unique address with stateless address autoconfiguration. At this
Shelby, et al. Expires November 29, 2009 [Page 15]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
point the node has also chosen one or more default routers.
2. Next the node will attempt to perform initial registration with
an Edge Router. As the node is not yet known in a routing algorithm,
and its addresses are optimistic, initial registration is always
performed with a link-local Edge Router or router by sending a
unicast Node Registration (NR) message to it. Registering directly
with an Edge Router is of course preferred as shown in Figure 4 (the
ER is differentiated by the Prf flag in its RA), although all LoWPAN
Routers have the ability to relay NR/NC messages on behalf of a node
as shown in Figure 5.
These message exchanges are illustrated below. The NR contains the
addresses the node wants to register. A node may request a short
address to be generated on its behalf by including an Address Option
with the A flag and an address of length 0 in the NR.
3. The Edge Router replies either directly with a Node Confirmation
(NC), or through the relaying router. Note that routers only exist
in Route Over configurations, and in pure Mesh Under configurations
nodes are always within link-local scope of an Edge Router. This NC
includes the set of addresses now confirmed to be bound to the
Whiteboard of the ER. The Host is now capable of using the LoWPAN
fully, and the ER forwards on its behalf.
Node Router
| |
| ---------- Router Solicitation --------> |
| |
| <-------- Router Advertisement --------- |
| |
Figure 3: Basic RS/RA exchange between a node and any on-link router
(LoWPAN Router or Edge Router)
Node Edge Router
| |
| ---------- Node Registration --------> |
| |
| <--------- Node Confirmation --------- |
| |
Figure 4: Basic ND registration exchange when the Edge Router is on-
Shelby, et al. Expires November 29, 2009 [Page 16]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
link
Node Router (ICMP relay) Edge Router
| | |
| ---- NR ---> | ---- NR ---> |
| | |
| <---- NC ---- | <---- NC ---- |
| | |
Figure 5: Registration exchange relayed by a router (no on-link ER),
the messages are ICMP relayed
3.4. Basic operation
The node may now send packets to any IPv6 address inside or outside
the LoWPAN. Destinations are assumed to be off-link unless known to
be within link-local scope (valid entry in the neighbor cache).
Address resolution is not performed with neighbors as in [RFC4861],
but instead the IID part of the IPv6 address directly corresponds to
a MAC address. The support of NS/NA is optional for nodes.
The Whiteboard address bindings and assignments are soft, and thus
must be renewed periodically as indicated by the lifetime of the
binding. This is achieved by periodically sending a new NR to the
ER. If a host moves, or the network topology changes, and the
current ER is no longer available, the host then starts the
registration process with another ER. If the host is still in the
same Extended LoWPAN (same subnet prefix), its IPv6 addresses remain
the same. Claim and defend addresses generated by the Whiteboard
must be remembered by the host and refreshed in order to keep the
address. If the host moves to a different LoWPAN (thus with a
different subnet prefix), the bootstrapping process is initiated
again. See Section 5 for details on node operation.
LoWPAN Routers periodically send RAs to their neighbors. The Edge
Router initiates the first RAs, and this information is included in
the RAs of each router. RA periods can be optimized to reduce
signalling using a Trickle algorithm. See Section 6 for detailed
router operation.
3.5. Optional features
This documents specifies a method for forming Extended LoWPAN
networks with multiple ERs on a backbone link. This optional Edge
Router feature allows for the detection of duplicate addresses across
Shelby, et al. Expires November 29, 2009 [Page 17]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
the entire Extended LoWPAN and backbone links, seen as a single
subnet. The method uniquely identifies the LoWPAN Host on the
backbone, and overrides the claim on an address on behalf of a LoWPAN
Host. Thus a Host can keep the same address, and appears the same to
other hosts on the backbone link, regardless of moving its binding
from one ER to another. See Section 7 for a description of Extended
LoWPAN operation. Extended LoWPAN operation does not require changes
to node operation.
Ad-hoc LoWPAN operation is also supported. By configuring a router
to implement Simple LoWPAN Edge Router functionality, and by
generating a ULA prefix, an Ad-hoc LoWPAN can operate in an identical
manner to a Simple LoWPAN. Section 8 explains the operation of Ad-
hoc LoWPANs.
4. 6LoWPAN ND Messages
This section introduces message formats for all messages used in this
document. The new messages are all ICMPv6 messages and extend the
capabilities of "The IPv6 Neighbor Discovery Protocol" [RFC4861]. In
addition, new options for the ICMPv6 Router Advertisement message are
defined.
The following [RFC4861] are used with modifications as specificed in
this section:
Router Solicitation
Router Advertisememt
Neighbor Solicitation (Extended LoWPAN only)
Neighbor Advertisement (Extended LoWPAN only)
The following new ICMPv6 message types are defined:
Node Registration
Node Confirmation
In addition, the following new ICMPv6 options are defined:
Address Option
6LoWPAN Prefix Information Option
Shelby, et al. Expires November 29, 2009 [Page 18]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
6LoWPAN Prefix Summary Option
Owner Interface Identifier Option
4.1. Node Registration/Confirmation Message
The Node Registration (NR) and Node Confirmation (NC) messages are
used by a node to register with an ER, and for the ER to confirm the
binding. Any option that is not recognized MUST be skipped silently.
The Node Registration message is sent by the LoWPAN Node to the link-
local unicast IPv6 address of an on-link Edge Router or LoWPAN
Router. NR/NC messages may be sent over multiple IP hops within the
LoWPAN by relaying routers, thus received messages with a hop limit
less than 255 MUST be accepted by LoWPAN Routers from senders with a
source address in the same LoWPAN. Relaying routers may also use the
6LOWPAN_ER anycast address as the destination.
When registering the first time (the node still has optimistic
addresses) it sends an NR to the link-local unicast address of an on-
link ER or LoWPAN Router. The source address must be the IPv6
unspecified address to comply with oDAD.
Nodes send susequent NR messages to an on-link ER or router, however
the IPv6 source address is then the link-local IPv6 address of the
sender. This same message format is also used for relayed NR/NC
messages, with an alternative code that is set when the message has
been relayed. When relaying, a new message is created with an
updated checksum, and a code is used to indicate relaying. The hop
limit is not decremented when relaying.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TID | Status |P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Interface Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Binding option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Node Registration/Confirmation message format
Shelby, et al. Expires November 29, 2009 [Page 19]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
IP Fields:
Source Address: The IPv6 address of the source. This address
MUST be the IPv6 unspecified address for initial registration.
Destination Address: The link-local unicast IPv6 address of an
on-link Edge Router or router when sent by a node. The
destination IPv6 address of an Edge Router or the 6LOWPAN_ER
anycast address when sent by a relaying router.
Hop Limit: 255
ICMP Fields:
Type: TBD1 for Node Registration, TBD2 for Node Confirmation.
Code: 0 indicates a message sent directly from the originating
host. 1 indicates that the message has been relayed by a
router. Values 128-255 are reserved for error codes. 128 is
sent in an NC response by a router to indicate that no ER is
available. 129 is sent by a router or edge router to indicate
that Whiteboard registration is not supported.
Checksum: The ICMP checksum.
TID: A unique Transaction ID assigned by the host and used to
match replies. A lollipop mechanism is used to increment the
TID at each new message. TID is set to 0 upon booting, and is
incremented with each NR message. After reaching 0xFFFF, the
value loops to 16 (0x10) and is incremented from there. Thus
the values between 0-15 MUST only used after a boot or reboot.
P: 1-bit Primary flag. Set to indicate that the Edge Router is
primary and MAY represent the node if used in a Extended
LoWPAN. If the flag is not set then the router MUST not
represent the node on the backbone. The flag is echoed in a
confirmation.
Status: 8-bit unsigned integer. Values TBD. 0 means unqualified
success. Any value below 128 is a positive status that means
that the binding was created or is being created
optimistically.
Lifetime: 32-bit unsigned integer. The amount of time in units
of seconds remaining before the binding of this owner interface
identifier, and all associated address options and
configuration options, MUST be considered expired. A value of
zero indicates that the Binding Cache entries for the
Shelby, et al. Expires November 29, 2009 [Page 20]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
registered owner interface identifier MUST be deleted.
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Owner Interface Identifier: A globally unique identifier for the
requesting host's interface. Typically the EUI-64 derived IID.
Possible Options:
Address Option(s): An Address Option is included for each address
the host wants to bind for this interface.
Configuration options: Other configuration information requests
and configuration settings may be carried in options of NR/NC
messages. Such options are not defined in this document.
Source link-layer address: This option SHOULD be added to the NC
by the relaying router to indicate the identity of the ER for
use by a host. Format as defined in [RFC4861] and [RFC4944].
Target link-layer address: This option MAY be included by a node
in an NR to indicate the preferred ER to be used by a relaying
router. Format as defined in [RFC4861] and [RFC4944].
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognized
and continue processing the message.
4.2. Router Solicitation Message
The RS message format for 6LoWPAN is identical to the [RFC4861] RS
message. The following changes are made regarding the use of RS in
LoWPANs. If a node has only optimistic addresses, not yet confirmed
by an Edge Router, then the IPv6 source address in the RS MUST be the
IPv6 unspecified address. The Source Link-Layer Address Option MUST
NOT be included in the RS at any time, as the MAC address is
implicitly known. Instead the Owner Interface Identifier specified
in this document MUST be included in the RS.
4.3. Router Advertisement Message
The RA message format for 6LoWPAN is identical to the [RFC4861] RA
message. The use of flags is however defined in the 6LoWPAN context,
and additional new options are identified. RA messages are sent
either to link-local all-nodes multicast, or to a link-local unicast
address as a response to an RS.
Shelby, et al. Expires November 29, 2009 [Page 21]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Updated Flag Definitions:
M: Managed mode here refers to the availability of an Edge Router
through this router, not DHCPv6 as in [RFC4861]. MUST be set
to 1 by Edge Routers, and SHOULD be set to 1 by LoWPAN routers
who are successfully registered with and have a route to an
Edge Router.
Prf: 2-bit signed integer. Default Router Preference as defined
in [RFC4191]. Indicates whether to prefer this router over
other default routers. LoWPAN Routers SHOULD set the
preference to (00) for normal, and LoWPAN Edge Routers SHOULD
set the preference to (01) for high.
Possible Options:
6LoWPAN Prefix Information Option: This option includes
information about the prefixes of the LoWPAN along with other
context information.
6LoWPAN Prefix Summary Option: This option provides a sequence
number associated with the current prefix options. It allows
the prefix options themselves to be sent only periodically in
unsolicited RAs.
Future versions of this protocol may define new option types.
Receivers MUST silently ignore any options they do not recognized
and continue processing the message.
4.4. NS/NA Messages
NS/NA messages are also employed between ERs on the backbone link.
For this use a unique identifier is required in the message as an
option to uniquely identify a host's interface. The standard NS/NA
message is used in this document is as per [RFC4861] with the an
additional Owner Interface Identifier Option defined in this
document. The Owner Interface Identifier is the same as that carried
in NR/NC messages and associated with bindings.
If NS/NA messages are sent on the LoWPAN link (which is not required
by this specification), they do not carry link-layer address options,
because of link non-transitivity and the Extended LoWPAN topologies
do not preserve the MAC address. For the same reason redirect is not
supported. Instead they MUST include the Owner Interface Identifier
option to help resolve conflict.
Shelby, et al. Expires November 29, 2009 [Page 22]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
4.5. 6LoWPAN ND Message Options
This section defines the new ND for 6LoWPAN message options.
4.5.1. Address Option
The Address Option is used to indicate the address which a node wants
to register with an ER in an NR, and to indicate the success or
failure of that binding in an NC. Multiple Address Options can be
included in a message. In order to be as compact as possible, fields
are used to indicate the compression of the IPv6 address. The
Address Option also allows for duplicate addresses (e.g. anycasts),
the request of a generated address for claim and defend, or for an
address to be removed.
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 | P | S |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|A|R| Reserved | IPv6 Address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Address Option format
Type: TBD3
Length: 8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets.
Status: 8-bit unsigned integer. Values TBD. 0 means unqualified
success. Any value below 128 is a positive status that means that
the binding for this address was created or is being created
optimistically. Only used in a confirmation.
D: 1-bit Duplicate flag. When set, indicates that duplicates are
allowed for this address (to support anycast) in a request.
A: 1-bit Address Generation flag. Set to indicate that the host is
requesting a generated address for claim and defend addressing.
In a request when A is set the IPv6 address length is 0. Set to
indicate that an address has been assigned in a confirmation. P
and S are set to indicate the type of address requested and
assigned when A is set. Otherwise must be 0.
Shelby, et al. Expires November 29, 2009 [Page 23]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
R: 1-bit Removal flag. When set, indicates that this particular
address binding MUST be removed from a whiteboard (in a request)
or MUST not be used any longer (in a confirmation).
P: 4-bit unsigned integer. Identifies prefix compression or type, if
any.
0: Prefix is carried inline.
1: Prefix compressed and link-local (fe80::) is assumed.
2: Prefix compressed and the default prefix (CID=0) is assumed.
3-15: Reserved.
S: 4-bit unsigned integer. Identifies suffix compression or type, if
any.
0: Suffix carried inline.
1: Suffix compressed and assumes the same value as the Owner
Interface Identifier field in the NR/NC message header.
2: Suffix compressed and is derived from the link-layer short
address as defined in RFC 4944.
3: Suffix is a 6LoWPAN 16-bit short address as defined in RFC 4944
or as appropriate for the link-layer of the LoWPAN.
4-15: Reserved.
IPv6 Address: The IPv6 address to be registered with the ER, or
confirmed by the ER. Parts of the address may be elided as per
the P and S fields.
4.5.2. 6LoWPAN Prefix Information Option
This option carries prefix information for LoWPANs, and is similar in
use to the Prefix Information Option of [RFC4861]. However this
option allows for the dissemination of multiple contexts identified
by a Context Identifier (CID) for use in 6LoWPAN address compression.
Shelby, et al. Expires November 29, 2009 [Page 24]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
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 | Prefix Length |L|A| CID | R |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Prefix .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: 6LoWPAN Prefix Information Option format
Type: TBD4
Length: 8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets.
Prefix Length: 8-bit unsigned integer. The number of leading bits
in the Prefix that are valid. The value ranges from 0 to 128.
The prefix length field provides necessary information for on-link
determination (when combined with the L flag in the prefix
information option). It also assists with address
autoconfiguration as specified in [RFC4862], for which there may
be more restrictions on the prefix length.
L: 1-bit on-link flag. This flag MUST be unset for Route Over
LoWPANs and Extended LoWPANs, and MAY be set for Mesh Under Simple
LoWPANs.
A: 1-bit autonomous address-configuration flag. When set indicates
that this prefix can be used for stateless address configuration
as specified in [RFC4861].
CID: 4-bit Context Identifier for this prefix information. CID is
used by context based header compression specified in
[I-D.ietf-6lowpan-hc]. The list of CIDs for a LoWPAN is
configured on Edge Routers, who distribute the prefix list to all
nodes in the LoWPAN. CID = 0 identified the default prefix for
the LoWPAN.
R: Reserved. This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Shelby, et al. Expires November 29, 2009 [Page 25]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Valid Lifetime: 32-bit unsigned integer. The length of time in
seconds (relative to the time the packet is sent) that the prefix
is valid for the purpose of on-link determination. A value of all
one bits (0xffffffff) represents infinity.
Prefix: The IPv6 Prefix indicated for this context. This may be a
partial prefix, or even an entire IPv6 address for use as a
context for compression.
4.5.3. 6LoWPAN Prefix Summary Option
This option identifies the set of prefix information options by a
sequence number. This allows for the full set of prefix information
options to be sent only periodically in unsolicited RAs. If a host
detects a difference in the sequence number of this option, then the
prefix information has likely changed, and is then requested with an
RS. An RA sent in response to a unicast RS always includes the full
set of prefix information.
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 | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V| Reserved | ER Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: 6LoWPAN Prefix Summary Option
Type: TBD5
Length: 1
Sequence Number: 16-bit signed integer. Indicates the freshness of
the information advertised by the RA.
ER Metric: 16-bit unsigned integer. The ER Metric gives an
indication of the cost (in routing metric terms) of reaching nodes
outside the LoWPAN via an ER through this router. The metric
SHOULD be derived in a well-defined way from the routing protocol
used in the LoWPAN (possibly by structuring the 16 bits available
e.g. into a major and a minor metric), and has a mid-range default
value of 0x8000. Edge Routers most likely set this field to 0. A
host SHOULD take this metric into account when choosing default
routers by making a scalar comparison, preferring routers with
numerically lower ER Metric values.
Shelby, et al. Expires November 29, 2009 [Page 26]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
V: 1-bit flag. Indicates if the sequence number is valid and the
router is advertising information obtained from another router.
Reserved: This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
4.5.4. Owner Interface Identifier Option
This option is for use with standard NS and NA messages between ERs
over a backbone link. By using this option, the binding in question
can be uniquely identified and matched with the whiteboard entries of
each ER.
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 | TID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Interface Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Owner Interface Identifier Option
Type: TBD6
Length: 2
TID: A unique Transaction ID assigned by the host in the associated
NR and used to match NC replies.
Reserved: This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
Owner Interface Identifier: A globally unique identifier for the
host's interface associated with the binding for the NS/NA message
in question. This is typically the EUI-64 of the interface.
5. LoWPAN Node Specification
This section specifies LoWPAN node operations, and explains the
differences to [RFC4861] node operation, while specifying the new
operations. Instead of relying on multicast ND messages for DAD and
neighbor unreachability detection, LoWPAN Nodes send unicast messages
Shelby, et al. Expires November 29, 2009 [Page 27]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
to an Edge Router in the LoWPAN which keeps a Whiteboard of all bound
addresses from nodes attached to that ER. Thus these functions are
performed across the entire LoWPAN using the Whiteboard, which allows
ND for 6LoWPAN to operate over asymmetric, non-transitive links and
with sleeping nodes. Node complexity and energy consumption are
reduced as address resolution and the support of redirect are not
required, ND traffic is reduced and nodes do not need to answer NS
messages. In an Extended LoWPAN topology, ND functions are performed
across the entire Extended LoWPAN, and a node may change its point of
attachment within the LoWPAN without changing its IPv6 addresses.
Extended LoWPAN operation is transparent for nodes.
5.1. Conceptual structures and variables
LoWPAN Nodes make use of the same conceptual data structures as
defined in [RFC4861] Section 5.1, with the following differences:
Neighbor Cache - The neighbor unreachability detection entry is not
kept in this cache, but instead MAY be used with destination cache
entries.
Destination Cache - The destination cache MAY include a neighbor
unreachability detection entry, for destinations within the same
LoWPAN.
Prefix List - The list of prefixes and their associated CID which
are advertised in Router Advertisements, along with an associated
invalidation timer. Each entry is associated with the LoWPAN
prefix (CID = 0) and the sequence number last advertised in the
6LoWPAN Prefix Summary Option. Unlike in [RFC4861], these
prefixes are always assumed to be off-link.
Default Router List - As in [RFC4861], with the addition that Edge
Routers are also be tracked by entries in this list.
Edge Router List - This new structure contains the list of Edge
Routers the node is registered with an associated timeout and
primary flag. This list may be combined with the Default Router
List. Off-link ERs can be included in this list but this is not
required as they can be reached using the 6LOWPAN_ER anycast
address through a default router.
These conceptual data structure may be realized in many ways. As
LoWPAN Nodes have very limited memory the number of cache entries
should be limited, duplicate entries between caches referenced, and
full IPv6 addresses represented in a compressed format where
possible.
Shelby, et al. Expires November 29, 2009 [Page 28]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
The neighbor discovery variables defined in [RFC4861] Section 6.3.2
are valid for 6LoWPAN for ND, and default values are overridden by
information in Router Advertisements. The LinkMTU variable is always
1280 octets for 6LoWPAN. ReachableTime and RetransTimer variables
are used for neighbor unreachability detection using the Whiteboard.
5.2. Interface initialization
All nodes are required to autoconfigure at least one address, a link-
local address, which is derived from the IEEE 64-bit extended MAC
address that is globally unique to the interface as in [RFC4944]. As
a result, knowledge of the 64-bit address of another LoWPAN Node is
enough to derive its link-local address and reach it if on the same
link. Another consequence is that the link-local address is
presumably unique on the Extended LoWPAN, which enables the use of
Optimistic Duplicate Address Detection (oDAD) [RFC4429] over the
backbone link and the LoWPAN. The address SHOULD be created as
optimistic before it has been confirmed by an Edge Router. Due to
the way 6LoWPAN networks perform address compression [RFC4944] nodes
within a LoWPAN use addresses in a homogeneous way and the unicast
IPv6 address IID resolves directly to a corresponding link-layer
address. As a result, address resolution within the LoWPAN is not
required.
A node MUST join the all-nodes multicast address, which is used for
receiving RAs from routers. A node MAY join other multicast
addresses such as the solicited-node multicast address if its link-
layer includes multicast support, but that is not required by this
specification.
Nodes MAY learn the address of Edge Routers or routers using
traditional means such as L2 configuration or Router Advertisement
messages as in [RFC4861]. When sending a Router Solicitation it MUST
not have the SLLA Option, but instead MUST include the OII Option.
If the sender of the RS has only optimistic addresses, it MUST not
use them as the IPv6 source address for the RS, but instead uses the
IPv6 unspecified address. This procedure is to comply with the use
of optimistic addresses as per oDAD [RFC4429].
The node SHOULD also form a global unicast address for routing inside
the LoWPAN and reachability from outside the LoWPAN. If a valid
prefix is available from an RA ('A' flag is set), then a global
unicast address is derived using stateless address autoconfiguration.
This address is marked optimistic until confirmed by the ER. If the
LoWPAN is operating in ad-hoc mode, then the prefix is a Unique Local
IPv6 Address (ULA) prefix [RFC4193] as specified in Section 8.
Shelby, et al. Expires November 29, 2009 [Page 29]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
5.3. Registration process
The binding process is very similar to that of a MIPv6 mobile node,
though the messages used are new Neighbor Discovery ICMP messages. A
LoWPAN Node address is tentative or optimistic as long as the binding
is not confirmed by the ER.
The LoWPAN Node uses unicast Node Registrations with on-link ERs or
LoWPAN Routers to perform the binding. The destination address is
the link-local unicast address of an on-link ER or LoWPAN Router.
While a nodes addresses are still optimistic (first registration in a
LoWPAN), the IPv6 unspecified address must be used as the source.
Registration SHOULD be preferred with on-link ERs rather than LoWPAN
Routers if available. The Preference Flag of the RA is used to
differentiate between ERs (Prf=01) and LoWPAN Routers (Prf=00). The
M Flag of the RA indicates if an ER is available through a neighbor
LoWPAN Router. If the M Flag is unset, that router SHOULD NOT be
used for registration. Furthermore the ER Metric in the 6LoWPAN
Prefix Summary Option SHOULD be used to choose a router to use for
registration.
A unique Owner Interface Indentifier is included in the Node
Registration so the binding can be identified throughout the LoWPAN.
This is usually the EUI-64 identifier of the interface. The NR
message includes an Address Option for each address to be registered.
Thus the message is structured as follows:
ICMPv6 (Node Registration (Address Option[0], Address Option[1],
Address Option[n]))
This registration method includes a way of requesting a unique
address from the ER by setting the 'A' flag in an Address Option
during registration. This is useful for receiving a unique short
link-layer address, and works in a claim and defend fashion. Address
generation using this NR/NC mechanism is stateless. Although the
address is generated by the ER and checked for uniqueness across the
LoWPAN, it is just like any other address binding in the whiteboard
of the ER after assignment. Thus in order to keep using this address
the host must keep refreshing the address binding, including when
moving to another ER in the same LoWPAN.
A unique Transaction ID (TID) is included by the host in the NR
message and used to match replies. A lollipop mechanism is used.
TID is set to 0 upon booting, and is incremented with each NR
message. After reaching 0xFFFF, the value loops to 16 (0x10) and is
incremented from there. Thus the values between 0-15 MUST only used
after a boot or reboot.
Shelby, et al. Expires November 29, 2009 [Page 30]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
The acknowledgment to a Node Registration is a unicast Node
Confirmation message that contains the status of the binding. The
source of the packet is the link-local address of the on-link ER or
LoWPAN Router. The destination address is the link-local address of
the node. An Address Option for each confirmed or assigned address
is included. Upon successful completion in the Node Confirmation
message, the LoWPAN Node sets the address from optimistic or
tentative to preferred. See Section 9 for detailed message examples.
If a Node Confirmation is received with an error code (128 or
greater), then the registration has failed. See Section 4.1 for an
explanation of NR/NC codes. If no successful Node Confirmation is
received within an implementation specific timeout and number of
retries, then there may be no Edge Routers in the LoWPAN. See
Section 8 for more information on ad-hoc network operation.
This specification also introduces the concept of a secondary
binding. For redundancy, a node might place a secondary binding with
one or more other Edge Routers on the same or different LoWPANs. The
'P' flag in the Router Registration Indentity Request Option
indicates whether the binding is primary. A primary binding MUST be
maintained with exactly one Edge Router in each LoWPAN at any time.
The use of this mechanism for fault tolerance is explained in
Section 7.8.
ER bindings have a timeout associated with them, therefore nodes must
periodically send a new Node Registration message to renew the
bindings. If a node no longer receives RCs from any router in the
current subnet, the registration process begins from the beginning.
5.4. Next-hop determination
Next-hop determination is performed as in Section 5.2 of [RFC4861]
with the following exceptions. All prefixes are assumed to be off-
link as the subnet with that prefix may be larger than the link (non-
transitive property), unless the destination address exists in the
neighbor cache. Exact-match search is performed on the neighbor and
destination caches. A node MAY attempt to transmit a packet to the
link for destinations with the same LoWPAN prefix if no neighbor or
destination cache entry is found before sending to a default router.
Link-layer information and packet transmissions SHOULD be used to
maintain the neighbor cache. Multicast addresses are considered to
be on-link and are resolved as specified in [RFC4944] or relative
future documents. A LoWPAN Node is not required to be a minimum of
one buffer per neighbor as specied in [RFC4861], as address lookup is
not performed as part of next-hop determination.
Care must be used with anycast addresses, as anycast address
Shelby, et al. Expires November 29, 2009 [Page 31]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
resolution is normally performed with a multicast NS/NA exchange in
[RFC4861]. As LoWPAN Nodes are not required to perform address
resolution, and do no need to answer NS messages, anycast addresses
MUST be considered to be off-link. If a node does answer an NS with
an NA, it MUST not include link-layer address options, but instead
MUST include the OII Option.
5.5. Destination unreachability detection
LoWPAN Nodes do not perform [RFC4861] address resolution, DAD or NUD.
Therefore the implementation of NS/NA message support by a node is
optional, and thus to minimize implementation size a node MAY choose
not to support NS/NA messages.
In order to detect unreachable destinations, nodes SHOULD support
type 1 ICMPv6 destination unreachable messages [RFC4443]. LoWPAN
Routers or Edge Routers make use of ICMPv6 destination unreachable to
indicate that delivery to that destination is not possible.
6. LoWPAN Router Specification
LoWPAN Routers are used in a route over configuration where the
network is composed of overlapping link-local scopes. As a result,
we extend ND as specified in [RFC4861] to operate over such non-
transitive LoWPAN links. This section describes ND for 6LoWPAN
router operations. Note that this section does not apply to pure
Mesh Under LoWPANs where the are no LoWPAN Routers. In addition to
the operations described in this section, LoWPAN Routers also need to
implement the basic LoWPAN Node operations in Section 5.
Network configuration parameters carried in Router Advertisements
originate at edge routers and must disseminate to all routers and
hosts within the LoWPAN. The 6LoWPAN Prefix Summary Option is used
to support information dissemination from one or more edge routers to
all other nodes in the LoWPAN. The option includes a "V" flag which
indicates that the information contained in the Router Advertisement
is valid. The option also includes a sequence number to ensure that
all nodes converge on the same settings.
Because Node Registration/Confirmation exchanges between LoWPAN Nodes
and LoWPAN Routers only occur over link-local scope, such messages
must be relayed between nodes and ERs when separated by multiple IP
hops. Every LoWPAN Router MUST also serve as a relay to ensure that
any neighboring node can successfully participate in the LoWPAN.
Shelby, et al. Expires November 29, 2009 [Page 32]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
6.1. Router Configuration Variables
A router MUST allow conceptual variables as defined in Section 6.2.1
of [RFC4861].
6.2. Becoming an Advertising Interface
An interface may become an advertising interace as specified in
Section 6.2.2 of [RFC4861].
A LoWPAN Router's interface MAY become an advertising interface
before all of its router variables have been initialized. The router
MUST learn these variables (e.g. AdvCurHopLimit, AdvReachableTime,
prefix information, etc.) from neighboring routers. While the
variables are not initialized, the router MAY send Router
Advertisement with the "Solicit" flag set to solicit Router
Advertisements from neighboring routers. However, the router MUST
set the Router Lifetime field to zero while one or more of its
variables are uninitialized.
6.3. Router Advertisement Message Content
A router sends periodic as well as solicited Router Advertisements
out its advertising interface. Outgoing Router Advertisements are
filled with the following values constistent with the message format
given in this document.
- In the Router Lifetime field: if the router has a default route,
the interface's configured AdvDefaultLifetime. If the router does
not have a default route, zero.
- In the M and O flags: the current value of AdvManagedFlag and
AdvOtherConfigFlag, respectively.
- In the Preference flag: this flag is set to 00 to indicate that
the sender is a LoWPAN Router.
- In the Cur Hop Limit field: the current value of CurHopLimit.
- In the Reachable Time field: the current value of
AdvReachableTime.
- In the Retrans Timer field: the current value of
AdvRetransTimer.
- In the options:
Shelby, et al. Expires November 29, 2009 [Page 33]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
- 6LoWPAN Prefix Summary Option: to indicate if the information
contained in the Router Advertisement is valid and, if so, the
freshness of the information contained in the Router
Advertisement message. The option fields are set as follows:
- In the "valid" flag: the current value of
AdvInformationValid.
- In the Sequence Number field: the current value of
AdvInformationSequence.
- The ER Metric field is used by a routing algorithm to
indicate the cost of reaching an ER through this router.
- 6LoWPAN Prefix Information options: one 6LoWPAN Prefix
Information option for each prefix listed in AdvPrefixList with
the option fields set from the information in the AdvPrefxList
entry as follows:
- In the "on-link" flag: the entry's AdvOnLinkFlag.
- In the "Autonomous address configuration" flag: the
entry's AdvAutonomousFlag.
- In the Valid Lifetime field: the entry's AdvValidLifetime.
6.4. Sending Unsolicited Router Advertisements
As specified in Section 6.2.4 of [RFC4861].
6.5. Ceasing To Be an Advertising Interface
As specified in Section 6.2.5 of [RFC4861].
6.6. Processing Router Solicitations
As specified in Section 6.2.6 of [RFC4861].
6.7. Relaying a Node Registration Message
When a router receives a Node Registration message from a LoWPAN
Node, it sets the Code field to 1 indicating that the message has
been relayed. The IPv6 source address is set to that of the router.
Furthermore the checksum is re-calculated and the hop limit is set to
255.
By default, the router relays Node Registration messages to the
6LOWPAN_ER anycast address. However, the router MAY be configured to
Shelby, et al. Expires November 29, 2009 [Page 34]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
use a list of destination addresses, which MAY include unicast
addresses, the 6LOWPAN_ER anycast address, or other addresses
selected by the network administrator. If a target link-layer
address option is included, the router SHOULD take this into account
as the prefered ER of the node.
As initial Node Registration messages are sent with an unspecified
IPv6 source address, the router needs to keep state regarding the
node's OII to link-layer address mapping while waiting for the Node
Confirmation. This state is used to send the relayed NC to the
correct MAC address for the node.
6.8. Relaying a Node Confirmation Message
When the router receives a Relay Node Confirmation message from an
Edge Router, the Code field is set to 1. The Owner Interface
Identifier and relay state are used to form the link-local IPv6
Destination Address for the Node Confirmation message. The IPv6
source address is set to the link-local address of the Router. The
Hop Limit of the Node Confirmation message is set to 255.
Upon relaying a successful NC message back to a node, the router
SHOULD use the information about IPv6 addresses in the message to
update its neighbor cache.
7. LoWPAN Edge Router Specification
Edge Routers are the routers that connect LoWPANs to an IPv6
infrastructure via backhaul or backbone links when such an
infrastructure is available. To achieve that role:
Edge Routers MUST implement LoWPAN Router features on their LoWPAN
interfaces,
Edge Routers MUST support Whiteboard registration for LoWPAN Nodes
within their subnets.
Edge Routers MAY support the Extended LoWPAN modality where a
LoWPAN subnet is aggregated over a higher speed backbone link.
Edge Routers supporting the extended LoWPAN modality MUST perform
ND proxy over the backbone on behalf of their registered LoWPAN
Nodes.
This specification documents the LoWPAN Whiteboard, a conceptual data
structure that is used by the Edge Routers to maintain LoWPAN Node
registrations. This specification documents extensions to the IPv6
Shelby, et al. Expires November 29, 2009 [Page 35]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Neighbor Discovery Protocol [RFC4861] that enables a LoWPAN Node to
locate an Edge Rsouter and then claim and register addresses using
unicast exchanges with that Edge Router.
Another function of the Edge Router is to perform 6LoWPAN compression
and uncompression between the LoWPAN and the rest of the IP network
and ensure MTU compatibility. Packets flow uncompressed over the
Backbone or Backhaul Links and are routed normally towards a Gateway
or an Application sitting outside of the LoWPAN.
In the Extended LoWPAN case, the Edge Router also performs proxy ND
operations over the Backbone Link on behalf of the LoWPAN Nodes that
are registered to it. The draft documents the proxy ND operation by
the Edge Routers over the Backbone link and the conflict resolution
process that enables transparent micro-mobility for the LoWPAN Nodes.
7.1. The Whiteboard
The white board is a conceptual data structure that is maintained by
the Edge Routers to store their knowledge of the registered LoWPAN
Nodes. Information maintained for each registered node includes:
IPv6 address: The IPv6 address being registered. This is an IPv6
unicast address of any scope.
Owner Interface Identifier: The OII of the LoWPAN Node is used for
Address collision detection and resolution. (Section 7.6).
Transaction Identifier History: The TID history of the last
successful registrations for a LoWPAN Node is used for Duplicate
OII detection (Section 7.7)
Primary flag: Influences the proxy ND operation in the Extended
LoWPAN case.
Registration Age and Lifetime: The registration age indicates how
long ago the last registration flow took place. When the age
reaches the registration lifetime, the whiteboard entry is
removed.
It can be noted that no link-layer information is stored there. If
the Edge Router is also used as the default gateway for the LoWPAN
node then it would possess LLA information in its neighbor cache.
Otherwise, it will route packets towards the LoWPAN nodes and thus
will not need or use the LLA of the LoWPAN node.
It can also be noted that in the Extended LoWPAN case, an Edge Router
only maintains the information on the LoWPAN Nodes that are
Shelby, et al. Expires November 29, 2009 [Page 36]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
registered to it. So the full registry of all the LoWPAN Nodes in a
subnet is actually distributed between the Edge Routers.
7.2. Simple LoWPAN
The support of the Simple LoWPAN modality is REQUIRED. In that
configuration, a single Edge Router serves a subnet that is formed by
the LoWPAN nodes that are registered to that Edge Router, as
represented in Figure 1. The ER may be connected to an IP
infrastructure and may inject the prefixes for its subnet in the
routed infrastructure.
In a Simple LoWPAN, the Edge Router is the repository of all
registrations and can detect a registration collision by simply
looking up its whiteboard, so the whiteboard is the reference for
Neighbor Discovery operations.
The Edge Router forms a link-local address in exactly the same way as
any other node on the LoWPAN, for instance based on its link layer
addresses to enable 6LoWPAN Header Compression. If the resulting
address is not present in the Whiteboard then the Edge Router owns
the address right away. The Edge Router announces itself using
Router Advertisement (RA) messages that are broadcasted periodically
over the LOWPAN.
7.3. Extended LoWPAN
The support of the Extended LoWPAN modality is OPTIONAL. In that
modality, a high speed Backbone Link interconnects multiple devices
and Edge Routers to form a single subnet that encompasses IPv6 nodes
attached to the Backbone Link and LoWPAN Nodes registered to the Edge
Routers as represented in Figure 2. As a result, all further
reference to the Backbone Link and ND proxy operation over that link
is OPTIONAL but come as a whole.
In the Extended LoWPAN modality, the Backbone Link is used as a
reference for address ownership and registration collision detection.
Addresses that are not found in the Whiteboard are queried over the
backbone using the ND operation in place for that type of link,
typically [RFC4861]; Edge Routers represent themselves and the LoWPAN
Nodes that are proactively registered to them. An ND lookup over the
backbone is not propagated over the LoWPANs, but answered by the Edge
Router that has the registration for the target, if any.
To enable proxying over the Backbone Link, an Edge Router must join
the solicited-node multicast address on that link for all the
registered addresses of the nodes in its LoWPANs. The Edge Router
answers the Neighbor Solicitation with a Neighbor Advertisement that
Shelby, et al. Expires November 29, 2009 [Page 37]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
indicates its own link-layer address in the Target link-layer address
option.
The Backbone Link Maximum Transmission Unit serves as base for Path
MTU discovery and Transport layer Maximum Segment Size negotiation
(see section 8.3 of [RFC2460]) for all nodes in the LoWPANs. To
achieve this, the Edge Router announces the MTU of the Backbone Link
over the LoWPAN using the MTU option in the RA message as prescribed
in section "4.6.4. MTU" of IPv6 Neighbor Discovery [RFC4861].
More information on the MTU issue with regard to ND-proxying can be
found in Neighbor Discovery Proxies [RFC4389] and
[I-D.van-beijnum-multi-mtu].
7.4. Registration process
An Edge Router configures the well-known 6LOWPAN_ER anycast address
on the LoWPAN interfaces where it serves as Edge Router. Note that
the Edge Router will accept Node Registration messages with a hop
limit that is lower than 255 but it MUST drop a Node Registration
that does not come from a LoWPAN interface that is associated to the
same subnet.
The new Owner Interface Identifier Option in ND messages that carries
the node EUI-64 address and the lollipop mechanism on the TID help
differentiate an address collision from a new registration from the
same node. More details on collision detection and resolution are
provided in Section 7.6.
The Edge Router responds to a Node Registration with a Node
Confirmation. If the source address of the NR was not the
Unspecified Address, then the destination address in the confirmation
is the source in the Registration. If the source address of the NR
was the Unspecified Address, then the ER acts as LoWPAN Router for
the source, and the destination address is the optimistic address
being registered. The destination Link Layer address is not taken
from the ND cache but from the source Link Layer address in the NR.
The source address is a unicast address of the ER that matches the
scope of the destination, preferrably the destination in the NR if it
is not anycast.
The remainder of this section deals with the case of an Extended
LoWPAN configuration. In that case:
When it inserts an address in its Whiteboard, an Edge Router SHOULD
perform Duplicate Address Detection (DAD) over the Backbone Link to
detect a collision. Upon a new registration for a link-local, unique
local or global unicast address based on an IEEE 64-bit extended MAC
Shelby, et al. Expires November 29, 2009 [Page 38]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
address, the Edge Router MAY use Optimistic DAD [RFC4429] on the
Backbone Link. A positive acknowledgement can be sent to the 6LoWPAN
node right away if oDAD is used on the Backbone Link.
A LoWPAN Node should be able to join a different Edge Router at any
time without the complexities of terminating a current registration
and renumbering. To enable this, the ND operation on the backbone
link upon a Node Registration/Confirmation flow wins the address
ownership over an ND operation that is done asynchronously, on behalf
of the same LoWPAN Node, upon a prior registration. So an Edge
Router that would happen to have a binding for that same address for
the same LoWPAN Node identified by its EUI-64 address will yield and
depreciate its binding.
The override (O) bit is used to differentiate a registration flow
from the asynchronous defense of an address by an Edge Router acting
as a proxy. Upon a registration flow, an Edge Router doing DAD or
accepting a reregistration SHOULD set the override (O) bit in its NA
messages. Asynchronously to the registration, the Edge Router SHOULD
NOT set the override (O) bit in its NA messages and should yield to
an NA message with the override (O) bit set.
So the Edge Router operation on the Backbone Link is similar to that
of a Home Agent as specified in "Mobility Support for IPv6" [RFC3775]
yet different. In particular, the Neighbor Advertisement message is
used as specified in section "10.4.1. Intercepting Packets for a
Mobile Node" with the exception that the override (O) bit is not set,
indicating that this Edge Router acts as a proxy for the LoWPAN and
will yield should another Edge Router claim that address on the
Backbone Link.
This specification also introduces the concept of a secondary
binding. Upon a secondary binding, the Edge Router will not announce
or defend the address on the backbone link, but will be able to
forward packets to the node over its LoWPAN interface. This feature
is used for fault tolerance, explained in Section 7.8.
If the Edge Router is primary for a registration as indicated by the
'P' flag and it is connected to a Backbone, then it SHOULD perform ND
operations on the backbone. In particular the Egde Router SHOULD
reject the registration if DAD fails on the backbone. When oDAD is
used over the backbone the Edge Router MAY issue the Node
Confirmation right away with a positive code, but if a collision is
finally detected, it cancels the registration with an asynchronous
Node Confirmation and a negative completion code on the same TID.
If the NR message includes an Address Option with the 'A' flag set,
this indicated the request of stateless address generation. The ER
Shelby, et al. Expires November 29, 2009 [Page 39]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
aquires an appropriate, unique link-layer address for the network
either by generating it and performing DAD, or with some other
method. If successful, this address is returned in an Address Option
of the NC with the 'A' flag set and the assigned IPv6 address formed
from the generated link-layer address with the defualt prefix inline.
7.5. Forwarding packets between a LoWPAN and an IPv6 infrastructure
Upon receiving packets on one of its LoWPAN interfaces, the Edge
Router checks whether it has a binding for the source address. If it
does, then the Edge Router can forward the packet; otherwise, the
Edge Router MUST discard the packet.
If the packet is to be transmitted over a Backbone or Backhaul Link,
then the 6LoWPAN sublayer is terminated and the full IPv6 packet is
reassembled and expanded. When forwarding a packet from the Backbone
or Backhaul Link towards a LoWPAN interface, the Edge Router performs
the 6LoWPAN sublayer operations of compression and fragmentation and
passes the packet to the lower layer for transmission.
From the standpoint of an Edge Router, the view of the subnet in the
Extended LoWPAN modality is that all nodes in the subnet are either
LoWPAN nodes registered to this ER or on-link on the Backbone Link,
though in fact they might be proxide for by other ERs. If the
destination is a LoWPAN node registered to this ER, the ER will
forward the packet over the LoWPAN interface either as a local
delivery if the node is on-link or via intermediate LoWPAN routers
using the routing in place in the LoWPAN. If the destination is not
a registered LoWPAN node, then the ER acts as if the subnet was on-
link on the Backbone and looks up the node there using ND. If the
node is not found there either, it is assumed unreachable and an
"Destination Unreachable" ICMP message is sent to the source as
prescribed by [RFC4443].
7.6. Address collision detection and resolution
The assumption in this section is that the OII that is carried in the
registration messages and in the NS/NA messages is globally unique.
When this assumption fails, and additional collision resolution
mechanism takes place, as detailed in Section 7.7.
The address collision can be detected within the Edge Router if the
Edge Router already has a registration for a given address, or over
the Backbone Link using Duplicate Address Detection. In the latter
case, a new ND option, the Owner Interface Identifier Option is used
in NS/NA messages to carry the Transaction ID and the Owner Interface
Identifier that are required for the resolution th conflict
resolution. In any case, the Edge Router in charge of the resolution
Shelby, et al. Expires November 29, 2009 [Page 40]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
is the Edge Router that handles the registration.
A registration is identified by the (OII, IPv6 address) pair. A
conflict occurs when a Node Registration is received for an IPv6
address that is already registered with a different OII at the same
or another Edge Router. The resolution of such conflict is explained
below.
Additionally, the following principles apply to the resolution in the
Extended LoWPAN modality:
Mobility within a subnet is included and welcome. In an Extended
LoWPAN, a LoWPAN Node may migrate its registration to a new Edge
Router transparently and at any time. The protocol is designed to
recognize the mobility and silently cleanup the registration
states.
A synchronous operation wins against a delayed proxy operation.
An Edge Router that processes a Node Registration normally takes
over an existing registration maintained by a defendant Edge
Router.
The decision to migrate the registration from an Edge Router to
another is made by the Edge Router that processes a Node
Registration message based on its own states for that registration
and ND exchanges over the Backbone Link.
A conflict may also occur with a node that is already present on
the Backbone Link when the registration occurs, or with a node
appears on the Backbone Link while a registration already exists
for its claimed address. The resolution of such conflict is done
using standard Duplicate Address Detection as prescribed by
[RFC4862].
Upon a Node Registration message, an Edge Router looks up an existing
registration for that IPv6 address in its LoWPAN whiteboard. If the
entry does not exist then the Edge Router looks up the address over
the Backbone Link using the NS (DAD) mechanism. The Edge Router
SHOULD include an Owner Interface Identifier Option in the NS
message. An Edge Router that defends that address for an existing
registration MUST include an Owner Interface Identifier Option in the
NA message and SHOULD NOT set set the Override (O) bit.
If no entry is found for that address and DAD times out, the Edge
Router accepts the registration: it creates an entry on the
whiteboard, sends a positive Node Confirmation Message to the node,
and advertises the address on the Backbone Link. Since this happens
asynchronously to the Node Registration, the Edge Router SHOULD NOT
Shelby, et al. Expires November 29, 2009 [Page 41]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
set set Override (O) bit in the NA message.
If an entry is found in the whiteboard for the same (OII, IPv6
address) pair, additional checking is performed for duplicate OII
detection as detailed in Section 7.7. If no duplication is detected,
then the Edge Router accepts the update of the reservation: it
updates a entry on the whiteboard, sends a positive Node Confirmation
Message to the node, and advertises the address on the Backbone Link.
Since this happens synchronously to the Node Registration, the Edge
Router SHOULD set set Override (O) bit in the NA message.
If the address is already present on the Backbone Link and defended
by a remote Edge Router, then that Edge Router defends the address
with the Override (O) bit reset and the Owner Interface Identifier
Option in the NA message.
If the Edge Router receives an NA message during the DAD period, it
checks for an Owner Interface Identifier Option in the NA message.
If there is no OII or the (O) bit is set then this is a duplicate
address, DAD fails and the registration is rejected. If there is an
Owner Interface Identifier Option in the NA message and the OII is
different, then DAD fails and the registration is rejected. If the
OII is the same, additional checking is performed for duplicate OII
detection as detailed in Section 7.7. If there is no duplication
then the NA is ignored and the DAD timer keeps going.
If the Edge Router receives an NS (DAD) message from another node
during the DAD period, it checks for a Owner Interface Identifier
Option in the NS message. If there is no OII then DAD fails and the
registration is rejected. If there is an Owner Interface Identifier
Option in the NA message and the OII is different, then DAD fails and
the registration is rejected. If the OII is the same, then the
greatest TID wins. In other words, if the TID in the registration is
smaller than or equal to the TID in the OII Option then DAD fails and
the registration is rejected. Otherwise the NS is ignored and the
DAD timer keeps going.
Other Edge Routers are informed of a take over decision by an NA with
the Override (O) bit set and silently set their own state to non-
operational. An Edge Router that looses ownership should attempt to
keep the registration entry in the whiteboard till the end of the
registration lifetime for the purpose of duplicate OII detection if
memory capacity allows. The TID in the whiteboard entry is updated
with that in the OII option in the NA.
Shelby, et al. Expires November 29, 2009 [Page 42]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
7.7. Duplicate OII detection
The TID is a sequential number that is used to control the normal
operation of a registration and detect a duplicate Owner Interface
Identifier during the Neighbor Discovery operations. The TID is set
by a node in its Router Registration message and echoed by the Edge
Router in the Node Confirmation message. At least the 4 most recent
values for a TID are also kept by the edge router in the whiteboard
entry for validation purpose.
The TID is maintained using the lollipop mechanism. When a node
starts or restarts, the TID is reset to zero. After that, it is
incremented with each Node Registration. When the TID reaches its
maximum value (0xFFFF) it wraps directly to its looping value at the
base of the lollipop that is 16. So a value in the straight part of
the lollipop (between 0 and 0xF) is only used after a reboot and
before the circular part of the lollipop is entered.
Upon a positive Node Confirmation, if the current TID is less than
16, then the node sets it to 16. So a TID in the straight part
denotes a node that just started/restarted and did not get registered
yet.
To compare TID1 and TID2, the following rules apply:
If at least one of TID1 and TID2 is in the straight part of the
lollipop (smaller than 16) then they compare directly.
If both TID1 and TID2 are in the circular part then TID2 is
greater than TID1 if (TID2 - TID1) is smaller than (TID1 - TID2).
A TID value is consistent with the preceeding one if it is a small
increment or decrement (more or less 16) from it. During normal
operations, the TIDs saved in the white board entry should be
consistent. As long as a TID is consistent with the previous one, it
appears that the new message is coming from the same source as the
previous one and there is no OII collision. If the TID is a small
decrement then the registration messages crossed and that message
should be ignored, but still there's no collision.
If the TID jumps to a low value in the lollipop this can be
interpreted as either a new node competing for the OII and a reboot
by the node owning the registration. With this specification, this
situation is optimistically interpreted as a reboot and not reported
as a collision, but an actual collision will be detected and filtered
out next.
Otherwise, if an inconsistent TID value is detected between the new
Shelby, et al. Expires November 29, 2009 [Page 43]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
TID and the most recently accepted value, then the Edge Router
compares with the older TID values that are saved in the whiteboard
entry for that registration. This might occur for instance with an
entry that was rendered non-operational when the address was taken
over by another Edge Router.
If the new value is consistent with a recent value then it appears
that 2 sources are competing for the same OII and an OII collision
should be logged. In that case the greater TID wins, that is if the
new TID is greater than the previous one it is accepted, otherwise it
is reported as a collision.
If the new value is not consistent with a recent value saved in the
whiteboard entry then it is rejected as a collision.
7.8. Fault tolerance
This specification allows for a secondary registration. The
secondary registration enables the node to prepare states within the
network and make the move quicker between primary and secondary.
If an external keep alive mechanism is in place between the primary
and the secondary Edge Routers, then the secondary registration
enables the secondary Edge Router to start intercepting packets on
the backbone and forwarding them to the node before the node even
knows that the primary is no longer operational.
The secondary registration also enables the node to bicast a packet
for extra reliability, that is send a copy of a packet to both Edge
Routers without being subject to ingress filtering. The mechanism
that enables this filtering is not specified here.
8. Ad-hoc LoWPAN Operation
LoWPAN networks by nature may often work in an ad-hoc fasion, without
an infrastructure. Neighbor Discovery for 6LoWPAN may still be
applied in such ad-hoc networks.
If a LoWPAN Router in the Ad-hoc LoWPAN is configured to implement
basic edge router Whiteboard functionality and generates a ULA prefix
[RFC4193], then ND for 6LoWPAN can be applied throughout the LoWPAN
as specified in this document. There SHOULD be only one edge router
in an Ad-hoc LoWPAN (just as in a Simple LoWPAN) to keep consistancy
in the Whiteboard and ULA prefix. However if edge routers in an ad-
hoc LoWPAN are able to emulate backbone link functionality between
each other, and to coordinate the ULA prefix then there MAY be
multiple Edge Routers if they implement full Edge Router
Shelby, et al. Expires November 29, 2009 [Page 44]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
functionality.
Ad-hoc LoWPANs make use of Unique Local IPv6 Unicast Addresses (ULAs)
as defined in [RFC4193]. A ULA is made up of the prefix fc00::/7, a
global ID and a subnet ID. The global ID is randomly generated, and
in ad-hoc LoWPANs the subnet ID is not used. The edge router is
responsible for the generation of the ULA prefix to be advertised to
the LoWPAN and used by all nodes. ULA generation may use the
algorithm suggested Section 3.2.2 of [RFC4193] or something
appropriate to the Edge Router's capabilities.
9. Message Examples
This section provides basic examples of messages and options from
this document.
9.1. Basic NR/NC message exchange
In the basic case, when a host wanting to register to the whiteboard
is on the same link with an ER, a simple NR/NC message exchange
occurs. In this example a host wants to register its address
generated with SAA, and in addition requests a generated short
address.
First the Host sends an NR message to the link-local address of the
ER. In this example the host wants to use the edge router as
primary, uses a 600s lifetime, and its EUI-64 as the Owner Interface
Indentifier. The message has two Address Options. The host has just
booted, therefore the TID starts with 0.
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 = TBD | Code = 0 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TID = 0 | Status = 0 |1| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime = 600 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Interface Identifier = +
| EUI-64 of the interface |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Basic NR message.
Shelby, et al. Expires November 29, 2009 [Page 45]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
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 = TBD | Length = 1 | Status = 0 | P=2 | S=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|0| Reserved | Padding = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Address Option 1, for the SAA address.
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 = TBD | Length = 1 | Status = 0 | P=2 | S=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|0| Reserved | Padding = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Address Option 2, for the requested address.
9.2. Relaying an NR message
In case an ER is not on-link for initial node registration, then the
NR message from the previous example is sent to any on-link router in
exactly the same format. This router in turn relays the message to
an ER. As the OII of the Host is the same as its IID, the Router
simply sets Code = 1 to indicate that the message was relayed. The
destination IPv6 address is that of an edge router or the 6LOWPAN_ER
Anycast address and the source IPv6 address that of the relaying
router. The Address Options are not modified.
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 = TBD | Code = 1 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TID = 0 | Status = 0 |1| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime = 600 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Interface Identifier = +
| EUI-64 of the interface |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Shelby, et al. Expires November 29, 2009 [Page 46]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Figure 14: Relayed NR message.
9.3. Router advertisement
Routers and edge routers in LoWPAN networks periodically send RA
messages. In the following example is of an RA message sent by a
router. The only difference if an edge router would send the message
is that the Preference flag would be 01 for high.
In the example the M flag is set to indicate that an ER is available
through this router, the Preference flag is 00 for normal, and a
1200s Route Lifetime is advertised. A 6LoWPAN Prefix Information
Option is included.
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 = 134 | Code = 0 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |1|0|0|00 |Rsrvd| Router Lifetime = 1200 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: RA message example.
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 = TBD | Length = 2 | PL = 60 |0|1| CID=0 | R |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime = 3000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Prefix = 2001:DB8::/64 .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: 6LoWPAN Prefix Information Option example.
Shelby, et al. Expires November 29, 2009 [Page 47]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
10. Security Considerations
The security considerations of IPv6 Neighbor Discovery [RFC4861]
apply. Additional considerations can be found in [RFC3756].
This specification expects that the link layer is sufficiently
protected, either by means of physical or IP security for the
backbone link or MAC sublayer cryptography. In other words, model 1
from [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 RA messages. However, any future 6LoWPAN security
protocol that applies to Neighbor Discovery for 6LoWPAN protocol, is
out of scope of this document.
The use of EUI-64 for forming the Interface ID in the link local
address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
address privacy techniques. Considering the envisioned deployments
and the MAC layer security applied, this is not considered an issue
at this time.
The use of IP-level forwarding of NR/NC ND messages requires relaxed
checking of Hop Limit values in ND packets received, compared to the
validation required by [RFC4861]. This may make ND vulnerable to
off-LoWPAN senders that accidentally or intentionally send ND
messages. This specification states that Edge Routers MUST implement
measures to filter out such off-LoWPAN ND messages.
11. IANA Considerations
This document requires two new ICMPv6 message types:
Node Registration (TBD1)
Node Confirmation (TBD2)
The document also requires four new ND option types under the
subregistry "IPv6 Neighbor Discovery Option Formats":
Address Option (TBD3)
6LoWPAN Prefix Information Option (TBD4)
6LoWPAN Prefix Summary Option (TBD5)
Owner Interface Identifier Option (TBD6)
Shelby, et al. Expires November 29, 2009 [Page 48]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
[TO BE REMOVED: This registration should take place at the following
location: http://www.iana.org/assignments/icmpv6-parameters]
There is also the need for a new link local anycast address,
6LOWPAN_ER for 6LoWPAN edge routers and Routers; used as a functional
address.
[TO BE REMOVED: This registration should take place at the following
location: http://www.iana.org/assignments/ipv6-anycast-addresses]
12. Acknowledgments
Special thanks to Carsten Bormann who has provided several important
technical contributions, authored the security considerations section
along with giving extensive comments on the document.
The authors thank Geoff Mulligan, Julien Abeille, Alexandru Petrescu,
Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs and Phil
Roberts for useful discussions and comments that have helped shaped
and improve this document.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks",
RFC 2491, January 1999.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
Shelby, et al. Expires November 29, 2009 [Page 49]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
13.2. Informative References
[I-D.ietf-6lowpan-hc]
Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams in 6LoWPAN Networks", draft-ietf-6lowpan-hc-04
(work in progress), December 2008.
[I-D.van-beijnum-multi-mtu]
Beijnum, I., "Extensions for Multi-MTU Subnets",
draft-van-beijnum-multi-mtu-02 (work in progress),
February 2008.
[RFC2022] Armitage, G., "Support for Multicast over UNI 3.0/3.1
based ATM Networks", RFC 2022, November 1996.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
Shelby, et al. Expires November 29, 2009 [Page 50]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, August 2007.
Authors' Addresses
Zach Shelby (editor)
Sensinode
Hallituskatu 13-17D
Oulu 90100
FINLAND
Phone: +358407796297
Email: zach@sensinode.com
Pascal Thubert
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE
Phone: +33 4 97 23 26 34
Email: pthubert@cisco.com
Jonathan W. Hui
Arch Rock Corporation
501 2nd St. Ste. 410
San Francisco, California 94107
USA
Phone: +415 692 0828
Email: jhui@archrock.com
Shelby, et al. Expires November 29, 2009 [Page 51]
Internet-Draft Neighbor Discovery for 6LoWPAN May 2009
Samita Chakrabarti
IP Infusion
1188 Arquest Street
Sunnyvale, California
USA
Phone:
Email: samitac@ipinfusion.com
Erik Nordmark
Sun Microsystems
17 Network Circle
Menlo Park, California 94025
USA
Phone:
Email: Erik.Nordmark@Sun.COM
Shelby, et al. Expires November 29, 2009 [Page 52]
