Internet DRAFT - draft-ietf-6lowpan-nd
draft-ietf-6lowpan-nd
6LoWPAN Working Group Z. Shelby, Ed.
Internet-Draft Sensinode
Updates: 4944 (if approved) S. Chakrabarti
Intended status: Standards Track Ericsson
Expires: February 25, 2013 E. Nordmark
Cisco Systems
August 24, 2012
Neighbor Discovery Optimization for Low Power and Lossy Networks
(6LoWPAN)
draft-ietf-6lowpan-nd-21
Abstract
The IETF 6LoWPAN work defines IPv6 over Low-power Wireless Personal
Area Networks such as IEEE 802.15.4. This and other similar link
technologies have limited or no usage of multicast signaling due to
energy conservation. In addition, the wireless network may not
strictly follow the traditional concept of IP subnets and IP links.
IPv6 Neighbor Discovery was not designed for non-transitive wireless
links, as its reliance on the traditional IPv6 link concept and its
heavy use of multicast make it inefficient and sometimes impractical
in a low-power and lossy network. This document describes simple
optimizations to IPv6 Neighbor Discovery, its addressing mechanisms
and duplicate address detection for Low-power Wireless Personal Area
Networks and similar networks. The document thus updates RFC 4944 to
specify the use of the optimizations defined here.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 25, 2013.
Copyright Notice
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Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. The Shortcomings of IPv6 Neighbor Discovery . . . . . . . 5
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Goals and Assumptions . . . . . . . . . . . . . . . . . . 6
1.4. Substitutable Features . . . . . . . . . . . . . . . . . . 8
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Extensions to RFC4861 . . . . . . . . . . . . . . . . . . 11
3.2. Address Assignment . . . . . . . . . . . . . . . . . . . . 12
3.3. Host-to-Router Interaction . . . . . . . . . . . . . . . . 12
3.4. Router-to-Router Interaction . . . . . . . . . . . . . . . 13
3.5. Neighbor Cache Management . . . . . . . . . . . . . . . . 14
4. New Neighbor Discovery Options and Messages . . . . . . . . . 15
4.1. Address Registration Option . . . . . . . . . . . . . . . 15
4.2. 6LoWPAN Context Option . . . . . . . . . . . . . . . . . . 17
4.3. Authoritative Border Router Option . . . . . . . . . . . . 18
4.4. Duplicate Address messages . . . . . . . . . . . . . . . . 20
5. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 21
5.2. Interface Initialization . . . . . . . . . . . . . . . . . 21
5.3. Sending a Router Solicitation . . . . . . . . . . . . . . 22
5.4. Processing a Router Advertisement . . . . . . . . . . . . 22
5.4.1. Address configuration . . . . . . . . . . . . . . . . 23
5.4.2. Storing Contexts . . . . . . . . . . . . . . . . . . . 23
5.4.3. Maintaining Prefix and Context Information . . . . . . 23
5.5. Registration and Neighbor Unreachability Detection . . . . 24
5.5.1. Sending a Neighbor Solicitation . . . . . . . . . . . 24
5.5.2. Processing a Neighbor Advertisement . . . . . . . . . 25
5.5.3. Recovering from Failures . . . . . . . . . . . . . . . 25
5.6. Next-hop Determination . . . . . . . . . . . . . . . . . . 26
5.7. Address Resolution . . . . . . . . . . . . . . . . . . . . 26
5.8. Sleeping . . . . . . . . . . . . . . . . . . . . . . . . . 26
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5.8.1. Picking an Appropriate Registration Lifetime . . . . . 27
5.8.2. Behavior on Wakeup . . . . . . . . . . . . . . . . . . 27
6. Router Behavior for 6LR and 6LBR . . . . . . . . . . . . . . . 27
6.1. Forbidden Actions . . . . . . . . . . . . . . . . . . . . 28
6.2. Interface Initialization . . . . . . . . . . . . . . . . . 28
6.3. Processing a Router Solicitation . . . . . . . . . . . . . 28
6.4. Periodic Router Advertisements . . . . . . . . . . . . . . 29
6.5. Processing a Neighbor Solicitation . . . . . . . . . . . . 30
6.5.1. Checking for Duplicates . . . . . . . . . . . . . . . 30
6.5.2. Returning Address Registration Errors . . . . . . . . 30
6.5.3. Updating the Neighbor Cache . . . . . . . . . . . . . 31
6.5.4. Next-hop Determination . . . . . . . . . . . . . . . . 31
6.5.5. Address Resolution between Routers . . . . . . . . . . 31
7. Border Router Behavior . . . . . . . . . . . . . . . . . . . . 32
7.1. Prefix Determination . . . . . . . . . . . . . . . . . . . 33
7.2. Context Configuration and Management . . . . . . . . . . . 33
8. Substitutable Feature Behavior . . . . . . . . . . . . . . . . 34
8.1. Multihop Prefix and Context Distribution . . . . . . . . . 34
8.1.1. 6LBRs Sending Router Advertisements . . . . . . . . . 34
8.1.2. Routers Sending Router Solicitations . . . . . . . . . 35
8.1.3. Routers Processing Router Advertisements . . . . . . . 35
8.1.4. Storing the Information . . . . . . . . . . . . . . . 35
8.1.5. Sending Router Advertisements . . . . . . . . . . . . 36
8.2. Multihop Duplicate Address Detection . . . . . . . . . . . 36
8.2.1. Message Validation for DAR and DAC . . . . . . . . . . 38
8.2.2. Conceptual Data Structures . . . . . . . . . . . . . . 39
8.2.3. 6LR Sending a Duplicate Address Request . . . . . . . 39
8.2.4. 6LBR Receiving a Duplicate Address Request . . . . . . 39
8.2.5. Processing a Duplicate Address Confirmation . . . . . 40
8.2.6. Recovering from Failures . . . . . . . . . . . . . . . 40
9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 40
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.1. Message Examples . . . . . . . . . . . . . . . . . . . . . 41
10.2. Host Bootstrapping Example . . . . . . . . . . . . . . . . 43
10.2.1. Host Bootstrapping Messages . . . . . . . . . . . . . 44
10.3. Router Interaction Example . . . . . . . . . . . . . . . . 47
10.3.1. Bootstrapping a Router . . . . . . . . . . . . . . . . 47
10.3.2. Updating the Neighbor Cache . . . . . . . . . . . . . 47
11. Security Considerations . . . . . . . . . . . . . . . . . . . 48
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49
13. Interaction with other Neighbor Discovery Extensions . . . . . 50
14. Guideline for New Features . . . . . . . . . . . . . . . . . . 50
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 52
16. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 52
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 59
17.1. Normative References . . . . . . . . . . . . . . . . . . . 59
17.2. Informative References . . . . . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 61
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1. Introduction
The IPv6-over-IEEE 802.15.4 [RFC4944] document specifies how IPv6 is
carried over an IEEE 802.15.4 network with the help of an adaptation
layer which sits between the MAC layer and the IP network layer. A
link in a Low-power Wireless Personal Area Network (LoWPAN) is
characterized as lossy, low-power, low bit-rate, short range, with
many nodes saving energy with long sleep periods. Multicast as used
in IPv6 Neighbor Discovery [RFC4861] is not desirable in such a
wireless low-power and lossy network. Moreover, LoWPAN links are
asymmetric and non-transitive in nature. A LoWPAN is potentially
composed of a large number of overlapping radio ranges. Although a
given radio range has broadcast capabilities, the aggregation of
these is a complex Non-Broadcast MultiAccess (NBMA, [RFC2491])
structure with generally no LoWPAN-wide multicast capabilities.
Link-local scope is in reality defined by reachability and radio
strength. Thus we can consider a LoWPAN to be made up of links with
undetermined connectivity properties as in [RFC5889], along with the
corresponding address model assumptions defined therein.
This specification introduces the following optimizations to IPv6
Neighbor Discovery [RFC4861] specifically aimed at low-power and
lossy networks such as LoWPANs:
o Host-initiated interactions to allow for sleeping hosts.
o Elimination of multicast-based address resolution for hosts.
o A host address registration feature using a new option in unicast
Neighbor Solicitation and Neighbor Advertisement messages.
o A new optional Neighbor Discovery option to distribute 6LoWPAN
header compression context to hosts.
o Multihop distribution of prefix and 6LoWPAN header compression
context.
o Multihop duplicate address detection which uses two new ICMPv6
message types.
The two multihop items can be substituted by a routing protocol
mechanism if that is desired, see Section 1.4.
The document defines three new ICMPv6 message options: the Address
Registration, Authoritative Border Router, and 6LoWPAN Context
options. It also defines two new ICMPv6 message types: the Duplicate
Address Request and Duplicate Address Confirmation.
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1.1. The Shortcomings of IPv6 Neighbor Discovery
IPv6 Neighbor Discovery [RFC4861] provides several important
mechanisms used for Router Discovery, Address Resolution, Duplicate
Address Detection, Redirect, along with 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. If the host
receives a valid Router Advertisement with the "A" flag, it
autoconfigures the IPv6 address with the advertised prefix in the
Router Advertisement (RA) message. Besides this, the IPv6 routers
usually send router advertisements periodically on the network. RAs
are sent to the all-node multicast address. Nodes send Neighbor
Solicitation/Neighbor Advertisement messages to resolve the IPv6
address of the destination on the link. The Neighbor Solicitation
messages used for address resolution are multicast. The Duplicate
Address Detection procedure and the use of periodic Router
Advertisement messages assumes that the nodes are powered on and
reachable most of the time.
In Neighbor Discovery the routers find the hosts by assuming that a
subnet prefix maps to one broadcast domain, and then multicast
Neighbor Solicitation messages to find the host and its link-layer
address. Furthermore, the DAD use of multicast assumes that all
hosts that autoconfigure IPv6 addresses from the same prefix can be
reached using link-local multicast messages.
Note that the 'L' (on-link) bit in the Prefix Information option can
be set to zero in Neighbor Discovery, which makes the host not use
multicast Neighbor Solicitation (NS) messages for address resolution
of other hosts, but routers still use multicast NS messages to find
the hosts.
Due to the lossy nature of wireless communication and a changing
radio environment, the IPv6-link node-set may change due to external
physical factors. Thus the link is often unstable and the nodes
appear to be moving without necessarily moving physically.
A LoWPAN can use two types of link-layer addresses; 16-bit short
addresses and 64-bit unique addresses as defined in [RFC4944].
Moreover, the available link-layer payload size is on the order of
less than 100 bytes thus header compression is very useful.
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Considering the above characteristics in a LoWPAN, and the IPv6
Neighbor Discovery [RFC4861] protocol design, some optimizations and
extensions to Neighbor Discovery are useful for the wide deployment
of IPv6 over low-powered and lossy networks (example: 6LoWPAN and
other homogeneous low-power networks).
1.2. Applicability
In its Section 1, [RFC4861] foresees a document that covers operating
IP over a particular link type and defines an exception to the
otherwise general applicability of unmodified [RFC4861]. The present
specification improves the usage of IPv6 Neighbor Discovery for
LoWPANs in order to save energy and processing power of such nodes.
The document, thus updates [RFC4944] to specify the use of the
optimizations defined here.
The applicability of this specification is limited to LoWPANs where
all nodes on the subnet implement these optimizations in a
homogeneous way. Although it is noted that some of these
optimizations may be useful outside of 6LoWPAN, for example in
general IPv6 low-power and lossy networks and possibly even in
combination with [RFC4861], the usage of such combinations is out of
scope of this document.
In this document, we specify a set of behaviors between hosts and
routers in LoWPANs. An implementation that adheres to this document
MUST implement those behaviors. The document also specifies a set of
behaviors (multihop prefix or context dissemination, and separately
multihop duplicate address detection) which are needed in route-over
configurations. An implementation of this specification MUST support
those pieces, unless the implementation supports some alternative
("substitute") from some some other specification.
The optimizations described in this document apply to different
topologies. They are most useful for route-over and mesh-under
configurations in Mesh topologies. However, Star topology
configurations will also benefit from the optimizations due to
reduced signaling, robust handling of the non-transitive link, and
header compression context information.
1.3. Goals and Assumptions
The document has the following main goals and assumptions.
Goals:
o Optimize Neighbor Discovery with a mechanism that is minimal yet
sufficient for the operation in both mesh-under and route-over
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configurations.
o Minimize signaling by avoiding the use of multicast flooding and
reducing the use of link-scope multicast messages.
o Optimize the interfaces between hosts and their default routers.
o Support for sleeping hosts.
o Disseminate context information to hosts as needed by 6LoWPAN
Header Compression [RFC6282].
o Disseminate context information and prefix information from the
border to all routers in a LoWPAN.
o Multihop duplicate address detection mechanism suitable for route-
over LoWPANs.
Assumptions:
o EUI-64 addresses are globally unique and the LoWPAN is
homogeneous.
o All nodes in the network have an EUI-64 interface identifier in
order to do address auto-configuration and detect duplicate
addresses.
o The link layer technology is assumed to be low-power and lossy,
exhibiting undetermined connectivity, such as IEEE 802.15.4
[RFC4944]. However, the Address Registration mechanism might be
useful for other link layer technologies.
o A 6LoWPAN is configured to share one or more global IPv6 address
prefixes to enable hosts to move between routers in the LoWPAN
without changing their IPv6 addresses.
o When using the multihop DAD mechanism of Section 8.2 each 6LR
registers with all the 6LBRs available in the LoWPAN.
o If IEEE 802.15.4 16-bit short addresses are used, then some
technique is used to ensure uniqueness of those link-layer
addresses. That could be done using DHCPv6, the Address
Registration Option based duplicate address detection (specified
in Section 8.2) or other techniques outside of the scope of this
document.
o In order to preserve the uniqueness of addresses (see Section 5.4,
[RFC4862]) not derived from an EUI-64, they must be either
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assigned or checked for duplicates in the same way throughout the
LoWPAN. This can be done using DHCPv6 for assignment and/or using
the duplicate address detection mechanism specified in Section 8.2
(or any other protocols developed for that purpose).
o In order for 6LoWPAN Header Compression [RFC6282] to operate
correctly, the compression context must match for all the hosts,
6LRs, and 6LBRs that can send, receive, or forward a given packet.
If Section 8.1 is used to distribute context information this
implies that all the 6LBRs must coordinate the context information
they distribute within a single LoWPAN.
o This specification describes the operation of ND within a single
LoWPAN. The participation of a node in multiple LoWPANs
simultaneously may be possible, but is out of scope of this
document.
o Since the LoWPAN shares its prefix(es) throughout the network,
mobility of nodes within the LoWPAN is transparent. Inter-LoWPAN
mobility is out-of-scope of this document.
1.4. Substitutable Features
This document defines the optimization of Neighbor Discovery messages
for the host-router interface and introduces two new mechanisms in a
Route-over topology.
Unless specified otherwise (in a document that defines a routing
protocol that is used in a 6LoWPAN) this document applies to networks
with any routing protocol. However, because the routing protocol may
provide good alternate mechanisms, this document defines certain
features as "substitutable", meaning they can be substituted by a
routing protocol specification that provides mechanisms achieving the
same overall effect.
The features that are substitutable (individually or in a group):
o Multihop distribution of prefix and 6LoWPAN header compression
context
o Multihop duplicate address detection
Thus Multihop prefix distribution (ABRO option) and 6LoWPAN Context
Option (6CO, for distributing Header Compression Contexts) go hand-
in-hand. If substitution is intended for one of them, then both of
them MUST be substituted.
A guideline for feature implementation and deployment is provided at
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the end of the document.
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 "Neighbor Discovery for IP version
6" [RFC4861] "IPv6 Stateless Address Autoconfiguration" [RFC4862],
"IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
"Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944]
and "IP Addressing Model in Ad Hoc Networks" [RFC5889].
This specification makes extensive use of the same terminology
defined in [RFC4861] unless otherwise defined below.
6LoWPAN link:
A wireless link determined by single IP hop reachability of
neighboring nodes. These are considered links with undetermined
connectivity properties as in [RFC5889].
6LoWPAN Node (6LN):
A 6LoWPAN Node is any host or router participating in a LoWPAN.
This term is used when referring to situations in which either a
host or router can play the role described.
6LoWPAN Router (6LR):
An intermediate router in the LoWPAN that is able to send and
receive Router Advertisements, Router Solicitations as well as
forward and route IPv6 packets. 6LoWPAN routers are present only
in route-over topologies.
6LoWPAN Border Router (6LBR):
A border router located at the junction of separate 6LoWPAN
networks or between a 6LoWPAN network and another IP network.
There may be one or more 6LBRs at the 6LoWPAN network boundary. A
6LBR is the responsible authority for IPv6 Prefix propagation for
the 6LoWPAN network it is serving. An isolated LoWPAN also
contains a 6LBR in the network, which provides the prefix(es) for
the isolated network.
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Router:
Either a 6LR or a 6LBR. Note that nothing in this document
precludes a node being a router on some interfaces and a host on
other interfaces as allowed by [RFC2460].
Mesh-under:
A topology where nodes are connected to a 6LBR through a mesh
using link-layer forwarding. Thus in a mesh-under configuration
all IPv6 hosts in a LoWPAN are only one IP hop away from the 6LBR.
This topology simulates the typical IP-subnet topology with one
router with multiple nodes in the same subnet.
Route-over:
A topology where hosts are connected to the 6LBR through the use
of intermediate layer-3 (IP) routing. Here hosts are typically
multiple IP hops away from a 6LBR. The route-over topology
typically consists of a 6LBR, a set of 6LRs and hosts.
Non-Transitive Link:
A link which exhibits asymmetric reachability as defined in
Section 2.2 of [RFC4861].
IP-over-foo Document:
A specification that covers operating IP over a particular link
type, for example [RFC4944] "Transmission of IPv6 Packets over
IEEE 802.15.4 Networks".
Header Compression Context:
Address information shared across a LoWPAN and used by 6LoWPAN
Header Compression [RFC6282] to enable the elision of information
that would otherwise be sent repeatedly. In a "context", a
(potentially partial) address is associated with a Context
Identifier, which is then used in header compression as a shortcut
for (parts of) a source or destination address.
Registration:
The process during which a LoWPAN node sends an Neighbor
Solicitation message with an Address Registration option to a
Router creating a Neighbor Cache entry for the LoWPAN node with a
specific timeout. Thus for 6LoWPAN Routers the Neighbor Cache
doesn't behave like a cache. Instead it behaves as a registry of
all the host addresses that are attached to the Router.
3. Protocol Overview
These Neighbor Discovery optimizations are applicable to both mesh-
under and route-over configurations. In a mesh-under configuration
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only 6LoWPAN Border Routers and hosts exist; there are no 6LoWPAN
routers in mesh-under topologies.
The most important part of the optimizations is the evolved host-to-
router interaction that allows for sleeping nodes and avoids using
multicast Neighbor Discovery messages except for the case of a host
finding an initial set of default routers, and redoing such
determination when that set of routers have become unreachable.
The protocol also provides for header compression [RFC6282] by
carrying header compression information in a new option in Router
Advertisement messages.
In addition, there are separate mechanisms that between 6LRs and
6LBRs to perform multihop Duplicate Address Detection and
distribution of the Prefix and compression Context information from
the 6LBRs to all the 6LRs, which in turn use normal Neighbor
Discovery mechanisms to convey this information to the hosts.
The protocol is designed so that the host-to-router interaction is
not affected by the configuration of the 6LoWPAN; the host-to-router
interaction is the same in a mesh-under and route-over configuration.
3.1. Extensions to RFC4861
This document specifies the following optimizations and extensions to
IPv6 Neighbor Discovery [RFC4861]:
o Host initiated refresh of Router Advertisement information. This
removes the need for periodic or unsolicited Router Advertisements
from routers to hosts.
o No Duplicate Address Detection (DAD) is performed if EUI-64 based
IPv6 addresses are used (as these addresses are assumed to be
globally unique).
o DAD is optional if DHCPv6 is used to assign addresses.
o A New Address Registration mechanism using a new Address
Registration option between hosts and routers. This removes the
need for Routers to use multicast Neighbor Solicitations to find
hosts, and supports sleeping hosts. This also enables the same
IPv6 address prefix(es) to be used across a route-over 6LoWPAN.
It provides the host-to-router interface for Duplicate Address
Detection.
o A new Router Advertisement option for Context information used by
6LoWPAN header compression.
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o A new mechanism to perform Duplicate Address Detection across a
route-over 6LoWPAN using the new Duplicate Address Request and
Confirmation messages.
o New mechanisms to distribute Prefixes and Context information
across a route-over network which uses a new Authoritative Border
Router option to control the flooding of configuration changes.
o A few new default protocol constants are introduced and some
existing Neighbor Discovery protocol constants are tuned.
3.2. Address Assignment
Hosts in a 6LoWPAN configure their IPv6 address as specified in
[RFC4861] and [RFC4862] based on the information received in Router
Advertisement messages. The use of the M flag in this optimization
is however more restrictive than in [RFC4861]. When the M flag is
set a host is assumed to use DHCPv6 to assign any non-EUI-64
addresses. When the M flag is not set, the nodes in the LoWPAN
support duplicate address detection, thus a host can then safely use
the address registration mechanism to check non-EUI-64 addresses for
uniqueness.
6LRs MAY use the same mechanisms to configure their IPv6 addresses.
The 6LBRs are responsible for managing the prefix(es) assigned to the
6LoWPAN, using manual configuration, DHCPv6 Prefix Delegation
[RFC3633], or other mechanisms. In an isolated LoWPAN a ULA
[RFC4193] prefix SHOULD be generated by the 6LBR.
3.3. Host-to-Router Interaction
A host sends Router Solicitation messages at startup and also when
Neighbor Unreachability Detection towards one of its default routers
fails.
Hosts receive Router Advertisement messages typically containing the
Authoritative Border Router option (ABRO) and may optionally contain
one or more 6LoWPAN Context options (6CO) in addition to the existing
Prefix Information options (PIO) as described in [RFC4861].
When a host has configured a non-link-local IPv6 address, it
registers that address with one or more of its default routers using
the Address Registration option (ARO) in an NS message. The host
chooses a lifetime of the registration and repeats the ARO option
periodically (before the lifetime runs out) to maintain the
registration. The lifetime should be chosen in such a way as to
maintain the registration even while a host is sleeping. Likewise,
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mobile nodes that change their point of attachment often, should use
a suitably short lifetime. See Section 5.5 for registration details
and Section 9 for protocol constants.
The registration fails when an ARO option is returned to the host
with a non-zero Status. One reason may be that the router determines
that the IPv6 address is already used by another host, that is, is
used by a host with a different EUI-64. This can be used to support
non-EUI-64 based addresses such as temporary IPv6 addresses [RFC4941]
or addresses based on an Interface ID that is a IEEE 802.15.4 16-bit
short addresses. Failure can also occur if the Neighbor Cache on
that router is full.
The re-registration of an address can be combined with Neighbor
Unreachability Detection (NUD) of the router since both use unicast
Neighbor Solicitation messages. This makes things efficient when a
host wakes up to send a packet and both need to perform NUD to check
that the router is still reachable, and refresh its registration with
the router.
The response to an address registration might not be immediate since
in route-over configurations the 6LR might perform Duplicate Address
Detection against the 6LBR. A host retransmits the Address
Registration option until it is acknowledged by the receipt of a
Address Registration option.
As part of the optimizations, Address Resolution is not performed by
multicasting Neighbor Solicitation messages as in [RFC4861].
Instead, the routers maintain Neighbor Cache entries for all
registered IPv6 addresses. If the address is not in the Neighbor
Cache in the router, then the address either doesn't exist, or is
assigned to a host attached to some other router in the 6LoWPAN, or
is external to the 6LoWPAN. In a route-over configuration the
routing protocol is used to route such packets toward the
destination.
3.4. Router-to-Router Interaction
The new router-to-router interaction is only for the route-over
configuration where 6LRs are present. See also Section 1.4.
6LRs MUST act like a host during system startup and prefix
configuration by sending Router Solicitation messages and
autoconfiguring their IPv6 addresses unlike routers in [RFC4861].
When multihop prefix and context dissemination are used then the 6LRs
store the ABRO, 6CO and Prefix Information received (directly or
indirectly) from the 6LBRs and redistribute this information in the
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Router Advertisement they send to other 6LRs or send to hosts in
response to a Router Solicitations. There is a version number field
in the ABRO which is used to limit the flooding of updated
information between the 6LRs.
A 6LR can perform Duplicate Address Detection against one or more
6LBRs using the new Duplicate Address Request (DAR) and Confirmation
(DAC) messages, which carry the information from the Address
Registration option. The DAR and DAC messages will be forwarded
between the 6LR and 6LBRs thus the [RFC4861] rule for checking hop
limit=255 does not apply to the DAR and DAC messages. Those multihop
DAD messages MUST NOT modify any Neighbor Cache entries on the
routers since we do not have the security benefits provided by the
hop limit=255 check.
3.5. Neighbor Cache Management
The use of explicit registrations with lifetimes plus the desire to
not multicast Neighbor Solicitation messages for hosts imply that we
manage the Neighbor Cache entries (NCE) slightly differently than in
[RFC4861]. This results in three different types of NCEs and the
types specify how those entries can be removed:
Garbage-collectible: Entries that are subject to the normal rules in
[RFC4861] that allow for garbage collection
when low on memory.
Registered: Entries that have an explicit registered
lifetime and are kept until this lifetime
expires or they are explicitly unregistered.
Tentative: Entries that are temporary with a short
lifetime, which typically get converted to
Registered entries.
Note that the type of the NCE is orthogonal to the states specified
in [RFC4861].
When a host interacts with a router by sending Router Solicitations
this results in a Tentative NCE. Once a router has successfully had
a node register with it, the result is a Registered NCE. When
Routers send RAs to hosts, and when routers receive RA messages or
receive multicast NS messages from other Routers, the result is
Garbage-collectible NCEs. There can only be one kind of NCE for an
IP address at a time.
Neighbor Cache entries on Routers can additionally be added or
deleted by a routing protocol used in the 6LoWPAN. This is useful if
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the routing protocol carries the link-layer addresses of the
neighboring routers. Depending on the details of such routing
protocols such NCEs could be either Registered or Garbage-
collectible.
4. New Neighbor Discovery Options and Messages
This section defines new Neighbor Discovery message options used by
this specification. The Address Registration Option is used by
hosts, whereas the Authoritative Border Router Option and 6LoWPAN
Context Option are used in the substitable router-to-router
interaction. This section also defines the new router-to-router
Duplicate Address Request and Confirmation messages.
4.1. Address Registration Option
The routers need to know the set of host IP addresses that are
directly reachable and their corresponding link-layer addresses.
This needs to be maintained as the radio reachability changes. For
this purpose an Address Registration Option (ARO) is introduced,
which can be included in unicast Neighbor Solicitation (NS) messages
sent by hosts. Thus it can be included in the unicast NS messages
that a host sends as part of Neighbor Unreachability Detection to
determine that it can still reach a default router. The ARO is used
by the receiving router to reliably maintain its Neighbor Cache. The
same option is included in corresponding Neighbor Advertisement (NA)
messages with a Status field indicating the success or failure of the
registration. This option is always host initiated.
The information contained in the ARO is also included in the multihop
DAR and DAC messages used between 6LRs to 6LBRs, but the option
itself is not used in those messages.
The ARO is required for reliability and power saving. The lifetime
field provides flexibility to the host to register an address which
should be usable (continue to be advertised by the 6LR in the routing
protocol etc.) during its intended sleep schedule.
The sender of the NS also includes the EUI-64 [EUI64] of the
interface it is registering an address from. This is used as a
unique ID for the detection of duplicate addresses. It is used to
tell the difference between the same node re-registering its address
and a different node (with a different EUI-64) registering an address
that is already in use by someone else. The EUI-64 is also used to
deliver an NA carrying an error Status code to the EUI-64 based link-
local IPv6 address of the host (see Section 6.5.2).
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When the ARO is used by hosts an SLLA (Source Link-layer Address)
option [RFC4861] MUST be included and the address that is to be
registered MUST be the IPv6 source address of the Neighbor
Solicitation message.
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 = 2 | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ EUI-64 +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: TBD1
Length: 8-bit unsigned integer. The length of the option in
units of 8 bytes. Always 2.
Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in
NS messages. See below.
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Registration Lifetime: 16-bit unsigned integer. The amount of time
in a unit of 60 seconds that the router should retain
the Neighbor Cache entry for the sender of the NS that
includes this option.
EUI-64: 64 bits. This field is used to uniquely identify the
interface of the registered address by including the
EUI-64 identifier [EUI64] assigned to it unmodified.
The Status values used in Neighbor Advertisements are:
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+--------+--------------------------------------------+
| Status | Description |
+--------+--------------------------------------------+
| 0 | Success |
| 1 | Duplicate Address |
| 2 | Neighbor Cache Full |
| 3-255 | Allocated using Standards Action [RFC5226] |
+--------+--------------------------------------------+
Table 1
4.2. 6LoWPAN Context Option
The optional 6LoWPAN Context Option (6CO) carries prefix information
for LoWPAN header compression, and is similar to the Prefix
Information Option of [RFC4861]. However, the prefixes can be remote
as well as local to the LoWPAN since header compression potentially
applies to all IPv6 addresses. This option allows for the
dissemination of multiple contexts identified by a Context Identifier
(CID) for use as specified in [RFC6282]. A context may be a prefix
of any length or an address (/128), and up to 16 6LoWPAN Context
options may be carried in an Router Advertisement message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Context Length | Res |C| CID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Context Prefix .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: 6LoWPAN Context Option format
Type: TBD2
Length: 8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 bytes. May be 2 or 3
depending on the length of the Context Prefix field.
Context Length: 8-bit unsigned integer. The number of leading bits
in the Context Prefix field that are valid. The value ranges from
0 to 128. If it is more than 64 then the Length MUST be 3.
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C: 1-bit context compression flag. This flag indicates if the
context is valid for use in compression. A context that is not
valid MUST NOT be used for compression, but SHOULD be used in
decompression in case another compressor has not yet received the
updated context information. This flag is used to manage the
context lifecycle based on the recommendations in Section 7.2.
CID: 4-bit Context Identifier for this prefix information. CID is
used by context based header compression specified in [RFC6282].
The list of CIDs for a LoWPAN is configured by on the 6LBR that
originates the context information for the 6LoWPAN.
Res, Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Valid Lifetime: 16-bit unsigned integer. The length of time in a
unit of 60 seconds (relative to the time the packet is received)
that the context is valid for the purpose of header compression or
decompression. A value of all zero bits (0x0) indicates that this
context entry MUST be removed immediately.
Context Prefix: The IPv6 prefix or address corresponding to the
Context ID (CID) field. The valid length of this field is
included in the Context Length field. This field is padded with
zeros in order to make the option a multiple of 8-bytes.
4.3. Authoritative Border Router Option
The Authoritative Border Router Option (ABRO) is needed when Router
Advertisement (RA) messages are used to disseminate prefixes and
context information across a route-over topology. In this case 6LRs
receive Prefix Information options from other 6LRs. This implies
that a 6LR can't just let the most recently received RA win. In
order to be able to reliably add and remove prefixes from the 6LoWPAN
we need to carry information from the authoritative 6LBR. This is
done by introducing a version number which the 6LBR sets and 6LRs
propagate as they propagate the prefix and context information with
this Authoritative Border Router Option. When there are multiple
6LBRs they would have separate version number spaces. Thus this
option needs to carry the IP address of the 6LBR that originated that
set of information.
The Authoritative Border Router option MUST be included in all Router
Advertisement messages in the case when Router Advertisements are
used to propagate information between routers (as described in
Section 8.2).
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length = 3 | Version Low |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version High | Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ 6LBR Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: TBD3
Length: 8-bit unsigned integer. The length of the option in
units of 8 bytes. Always 3.
Version Low, Version High: Together, Version Low and Version High
are a 32-bit unsigned integer, where Version Low is
the least significant 16 bits and Version High is the
most significant 16 bits. The version number
corresponding to this set of information contained in
the RA message. The authoritative 6LBR originating
the prefix increases this version number each time its
set of prefix or context information changes.
Valid Lifetime: 16-bit unsigned integer. The length of time in a
unit of 60 seconds (relative to the time the packet is
received) that this set of border router information
is valid. A value of all zero bits (0x0) assumes a
default value of 10,000 (~ one week).
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
6LBR Address: IPv6 address of the 6LBR that is the origin of the
included version number.
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4.4. Duplicate Address messages
For the multihop DAD exchanges between 6LR and 6LBR specified in
Section 8.2 there are two new ICMPv6 message types called the
Duplicate Address Request (DAR) and Duplicate Address Confirmation
(DAC). We avoid reusing the Neighbor Solicitation and Neighbor
Advertisement messages for this purpose since these messages are not
subject to the hop limit=255 check as they are forwarded by
intermediate 6LRs. The information contained in the messages are
otherwise the same as would be in a Neighbor Solicitation carrying a
Address Registration option, with the message format inlining the
fields that are in the ARO.
The DAR and DAC use the same message format with different ICMPv6
type values, and the Status field is only meaningful in the DAC
message.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status | Reserved | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ EUI-64 +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Registered Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IP fields:
IPv6 source: A non link-local address of the sending router.
IPv6 destination: A non link-local address of the sending router.
In a DAC this is just the source from the DAR.
Hop Limit: Set to MULTIHOP_HOPLIMIT on transmit. MUST be ignored
on receipt.
ICMP Fields:
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Type: TBD4 for DAR and TBD5 for DAC
Code: Set to zero on transmit. MUST be ignored on receipt.
Checksum: The ICMP checksum. See [RFC4443].
Status: 8-bit unsigned integer. Indicates the status of a
registration in the DAC. MUST be set to 0 in DAR.
See Table 1.
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
Registration Lifetime: 16-bit unsigned integer. The amount of time
in a unit of 60 seconds that the router should retain
the Neighbor Cache entry for the sender of the NS that
includes this option. A value of 0 indicates in an NS
that the neighbor cache entry should be removed.
EUI-64: 64 bits. This field is used to uniquely identify the
interface of the registered address by including the
EUI-64 identifier [EUI64] assigned to it unmodified.
Registered Address: 128-bit field. Carries the host address, which
was contained in the IPv6 Source field in the NS that
contained the ARO option sent by the host.
5. Host Behavior
Hosts in a LoWPAN use the Address Registration option in the Neighbor
Solicitation messages they send as a way to maintain the Neighbor
Cache in the routers thereby removing the need for multicast Neighbor
Solicitations to do address resolution. Unlike in [RFC4861] the
hosts initiate updating the information they receive in Router
Advertisements by sending Router Solicitations before the information
expires. Finally, when Neighbor Unreachability Detection indicates
that one or all default routers have become unreachable, then the
host uses Router Solicitations to find a new set of default routers.
5.1. Forbidden Actions
A host MUST NOT multicast a Neighbor Solicitation message.
5.2. Interface Initialization
When the interface on a host is initialized it follows the
specification in [RFC4861]. A link-local address is formed based on
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the EUI-64 identifier [EUI64] assigned to the interface as per
[RFC4944] or the appropriate IP-over-foo document for the link, and
then the host sends Router Solicitation messages as described in
[RFC4861] Section 6.3.7.
There is no need to join the Solicited-Node multicast address since
nobody multicasts Neighbor Solicitations in this type of network. A
host MUST join the all-nodes multicast address.
5.3. Sending a Router Solicitation
The Router Solicitation is formatted as specified in [RFC4861] and
sent to the IPv6 All-Routers multicast address (see [RFC4861] Section
6.3.7 for details). An SLLA option MUST be included to enable
unicast Router Advertisements in response. An unspecified source
address MUST NOT be used in RS messages.
If the link layer supports a way to send packets to some kind of all-
routers anycast link-layer address, then that MAY be used to convey
these packets to a router.
Since hosts do not depend on multicast Router Advertisements to
discover routers, the hosts need to intelligently retransmit Router
Solicitations whenever the default router list is empty, one of its
default routers becomes unreachable, or the lifetime of the prefixes
and contexts in the previous RA are about to expire. The RECOMMENDED
retransmissions is to initially send up to 3 (MAX_RTR_SOLICITATIONS)
RS messages separated by at least 10 seconds
(RTR_SOLICITATION_INTERVAL) as specified in [RFC4861], and then
switch to slower retransmissions. After the initial retransmissions
the host SHOULD do truncated binary exponential backoff [ETHERNET] of
the retransmission timer for each subsequent retransmission,
truncating the increase of the retransmission timer at 60 seconds
(MAX_RTR_SOLICITATION_INTERVAL). In all cases the RS retransmissions
are terminated when a RA is received. See Section 9 for protocol
constants.
5.4. Processing a Router Advertisement
The processing of Router Advertisements is as in [RFC4861] with the
addition of handling the 6LoWPAN Context option and triggering
address registration when a new address has been configured.
Furthermore, the SLLA option MUST be included in the RA. Unlike in
[RFC4861], the maximum value of the RA Router Lifetime field MAY be
up to 0xFFFF (approximately 18 hours).
Should the host erroneously receive a Prefix Information option with
the 'L' (on-link) flag set, then that Prefix Information Option (PIO)
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MUST be ignored.
5.4.1. Address configuration
Address configuration follows [RFC4862]. For an address not derived
from an EUI-64, the M flag of the RA determines how the address can
be configured. If the M flag is set in the RA, then DHCPv6 MUST be
used to assign the address. If the M flag is not set, then the
address can be configured by any other means (and duplicate detection
is performed as part of the registration process).
Once an address has been configured it will be registered by
unicasting a Neighbor Solicitation with the Address Registration
option to one or more routers.
5.4.2. Storing Contexts
The host maintains a conceptual data structure for the context
information it receives from the routers, which is called the Context
Table. This includes the Context ID, the prefix (from the Context
Prefix field in the 6CO), the Compression bit, and the Valid
Lifetime. A Context Table entry that has the Compression bit clear
is used for decompression when receiving packets, but MUST NOT be
used for compression when sending packets.
When a 6CO option is received in a Router Advertisement it is used to
add or update the information in the Context Table. If the Context
ID field in the 6CO matches an existing Context Table entry, then
that entry is updated with the information in the 6CO. If the Valid
Lifetime field in the 6CO is zero, then the entry is immediately
deleted.
If there is no matching entry in the Context Table, and the Valid
Lifetime field is non-zero, then a new context is added to the
Context Table. The 6CO is used to update the created entry.
When the 6LBR changes the context information a host might not
immediately notice. And in the worst case a host might have stale
context information. For this reason 6LBRs use the recommendations
in Section 7.2 for carefully managing the context lifecycle. Nodes
should be careful about using header compression in RA messages that
include 6COs.
5.4.3. Maintaining Prefix and Context Information
The prefix information is timed out as specified in [RFC4861]. When
the Valid Lifetime for a Context Table entry expires the entry is
placed in a receive-only mode, which is the equivalent of receiving a
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6CO for that context with C=0. The entry is held in receive-only
mode for a period of twice the Default Router Lifetime, after which
the entry is removed.
A host should inspect the various lifetimes to determine when it
should next initiate sending a Router Solicitation to ask for any
updates to the information. The lifetimes that matter are the
Default Router lifetime, the Valid Lifetime in the Prefix Information
options, and the Valid Lifetime in the 6CO. The host SHOULD unicast
one or more Router Solicitations to the router well before the
minimum of those lifetimes (across all the prefixes and all the
contexts) expire, and switch to multicast RS messages if there is no
response to the unicasts. The retransmission behavior for the Router
Solicitations is specified in Section 5.3.
5.5. Registration and Neighbor Unreachability Detection
Hosts send Unicast Neighbor Solicitation (NS) messages to register
their IPv6 addresses, and also to do NUD to verify that their default
routers are still reachable. The registration is performed by the
host including an ARO in the Neighbor Solicitation it sends. Even if
the host doesn't have data to send, but is expecting others to try to
send packets to the host, the host needs to maintain its Neighbor
Cache entries in the routers. This is done by sending NS messages
with the ARO to the router well in advance of the registration
lifetime expiring. NS messages are retransmitted up to
MAX_UNICAST_SOLICIT times using a minimum timeout of RETRANS_TIMER
until the host receives an Neighbor Advertisement message with an ARO
option.
Hosts that receive Router Advertisement messages from multiple
default routers SHOULD attempt to register with more than one of them
in order to increase the robustness of the network.
Note that Neighbor Unreachability Detection probes can be suppressed
by Reachability Confirmations from transport protocols or
applications as specified in [RFC4861].
When a host knows it will no longer use a router it is registered to,
it SHOULD de-register with the router by sending an NS with an ARO
containing a lifetime of 0. To handle the case when a host loses
connectivity with the default router involuntarily, the host SHOULD
use a suitably low registration lifetime.
5.5.1. Sending a Neighbor Solicitation
The host triggers sending Neighbor Solicitation (NS) messages
containing an ARO when a new address is configured, when it discovers
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a new default router, or well before the Registration Lifetime
expires. Such an NS MUST include a Source Link-Layer Address (SLLA)
option, since the router needs to record the link-layer address of
the host. An unspecified source address MUST NOT be used in NS
messages.
5.5.2. Processing a Neighbor Advertisement
A host handles Neighbor Advertisement messages as specified in
[RFC4861], with added logic described in this section for handling
the Address Registration option.
In addition to the normal validation of a Neighbor Advertisement and
its options, the Address Registration option is verified as follows
(if present). If the Length field is not two, the option is silently
ignored. If the EUI-64 field does not match the EUI-64 of the
interface, the option is silently ignored.
If the status field is zero, then the address registration was
successful. The host saves the Registration Lifetime from the
Address Registration option for use to trigger a new NS well before
the lifetime expires. If the Status field is not equal to zero, the
address registration has failed.
5.5.3. Recovering from Failures
The procedure for maintaining reachability information about a
neighbor is the same as in [RFC4861] Section 7.3 with the exception
that address resolution is not performed.
The address registration procedure may fail for two reasons: no
response to Neighbor Solicitations is received (NUD failure), or an
Address Registration option with a failure Status (Status > 0) is
received. In the case of NUD failure the entry for that router will
be removed thus address registration is no longer of importance.
When an Address Registration option with a non-zero Status field is
received this indicates that registration for that address has
failed. A failure Status of one indicates that a duplicate address
was detected and the procedure described in [RFC4862] Section 5.4.5
is followed. The host MUST NOT use the address it tried to register.
If the host has valid registrations with other routers, these MUST be
removed by registering with each using a zero ARO lifetime.
A Status code of two indicates that the Neighbor Cache of that router
is full. In this case the host SHOULD remove this router from its
default router list and attempt to register with another router. If
the host's default router list is empty, it needs to revert to
sending Router Solicitations as specified in Section 5.3.
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Other failure codes may be defined in future documents.
5.6. Next-hop Determination
The IP address of the next-hop for a destination is determined as
follows. Destinations to the link-local prefix (FE80::) are always
sent on the link to that destination. It is assumed that link-local
addresses are formed as specified in Section 5.2 from the EUI-64, and
address resolution is not performed. Packets are sent to link local
destinations by reversing the procedure in Appendix A of [RFC4291].
Multicast addresses are considered to be on-link and are resolved as
specified in [RFC4944] or the appropriate IP-over-foo document. Note
that [RFC4944] only defines how to represent a multicast destination
address in the LoWPAN header. Support for multicast scopes larger
than link-local needs an appropriate multicast routing algorithm.
All other prefixes are assumed to be off-link [RFC5889]. Anycast
addresses are always considered to be off-link. They are therefore
sent to one of the routers in the Default Router List.
A LoWPAN Node is not required to maintain a minimum of one buffer per
neighbor as specified in [RFC4861], since packets are never queued
while waiting for address resolution.
5.7. Address Resolution
The address registration mechanism and the SLLA option in Router
Advertisement messages provide sufficient a priori state in routers
and hosts to resolve an IPv6 address to its associated link-layer
address. As all prefixes, except the link-local prefix and multicast
addresses, are always assumed to be off-link, multicast-based address
resolution between neighbors is not needed.
Link-layer addresses for neighbors are stored in Neighbor Cache
entries [RFC4861]. In order to achieve LoWPAN compression, most
global addresses are formed using a link-layer address. Thus a host
can reduce memory usage by optimizing for this case and only storing
link-layer address information if it differs from the link-layer
address corresponding to the Interface ID of the IPv6 address (i.e.,
differs in more than the on-link/global bit being inverted).
5.8. Sleeping
It is often advantageous for battery-powered hosts in LoWPANs to keep
a low duty cycle. The optimizations described in this document
enable hosts to sleep as described further in this section. Routers
may want to cache traffic destined to a host which is sleeping, but
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such functionality is out of the scope of this document.
5.8.1. Picking an Appropriate Registration Lifetime
As all Neighbor Discovery messages are initiated by the hosts, this
allows a host to sleep or otherwise be unreachable between NS/NA
message exchanges. The Address Registration option attached to NS
messages indicates to a router to keep the Neighbor Cache entry for
that address valid for the period in the Registration Lifetime field.
A host should choose a sleep time appropriate for its energy
characteristics, and set a registration lifetime larger than the
sleep time to ensure the registration is renewed successfully
(considering e.g. clock drift and additional time for potential
retransmissions of the re-registration). External configuration of a
host should also consider the stability of the network (how quickly
the topology changes) when choosing its sleep time (and thus
registration lifetime). A dynamic network requires a shorter sleep
time so that routers don't keep invalid neighbor cache entries for
nodes longer than necessary.
5.8.2. Behavior on Wakeup
When a host wakes up from a sleep period it SHOULD refresh its
current address registrations that will timeout before the next
wakeup. This is done by sending Neighbor Solicitation messages with
the Address Registration option as described in Section 5.5.1. The
host may also need to refresh its prefix and context information by
sending a new unicast Router Solicitation (the maximum Router
Lifetime is about 18 hours whereas the maximum Registration lifetime
is about 45.5 days). If after wakeup the host (using NUD) determines
that some or all previous default routers have become unreachable,
then the host will send multicast Router Solicitations to discover
new default router(s) and restart the address registration process.
6. Router Behavior for 6LR and 6LBR
Both 6LRs and 6LBRs maintain the Neighbor Cache [RFC4861] based on
the Address Registration Options they receive in Neighbor
Advertisement messages from hosts, Neighbor Discovery packets from
other nodes, and potentially a routing protocol used in the 6LoWPAN
as outlined in Section 3.5.
The routers SHOULD NOT garbage collect Registered Neighbor Cache
entries (see Section 3.4) since they need to retain them until the
Registration Lifetime expires. Similarly, if Neighbor Unreachability
Detection on the router determines that the host is UNREACHABLE
(based on the logic in [RFC4861]), the Neighbor Cache entry SHOULD
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NOT be deleted but be retained until the Registration Lifetime
expires. A renewed ARO should mark the cache entry as STALE. Thus
for 6LoWPAN Routers the Neighbor Cache doesn't behave like a cache.
Instead it behaves as a registry of all the host addresses that are
attached to the Router.
Routers MAY implement the Default Router Preferences [RFC4191] and
use that to indicate to the host whether the router is a 6LBR or a
6LR. If this is implemented then 6LRs with no route to a border
router MUST set Prf to (11) for low preference, other 6LRs MUST set
Prf to (00) for normal preference, and 6LBRs MUST set Prf to (01) for
high preference.
6.1. Forbidden Actions
Even if a router in a route-over topology can reach both a host and
another target, because of radio propagation it generally cannot know
whether the host can directly reach the other target. Therefore it
cannot assume that redirect will actually work from one host to
another. Therefore it SHOULD NOT send Redirect messages. The only
potential exception to this "SHOULD NOT" is when the deployment/
implementation has a way to know how the host can reach the intended
target. Hence it is RECOMMENDED that the implementation by default
does not send redirect messages but can be configurable when the
deployment calls for this. In contrast, for mesh-under topologies,
the same considerations about Redirects apply as in 4861.
A router MUST NOT set the 'L' (on-link) flag in the Prefix
Information options, since that might trigger hosts to send multicast
Neighbor Solicitations.
6.2. Interface Initialization
The 6LBR router interface initialization behavior is the same as in
[RFC4861]. However, in dynamic configuration scenario (see
Section 8.1), a 6LR comes up as a non-router and waits to receive the
advertisement for configuring its own interface address first before
making its interfaces advertising and turning into a router.
6.3. Processing a Router Solicitation
A router processes Router Solicitation messages as specified in
[RFC4861]. The differences relate to the inclusion of Authoritative
Border Router options in the Router Advertisement (RA) messages, and
the exclusive use of unicast Router Advertisements. If a 6LR has
received an ABRO from a 6LBR, then it will include that option
unmodified in the Router Advertisement messages it sends. And if the
6LR has received RAs, whether with the same prefixes and context
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information or different, from a different 6LBR, then it will need to
keep those prefixes and context information separately so that the
RAs the 6LR sends will maintain the association between the ABRO and
the prefixes and context information. The router can tell which 6LBR
originated the prefixes and context information from the 6LBR Address
field in the ABRO. When a router has information tied to multiple
ABROs, a single RS will result in multiple RAs each containing a
different ABRO.
When the ABRO Valid Lifetime associated with a 6LBR times out, all
information related to that 6LBR MUST be removed. As an
implementation note, it is recommend that RAs are sent sufficiently
more frequently than the ABRO Valid Lifetime so that missing an RA
does not result in removing all information related to a 6LBR.
A Router Solicitation might be received from a host that has not yet
registered its address with the router. Thus the router MUST NOT
modify an existing Neighbor Cache entry based on the SLLA option from
the Router Solicitation. However, a router MAY create a Tentative
Neighbor Cache entry based on the SLLA option. Such a Tentative
Neighbor Cache entry SHOULD be timed out in TENTATIVE_NCE_LIFETIME
seconds unless a registration converts it into a Registered NCE.
A 6LR or 6LBR MUST include a Source Link-layer address option in the
Router Advertisements it sends. That is required so that the hosts
will know the link-layer address of the router. Unlike in [RFC4861],
the maximum value of the RA Router Lifetime field MAY be up to 0xFFFF
(approximately 18 hours).
Unlike [RFC4861] which suggests multicast Router Advertisements, this
specification improves the exchange by always unicasting RAs in
response to RSs. This is possible since the RS always includes a
SLLA option, which is used by the router to unicast the RA.
6.4. Periodic Router Advertisements
A router does not need to send any periodic Router Advertisement
messages since the hosts will solicit updated information by sending
Router Solicitations before the lifetimes expire.
However, if the routers use Router Advertisements to distribute
prefix and/or context information across a route-over topology, that
might require periodic Router Advertisement messages. Such RAs are
sent using the configurable MinRtrAdvInterval and MaxRtrAdvInterval
as per [RFC4861].
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6.5. Processing a Neighbor Solicitation
A router handles Neighbor Solicitation messages as specified in
[RFC4861], with added logic described in this section for handling
the Address Registration option.
In addition to the normal validation of a Neighbor Solicitation and
its options, the Address Registration option is verified as follows
(if present). If the Length field is not two, or if the Status field
is not zero, then the Neighbor Solicitation is silently ignored.
If the source address of the NS is the unspecified address, or if no
SLLA option is included, then any included ARO is ignored, that is,
the NS is processed as if it did not contain an ARO.
6.5.1. Checking for Duplicates
If the NS contains a valid ARO, then the router inspects its Neighbor
Cache on the arriving interface to see if it is a duplicate. If
there is no Neighbor Cache entry for the IPv6 source address of the
NS, then it isn't a duplicate. If there is such a Neighbor Cache
entry and the EUI-64 is the same, then it isn't a duplicate either.
Otherwise it is a duplicate address. Note that if multihop DAD
(Section 8.2) is used then the checks are slightly different to take
into account Tentative Neighbor Cache entries. In the case it is a
duplicate address then the router responds with a unicast Neighbor
Advertisement (NA) message with the ARO Status field set to one (to
indicate the address is a duplicate) as described in Section 6.5.2.
In this case there is no modification to the Neighbor Cache.
6.5.2. Returning Address Registration Errors
Address registration errors are not sent back to the source address
of the NS due to a possible risk of L2 address collision. Instead
the NA is sent to the link-local IPv6 address with the IID part
derived from the EUI-64 field of the ARO as per [RFC4944]. In
particular, this means that the universal/local bit needs to be
inverted. The NA is formatted with a copy of the ARO from the NS,
but with the Status field set to indicate the appropriate error.
The error is sent to the link-local address with the IID derived from
the EUI-64. Thus if the ARO was from and for a short address, the L2
destination address for the NA with the ARO error will be the 64-bit
unique addresses.
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6.5.3. Updating the Neighbor Cache
If ARO did not result in a duplicate address being detected as above,
then if the Registration Lifetime is non-zero the router creates (if
it didn't exist) or updates (otherwise) a Neighbor Cache entry for
the IPv6 source address of the NS. If the Neighbor Cache is full and
a new entry needs to be created, then the router responds with a
unicast NA with the ARO Status field set to two (to indicate the
router's Neighbor Cache is full) as described in Section 6.5.2.
The Registration Lifetime and the EUI-64 are recorded in the Neighbor
Cache entry. A unicast Neighbor Advertisement (NA) is then sent in
response to the NS. This NA SHOULD include a copy of the ARO, with
the Status field set to zero. A TLLA (Target Link-layer Address)
option [RFC4861] is not required in the NA, since the host already
knows the router's link-layer address from Router Advertisements.
If the ARO contains a zero Registration Lifetime then any existing
Neighbor Cache entry for the IPv6 source address of the NS MUST be
deleted, and a NA sent as above.
Should the Registration Lifetime in a Neighbor Cache entry expire,
then the router MUST delete the cache entry.
The addition and removal of Registered Neighbor Cache entries would
result in notifying the routing protocol.
Note: If the substitutable multihop DAD (Section 8.2) is used, then
the updating of the Neighbor Cache is slightly different due to
Tentative NCEs.
6.5.4. Next-hop Determination
In order to deliver a packet destined for a 6LN registered with a
router, next-hop determination is slightly different for routers than
hosts (see Section 5.6. The routing table is checked to determine
the next hop IP address. A registered Neighbor Cache Entry (NCE)
determines if the next hop IP-address is on-link. It is the
responsibility of the routing protocol of the router to maintain on-
link information about its registered neighbors. Tentative NCEs MUST
NOT be used to determine on-link status of the registered nodes.
6.5.5. Address Resolution between Routers
There needs to be a mechanism somewhere for the routers to discover
each others' link-layer addresses. If the routing protocol used
between the routers provides this, then there is no need for the
routers to use the Address Registration option between each other.
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Otherwise, the routers SHOULD use the ARO. When routers use ARO to
register with each other and the multihop DAD Section 8.2 is in use,
then care must be taken to ensure that there isn't a flood of ARO-
carrying messages sent to the 6LBR as each router hears an ARO from
their neighboring routers. The details for this is out of scope of
this document.
Routers MAY also use multicast Neighbor Solicitations as in [RFC4861]
to resolve each others link-layer addresses. Thus Routers MAY
multicast Neighbor Solicitations for other routers, for example as a
result of receiving some routing protocol update. Routers MUST
respond to multicast Neighbor Solicitations. This implies that
Routers MUST join the Solicited-node multicast addresses as specified
in [RFC4861].
7. Border Router Behavior
A 6LBR handles sending of Router Advertisements and processing of
Neighbor Solicitations from hosts as specified above in section
Section 6. A 6LBR SHOULD always include an Authoritative Border
Router option in the Router Advertisements it sends, listing itself
as the 6LBR Address. That requires that the 6LBR maintain the
version number in stable storage, and increases the version number
when some information in its Router Advertisements change. The
information whose change affects the version are in the Prefix
Information options (the prefixes or their lifetimes) and in the 6CO
option (the prefixes, Context IDs, or lifetimes.)
In addition, a 6LBR is somehow configured with the prefix or prefixes
that are assigned to the LoWPAN, and advertises those in Router
Advertisements as in [RFC4861]. In the case of route-over, those
prefixes can be disseminated to all the 6LRs using the technique in
Section 8.1. However, there might be mechanisms outside of the scope
of this document that can be used as a substitute for prefix
dissemination in the route-over topology (see Section 1.4).
If the 6LoWPAN uses Header Compression [RFC6282] with context then
the 6LBR needs to manage the context IDs, and advertise those in
Router Advertisements by including 6CO options in its Router
Advertisements so that directly attached hosts are informed about the
context IDs. Below we specify things to consider when the 6LBR needs
to add, remove, or change the context information. In the case of
route-over, the context information is disseminated to all the 6LRs
using the technique in Section 8 unless a different specification
provides a substitute for this multihop distribution.
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7.1. Prefix Determination
The prefix or prefixes used in a LoWPAN can be manually configured,
or can be acquired using DHCPv6 Prefix Delegation [RFC3633]. For a
LoWPAN that is isolated from the network, either permanently or
occasionally, the 6LBR can assign a ULA prefix using [RFC4193]. The
ULA prefix should be stored in stable storage so that the same prefix
is used after a failure of the 6LBR. If the LoWPAN has multiple
6LBRs, then they should be configured with the same set of prefixes.
The set of prefixes are included in the Router Advertisement messages
as specified in [RFC4861].
7.2. Context Configuration and Management
If the LoWPAN uses Header Compression [RFC6282] with context then the
6LBR must be configured with context information and related context
IDs. If the LoWPAN has multiple 6LBRs, then they MUST be configured
with the same context information and context IDs. For [RFC6282],
maintaining consistency of context information is crucial for
ensuring packets will be decompressed correctly.
The context information carried in Router Advertisement (RA) messages
originate at 6LBRs and must be disseminated to all the routers and
hosts within the LoWPAN. RAs include one 6CO for each context.
For the dissemination of context information using the 6CO, a strict
lifecycle SHOULD be used in order to ensure the context information
stays synchronized throughout the LoWPAN. New context information
SHOULD be introduced into the LoWPAN with C=0, to ensure it is known
by all nodes that may have to decompress based on this context
information. Only when it is reasonable to assume that this
information was successfully disseminated SHOULD an option with C=1
be sent, enabling the actual use of the context information for
compression.
Conversely, to avoid that nodes send packets making use of previous
values of contexts, resulting in ambiguity when receiving a packet
that uses a recently changed context, old values of a context SHOULD
be taken out of use for a while before new values are assigned to
this specific context. That is, in preparation for a change of
context information, its dissemination SHOULD continue for at least
MIN_CONTEXT_CHANGE_DELAY with C=0. Only when it is reasonable to
assume that the fact that the context is now invalid was successfully
disseminated, should the context ID be taken out of dissemination or
reused with a different Context Prefix field. In the latter case,
dissemination of the new value again SHOULD start with C=0, as above.
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8. Substitutable Feature Behavior
Normally in a 6LoWPAN multihop network, the Router Advertisement
messages are used to disseminate prefixes and context information to
all the 6LRs in a route-over topology. If all routers are configured
to use a substitute mechanism for such information distribution, any
remaining use of the 6LoWPAN-ND mechanisms is governed by the
substitute specification.
There is also the option for a 6LR to perform multihop DAD (for non-
EUI-64 derived IPv6 addresses) against a 6LBR in a route-over
topology by using the DAR and DAC messages. This is substitutable
because there might be other ways to either allocate unique address,
such as DHCPv6 [RFC3315], or other future mechanisms for multihop
DAD. Again in this case, any remaining use of the 6LoWPAN-ND
mechanisms is governed by the substitute specification.
To be clear: Implementations MUST support the features describes in
Section 8.1 and Section 8.2, unless the implementation supports some
alternative ("substitute") from some some other specification.
8.1. Multihop Prefix and Context Distribution
The multihop distribution relies on Router Solicitation messages and
Router Advertisement (RA) messages sent between routers, and using
the ABRO version number to control the propagation of the information
(prefixes and context information) that is being sent in the RAs.
This multihop distribution mechanism can handle arbitrary information
from an arbitrary number of 6LBRs. However, the semantics of the
context information requires that all the 6LNs use the same
information, whether they send, forward, or receive compressed
packets. Thus the manager of the 6LBRs need to somehow ensure that
the context information is in synchrony across the 6LBRs. This can
be handled in different ways. One possible way to ensure it is to
treat the context and prefix information as originating from some
logical or virtual source, which in essence means that it looks like
the information is distributed from a single source.
If a set of 6LBRs behave as a single one (using mechanisms out of
scope of this document) so that the prefixes and contexts and ABRO
version number will be the same from all the 6LBRs, then those 6LBRs
can pick a single IP address to use in the ABRO option.
8.1.1. 6LBRs Sending Router Advertisements
6LBRs supporting multihop prefix and context distribution MUST
include an ABRO in each of its RAs. The ABRO Version Number field is
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used to keep prefix and context information consistent throughout the
LoWPAN along with the guidelines in Section 7.2. Each time any
information in the set of PIO or 6CO options change, the ABRO Version
is increased by one.
This requires that the 6LBR maintain the PIO, 6CO, and ABRO Version
Number in stable storage, since an old version number will be
silently ignored by the 6LRs.
8.1.2. Routers Sending Router Solicitations
In a 6LoWPAN, unless substituted, multihop distribution is done using
Router Advertisement (RA) messages. Thus on interface initialization
a router (6LR) MUST send Router Solicitation messages following the
rules specified for hosts in [RFC4861]. That will cause the routers
to respond with RA messages which then can be used to initially seed
the prefix and context information.
8.1.3. Routers Processing Router Advertisements
If multihop distribution is not done using RA messages, then the
routers follow [RFC4861] which states that they merely do some
consistency checks and nothing in Section 8.1 applies. Otherwise the
routers will check and record the prefix and context information from
the receive RAs, and use that information as follows.
If a received RA does not contain a Authoritative Border Router
option, then the RA MUST be silently ignored.
The router uses the 6LBR Address field in the ABRO to check if it has
previously received information from the 6LBR. If it finds no such
information, then it just records the 6LBR Address, Version, Valid
Lifetime and the associated prefixes and context information. If the
6LBR is previously known, then the Version number field MUST be
compared against the recorded version number for that 6LBR. If the
version number received in the packet is less than the stored version
number then the information in the RA is silently ignored. Otherwise
the recorded information and version number are updated.
8.1.4. Storing the Information
The router keeps state for each 6LBR that it sees with an ABRO. This
includes the Version number, the Valid Lifetime, and the complete set
of Prefix Information options and 6LoWPAN Context options. The
prefixes are timed out based on the Valid lifetime in the Prefix
Information Option. The Context Prefix is timed out based on the
Valid lifetime in the 6LoWPAN Context option.
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While the prefixes and context information are stored in the router
their valid and preferred lifetimes are decremented as time passes.
This ensures that when the router is in turn later advertising that
information in the Router Advertisements it sends, the 'expiry time'
doesn't accidentally move further into the future. For example, if a
6CO with a Valid lifetime of 10 minutes is received at time T, and
the router includes this in a RA it sends at time T+5 minutes, the
Valid lifetime in the 6CO it sends will be only 5 minutes.
8.1.5. Sending Router Advertisements
When multihop distribution is performed using RA messages, the
routers MUST ensure that the ABRO always stay together with the
prefixes and context information received with that ABRO. Thus if
the router has received prefix P1 with ABRO saying it is from one
6LBR, and prefix P2 from another 6LBR, then the router MUST NOT
include the two prefixes in the same RA message. Prefix P1 MUST be
in a RA that include a ABRO from the first 6LBR etc. Note that
multiple 6LBRs might advertise the same prefix and context
information, but they still need to be associated with the 6LBRs that
advertised them.
The routers periodically send Router Advertisements as in [RFC4861].
This is for the benefit of the other routers receiving the prefixes
and context information. And the routers also respond to Router
Solicitations by unicasting RA messages. In both cases the above
constraint of keeping the ABRO together with 'its' prefixes and
context information apply.
When a router receives new information from a 6LBR, that is, either
it hears from a new 6LBR (a new 6LBR Address in the ABRO) or the ABRO
version number of an existing 6LBR has increased, then it is useful
to send out a few triggered updates. The recommendation is to behave
the same as when an interface has become an advertising interface in
[RFC4861], that is, send up to three RA messages. This ensures rapid
propagation of new information to all the 6LRs.
8.2. Multihop Duplicate Address Detection
The ARO can be used, in addition to registering an address in a 6LR,
to have the 6LR verify that the address isn't used by some other host
known to the 6LR. However, that isn't sufficient in a route-over
topology (or in a LoWPAN with multiple 6LBRs) since some host
attached to another 6LR could be using the same address. There might
be different ways for the 6LRs to coordinate such Duplicate Address
Detection in the future, or addresses could be assigned using a
DHCPv6 server that verifies uniqueness as part of the assignment.
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This specification offers a substitutable simple technique for 6LRs
and 6LBRs to perform Duplicate Address Detection that reuses the
information from Address Registration option in the DAR and DAC
messages. This technique is not needed when the Interface ID in the
address is based on an EUI-64, since those are assumed to be globally
unique. The technique assumes that the 6LRs either register with all
the 6LBRs, or that the network uses some out-of-scope mechanism to
keep the DAD tables in the 6LBRs synchronized.
The multihop DAD mechanism is used synchronously the first time an
address is registered with a particular 6LR. That is, the ARO option
is not returned to the host until multihop DAD has been completed
against the 6LBRs. For existing registrations in the 6LR the
multihop DAD needs to be repeated against the 6LBRs to ensure that
the entry for the address in the 6LBRs does not time out, but that
can be done asynchronously with the response to the hosts. For
instance, by tracking how much is left of the lifetime the 6LR
registered with the 6LBRs and re-registering with the 6LBR when this
lifetime is about to run out.
For the synchronous multihop DAD the 6LR performs some additional
checks to ensure that it has a Neighbor Cache entry it can use to
respond to the host when it receives a response from a 6LBR. This
consists of checking for an already existing (Tentative or
Registered) Neighbor Cache entry for the registered address with a
different EUI-64. If such a Registered NCE exists, then the 6LR
SHOULD respond that the address is a duplicate. If such a Tentative
NCE exists, then the 6LR SHOULD silently ignore the ARO thereby
relying on the host retransmitting the ARO. This is needed to handle
the case when multiple hosts try to register the same IPv6 address at
the same time. If no Neighbor Cache entry exists, then the 6LR MUST
create a Tentative Neighbor Cache entry with the EUI-64 and the SLLA
option. This entry will be used to send the response to the host
when the 6LBR responds positively.
When a 6LR receives a Neighbor Solicitation containing an Address
Registration option with a non-zero Registration Lifetime and it has
no existing Registered Neighbor Cache entry, then with this mechanism
the 6LR will invoke synchronous multihop DAD.
The 6LR will unicast a Duplicate Address Request message to one or
more 6LBRs, where the DAR contains the host's address in the
Registered Address field. The DAR will be forwarded by 6LRs until it
reaches the 6LBR, hence its IPv6 hop limit field will not be 255 when
received by the 6LBR. The 6LBR will respond with a Duplicate Address
Confirmation message, which will have a hop limit less than 255 when
it reaches the 6LR.
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When the 6LR receives the DAC from the 6LBR, it will look for a
matching (same IP address and EUI-64) (Tentative or Registered)
Neighbor Cache entry. If no such entry is found then the DAC is
silently ignored. If an entry is found and the DAC had Status=0 then
the 6LR will mark the Tentative Neighbor Cache entry as Registered.
In all cases when an entry is found then the 6LR will respond to the
host with an NA, copying the Status and EUI-64 fields from the DAC to
an ARO option in the NA. In case the status is an error, then the
destination IP address of the NA is derived from the EUI-64 field of
the DAC.
A Tentative Neighbor Cache entry SHOULD be timed out
TENTATIVE_NCE_LIFETIME seconds after it was created in order to allow
for another host to attempt to register the IPv6 address.
8.2.1. Message Validation for DAR and DAC
A node MUST silently discard any received Duplicate Address Request
and Confirmation messages for which at least one of the following
validity checks is not satisfied:
o If the message includes an IP Authentication Header, the message
authenticates correctly.
o ICMP Checksum is valid.
o ICMP Code is 0.
o ICMP length (derived from the IP length) is 32 or more bytes.
o The Registered Address is not a multicast address.
o All included options have a length that is greater than zero.
o The IP source address is not the unspecified address, nor a
multicast address.
The contents of the Reserved field, and of any unrecognized options,
MUST be ignored. Future, backward-compatible changes to the protocol
may specify the contents of the Reserved field or add new options;
backward-incompatible changes may use different Code values.
Note that due to the forwarding of the DAR and DAC messages between
the 6LR and 6LBR there is no hop limit check on receipt for these
ICMPv6 message types.
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8.2.2. Conceptual Data Structures
A 6LBR implementing multihop DAD needs to maintain some state
separate from the Neighbor Cache. We call this conceptual data
structure the DAD table. It is indexed by the IPv6 address - the
Registered Address in the DAR - and contains the EUI-64 and the
registration lifetime of the host that is using that address.
8.2.3. 6LR Sending a Duplicate Address Request
When a 6LR that implements multihop DAD receives an NS from a host
and subject to the above checks, the 6LR forms and sends a DAR to at
least one 6LBR. The DAR contains the following information:
o In the IPv6 source address, a global address of the 6LR.
o In the IPv6 destination address, the address of the 6LBR.
o In the IPv6 hop limit, MULTIHOP_HOPLIMIT.
o The Status field MUST be set to zero
o The EUI-64 and Registration lifetime are copied from the ARO
received from the host.
o The Registered Address set to the IPv6 address of the host, that
is, the sender of the triggering NS.
When a 6LR receives an NS from a host with a zero Registration
Lifetime then, in addition to removing the Neighbor Cache entry for
the host as specified in Section 6, an DAR is sent to the 6LBRs as
above.
A router MUST NOT modify the Neighbor Cache as a result of receiving
a Duplicate Address Request.
8.2.4. 6LBR Receiving a Duplicate Address Request
When a 6LBR that implements the substitutable multihop DAD receives
an DAR from a 6LR, it performs the message validation specified in
Section 8.2.1. If the DAR is valid the 6LBR proceeds to look for the
Registration Address in the DAD Table. If an entry is found and the
recorded EUI-64 is different than the EUI-64 in the DAR, then it
returns a DAC NA with the Status set to 1 ('Duplicate Address').
Otherwise it returns a DAC with Status set to zero and updates the
lifetime.
If no entry is found in the DAD Table and the Registration Lifetime
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is non-zero, then an entry is created and the EUI-64 and Registered
Address from the DAR are stored in that entry.
If an entry is found in the DAD Table, the EUI-64 matches, and the
Registration Lifetime is zero then the entry is deleted from the
table.
In both of the above cases the 6LBR forms an DAC with the information
copied from the DAR and the Status field is set to zero. The DAC is
sent back to the 6LR i.e., back to the source of the DAR. The IPv6
hop limit is set to MULTIHOP_HOPLIMIT
8.2.5. Processing a Duplicate Address Confirmation
When a 6LR implementing multihop DAD receives a DAC message, then it
first validates the message per Section 8.2.1. For a valid DAC, if
there is no Tentative Neighbor Cache entry matching the Registered
address and EUI-64, then the DAC is silently ignored. Otherwise, the
information in the DAC and in the Tentative Neighbor Cache entry is
used to form an NA to send to the host. The Status code is copied
from the DAC to the ARO that is sent to the host. In case of the DAC
indicates an error (the Status is non-zero), the NA is returned to
the host as described in Section 6.5.2 and the Tentative Neighbor
Cache entry for the Registered Address is removed. Otherwise it is
made into a Registered Neighbor Cache entry.
A router MUST NOT modify the Neighbor Cache as a result of receiving
a Duplicate Address Confirmation, unless there is a Tentative
Neighbor Cache entry matching the IPv6 address and EUI-64.
8.2.6. Recovering from Failures
If there is no response from a 6LBR after RETRANS_TIMER [RFC4861]
then the 6LR would retransmit the DAR to the 6LBR up to
MAX_UNICAST_SOLICIT [RFC4861] times. After this the 6LR SHOULD
respond to the host with an ARO Status of zero.
9. Protocol Constants
This section defines the relevant protocol constants used in this
document based on a subset of [RFC4861] constants. (*) indicates
constants modified from [RFC4861] and (+) indicates new constants.
Additional protocol constants are defined in Section 4.
6LBR Constants:
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MIN_CONTEXT_CHANGE_DELAY+ 300 seconds
6LR Constants:
MAX_RTR_ADVERTISEMENTS 3 transmissions
MIN_DELAY_BETWEEN_RAS* 10 seconds
MAX_RA_DELAY_TIME* 2 seconds
TENTATIVE_NCE_LIFETIME+ 20 seconds
Router Constants:
MULTIHOP_HOPLIMIT+ 64
Host Constants:
RTR_SOLICITATION_INTERVAL* 10 seconds
MAX_RTR_SOLICITATIONS 3 transmissions
MAX_RTR_SOLICITATION_INTERVAL+ 60 seconds
10. Examples
10.1. Message Examples
STEP
6LN 6LR
| |
1. | ---------- Router Solicitation --------> |
| [SLLAO] |
| |
2. | <-------- Router Advertisement --------- |
| [PIO + 6CO + ABRO + SLLAO] |
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Figure 2: Basic Router Solicitation/Router Advertisement exchange
between a node and 6LR or 6LBR
6LN 6LR
| |
1. | ------- NS with Address Registration ------> |
| [ARO + SLLAO] |
| |
2. | <----- NA with Address Registration -------- |
| [ARO with Status] |
Figure 3: Neighbor Discovery Address Registration
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6LN 6LR 6LBR
| | |
1. | --- NS with Address Reg --> | |
| [ARO + SLLAO] | |
| | |
2. | | ----------- DAR ----------> |
| | |
3. | | <---------- DAC ----------- |
| | |
4. | <-- NA with Address Reg --- | |
| [ARO with Status] |
Figure 4: Neighbor Discovery Address Registration with Multihop DAD
10.2. Host Bootstrapping Example
The following example describes the address bootstrapping scenarios
using the improved ND mechanisms specified in this document. It is
assumed that the 6LN first performs a sequence of operations in order
to get secure access at the link-layer of the LoWPAN and obtain a key
for link-layer security. The methods of how to establish the link-
layer security is out of scope of this document. In this example an
IEEE 802.15.4 6LN forms a 16-bit short-address based IPv6 addresses
without using DHCPv6 (i.e., the M flag is not set in the Router
Advertisements).
1. After obtaining link-level security, a 6LN assigns a link-local
IPv6 address to itself. A link-local IPv6 address is configured
based on the 6LN's EUI-64 link-layer address formed as per [RFC4944].
2. Next the 6LN determines one or more default routers in the
network by sending an RS to the all-routers multicast address with
the SLLA Option set to its EUI-64 link-local address. If the 6LN was
able to obtain the link-layer address of a router through its link-
layer operations then the 6LN may form a link-local destination IPv6
address for the router and send it a unicast RS. The 6LR responds
with a unicast RA to the IP source using the SLLA option from the RS
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(it may have created a tentative NCE). See Figure 2.
3. In order to communicate more than one IP hop away the 6LN
configures a global IPv6 address. In order to save overhead, this
6LN wishes to configure its IPv6 address based on a 16-bit short
address as per [RFC4944]. As the network is unmanaged (M flag not
set in RA), the 6LN randomly chooses a 16-bit link-layer address and
forms a tentative IPv6 address from it.
4. Next the 6LN registers that address with one or more of its
default routers by sending a unicast NS message with an ARO
containing its tentative global IPv6 address to register, the
registration lifetime and its EUI-64. An SLLA option is also
included with the link-layer address corresponding to the address
being registered. If a successful (status 0) NA message is received
the address can then be used and the 6LN assumes it has been
successfully checked for duplicates. If a duplicate address (status
1) NA message is received, the 6LN then removes the temporary IPv6
address and 16-bit link-layer address and goes back to step 3. If a
neighbor cache full (status 2) message is received, the 6LN attempts
to register with another default router, or if none, goes back to
step 2. See Figure 3. Note that an NA message returning an error
would be sent back to the link-local EUI-64 based IPv6 address of the
6LN instead of the 16-bit (duplicate) address.
5. The 6LN now performs maintenance by sending a new NS address
registration before the lifetime expires.
If multihop DAD and multihop prefix and context distribution is used,
the effect of the 6LRs and hosts following the above bootstrapping is
a "wavefront" of 6LRs and host being configured spreading from the
6LBRs. First the hosts and 6LRs that can directly reach a 6LBR would
receive one or more RAs and configure and register their IPv6
addresses. Once that is done they would enable the routing protocol
and start sending out Router Advertisements. That would result in a
new set of 6LRs and hosts to receive responses to their Router
Solicitations, form and register their addresses, etc. That repeats
until all of the 6LRs and hosts have been configured.
10.2.1. Host Bootstrapping Messages
This section brings specific message examples to the previous
bootstrapping process. When discussing messages, the following
notation is used:
LL64: Link-Local Address based on the EUI-64, which is also the
802.15.4 Long Address.
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GP16: Global Address based on the 802.15.4 Short Address. This
address may not be unique.
GP64: Global addresses derived from the EUI-64 address as specified
in [RFC4944].
MAC64: EUI-64 address used as the link-layer address.
MAC16: IEEE 802.15.4 16-bit short address.
Note that some implementations may use LL64 and GP16 style addresses
instead of LL64 and GP64. In the following, we will show an example
message flow as to how a node uses LL64 to register a GP16 address
for multihop DAD verification.
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6LN-----RS-------->6LR
Src= LL64 (6LN)
Dst= All-router-link-scope-multicast
SLLAO= MAC64 (6LN)
6LR------RA--------->6LN
Src= LL64 (6LR)
Dst= LL64 (6LN)
Note: Source address of RA must be a link-local
address (Section 4.2, RFC 4861).
6LN-------NS Reg------>6LR
Src= GP16 (6LN)
Dst= LL64 (6LR)
ARO
SLLAO= MAC16 (6LN)
6LR---------DAR----->6LBR
Src= GP64 or GP16 (6LR)
Dst= GP64 or GP16 (6LBR)
Registered Address= GP16 (6LN) and EUI-64 (6LN)
6LBR-------DAC--------->6LR
Src= GP64 or GP16 (6LBR)
Dst= GP64 or GP16 (6LR)
Copy of information from DAR
If Status is a Success:
6LR ---------NA-Reg------->6LN
Src= LL64 (6LR)
Dst= GP16 (6LN)
ARO with Status = 0
If Status is not a success:
6LR ---------NA-Reg-------->6LN
Src= LL64 (6LR)
Dst= LL64 (6LN) --> Derived from the EUI-64 of ARO
ARO with Status > 0
Figure 5: Detailed Message Address Examples
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10.3. Router Interaction Example
In the Route-over topology, when a routing protocol is run across
6LRs the bootstrapping and neighbor cache management are handled a
little differently. The description in this paragraph provides only
a guideline for an implementation.
At the initialization of a 6LR, it may choose to bootstrap as a host
with the help of a parent 6LR if the substitutable multihop DAD is
performed with the 6LBR. The neighbor cache management of a router
and address resolution among the neighboring routers are described in
Section 6.5.3 and Section 6.5.5, respectively. In this example, we
assume that the neighboring 6LoWPAN link is secure.
10.3.1. Bootstrapping a Router
In this scenario, the bootstrapping 6LR, 'R1', is multiple hops away
from the 6LBR and surrounded by other 6LR neighbors. Initially R1
behaves as a host. It sends multicast RS and receives an RA from one
or more neighboring 6LRs. R1 picks one 6LR as its temporary default
router and performs address resolution via this default router.
Note, if multihop DAD is not required (e.g. in a managed network or
using EUI-64 based addresses) then it does not need to pick a
temporary default router, however it may still want to send the
initial RS message if it wants to autoconfigure its address with the
global prefix disseminated by the 6LBR.
Based on the information received in the RAs, R1 updates its cache
with entries for all the neighboring 6LRs. Upon completion of the
address registration, the bootstrapping router deletes the temporary
entry of the default router and the routing protocol is started.
Also note that R1 may refresh its multihop DAD registration directly
with the 6LBR (using the next hop neighboring 6LR determined by the
routing protocol for reaching the 6LBR).
10.3.2. Updating the Neighbor Cache
In this example, there are three 6LRs, R1, R2, R3. Initially when R2
boots it sees only R1, and accordingly R2 creates a neighbor cache
entry for R1. Now assume R2 receives a valid routing update from
router R3. R2 does not have any neighbor cache entry for R3. If the
implementation of R2 supports detecting link-layer address from the
routing information packets then it directly updates the its neighbor
cache using that link-layer information. If this is not possible,
then R2 should perform multicast NS with source set with its link-
local or global address depending on the scope of the source IP-
address received in the routing update packet. The target address of
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the NS message is the source IPv6 address of the received routing
update packet. The format of the NS message is as described in
Section 4.3 of [RFC4861].
More generally any 6LR that receives a valid route-update from a
neighboring router for which it does not have any neighbor cache
entry is required to update its neighbor cache as described above.
The router (6LR and 6LBR) IP-addresses learned via Neighbor Discovery
are not redistributed to the routing protocol.
11. Security Considerations
The security considerations of IPv6 Neighbor Discovery [RFC4861] and
Address Autoconfiguration [RFC4862] apply. Additional considerations
can be found in [RFC3756].
There is a slight modification to those considerations due to the
fact that in this specification the M-flag in the Router
Advertisements disable the use of stateless address autoconfiguration
for addresses not derived from EUI-64. Thus a rogue router on the
link can force the use of only DHCP for short addresses, whereas in
[RFC4861] and [RFC4862] the rogue router could only cause the
addition of DHCP and not disable SLAAC for short addresses.
This specification assumes that the link layer is sufficiently
protected, for instance using MAC sublayer cryptography. Thus, its
threat model is no different from that of IPv6 Neighbor Discovery
[RFC4861]. The threat model number 1 in section 3 of [RFC3756]
applies here. However, any future 6LoWPAN security protocol that
applies to Neighbor Discovery for 6LoWPAN protocol, is out of scope
of this document.
The multihop DAD mechanisms rely on DAR and DAC messages that are
forwarded by 6LRs, and as a result the hop_limit=255 check on the
receiver does not apply to those messages. This implies that any
node on the Internet could successfully send such messages. We avoid
any additional security issues due to this by requiring that the
routers never modify the Neighbor Cache entry due to such messages,
and that they discard them unless they are received on an interface
that has been explicitly configured to use these optimizations.
In some future deployments one might want to use SEcure Neighbor
Discovery [RFC3971] [RFC3972]. This is possible with the Address
Registration option as sent between hosts and routers, since the
address that is being registered is the IPv6 source address of the
Neighbor Solicitation and SeND verifies the IPv6 source address of
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the packet. Applying SeND to the router-to-router communication in
this document is out of scope.
12. IANA Considerations
The document requires three new Neighbor Discovery option types under
the subregistry "IPv6 Neighbor Discovery Option Formats":
o Address Registration Option (TBD1)
o 6LoWPAN Context Option (TBD2)
o Authoritative Border Router Option (TBD3)
The document requires two new ICMPv6 types under the subregistry
"ICMPv6 type Numbers":
o Duplicate Address Request (TBD4)
o Duplicate Address Confirmation (TBD5)
This document also requests IANA to create a new sub-registry for the
Status values of the Address Registration Option, under the ICMPv6
parameters registry.
Address Registration Option Status Values registry:
Possible values are 8-bit unsigned integers (0..255).
Registration procedure is "Standards Action" [RFC5226].
Initial allocation is as indicated in Table 2:
+--------+--------------------------------------------+
| Status | Description |
+--------+--------------------------------------------+
| 0 | Success |
| 1 | Duplicate Address |
| 2 | Neighbor Cache Full |
| 3-255 | Allocated using Standards Action [RFC5226] |
+--------+--------------------------------------------+
Table 2
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13. Interaction with other Neighbor Discovery Extensions
There are two classes of Neighbor Discovery Extensions that have
different interaction with this specification.
One class are extensions to to the Duplicate Address Detection
mechanisms in [RFC4861] and [RFC4862]. An example of this is
Optimistic DAD [RFC4429]. Such extensions does not apply when this
specification is being used, since it uses ARO for DAD (which is
neither optimistic nor pessimistic - always one roundtrip to the
router to check DAD).
All other (non-DAD) Neighbor Discovery extensions, be it path
selection ones like Default Router Preferences [RFC4191],
configuration ones like DNS config [RFC5006], or others like DNA
[RFC6059], are completely orthogonal to this specification, and will
work as is.
14. Guideline for New Features
This section discusses a guideline of new protocol features defined
in this document. It also sets some expectations for implementation
and deployment of these features. This section is informative in
nature: It does not override the detailed specifications of the
previous sections, but summarizes them and presents them in a compact
form that can be used as a checklist. The checklist acts as a
guideline to indicate the possible importance of a feature in terms
of a deployment as per information available as of the writing of the
document. Note that in some cases the deployment is 'SHOULD' where
the implementation is a 'MUST'. This is due to the presence of
substitutable features; the deployment may use alternative methods
for those. Therefore, implementing a configuration knob is
recommended for the substitutable features. The lists emphasize
conciseness over completeness.
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+----------+---------------------------------+----------+-----------+
| Section | Description | Deploy | Implement |
+----------+---------------------------------+----------+-----------+
| 3.1 | Host initiated RA | MUST | MUST |
| 3.2 | EUI-64 based IPv6-address | MUST | MUST |
| | 16bit-MAC based address | MAY | SHOULD |
| | Other non-unique addresses | MAY | MAY |
| 3.3 | Host Initiated RS | MUST | MUST |
| | ABRO Processing | SHOULD | MUST |
| 4.1 | Registration with ARO | MUST | MUST |
| 4.2, 5.4 | 6LoWPAN Context Option | SHOULD | SHOULD |
| 5.1 | Re-direct Message Acceptance | MUST NOT | MUST NOT |
| | Joining Solicited Node | N/A | N/A |
| | Multicast | | |
| | Joining all-node Multicast | MUST | MUST |
| | Using link-layer indication for | MAY | MAY |
| | NUD | | |
| 5.5 | 6LoWPAN-ND NUD | MUST | MUST |
| 5.8.2 | Behavior on wake-up | SHOULD | SHOULD |
+----------+---------------------------------+----------+-----------+
Table 3: Guideline for 6LoWPAN-ND features for hosts
+---------------+-------------------------+------------+------------+
| Section | Description | deploy | implement |
+---------------+-------------------------+------------+------------+
| 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT |
| 3.2 | Address assignment | SHOULD | MUST |
| | during Startup | | |
| 3.3 | Supporting EUI-64 based | MUST | MUST |
| | MAC Hosts | | |
| | Supporting 16-bit MAC | MAY | SHOULD |
| | hosts | | |
| 3.4, 4.3, | ABRO Processing/sending | SHOULD | MUST |
| 8.1.3, 8.1.4 | | | |
| 8.1 | Multihop Prefix storing | SHOULD | MUST |
| | and re-distribution | | |
| 3.5 | Tentative NCE | MUST | MUST |
| 8.2 | Multihop DAD | SHOULD | MUST |
| 4.1, 6.5, | ARO Support | MUST | MUST |
| 6.5.1 - 6.5.5 | | | |
| 4.2 | 6LoWPAN Context Option | SHOULD | SHOULD |
| 6.3 | Process RS/ARO | MUST | MUST |
+---------------+-------------------------+------------+------------+
Table 4: Guideline for 6LR features in 6LoWPAN-ND
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+--------------+--------------------------+------------+------------+
| Section | Description | deploy | implement |
+--------------+--------------------------+------------+------------+
| 3.1 | Periodic RA | SHOULD NOT | SHOULD NOT |
| 3.2 | Address autoconf on | MUST NOT | MUST NOT |
| | Router interface | | |
| 3.3 | EUI-64 MAC support on | MUST | MUST |
| | 6LoWPAN interface | | |
| 8.1 - 8.1.1, | Multihop Prefix | SHOULD | MUST |
| 8.1.5 | distribution | | |
| 8.2 | Multihop DAD | SHOULD | MUST |
+--------------+--------------------------+------------+------------+
Table 5: Guideline for 6LBR features in 6LoWPAN-ND
15. Acknowledgments
The authors thank Pascal Thubert, Jonathan Hui, Carsten Bormann,
Richard Kelsey, Geoff Mulligan, Julien Abeille, Alexandru Petrescu,
Peter Siklosi, Pieter De Mil, Fred Baker, Anthony Schoofs, Phil
Roberts, Daniel Gavelle, Joseph Reddy, Robert Cragie, Mathilde Durvy,
Colin O'Flynn, Dario Tedeschi, Esko Dijk and Joakim Eriksson for
useful discussions and comments that have helped shaped and improve
this document.
Additionally, the authors would like to recognize Carsten Bormann for
the suggestions on the Context Prefix Option and contribution to
earlier version of the draft, Pascal Thubert for contribution of the
original registration idea and extensive contributions to earlier
versions of the draft, Jonathan Hui for original ideas on prefix/
context distribution and extensive contributions to earlier versions
of the draft, Colin O'Flynn for useful Error-to suggestions and
contributions to the Examples section, Geoff Mulligan for suggesting
the use of Address Registration as part of existing IPv6 Neighbor
Discovery messages, and Mathilde Durvy for helping to clarify router
interaction.
16. Changelog
Changes from -20 to -21:
o Clarified the address an address registration error is sent to.
o Added a new section explaining the interaction with other
Neighbor Discovery extensions.
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Changes from -19 to -20:
o Further clarification on substitutable features.
o Changed RFC 6282 to a normative reference.
Changes from -18 to -19:
o Editorial improvements as a result of IESG comments (#135,
#142).
o Extended ABRO with longer version number and valid lifetime,
while maintaining backward compatibility (#141).
o Renamed optional features and described them as substitutable
(#138).
Changes from -17 to -18:
o Fixed nits related to IESG submission.
Changes from -16 to -17:
o Removed unnecessary normative text from Assumptions.
o Clarified the next-hop determination of multicast addresses.
o Editorial improvements from WGLC review.
Changes from -15 to -16:
o Added an applicability section (#133)
o Updated document title to align with HC
o Minor editing as result of WGLC review (#134)
Changes from -14 to -15:
o Changed use of redirect to SHOULD NOT for route-over and MAY for
mesh-under. (#130)
o Changed the 16-bit lifetimes to a unit of 60 seconds (#131)
o Added text to Section 5.4.2 adding a receive-only state to
context entries that timeout. (#132)
Changes from -13 to -14:
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o Introduced the new DAR and DAC ICMPv6 message types for multihop
DAD to avoid relying on the Length=4 checks for the ARO. This
simplifies implementing the hop limit check.
o Clarified the hop limit values for the multihop DAD messages by
introducing the MULTIHOP_HOPLIMIT constant set to 64.
o Clarified when a host should de-register from a router.
o Added a section on next-hop determination for routers.
o Removed the infinite lifetime from 6CO.
o Increased MIN_CONTEXT_CHANGE_DELAY to 300 seconds.
Changes from -12 to -13:
o Error-to solution added for returning NA messages carrying an
error ARO option to the link-local EUI-64 based IPv6 address of
the host (#126).
o New examples added.
Changes from -11 to -12:
o Version field of ABRO moved after Length for 32-bit alignment of
the reserved space (#90).
o Several clarifications were made on router interaction,
including a new section with router interaction examples (#91).
o Temporary Neighbor Cache Entry created upon host sending NS+ARO,
and SLLAO removed from multihop DAD NS/NA messages (#87).
Changes from -10 to -11:
o Reference to RFC1982 for version number comparison (#80)
o RA Router Lifetime field use clarified (#81)
o Make fields 16-bit rather than 32-bit where possible (#83)
o Unicast RA clarification (#84)
o Temporary ND option types (#85)
o SLLA/TLLA clarification (#86)
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o GP16 as source address in initial NS clarification (#87)
Changes from -09 to -10:
o Clarifications made to Section 8.2 (#66)
o Explained behavior of Neighbor Cache (#67)
o Clarified use of SLLAO in RS and NS messages (#68)
o Added new term 6LN (#69)
o Small clarification on 6CO flag (#70)
o Defined host behavior on ARO failure better (#72)
o Added bootstrapping example for a host (#73)
o Added new Neighbor Cache Full ARO error (#74)
o Added rule on the use of the M flag (#75)
Changes from -08 to -09:
o Clean re-write of the draft (re-use of some introductory
material)
o Merged in draft-chakrabarti-6lowpan-ipv6-nd-simple-00
o Changed address registration to an option piggybacked on NS/NA
o New Authoritative Border Router option
o New Address Registration Option
o Separated Prefix Information and Content Information
o Optional DAD to the edge
Changes from -07 to -08:
o Removed Extended LoWPAN and Whiteboard related sections.
o Included reference to the autoconf addressing model.
o Added Optimistic Flag to 6AO.
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o Added guidelines on routers performing DAD.
o Removed the NR/NC Advertising Interval.
o Added assumption of uniform IID formation and DAD throughout a
LoWPAN.
Changes from -06 to -07:
o Updated addressing and address resolution (#60).
o Changed the Address Option to 6LoWPAN Address Option, fixed S
values (#61).
o Added support for classic RFC4861 RA Prefix Information messages
to be processed (#62).
o Added a section on using 6LoWPAN-ND under a hard-wired RFC4861
stack (#63).
o Updated the NR/NC message with a new Router flag, combined the
Code and Status fields into one byte, and added the capability to
carry 6IOs (#64).
o Made co-existence with other ND mechanisms clear (#59).
o Added a new Protocol Specification section with all mechanisms
specified there (#59).
o Removed dependencies and conflicts with RFC4861 wherever
possible (#59).
o Some editorial cleanup.
Changes from -05 to -06:
o Fixed the Prf codes (#52).
o Corrected the OIIO TID field to 8-bits. Changed the Nonce/OII
order in both the OIIO and the NR/NC. (#53)
o Corrected an error in Table 1 (#54).
o Fixed asymmetric and a misplaced transient in the 6LoWPAN
terminology section.
o Added Updates RFC4861 to header
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Changes from -04 to -05:
o Meaning of the RA's M-bit changed to original [RFC4861] meaning
(#46).
o Terms "on-link" and "off-link" used in place of "on-link" and
"off-link".
o Next-hop determination text simplified (#49).
o Neighbor cache and destination cache removed.
o IID to link-layer address requirement relaxed.
o NR/NC changes to enable on-link refresh with routers (#48).
o Modified 6LoWPAN Information Option (#47).
o Added a Protocol Constants section (#24)
o Added the NR processing table (#51)
o Considered the use of SeND on backbone NS/NA messages (#50)
Changes from -03 to -04:
o Moved Ad-hoc LoWPAN operation to Section 7 and made ULA prefix
generation a features useful also in Simple and Extended LoWPANs.
(#41)
o Added a 32-bit Owner Nonce to the NR/NC messages and the
Whiteboard, removed the TID history. (#39)
o Improved the duplicate OII detection algorithm using the Owner
Nonce. (#39)
o Clarified the use of Source and Target link-layer options in
NR/NC. (#43)
o Included text on the use of alternative methods to acquire
addresses. (#38)
o Removed S=2 from Address Option (not needed). (#36)
o Added a section on router dissemination consistency. (#44)
o Small improvements and extensive editing. (#42, #37, #35)
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Changes from -02 to -03:
o Updated terminology, with RFC4861 non-transitive link model.
o 6LoWPAN and ND terminology separated.
o Protocol overview explains RFC4861 diff in detail.
o RR/RC is now Node Registration/Confirmation (NR/NC).
o Added NR failure codes.
o ER Metric now included in 6LoWPAN Summary Option for use in
default router determination by hosts.
o Examples of host data structures, and the Whiteboard given.
o Whiteboard is supported by all Edge Routers for option
simplicity.
o Edge Router Specification chapter re-structured, clarifying
optional Extended LoWPAN operation.
o NS/NA now completely optional for nodes. No address resolution
or NS/NA NUD required.
o link-local operation now compatible with oDAD (was broken).
o Exception to hop limit = 255 for NR/NC messages.
o Security considerations improved.
o ICMPv6 destination unreachable supported.
Changes from -01 to -02:
o Fixed 16 != 0xff bug (ticket closed).
o Specified use of ULAs in ad-hoc LoWPAN section 9 (ticket
closed).
o Terminology cleanup based on Alex's comments.
o General editing improvements.
Changes from -00 to -01:
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o Specified the duplicate owner interface identifier procedures.
A TID lollipop algorithm was sufficient (nonce unnecessary).
o Defined fault tolerance using secondary bindings.
o Defined ad-hoc network operation.
o Removed the E flag from RA and the X flag from RR/RC.
o Completed message examples.
o Lots of improvements in text quality and consistency were made.
17. References
17.1. Normative References
[ETHERNET]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
3: Carrier sense multiple access with Collision Detection
(CSMA/CD) Access Method and Physical Layer
Specifications", IEEE Std 802.3-2008, December 2008, <http
://standards.ieee.org/getieee802/download/
802.3-2008_section1.pdf>.
[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.
[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.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
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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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011.
17.2. Informative References
[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority", <http://standards.ieee.org/
regauth/oui/tutorials/EUI64.html>.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[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.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006.
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[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.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5006] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Option for DNS Configuration",
RFC 5006, September 2007.
[RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad
Hoc Networks", RFC 5889, September 2010.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059,
November 2010.
Authors' Addresses
Zach Shelby (editor)
Sensinode
Konekuja 2
Oulu 90620
FINLAND
Phone: +358407796297
Email: zach@sensinode.com
Samita Chakrabarti
Ericsson
Email: samita.chakrabarti@ericsson.com
Erik Nordmark
Cisco Systems
Email: nordmark@cisco.com
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