IPv6 Neighbor Discovery on Wireless Networks
draft-thubert-6man-ipv6-over-wireless-11
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draft-thubert-6man-ipv6-over-wireless-11
6MAN P. Thubert, Ed.
Internet-Draft Cisco Systems
Intended status: Informational 15 December 2021
Expires: 18 June 2022
IPv6 Neighbor Discovery on Wireless Networks
draft-thubert-6man-ipv6-over-wireless-11
Abstract
This document describes how the original IPv6 Neighbor Discovery and
Wireless ND (WiND) can be applied on various abstractions of wireless
media.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 18 June 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. IP Links . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. IP Subnets . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 6
3. ND-Classic, Wireless ND and ND-Proxies . . . . . . . . . . . 6
4. IP Models . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Physical Broadcast Domain . . . . . . . . . . . . . . . . 8
4.2. link-layer Broadcast Emulations . . . . . . . . . . . . . 9
4.3. Mapping the IPv6 link Abstraction . . . . . . . . . . . . 11
4.4. Mapping the IPv6 subnet Abstraction . . . . . . . . . . . 12
5. Wireless Neighbor Discovery . . . . . . . . . . . . . . . . . 13
5.1. Introduction to Stateful Address Autoconfiguration . . . 13
5.2. links and Link-Local Addresses . . . . . . . . . . . . . 14
5.3. Subnets and Global Addresses . . . . . . . . . . . . . . 15
5.4. Anycast and Multicast Addresses . . . . . . . . . . . . . 15
6. WiND Applicability . . . . . . . . . . . . . . . . . . . . . 16
6.1. Case of LPWANs . . . . . . . . . . . . . . . . . . . . . 17
6.2. Case of Infrastructure BSS and ESS . . . . . . . . . . . 17
6.3. Case of Mesh Under Technologies . . . . . . . . . . . . . 18
6.4. Case of DMB radios . . . . . . . . . . . . . . . . . . . 18
6.4.1. Using ND-Classic only . . . . . . . . . . . . . . . . 19
6.4.2. Using Wireless ND . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
10. Normative References . . . . . . . . . . . . . . . . . . . . 22
11. Informative References . . . . . . . . . . . . . . . . . . . 23
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
IEEE Std. 802.1 [IEEE Std. 802.1] Ethernet Bridging provides an
efficient and reliable broadcast service for wired networks;
applications and protocols have been built that heavily depend on
that feature for their core operation. Unfortunately, Low-Power
Lossy Networks (LLNs) and Wireless Local Area Networks (WLANs)
generally do not benefit from the same reliable and cheap broadcast
capabilities as Ethernet links.
As opposed to unicast transmissions, the broadcast transmissions over
wireless links are not subject to automatic retries (ARQ) and can be
very unreliable. Reducing the speed at the physical (PHY) layer for
broadcast transmissions can increase the reliability, at the expense
of a higher relative cost of broadcast on the overall available
bandwidth. As a result, protocols designed for bridged networks that
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rely on broadcast transmissions often exhibit disappointing
behaviours when employed unmodified on a local wireless medium (see
[MCAST PROBLEMS]).
Like Transparent Bridging, the IPv6 [RFC8200] Neighbor Discovery
[RFC4861] [RFC4862] Protocol (ND-Classic) is reactive, and relies on
on-demand Network Layer multicast to locate an on-link correspondent
(Address Resolution, AR) and ensure the uniqueness of an IPv6 address
(Duplicate Address Detection, aka DAD) in the case of Stateless
Address Autoconfiguration (SLAAC). On Ethernet LANs and most WLANs
and Low-Power Personal Area Networks (LoWPANs), the Network Layer
multicast operation is typically implemented as a link-layer
broadcast for the lack of an adapted and scalable link-layer
multicast operation.
It results that on wireless, an ND-Classic multicast message is
typically broadcasted. So even though there are very few nodes
subscribed to the Network Layer multicast group, and there is at most
one intended Target, the broadcast is received by many wireless nodes
over the whole subnet (e.g., the ESS fabric). And yet, the broadcast
transmission being unreliable, the intended Target may effectively
have missed the packet.
On paper, a Wi-Fi station must keep its radio turned on to listen to
the periodic series of broadcast frames, which for the most part will
be dropped when they reach Network Layer. In order to avoid this
waste of energy and increase its battery life, a typical battery-
operated device such as an IoT sensor or a smartphone will blindly
ignore a ratio of the broadcasts, making ND-Classic operations even
less reliable.
Wi-Fi [IEEE Std. 802.11] Access Points (APs) deployed in an Extended
Service Set (ESS) act as [IEEE Std. 802.1] bridges between the
wireless stations (STA) and the wired backbone. As opposed to the
classical Transparent (aka Learning) Bridge operation that installs
the forwarding state reactively to traffic, the bridging state in the
AP is established proactively, at the time of association. This
protects the wireless medium against broadcast-intensive Transparent
Bridging lookups. The association process registers the link-layer
(MAC) Address (LLA) of the STA to the AP proactively, i.e., before it
is needed. The AP maintains the list of the associated addresses and
blocks the lookups for destinations that are not registered. This
solves the broadcast issue for the link-layer lookups, but the
Network Layer problem remains.
Though ND-Classic was the state of the art when designed for an
Ethernet wire at the end of the twentieth century, it must be
reevaluated for the new technologies, such as wireless and overlays,
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that evolved since then. This document discusses the applicability
of ND-Classic over wireless links, as compared with routing-based
alternatives such as prefix-per node and multi-link subnets (MLSN),
and with Wireless ND (WiND), that is similar to the Wi-Fi association
and reduces the need for Network Layer multicast.
2. Terminology
2.1. IP Links
For a long time, the term link has been used to refer to the layer 2
communication medium that can be leveraged at layer 3 to instantiate
one IP hop. In this document we conserve that term but differentiate
it from an IP link, which is a layer 3 abstraction that represents
the layer 2 link but is not the layer 2 link, like the map is not the
country.
With IPv6, IP has moved to layer 3 abstractions for its operations,
e.g., with the use of link local address (LLA), and that of IP
multicast for link-scoped operations. At the same time, the concept
of an IP link emerged as an abstraction that represents how IP layer
considers the layer 2 link:
* An IP link connects an IP node to one or more other IP nodes using
a lower layer subnetwork. The lower layer subnetwork may comprise
multiple lower layer links, e.g., in the case of a switched fabric
or a mesh-under LLN.
* an IP link defines the scope of an LLA, and defines the domain in
which the LLA must be unique
* an IP link provides a subset of the connectivity that is offered
by the lower layer; if the IP link is narrower than the layer 2
reachable domain, then layer 3 filters must restrict the link-
scoped communication to remain between peers on a same IP link,
and more than one IP link may be installed on the same physical
interface to connect to different peers.
* an IP link can be Point to Point (P2P), Point to Point (P2MP,
forming a partial mesh), NBMA (non-broadcast multi-access, fully
meshed), or transit (broadcast-capable and any-to-any).
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It is a network design decision to use one IP link model or another
over a given lower layer network, e.g., to map a Frame Relay network
as a P2MP IP link, or as a collection of P2P IP links. As another
example, an Ethernet fabric may be bridged, in which case the nodes
that interconnect the layer 2 links are L2 switches, and the fabric
can be abstracted as a single transit IP link; or the fabric can be
routed, in which case the P2P IP links are congruent with the layer 2
links, and the nodes that interconnect the links are routers.
2.2. IP Subnets
IPv6 builds another abstraction, the IP subnet, over one shared IP
link or over a collection IP links, forming a MLSN in the latter
case. An MLSN is formed over IP links (e.g., P2P or P2MP) that are
interconnected by routers that either inject hosts routes in an IGP,
in which case the topology can be anything, or perform ND proxy
operations, in which case the structure of links must be strictly
hierarchical to avoid loops.
[RFC8929] defines bridging and routing IPv6 ND proxies. Both forms
of ND proxies interconnect IP links and enable to isolate the layer 2
broadcast domains. But in the case of a bridging proxy, the layer 2
unicast communication can still exist between the layer 2 domains
that are coverered by the layer 3 links, whereas in the base of a
routing proxy, they are isolated and packets must be routed back and
forth. Bridging proxies are possible between compatible technologies
and translational bridges (e.g., Wi-Fi to Ethernet), whereas routing
proxies are required between non-bridgeable technologies and
desirable to avoid exposing the layer 2 addresses across, e.g., for
reasons of stability and scalability.
It is another network design decision to use one IP subnet model or
another over a given lower layer network. A switched fabric can host
one or more IP subnets, in which case the IP links can reach all and
beyond one subnet. On the other hand, a subnet can encompass a
collection of links; in that case, the scope of the link local
addresses, which is the IP Link, is narrower than the span of the
subnet.
A subnet prefix is associated with the IP subnet, and a node is a
member of an IP subnet when it has an IP address that derives from
that prefix. The IP address is either a Unique Local (ULA) or a
Global Unicast Address (GUA), and as opposed to the case of LLAs, the
scope of the address is not limited to the IP subnet.
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The switched and routed fabric above could be the exact same network
of physical links and boxes, what changes is the way the networking
abstractions are mapped onto the system, and the implication of such
decision include the capability to reach another node at layer-2, and
the size of the broadcast domain and related broadcast storms.
2.3. Acronyms
This document uses the following abbreviations:
6BBR: 6LoWPAN Backbone Router
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router
ARO: Address Registration Option
DAC: Duplicate Address Confirmation
DAD: Duplicate Address Detection
DAR: Duplicate Address Request
EDAC: Extended Duplicate Address Confirmation
EDAR: Extended Duplicate Address Request
MLSN: Multi-link subnet
LLN: Low-Power and Lossy Network
LoWPAN: Low-Power Wireless Personal Area Network
NA: Neighbor Advertisement
NBMA: Non-Broadcast Multi-Access
NCE: Neighbor Cache Entry
ND: Neighbor Discovery
NDP: Neighbor Discovery Protocol
NS: Neighbor Solicitation
RPL: IPv6 Routing Protocol for LLNs
RA: Router Advertisement
RS: Router Solicitation
VLAN: Virtual Local Area Network
WiND: Wireless Neighbor Discovery
WLAN: Wireless Local Area Network
WPAN: Wireless Personal Area Network
3. ND-Classic, Wireless ND and ND-Proxies
The ND-Classic Neighbor Solicitation (NS) [RFC4861] message is used
as a multicast IP packet for Address Resolution (AR) and Duplicate
Address Detection (DAD) [RFC4862]. In those cases, the NS message is
sent at the Network Layer to a Solicited-Node Multicast Address
(SNMA) [RFC4291] and should in theory only reach a very small group
of nodes. It is intended for one Target, that may or may not be
present in the network, but it is often turned into a MAC-Layer
broadcast and effectively reaches most of the nodes that are attached
to the layer 2 link.
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DAD was designed for the efficient broadcast operation of Ethernet.
Experiments show that DAD often fails to discover the duplication of
IPv6 addresses in large wireless access networks [DAD ISSUES]. In
practice, IPv6 addresses very rarely conflict, not because the
address duplications are detected and resolved by the DAD operation,
but thanks to the entropy of the 64-bit Interface IDs (IIDs) that
makes a collision quasi-impossible for randomized IIDs.
Multicast NS transmissions may occur when a node joins the network,
moves, or wakes up and reconnects to the network. Over a very large
fabric, this can generate hundreds of broadcasts per second. If the
broadcasts were blindly copied over Wi-Fi, the MAC-layer broadcast
traffic associated to ND IP-layer multicast could consume enough
bandwidth to cause a substantial degradation to the unicast service
[MCAST EFFICIENCY]. To protect their bandwidth, some networks
throttle ND-related broadcasts, which reduces the capability for the
ND protocol to operate as expected.
This problem can be alleviated by reducing the size of the broadcast
domain that encompasses wireless access links. This has been done in
the art of IP subnetting by partitioning the subnets and by routing
between them, at the extreme by assigning a /64 prefix to each
wireless node (see [RFC8273]).
Another way to split the broadcast domain within a subnet is to proxy
at the boundary of the wired and wireless domains the Network Layer
protocols that rely on link-layer broadcast operations. [IEEE Std.
802.11] recommends to deploy proxies for the IPv4 Address Resolution
Protocol (ARP) and IPv6 ND at the APs. This requires the exhaustive
list of the IP addresses for which proxying is provided. Forming and
maintaining that knowledge a hard problem in the general case of
radio connectivity, which keeps changing with movements and
variations in the environment that alter the range of transmissions.
[SAVI] suggests to discover the addresses by snooping the ND-Classic
protocol, but that can also be unreliable. An IPv6 address may not
be discovered immediately due to a packet loss. It may never be
discovered in the case of a "silent" node that is not currently using
one of its addresses, e.g., a printer that waits in wake-on-lan
state. A change of anchor, e.g. due to a movement, may be missed or
misordered, leading to unreliable connectivity and an incomplete list
of addresses.
Wireless ND (WiND) introduces a new approach to IPv6 Neighbor
Discovery that is designed to apply to the WLANs and LoWPANs types of
networks, as well as other Non-Broadcast Multi-Access (NBMA) networks
such as Data-Center overlays. WiND applies routing inside the
subnets, which enables to form potentially large MLSNs without
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creating a large broadcast domain at the link-layer. In a fashion
similar to a Wi-Fi Association, IPv6 Hosts register their addresses
to their serving router(s), using [RFC8505]. With the registration,
the routers have a complete knowledge of the hosts they serve and in
return, hosts obtain routing services for their registered addresses.
The registration is abstract to the routing service, and it can be
protected to prevent impersonation attacks with [RFC8928].
The routing service can be a simple reflexion in a Hub-and-Spoke
subnet that emulates an IEEE Std. 802.11 Infrastructure BSS at the
Network Layer. It can also be a full-fledge routing protocol, in
particular RPL [RFC6550], which is designed to adapt to various LLNs
such as WLAN and WPAN radio meshes. Finally, the routing service can
also be an ND proxy that emulates an IEEE Std. 802.11 Infrastructure
ESS at the Network Layer, as specified in the IPv6 Backbone Router
[RFC8929].
On the one hand, WiND avoids the use of broadcast operation for DAD
and AR, and on the other hand, WiND supports use cases where subnet
and link-layer domains are not congruent, which is common in wireless
networks unless a specific link-layer emulation is provided. More
details on WiND can be found in Section 5.1.
4. IP Models
4.1. Physical Broadcast Domain
At the physical (PHY) Layer, a broadcast domain is the set of nodes
that may receive a transmission that one sends over an interface, in
other words the set of nodes in range of the radio transmission.
This set can comprise a single peer on a serial cable used as point-
to-point link. It may also comprise multiple peer nodes on a
broadcast radio or a shared physical resource such as the Ethernet
wires and hubs for which ND-Classic was initially designed.
On WLAN and LoWPAN radios, the physical broadcast domain is defined
relative to a particular transmitter, as the set of nodes that can
receive what this transmitter is sending. Literally every frame
defines its own broadcast domain since the chances of reception of a
given frame are statistical. In average and in stable conditions,
the broadcast domain of a particular node can be still be seen as
mostly constant and can be used to define a closure of nodes on which
an upper Layer abstraction can be built.
A PHY Layer communication can be established between two nodes if the
physical broadcast domains of their unicast transmissions overlap.
On WLAN and LoWPAN radios, that relation is usually not reflexive,
since nodes disable the reception when they transmit; still they may
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retain a copy of the transmitted frame, so it can be seen as
reflexive at the MAC Layer. It is often symmetric, meaning that if B
can receive a frame from A, then A can receive a frame from B. But
there can be asymmetries due to power levels, interferers near one of
the receivers, or differences in the quality of the hardware (e.g.,
crystals, PAs and antennas) that may affect the balance to the point
that the connectivity becomes mostly uni-directional, e.g., A to B
but practically not B to A.
It takes a particular effort to place a set of devices in a fashion
that all their physical broadcast domains fully overlap, and that
specific situation can not be assumed in the general case. In other
words, the relation of radio connectivity is generally not
transitive, meaning that A in range with B and B in range with C does
not necessarily imply that A is in range with C.
4.2. link-layer Broadcast Emulations
We call Direct MAC Broadcast (DMB) the transmission mode where the
broadcast domain that is usable at the MAC layer is directly the
physical broadcast domain. IEEE Std. 802.15.4 [IEEE Std. 802.15.4]
and IEEE Std. 802.11 [IEEE Std. 802.11] OCB (for Out of the Context
of a BSS) are examples of DMB radios. DMB networks provide mostly
symmetric and non-transitive transmission. This contrasts with a
number of link-layer Broadcast Emulation (LLBE) schemes that are
described in this section.
In the case of Ethernet, while a physical broadcast domain is
constrained to a single shared wire, the IEEE Std. 802.1 [IEEE Std.
802.1] bridging function emulates the broadcast properties of that
wire over a whole physical mesh of Ethernet links. For the upper
layer, the qualities of the shared wire are essentially conserved,
with a reliable and cheap broadcast operation over a transitive
closure of nodes defined by their connectivity to the emulated wire.
In large switched fabrics, overlay techniques enable a limited
connectivity between nodes that are known to a Map Resolver. The
emulated broadcast domain is configured to the system, e.g., with a
VXLAN network identifier (VNID). Broadcast operations on the overlay
can be emulated but can become very expensive, and it makes sense to
proactively install the relevant state in the mapping server as
opposed to rely on reactive broadcast lookups to do so.
An IEEE Std. 802.11 [IEEE Std. 802.11] Infrastructure Basic Service
Set (BSS) also provides a transitive closure of nodes as defined by
the broadcast domain of a central AP. The AP relays both unicast and
broadcast packets and provides the symmetric and transitive emulation
of a shared wire between the associated nodes, with the capability to
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signal link-up/link-down to the upper layer. Within a BSS, the
physical broadcast domain of the AP serves as emulated broadcast
domain for all the nodes that are associated to the AP. Broadcast
packets are relayed by the AP and are not acknowledged. To increase
the chances that all nodes in the BSS receive the broadcast
transmission, AP transmits at the slowest PHY speed. This translates
into maximum co-channel interferences for others and the longest
occupancy of the medium, for a duration that can be a hundred times
that of the unicast transmission of a frame of the same size.
For that reason, upper layer protocols should tend to avoid the use
of broadcast when operating over Wi-Fi. To cope with this problems,
APs may implement strategies such as turn a broadcast into a series
of unicast transmissions, or drop the message altogether, which may
impact the upper layer protocols. For instance, some APs may not
copy Router Solicitation (RS) messages under the assumption that
there is no router across the wireless interface. This assumption
may be correct at some point of time and may become incorrect in the
future. Another strategy used in Wi-Fi APS is to proxy protocols
that heavily rely on broadcast, such as the Address Resolution in ARP
and ND-Classic, and either respond on behalf or preferably forward
the broadcast frame as a unicast to the intended Target.
In an IEEE Std. 802.11 [IEEE Std. 802.11] Infrastructure Extended
Service Set (ESS), infrastructure BSSes are interconnected by a
bridged network, typically running Transparent Bridging and the
Spanning tree Protocol or a more advanced Layer 2 Routing (L2R)
scheme. In the original model of learning bridges, the forwarding
state is set by observing the source MAC address of the frames. When
a state is missing for a destination MAC address, the frame is
broadcasted with the expectation that the response will populate the
state on the reverse path. This is a reactive operation, meaning
that the state is populated reactively to the need to reach a
destination. It is also possible in the original model to broadcast
a gratuitous frame to advertise self throughout the bridged network,
and that is also a broadcast.
The process of the Wi-Fi association prepares a bridging state
proactively at the AP, which avoids the need for a reactive broadcast
lookup over the wireless access. In an ESS, the AP may also generate
a gratuitous broadcast sourced at the MAC address of the STA to
prepare or update the state in the learning bridges so they point
towards the AP for the MAC address of the STA. WiND emulates that
proactive method at the Network Layer for the operations of AR, DAD
and ND proxy.
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In some instances of WLANs and LoWPANs, a Mesh-Under technology
(e.g., a IEEE Std. 802.11s or IEEE Std. 802.15.10) provides meshing
services that are similar to bridging, and the broadcast domain is
well-defined by the membership of the mesh. Mesh-Under emulates a
broadcast domain by flooding the broadcast packets at the link-layer.
When operating on a single frequency, this operation is known to
interfere with itself, and requires inter-frame gaps to dampen the
collisions, which reduces further the amount of available bandwidth.
As the cost of broadcast transmissions becomes increasingly
expensive, there is a push to rethink the upper Layer protocols to
reduce the dependency on broadcast operations.
4.3. Mapping the IPv6 link Abstraction
As introduced in Section 2.1, IPv6 defines a concept of link, link
scope and Link-Local Addresses (LLA), an LLA being unique and usable
only within the Scope of a Link. The ND-Classic [RFC4861] DAD
[RFC4862] process uses a multicast transmission to detect a duplicate
address, which requires that the owner of the address is connected to
the link-layer broadcast domain of the sender.
On a wired medium, the IP link is often confused with the physical
broadcast domain because both are determined by the serial cable or
the Ethernet shared wire. Ethernet Bridging reinforces that illusion
with a link-layer broadcast domain that emulates a physical broadcast
domain over the mesh of wires. But the difference shows on legacy
P2MP and NBMA networks such as ATM and Frame-Relay, on shared links
and on newer types of NBMA networks such as radio and composite
radio-wires networks. It also shows when private VLANs or link-layer
cryptography restrict the capability to read a frame to a subset of
the connected nodes.
In Mesh-Under and Infrastructure BSS, the IP link extends beyond the
physical broadcast domain to the emulated link-layer broadcast
domain. Relying on Multicast for the ND operation remains feasible
but becomes highly detrimental to the unicast traffic, and becomes
less and less energy-efficient and reliable as the network grows.
On DMB radios, IP links between peers come and go as the individual
physical broadcast domains of the transmitters meet and overlap. The
DAD operation cannot provide once and for all guarantees over the
broadcast domain defined by one radio transmitter if that transmitter
keeps meeting new peers on the go.
The scope on which the uniqueness of an LLA must be checked is each
new pair of nodes for the duration of their conversation. As long as
there's no conflict, a node may use the same LLA with multiple peers
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but it has to perform DAD again with each new peer. A node may need
to form a new LLA to talk to a new peer, and multiple LLAs may be
present in the same radio interface to talk to different peers. In
practice, each pair of nodes defines a temporary P2P link, which can
be modeled as a sub-interface of the radio interface.
The DAD and AR procedures in ND-Classic expect that a node in a
subnet is reachable within the broadcast domain of any other node in
the subnet when that other node attempts to form an address that
would be a duplicate or attempts to resolve the MAC address of this
node. This is why ND is applicable for P2P and transit links, but
requires extensions for more complex topologies.
4.4. Mapping the IPv6 subnet Abstraction
As introduced in Section 2.2, IPv6 also defines the concept of a
subnet for Global and Unique Local Addresses (GLA and ULA). All the
addresses in a subnet share the same prefix, and by extension, a node
belongs to a subnet if it has an address that derives from the prefix
of the subnet. That address must be topologically correct, meaning
that it must be installed on an interface that is connected to the
subnet.
Unless intently replicated in different locations for very specific
purposes, a subnet prefix is unique within a routing system; for
ULAs, the routing system is typically a limited domain, whereas for
GLAs, it is the whole Internet.
For that reason, it is sufficient to validate that an address that is
formed from a subnet prefix is unique within the scope of that subnet
to guarantee that it is globally unique within the whole routing
system. Note that a subnet may become partitioned due to the loss of
a wired or wireless link, so even that operation is not necessarily
obvious, more in [DAD APPROACHES].
The IPv6 aggregation model relies on the property that a packet from
the outside of a subnet can be routed to any router that belongs to
the subnet, and that this router will be able to either resolve the
destination link-layer address and deliver the packet, or, in the
case of an MLSN, route the packet to the destination within the
subnet.
If the subnet is known as on-link, then any node may also resolve the
destination link-layer address and deliver the packet, but if the
subnet is not on-link, then a host in the subnet that does not have a
Neighbor Cache Entry (NCE) for the destination will also need to pass
the packet to a router, more in [RFC5942].
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On Ethernet, an IP subnet is often congruent with an IP link because
both are determined by the physical attachment to a shared wire or an
IEEE Std. 802.1 bridged domain. In that case, the connectivity over
the IP link is both symmetric and transitive, the subnet can appear
as on-link, and any node can resolve a destination MAC address of any
other node directly using ND-Classic.
But an IP link and an IP subnet are not always congruent. In the
case of a Shared Link, individual subnets may each encompass only a
subset of the nodes connected to the link. Conversely, in Route-Over
Multi-link subnets (MLSN) [RFC4903], routers federate the links
between nodes that belong to the subnet, the subnet is not on-link
and it extends beyond any of the federated links.
5. Wireless Neighbor Discovery
5.1. Introduction to Stateful Address Autoconfiguration
Stateful Address Autoconfiguration (SFAAC)
[RFC6775][RFC8505][RFC8929][RFC8928] defines a new operation for ND
that is based on 2 major paradigm changes, proactive address
registration by hosts to their attachment routers and routing to host
routes (/128) within the subnet. This allows ND to avoid the
expectations of transit links and subnet-wide broadcast domains.
SFAAC is agnostic to the method used for Address Assignment, e.g.,
Manual, Semantically Opaque Autoconfiguration [RFC7217], randomized
[RFC8981], or DHCPv6 [RFC8415]. It does not change the IPv6
addressing [RFC4291] or the current practices of assigning prefixes,
typically a /64, to a subnet. But the DAD operation is performed as
a unicast exchange with a central registrar, using new ND Extended
Duplicate Address messages (EDAR and EDAC) [RFC6775][RFC8505]. This
modernizes ND for application in overlays with Map Resolvers and
enables unicast lookups [UNICAST AR] for addresses registered to the
resolver.
The proactive address registration is performed with a new option in
NS/NA messages, the Extended Address Registration Option (EARO)
defined in [RFC8505]. This method allows to prepare and maintain the
host routes in the routers and avoids the reactive Address Resolution
in ND-Classic and the associated link-layer broadcasts transmissions.
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The EARO provides information to the router that is independent to
the routing protocol and routing can take multiple forms, from a
traditional IGP to a collapsed Hub-and-Spoke model where only one
router owns and advertises the prefix. [RFC8505] is already
referenced as the registration interface to "RIFT: Routing in Fat
Trees" [I-D.ietf-rift-rift] and "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RFC6550] with [RPL UNAWARE LEAVES].
Wireless ND (WiND) combines SFAAC with the not-onlink model on the
wireless interfaces, and a Backbone Router (6BBR) ND proxy function
(more in [RFC8929]) operating as a Layer-3 AP. Multiple 6BBRs placed
along the wireless edge of a Backbone link handle IPv6 Neighbor
Discovery and forward packets over the backbone on behalf of the
registered nodes on the wireless edge. This enables to span a subnet
over an MLSN that federates edge wireless links with a high-speed,
typically Ethernet, backbone (as a Layer-3 ESS). The ND proxy
maintains the reachability for Global Unicast and Link-LOcal
Addresses within the federated MLSN, either as a routing proxy where
it replies with its own MAC address or as a bridging proxy that
typically forwards the multicast ND messages as unicast Layer-2
frames to their target. The wireless nodes can form any address they
want and move freely from a wireless edge link to another, without
renumbering.
5.2. links and Link-Local Addresses
For Link-Local Addresses, DAD is typically performed between
communicating pairs of nodes and an NCE can be populated with a
single unicast exchange. In the case of a bridging proxies, though,
the Link-Local traffic is bridged over the backbone and the DAD must
proxied there as well.
For instance, in the case of Bluetooth Low Energy (BLE)
[RFC7668][IEEEstd802151], the uniqueness of Link-Local Addresses
needs only to be verified between the pair of communicating nodes,
the central router and the peripheral host. In that example, 2
peripheral hosts connected to the same central router can not have
the same Link-Local Address because the addresses would collision at
the central router which could not talk to both over the same
interface. The DAD operation from SFAAC is appropriate for that use
case, but the one from ND is not, because the peripheral hosts are
not on the same broadcast domain.
On the other hand, the uniqueness of Global and Unique-Local
Addresses is validated at the subnet Level, using a logical registrar
that is global to the subnet.
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5.3. Subnets and Global Addresses
SFAAC extends ND-Classic for Hub-and-Spoke (e.g., BLE) and Route-Over
(e.g., RPL) Multi-link subnets (MLSNs).
In the Hub-and-Spoke case, each Hub-Spoke pair is a distinct IP Link,
and a subnet can be mapped on a collection of links that are
connected to the Hub. The subnet prefix is associated to the Hub.
Acting as a router, the Hub advertises the prefix as not-on-link to
the spokes in RA messages Prefix Information Options (PIO). Acting
as hosts, the Spokes autoconfigure addresses from that prefix and
register them to the Hub with a corresponding lifetime.
Acting as a registrar, the Hub maintains a binding table of all the
registered IP addresses and rejects duplicate registrations, thus
ensuring a DAD protection for a registered address even if the
registering node is sleeping.
The Hub also maintains an NCE for the registered addresses and can
deliver a packet to any of them during their respective lifetimes.
It can be observed that this design builds a form of Network Layer
Infrastructure BSS.
A Route-Over MLSN is considered as a collection of Hub-and-Spoke
where the Hubs form a connected dominating set of the member nodes of
the subnet, and IPv6 routing takes place between the Hubs within the
subnet. A single logical registrar is deployed to serve the whole
mesh.
The registration in [RFC8505] is abstract to the routing protocol and
provides enough information to feed a routing protocol such as RPL as
specified in [RPL UNAWARE LEAVES]. In a degraded mode, all the Hubs
are connected to a same high speed backbone such as an Ethernet
bridging domain where ND-Classic is operated. In that case, it is
possible to federate the Hub, Spoke and Backbone nodes as a single
subnet, operating ND proxy operations [RFC8929] at the Hubs, acting
as 6BBRs. It can be observed that this latter design builds a form
of Network Layer Infrastructure ESS.
5.4. Anycast and Multicast Addresses
While IPv6 ND is defined for unicast addresses only,
[I-D.ietf-6lo-multicast-registration] extends [RFC8505] for anycast
and multicast IPv6 addresses.
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[I-D.ietf-6lo-multicast-registration] can be used as a replacement
for MLDv2 [RFC3810] for use cases where broadcast are not desirable,
and when a device push model such as SFAAC is preferred over a
network pull such as MDv2 and classical ND. With [RFC8505], the host
does not need to define SNMAs for its unicast addresses and does not
perform the associated MLDv2 operation. With
[I-D.ietf-6lo-multicast-registration], MLDv2 and its extensive use of
broadcast can be totally eliminated.
In the case of anycast, the signal enables the 6BBRs to accept more
than one registration for the same address, and collectively elect
the registering host receives a packet for a given anycast address.
6. WiND Applicability
WiND applies equally to P2P links, P2MP Hub-and-Spoke, link-layer
Broadcast Domain Emulation such as Mesh-Under and Wi-Fi BSS, and
Route-Over meshes.
There is an intersection where The IP link and the IP subnet are
congruent and where both ND and WiND could apply. These includes
P2P, the MAC emulation of a PHY broadcast domain, and the particular
case of always on, fully overlapping physical radio broadcast domain.
But even in those cases where both are possible, WiND is preferable
vs. ND because it reduces the need of broadcast.
This is discussed in more details in the introduction of [RFC8929].
There are also a number of practical use cases in the wireless world
where links and subnets are not congruent:
* The IEEE Std. 802.11 infrastructure BSS enables one subnet per AP,
and emulates a broadcast domain at the link-layer. The
Infrastructure ESS extends that model over a backbone and
recommends the use of an ND proxy [IEEE Std. 802.11] to
interoperate with Ethernet-connected nodes. WiND incorporates an
ND proxy to serve that need, which was missing so far.
* BlueTooth is Hub-and-Spoke at the link-layer. It would make
little sense to configure a different subnet between the central
and each individual peripheral node (e.g., sensor). Rather,
[RFC7668] allocates a prefix to the central node acting as router,
and each peripheral host (acting as a host) forms one or more
address(es) from that same prefix and registers it.
* A typical Smartgrid networks puts together Route-Over MLSNs that
comprise thousands of IPv6 nodes. The 6TiSCH architecture
[I-D.ietf-6tisch-architecture] presents the Route-Over model over
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an IEEE Std. 802.15.4 Time-Slotted Channel-Hopping (TSCH)
[IEEEstd802154] mesh, and generalizes it for multiple other
applications.
Each node in a Smartgrid network may have tens to a hundred others
nodes in range. A key problem for the routing protocol is which
other node(s) should this node peer with, because most of the
possible peers do not provide added routing value. When both
energy and bandwidth are constrained, talking to them is a waste
of resources and most of the possible P2P links are not even used.
Peerings that are actually used come and go with the dynamics of
radio signal propagation. It results that allocating prefixes to
all the possible P2P links and maintain as many addresses in all
nodes is not even considered.
6.1. Case of LPWANs
LPWANs are by nature so constrained that the addresses and subnets
are fully pre-configured and operate as P2P or Hub-and-Spoke. This
saves the steps of neighbor Discovery and enables a very efficient
stateful compression of the IPv6 header.
6.2. Case of Infrastructure BSS and ESS
In contrast to IPv4, IPv6 enables a node to form multiple addresses,
some of them temporary to elusive, and with a particular attention
paid to privacy. Addresses may be formed and deprecated
asynchronously to the association.
Snooping protocols such as ND-Classic and DHCPv6 and observing data
traffic sourced at the STA provides an imperfect knowledge of the
state of the STA at the AP. Missing a state or a transition may
result in the loss of connectivity for some of the addresses, in
particular for an address that is rarely used, belongs to a sleeping
node, or one in a situation of mobility. This may also result in
undesirable remanent state in the AP when the STA ceases to use an
IPv6 address while remaining associated. It results that snooping
protocols is not a recommended technique and that it should only be
used as last resort, when the WiND registration is not available to
populate the state.
The recommended alternative method is to use the WiND Registration
for IPv6 Addresses. This way, the AP exposes its capability to proxy
ND to the STA in Router Advertisement messages. In turn, the STA may
request proxy ND services from the AP for all of its IPv6 addresses,
using the Extended Address Registration Option, which provides the
following elements:
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* The registration state has a lifetime that limits unwanted state
remanence in the network.
* The registration is optionally secured using [RFC8928] to prevent
address theft and impersonation.
* The registration carries a sequence number, which enables to
figure the order of events in a fast mobility scenario without
loss of connectivity.
The ESS mode requires a proxy ND operation at the AP. The proxy ND
operation must cover Duplicate Address Detection, Neighbor
Unreachability Detection, Address Resolution and Address Mobility to
transfer a role of ND proxy to the AP where a STA is associated
following the mobility of the STA.
The WiND proxy ND specification that associated to the Address
Registration is [RFC8929]. With that specification, the AP
participates to the protocol as a Backbone Router, typically
operating as a bridging proxy though the routing proxy operation is
also possible. As a bridging proxy, the backbone router either
replies to NS lookups with the MAC address of the STA, or preferably
forwards the lookups to the STA as link-layer unicast frames to let
the STA answer. For the data plane, the backbone router acts as a
normal AP and bridges the packets to the STA as usual. As a routing
proxy, the backbone router replies with its own MAC address and then
routes to the STA at the IP layer. The routing proxy reduces the
need to expose the MAC address of the STA on the wired side, for a
better stability and scalability of the bridged fabric.
6.3. Case of Mesh Under Technologies
The Mesh-Under provides a broadcast domain emulation with symmetric
and Transitive properties and defines a transit link for IPv6
operations. It results that the model for IPv6 operation is similar
to that of a BSS, with the root of the mesh operating as an Access
Point does in a BSS/ESS.
While it is still possible to operate ND-Classic, the inefficiencies
of the flooding operation make the associated operations even less
desirable than in a BSS, and the use of WiND is highly recommended.
6.4. Case of DMB radios
IPv6 over DMB radios uses P2P links that can be formed and maintained
when a pair of DMB radios transmitters are in range from one another.
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6.4.1. Using ND-Classic only
DMB radios do not provide MAC level broadcast emulation. An example
of that is IEEE Std. 802.11 OCB which uses IEEE Std. 802.11 MAC/PHYs
but does not provide the BSS functions.
It is possible to form P2P IP links between each individual pairs of
nodes and operate ND-Classic over those links with Link-Local
addresses. DAD must be performed for all addresses on all P2P IP
links.
If special deployment care is taken so that the physical broadcast
domains of a collection of the nodes fully overlap, then it is also
possible to build an IP subnet within that collection of nodes and
operate ND-Classic.
If an external mechanism avoids duplicate addresses and if the
deployment ensures the connectivity between peers, a non-transit Hub-
and-Spoke deployment is also possible where the Hub is the only
router in the subnet and the Prefix is advertised as not on-link.
6.4.2. Using Wireless ND
Though this can be achieved with ND-Classic, WiND is the recommended
approach since it uses unicast communications which are more reliable
and less impacting for other users of the medium.
The routers send RAs with a SLLAO at a regular period. The period
can be indicated in the RA-Interval Option [RFC6275]. If available,
the message can be transported in a compressed form in a beacon,
e.g., in OCB Basic Safety Messages (BSM) that are nominally sent
every 100ms.
An active beaconing mode is possible whereby the Host sends broadcast
RS messages to which a router can answer with a unicast RA.
A router that has Internet connectivity and is willing to serve as an
Internet Access may advertise itself as a default router [RFC4191] in
its RA messages. The RA is sent over an unspecified IP link where it
does not conflict to anyone, so DAD is not necessary at that stage.
The host instantiates an IP link where the router's address is not a
duplicate. To achieve this, it forms an LLA that does not conflict
with that of the router and registers to the router using [RFC8505].
If the router sent an RA(PIO), the host can also autoconfigure an
address from the advertised prefix and register it.
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(host) (router)
| |
| DMB link |
| |
| IPv6 ND RS |
|-------------->|
|-----------> |
|------------------>
| IPv6 ND RA |
|<--------------|
| |
| NS(EARO) |
|-------------->|
| |
| NA(EARO) |
|<--------------|
| |
Figure 1: Initial Registration Flow
The lifetime in the registration should start with a small value
(X=RMin, TBD), and exponentially grow with each re-registration to a
larger value (X=Rmax, TBD). The IP link is considered down when
(X=NbBeacons, TDB) expected messages are not received in a row. It
must be noted that the physical link flapping does not affect the
state of the registration and when a physical link comes back up, the
active registrations (i.e., registrations for which lifetime is not
elapsed) are still usable. Packets should be held or destroyed when
the IP link is down.
P2P links may be federated in Hub-and-Spoke and then in Route-Over
MLSNs as illustrated in Figure 2. More details on the operation of
WiND and RPL over the MLSN can be found in section 3.1, 3.2, 4.1 and
4.2.2 of [I-D.ietf-6tisch-architecture].
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6LoWPAN Node 6LR 6LBR 6BBR
(RPL leaf) (router) (root)
| | | |
| 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | ND-Classic
| LLN link |Route-Over mesh|Ethernet/serial| Backbone
| | | |
| IPv6 ND RS | | |
|-------------->| | |
|-----------> | | |
|------------------> | |
| IPv6 ND RA | | |
|<--------------| | |
| | <once> | |
| NS(EARO) | | |
|-------------->| | |
| 6LoWPAN ND | Extended DAR | |
| |-------------->| |
| | | NS(EARO) |
| | |-------------->|
| | | | NS-DAD
| | | |------>
| | | | (EARO)
| | | |
| | | NA(EARO) |<timeout>
| | |<--------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<--------------| | |
| | | |
Figure 2: Initial Registration Flow over Multi-link subnet
An example Hub-and-Spoke is an OCB Road-Side Unit (RSU) that owns a
prefix, provides Internet connectivity using that prefix to On-Board
Units (OBUs) within its physical broadcast domain. An example of
Route-Over MLSN is a collection of cars in a parking lot operating
RPL to extend the connectivity provided by the RSU beyond its
physical broadcast domain. Cars may then operate NEMO [RFC3963] for
their own prefix using their address derived from the prefix of the
RSU as CareOf Address.
7. IANA Considerations
This specification does not require IANA action.
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8. Security Considerations
This specification refers to the security sections of ND-Classic and
WiND, respectively.
9. Acknowledgments
Many thanks to the participants of the 6lo WG where a lot of the work
discussed here happened. Also ROLL, 6TiSCH, and 6LoWPAN.
10. Normative References
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, DOI 10.17487/RFC3963, January 2005,
<https://www.rfc-editor.org/info/rfc3963>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC5942] Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model: The Relationship between Links and Subnet
Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
<https://www.rfc-editor.org/info/rfc5942>.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
2011, <https://www.rfc-editor.org/info/rfc6275>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
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[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
"Address-Protected Neighbor Discovery for Low-Power and
Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
2020, <https://www.rfc-editor.org/info/rfc8928>.
[RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
"IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
November 2020, <https://www.rfc-editor.org/info/rfc8929>.
11. Informative References
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
DOI 10.17487/RFC4903, June 2007,
<https://www.rfc-editor.org/info/rfc4903>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<https://www.rfc-editor.org/info/rfc7668>.
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[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
<https://www.rfc-editor.org/info/rfc8273>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[I-D.ietf-rift-rift]
Sharma, A., Thubert, P., Rijsman, B., and D. Afanasiev,
"RIFT: Routing in Fat Trees", Work in Progress, Internet-
Draft, draft-ietf-rift-rift-13, 12 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-rift-
rift-13>.
[RPL UNAWARE LEAVES]
Thubert, P. and M. C. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", Work in Progress, Internet-Draft, draft-ietf-
roll-unaware-leaves-30, 22 January 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-roll-
unaware-leaves-30>.
[DAD ISSUES]
Yourtchenko, A. and E. Nordmark, "A survey of issues
related to IPv6 Duplicate Address Detection", Work in
Progress, Internet-Draft, draft-yourtchenko-6man-dad-
issues-01, 3 March 2015,
<https://datatracker.ietf.org/doc/html/draft-yourtchenko-
6man-dad-issues-01>.
[MCAST EFFICIENCY]
Vyncke, E., Thubert, P., Levy-Abegnoli, E., and A.
Yourtchenko, "Why Network-Layer Multicast is Not Always
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Efficient At Datalink Layer", Work in Progress, Internet-
Draft, draft-vyncke-6man-mcast-not-efficient-01, 14
February 2014, <https://datatracker.ietf.org/doc/html/
draft-vyncke-6man-mcast-not-efficient-01>.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
Work in Progress, Internet-Draft, draft-ietf-6tisch-
architecture-30, 26 November 2020,
<https://datatracker.ietf.org/doc/html/draft-ietf-6tisch-
architecture-30>.
[MCAST PROBLEMS]
Perkins, C. E., McBride, M., Stanley, D., Kumari, W., and
J. C. Zuniga, "Multicast Considerations over IEEE 802
Wireless Media", Work in Progress, Internet-Draft, draft-
ietf-mboned-ieee802-mcast-problems-15, 28 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-mboned-
ieee802-mcast-problems-15>.
[SAVI] Bi, J., Wu, J., Lin, T., Wang, Y., and L. He, "A SAVI
Solution for WLAN", Work in Progress, Internet-Draft,
draft-bi-savi-wlan-22, 10 November 2021,
<https://datatracker.ietf.org/doc/html/draft-bi-savi-wlan-
22>.
[UNICAST AR]
Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery
Unicast Lookup", Work in Progress, Internet-Draft, draft-
thubert-6lo-unicast-lookup-02, 8 November 2021,
<https://datatracker.ietf.org/doc/html/draft-thubert-6lo-
unicast-lookup-02>.
[DAD APPROACHES]
Nordmark, E., "Possible approaches to make DAD more robust
and/or efficient", Work in Progress, Internet-Draft,
draft-nordmark-6man-dad-approaches-02, 19 October 2015,
<https://datatracker.ietf.org/doc/html/draft-nordmark-
6man-dad-approaches-02>.
[I-D.ietf-6lo-multicast-registration]
Thubert, P., "IPv6 Neighbor Discovery Multicast Address
Listener Registration", Work in Progress, Internet-Draft,
draft-ietf-6lo-multicast-registration-03, 13 December
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
6lo-multicast-registration-03>.
Thubert Expires 18 June 2022 [Page 25]
Internet-Draft Applying Wireless ND December 2021
[IEEE Std. 802.15.4]
IEEE standard for Information Technology, "IEEE Std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks".
[IEEE Std. 802.11]
IEEE standard for Information Technology, "IEEE Standard
for Information technology -- Telecommunications and
information exchange between systems Local and
metropolitan area networks-- Specific requirements Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specifications".
[IEEEstd802151]
IEEE standard for Information Technology, "IEEE Standard
for Information Technology - Telecommunications and
Information Exchange Between Systems - Local and
Metropolitan Area Networks - Specific Requirements. - Part
15.1: Wireless Medium Access Control (MAC) and Physical
Layer (PHY) Specifications for Wireless Personal Area
Networks (WPANs)".
[IEEEstd802154]
IEEE standard for Information Technology, "IEEE Standard
for Local and metropolitan area networks -- Part 15.4:
Low-Rate Wireless Personal Area Networks (LR-WPANs)".
[IEEE Std. 802.1]
IEEE standard for Information Technology, "IEEE Standard
for Information technology -- Telecommunications and
information exchange between systems Local and
metropolitan area networks Part 1: Bridging and
Architecture".
Author's Address
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 Mougins - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Thubert Expires 18 June 2022 [Page 26]