Internet DRAFT - draft-ietf-6lo-backbone-router
draft-ietf-6lo-backbone-router
6lo P. Thubert, Ed.
Internet-Draft Cisco Systems
Updates: 6775, 8505 (if approved) C.E. Perkins
Intended status: Standards Track Blue Meadow Networking
Expires: 24 September 2020 E. Levy-Abegnoli
Cisco Systems
23 March 2020
IPv6 Backbone Router
draft-ietf-6lo-backbone-router-20
Abstract
This document updates RFC 6775 and RFC 8505 in order to enable proxy
services for IPv6 Neighbor Discovery by Routing Registrars called
Backbone Routers. Backbone Routers are placed along the wireless
edge of a Backbone, and federate multiple wireless links to form a
single Multi-Link Subnet.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 24 September 2020.
Copyright Notice
Copyright (c) 2020 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
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as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 6
2.4. References . . . . . . . . . . . . . . . . . . . . . . . 7
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Updating RFC 6775 and RFC 8505 . . . . . . . . . . . . . 10
3.2. Access Link . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Route-Over Mesh . . . . . . . . . . . . . . . . . . . . . 13
3.4. The Binding Table . . . . . . . . . . . . . . . . . . . . 14
3.5. Primary and Secondary 6BBRs . . . . . . . . . . . . . . . 15
3.6. Using Optimistic DAD . . . . . . . . . . . . . . . . . . 16
4. Multi-Link Subnet Considerations . . . . . . . . . . . . . . 17
5. Optional 6LBR serving the Multi-Link Subnet . . . . . . . . . 17
6. Using IPv6 ND Over the Backbone Link . . . . . . . . . . . . 18
7. Routing Proxy Operations . . . . . . . . . . . . . . . . . . 20
8. Bridging Proxy Operations . . . . . . . . . . . . . . . . . . 21
9. Creating and Maintaining a Binding . . . . . . . . . . . . . 22
9.1. Operations on a Binding in Tentative State . . . . . . . 23
9.2. Operations on a Binding in Reachable State . . . . . . . 24
9.3. Operations on a Binding in Stale State . . . . . . . . . 25
10. Registering Node Considerations . . . . . . . . . . . . . . . 26
11. Security Considerations . . . . . . . . . . . . . . . . . . . 27
12. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 30
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
15. Normative References . . . . . . . . . . . . . . . . . . . . 30
16. Informative References . . . . . . . . . . . . . . . . . . . 32
Appendix A. Possible Future Extensions . . . . . . . . . . . . . 34
Appendix B. Applicability and Requirements Served . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Introduction
IEEE STD. 802.1 [IEEEstd8021] 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 local wireless networks generally do not provide the broadcast
capabilities of Ethernet Bridging in an economical fashion.
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As a result, protocols designed for bridged networks that rely on
multicast and broadcast often exhibit disappointing behaviours when
employed unmodified on a local wireless medium (see
[I-D.ietf-mboned-ieee802-mcast-problems]).
Wi-Fi [IEEEstd80211] Access Points (APs) deployed in an Extended
Service Set (ESS) act as Ethernet Bridges [IEEEstd8021], with the
property that the bridging state is established at the time of
association. This ensures connectivity to the end node (the Wi-Fi
STA) and protects the wireless medium against broadcast-intensive
Transparent Bridging reactive Lookups. In other words, the
association process is used to register the MAC Address of the STA to
the AP. The AP subsequently proxies the bridging operation and does
not need to forward the broadcast Lookups over the radio.
In the same way as Transparent Bridging, IPv6 [RFC8200] Neighbor
Discovery [RFC4861] [RFC4862] Protocol (IPv6 ND) is a reactive
protocol, based on multicast transmissions to locate an on-link
correspondent and ensure the uniqueness of an IPv6 address. The
mechanism for Duplicate Address Detection (DAD) [RFC4862] was
designed for the efficient broadcast operation of Ethernet Bridging.
Since broadcast can be unreliable over wireless media, DAD often
fails to discover duplications [I-D.yourtchenko-6man-dad-issues]. In
practice, the fact that IPv6 addresses very rarely conflict is mostly
attributable to the entropy of the 64-bit Interface IDs as opposed to
the succesful operation of the IPv6 ND duplicate address detection
and resolution mechanisms.
The IPv6 ND Neighbor Solicitation (NS) [RFC4861] message is used for
DAD and address Lookup when a node moves, or wakes up and reconnects
to the wireless network. The NS message is targeted to a Solicited-
Node Multicast Address (SNMA) [RFC4291] and should in theory only
reach a very small group of nodes. But in reality, IPv6 multicast
messages are typically broadcast on the wireless medium, and so they
are processed by most of the wireless nodes over the subnet (e.g.,
the ESS fabric) regardless of how few of the nodes are subscribed to
the SNMA. As a result, IPv6 ND address Lookups and DADs over a large
wireless and/or a LowPower Lossy Network (LLN) can consume enough
bandwidth to cause a substantial degradation to the unicast traffic
service.
Because IPv6 ND messages sent to the SNMA group are broadcast at the
radio MAC Layer, wireless nodes that do not belong to the SNMA group
still have to keep their radio turned on to listen to multicast NS
messages, which is a waste of energy for them. In order to reduce
their power consumption, certain battery-operated devices such as IoT
sensors and smartphones ignore some of the broadcasts, making IPv6 ND
operations even less reliable.
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These problems can be alleviated by reducing the IPv6 ND broadcasts
over wireless access links. This has been done by splitting the
broadcast domains and routing between subnets, at the extreme by
assigning a /64 prefix to each wireless node (see [RFC8273]). But
deploying a single large subnet can still be attractive to avoid
renumbering in situations that involve large numbers of devices and
mobility within a bounded area.
A way to reduce the propagation of IPv6 ND broadcast in the wireless
domain while preserving a large single subnet is to form a Multi-Link
Subnet (MLSN). Each Link in the MLSN, including the backbone, is its
own broadcast domain. A key property of MLSNs is that Link-Local
unicast traffic, link-scope multicast, and traffic with a hop limit
of 1 will not transit to nodes in the same subnet on a different
link, something that may produce unexpected behavior in software that
expects a subnet to be entirely contained within a single link.
This specification considers a special type of MLSN with a central
backbone that federates edge (LLN) links, each Link providing its own
protection against rogue access and tempering or replaying packets.
In particular, the use of classical IPv6 ND on the backbone requires
that the all nodes are trusted and that rogue access to the backbone
is prevented at all times (see Section 11).
In that particular topology, ND proxies can be placed at the boundary
of the edge links and the backbone to handle IPv6 ND on behalf of
Registered Nodes and forward IPv6 packets back and forth. The ND
proxy enables the continuity of IPv6 ND operations beyond the
backbone, and enables communication using Global or Unique Local
Addresses between any pair of nodes in the MLSN.
The 6LoWPAN Backbone Router (6BBR) is a Routing Registrar [RFC8505]
that provides proxy-ND services. A 6BBR acting as a Bridging Proxy
provides a proxy-ND function with Layer-2 continuity and can be
collocated with a Wi-Fi Access Point (AP) as prescribed by IEEE Std
802.11 [IEEEstd80211]. A 6BBR acting as a Routing Proxy is
applicable to any type of LLN, including LLNs that cannot be bridged
onto the backbone, such as IEEE Std 802.15.4 [IEEEstd802154].
Knowledge of which address to proxy for can be obtained by snooping
the IPV6 ND protocol (see [I-D.bi-savi-wlan]), but it has been found
to be unreliable. An IPv6 address may not be discovered immediately
due to a packet loss, or if a "silent" node is not currently using
one of its addresses. A change of state (e.g., due to movement) may
be missed or misordered, leading to unreliable connectivity and
incomplete knowledge of the state of the network.
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With this specification, the address to be proxied is signaled
explicitly through a registration process. A 6LoWPAN node (6LN)
registers all its IPv6 Addresses using NS messages with an Extended
Address Registration Option (EARO) as specified in [RFC8505] to a
6LoWPAN Router (6LR) to which it is directly attached. If the 6LR is
a 6BBR then the 6LN is both the Registered Node and the Registering
Node. If not, then the 6LoWPAN Border Router (6LBR) that serves the
LLN proxies the registration to the 6BBR. In that case, the 6LN is
the Registered Node and the 6LBR is the Registering Node. The 6BBR
performs IPv6 Neighbor Discovery (IPv6 ND) operations on its Backbone
interface on behalf of the 6LNs that have registered addresses on its
LLN interfaces without the need of a broadcast over the wireless
medium.
A Registering Node that resides on the backbone does not register to
the SNMA groups associated to its Registered Addresses and defers to
the 6BBR to answer or preferably forward to it as unicast the
corresponding multicast packets.
2. Terminology
2.1. BCP 14
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. New Terms
This document introduces the following terminology:
Federated: A subnet that comprises a Backbone and one or more
(wireless) access links, is said to be federated into one Multi-
Link Subnet. The proxy-ND operation of 6BBRs over the Backbone
extends IPv6 ND operation over the access links.
Sleeping Proxy: A 6BBR acts as a Sleeping Proxy if it answers IPv6
ND Neighbor Solicitations over the Backbone on behalf of the
Registering Node that is in a sleep state and cannot answer in due
time.
Routing Proxy: A Routing Proxy provides IPv6 ND proxy functions and
enables the MLSN operation over federated links that may not be
compatible for bridging. The Routing Proxy advertises its own MAC
Address as the Target Link Layer Address (TLLA) in the proxied NAs
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over the Backbone, and routes at the Network Layer between the
federated links.
Bridging Proxy: A Bridging Proxy provides IPv6 ND proxy functions
while preserving forwarding continuity at the MAC Layer. In that
case, the MAC Address and the mobility of the Registering Node is
visible across the bridged Backbone. The Bridging Proxy
advertises the MAC Address of the Registering Node as the TLLA in
the proxied NAs over the Backbone, and proxies ND for all unicast
addresses including Link-Local Addresses. Instead of replying on
behalf of the Registering Node, a Bridging Proxy will preferably
forward the NS Lookup and NUD messages that target the Registered
Address to the Registering Node as unicast frames and let it
respond in its own.
Binding Table: The Binding Table is an abstract database that is
maintained by the 6BBR to store the state associated with its
registrations.
Binding: A Binding is an abstract state associated to one
registration, in other words one entry in the Binding Table.
2.3. Abbreviations
This document uses the following abbreviations:
6BBR: 6LoWPAN Backbone Router
6LBR: 6LoWPAN Border Router
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router
ARO: Address Registration Option
DAC: Duplicate Address Confirmation
DAD: Duplicate Address Detection
DAR: Duplicate Address Request
EARO: Extended Address Registration Option
EDAC: Extended Duplicate Address Confirmation
EDAR: Extended Duplicate Address Request
DODAG: Destination-Oriented Directed Acyclic Graph
ID: Identifier
LLN: Low-Power and Lossy Network
NA: Neighbor Advertisement
MAC: Medium Access Control
NCE: Neighbor Cache Entry
ND: Neighbor Discovery
NDP: Neighbor Discovery Protocol
NS: Neighbor Solicitation
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NS(DAD): NDP NS message used for the purpose of duplication
avoidance (multicast)
NS(Lookup): NDP NS message used for the purpose of address
resolution (multicast)
NS(NUD): NDP NS message used for the purpose of unreachability
detection (unicast)
NUD: Neighbor Unreachability Detection
ROVR: Registration Ownership Verifier
RPL: IPv6 Routing Protocol for LLNs
RA: Router Advertisement
RS: Router Solicitation
SNMA: Solicited-Node Multicast Address
LLA: Link Layer Address (aka MAC address)
SLLA: Source Link Layer Address
TLLA: Target Link Layer Address
TID: Transaction ID
2.4. References
In this document, readers will encounter terms and concepts that are
discussed in the following documents:
Classical IPv6 ND: "Neighbor Discovery for IP version 6" [RFC4861],
"IPv6 Stateless Address Autoconfiguration" [RFC4862] and
"Optimistic Duplicate Address Detection" [RFC4429],
IPv6 ND over multiple links: "Neighbor Discovery Proxies (proxy-ND)"
[RFC4389] and "Multi-Link Subnet Issues" [RFC4903],
6LoWPAN: "Problem Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], and
6LoWPAN ND: Neighbor Discovery Optimization for Low-Power and Lossy
Networks [RFC6775], "Registration Extensions for 6LoWPAN Neighbor
Discovery" [RFC8505], and " Address Protected Neighbor Discovery
for Low-power and Lossy Networks" [I-D.ietf-6lo-ap-nd].
3. Overview
This section and its subsections present a non-normative high level
view of the operation of the 6BBR. The following sections cover the
normative part.
Figure 1 illustrates a backbone link that federates a collection of
LLNs as a single IPv6 Subnet, with a number of 6BBRs providing proxy-
ND services to their attached LLNs.
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|
+-----+ +-----+ +-----+ IPv6
(default) | | (Optional) | | | | Node
Router | | 6LBR | | | | or
+-----+ +-----+ +-----+ 6LN
| Backbone side | |
----+-------+-----------------+---+-------------+----+-----
| | |
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
| | | | | |
+------+ +------+ +------+
o Wireless side o o o o o o
o o o o o o o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o o o o o
o o o o o o o o o LLN o o o o o o o o o
o o o o o o o o o o o o o o
o o o
Figure 1: Backbone Link and Backbone Routers
The LLN may be a hub-and-spoke access link such as (Low-Power) IEEE
STD. 802.11 (Wi-Fi) [IEEEstd80211] and IEEE STD. 802.15.1 (Bluetooth)
[IEEEstd802151], or a Mesh-Under or a Route-Over network [RFC8505].
The proxy state can be distributed across multiple 6BBRs attached to
the same Backbone.
The main features of a 6BBR are as follows:
* Multi-Link-subnet functions (provided by the 6BBR on the backbone)
performed on behalf of Registered Nodes, and
* Routing registrar services that reduce multicast within the LLN:
- Binding Table management
- failover, e.g., due to mobility
Each Backbone Router (6BBR) maintains a data structure for its
Registered Addresses called a Binding Table. The abstract data that
is stored in the Binding Table includes the Registered Address,
anchor information on the Registering Node such as connecting
interface, Link-Local Address and Link-Layer Address of the
Registering Node on that interface, the EARO including ROVR and TID,
a state that can be either Reachable, Tentative, or Stale, and other
information such as a trust level that may be configured, e.g., to
protect a server. The combined Binding Tables of all the 6BBRs on a
backbone form a distributed database of Registered Nodes that reside
in the LLNs or on the IPv6 Backbone.
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Unless otherwise configured, a 6BBR does the following:
* Create a new entry in a Binding Table for a new Registered Address
and ensure that the Address is not duplicated over the Backbone.
* Advertise a Registered Address over the Backbone using an NA
message, either unsolicited or as a response to a NS message.
This includes joining the multicast group associated to the SNMA
derived from the Registered Address as specified in section 7.2.1.
of [RFC4861] over the Backbone.
* The 6BBR MAY respond immediately as a Proxy in lieu of the
Registering Node, e.g., if the Registering Node has a sleeping
cycle that the 6BBR does not want to interrupt, or if the 6BBR has
a recent state that is deemed fresh enough to permit the proxied
response. It is preferred, though, that the 6BBR checks whether
the Registering Node is still responsive on the Registered
Address. To that effect:
- as a Bridging Proxy:
the 6BBR forwards the multicast DAD and Address Lookup messages
as a unicast MAC-Layer frames to the MAC address of the
Registering Node that matches the Target in the ND message, and
forwards as is the unicast Neighbor Unreachability Detection
(NUD) messages, so as to let the Registering Node answer with
the ND Message and options that it sees fit;
- as a Routing Proxy:
the 6BBR checks the liveliness of the Registering Node, e.g.,
using a NUD verification, before answering on its behalf.
* Deliver packets arriving from the LLN, using Neighbor Solicitation
messages to look up the destination over the Backbone.
* Forward or bridge packets between the LLN and the Backbone.
* Verify liveness for a registration, when needed.
The first of these functions enables the 6BBR to fulfill its role as
a Routing Registrar for each of its attached LLNs. The remaining
functions fulfill the role of the 6BBRs as the border routers that
federate the Multi-link IPv6 subnet.
The operation of IPv6 ND and of proxy-ND are not mutually exclusive
on the Backbone, meaning that nodes attached to the Backbone and
using IPv6 ND can transparently interact with 6LNs that rely on a
6BBR to proxy ND for them, whether the 6LNs are reachable over an LLN
or directly attached to the Backbone.
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The [RFC8505] registration mechanism used to learn addresses to be
proxied may co-exist in a 6BBR with a proprietary snooping or the
traditional bridging functionality of an Access Point, in order to
support legacy LLN nodes that do not support this specification.
The registration to a proxy service uses an NS/NA exchange with EARO.
The 6BBR operation resembles that of a Mobile IPv6 (MIPv6) [RFC6275]
Home Agent (HA). The combination of a 6BBR and a MIPv6 HA enables
full mobility support for 6LNs, inside and outside the links that
form the subnet.
The 6BBRs performs IPv6 ND functions over the backbone as follows:
* The EARO [RFC8505] is used in the IPv6 ND exchanges over the
Backbone between the 6BBRs to help distinguish duplication from
movement. Extended Duplicate Address Messages (EDAR and EDAC) may
also be used to communicate with a 6LBR, if one is present.
Address duplication is detected using the ROVR field. Conflicting
registrations to different 6BBRs for the same Registered Address
are resolved using the TID field which forms an order of
registrations.
* The Link Layer Address (LLA) that the 6BBR advertises for the
Registered Address on behalf of the Registered Node over the
Backbone can belong to the Registering Node; in that case, the
6BBR (acting as a Bridging Proxy (see Section 8)) bridges the
unicast packets. Alternatively, the LLA can be that of the 6BBR
on the Backbone interface, in which case the 6BBR (acting as a
Routing Proxy (see Section 7)) receives the unicast packets at
Layer 3 and routes over.
3.1. Updating RFC 6775 and RFC 8505
This specification adds the EARO as a possible option in RS, NS(DAD)
and NA messages over the backbone. This document specifies the use
of those ND messages by 6BBRs over the backbone, at a high level in
Section 6 and in more detail in Section 9.
Note: [RFC8505] requires that the registration NS(EARO) contains an
Source Link Layer Address Option (SLLAO). [RFC4862] requires that
the NS(DAD) is sent from the unspecified address for which there
cannot be a SLLAO. Consequently, an NS(DAD) cannot be confused with
a registration.
This specification allows to deploy a 6LBR on the backbone where EDAR
and EDAC messages coexist with classical ND. It also adds the
capability to insert IPv6 ND options in the EDAR and EDAC messages.
A 6BBR acting as a 6LR for the Registered Address can insert an SLLAO
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in the EDAR to the 6LBR in order to avoid a Lookup back. This
enables the 6LBR to store the MAC address associated to the
Registered Address on a Link and to serve as a mapping server as
described in [I-D.thubert-6lo-unicast-lookup].
This specification allows for an address to be registered to more
than one 6BBR. Consequently a 6LBR that is deployed on the backbone
MUST be capable of maintaining state for each of the 6BBR having
registered with the same TID and same ROVR.
3.2. Access Link
The simplest Multi-Link Subnet topology from the Layer 3 perspective
occurs when the wireless network appears as a single hop hub-and-
spoke network as shown in Figure 2. The Layer 2 operation may
effectively be hub-and-spoke (e.g., Wi-Fi) or Mesh-Under, with a
Layer 2 protocol handling the complex topology.
|
+-----+ +-----+ +-----+ IPv6
(default) | | (Optional) | | | | Node
Router | | 6LBR | | | | or
+-----+ +-----+ +-----+ 6LN
| Backbone side | |
----+-------+-----------------+---+-------------+----+-----
| | |
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
| 6LR | | 6LR | | 6LR |
+------+ +------+ +------+
(6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN)
Figure 2: Access Link Use case
Figure 3 illustrates a flow where 6LN forms an IPv6 Address and
registers it to a 6BBR acting as a 6LR [RFC8505]. The 6BBR applies
ODAD (see Section 3.6) to the registered address to enable
connectivity while the message flow is still in progress.
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6LN(STA) 6BBR(AP) 6LBR default GW
| | | |
| LLN Access Link | IPv6 Backbone (e.g., Ethernet) |
| | | |
| RS(multicast) | | |
|---------------->| | |
| RA(PIO, Unicast)| | |
|<----------------| | |
| NS(EARO) | | |
|---------------->| | |
| | Extended DAR | |
| |--------------->| |
| | Extended DAC | |
| |<---------------| |
| | |
| | NS-DAD(EARO, multicast) |
| |--------> |
| |----------------------------------->|
| | |
| | RS(no SLLAO, for ODAD) |
| |----------------------------------->|
| | if (no fresher Binding) NS(Lookup) |
| | <----------------|
| |<-----------------------------------|
| | NA(SLLAO, not(O), EARO) |
| |----------------------------------->|
| | RA(unicast) |
| |<-----------------------------------|
| | |
| IPv6 Packets in optimistic mode |
|<---------------------------------------------------->|
| | |
| |
| NA(EARO) |<DAD timeout>
|<----------------|
| |
Figure 3: Initial Registration Flow to a 6BBR acting as Routing Proxy
In this example, a 6LBR is deployed on the backbone link to serve the
whole subnet, and EDAR / EDAC messages are used in combination with
DAD to enable coexistence with IPv6 ND over the backbone.
The RS sent initially by the 6LN (e.g., a Wi-Fi STA) is transmitted
as a multicast but since it is intercepted by the 6BBR, it is never
effectively broadcast. The multiple arrows associated to the ND
messages on the Backbone denote a real Layer 2 broadcast.
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3.3. Route-Over Mesh
A more complex Multi-Link Subnet topology occurs when the wireless
network appears as a Layer 3 Mesh network as shown in Figure 4. A
so-called Route-Over routing protocol exposes routes between 6LRs
towards both 6LRs and 6LNs, and a 6LBR acts as Root of the Layer 3
Mesh network and proxy-registers the LLN addresses to the 6BBR.
|
+-----+ +-----+ +-----+ IPv6
(default) | | (Optional) | | | | Node
Router | | 6LBR | | | | or
+-----+ +-----+ +-----+ 6LN
| Backbone side | |
----+-------+-----------------+---+-------------+----+-----
| | |
+------+ +------+ +------+
| 6BBR | | 6BBR | | 6BBR |
+------+ +------+ +------+
| | |
+------+ +------+ +------+
| 6LBR | | 6LBR | | 6LBR |
+------+ +------+ +------+
(6LN) (6LR) (6LN) (6LR) (6LN) (6LR) (6LR) (6LR)(6LN)
(6LN)(6LR) (6LR) (6LN) (6LN) (6LR)(6LN) (6LR) (6LR) (6LR) (6LN)
(6LR)(6LR) (6LR) (6LR) (6LR)(6LN) (6LR) (6LR)(6LR)
(6LR) (6LR) (6LR) (6LR) (6LN)(6LR) (6LR) (6LR) (6LR) (6LR)
(6LN) (6LN)(6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN) (6LN)
Figure 4: Route-Over Mesh Use case
Figure 5 illustrates IPv6 signaling that enables a 6LN (the
Registered Node) to form a Global or a Unique-Local Address and
register it to the 6LBR that serves its LLN using [RFC8505] using a
neighboring 6LR as relay. The 6LBR (the Registering Node) then
proxies the [RFC8505] registration to the 6BBR to obtain proxy-ND
services from the 6BBR.
The RS sent initially by the 6LN is a transmitted as a multicast and
contained within 1-hop broadcast range where hopefully a 6LR is
found. The 6LR is expected to be already connected to the LLN and
capable to reach the 6LBR, possibly multiple hops away, using unicast
messages.
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6LoWPAN Node 6LR 6LBR 6BBR
(mesh leaf) (mesh router) (mesh root)
| | | |
| 6LoWPAN ND |6LoWPAN ND | 6LoWPAN ND | IPv6 ND
| LLN link |Route-Over mesh|Ethernet/serial| Backbone
| | |/Internal call |
| IPv6 ND RS | | |
|-------------->| | |
|-----------> | | |
|------------------> | |
| IPv6 ND RA | | |
|<--------------| | |
| | | |
| NS(EARO) | | |
|-------------->| | |
| 6LoWPAN ND | Extended DAR | |
| |-------------->| |
| | | NS(EARO) |
| | |-------------->|
| | | (proxied) | NS-DAD
| | | |------>
| | | | (EARO)
| | | |
| | | NA(EARO) |<timeout>
| | |<--------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<--------------| | |
| | | |
Figure 5: Initial Registration Flow over Route-Over Mesh
As a non-normative example of a Route-Over Mesh, the 6TiSCH
architecture [I-D.ietf-6tisch-architecture] suggests using the RPL
[RFC6550] routing protocol and collocating the RPL root with a 6LBR
that serves the LLN. The 6LBR is also either collocated with or
directly connected to the 6BBR over an IPv6 Link.
3.4. The Binding Table
Addresses in an LLN that are reachable from the Backbone by way of
the 6BBR function must be registered to that 6BBR, using an NS(EARO)
with the R flag set [RFC8505]. The 6BBR answers with an NA(EARO) and
maintains a state for the registration in an abstract Binding Table.
An entry in the Binding Table is called a "Binding". A Binding may
be in Tentative, Reachable or Stale state.
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The 6BBR uses a combination of [RFC8505] and IPv6 ND over the
Backbone to advertise the registration and avoid a duplication.
Conflicting registrations are solved by the 6BBRs, transparently to
the Registering Nodes.
Only one 6LN may register a given Address, but the Address may be
registered to Multiple 6BBRs for higher availability.
Over the LLN, Binding Table management is as follows:
* De-registrations (newer TID, same ROVR, null Lifetime) are
accepted with a status of 4 ("Removed"); the entry is deleted;
* Newer registrations (newer TID, same ROVR, non-null Lifetime) are
accepted with a status of 0 (Success); the Binding is updated with
the new TID, the Registration Lifetime and the Registering Node;
in Tentative state the EDAC response is held and may be
overwritten; in other states the Registration Lifetime timer is
restarted and the entry is placed in Reachable state.
* Identical registrations (same TID, same ROVR) from the same
Registering Node are accepted with a status of 0 (Success). In
Tentative state, the response is held and may be overwritten, but
the response is eventually produced, carrying the result of the
DAD process;
* Older registrations (older TID, same ROVR) from the same
Registering Node are discarded;
* Identical and older registrations (not-newer TID, same ROVR) from
a different Registering Node are rejected with a status of 3
(Moved); this may be rate limited to avoid undue interference;
* Any registration for the same address but with a different ROVR is
rejected with a status of 1 (Duplicate).
The operation of the Binding Table is specified in detail in
Section 9.
3.5. Primary and Secondary 6BBRs
A Registering Node MAY register the same address to more than one
6BBR, in which case the Registering Node uses the same EARO in all
the parallel registrations. On the other hand, there is no provision
in 6LoWPAN ND for a 6LN (acting as Registered Node) to select its
6LBR (acting as Registering Node), so it cannot select more than one
either. To allow for this, NS(DAD) and NA messages with an EARO
received over the backbone that indicate an identical Binding in
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another 6BBR (same Registered address, same TID, same ROVR) are
silently ignored but for the purpose of selecting the primary 6BBR
for that registration.
A 6BBR may be either primary or secondary. The primary is the 6BBR
that has the highest EUI-64 Address of all the 6BBRs that share a
registration for the same Registered Address, with the same ROVR and
same Transaction ID, the EUI-64 Address being considered as an
unsigned 64bit integer. A given 6BBR can be primary for a given
Address and secondary for another Address, regardless of whether or
not the Addresses belong to the same 6LN.
In the following sections, it is expected that an NA is sent over the
backbone only if the node is primary or does not support the concept
of primary. More than one 6BBR claiming or defending an address
generates unwanted traffic but no reachability issue since all 6BBRs
provide reachability from the Backbone to the 6LN.
If a Registering Node loses connectivity to its or one of the 6BBRs
to which it registered an address, it retries the registration to the
(one or more) available 6BBR(s). When doing that, the Registering
Node MUST increment the TID in order to force the migration of the
state to the new 6BBR, and the reselection of the primary 6BBR if it
is the node that was lost.
3.6. Using Optimistic DAD
Optimistic Duplicate Address Detection [RFC4429] (ODAD) specifies how
an IPv6 Address can be used before completion of Duplicate Address
Detection (DAD). ODAD guarantees that this behavior will not cause
harm if the new Address is a duplicate.
Support for ODAD avoids delays in installing the Neighbor Cache Entry
(NCE) in the 6BBRs and the default router, enabling immediate
connectivity to the registered node. As shown in Figure 3, if the
6BBR is aware of the Link-Layer Address (LLA) of a router, then the
6BBR sends a Router Solicitation (RS), using the Registered Address
as the IP Source Address, to the known router(s). The RS is sent
without a Source LLA Option (SLLAO), to avoid invalidating a
preexisting NCE in the router.
Following ODAD, the router may then send a unicast RA to the
Registered Address, and it may resolve that Address using an
NS(Lookup) message. In response, the 6BBR sends an NA with an EARO
and the Override flag [RFC4861] that is not set. The router can then
determine the freshest EARO in case of conflicting NA(EARO) messages,
using the method described in section 5.2.1 of [RFC8505]. If the
NA(EARO) is the freshest answer, the default router creates a Binding
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with the SLLAO of the 6BBR (in Routing Proxy mode) or that of the
Registering Node (in Bridging Proxy mode) so that traffic from/to the
Registered Address can flow immediately.
4. Multi-Link Subnet Considerations
The Backbone and the federated LLN Links are considered as different
links in the Multi-Link Subnet, even if multiple LLNs are attached to
the same 6BBR. ND messages are link-scoped and are not forwarded by
the 6BBR between the backbone and the LLNs though some packets may be
reinjected in Bridging Proxy mode (see Section 8).
Legacy nodes located on the backbone expect that the subnet is
deployed within a single link and that there is a common Maximum
Transmission Unit (MTU) for intra-subnet communication, the Link MTU.
They will not perform the IPv6 Path MTU Discovery [RFC8201] for a
destination within the subnet. For that reason, the MTU MUST have
the same value on the Backbone and all federated LLNs in the MLSN.
As a consequence, the 6BBR MUST use the same MTU value in RAs over
the Backbone and in the RAs that it transmits towards the LLN links.
5. Optional 6LBR serving the Multi-Link Subnet
A 6LBR can be deployed to serve the whole MLSN. It may be attached
to the backbone, in which case it can be discovered by its capability
advertisement (see section 4.3. of [RFC8505]) in RA messages.
When a 6LBR is present, the 6BBR uses an EDAR/EDAC message exchange
with the 6LBR to check if the new registration corresponds to a
duplication or a movement. This is done prior to the NS(DAD)
process, which may be avoided if the 6LBR already maintains a
conflicting state for the Registered Address.
If this registration is duplicate or not the freshest, then the 6LBR
replies with an EDAC message with a status code of 1 ("Duplicate
Address") or 3 ("Moved"), respectively. If this registration is the
freshest, then the 6LBR replies with a status code of 0. In that
case, if this registration is fresher than an existing registration
for another 6BBR, then the 6LBR also sends an asynchronous EDAC with
a status of 4 ("Removed") to that other 6BBR.
The EDAR message SHOULD carry the SLLAO used in NS messages by the
6BBR for that Binding, and the EDAC message SHOULD carry the Target
Link Layer Address Option (TLLAO) associated with the currently
accepted registration. This enables a 6BBR to locate the new
position of a mobile 6LN in the case of a Routing Proxy operation,
and opens the capability for the 6LBR to serve as a mapping server in
the future.
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Note that if Link-Local Addresses are registered, then the scope of
uniqueness on which the address duplication is checked is the total
collection of links that the 6LBR serves as opposed to the sole link
on which the Link-Local Address is assigned.
6. Using IPv6 ND Over the Backbone Link
On the Backbone side, the 6BBR MUST join the SNMA group corresponding
to a Registered Address as soon as it creates a Binding for that
Address, and maintain that SNMA membership as long as it maintains
the registration. The 6BBR uses either the SNMA or plain unicast to
defend the Registered Addresses in its Binding Table over the
Backbone (as specified in [RFC4862]). The 6BBR advertises and
defends the Registered Addresses over the Backbone Link using RS,
NS(DAD) and NA messages with the Registered Address as the Source or
Target address.
The 6BBR MUST place an EARO in the IPv6 ND messages that it generates
on behalf of the Registered Node. Note that an NS(DAD) does not
contain an SLLAO and cannot be confused with a proxy registration
such as performed by a 6LBR.
IPv6 ND operates as follows on the backbone:
* Section 7.2.8 of [RFC4861] specifies that an NA message generated
as a proxy does not have the Override flag set in order to ensure
that if the real owner is present on the link, its own NA will
take precedence, and that this NA does not update the NCE for the
real owner if one exists.
* A node that receives multiple NA messages updates an existing NCE
only if the Override flag is set; otherwise the node will probe
the cached address.
* When an NS(DAD) is received for a tentative address, which means
that two nodes form the same address at nearly the same time,
section 5.4.3 of [RFC4862] cannot detect which node first claimed
the address and the address is abandoned.
* In any case, [RFC4862] indicates that a node never responds to a
Neighbor Solicitation for a tentative address.
This specification adds information about proxied addresses that
helps sort out a duplication (different ROVR) from a movement (same
ROVR, different TID), and in the latter case the older registration
from the fresher one (by comparing TIDs).
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When a Registering Node moves from one 6BBR to the next, the new 6BBR
sends NA messages over the backbone to update existing NCEs. A node
that supports this specification and that receives multiple NA
messages with an EARO option and the same ROVR MUST favor the NA with
the freshest EARO over the others.
The 6BBR MAY set the Override flag in the NA messages if it does not
compete with the Registering Node for the NCE in backbone nodes.
This is assured if the Registering Node is attached via an interface
that cannot be bridged onto the backbone, making it impossible for
the Registering Node to defend its own addresses there. This may
also be signaled by the Registering Node through a protocol extension
that is not in scope for this specification.
When the Binding is in Tentative state, the 6BBR acts as follows:
* an NS(DAD) that indicates a duplication can still not be asserted
for first come, but the situation can be avoided using a 6LBR on
the backbone that will serialize the order of appearance of the
address and ensure first-come/first-serve.
* an NS or an NA that denotes an older registration for the same
Registered Node is not interpreted as a duplication as specified
in section 5.4.3 and 5.4.4 of [RFC4862], respectively.
When the Binding is no longer in Tentative state, the 6BBR acts as
follows:
* an NS or an NA with an EARO that denotes a duplicate registration
(different ROVR) is answered with an NA message that carries an
EARO with a status of 1 (Duplicate), unless the received message
is an NA that carries an EARO with a status of 1.
In any state, the 6BBR acts as follows:
* an NS or an NA with an EARO that denotes an older registration
(same ROVR) is answered with an NA message that carries an EARO
with a status of 3 (Moved) to ensure that the stale state is
removed rapidly.
This behavior is specified in more detail in Section 9.
This specification enables proxy operation for the IPv6 ND resolution
of LLN devices and a prefix that is used across a Multi-Link Subnet
MAY be advertised as on-link over the Backbone. This is done for
backward compatibility with existing IPv6 hosts by setting the L flag
in the Prefix Information Option (PIO) of RA messages [RFC4861].
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For movement involving a slow reattachment, the NUD procedure defined
in [RFC4861] may time out too quickly. Nodes on the backbone SHOULD
support [RFC7048] whenever possible.
7. Routing Proxy Operations
A Routing Proxy provides IPv6 ND proxy functions for Global and
Unique Local addresses between the LLN and the backbone, but not for
Link-Local addresses. It operates as an IPv6 border router and
provides a full Link-Layer isolation.
In this mode, it is not required that the MAC addresses of the 6LNs
are visible at Layer 2 over the Backbone. It is thus useful when the
messaging over the Backbone that is associated to wireless mobility
becomes expensive, e.g., when the Layer 2 topology is virtualized
over a wide area IP underlay.
This mode is definitely required when the LLN uses a MAC address
format that is different from that on the Backbone (e.g., EUI-64 vs.
EUI-48). Since a 6LN may not be able to resolve an arbitrary
destination in the MLSN directly, a prefix that is used across a MLSN
MUST NOT be advertised as on-link in RA messages sent towards the
LLN.
In order to maintain IP connectivity, the 6BBR installs a connected
Host route to the Registered Address on the LLN interface, via the
Registering Node as identified by the Source Address and the SLLA
option in the NS(EARO) messages.
When operating as a Routing Proxy, the 6BBR MUST use its Layer 2
Address on its Backbone Interface in the SLLAO of the RS messages and
the TLLAO of the NA messages that it generates to advertise the
Registered Addresses.
For each Registered Address, multiple peers on the Backbone may have
resolved the Address with the 6BBR MAC Address, maintaining that
mapping in their Neighbor Cache. The 6BBR SHOULD maintain a list of
the peers on the Backbone which have associated its MAC Address with
the Registered Address. If that Registered Address moves to another
6BBR, the previous 6BBR SHOULD unicast a gratuitous NA to each such
peer, to supply the LLA of the new 6BBR in the TLLA option for the
Address. A 6BBR that does not maintain this list MAY multicast a
gratuitous NA message; this NA will possibly hit all the nodes on the
Backbone, whether or not they maintain an NCE for the Registered
Address. In either case, the 6BBR MAY set the Override flag if it is
known that the Registered Node cannot attach to the backbone, so as
to avoid interruptions and save probing flows in the future.
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If a correspondent fails to receive the gratuitous NA, it will keep
sending traffic to a 6BBR to which the node was previously
registered. Since the previous 6BBR removed its Host route to the
Registered Address, it will look up the address over the backbone,
resolve the address with the LLA of the new 6BBR, and forward the
packet to the correct 6BBR. The previous 6BBR SHOULD also issue a
redirect message [RFC4861] to update the cache of the correspondent.
8. Bridging Proxy Operations
A Bridging Proxy provides IPv6 ND proxy functions between the LLN and
the backbone while preserving the forwarding continuity at the MAC
Layer. It acts as a Layer 2 Bridge for all types of unicast packets
including link-scoped, and appears as an IPv6 Host on the Backbone.
The Bridging Proxy registers any Binding including for a Link-Local
address to the 6LBR (if present) and defends it over the backbone in
IPv6 ND procedures.
To achieve this, the Bridging Proxy intercepts the IPv6 ND messages
and may reinject them on the other side, respond directly or drop
them. For instance, an ND(Lookup) from the backbone that matches a
Binding can be responded directly, or turned into a unicast on the
LLN side to let the 6LN respond.
As a Bridging Proxy, the 6BBR MUST use the Registering Node's Layer 2
Address in the SLLAO of the NS/RS messages and the TLLAO of the NA
messages that it generates to advertise the Registered Addresses.
The Registering Node's Layer 2 address is found in the SLLA of the
registration NS(EARO), and maintained in the Binding Table.
The Multi-Link Subnet prefix SHOULD NOT be advertised as on-link in
RA messages sent towards the LLN. If a destination address is seen
as on-link, then a 6LN may use NS(Lookup) messages to resolve that
address. In that case, the 6BBR MUST either answer the NS(Lookup)
message directly or reinject the message on the backbone, either as a
Layer 2 unicast or a multicast.
If the Registering Node owns the Registered Address, meaning that the
Registering Node is the Registered Node, then its mobility does not
impact existing NCEs over the Backbone. In a network where proxy
registrations are used, meaning that the Registering Node acts on
behalf of the Registered Node, if the Registered Node selects a new
Registering Node then the existing NCEs across the Backbone pointing
at the old Registering Node must be updated. In that case, the 6BBR
SHOULD attempt to fix the existing NCEs across the Backbone pointing
at other 6BBRs using NA messages as described in Section 7.
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This method can fail if the multicast message is not received; one or
more correspondent nodes on the Backbone might maintain an stale NCE,
and packets to the Registered Address may be lost. When this
condition happens, it is eventually discovered and resolved using NUD
as defined in [RFC4861].
9. Creating and Maintaining a Binding
Upon receiving a registration for a new Address (i.e., an NS(EARO)
with the R flag set), the 6BBR creates a Binding and operates as a
6LR according to [RFC8505], interacting with the 6LBR if one is
present.
An implementation of a Routing Proxy that creates a Binding MUST also
create an associated Host route pointing to the registering node in
the LLN interface from which the registration was received.
Acting as a 6BBR, the 6LR operation is modified as follows:
* Acting as Bridging Proxy the 6LR MUST proxy ND over the backbone
for registered Link-Local Addresses.
* EDAR and EDAC messages SHOULD carry a SLLAO and a TLLAO,
respectively.
* An EDAC message with a status of 9 (6LBR Registry Saturated) is
assimilated as a status of 0 if a following DAD process protects
the address against duplication.
This specification enables nodes on a Backbone Link to co-exist along
with nodes implementing IPv6 ND [RFC4861] as well as other non-
normative specifications such as [I-D.bi-savi-wlan]. It is possible
that not all IPv6 addresses on the Backbone are registered and known
to the 6LBR, and an EDAR/EDAC echange with the 6LBR might succeed
even for a duplicate address. Consequently the 6BBR still needs to
perform IPv6 ND DAD over the backbone after an EDAC with a status
code of 0 or 9.
For the DAD operation, the Binding is placed in Tentative state for a
duration of TENTATIVE_DURATION (Section 12), and an NS(DAD) message
is sent as a multicast message over the Backbone to the SNMA
associated with the registered Address [RFC4862]. The EARO from the
registration MUST be placed unchanged in the NS(DAD) message.
If a registration is received for an existing Binding with a non-null
Registration Lifetime and the registration is fresher (same ROVR,
fresher TID), then the Binding is updated, with the new Registration
Lifetime, TID, and possibly Registering Node. In Tentative state
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(see Section 9.1), the current DAD operation continues unaltered. In
other states (see Section 9.2 and Section 9.3 ), the Binding is
placed in Reachable state for the Registration Lifetime, and the 6BBR
returns an NA(EARO) to the Registering Node with a status of 0
(Success).
Upon a registration that is identical (same ROVR, TID, and
Registering Node), the 6BBR does not alter its current state. In
Reachable State it returns an NA(EARO) back to the Registering Node
with a status of 0 (Success). A registration that is not as fresh
(same ROVR, older TID) is ignored.
If a registration is received for an existing Binding and a
registration Lifetime of zero, then the Binding is removed, and the
6BBR returns an NA(EARO) back to the Registering Node with a status
of 0 (Success). An implementation of a Routing Proxy that removes a
binding MUST remove the associated Host route pointing on the
registering node.
The old 6BBR removes its Binding Table entry and notifies the
Registering Node with a status of 3 (Moved) if a new 6BBR claims a
fresher registration (same ROVR, fresher TID) for the same address.
The old 6BBR MAY preserve a temporary state in order to forward
packets in flight. The state may for instance be a NCE formed based
on a received NA message. It may also be a Binding Table entry in
Stale state and pointing at the new 6BBR on the backbone, or any
other abstract cache entry that can be used to resolve the Link-Layer
Address of the new 6BBR. The old 6BBR SHOULD also use REDIRECT
messages as specified in [RFC4861] to update the correspondents for
the Registered Address, pointing to the new 6BBR.
9.1. Operations on a Binding in Tentative State
The Tentative state covers a DAD period over the backbone during
which an address being registered is checked for duplication using
procedures defined in [RFC4862].
For a Binding in Tentative state:
* The Binding MUST be removed if an NA message is received over the
Backbone for the Registered Address with no EARO, or containing an
EARO that indicates an existing registration owned by a different
Registering Node (different ROVR). In that case, an NA is sent
back to the Registering Node with a status of 1 (Duplicate) to
indicate that the binding has been rejected. This behavior might
be overridden by policy, in particular if the registration is
trusted, e.g., based on the validation of the ROVR field (see
[I-D.ietf-6lo-ap-nd]).
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* The Binding MUST be removed if an NS(DAD) message is received over
the Backbone for the Registered Address with no EARO, or
containing an EARO with a different ROVR that indicates a
tentative registration by a different Registering Node. In that
case, an NA is sent back to the Registering Node with a status of
1 (Duplicate). This behavior might be overridden by policy, in
particular if the registration is trusted, e.g., based on the
validation of the ROVR field (see [I-D.ietf-6lo-ap-nd]).
* The Binding MUST be removed if an NA or an NS(DAD) message is
received over the Backbone for the Registered Address containing
an EARO with a that indicates a fresher registration ([RFC8505])
for the same Registering Node (same ROVR). In that case, an NA
MUST be sent back to the Registering Node with a status of 3
(Moved).
* The Binding MUST be kept unchanged if an NA or an NS(DAD) message
is received over the Backbone for the Registered Address
containing an EARO with a that indicates an older registration
([RFC8505]) for the same Registering Node (same ROVR). The
message is answered with an NA that carries an EARO with a status
of 3 (Moved) and the Override flag not set. This behavior might
be overridden by policy, in particular if the registration is not
trusted.
* Other NS(DAD) and NA messages from the Backbone are ignored.
* NS(Lookup) and NS(NUD) messages SHOULD be optimistically answered
with an NA message containing an EARO with a status of 0 and the
Override flag not set (see Section 3.6). If optimistic DAD is
disabled, then they SHOULD be queued to be answered when the
Binding goes to Reachable state.
When the TENTATIVE_DURATION (Section 12) timer elapses, the Binding
is placed in Reachable state for the Registration Lifetime, and the
6BBR returns an NA(EARO) to the Registering Node with a status of 0
(Success).
The 6BBR also attempts to take over any existing Binding from other
6BBRs and to update existing NCEs in backbone nodes. This is done by
sending an NA message with an EARO and the Override flag not set over
the backbone (see Section 7 and Section 8).
9.2. Operations on a Binding in Reachable State
The Reachable state covers an active registration after a successful
DAD process.
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If the Registration Lifetime is of a long duration, an implementation
might be configured to reassess the availability of the Registering
Node at a lower period, using a NUD procedure as specified in
[RFC7048]. If the NUD procedure fails, the Binding SHOULD be placed
in Stale state immediately.
For a Binding in Reachable state:
* The Binding MUST be removed if an NA or an NS(DAD) message is
received over the Backbone for the Registered Address containing
an EARO that indicates a fresher registration ([RFC8505]) for the
same Registered Node (i.e., same ROVR but fresher TID). A status
of 4 (Removed) is returned in an asynchronous NA(EARO) to the
Registering Node. Based on configuration, an implementation may
delay this operation by a timer with a short setting, e.g., a few
seconds to a minute, in order to a allow for a parallel
registration to reach this node, in which case the NA might be
ignored.
* NS(DAD) and NA messages containing an EARO that indicates a
registration for the same Registered Node that is not as fresh as
this binding MUST be answered with an NA message containing an
EARO with a status of 3 (Moved).
* An NS(DAD) with no EARO or with an EARO that indicates a duplicate
registration (i.e., different ROVR) MUST be answered with an NA
message containing an EARO with a status of 1 (Duplicate) and the
Override flag not set, unless the received message is an NA that
carries an EARO with a status of 1, in which case the node
refrains from answering.
* Other NS(DAD) and NA messages from the Backbone are ignored.
* NS(Lookup) and NS(NUD) messages SHOULD be answered with an NA
message containing an EARO with a status of 0 and the Override
flag not set. The 6BBR MAY check whether the Registering Node is
still available using a NUD procedure over the LLN prior to
answering; this behaviour depends on the use case and is subject
to configuration.
When the Registration Lifetime timer elapses, the Binding is placed
in Stale state for a duration of STALE_DURATION (Section 12).
9.3. Operations on a Binding in Stale State
The Stale state enables tracking of the Backbone peers that have a
NCE pointing to this 6BBR in case the Registered Address shows up
later.
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If the Registered Address is claimed by another 6LN on the Backbone,
with an NS(DAD) or an NA, the 6BBR does not defend the Address.
For a Binding in Stale state:
* The Binding MUST be removed if an NA or an NS(DAD) message is
received over the Backbone for the Registered Address containing
no EARO or an EARO that indicates either a fresher registration
for the same Registered Node or a duplicate registration. A
status of 4 (Removed) MAY be returned in an asynchronous NA(EARO)
to the Registering Node.
* NS(DAD) and NA messages containing an EARO that indicates a
registration for the same Registered Node that is not as fresh as
this MUST be answered with an NA message containing an EARO with a
status of 3 (Moved).
* If the 6BBR receives an NS(Lookup) or an NS(NUD) message for the
Registered Address, the 6BBR MUST attempt a NUD procedure as
specified in [RFC7048] to the Registering Node, targeting the
Registered Address, prior to answering. If the NUD procedure
succeeds, the operation in Reachable state applies. If the NUD
fails, the 6BBR refrains from answering.
* Other NS(DAD) and NA messages from the Backbone are ignored.
When the STALE_DURATION (Section 12) timer elapses, the Binding MUST
be removed.
10. Registering Node Considerations
A Registering Node MUST implement [RFC8505] in order to interact with
a 6BBR (which acts as a routing registrar). Following [RFC8505], the
Registering Node signals that it requires IPv6 proxy-ND services from
a 6BBR by registering the corresponding IPv6 Address using an
NS(EARO) message with the R flag set.
The Registering Node may be the 6LN owning the IPv6 Address, or a
6LBR that performs the registration on its behalf in a Route-Over
mesh.
A 6LN MUST register all of its IPv6 Addresses to its 6LR, which is
the 6BBR when they are connected at Layer 2. Failure to register an
address may result in the address being unreachable by other parties.
This would happen for instance if the 6BBR propagates the NS(Lookup)
from the backbone only to the LLN nodes that do not register their
addresses.
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The Registering Node MUST refrain from using multicast NS(Lookup)
when the destination is not known as on-link, e.g., if the prefix is
advertised in a PIO with the L flag that is not set. In that case,
the Registering Node sends its packets directly to its 6LR.
The Registering Node SHOULD also follow BCP 202 [RFC7772] in order to
limit the use of multicast RAs. It SHOULD also implement Simple
Procedures for Detecting Network Attachment in IPv6 [RFC6059] (DNA
procedures) to detect movements, and support Packet-Loss Resiliency
for Router Solicitations [RFC7559] in order to improve reliability
for the unicast RS messages.
11. Security Considerations
The procedures in this document modify the mechanisms used for IPv6
ND and DAD and should not affect other aspects of IPv6 or higher-
level-protocol operation. As such, the main classes of attacks that
are in play are those which week to block neighbor discovery or to
forcibly claim an address that another node is attempting to use. In
the absence of cryptographic protection at higher layers, the latter
class of attacks can have significant consequences, with the attacker
being able to read all the "stolen" traffic that was directed to the
target of the attack.
This specification applies to LLNs and a backbone in which the
individual links are protected against rogue access, on the LLN by
authenticating a node that attaches to the network and encrypting at
the MAC layer the transmissions, and on the backbone side using the
physical security and access control measures that are typically
applied there, so packets may neither be forged or nor overheard.
In particular, the LLN MAC is required to provide secure unicast to/
from the Backbone Router and secure broadcast from the routers in a
way that prevents tampering with or replaying the ND messages.
For the IPv6 ND operation over the backbone, and unless the classical
ND is disabled (e.g., by configuration), the classical ND messages
are interpreted as emitted by the address owner and have precedence
over the 6BBR that is only a proxy.
It results that the security threats that are detailed in section
11.1 of [RFC4861] fully apply to this specification as well. In very
short:
* Any node that can send a packet on the backbone can take over any
address including addresses of LLN nodes by claiming it with an NA
message and the Override bit set. This means that the real owner
will stop receiving its packets.
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* Any node that can send a packet on the backbone can forge traffic
and pretend it is issued from a address that it does not own, even
if it did not claim the address using ND.
* Any node that can send a packet on the backbone can present itself
as a preferred router to intercept all traffic outgoing the
subnet. It may even expose a prefix on the subnet as not-on-link
and intercept all the traffic within the subnet.
* If the rogue can receive a packet from the backbone it can also
snoop all the intercepted traffic, be it by stealing an address or
the role of a router.
This means that any rogue access to the backbone must be prevented at
all times, and that nodes that are attached to the backbone must be
fully trusted / never compromised.
Using address registration as the sole ND mechanism on a link and
coupling it with [I-D.ietf-6lo-ap-nd] guarantees the ownership of a
registered address within that link.
* The protection is based on a proof-of-ownership encoded in the
ROVR field and protects against address theft and impersonation by
a 6LN, because the 6LR can challenge the Registered Node for a
proof-of-ownership.
* The protection extends to the full LLN in the case of an LLN Link,
but does not extend over the backbone since the 6BBR cannot
provide the proof-of-ownership when it defends the address.
A possible attack over the backbone can be done by sending an NS with
an EARO and expecting the NA(EARO) back to contain the TID and ROVR
fields of the existing state. With that information, the attacker
can easily increase the TID and take over the Binding.
If the classical ND is disabled on the backbone and the use of
[I-D.ietf-6lo-ap-nd] and a 6LBR are mandated, the network will
benefit from the following new advantages:
Zero-trust security for ND flows within the whole subnet: the
increased security that [I-D.ietf-6lo-ap-nd] provides on the LLN
will also apply to the backbone; it becomes impossible for an
attached node to claim an address that belongs to another node
using ND, and the network can filter packets that are not
originated by the owner of the source address (SAVI), as long as
that the routers are known and trusted.
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Remote ND DoS attack avoidance: the complete list of addresses in
the network will be known to the 6LBR and available to the default
router; with that information the router does not need to send a
multicast NA(Lookup) in case of a Neighbor Cache miss for an
incoming packet, which is a source of remote DoS attack against
the network
Less IPv6 ND-related multicast on the backbone: DAD and NS(Lookup)
become unicast queries to the 6LBR
Better DAD operation on wireless: DAD has been found to fail to
detect duplications on large Wi-Fi infrastructures due to the
unreliable broadcast operation on wireless; using a 6LBR enables a
unicast lookup
Less Layer-2 churn on the backbone: Using the Routing Proxy
approach, the Link-Layer address of the LLN devices and their
mobility are not visible in the backbone; only the Link-Layer
addresses of the 6BBR and backbone nodes are visible at Layer 2 on
the backbone. This is mandatory for LLNs that cannot be bridged
on the backbone, and useful in any case to scale down, stabilize
the forwarding tables at Layer 2 and avoid the gratuitous frames
that are typically broadcasted to fix the transparent bridging
tables when a wireless node roams from an AP to the next.
This specification introduces a 6BBR that is a router on the path of
the LLN traffic and a 6LBR that is used for the lookup. They could
be interesting targets for an attacker. A compromised 6BBR can
accept a registration but block the traffic, or refrain from
proxying. A compromised 6LBR may accept unduly the transfer of
ownership of an address, or block a new comer by faking that its
address is a duplicate. But those attacks are possible in a
classical network from a compromised default router and a DHCP
server, respectively, and can be prevented using the same methods.
A possible attack over the LLN can still be done by compromising a
6LR. A compromised 6LR may modify the ROVR of EDAR messages in
flight and transfer the ownership of the Registered Address to itself
or a tier. It may also claim that a ROVR was validated when it
really wasn't, and reattribute an address to self or to an attached
6LN. This means that 6LRs, as well as 6LBRs and 6BBRS must still be
fully trusted / never compromised.
This specification mandates to check on the 6LBR on the backbone
before doing the classical DAD, in case the address already exists.
This may delay the DAD operation and should be protected by a short
timer, in the order of 100ms or less, which will only represent a
small extra delay versus the 1s wait of the DAD operation.
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12. Protocol Constants
This Specification uses the following constants:
TENTATIVE_DURATION: 800 milliseconds
STALE_DURATION: see below
In LLNs with long-lived Addresses such as LPWANs, STALE_DURATION
SHOULD be configured with a relatively long value to cover an
interval when the address may be reused, and before it is safe to
expect that the address was definitively released. A good default
value can be 24 hours. In LLNs where addresses are renewed rapidly,
e.g., for privacy reasons, STALE_DURATION SHOULD be configured with a
relatively shorter value, by default 5 minutes.
13. IANA Considerations
This document has no request to IANA.
14. Acknowledgments
Many thanks to Dorothy Stanley, Thomas Watteyne and Jerome Henry for
their various contributions. Also many thanks to Timothy Winters and
Erik Nordmark for their help, review and support in preparation to
the IESG cycle, and to Kyle Rose, Elwyn Davies, Barry Leiba, Mirja
Kuhlewind, Alvaro Retana, Roman Danyliw and very especially Dominique
Barthel and Benjamin Kaduk for their useful contributions through the
IETF last call and IESG process.
15. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
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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>.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059,
DOI 10.17487/RFC6059, November 2010,
<https://www.rfc-editor.org/info/rfc6059>.
[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>.
[RFC7048] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
Detection Is Too Impatient", RFC 7048,
DOI 10.17487/RFC7048, January 2014,
<https://www.rfc-editor.org/info/rfc7048>.
[RFC7559] Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss
Resiliency for Router Solicitations", RFC 7559,
DOI 10.17487/RFC7559, May 2015,
<https://www.rfc-editor.org/info/rfc7559>.
[RFC7772] Yourtchenko, A. and L. Colitti, "Reducing Energy
Consumption of Router Advertisements", BCP 202, RFC 7772,
DOI 10.17487/RFC7772, February 2016,
<https://www.rfc-editor.org/info/rfc7772>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
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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>.
16. Informative References
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <https://www.rfc-editor.org/info/rfc4389>.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
DOI 10.17487/RFC4903, June 2007,
<https://www.rfc-editor.org/info/rfc4903>.
[RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415,
DOI 10.17487/RFC5415, March 2009,
<https://www.rfc-editor.org/info/rfc5415>.
[RFC5568] Koodli, R., Ed., "Mobile IPv6 Fast Handovers", RFC 5568,
DOI 10.17487/RFC5568, July 2009,
<https://www.rfc-editor.org/info/rfc5568>.
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing",
RFC 6606, DOI 10.17487/RFC6606, May 2012,
<https://www.rfc-editor.org/info/rfc6606>.
[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>.
[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>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
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[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>.
[I-D.yourtchenko-6man-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://tools.ietf.org/html/
draft-yourtchenko-6man-dad-issues-01>.
[I-D.nordmark-6man-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://tools.ietf.org/html/draft-nordmark-6man-dad-
approaches-02>.
[I-D.ietf-6man-rs-refresh]
Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6
Neighbor Discovery Optional RS/RA Refresh", Work in
Progress, Internet-Draft, draft-ietf-6man-rs-refresh-02,
31 October 2016, <https://tools.ietf.org/html/draft-ietf-
6man-rs-refresh-02>.
[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
"Address Protected Neighbor Discovery for Low-power and
Lossy Networks", Work in Progress, Internet-Draft, draft-
ietf-6lo-ap-nd-20, 9 March 2020,
<https://tools.ietf.org/html/draft-ietf-6lo-ap-nd-20>.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", Work in Progress, Internet-Draft,
draft-ietf-6tisch-architecture-28, 29 October 2019,
<https://tools.ietf.org/html/draft-ietf-6tisch-
architecture-28>.
[I-D.ietf-mboned-ieee802-mcast-problems]
Perkins, C., McBride, M., Stanley, D., Kumari, W., and J.
Zuniga, "Multicast Considerations over IEEE 802 Wireless
Media", Work in Progress, Internet-Draft, draft-ietf-
mboned-ieee802-mcast-problems-11, 11 December 2019,
<https://tools.ietf.org/html/draft-ietf-mboned-ieee802-
mcast-problems-11>.
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[I-D.bi-savi-wlan]
Bi, J., Wu, J., Wang, Y., and T. Lin, "A SAVI Solution for
WLAN", Work in Progress, Internet-Draft, draft-bi-savi-
wlan-18, 17 November 2019,
<https://tools.ietf.org/html/draft-bi-savi-wlan-18>.
[I-D.thubert-6lo-unicast-lookup]
Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery
Unicast Lookup", Work in Progress, Internet-Draft, draft-
thubert-6lo-unicast-lookup-00, 25 January 2019,
<https://tools.ietf.org/html/draft-thubert-6lo-unicast-
lookup-00>.
[IEEEstd8021]
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".
[IEEEstd80211]
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)".
Appendix A. Possible Future Extensions
With the current specification, the 6LBR is not leveraged to avoid
multicast NS(Lookup) on the Backbone. This could be done by adding a
lookup procedure in the EDAR/EDAC exchange.
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By default the specification does not have a fine-grained trust
model: all nodes that can authenticate to the LLN MAC or attach to
the backbone are equally trusted. It would be desirable to provide a
stronger authorization model, e.g., whereby nodes that associate
their address with a proof-of-ownership [I-D.ietf-6lo-ap-nd] should
be more trusted than nodes that do not. Such a trust model and
related signaling could be added in the future to override the
default operation and favor trusted nodes.
Future documents may extend this specification by allowing the 6BBR
to redistribute Host routes in routing protocols that would operate
over the Backbone, or in MIPv6 [RFC6275], or FMIP [RFC5568], or the
Locator/ID Separation Protocol (LISP) [RFC6830] to support mobility
on behalf of the 6LNs, etc... LISP may also be used to provide an
equivalent to the EDAR/EDAC exchange using a Map Server / Map
Resolver as a replacement to the 6LBR.
Appendix B. Applicability and Requirements Served
This document specifies proxy-ND functions that can be used to
federate an IPv6 Backbone Link and multiple IPv6 LLNs into a single
Multi-Link Subnet. The proxy-ND functions enable IPv6 ND services
for Duplicate Address Detection (DAD) and Address Lookup that do not
require broadcasts over the LLNs.
The term LLN is used to cover multiple types of WLANs and WPANs,
including (Low-Power) Wi-Fi, BLUETOOTH(R) Low Energy, IEEE STD
802.11ah and IEEE STD.802.15.4 wireless meshes, covering the types of
networks listed in Appendix B.3 of [RFC8505] "Requirements Related to
Various Low-Power Link Types".
Each LLN in the subnet is attached to an IPv6 Backbone Router (6BBR).
The Backbone Routers interconnect the LLNs and advertise the
Addresses of the 6LNs over the Backbone Link using proxy-ND
operations.
This specification updates IPv6 ND over the Backbone to distinguish
Address movement from duplication and eliminate stale state in the
Backbone routers and Backbone nodes once a 6LN has roamed. This way,
mobile nodes may roam rapidly from one 6BBR to the next and
requirements in Appendix B.1 of [RFC8505] "Requirements Related to
Mobility" are met.
A 6LN can register its IPv6 Addresses and thereby obtain proxy-ND
services over the Backbone, meeting the requirements expressed in
Appendix B.4 of [RFC8505], "Requirements Related to Proxy
Operations".
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The negative impact of the IPv6 ND-related broadcasts can be limited
to one of the federated links, enabling the number of 6LNs to grow.
The Routing Proxy operation avoids the need to expose the MAC
addresses of the 6LNs onto the backbone, keeping the Layer 2 topology
simple and stable. This meets the requirements in Appendix B.6 of
[RFC8505] "Requirements Related to Scalability", as long has the
6BBRs are dimensioned for the number of registrations that each needs
to support.
In the case of a Wi-Fi access link, a 6BBR may be collocated with the
Access Point (AP), or with a Fabric Edge (FE) or a CAPWAP [RFC5415]
Wireless LAN Controller (WLC). In those cases, the wireless client
(STA) is the 6LN that makes use of [RFC8505] to register its IPv6
Address(es) to the 6BBR acting as Routing Registrar. The 6LBR can be
centralized and either connected to the Backbone Link or reachable
over IP. The 6BBR proxy-ND operations eliminate the need for
wireless nodes to respond synchronously when a Lookup is performed
for their IPv6 Addresses. This provides the function of a Sleep
Proxy for ND [I-D.nordmark-6man-dad-approaches].
For the TimeSlotted Channel Hopping (TSCH) mode of [IEEEstd802154],
the 6TiSCH architecture [I-D.ietf-6tisch-architecture] describes how
a 6LoWPAN ND host could connect to the Internet via a RPL mesh
Network, but doing so requires extensions to the 6LOWPAN ND protocol
to support mobility and reachability in a secure and manageable
environment. The extensions detailed in this document also work for
the 6TiSCH architecture, serving the requirements listed in
Appendix B.2 of [RFC8505] "Requirements Related to Routing
Protocols".
The registration mechanism may be seen as a more reliable alternate
to snooping [I-D.bi-savi-wlan]. It can be noted that registration
and snooping are not mutually exclusive. Snooping may be used in
conjunction with the registration for nodes that do not register
their IPv6 Addresses. The 6BBR assumes that if a node registers at
least one IPv6 Address to it, then the node registers all of its
Addresses to the 6BBR. With this assumption, the 6BBR can possibly
cancel all undesirable multicast NS messages that would otherwise
have been delivered to that node.
Scalability of the Multi-Link Subnet [RFC4903] requires avoidance of
multicast/broadcast operations as much as possible even on the
Backbone [I-D.ietf-mboned-ieee802-mcast-problems]. Although hosts
can connect to the Backbone using IPv6 ND operations, multicast RAs
can be saved by using [I-D.ietf-6man-rs-refresh], which also requires
the support of [RFC7559].
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Authors' Addresses
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
Charles E. Perkins
Blue Meadow Networking
Saratoga, 95070
United States of America
Email: charliep@computer.org
Eric Levy-Abegnoli
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 20
Email: elevyabe@cisco.com
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