6lo P. Thubert, Ed.
Internet-Draft cisco
Intended status: Standards Track February 23, 2018
Expires: August 27, 2018
IPv6 Backbone Router
draft-ietf-6lo-backbone-router-06
Abstract
This specification proposes proxy operations for IPv6 Neighbor
Discovery on behalf of devices located on broadcast-inefficient
wireless networks. A broadcast-efficient backbone running classical
IPv6 Neighbor Discovery federates multiple wireless links to form a
large MultiLink Subnet, but the broadcast domain does not need to
extend to the wireless links for the purpose of ND operation.
Backbone Routers placed at the wireless edge of the backbone proxy
the ND operation and route packets from/to registered nodes, and
wireless nodes register or are proxy-registered to the Backbone
Router to setup proxy services in a fashion that is essentially
similar to a classical Layer-2 association.
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 August 27, 2018.
Copyright Notice
Copyright (c) 2018 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
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publication of this document. Please review these documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability and Requirements Served . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Backbone Router Routing Operations . . . . . . . . . . . . . 9
5.1. Over the Backbone Link . . . . . . . . . . . . . . . . . 10
5.2. Over the LLN Link . . . . . . . . . . . . . . . . . . . . 11
6. BackBone Router Proxy Operations . . . . . . . . . . . . . . 13
6.1. Registration and Binding State Creation . . . . . . . . . 15
6.2. Defending Addresses . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 20
11.3. External Informative References . . . . . . . . . . . . 23
Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 24
A.1. Requirements Related to Mobility . . . . . . . . . . . . 24
A.2. Requirements Related to Routing Protocols . . . . . . . . 25
A.3. Requirements Related to the Variety of Low-Power Link
types . . . . . . . . . . . . . . . . . . . . . . . . . . 26
A.4. Requirements Related to Proxy Operations . . . . . . . . 26
A.5. Requirements Related to Security . . . . . . . . . . . . 27
A.6. Requirements Related to Scalability . . . . . . . . . . . 28
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
One of the key services provided by IEEE std. 802.1 [IEEEstd8021]
Ethernet Bridging is an efficient and reliable broadcast service, and
multiple applications and protocols have been built that heavily
depend on that feature for their core operation. But a wide range of
wireless networks do not provide the solid and cheap broadcast
capabilities of Ethernet Bridging, and protocols designed for bridged
networks that rely on broadcast often exhibit disappointing
behaviours when applied unmodified to a wireless medium.
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IEEE std. 802.11 [IEEEstd80211] Access Points (APs) deployed in an
Extended Service Set (ESS) effectively act as bridges, but, in order
to ensure a solid connectivity to the devices and protect the medium
against harmful broadcasts, they refrain from relying on broadcast-
intensive protocols such as Transparent Bridging on the wireless
side. Instead, an association process is used to register
proactively the MAC addresses of the wireless device (STA) to the AP,
and then the APs proxy the bridging operation and cancel the
broadcasts.
Classical IPv6 [RFC8200] Neighbor Discovery [RFC4861] [RFC4862]
Protocol (NDP) operations are reactive and rely heavily on multicast
operations to locate an on-link correspondent and ensure address
uniqueness, which is a pillar that sustains the whole IP
architecture. When the Duplicate Address Detection [RFC4862] (DAD)
mechanism was designed, it was a natural match with the efficient
broadcast operation of Ethernet Bridging, but with the unreliable
broadcast that is typical of wireless media, DAD is bound to fail to
discover duplications [I-D.yourtchenko-6man-dad-issues]. In other
words, because the broadcast service is unreliable, DAD appears to
work on wireless media not because address duplication is detected
and solved as designed, but because the duplication is a very rare
event as a side effect of the sheer amount of entropy in 64-bits
Interface IDs.
In the real world, IPv6 multicast messages are effectively broadcast,
so they are processed by most if not all wireless nodes over the ESS
fabric even when very few if any of the nodes is effectively
listening to the multicast address. It results that a simple
Neighbor Solicitation (NS) lookup message [RFC4861], that is
supposedly targeted to a very small group of nodes, ends up polluting
the whole wireless bandwidth across the fabric
[I-D.vyncke-6man-mcast-not-efficient]. In other words, the reactive
IPv6 ND operation leads to undesirable power consumption in battery-
operated devices.
The inefficiencies of using radio broadcasts to support IPv6 NDP lead
the community to consider (again) splitting the broadcast domain
between the wired and the wireless access links. One classical way
to achieve this is to split the subnet in multiple ones, and at the
extreme provide a /64 per wireless device. Another is to proxy the
Layer-3 protocols that rely on broadcast operation at the boundary of
the wired and wireless domains, effectively emulating the Layer-2
association at layer-3. To that effect, the current IEEE std. 802.11
specifications require the capability to perform ARP and ND proxy
[RFC4389] functions at the Access Points (APs).
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But for the lack a comprehensive specification for the ND proxy and
in particular the lack of an equivalent to an association process,
implementations have to rely on snooping for acquiring the related
state, which is unsatisfactory in a lossy and mobile conditions.
With snooping, a state (e.g. a new IPv6 address) may not be
discovered or a change of state (e.g. a movement) may be missed,
leading to unreliable connectivity.
In the context of IEEE std. 802.15.4 [IEEEstd802154], the step of
considering the radio as a medium that is different from Ethernet was
already taken with the publication of Neighbor Discovery Optimization
for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)
[RFC6775]. RFC 6775 is updated as [I-D.ietf-6lo-rfc6775-update]; the
update includes changes that are required by this document.
This specification applies that same thinking to other wireless links
such as Low-Power IEEE std. 802.11 (Wi-Fi) and IEEE std. 802.15.1
(Bluetooth) [IEEEstd802151], and extends [RFC6775] to enable proxy
operation by the 6BBR so as to decouple the broadcast domain in the
backbone from the wireless links. The proxy operation can be
maintained asynchronous so that low-power nodes or nodes that are
deep in a mesh do not need to be bothered synchronously when a lookup
is performed for their addresses, effectively implementing the ND
contribution to the concept of a Sleep Proxy
[I-D.nordmark-6man-dad-approaches].
2. Applicability and Requirements Served
Efficiency aware IPv6 Neighbor Discovery Optimizations
[I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND
[RFC6775] can be extended to other types of links beyond IEEE std.
802.15.4 for which it was defined. The registration technique is
beneficial when the Link-Layer technique used to carry IPv6 multicast
packets is not sufficiently efficient in terms of delivery ratio or
energy consumption in the end devices, in particular to enable
energy-constrained sleeping nodes. The value of such extension is
especially apparent in the case of mobile wireless nodes, to reduce
the multicast operations that are related to classical ND ([RFC4861],
[RFC4862]) and plague the wireless medium.
This specification updates and generalizes 6LoWPAN ND to a broader
range of Low power and Lossy Networks (LLNs) with a solid support for
Duplicate Address Detection (DAD) and address lookup that does not
require broadcasts over the LLNs. The term LLN is used loosely in
this specification 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, so as to address the
requirements listed in Appendix A.3
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The scope of this draft is a Backbone Link that federates multiple
LLNs as a single IPv6 MultiLink Subnet. Each LLN in the subnet is
anchored at an IPv6 Backbone Router (6BBR). The Backbone Routers
interconnect the LLNs over the Backbone Link and emulate that the LLN
nodes are present on the Backbone using proxy-ND operations. This
specification extends IPv6 ND over the backbone to discriminate
address movement from duplication and eliminate stale state in the
backbone routers and backbone nodes once a LLN node has roamed. This
way, mobile nodes may roam rapidly from a 6BBR to the next and
requirements in Appendix A.1 are met.
This specification can be used by any wireless node to associate at
Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
services including proxy-ND operations over the backbone, effectively
providing a solution to the requirements expressed in Appendix A.4.
The Link Layer Address (LLA) that is returned as Target LLA (TLLA) in
Neighbor Advertisements (NA) messages by the 6BBR on behalf of the
Registered Node over the backbone may be that of the Registering
Node, in which case the 6BBR needs to bridge the unicast packets
(Bridging proxy), or that of the 6BBR on the backbone, in which case
the 6BBRs needs to route the unicast packets (Routing proxy). In the
latter case, the 6BBR may maintain the list of correspondents to
which it has advertised its own MAC address on behalf of the LLN node
and the IPv6 ND operation is minimized as the number of nodes scale
up in the LLN. This enables to meet the requirements in Appendix A.6
as long has the 6BBRs are dimensioned for the number of registration
that each needs to support.
In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
[IEEEstd802154], the 6TiSCH architecture
[I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could
connect to the Internet via a RPL mesh Network, but this requires
additions to the 6LOWPAN ND protocol to support mobility and
reachability in a secured and manageable environment. This
specification details the new operations that are required to
implement the 6TiSCH architecture and serves the requirements listed
in Appendix A.2.
In the case of Low-Power IEEE std. 802.11, a 6BBR may be collocated
with a standalone AP or a CAPWAP [RFC5415] wireless controller, and
the wireless client (STA) leverages this specification to register
its IPv6 address(es) to the 6BBR over the wireless medium. In the
case of a 6TiSCH LLN mesh, the RPL root is collocated with a 6LoWPAN
Border Router (6LBR), and either collocated with or connected to the
6BBR over an IPv6 Link. The 6LBR leverages this specification to
register the LLN nodes on their behalf to the 6BBR. In the case of
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BTLE, the 6BBR is collocated with the router that implements the BTLE
central role as discussed in section 2.2 of [RFC7668].
3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Readers are expected to be familiar with all the terms and concepts
that are discussed in "Neighbor Discovery for IP version 6"
[RFC4861], "IPv6 Stateless Address Autoconfiguration" [RFC4862],
"IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
Neighbor Discovery Optimization for Low-power and Lossy Networks
[RFC6775] and "Multi-link Subnet Support in IPv6"
[I-D.ietf-ipv6-multilink-subnets].
Readers would benefit from reading "Multi-Link Subnet Issues"
[RFC4903], ,"Mobility Support in IPv6" [RFC6275], "Neighbor Discovery
Proxies (ND Proxy)" [RFC4389] and "Optimistic Duplicate Address
Detection" [RFC4429] prior to this specification for a clear
understanding of the art in ND-proxying and binding.
Additionally, this document uses terminology from [RFC7102],
[I-D.ietf-6lo-rfc6775-update] and [I-D.ietf-6tisch-terminology], and
introduces the following terminology:
Sleeping Proxy A 6BBR acts as a Sleeping Proxy if it answers ND
Neighbor Solicitation over the backbone on behalf of the
Registered Node whenever possible. This is the default mode
for this specification but it may be overridden, for instance
by configuration, into Unicasting Proxy.
Unicasting Proxy As a Unicasting Proxy, the 6BBR forwards NS
messages to the Registering Node, transforming Layer-2
multicast into unicast whenever possible.
Routing proxy A 6BBR acts as a routing proxy if it advertises its
own MAC address, as opposed to that of the node that performs
the registration, as the TLLA in the proxied NAs over the
backbone. In that case, the MAC address of the node is not
visible at Layer-2 over the backbone and the bridging fabric is
not aware of the addresses of the LLN devices and their
mobility. The 6BBR installs a connected host route towards the
registered node over the interface to the node, and acts as a
Layer-3 router for unicast packets to the node. The 6BBR
updates the ND Neighbor Cache Entries (NCE) in correspondent
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nodes if the wireless node moves and registers to another 6BBR,
either with a single broadcast, or with a series of unicast
NA(O) messages, indicating the TLLA of the new router.
Bridging proxy A 6BBR acts as a bridging proxy if it advertises the
MAC address of the node that performs the registration as the
TLLA in the proxied NAs over the backbone. In that case, the
MAC address and the mobility of the node is still visible
across the bridged backbone fabric, as is traditionally the
case with Layer-2 APs. The 6BBR acts as a Layer-2 bridge for
unicast packets to the registered node. The MAC address
exposed in the S/TLLA is that of the Registering Node, which is
not necessarily the Registered Device. When a device moves
within a LLN mesh, it may end up attached to a different 6LBR
acting as Registering Node, and the LLA that is exposed over
the backbone will change.
Primary BBR The BBR that will defend a Registered Address for the
purpose of DAD over the backbone.
Secondary BBR A BBR to which the address is registered. A Secondary
Router MAY advertise the address over the backbone and proxy
for it.
4. Overview
An LLN node can move freely from an LLN anchored at a Backbone Router
to an LLN anchored at another Backbone Router on the same backbone
and conserve any of the IPv6 addresses that it has formed,
transparently.
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|
+-----+
| | Other (default) Router
| |
+-----+
|
| Backbone Link
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
| | router | | router | | router
+-----+ +-----+ +-----+
o o o o o o
o o o o o o o o o o o o o o
o o o o o o o o o o o o o o o
o o o o o o o o o o
o o o o o o o
LLN LLN LLN
Figure 1: Backbone Link and Backbone Routers
The Backbone Routers maintain an abstract Binding Table of their
Registered Nodes. The Binding Table operates as a distributed
database of all the wireless Nodes whether they reside on the LLNs or
on the backbone, and use an extension to the Neighbor Discovery
Protocol to exchange that information across the Backbone in the
classical ND reactive fashion.
The Extended Address Registration Option (EARO) defined in
[I-D.ietf-6lo-rfc6775-update] is used to enable the registration for
routing and proxy option is included in the ND exchanges over the
backbone between the 6BBRs to sort out duplication from movement.
Address duplication is sorted out with the Owner Unique-ID field in
the EARO, which is a generalization of the EUI-64 that allows
different types of unique IDs beyond the name space derived from the
MAC addresses. First-Come First-Serve rules apply, whether the
duplication happens between LLN nodes as represented by their
respective 6BBRs, or between an LLN node and a classical node that
defends its address over the backbone with classical ND and does not
include the EARO option.
In case of conflicting registrations to multiple 6BBRs from a same
node, a sequence counter called Transaction ID (TID) in the EARO
enables 6BBRs to sort out the latest anchor for that node.
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Registrations with a same TID are compatible and maintained, but, in
case of different TIDs, only the freshest registration is maintained
and the stale state is eliminated. The EARO also transports a 'R'
flag to be used by a 6LN when registering, to indicate that this 6LN
is not a router and that it will not handle its own reachability.
With this specification, Backbone Routers perform a ND proxy
operation over the Backbone Link on behalf of their Registered Nodes.
The registration to the proxy service is done with a NS/NA(EARO)
exchange. The EARO option with a 'R' flag is used in this
specification to indicate to the 6BBR that it is expected to perform
this proxy operation. The Backbone Router operation is essentially
similar to that of a Mobile IPv6 (MIPv6) [RFC6275] Home Agent. This
enables mobility support for LLN nodes that would move outside of the
network delimited by the Backbone link attach to a Home Agent from
that point on. This also enables collocation of Home Agent
functionality within Backbone Router functionality on the same
backbone interface of a router. Further specification may extend
this be allowing the 6BBR to redistribute host routes in routing
protocols that would operate over the backbone, or in MIPv6 or the
Locator/ID Separation Protocol (LISP) [RFC6830] to support mobility
on behalf of the nodes, etc...
The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
specification details how an address can be used before a Duplicate
Address Detection (DAD) is complete, and insists that an address that
is TENTATIVE should not be associated to a Source Link-Layer Address
Option in a Neighbor Solicitation message. This specification
leverages ODAD to create a temporary proxy state in the 6BBR till DAD
is completed over the backbone. This way, the specification enables
to distribute proxy states across multiple 6BBR and co-exist with
classical ND over the backbone.
5. Backbone Router Routing Operations
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|
+-----+
| | Other (default) Router
| |
+-----+
| /64
| Backbone Link
+-------------------+-------------------+
| /64 | /64 | /64
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
| | router | | router | | router
+-----+ +-----+ +-----+
o N*/128 o o o M*/128 o o P*/128
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 LLN LLN
Figure 2: Routing Configuration in the ML Subnet
5.1. Over the Backbone Link
The Backbone Router is a specific kind of Border Router that performs
proxy Neighbor Discovery on its backbone interface on behalf of the
nodes that it has discovered on its LLN interfaces.
The backbone is expected to be a high speed, reliable Backbone link,
with affordable and reliable multicast capabilities, such as a
bridged Ethernet Network, and to allow a full support of classical ND
as specified in [RFC4861] and subsequent RFCs. In other words, the
backbone is not a LLN.
Still, some restrictions of the attached LLNs will apply to the
backbone. In particular, it is expected that the MTU is set to the
same value on the backbone and all attached LLNs, and the scalability
of the whole subnet requires that broadcast operations are avoided as
much as possible on the backbone as well. Unless configured
otherwise, the Backbone Router MUST echo the MTU that it learns in
RAs over the backbone in the RAs that it sends towards the LLN links.
As a router, the Backbone Router behaves like any other IPv6 router
on the backbone side. It has a connected route installed towards the
backbone for the prefixes that are present on that backbone and that
it proxies for on the LLN interfaces.
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As a proxy, the 6BBR uses an EARO option in the NS-DAD and the
multicast NA messages that it generates over the Backbone Link on
behalf of a Registered Node, and it places an EARO in its unicast NA
messages, if and only if the NS/NA that stimulates it had an EARO in
it and the 'R' bit set.
When possible, the 6BBR SHOULD use unicast or solicited-node
multicast address (SNMA) [RFC4291] to defend its Registered Addresses
over the backbone. In particular, the 6BBR MUST join the SNMA group
that corresponds to a Registered Address as soon as it creates an
entry for that address and as long as it maintains that entry,
whatever the state of the entry. The expectation is that it is
possible to get a message delivered to all the nodes on the backbone
that listen to a particular address and support this specification -
which includes all the 6BBRs in the MultiLink Subnet - by sending a
multicast message to the associated SNMA over the backbone.
The support of Optimistic DAD (ODAD) [RFC4429] is recommended for all
nodes in the backbone and followed by the 6BBRs in their proxy
activity over the backbone. With ODAD, any optimistic node MUST join
the SNMA of a Tentative address, which interacts better with this
specification.
This specification allows the 6BBR in Routing Proxy mode to advertise
the Registered IPv6 Address with the 6BBR Link Layer Address, and
attempts to update Neighbor Cache Entries (NCE) in correspondent
nodes over the backbone, using gratuitous NA(Override). This method
may fail of the multicast message is not properly received, and
correspondent nodes may maintain an incorrect neighbor state, which
they will eventually discover through Neighbor Unreachability
Detection (NUD). Because mobility may be slow, the NUD procedure
defined in [RFC4861] may be too impatient, and the support of
[RFC7048] is recommended in all nodes in the network.
Since the MultiLink Subnet may grow very large in terms of individual
IPv6 addresses, multicasts should be avoided as much as possible even
on the backbone. Though it is possible for plain hosts to
participate with legacy IPv6 ND support, the support by all nodes
connected to the backbone of [I-D.ietf-6man-rs-refresh] is
recommended, and this implies the support of [RFC7559] as well.
5.2. Over the LLN Link
As a router, the Nodes and Backbone Router operation on the LLN
follows [RFC6775]. Per that specification, LLN Hosts generally do
not depend on multicast RAs to discover routers. It is still
generally required for LLN nodes to accept multicast RAs [RFC7772],
but those are rare on the LLN link. Nodes are expected to follow the
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Simple Procedures for Detecting Network Attachment in IPv6 [RFC6059]
(DNA procedures) to assert movements, and to support the Packet-Loss
Resiliency for Router Solicitations [RFC7559] to make the unicast RS
more reliable.
An LLN node signals that it requires IPv6 ND proxy services from a
6BBR by registering the corresponding IPv6 Address with an NS(EARO)
message with the 'R' flag set. The LLN node that performs the
registration (the Registering Node) may be the owner of the IPv6
Address (the Registered Node) or a 6LBR that performs the
registration on its behalf.
When operating as a Routing Proxy, the router installs hosts routes
(/128) to the Registered Addresses over the LLN links, via the
Registering Node as identified by the Source Address and the SLLAO
option in the NS(EARO) messages.
In that mode, the 6BBR handles the ND protocol over the backbone on
behalf of the Registered Nodes, using its own MAC address in the TLLA
and SLLA options in proxyed NS and NA messages. It results that for
each Registered Address, a number of peer Nodes on the backbone have
resolved the address with the 6BBR MAC address and keep that mapping
stored in their Neighbor cache.
The 6BBR SHOULD maintain, per Registered Address, the list of the
peers on the backbone to which it answered with it MAC address, and
when a binding moves to a different 6BBR, it SHOULD send a unicast
gratuitous NA(O) individually to each of them to inform them that the
address has moved and pass the MAC address of the new 6BBR in the
TLLAO option. If the 6BBR can not maintain that list, then it SHOULD
remember whether that list is empty or not and if not, send a
multicast NA(O) to all nodes to update the impacted Neighbor Caches
with the information from the new 6BBR.
The Bridging Proxy is a variation where the BBR function is
implemented in a Layer-3 switch or an wireless Access Point that acts
as a Host from the IPv6 standpoint, and, in particular, does not
operate the routing of IPv6 packets. In that case, the SLLAO in the
proxied NA messages is that of the Registering Node and classical
bridging operations take place on data frames.
If a registration moves from one 6BBR to the next, but the
Registering Node does not change, as indicated by the S/TLLAO option
in the ND exchanges, there is no need to update the Neighbor Caches
in the peers Nodes on the backbone. On the other hand, if the LLAO
changes, the 6BBR SHOULD inform all the relevant peers as described
above, to update the impacted Neighbor Caches. In the same fashion,
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if the Registering Node changes with a new registration, the 6BBR
SHOULD also update the impacted Neighbor Caches over the backbone.
6. BackBone Router Proxy Operations
This specification enables a Backbone Router to proxy Neighbor
Discovery operations over the backbone on behalf of the nodes that
are registered to it, allowing any node on the backbone to reach a
Registered Node as if it was on-link. The backbone and the LLNs are
considered different Links in a MultiLink subnet but the prefix that
is used may still be advertised as on-link on the backbone to support
legacy nodes; multicast ND messages are link-scoped and not forwarded
across the backbone routers.
ND Messages on the backbone side that do not match to a registration
on the LLN side are not acted upon on the LLN side, which stands
protected. On the LLN side, the prefixes associated to the MultiLink
Subnet are presented as not on-link, so address resolution for other
hosts do not occur.
The default operation in this specification is Sleeping proxy which
means:
o creating a new entry in an abstract Binding Table for a new
Registered Address and validating that the address is not a
duplicate over the backbone
o defending a Registered Address over the backbone using NA messages
with the Override bit set on behalf of the sleeping node whenever
possible
o advertising a Registered Address over the backbone using NA
messages, asynchronously or as a response to a Neighbor
Solicitation messages.
o Looking up a destination over the backbone in order to deliver
packets arriving from the LLN using Neighbor Solicitation
messages.
o Forwarding packets from the LLN over the backbone, and the other
way around.
o Eventually triggering a liveliness verification of a stale
registration.
A 6BBR may act as a Sleeping Proxy only if the state of the binding
entry is REACHABLE, or TENTATIVE in which case the answer is delayed.
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In any other state, the Sleeping Proxy operates as a Unicasting
Proxy.
As a Unicasting Proxy, the 6BBR forwards NS lookup messages to the
Registering Node, transforming Layer-2 multicast into unicast
whenever possible. This is not possible in UNREACHABLE state, so the
NS messages are multicasted, and rate-limited to protect the medium
with an exponential back-off. In other states, The messages are
forwarded to the Registering Node as unicast Layer-2 messages. In
TENTATIVE state, the NS message is either held till DAD completes, or
dropped.
The draft introduces the optional concept of primary and secondary
BBRs. The primary is the backbone router that has the highest EUI-64
address of all the 6BBRs that share a registration for a same
Registered Address, with the same Owner Unique ID and same
Transaction ID, the EUI-64 address being considered as an unsigned
64bit integer. The concept is defined with the granularity of an
address, that is a given 6BBR can be primary for a given address and
secondary or another one, regardless on whether the addresses belong
to the same node or not. The primary Backbone Router is in charge of
protecting the address for DAD over the Backbone. Any of the Primary
and Secondary 6BBR may claim the address over the backbone, since
they are all capable to route from the backbone to the LLN node, and
the address appears on the backbone as an anycast address.
The Backbone Routers maintain a distributed binding table, using
classical ND over the backbone to detect duplication. This
specification requires that:
1. All addresses that can be reachable from the backbone, including
IPv6 addresses based on burn-in EUI64 addresses MUST be
registered to the 6BBR.
2. A Registered Node MUST include the EARO option in an NS message
that used to register an addresses to a 6LR; the 6LR MUST
propagate that option unchanged to the 6LBR in the DAR/DAC
exchange, and the 6LBR MUST propagate that option unchanged in
proxy registrations.
3. The 6LR MUST echo the same EARO option in the NA that it uses to
respond, but for the status filed which is not used in NS
messages, and significant in NA.
A false positive duplicate detection may arise over the backbone, for
instance if the Registered Address is registered to more than one
LBR, or if the node has moved. Both situations are handled
gracefully unbeknownst to the node. In the former case, one LBR
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becomes primary to defend the address over the backbone while the
others become secondary and may still forward packets back and forth.
In the latter case the LBR that receives the newest registration wins
and becomes primary.
The expectation in this specification is that there is a single
Registering Node at a time per Backbone Router for a given Registered
Address, but that a Registered Address may be registered to Multiple
6BBRs for higher availability.
Over the LLN, and for any given Registered Address, it is REQUIRED
that:
de-registrations (newer TID, same OUID, null Lifetime) are
accepted and responded immediately with a status of 4; the entry
is deleted;
newer registrations (newer TID, same OUID, non-null Lifetime) are
accepted and responded with a status of 0 (success); the entry is
updated with the new TID, the new Registration Lifetime and the
new Registering Node, if any has changed; in TENTATIVE state the
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 OUID) from a same
Registering Node are not processed but responded with a status of
0 (success); they are expected to be identical and an error may be
logged if not; in TENTATIVE state, the response is held and may be
overwritten, but it MUST be eventually produced and it carries the
result of the DAD process;
older registrations (not(newer or equal) TID, same OUID) from a
same Registering Node are ignored;
identical and older registrations (not-newer TID, same OUID) from
a different Registering Node are responded immediately with a
status of 3 (moved); this may be rate limited to protect the
medium;
and any registration for a different Registered Node (different
OUID) are responded immediately with a status of 1 (duplicate).
6.1. Registration and Binding State Creation
Upon a registration for a new address with an NS(EARO) with the 'R'
bit set, the 6BBR performs a DAD operation over the backbone placing
the new address as target in the NS-DAD message. The EARO from the
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registration MUST be placed unchanged in the NS-DAD message, and an
entry is created in TENTATIVE state for a duration of
TENTATIVE_DURATION. The NS-DAD message is sent multicast over the
backbone to the SNMA address associated with the registered address.
If that operation is known to be costly, and the 6BBR has an
indication from another source (such as a NCE) that the Registered
Address was present on the backbone, that information may be
leveraged to send the NS-DAD message as a Layer-2 unicast to the MAC
that was associated with the Registered Address.
In TENTATIVE state:
o the entry is removed if an NA is received over the backbone for
the Registered Address with no EARO option, or with an EARO option
with a status of 1 (duplicate) that indicates an existing
registration for another LLN node. The OUID and TID fields in the
EARO option received over the backbone are ignored. A status of 1
is returned in the EARO option of the NA back to the Registering
Node;
o the entry is also removed if an NA with an ARO option with a
status of 3 (moved), or a NS-DAD with an ARO option that indicates
a newer registration for the same Registered Node, is received
over the backbone for the Registered Address. A status of 3 is
returned in the NA(EARO) back to the Registering Node;
o when a registration is updated but not deleted, e.g. from a newer
registration, the DAD process on the backbone continues and the
running timers are not restarted;
o Other NS (including DAD with no EARO option) and NA from the
backbone are not responded in TENTATIVE state, but the list of
their origins may be kept in memory and if so, the 6BBR may send
them each a unicast NA with eventually an EARO option when the
TENTATIVE_DURATION timer elapses, so as to cover legacy nodes that
do not support ODAD.
o When the TENTATIVE_DURATION timer elapses, a status 0 (success) is
returned in a NA(EARO) back to the Registering Node(s), and the
entry goes to REACHABLE state for the Registration Lifetime; the
DAD process is successful and the 6BBR MUST send a multicast
NA(EARO) to the SNMA associated to the Registered Address over the
backbone with the Override bit set so as to take over the binding
from other 6BBRs.
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6.2. Defending Addresses
If a 6BBR has an entry in REACHABLE state for a Registered Address:
o If the 6BBR is primary, or does not support the function of
primary, it MUST defend that address over the backbone upon an
incoming NS-DAD, either if the NS does not carry an EARO, or if an
EARO is present that indicates a different Registering Node
(different OUID). The 6BBR sends a NA message with the Override
bit set and the NA carries an EARO option if and only if the NS-
DAD did so. When present, the EARO in the NA(O) that is sent in
response to the NS-DAD(EARO) carries a status of 1 (duplicate),
and the OUID and TID fields in the EARO option are obfuscated with
null or random values to avoid network scanning and impersonation
attacks.
o If the 6BBR receives an NS-DAD(EARO) that reflect a newer
registration, the 6BBR updates the entry and the routing state to
forward packets to the new 6BBR, but keeps the entry REACHABLE.
In that phase, it MAY use REDIRECT messages to reroute traffic for
the Registered Address to the new 6BBR.
o If the 6BBR receives an NA(EARO) that reflect a newer
registration, the 6BBR removes its entry and sends a NA(AERO) with
a status of 3 (moved) to the Registering Node, if the Registering
Node is different from the Registered Node. If necessary, the
6BBR cleans up ND cache in peers nodes as discussed in
Section 5.1, by sending a series of unicast to the impacted nodes,
or one broadcast NA(O) to all-nodes.
o If the 6BBR received a NS(LOOKUP) for a Registered Address, it
answers immediately with an NA on behalf of the Registered Node,
without polling it. There is no need of an EARO in that exchange.
o When the Registration-Lifetime timer elapses, the entry goes to
STALE state for a duration of STABLE_STALE_DURATION in LLNs that
keep stable addresses such as LWPANs, and UNSTABLE_STALE_DURATION
in LLNs where addresses are renewed rapidly, e.g. for privacy
reasons.
The STALE state is a chance to keep track of the backbone peers that
may have an ND cache pointing on this 6BBR in case the Registered
Address shows back up on this or a different 6BBR at a later time.
In STALE state:
o If the Registered Address is claimed by another node on the
backbone, with an NS-DAD or an NA, the 6BBR does not defend the
address. Upon an NA(O), or the stale time elapses, the 6BBR
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removes its entry and sends a NA(AERO) with a status of 4
(removed) to the Registering Node.
o If the 6BBR received a NS(LOOKUP) for a Registered Address, the
6BBR MUST send an NS(NUD) following rules in [RFC7048] to the
Registering Node targeting the Registered Address prior to
answering. If the NUD succeeds, the operation in REACHABLE state
applies. If the NUD fails, the 6BBR refrains from answering the
lookup. The NUD expected to be mapped by the Registering Node
into a liveliness validation of the Registered Node if they are in
fact different nodes.
7. Security Considerations
This specification expects that the link layer is sufficiently
protected, either by means of physical or IP security for the
Backbone Link or MAC sublayer cryptography. In particular, it is
expected that the LLN MAC provides secure unicast to/from the
Backbone Router and secure Broadcast from the Backbone Router in a
way that prevents tempering with or replaying the RA messages.
The use of EUI-64 for forming the Interface ID in the link local
address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
address privacy techniques. This specification RECOMMENDS the use of
additional protection against address theft such as provided by
[I-D.ietf-6lo-ap-nd], which guarantees the ownership of the OUID.
When the ownership of the OUID cannot be assessed, this specification
limits the cases where the OUID and the TID are multicasted, and
obfuscates them in responses to attempts to take over an address.
8. Protocol Constants
This Specification uses the following constants:
TENTATIVE_DURATION: 800 milliseconds
STABLE_STALE_DURATION: 24 hours
UNSTABLE_STALE_DURATION: 5 minutes
DEFAULT_NS_POLLING: 3 times
9. IANA Considerations
This document has no request to IANA.
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10. Acknowledgments
Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure at Cisco.
11. References
11.1. Normative References
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "An Update to 6LoWPAN ND", draft-ietf-6lo-
rfc6775-update-13 (work in progress), February 2018.
[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,
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>.
[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>.
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[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>.
[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>.
11.2. Informative References
[I-D.chakrabarti-nordmark-6man-efficient-nd]
Chakrabarti, S., Nordmark, E., Thubert, P., and M.
Wasserman, "IPv6 Neighbor Discovery Optimizations for
Wired and Wireless Networks", draft-chakrabarti-nordmark-
6man-efficient-nd-07 (work in progress), February 2015.
[I-D.delcarpio-6lo-wlanah]
Vega, L., Robles, I., and R. Morabito, "IPv6 over
802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
progress), October 2015.
[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-06 (work in progress),
February 2018.
[I-D.ietf-6lo-nfc]
Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
"Transmission of IPv6 Packets over Near Field
Communication", draft-ietf-6lo-nfc-09 (work in progress),
January 2018.
[I-D.ietf-6man-rs-refresh]
Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6
Neighbor Discovery Optional RS/RA Refresh", draft-ietf-
6man-rs-refresh-02 (work in progress), October 2016.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work
in progress), November 2017.
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[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-09 (work in
progress), June 2017.
[I-D.ietf-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-ietf-bier-architecture-08 (work in
progress), September 2017.
[I-D.ietf-ipv6-multilink-subnets]
Thaler, D. and C. Huitema, "Multi-link Subnet Support in
IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
progress), July 2002.
[I-D.nordmark-6man-dad-approaches]
Nordmark, E., "Possible approaches to make DAD more robust
and/or efficient", draft-nordmark-6man-dad-approaches-02
(work in progress), October 2015.
[I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks]
Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets
over IEEE 1901.2 Narrowband Powerline Communication
Networks", draft-popa-6lo-6loplc-ipv6-over-
ieee19012-networks-00 (work in progress), March 2014.
[I-D.vyncke-6man-mcast-not-efficient]
Vyncke, E., Thubert, P., Levy-Abegnoli, E., and A.
Yourtchenko, "Why Network-Layer Multicast is Not Always
Efficient At Datalink Layer", draft-vyncke-6man-mcast-not-
efficient-01 (work in progress), February 2014.
[I-D.yourtchenko-6man-dad-issues]
Yourtchenko, A. and E. Nordmark, "A survey of issues
related to IPv6 Duplicate Address Detection", draft-
yourtchenko-6man-dad-issues-01 (work in progress), March
2015.
[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>.
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[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[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>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
[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>.
[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>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[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>.
[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>.
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[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[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>.
[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015,
<https://www.rfc-editor.org/info/rfc7428>.
[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>.
[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>.
[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>.
[RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
M., and D. Barthel, "Transmission of IPv6 Packets over
Digital Enhanced Cordless Telecommunications (DECT) Ultra
Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
2017, <https://www.rfc-editor.org/info/rfc8105>.
[RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S.
Donaldson, "Transmission of IPv6 over Master-Slave/Token-
Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
May 2017, <https://www.rfc-editor.org/info/rfc8163>.
11.3. External Informative References
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[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. Requirements
This section lists requirements that were discussed at 6lo for an
update to 6LoWPAN ND. This specification meets most of them, but
those listed in Appendix A.5 which are deferred to a different
specification such as [I-D.ietf-6lo-ap-nd].
A.1. Requirements Related to Mobility
Due to the unstable nature of LLN links, even in a LLN of immobile
nodes a 6LoWPAN Node may change its point of attachment to a 6LR, say
6LR-a, and may not be able to notify 6LR-a. Consequently, 6LR-a may
still attract traffic that it cannot deliver any more. When links to
a 6LR change state, there is thus a need to identify stale states in
a 6LR and restore reachability in a timely fashion.
Req1.1: Upon a change of point of attachment, connectivity via a new
6LR MUST be restored timely without the need to de-register from the
previous 6LR.
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Req1.2: For that purpose, the protocol MUST enable to differentiate
between multiple registrations from one 6LoWPAN Node and
registrations from different 6LoWPAN Nodes claiming the same address.
Req1.3: Stale states MUST be cleaned up in 6LRs.
Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address
to multiple 6LRs, and this, concurrently.
A.2. Requirements Related to Routing Protocols
The point of attachment of a 6LoWPAN Node may be a 6LR in an LLN
mesh. IPv6 routing in a LLN can be based on RPL, which is the
routing protocol that was defined at the IETF for this particular
purpose. Other routing protocols than RPL are also considered by
Standard Defining Organizations (SDO) on the basis of the expected
network characteristics. It is required that a 6LoWPAN Node attached
via ND to a 6LR would need to participate in the selected routing
protocol to obtain reachability via the 6LR.
Next to the 6LBR unicast address registered by ND, other addresses
including multicast addresses are needed as well. For example a
routing protocol often uses a multicast address to register changes
to established paths. ND needs to register such a multicast address
to enable routing concurrently with discovery.
Multicast is needed for groups. Groups MAY be formed by device type
(e.g. routers, street lamps), location (Geography, RPL sub-tree), or
both.
The Bit Index Explicit Replication (BIER) Architecture
[I-D.ietf-bier-architecture] proposes an optimized technique to
enable multicast in a LLN with a very limited requirement for routing
state in the nodes.
Related requirements are:
Req2.1: The ND registration method SHOULD be extended in such a
fashion that the 6LR MAY advertise the Address of a 6LoWPAN Node over
the selected routing protocol and obtain reachability to that Address
using the selected routing protocol.
Req2.2: Considering RPL, the Address Registration Option that is used
in the ND registration SHOULD be extended to carry enough information
to generate a DAO message as specified in [RFC6550] section 6.4, in
particular the capability to compute a Path Sequence and, as an
option, a RPLInstanceID.
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Req2.3: Multicast operations SHOULD be supported and optimized, for
instance using BIER or MPL. Whether ND is appropriate for the
registration to the 6BBR is to be defined, considering the additional
burden of supporting the Multicast Listener Discovery Version 2
[RFC3810] (MLDv2) for IPv6.
A.3. Requirements Related to the Variety of Low-Power Link types
6LoWPAN ND [RFC6775] was defined with a focus on IEEE std. 802.15.4
and in particular the capability to derive a unique Identifier from a
globally unique MAC-64 address. At this point, the 6lo Working Group
is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique
to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token-
Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field
Communication [I-D.ietf-6lo-nfc], IEEE std. 802.11ah
[I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband
Powerline Communication Networks
[I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R)
Low Energy [RFC7668].
Related requirements are:
Req3.1: The support of the registration mechanism SHOULD be extended
to more LLN links than IEEE 802.15.4, matching at least the LLN links
for which an "IPv6 over foo" specification exists, as well as Low-
Power Wi-Fi.
Req3.2: As part of this extension, a mechanism to compute a unique
Identifier should be provided, with the capability to form a Link-
Local Address that SHOULD be unique at least within the LLN connected
to a 6LBR discovered by ND in each node within the LLN.
Req3.3: The Address Registration Option used in the ND registration
SHOULD be extended to carry the relevant forms of unique Identifier.
Req3.4: The Neighbour Discovery should specify the formation of a
site-local address that follows the security recommendations from
[RFC7217].
A.4. Requirements Related to Proxy Operations
Duty-cycled devices may not be able to answer themselves to a lookup
from a node that uses classical ND on a backbone and may need a
proxy. Additionally, the duty-cycled device may need to rely on the
6LBR to perform registration to the 6BBR.
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The ND registration method SHOULD defend the addresses of duty-cycled
devices that are sleeping most of the time and not capable to defend
their own Addresses.
Related requirements are:
Req4.1: The registration mechanism SHOULD enable a third party to
proxy register an Address on behalf of a 6LoWPAN node that may be
sleeping or located deeper in an LLN mesh.
Req4.2: The registration mechanism SHOULD be applicable to a duty-
cycled device regardless of the link type, and enable a 6BBR to
operate as a proxy to defend the registered Addresses on its behalf.
Req4.3: The registration mechanism SHOULD enable long sleep
durations, in the order of multiple days to a month.
A.5. Requirements Related to Security
In order to guarantee the operations of the 6LoWPAN ND flows, the
spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a
node successfully registers an address, 6LoWPAN ND should provide
energy-efficient means for the 6LBR to protect that ownership even
when the node that registered the address is sleeping.
In particular, the 6LR and the 6LBR then should be able to verify
whether a subsequent registration for a given Address comes from the
original node.
In a LLN it makes sense to base security on layer-2 security. During
bootstrap of the LLN, nodes join the network after authorization by a
Joining Assistant (JA) or a Commissioning Tool (CT). After joining
nodes communicate with each other via secured links. The keys for
the layer-2 security are distributed by the JA/CT. The JA/CT can be
part of the LLN or be outside the LLN. In both cases it is needed
that packets are routed between JA/CT and the joining node.
Related requirements are:
Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR, 6LBR and 6BBR to authenticate and authorize one another for
their respective roles, as well as with the 6LoWPAN Node for the role
of 6LR.
Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR and the 6LBR to validate new registration of authorized
nodes. Joining of unauthorized nodes MUST be impossible.
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Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet
sizes. In particular, the NS, NA, DAR and DAC messages for a re-
registration flow SHOULD NOT exceed 80 octets so as to fit in a
secured IEEE std. 802.15.4 frame.
Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be
computationally intensive on the LoWPAN Node CPU. When a Key hash
calculation is employed, a mechanism lighter than SHA-1 SHOULD be
preferred.
Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate
SHOULD be minimized.
Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable CCM* for use
at both Layer 2 and Layer 3, and SHOULD enable the reuse of security
code that has to be present on the device for upper layer security
such as TLS.
Req5.7: Public key and signature sizes SHOULD be minimized while
maintaining adequate confidentiality and data origin authentication
for multiple types of applications with various degrees of
criticality.
Req5.8: Routing of packets should continue when links pass from the
unsecured to the secured state.
Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR and the 6LBR to validate whether a new registration for a
given address corresponds to the same 6LoWPAN Node that registered it
initially, and, if not, determine the rightful owner, and deny or
clean-up the registration that is duplicate.
A.6. Requirements Related to Scalability
Use cases from Automatic Meter Reading (AMR, collection tree
operations) and Advanced Metering Infrastructure (AMI, bi-directional
communication to the meters) indicate the needs for a large number of
LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected
to the 6LBR over a large number of LLN hops (e.g. 15).
Related requirements are:
Req6.1: The registration mechanism SHOULD enable a single 6LBR to
register multiple thousands of devices.
Req6.2: The timing of the registration operation should allow for a
large latency such as found in LLNs with ten and more hops.
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Author's Address
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
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