6lo P. Thubert, Ed.
Internet-Draft cisco
Intended status: Standards Track January 5, 2016
Expires: July 8, 2016
IPv6 Backbone Router
draft-ietf-6lo-backbone-router-00
Abstract
This specification proposes an update to IPv6 Neighbor Discovery, to
enhance the operation of IPv6 over wireless links that exhibit lossy
multicast support, and enable a large degree of scalability by
splitting the broadcast domains. A higher speed backbone federates
multiple wireless links to form a large MultiLink Subnet. Backbone
Routers acting as Layer-3 Access Point route packets to registered
nodes, where an classical Layer-2 Access Point would bridge.
Conversely, wireless nodes register to the Backbone Router to setup
routing 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-
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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 July 8, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability and Requirements Served . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. New Types And Formats . . . . . . . . . . . . . . . . . . . . 10
5.1. Transaction ID . . . . . . . . . . . . . . . . . . . . . 10
5.2. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 11
5.3. The Enhanced Address Registration Option (EARO) . . . . . 11
6. Backbone Router Routing Operations . . . . . . . . . . . . . 14
6.1. Over the Backbone Link . . . . . . . . . . . . . . . . . 14
6.2. Over the LLN Link . . . . . . . . . . . . . . . . . . . . 15
7. BackBone Router Proxy Operations . . . . . . . . . . . . . . 17
7.1. Registration and Binding State Creation . . . . . . . . . 19
7.2. Defending Addresses . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . 24
12.3. External Informative References . . . . . . . . . . . . 28
Appendix A. Requirements . . . . . . . . . . . . . . . . . . . . 28
A.1. Requirements Related to Mobility . . . . . . . . . . . . 28
A.2. Requirements Related to Routing Protocols . . . . . . . . 29
A.3. Requirements Related to the Variety of Low-Power Link
types . . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.4. Requirements Related to Proxy Operations . . . . . . . . 31
A.5. Requirements Related to Security . . . . . . . . . . . . 31
A.6. Requirements Related to Scalability . . . . . . . . . . . 32
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
Though in most cases, including Low-Power ones, IEEE802.11
[IEEE80211] is operated as a wireless extension to an Ethernet
bridged domain, the impact of radio broadcasts for IPv6 [RFC2460]
multicast operations, in particular related to the power consumption
of battery-operated devices, lead the community to rethink the plain
layer-2 approach and consider splitting the broadcast domain between
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the wired and the wireless access links. To that effect, the current
IEEE802.11 specifications require the capability to perform ARP and
ND proxy [RFC4389] functions at the Access Points (APs), but rely on
snooping for acquiring the related state, which is unsatisfactory in
a lossy and mobile environments.
Without a proxy, any IP multicast that circulates in the bridged
domain ends up broadcasted by the Access Points to all STAs,
including Low-Power battery-operated ones. With an incorrect or
missing state in the proxy, a packet may not be delivered to the
destination, which may have operational impacts depending on the
criticality of the packet.
Some messages are lost for the lack of retries, regardless of their
degree of criticality; it results for instance that Duplicate Address
Detection (DAD) as defined in [RFC4862] is mostly broken over Wi-Fi
[I-D.yourtchenko-6man-dad-issues].
On the other hand, IPv6 multicast messages are processed by most if
not all wireless nodes over the 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) 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].
It appears that in a variety of Wireless Local Area Networks (WLANs)
and Wireless Personal Area Networks (WPANs), the decision to leverage
the broadcast support of a particular link should be left to Layer-3
based on the criticality of the message and the number of interested
listeners on that link, for the lack of capability to indicate that
criticality to the lower layer. To achieve this, the operation at
the Access Point cannot be a Layer-2 bridge operation, but that of a
Layer-3 router; the concept of MultiLink Subnet (MLSN) must be
reintroduced, with IPv6 backbone routers (6BBRs) interconnecting the
various links and routing within the subnet. For link-scope
multicast operations, a 6BBR participates to MLD on its access links
and a multicast routing protocol is setup between the 6BBRs over the
backbone of the MLSN.
As the network scales up, none of the approaches of using either
broadcast or N*unicast for a multicast packet is really satisfying
and the protocols themselves need to be adapted to reduce their use
of multicast.
One degree of improvement can be achieved by changing the tuning of
the protocol parameters and operational practices, such as suggested
in Reducing energy consumption of Router Advertisements
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[I-D.ietf-v6ops-reducing-ra-energy-consumption] (RA). This works
enables to lower the rate of RA messages but does not solve the
problem associated with multicast NS and NA messages, which are a lot
more frequent in large-scale radio environments with mobile devices
which exhibit intermittent access patterns and short-lived IPv6
addresses.
In the context of IEEE802.15.4 [IEEE802154], the more drastic step of
considering the radio as a medium that is different from Ethernet
because of the impact of multicast, was already taken with the
adoption of Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs) [RFC6775]. This
specification applies that same thinking to other wireless links such
as Low-Power IEEE802.11 (Wi-Fi) and IEEE802.15.1 (Bluetooth)
[IEEE802151], 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].
DHCPv6 [RFC3315] is still a viable option in Low power and Lossy
Network (LLN) to assign IPv6 global addresses. However, the IETF
standard that supports address assignment specifically for LLNs is
6LoWPAN ND [RFC6775], which is a mix of IPv6 stateless
autoconfiguration mechanism (SLAAC) [RFC4862] and a new registration
process for ND. This specification introduces a Layer-3 association
process based on 6LoWPAN ND that maintains a proxy state in the 6BBR
to keep the LLN nodes reachable and protect their addresses through
sleeping periods.
A number of use cases, including the Industrial Internet, require a
large scale deployment of monitoring sensors that can only be
realized in a cost-effective fashion with wireless technologies.
Mesh networks are deployed when simpler hub-and-spoke topologies are
not sufficient for the expected size, throughput, and density.
Meshes imply the routing of packets, operated at either Layer-2 or
Layer-3. For routing over a mesh at Layer-3, the IETF has designed
the IPv6 Routing Protocol over LLN (RPL) [RFC6550]. 6LoWPAN ND was
designed as a stand-alone mechanism separately from RPL, and the
interaction between the 2 protocols was not defined. This
specification details how periodic updates from RPL can be used by
the RPL root to renew the association of the RPL node to the 6BBR on
its behalf so as to maintain the proxy operation active for that
node.
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This document suggests a limited evolution to [RFC6775] so as to
allow operation of a 6LoWPAN ND node while a routing protocol (in
first instance RPL) is present and operational. It also suggests a
more generalized use of the information in the ARO option of the ND
messages outside the strict LLN domain, for instance over a converged
backbone.
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 IEEE802.15.4
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, IEEE802.11AH and
IEEE802.15.4 wireless meshes, so as to address the requirements
listed in Appendix A.3
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
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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
[IEEE802154], 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 IEEE802.11, 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
BTLE, the 6BBR is collocated with the router that implements the BTLE
central role as discussed in section 2.2 of [I-D.ietf-6lo-btle].
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
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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
[I-D.ietf-roll-terminology] and [I-D.ietf-6tisch-terminology], and
introduces the following terminology:
LLN Low Power Lossy Network. Used loosely in this specification to
represent WLANs and WPANs. See [RFC4919]
Backbone This is an IPv6 transit link that interconnects 2 or more
Backbone Routers. It is expected to be deployed as a high
speed backbone in order to federate a potentially large set of
LLNS. Also referred to as a LLN backbone or Backbone network.
Backbone Router An IPv6 router that federates the LLN using a
Backbone link as a backbone. A BBR acts as a 6LoWPAN Border
Routers (6LBR) and an Energy Aware Default Router (NEAR).
Extended LLN This is the aggregation of multiple LLNs as defined in
[RFC4919], interconnected by a Backbone Link via Backbone
Routers, and forming a single IPv6 MultiLink Subnet.
Registration The process during which a wireless Node registers its
address(es) with the Border Router so the 6BBR can proxy ND for
it over the backbone.
Binding The state in the 6BBR that associates an IP address with a
MAC address, a port and some other information about the node
that owns the IP address.
Registered Node The node for which the registration is performed,
which owns the fields in the EARO option.
Registering Node The node that performs the registration to the
6BBR, either for one of its own addresses, in which case it is
Registered Node and indicates its own MAC Address as SLLA in
the NS(ARO), or on behalf of a Registered Node that is
reachable over a LLN mesh. In the latter case, if the
Registered Node is reachable from the 6BBR over a Mesh-Under
mesh, the Registering Node indicates the MAC Address of the
Registered Node as SLLA in the NS(ARO). Otherwise, it is
expected that the Registered Device is reachable over a Route-
Over mesh from the Registering Node, in which case the SLLA in
the NS(ARO) is that of the Registering Node, which causes it to
attract the packets from the 6BBR to the Registered Node and
route them over the LLN.
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Registered Address The address owned by the Registered Node node
that is being registered.
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
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.
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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.
|
+-----+
| | 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 Address Registration Option (ARO) defined in [RFC6775] is
extended to enable the registration for routing and proxy Neighbor
Discovery operations by the 6BBR, and the Extended ARO (EARO) 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
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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) is introduced
that enables 6BBRs to sort out the latest anchor for that node.
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.
With this specification, Backbone Routers perform ND proxy over the
Backbone Link on behalf of their Registered Nodes. 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. New Types And Formats
5.1. Transaction ID
The specification expects that the Registered Node can provide a
sequence number called Transaction ID (TID) that is incremented with
each re-registration. The TID essentially obeys the same rules as
the Path Sequence field in the Transit Information Option (TIO) found
in RPL's Destination Advertisement Object (DAO). This way, the LLN
node can use the same counter for ND and RPL, and a 6LBR acting as
RPL root may easily maintain the registration on behalf of a RPL node
deep inside the mesh by simply using the RPL TIO Path Sequence as TID
for EARO.
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When a Registered Node is registered to multiple BBRs in parallel, it
is expected that the same TID is used, to enable the 6BBRs to
correlate the registrations as being a single one, and differentiate
that situation from a movement.
If the TIDs are different, the resolution inherited from RPL sorts
out the most recent registration and other ones are removed. The
operation for computing and comparing the Path Sequence is detailed
in section 7 of [RFC6550] and applies to the TID in the exact same
fashion.
5.2. Owner Unique ID
The Owner Unique ID (OUID) enables to differentiate a real duplicate
address registration from a double registration or a movement. An ND
message from the 6BBR over the backbone that is proxied on behalf of
a Registered Node must carry the most recent EARO option seen for
that node. A NS/NA with an EARO and a NS/NA without a EARO thus
represent different nodes and if they relate to a same target then
they reflect an address duplication. The Owner Unique ID can be as
simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are
avoided.
Alternatively, the unique ID can be a cryptographic string that can
can be used to prove the ownership of the registration as discussed
in Address Protected Neighbor Discovery for Low-power and Lossy
Networks [I-D.sarikaya-6lo-ap-nd].
In any fashion, it is recommended that the node stores the unique Id
or the keys used to generate that ID in persistent memory.
Otherwise, it will be prevented to re-register after a reboot that
would cause a loss of memory until the Backbone Router times out the
registration.
5.3. The Enhanced Address Registration Option (EARO)
With the ARO option defined in 6LoWPAN ND [RFC6775], the address
being registered and its owner can be uniquely identified and matched
with the Binding Table entries of each Backbone Router.
The Enhanced Address Registration Option (EARO) is intended to be
used as a replacement to the ARO option within Neighbor Discovery NS
and NA messages between a LLN node and its 6LoWPAN Router (6LR), as
well as in Duplicate Address Request (DAR) and the Duplicate Address
Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes
such as 6TiSCH networks.
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An NS message with an EARO option is a registration if and only if it
also carries an SLLAO option. The AERO option also used in NS and NA
messages between Backbone Routers over the backbone link to sort out
the distributed registration state, and in that case, it does not
carry the SLLAO option and is not confused with a registration.
The EARO extends the ARO and is recognized by the setting of the TID
bit. A node that supports this specification MUST always use an EARO
as a replacement to an ARO in its registration to a router. This is
harmless since the TID bit and fields are reserved in [RFC6775] are
ignored by a legacy router. A router that supports this
specification answers to an ARO with an ARO and to an EARO with an
EARO.
This specification changes the behavior of the peers in a
registration flows. To enable backward compatibility, a node that
registers to a router that is not known to support this specification
MUST behave as prescribed by [RFC6775]. Once the router is known to
support this specification, the node MUST obey this specification.
When using the EARO option, the address being registered is found in
the Target Address field of the NS and NA messages. This differs
from 6LoWPAN ND [RFC6775] which specifies that the address being
registered is the source of the NS.
The reason for this change is to enable proxy-registrations on behalf
of other nodes in Route-Over meshes, for instance to enable that a
RPL root registers addresses on behalf LLN nodes that are deeper in a
6TiSCH mesh. In that case, the Registering Node MUST indicate its
own address as source of the ND message and its MAC address in the
Source Link-Layer Address Option (SLLAO), since it still expects to
get the packets and route them down the mesh. But the Registered
Address belongs to another node, the Registered Node, and that
address is indicated in the Target Address field of the NS message.
One way of achieving all the above is for a node to first register an
address that it owns in order to validate that the router supports
this specification, placing the same address in the Source and Target
Address fields of the NS message. The node may for instance register
an address that is based on EUI-64. For such address, DAD is not
required and using the SLLAO option in the NS is actually more
amenable with older ND specifications such as ODAD [RFC4429].
Once that first registration is complete, the node knows from the
setting of the TID in the response whether the router supports this
specification. If this is verified, the node may register other
addresses that it owns, or proxy-register addresses on behalf some
another node, indicating those addresses being registered in the
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Target Address field of the NS messages, while using one of its own,
already registered, addresses as source.
The format of the EARO option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length = 2 | Status | pref level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: EARO
Option Fields
Type:
Length: 2
Status: OK=0; Duplicate=1; Full=2; Moved=3; Removed=4;
Reserved: This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
T: One bit flag. Set if the next octet is a used as a TID.
TID: 1-byte integer; a transaction id that is maintained by the node
and incremented with each transaction. it is recommended that the
node maintains the TID in a persistent storage.
Registration Lifetime: 1-byte integer; expressed in minutes. 0
means that the registration has ended and the state should be
removed.
Owner Unique Identifier: A globally unique identifier for the node
associated. This can be the EUI-64 derived IID of an interface,
or some provable ID obtained cryptographically.
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6. Backbone Router Routing Operations
|
+-----+
| | 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 3: Routing Configuration in the ML Subnet
6.1. 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
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backbone for the prefixes that are present on that backbone and that
it proxies for on the LLN interfaces.
As a proxy, the 6BBR uses an EARO option in the NS-DAD and the
multicast NA messages that it generates 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.
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.nordmark-6man-rs-refresh] is
recommended, and this implies the support of [RFC7559] as well.
6.2. 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
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generally required for LLN nodes to accept multicast RAs
[I-D.ietf-v6ops-reducing-ra-energy-consumption], but those are rare
on the LLN link. Nodes are expected to follow the 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.
The Backbone Router acquires its states about the addresses on the
LLN side through a registration process from either the nodes
themselves, or from a node such as a RPL root / 6LBR (the Registering
Node) that performs the registration on behalf of the address owner
(the Registered Node).
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.
7. 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 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).
7.1. Registration and Binding State Creation
Upon a registration for a new address with an NS(EARO), the 6BBR
performs a DAD operation over the backbone placing the new address as
target in the NS-DAD message. The EARO from the registration MUST be
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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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7.2. 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 concept, 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 6.1, 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.
8. 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.sarikaya-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.
9. 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
10. IANA Considerations
This document requires the following additions:
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Address Registration Option Status Values Registry
+--------+----------------------------------------------------------+
| Status | Description |
+--------+----------------------------------------------------------+
| 3 | Moved: The registration fails because it is not the |
| | freshest. |
| | |
| 4 | Removed: The binding state was removed |
+--------+----------------------------------------------------------+
IANA is required to change the registry accordingly
Table 1: New ARO Status values
11. Acknowledgments
Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure at Cisco.
12. References
12.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<http://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,
<http://www.rfc-editor.org/info/rfc4861>.
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc6550>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<http://www.rfc-editor.org/info/rfc6775>.
12.2. 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-6lobac]
Lynn, K., Martocci, J., Neilson, C., and S. Donaldson,
"Transmission of IPv6 over MS/TP Networks", draft-ietf-
6lo-6lobac-03 (work in progress), October 2015.
[I-D.ietf-6lo-btle]
Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", draft-ietf-6lo-btle-17 (work in progress), August
2015.
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[I-D.ietf-6lo-dect-ule]
Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D.
Barthel, "Transmission of IPv6 Packets over DECT Ultra Low
Energy", draft-ietf-6lo-dect-ule-03 (work in progress),
September 2015.
[I-D.ietf-6lo-nfc]
Youn, J. and Y. Hong, "Transmission of IPv6 Packets over
Near Field Communication", draft-ietf-6lo-nfc-02 (work in
progress), October 2015.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-09 (work
in progress), November 2015.
[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-06 (work in
progress), November 2015.
[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-02 (work in
progress), July 2015.
[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.ietf-roll-terminology]
Vasseur, J., "Terms used in Routing for Low power And
Lossy Networks", draft-ietf-roll-terminology-13 (work in
progress), October 2013.
[I-D.ietf-v6ops-reducing-ra-energy-consumption]
Yourtchenko, A. and L. Colitti, "Reducing energy
consumption of Router Advertisements", draft-ietf-v6ops-
reducing-ra-energy-consumption-03 (work in progress),
November 2015.
[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.
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[I-D.nordmark-6man-rs-refresh]
Nordmark, E., Yourtchenko, A., and S. Krishnan, "IPv6
Neighbor Discovery Optional Unicast RS/RA Refresh", draft-
nordmark-6man-rs-refresh-01 (work in progress), October
2014.
[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.sarikaya-6lo-ap-nd]
Sarikaya, B. and P. Thubert, "Address Protected Neighbor
Discovery for Low-power and Lossy Networks", draft-
sarikaya-6lo-ap-nd-01 (work in progress), October 2015.
[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.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<http://www.rfc-editor.org/info/rfc3810>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<http://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<http://www.rfc-editor.org/info/rfc3972>.
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[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <http://www.rfc-editor.org/info/rfc4389>.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
DOI 10.17487/RFC4903, June 2007,
<http://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,
<http://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,
<http://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, <http://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,
<http://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,
<http://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,
<http://www.rfc-editor.org/info/rfc7048>.
[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,
<http://www.rfc-editor.org/info/rfc7217>.
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[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015,
<http://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,
<http://www.rfc-editor.org/info/rfc7559>.
12.3. External Informative References
[IEEE80211]
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".
[IEEE802151]
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)".
[IEEE802154]
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.sarikaya-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
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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.
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.
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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.
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 IEEE802.15.4 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 [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy
[I-D.ietf-6lo-dect-ule], Near Field Communication [I-D.ietf-6lo-nfc],
IEEE802.11ah [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 [I-D.ietf-6lo-btle].
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].
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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.
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
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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.
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 IEEE802.15.4 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:
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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.
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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