wdiff draft-ietf-6lo-rfc6775-update-07.txt draft-ietf-6lo-rfc6775-update-08.txt

6lo P. Thubert, Ed.
Internet-Draft cisco
Updates: 6775 (if approved) E. Nordmark
Intended status: Standards Track
Expires: January 29, March 24, 2018 S. Chakrabarti
July 28,
September 20, 2017

An Update to 6LoWPAN ND
draft-ietf-6lo-rfc6775-update-07
draft-ietf-6lo-rfc6775-update-08

Abstract

This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to
clarify the role of the protocol as a registration technique,
simplify the registration operation in 6LoWPAN routers, as well as to
provide enhancements to the registration capabilities and mobility
detection for different network topologies including the backbone
routers performing proxy Neighbor Discovery in a low power network.

Status of This Memo

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability of Address Registration Options . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Extended Address Registration Option (EARO . . . . . . . . . . 6 7
4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6 7
4.2.1. Comparing TID values . . . . . . . . . . . . . . . . 7 8
4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 8 9
4.4. Extended Duplicate Address Messages . . . . . . . . . . . 10
4.5. Registering the Target Address . . . . . . . . . . . . . 9
4.5. 10
4.6. Link-Local Addresses and Registration . . . . . . . . . . 9
4.6. 11
4.7. Maintaining the Registration States . . . . . . . . . . . 11 13
5. Detecting Enhanced ARO Capability Support . . . . . . . . . . 12 14
6. Updated Extended ND Options And Messages . . . . . . . . . . . . . . 15
6.1. Enhanced Address Registration Option (EARO) . . . . . . . 13
6.1. The Enhanced 15
6.2. Extended Duplicate Address Registration Option (EARO) Message Formats . . . . . 13
6.2. . . 18
6.3. New 6LoWPAN capability Capability Bits in the Capability Indication
Option . . . . . . . . . . . . . . . . . . . . . . . . . 15 19
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 16 19
7.1. Discovering the capabilities of an ND peer . . . . . . . 16 19
7.1.1. Using the E Flag in the CIO . . . . 6CIO Option . . . . . . . . . 16 19
7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 17 20
7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 17 21
7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 17 21
7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 18 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 22
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 24
10.1. ARO Flags . . . . . . . . . . . . . . . . . . . . . . . 24
10.2. ICMP Codes . . . . . . . . . . . . . . . . . . . . . . . 24
10.3. New ARO Status values . . . . . . . . . . . . . . . . . 25
10.4. New 6LoWPAN capability Bits . . . . . . . . . . . . . . 26
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 26
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 26
12.1. Normative References . . . . . . . . . . . . . . . . . . 22 26
12.2. Informative References . . . . . . . . . . . . . . . . . 23 27
12.3. External Informative References . . . . . . . . . . . . 26 30
Appendix A. Applicability and Requirements Served . . . . . . . 26 30
Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 27 31
B.1. Requirements Related to Mobility . . . . . . . . . . . . 27 32
B.2. Requirements Related to Routing Protocols . . . . . . . . 27 32
B.3. Requirements Related to the Variety of Low-Power Link
types . . . . . . . . . . . . . . . . . . . . . . . . . . 28 33
B.4. Requirements Related to Proxy Operations . . . . . . . . 29 34
B.5. Requirements Related to Security . . . . . . . . . . . . 29 34
B.6. Requirements Related to Scalability . . . . . . . . . . . 31 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 36

1. Introduction

The scope of this draft is an IPv6 Low Power Networks including star
and mesh topologies. This specification modifies and extends the
behavior and protocol elements of RFC 6775 "Neighbor Discovery Optimization
for IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)" Networks" (6LoWPAN ND)
[RFC6775] to enable additional capabilities such as:

o Support the indication of for indicating mobility vs retry (T-bit)

o Ease up requirement of registration for link-local addresses

* Introducing

o Enhancement to Address Registration Option (ARO)

o Permitting regitration registration of target address

o Clarification of support of privacy and temporary addresses

The following sections will discuss applicability of 6LoWPAN ND
registration, registration is discussed in
Section 2, and new extensions and updates to RFC 6775. Finally, we
will discuss how the extensions of registration framework can be
useful for a scenario such as Backbone router(6BBR) proxy ND
operations. 6775 are presented
in Section 4. Considerations on Backward Compatibility, Security and
Privacy are also elaborated upon in Section 7, Section 8 and in
Section 9, respectively.

2. Applicability of Address Registration Options

The original purpose of the Address Registration Option (ARO) [RFC6775] and of
the Extended ARO (EARO) that is introduced in this document the
original 6LoWPAN ND specification is to facilitate duplicate address
detection (DAD) for hosts and pre- as well as populate Neighbor Cache Entries
(NCE) [RFC4861] in the routers to
reduce routers. This reduces the need for sending 'multicast neighbor solicitations' which
may be harmful in low power constrained nodes networks where reliance on
multicast is most operations, which are often treated as broadcasts.

In some cases the address intrusive as broadcast, in
IPv6 ND operations.

With this specification, a registration can fail or becomes become useless
for reasons other than a duplicate address. address duplication. Examples are include: the
router having run out of space, space; a registration bearing a stale
sequence number (e.g. perhaps denoting a movement of the host after this the
registration was placed), placed; a host misbehaving and attempting to
register an invalid address such as the unspecified address [RFC4291],
[RFC4291]; or the a host using an address which is not topologically
correct on that link.

In such cases the host will receive an error to help diagnose the
issue and may retry, possibly with a different address, and possibly
registering to a different 6LR, router, depending on the returned error.
However, the ability to return errors to address registrations MUST
NOT is not
intended to be used to restrict the ability of hosts to form and use
addresses
addresses, as recommended in "Host Address Availability
Recommendations" [RFC7934].

In particular, this the freedom to form and register addresses is needed
for enhanced privacy, which implies that privacy; each host will may register a multiplicity of
address as part using mechanisms like such as "Privacy Extensions for Stateless
Address Autoconfiguration (SLAAC) in IPv6" [RFC4941].
This implies that

In the capabilities of 6LR and 6LBRs in terms classical IPv6 ND [RFC4861], a router must have enough storage
to hold neighbor cache entries for all the addresses to which it may
forward. A router using the Address Registration mechanism needs
enough storage to hold NCEs for all the addresses that may be
registered to it, regardless of whether or not they are actively
communicating. For this reason, the number of registrations
supported by a 6LoWPAN Router (6LR) or 6LoWPAN Border Router (6LBR)
must be clearly announced in the router
documentation, and that a documented.

A network administrator should deploy adapted 6LR/6LBRs to support
the number and type of devices in his network, based on the number of
IPv6 addresses that those devices require. require and their renewal rate and
behaviour.

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 RFC 2119 [RFC2119].

Readers are expected to be familiar with all the terms and concepts
that are discussed in

o "Neighbor Discovery for IP version 6" [RFC4861],

o "IPv6 Stateless Address Autoconfiguration" [RFC4862],

o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],

o "Neighbor Discovery Optimization for Low-power and Lossy Networks"
[RFC6775] and

o "Multi-link Subnet Support in IPv6"
[I-D.ietf-ipv6-multilink-subnets].
[I-D.ietf-ipv6-multilink-subnets],

as well as this additional the following terminology:

Backbone This is an Link An IPv6 transit link that interconnects 2 two or more
Backbone Routers. It is expected to be deployed as of a relatively high
speed Backbone compared to the LLN in order to support the trafic that
is required to federate a multiple segments of the potentially
large set of
LLNS. LLN into a single IPv6 subnet. Also referred to as a to
as a Backbone, a LLN Backbone, and a Backbone or Backbone network. Network.

Backbone Router An A logical network function in an IPv6 router that
federates the a LLN using over a Backbone link as a Backbone. A Link. In order to do so, the
Backbone Router (6BBR) proxies the 6LoWPAN ND operations
detailed in the document onto the matching operations that run
over the backbone, typically classical IPv6 ND. Note that 6BBR acts as
is a 6LoWPAN Border
Routers (6LBR) logical function, just like 6LR and an Energy Aware Default Router (NEAR). 6LBR, and that a same
physical router may operate all three.

Extended LLN This is the The aggregation of multiple LLNs as defined in RFC 4919
[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 serve as
proxy ND for
it ND operations over the Backbone.

Binding The state in the 6BBR that associates association between an IP address with a MAC address, a
port and some and/or other information about the node that owns the IP
address.

Registered Node The node for which the registration is performed,
and 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 may proxy for the registered node.

Registered Node and indicates its own MAC Address as Source
Link Layer Address (SLLA) in An address owned by the NS(EARO), or on behalf of a Registered Node node that
was or is reachable over a LLN mesh. being registered.

legacy and original vs. updated 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 context of this
specification, the Registered Node as SLLA in the NS(EARO).
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 terms "legacy" and "original" relate to the NS(ARO) is that
support of the Registering
Node, which causes it to attract the packets from RFC 6775 by a 6LN, a 6LR or a 6LBR, whereas the 6BBR
term "updated" refers to the Registered Node and route them over the LLN.

Registered Address The address owned by the Registered Node node
that is being registered. support of this specification.

4. Updating RFC 6775

This specification extends introduces the Extended Address Registration
Option (ARO) (EARO) based on the ARO as defined in RFC 6775 [RFC6775]; in
particular a "T" flag is added that must be set is NS messages when
this specification is used, and
echo'ed echoed in NA messages to confirm that
the protocol effectively is supported.

Support for this specification can thus be inferred from the presence
of the Extended ARO ("T" flag set) in 6LoWPAN ND messages.

The extensions to the ARO option are reported to the Duplicate
Address Request (DAR) and Duplicate Address Confirmation (DAC)
messages, so as to convey the additional information all the way to
the 6LBR, and in turn the 6LBR may proxy the registration using
classical ND over a backbone as illustrated in Figure 1.

6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | |
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |

Figure 1: (Re-)Registration Flow

In order to support various types of link layers, this specification
also adds recommendation RECOMMENDS to allow multiple registrations, including for
privacy / temporary addresses, and provides new mechanisms to help
clean up stale registration states as soon as possible.

A Registering Node that supports this specification will favor SHOULD prefer
registering to a 6LR that indicates is found to support for this specification specification, as
discussed in Section 7.1, over that of RFC 6775 [RFC6775]. a legacy one.

4.1. Extended Address Registration Option (EARO

This specification extends the ARO option that is used for the
process of address registration. The new ARO is referred to as
Extended ARO (EARO), and its it is backward compatible with the ARO.
More details on backward compatibility can be found in Section 7.

The semantics of the ARO are modified as follows:

o The address that is being registered with a Neighbor Solicitation
(NS) with an EARO is now the Target Address, as opposed to the
Source Address as specified in RFC 6775 [RFC6775] (see
Section 4.4 for
more). 4.5). This change enables a 6LBR to use an address one of his its
addresses as source to the proxy-registration of an address that
belongs to a LLN Node to a 6BBR. This also limits the use of an
address as source address before it is registered and the
associated Duplicate Address
Detection (DAD) DAD process is complete.

o The Unique ID in the EARO option does Option is no more have longer required to be a MAC
address (see Section 4.3 for more). 4.3). This enables in particular the use of
a Provable Temporary UID (PT-UID) as opposed to burn-in MAC
address,
address; the PT-UID providing a trusted provides an anchor trusted by the 6LR and 6LBR
to protect the state associated to the node.

o The specification introduces a Transaction ID (TID) field in the
EARO (see Section 4.2 for more on TID). 4.2). The TID MUST be provided by a node that
supports this specification and a new T "T" flag MUST be set to
indicate so. The T bit can be used to determine whether the peer
supports this specification.

o Finally, this specification introduces a number of new Status status codes to help
diagnose the cause of a registration failure (more in (see Table 1).

4.2. 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 is used to detect the freshness of the registration request and
useful to detect one single registration by multiple 6LOWPAN border
routers (e.g., 6LBRs and 6BBRs) supporting the same large 6LOWPAN, as
is 6LOWPAN. The TID
may also be used by the case for backbone routers (BBR).

For example, when network to track the sequence of movements of
a node in order to route to the current (freshest known) location of
a moving node.

When a Registered Node is registered with multiple BBRs in parallel, it is expected that
the same TID is SHOULD be used, to enable the 6BBRs to correlate determine that
the registrations as being a single one, are the same, and
differentiate distinguish that situation from a
movement.

Thus the TID could be tracked to follow the sequence of mobility of a
node. The details protocols of mobility verification by the border
routers is not part of this specification.

4.2.1. Comparing TID values

The TID is a sequence counter and by design, its operation is the exact match of
the path sequence specified in RPL, the IPv6 Routing Protocol for
Low-Power and Lossy Networks [RFC6550] specification.

In order to keep this document self-contained and yet compatible, the
text below is an exact copy from section 7.2. "Sequence Counter
Operation" of [RFC6550].

A TID is deemed to be fresher than another when its value is greater
per the operations detailed in this section.

The TID range is subdivided in a 'lollipop' fashion ([Perlman83]),
where the values from 128 and greater are used as a linear sequence
to indicate a restart and bootstrap the counter, and the values less
than or equal to 127 used as a circular sequence number space of size
128 as in [RFC1982]. Consideration is given to the mode of operation
when transitioning from the linear region to the circular region.
Finally, when operating in the circular region, if sequence numbers
are detected to be too far apart then they are not comparable, as
detailed below.

A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
a value of 2^N, where N is defined to be 4 in this specification.

For a given sequence counter,

1. The sequence counter SHOULD be initialized to an implementation
defined value which is 128 or greater prior to use. A
recommended value is 240 (256 - SEQUENCE_WINDOW).

2. When a sequence counter increment would cause the sequence
counter to increment beyond its maximum value, the sequence
counter MUST wrap back to zero. When incrementing a sequence
counter greater than or equal to 128, the maximum value is 255.
When incrementing a sequence counter less than 128, the maximum
value is 127.

3. When comparing two sequence counters, the following rules MUST be
applied:

1. When a first sequence counter A is in the interval [128..255]
and a second sequence counter B is in [0..127]:

1. If (256 + B - A) is less than or equal to
SEQUENCE_WINDOW, then B is greater than A, A is less than
B, and the two are not equal.

2. If (256 + B - A) is greater than SEQUENCE_WINDOW, then A
is greater than B, B is less than A, and the two are not
equal.

For example, if A is 240, and B is 5, then (256 + 5 - 240) is
21. 21 is greater than SEQUENCE_WINDOW (16), thus 240 is
greater than 5. As another example, if A is 250 and B is 5,
then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW
(16), thus 250 is less than 5.

2. In the case where both sequence counters to be compared are
less than or equal to 127, and in the case where both
sequence counters to be compared are greater than or equal to
128:

1. If the absolute magnitude of difference between the two
sequence counters is less than or equal to
SEQUENCE_WINDOW, then a comparison as described in
[RFC1982] is used to determine the relationships greater
than, less than, and equal.

2. If the absolute magnitude of difference of the two
sequence counters is greater than SEQUENCE_WINDOW, then a
desynchronization has occurred and the two sequence
numbers are not comparable.

4. If two sequence numbers are determined to be not comparable, i.e.
the results of the comparison are not defined, then a node should
consider the comparison as if it has evaluated in such a way so
as to give precedence to the sequence number that has most
recently been observed to increment. Failing this, the node
should consider the comparison as if it has evaluated in such a
way so as to minimize the resulting changes to its own state.

4.3. Owner Unique ID

The Owner Unique ID (OUID) enables to differentiate a real duplicate address registration
to be distinguished 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 nodes; if they relate to a same target then
they reflect an
address duplication. The duplication is likely.

With RFC 6775, the Owner Unique ID can be as
simple as a carries an EUI-64 burn-in address, if
which implies that duplicate EUI-64 addresses are avoided.

Alternatively, With this
specification, the unique Owner Unique ID is allowed to be extended to
different types of identifier, as long as the type is clearly
indicated. For instance, the type can be a cryptographic string that can
can be and
used to prove the ownership of the registration as discussed in
"Address Protected Neighbor Discovery for Low-power and Lossy
Networks" [I-D.ietf-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 a same address after a
reboot that would cause a loss of memory until the Backbone Router 6LBR times out the
registration.

4.4. Extended Duplicate Address Messages

In order to map the new EARO content in the DAR/DAC messages, a new
TID field is added to the Extended DAR (EDAR) and the Extended DAC
(EDAC) messages as a replacement to a Reserved field, and an odd
value of the ICMP Code indicates support for the TID, to transport
the "T" flag.

In order to prepare for new extensions, and though no option had been
earlier defined for the Duplicate Address messages, implementations
SHOULD expect ND options after the main body, and SHOULD ignore them.

As for the EARO, the Extended Duplicate Address messages are backward
compatible with the original versions, and remarks concerning
backwards compatibility between the 6LN and the 6LR apply similarly
between a 6LR and a 6LBR.

4.5. Registering the Target Address

The Registering Node is the node that performs the registration to
the 6BBR. As inherited from RFC 6775, it may be the Registered Node
as well, in which case it registers one of its own addresses, and
indicates its own MAC Address as Source Link Layer Address (SLLA) in
the NS(EARO).

This specification adds the capability to proxy the registration
operation on behalf of a Registered Node that is reachable over a LLN
mesh. In that 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(EARO). If the
Registered Node is reachable over a Route-Over mesh from the
Registering Node, the SLLA in the NS(ARO) is that of the Registering
Node. This enables the Registering Node to attract the packets from
the 6BBR and route them over the LLN to the Registered Node .

In order to enable the latter operation, this specification changes
the behavior of the 6LN and the 6LR so that the Registered Address is
found in the Target Address field of the NS and NA messages as
opposed to the Source Address.

The reason for this change is to enable proxy-registrations on behalf
of other nodes in Route-Over meshes, nodes, for instance to enable that a RPL root registers to register
addresses on behalf of other LLN nodes that are deeper in a
6TiSCH mesh, nodes, as discussed in Appendix B.4.
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 receive and route them
down
the mesh. But packets. Since the Registered Address belongs to another node, the Registered
Node, and that address is indicated in the Target Address field of the NS
message.

With this convention, a TLLA option indicates the link-layer address
of the 6LN that owns the address, whereas the SLLA Option in a NS
message indicates that of the Registering Node, which can be the
owner device, or a proxy.

Since the

The Registering Node is the one that has reachability with reachable from the 6LR, and is also the one
expecting packets for the 6LN, it makes sense to
maintain compatibility with RFC 6775 [RFC6775], and 6LN. Therefore, it is REQUIRED
that an MUST place its own Link
Layer Address in the SLLA Option is that MUST always be placed in a
registration NS(EARO) message.

4.5. This maintains compatibility with the
original 6LoWPAN ND [RFC6775].

4.6. Link-Local Addresses and Registration

Considering that LLN nodes are often not wired and may move, there is
no guarantee that a Link-Local address stays unique between a
potentially variable and unbounded set of neighboring nodes.

Compared to RFC 6775 [RFC6775], 6775, this specification only requires that a Link-Local Link-
Local address is unique from the perspective of the peering
nodes. nodes that use it
to communicate (e.g. the 6LN and the 6LR in an NS/NA exchange). This
simplifies the Duplicate Address Detection (DAD) DAD process for Link-Local addresses, and there is no
exchange of Duplicate Address Request (DAR)
/ Duplicate Address Confirmation (DAC) exchange messages between the 6LR and a 6LBR for
Link-Local addresses.

Additionally,

According to RFC 6775 [RFC6775] requires that 6775, a 6LoWPAN Node (6LN) uses the an address being
registered as the source of the registration message. This generates
complexities in the 6LR to be able to cope with a potential
duplication, in particular for global addresses.

To simplify this, a 6LN and a 6LR that conform this specification
MUST always use Link-Local addresses as source and destination
addresses for the registration NS/NA exchange. As a result, the
registration is globally faster, and some of the complexity is
removed.

In more details:

An exchange between two nodes using Link-Local addresses implies that
they are reachable over one hop and that at least one of the 2 nodes
acts as a 6LR. A node MUST register a Link-Local address to a 6LR in
order to obtain reachability from that 6LR beyond the current
exchange, and in particular to use the Link-Local address as source
address to register other addresses, e.g. global addresses.

If there is no collision with an address previously registered to
this 6LR by another 6LN, then, from the standpoint of this 6LR, this
Link-Local address is unique and the registration is acceptable.
Conversely, it may possibly happen that two different 6LRs expose the
same Link-Local address but different link-layer addresses. In that
case, a 6LN may only interact with one of the 6LR 6LRs so as to avoid
confusion in the 6LN neighbor cache.

The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR), 6LBR, which is based on a Duplicate Address Request (DAR) / an
exchange of Duplicate Address Confirmation (DAC) exchange as described in RFC 6775
[RFC6775], messages, does not need to take place
for Link-Local addresses.

It is desired that a 6LR does not need to modify its state associated
to the Source Address of an NS(EARO) message. For that reason, when
possible, it is RECOMMENDED to use an address that is already
registered with a 6LR

When registering to a 6LR that conforms this specification, a node
MUST use a Link-Local address as the source address of the
registration, whatever the type of IPv6 address that is being
registered. That Link-Local Address MUST be either already
registered, or the address that is being registered.

When a Registering Node does not have an already-Registered Address,
it MUST register a Link-Local address, using it as both the Source
and the Target Address of an NS(EARO) message. In that case, it is
RECOMMENDED to use a Link-Local address that is (expected to be)
globally unique, e.g. derived from a burn-in MAC address. An EARO
option in the response NA indicates that the 6LR supports this
specification.

Since there is no DAR/DAC Duplicate Address exchange for Link-Local
addresses, the 6LR may answer immediately to the registration of a
Link-Local address, based solely on its existing state and the Source
Link-Layer Option that MUST be placed in the NS(EARO) message as
required in RFC 6775 [RFC6775].

A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA)
(GUAs) to a 6LR in order to obtain a establish global reachability for these
addresses via that 6LR. As opposed to When registering with a node 6LR that complies to RFC 6775
[RFC6775], conforms
this specification, a Registering Node registering a GUA does not use that its GUA as Source Address for the registration
Address, in contrast to a 6LR node that conforms this
specification. The DAR/DAC exchange MUST take place for non-Link-
Local addresses as prescribed by complies to RFC 6775 [RFC6775].

4.6.
For non-Link-Local addresses, the Duplicate Address exchange MUST
conform to RFC 6775, but the extended formats described in this
specification for the DAR and the DAC are used to relay the extended
information in the case of an EARO.

4.7. Maintaining the Registration States

This section discusses protocol actions that involve the Registering
Node, the 6LR and the 6LBR. It must be noted that the portion that
deals with a 6LBR only applies to those addresses that are registered
to it, which, as discussed in Section 4.5, 4.6, is not the case for Link-
Local addresses. The registration state includes all data that is
stored in the router relative to that registration, in particular,
but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store
additional registration information in more complex data structures
and use protocols that are out of scope of this document to keep them
synchonized when they are distributed.

When its Neighbor Cache is full, a 6LR cannot accept a new
registration. In that situation, the EARO is returned in a NA
message with a Status of 2, and the Registering Node may attempt to
register to another 6LR.

Conversely the registry in the 6LBR may be saturated, in which case
the 6LBR LBR cannot guarantee that a new address is effectively not a
duplicate. In that case, the 6LBR replies to a
DAR EDAR message with a DAC
EDAC message that carries a Status code 9 indicating "6LBR Registry
saturated", and the address stays in TENTATIVE state. Note: this
code is used by 6LBRs instead of Status 2 when responding to a
Duplicate Address message exchange and passed on to the Registering
Node by the 6LR. There is no point for the node to retry this
registration immediately via another 6LR, since the problem is global
to the network. The node may either abandon that address, deregister
other addresses first to make room, or keep the address in TENTATIVE
state and retry later.

A node renews an existing registration by repeatedly sending NS(EARO)
messages for the Registered Address. In order to refresh the
registration state in the 6LBR, these registrations MUST be reported
to the 6LBR.

A node that ceases to use an address SHOULD attempt to deregister
that address from all the 6LRs to which it has registered the
address, which is achieved using an NS(EARO) message with a
Registration Lifetime of 0.

A node that moves away from a particular 6LR SHOULD attempt to
deregister all of its addresses registered to that 6LR and register
to a new 6LR with an incremented TID. When/if the node shows up
elsewhere, an used to clean up the state in the previous location.
For instance, the "Moved" status can be used by a 6BBR in a NA(EARO)
message to indicate that the ownership of the proxy state on the
Backbone was transferred to another 6BBR, as the consequence of a
movement of the device. The receiver of the message SHOULD propagate
the status down the chain towards the Registered node and clean up
its state.

Upon receiving a NS(EARO) message with a Registration Lifetime of 0
and determining that this EARO is the freshest for a given NCE (see
Section 4.2), a 6LR cleans up its NCE. If the address was registered
to the 6LBR, then the 6LR MUST report to the 6LBR, through a DAR/DAC
Duplicate Address exchange with the 6LBR, or an alternate protocol,
indicating the null Registration Lifetime and the latest TID that
this 6LR is aware of.

Upon the Extended DAR message, the 6LBR evaluates if this is the
freshest EARO TID it has received for that particular registry entry. If
it is, then the entry is scheduled to be removed, and the DAR EDAR is
answered with a
DAC EDAC message bearing a Status of 0 "Success". If it
is not the freshest, then a Status 2 3 "Moved" is returned instead, and
the existing entry is conserved.

Upon timing out a registration, a 6LR removes silently its binding
cache entry, and a 6LBR schedules its entry to be removed.

When an address is scheduled to be removed, the 6LBR SHOULD conserve keep its
entry in a DELAY state for a configurable period of time, so as to
protect a mobile node that deregistered from one 6LR and did not
register yet to a new one, or the new registration did not reach yet
the 6LBR due to propagation delays in the network. Once the DELAY
time is passed, the 6LBR removes silently its entry.

5. Detecting Enhanced ARO Capability Support

The nodes and routers in a network may be mixed and if a node wants
to use EARO feature "Generic Header Compression for address registration, it has to find a router
which supports it. Thus all implementations with EARO option MUST
provide the capability detection method using 6CIO option to support
both types of registrations (ARO and EARO) as described in later
sections. Moreover, any new implementation of 6LOWPAN is also
RECOMMENDED to support 6LoWPAN Capability Indication option(6CIO)in
general.

RFC 7400 IPv6 over 6LoWPANs" [RFC7400]
introduces the 6LoWPAN Capability Indication Option (6CIO) to
indicate a node's capabilities to its peers. This specification
extends the format defined in RFC 7400 to signal the support for
EARO, as well as the node's capability to act as a 6LR, 6LBR and
6BBR.

With RFC 7400 [RFC7400], 7400, the 6CIO is typically sent in a Router Solicitation
(RS) messages. message. When used to signal the capabilities above per this
specification, the 6CIO is typically present in Router Advertisement
(RA) messages but can also be present in RS, Neighbor Solicitation
(NS) and Neighbor Advertisement (NA) messages.

6. Updated Extended ND Options And Messages

This specification does not introduce new options, but it modifies
existing ones and updates the associated behaviors as follow: specified in
the following subsections.

6.1. The Enhanced Address Registration Option (EARO)

The Address Registration Option (ARO) is defined in section 4.1. of
[RFC6775].

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 6LN and its 6LoWPAN Router (6LR), as
well as in 6LR. Conversely, the Extended
Duplicate Address Request (DAR) messages, EDAR and EDAC, are to be used in
replacement of the Duplicate Address
Confirmation (DAC) DAR and DAC messages so as to transport the new
information between 6LRs and 6LBRs in across LLNs meshes such as 6TiSCH
networks.

An NS message with an EARO option is a registration if and only if it
also carries an SLLAO option. The EARO option also used in NS and NA
messages between Backbone Routers over the Backbone link to sort out
the distributed registration state, and state; in that case, it does not carry
the SLLAO option and is not confused with a registration.

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 RFC 6775 [RFC6775] which specifies that the address
being registered is the source of the NS.

The EARO extends the ARO and is recognized by the "T" flag set. 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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: 2: EARO

Option Fields

Type: 33

Length: 8-bit unsigned integer. The length of the option in
units of 8 bytes. Always 2.

Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in
NS messages. See Table 1 below.

+-------+-----------------------------------------------------------+
| Value | Description |
+-------+-----------------------------------------------------------+
| 0..2 | See RFC 6775 [RFC6775]. Note that Note: a Status of 1 "Duplicate |
| | "Duplicate Address" applies to the Registered Address. If the Source |
| | the Source Address conflicts with an existing registration, |
| | registration, "Duplicate Source Address" should be used. |
| | |
| 3 | Moved: The registration fails because it is not the |
| | freshest. This Status indicates that the registration is |
| | rejected because another more recent registration was |
| | done, as indicated by a same OUI and a more recent TID. |
| | One possible cause is a stale registration that has |
| | progressed slowly in the network and was passed by a more |
| | recent one. It could also indicate a OUI collision. |
| | |
| 4 | Removed: The binding state was removed. This may be |
| | placed in an asynchronous NS(ARO) message, or as the |
| | rejection of a proxy registration to a Backbone Router |
| | |
| 5 | Proof requested: Validation Requested: The Registering Node is challenged for |
| | for owning the Registered Address or for being an acceptable |
| | acceptable proxy for the registration. This Status is expected in |
| | expected in asynchronous messages from a registrar (6LR, 6LBR, 6BBR) |
| | 6LBR, 6BBR) to indicate that the registration state is removed, for |
| | removed, for instance due to time out of a lifetime, or a movement. |
| | The receiver movement of the NA is the device that has performed a |
| | registration that is now stale and it should clean up its |
| | state. device. |
| | |
| 6 | Duplicate Source Address: The address used as source of |
| | the NS(ARO) conflicts with an existing registration. |
| | |
| 7 | Invalid Source Address: The address used as source of the |
| | NS(ARO) is not a Link-Local address as prescribed by this |
| | document. |
| | |
| 8 | Registered Address topologically incorrect: The address |
| | being registered is not usable on this link, e.g. it is |
| | not topologically correct |
| | |
| 9 | 6LBR Registry saturated: A new registration cannot be |
| | accepted because the 6LBR Registry is saturated. Note: |
| | this code is used by 6LBRs instead of Status 2 when |
| | responding to a Duplicate Address message exchange and |
| | passed on to the Registering Node by the 6LR. |
| | |
| 10 | Incorrect proof: Validation Failed: The proof of ownership of the registered |
| | registered address is not correct. |
+-------+-----------------------------------------------------------+

Table 1: EARO Status

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
The node maintains SHOULD maintain the TID in a persistent
storage.

Registration Lifetime: 16-bit integer; expressed in minutes. 0
means that the registration has ended and the
associated state should be removed.

Owner Unique Identifier (OUI): 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.

Note:

6.2. Extended Duplicate Address Message Formats

The Duplicate Address Request (DAR) and the code "6LBR Registry saturated" is used by 6LBRs instead Duplicate Address
Confirmation (DAC) messages are defined in section 4.4. of
Status 2 when responding to [RFC6775].
Those messages follow a DAR/DAC exchange and passed on to the
Registering Node by common base format, which enables information
from the 6LR. There is no point for ARO to be transported over multiple hops.

The Duplicate Address Messages are extended to adapt to the node Extended
ARO format, 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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status | TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Registered Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Duplicate Address Messages Format

Modified Message Fields

Code: The ICMP Code as defined in [RFC4443]. The ICMP Code
MUST be set to retry 1 with this registration immediately via another 6LR, since specification. An odd
value of the problem ICMP Code indicates that the TID field
is
global to present and obeys this specification.

TID: 1-byte integer; same definition and processing as the network. The node may either abandon that address,
deregister other addresses first to make room, or keep
TID in the address EARO option as defined in
TENTATIVE state Section 6.1.

Owner Unique Identifier (OUI): 8 bytes; same definition and retry later.

6.2.
processing as the OUI in the EARO option as defined
in Section 6.1.

6.3. New 6LoWPAN capability Capability Bits in the Capability Indication Option

This specification defines a number of capability bits in the CIO 6CIO
that was introduced by RFC 7400 [RFC7400].

Support for use in IPv6 ND RA messages.

Routers that support this specification is indicated by setting SHOULD set the "E" flag
in a CIO option. and
6LN SHOULD favor 6LR routers that support this specification over
those that do not. Routers that are capable of acting as 6LR, 6LBR
and 6BBR SHOULD set the L, B "L", "B" and P "P" flags, respectively. In
particular, the function 6LR is usually collocated with that of 6LBR.

Those flags are not mutually exclusive and if a router is capable of
running multiple roles, functions, it SHOULD set all the related flags.

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 = 1 |_____________________|L|B|P|E|G| | Reserved |L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|_______________________________________________________________|
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: 4: New capability Bits L, B, P, E in the CIO 6CIO

Option Fields

Type: 36

L: Node is a 6LR, it can take registrations.

B: Node is a 6LBR.

P: Node is a 6BBR, proxying for nodes on this link.

E: This specification is supported and applied.

7. Backward Compatibility

7.1. Discovering the capabilities of an ND peer

7.1.1. Using the E Flag in the CIO 6CIO Option

If the CIO 6CIO is used in an ND message, message and the sending node supports
this specification, then the "E" Flag MUST be set by
the sending node if supports this specification.

It is RECOMMENDED that a set.

A router that supports this specification
indicates so SHOULD indicate that with a CIO option,
6CIO Option, but this might not be practical if the link-layer MTU is
too small.

If the Registering Node (RN) receives a CIO in a RA, Router Advertisement
message, then the setting of the E" "E" Flag indicates whether or not
this specification is supported.

A node which does not implement this draft or parse 6CIO option, MUST
ignore the packet and the sender of option RN SHOULD use legacy
registration method according to RFC 6775 [RFC6775] after favor a timeout
period. router that
supports this specification over those that do not.

7.1.2. Using the T Flag in the EARO

One alternate way for a 6LN to discover the router's capabilities to
first register a Link Local address, placing the same address in the
Source and Target Address fields of the NS message, and setting the
"T" Flag. 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 consistent with existing ND
specifications such as the "Optimistic Duplicate Address Detection
(DAD) for IPv6" [RFC4429].

Once that first registration is complete, the node knows from the
setting of the "T" Flag in the response whether the router supports
this specification. If this support 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
Target Address field of the NS messages, while using one of its own, already registered, own
previously registered addresses as source.

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 "T" flag and TID field are reserved in RFC 6775
[RFC6775]
are ignored by a legacy router. A router that supports this
specification answers to an ARO with an ARO and to answers an EARO with an
EARO.

This specification changes the behavior of the peers in a
registration flows. To enable backward compatibility, a node 6LB that
registers to a router 6LR that is not known to support this specification
MUST behave as prescribed by in a manner that is compatible with RFC 6775. A 6LN can
achieve that by sending a NS(EARO) message with a Link-Local Address
used as both Source and Target Address, as described in Section 4.6.
Once the router 6LR is known to support this specification, the node 6LN MUST
obey this specification.

7.2. Legacy 6LoWPAN Node

A legacy 6LN will use the Registered Address as source and will not
use an EARO option. In order to be backward compatible, an An updated 6LR needs to MUST accept that registration if
it is valid per the RFC 6775
[RFC6775] specification, 6775, and it MUST manage the binding cache
accordingly. The updated 6LR MUST then use the original Duplicate
Address messages as specified in RFC 6775 to indicate to the 6LBR
that the TID is not present in the messages.

The main difference with RFC 6775 is that DAR/DAC Duplicate Address exchange
for DAD
may be is avoided for Link-Local addresses. Additionally, In any case, the 6LR
SHOULD use an EARO in the reply, and may use any of the Status codes
defined in this specification.

7.3. Legacy 6LoWPAN Router

The first registration by a an updated 6LN is MUST be for a Link-Local
address, using that Link-Local address as source. A legacy 6LR will
not make a difference and accept -or reject- that registration as if
the 6LN was a legacy node.

An updated 6LN will always use an EARO option in the registration NS
message, whereas a legacy 6LR will always reply with an ARO option in
the NA message. So from that first registration, the updated 6LN can
figure whether the 6LR supports this specification or not.

When facing

After detecting a legacy 6LR, an updated 6LN may attempt to find an
alternate 6LR that is updated. In order to be backward compatible,
based on the discovery
after detecting that a 6LR is legacy, the 6LN needs to
fallback MUST adhere to legacy behavior RFC 6775
in future protocol exchanges with that 6LR, and source the packet
with the Registered Address.

The main difference is

Note that the updated 6LN SHOULD use an EARO in the request
regardless of the type of 6LR, legacy or updated, which implies that
the 'T' flag is set.

If an updated 6LN moves from an updated 6LR to a legacy 6LR, the
legacy 6LR will send a legacy DAR message, which can not be compared
with an updated one for freshness.

Allowing legacy DAR messages to replace a state established by the
updated protocol in the 6LBR would be an attack vector and that
cannot be the default behavior.

But if legacy and updated 6LRs coexist temporarily in a network, then
it makes sense for an administrator to install a policy that allows
so, and the capability to install such a policy should be
configurable in a 6LBR though it is out of scope for this document.

7.4. Legacy 6LoWPAN Border Router

With this specification, the DAR/DAC transports an Duplicate Address messages are extended
to transport the EARO option as
opposed information. Similarly to an ARO option. As described for the NS/NA exchange,
updated 6LBR devices that support this specification always use an EARO option the Extended Duplicate Address
messages and all the associated behavior. A behavior so they can amlways be
differentiated from legacy ones.

Note that a legacy 6LBR will accept and process an EARO option EDAR message as if
it was an ARO option, original one, so the legacy original support of DAD will function. But considering that there are a lot fewer 6LBR
than 6LR, the expectation is that they are upgraded as soon as
devices that implement this specification are deployed. preserved.

8. Security Considerations

This specification extends RFC 6775 [RFC6775], and the security
section of that draft also applies to this as well. In particular,
it is expected that the link layer is sufficiently protected to
prevent a rogue access, either by means of physical or IP security on
the Backbone Link and link layer cryptography on the LLN. This
specification also expects 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.

This specification recommends to using privacy techniques (more in
section (see
Section 9, and protection against address theft such as provided by
"Address Protected Neighbor Discovery for Low-power and Lossy
Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the
Registered Address using a cryptographic OUID.

The registration mechanism may be used by a rogue node to attack the
6LR or the 6LBR with a Denial-of-Service attack against the registry.
It may also happen that the registry of a 6LR or a 6LBR is saturated
and cannot take any more registration, which effectively denies the
requesting a node the capability to use a new address. In order to
alleviate those concerns, Section 4.6 4.7 provides a number of
recommendations that ensure that a stale registration is removed as
soon as possible from the 6LR and 6LBR. In particular, this
specification recommends that:

o A node that ceases to use an address should SHOULD attempt to deregister
that address from all the 6LRs to which it is registered. The
flow is propagated to the 6LBR when needed, and a sequence number
is used to make sure that only the freshest command is acted upon.

o The Registration lifetimes SHOULD be individually configurable for
each address or group of addresses. The nodes should SHOULD be
configured with a Registration Lifetime that reflects their
expectation of how long they will use the address with the 6LR to
which it is registered. In particular, use cases that involve
mobility or rapid address changes should SHOULD use lifetimes that are homogeneous with
larger yet of a same order as the duration of the expectation of
presence.

o The router (6LR or 6LBR) should SHOULD be configurable so as to limit the
number of addresses that can be registered by a single node, as
identified at least by MAC address and preferably by security
credentials. When that maximum is reached, the router should use
a Least-Recently-Used (LRU) logic so as to clean up the addresses
that were not used for the longest time, keeping at least one
Link-Local address, and attempting to keep one or more stable
addresses if such can be recognized, e.g. from the way the IID is
formed or because they are used over a much longer time span than
other (privacy, shorter-lived) addresses. The address lifetimes
SHOULD be individually configurable.

o Administrators should In order to avoid denial of registration for the lack of
resources, administrators SHOULD take great care to deploy
adequate numbers of 6LR 6LRs to cover the needs of the nodes in their
range, so as to avoid a situation of starving nodes. It is
expected that the 6LBR that serves a LLN is a more capable node
then the average 6LR, but in a network condition where it may
become saturated, a particular deployment should SHOULD distribute the
6LBR functionality, for instance by leveraging a high speed
Backbone and Backbone Routers to aggregate multiple LLNs into a
larger subnet.

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.

The LLN nodes depend on the 6LBR and the 6BBR for their operation. A
trust model must be put in place to ensure that the right devices are
acting in these roles, so as to avoid threats such as black-holing,
or bombing attack whereby an impersonated 6LBR would destroy state in
the network by using the "Removed" Status code.

9. Privacy Considerations

As indicated in section Section 2, this protocol does not aim at
limiting the number of IPv6 addresses that a device can form. A host
should be able to form and register any address that is topologically
correct in the subnet(s) advertised by the 6LR/6LBR.

This specification does not mandate any particular way for forming
IPv6 addresses, but it recognizes that use of discourages using EUI-64 for forming the
Interface ID in the Link-Local address because this method prevents
the usage of "SEcure Neighbor Discovery (SEND)" [RFC3971] and
"Cryptographically Generated Addresses (CGA)" [RFC3972], and that of
address privacy techniques.

"Privacy Considerations for IPv6 Adaptation-Layer Mechanisms"
[RFC8065] addresses explains why privacy is important and how to form such
addresses. All implementations and deployment must consider the
option of privacy addresses in their own environment. Also future
specifications involving 6LOWPAN Neighbor Discovery should consult
"Recommendation on Stable IPv6 Interface Identifiers" [RFC8064] for
default interface identifaction.

10. IANA Considerations

IANA is requested to create make a new subregistry for "ARO Flags" number of changes under the "Internet
Control Message Protocol version 6 (ICMPv6)
Parameters". Parameters" registry, as
follows.

10.1. ARO Flags

IANA is requested to create a new subregistry for "ARO Flags". This
specification defines 8 positions, bit 0 to bit 7, and assigns bit 7
for the "T" 'T' flag in Section 6.1. The policy is "IETF Review" or
"IESG Approval" [RFC8126]. The initial content of the registry is as
shown in Table 2.

New subregistry for ARO Flags under the "Internet Control Message
Protocol version 6 (ICMPv6) [RFC4443] Parameters"

+------------+--------------+-----------+
| ARO Status | Description | Document |
+------------+--------------+-----------+
| 0..6 | Unassigned | |
| | | |
| 7 | "T" 'T' Flag | RFC This |
+------------+--------------+-----------+

Table 2: new ARO Flags

10.2. ICMP Codes

IANA is requested to create a new entry in the ICMPv6 "Code" Fields
subregistry of the Internet Control Message Protocol version 6
(ICMPv6) Parameters for the ICMP codes related to the ICMP type 157
and 158 Duplicate Address Request (shown in Table 3) and Confirmation
(shown in Table 4), respectively, as follows:

New entries for ICMP types 157 DAR message

+------+----------------------+------------+
| Code | Name | Reference |
+------+----------------------+------------+
| 0 | Original DAR message | RFC 6775 |
| 1 | Extended DAR message | RFC This |
+------+----------------------+------------+

Table 3: new ICMPv6 Code Fields

New entries for ICMP types 158 DAC message

+------+----------------------+------------+
| Code | Name | Reference |
+------+----------------------+------------+
| 0 | Original DAC message | RFC 6775 |
| 1 | Extended DAC message | RFC This |
+------+----------------------+------------+

Table 4: new ICMPv6 Code Fields

10.3. New ARO Status values

IANA is requested to make additions to existing registries the Address Registration
Option Status Values Registry as follows:

Address Registration Option Status Values Registry

Table 3: 5: New ARO Status values

10.4. New 6LoWPAN capability Bits

IANA is requested to make additions to the Subregistry for "6LoWPAN
capability Bits" as follows:

Subregistry for "6LoWPAN capability Bits" under the "Internet Control
Message Protocol version 6 (ICMPv6) Parameters"

Table 4: 6: New 6LoWPAN capability Bits

11. Acknowledgments

Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure at Cisco, upon which the first backbone router wsa was implemented;
many thanks to Charlie Perkins for his in-depth reviews and
constructive suggestions, as well as to Sedat Gormus, Rahul Jadhav, Charlie
Perkins Jadhav
and Lorenzo Colitti for their various contributions and reviews.
Also many thanks to Thomas Watteyne for his early implementation of a
6LN that was instrumental to test the early tests of the 6LR, 6LBR and
Backbone Router.

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>.
<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, <http://www.rfc-editor.org/info/rfc4291>. <https://www.rfc-editor.org/info/rfc4291>.

[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.

[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>.
<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,
<http://www.rfc-editor.org/info/rfc4862>.
<https://www.rfc-editor.org/info/rfc4862>.

[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>.
<https://www.rfc-editor.org/info/rfc6282>.

[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>.
<https://www.rfc-editor.org/info/rfc6775>.

[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
2014, <http://www.rfc-editor.org/info/rfc7400>. <https://www.rfc-editor.org/info/rfc7400>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<http://www.rfc-editor.org/info/rfc8126>.
<https://www.rfc-editor.org/info/rfc8126>.

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-ap-nd]
Sarikaya, B., Thubert, P., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-02 (work in progress), May
2017.

[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-04 (work in progress), July 2017.

[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-07 (work in progress),
June 2017.

[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 draft-ietf-6tisch-architecture-12 (work
in progress), January August 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-07 draft-ietf-bier-architecture-08 (work in
progress), June 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.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.

[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<http://www.rfc-editor.org/info/rfc1982>.
<https://www.rfc-editor.org/info/rfc1982>.

[RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
2003, <http://www.rfc-editor.org/info/rfc3610>. <https://www.rfc-editor.org/info/rfc3610>.

[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>.
<https://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>.
<https://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>.
<https://www.rfc-editor.org/info/rfc3972>.

[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>.
<https://www.rfc-editor.org/info/rfc4429>.

[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>.
<https://www.rfc-editor.org/info/rfc4919>.

[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>.
<https://www.rfc-editor.org/info/rfc4941>.

[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>.
<https://www.rfc-editor.org/info/rfc6550>.

[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>.
<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,
<http://www.rfc-editor.org/info/rfc7428>.
<https://www.rfc-editor.org/info/rfc7428>.

[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,
<http://www.rfc-editor.org/info/rfc7668>.
<https://www.rfc-editor.org/info/rfc7668>.

[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016,
<http://www.rfc-editor.org/info/rfc7934>.
<https://www.rfc-editor.org/info/rfc7934>.

[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<http://www.rfc-editor.org/info/rfc8064>.
<https://www.rfc-editor.org/info/rfc8064>.

[RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation-
Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
February 2017, <http://www.rfc-editor.org/info/rfc8065>. <https://www.rfc-editor.org/info/rfc8065>.

[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, <http://www.rfc-editor.org/info/rfc8105>. <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, <http://www.rfc-editor.org/info/rfc8163>. <https://www.rfc-editor.org/info/rfc8163>.

12.3. External Informative References

[IEEEstd802154]
IEEE, "IEEE Standard for Low-Rate Wireless Networks",
IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875,
<http://ieeexplore.ieee.org/document/7460875/>.

[Perlman83]
Perlman, R., "Fault-Tolerant Broadcast of Routing
Information", North-Holland Computer Networks 7: 395-405,
1983, <http://www.cs.illinois.edu/~pbg/courses/cs598fa09/
readings/p83.pdf>.

Appendix A. Applicability and Requirements Served

This specification extends 6LoWPAN ND to sequence the registration
and serves the requirements expressed Appendix B.1 by enabling the
mobility of devices from one LLN to the next based on the
complementary work in the "IPv6 Backbone Router"
[I-D.ietf-6lo-backbone-router] specification.

In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
IEEE Std. 802.15.4 [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 B.2.

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 discussed in Appendix B.3

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 B.4.

"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 serves scalability
requirements listed in Appendix B.6.

Appendix B. 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 B.5 which are deferred to a different
specification such as [I-D.ietf-6lo-ap-nd], and those related to
multicast.

B.1. Requirements Related to Mobility

Due to the unstable nature of LLN links, even in a LLN of immobile
nodes a 6LN 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.

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.

B.2. Requirements Related to Routing Protocols

The point of attachment of a 6LN 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.

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.

B.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 Std.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].

B.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.

B.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.

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 [IEEEstd802154] 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 the
variation of CCM [RFC3610] called 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.

B.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.

Authors' Addresses

Pascal Thubert (editor)
Cisco Systems, Inc
Sophia Antipolis
FRANCE

Email: pthubert@cisco.com

Erik Nordmark
Santa Clara, CA
USA

Email: nordmark@sonic.net

Samita Chakrabarti
San Jose, CA
USA

Email: samitac.ietf@gmail.com