< draft-ietf-6lo-rfc6775-update-04.txt   draft-ietf-6lo-rfc6775-update-05.txt >
6lo P. Thubert, Ed. 6lo P. Thubert, Ed.
Internet-Draft cisco Internet-Draft cisco
Updates: 6775 (if approved) E. Nordmark Updates: 6775 (if approved) E. Nordmark
Intended status: Standards Track Intended status: Standards Track
Expires: November 2, 2017 S. Chakrabarti Expires: November 13, 2017 S. Chakrabarti
May 1, 2017 May 12, 2017
An Update to 6LoWPAN ND An Update to 6LoWPAN ND
draft-ietf-6lo-rfc6775-update-04 draft-ietf-6lo-rfc6775-update-05
Abstract Abstract
This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to
clarify the role of the protocol as a registration technique, clarify the role of the protocol as a registration technique,
simplify the registration operation in 6LoWPAN routers, and provide simplify the registration operation in 6LoWPAN routers, and provide
enhancements to the registration capabilities, in particular for the enhancements to the registration capabilities, in particular for the
registration to a Backbone Router for proxy ND operations. registration to a Backbone Router for proxy ND operations.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 2, 2017. This Internet-Draft will expire on November 13, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Considerations On Registration Rejection . . . . . . . . . . 3 2. Considerations On Registration Rejection . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Extending RFC 7400 . . . . . . . . . . . . . . . . . . . . . 5 4. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5
5. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Extended Address Registration Option . . . . . . . . . . 5
5.1. Extended Address Registration Option . . . . . . . . . . 6 4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6
5.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 6 4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 7
5.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 7 4.4. Registering the Target Address . . . . . . . . . . . . . 7
5.4. Registering the Target Address . . . . . . . . . . . . . 8 4.5. Link-Local Addresses and Registration . . . . . . . . . . 8
5.5. Link-Local Addresses and Registration . . . . . . . . . . 8 4.6. Maintaining the Registration States . . . . . . . . . . . 9
5.6. Maintaining the Registration States . . . . . . . . . . . 10 5. Extending RFC 7400 . . . . . . . . . . . . . . . . . . . . . 11
6. Updated ND Options . . . . . . . . . . . . . . . . . . . . . 11 6. Updated ND Options . . . . . . . . . . . . . . . . . . . . . 11
6.1. New 6LoWPAN capability Bits in the Capability Indication 6.1. The Enhanced Address Registration Option (EARO) . . . . . 11
Option . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.2. New 6LoWPAN capability Bits in the Capability Indication
6.2. The Enhanced Address Registration Option (EARO) . . . . . 12 Option . . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 14 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 14
7.1. Discovering the capabilities of an ND peer . . . . . . . 14 7.1. Discovering the capabilities of an ND peer . . . . . . . 14
7.1.1. Using the E Flag in the CIO . . . . . . . . . . . . . 14 7.1.1. Using the E Flag in the CIO . . . . . . . . . . . . . 14
7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 15 7.1.2. Using the T Flag in the EARO . . . . . . . . . . . . 15
7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 15 7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 15
7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 16 7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 16
7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 16 7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . 20 11.1. Normative References . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . 21 11.2. Informative References . . . . . . . . . . . . . . . . . 21
11.3. External Informative References . . . . . . . . . . . . 23 11.3. External Informative References . . . . . . . . . . . . 24
Appendix A. Applicability and Requirements Served . . . . . . . 24 Appendix A. Applicability and Requirements Served . . . . . . . 24
Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 24 Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 25
B.1. Requirements Related to Mobility . . . . . . . . . . . . 25 B.1. Requirements Related to Mobility . . . . . . . . . . . . 25
B.2. Requirements Related to Routing Protocols . . . . . . . . 25 B.2. Requirements Related to Routing Protocols . . . . . . . . 25
B.3. Requirements Related to the Variety of Low-Power Link B.3. Requirements Related to the Variety of Low-Power Link
types . . . . . . . . . . . . . . . . . . . . . . . . . . 26 types . . . . . . . . . . . . . . . . . . . . . . . . . . 26
B.4. Requirements Related to Proxy Operations . . . . . . . . 27 B.4. Requirements Related to Proxy Operations . . . . . . . . 27
B.5. Requirements Related to Security . . . . . . . . . . . . 27 B.5. Requirements Related to Security . . . . . . . . . . . . 27
B.6. Requirements Related to Scalability . . . . . . . . . . . 28 B.6. Requirements Related to Scalability . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction 1. Introduction
RFC 6775, the "Neighbor Discovery Optimization for IPv6 over Low- RFC 6775, the "Neighbor Discovery Optimization for IPv6 over Low-
Power Wireless Personal Area Networks (6LoWPANs)" [RFC6775] Power Wireless Personal Area Networks (6LoWPANs)" [RFC6775]
introduced a proactive registration mechanism to IPv6 Neighbor introduced a proactive registration mechanism to IPv6 Neighbor
Discovery (ND) services that is well suited to nodes belonging to a Discovery (ND) services that is well suited to nodes belonging to a
Low Power Lossy Network (LLN). Low Power Lossy Network (LLN).
The scope of this draft is an IPv6 LLN, which can be a simple star or The scope of this draft is an IPv6 LLN, which can be a simple star or
a more complex mesh topology. The LLN may be anchored at an IPv6 a more complex mesh topology. The LLN may be anchored at an IPv6
Backbone Router (6BBR) [I-D.ietf-6lo-backbone-router]. The 6BBRs Backbone Router (6BBR) [I-D.ietf-6lo-backbone-router]. This
interconnect the LLNs over a Backbone Link and emulate that the LLN specification modifies and extends the behavior and protocol elements
nodes are present on the Backbone using proxy-ND operations. of RFC 6775 [RFC6775] to enable additional capabilities, in
This specification modifies and extends the behavior and protocol
elements of RFC 6775 [RFC6775] to enable additional capabilities, in
particular the registration to a 6BBR for proxy ND operations. particular the registration to a 6BBR for proxy ND operations.
2. Considerations On Registration Rejection 2. Considerations On Registration Rejection
The purpose of the Address Registration Option (ARO) RFC 6775 The purpose of the Address Registration Option (ARO) [RFC6775] and of
[RFC6775] and of the Extended ARO (EARO) that is introduced in this the Extended ARO (EARO) that is introduced in this document is to
document is to facilitate duplicate address detection (DAD) for hosts facilitate duplicate address detection (DAD) for hosts and pre-
and pre-populate Neighbor Cache Entries (NCE) [RFC4861] in the populate Neighbor Cache Entries (NCE) [RFC4861] in the routers to
routers to reduce the need for sending multicast neighbor reduce the need for sending multicast neighbor solicitations and also
solicitations and also to be able to support IPv6 Backbone Routers. to be able to support IPv6 Backbone Routers.
In some cases the address registration can fail or be useless for In some cases the address registration can fail or be useless for
reasons other than a duplicate address. Examples are the router reasons other than a duplicate address. Examples are the router
having run out of space, a registration bearing a stale sequence having run out of space, a registration bearing a stale sequence
number (e.g. denoting a movement of the host after this registration number (e.g. denoting a movement of the host after this registration
was placed), a host misbehaving and attempting to register an invalid was placed), a host misbehaving and attempting to register an invalid
address such as the unspecified address [RFC4291], or the host using address such as the unspecified address [RFC4291], or the host using
an address which is not topologically correct on that link. In such 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 cases the host will receive an error to help diagnose the issue and
may retry, possibly with a different address, and possibly may retry, possibly with a different address, and possibly
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"Terms Used in Routing for Low-Power and Lossy Networks" [RFC7102] "Terms Used in Routing for Low-Power and Lossy Networks" [RFC7102]
and and
the "6TiSCH Terminology" [I-D.ietf-6tisch-terminology], the "6TiSCH Terminology" [I-D.ietf-6tisch-terminology],
as well as this additional terminology: as well as this additional terminology:
Backbone This is an IPv6 transit link that interconnects 2 or more Backbone This is an IPv6 transit link that interconnects 2 or more
Backbone Routers. It is expected to be deployed as a high Backbone Routers. It is expected to be deployed as a high
speed backbone in order to federate a potentially large set of speed Backbone in order to federate a potentially large set of
LLNS. Also referred to as a LLN backbone or Backbone network. LLNS. Also referred to as a LLN Backbone or Backbone network.
Backbone Router An IPv6 router that federates the LLN using a Backbone Router An IPv6 router that federates the LLN using a
Backbone link as a backbone. A 6BBR acts as a 6LoWPAN Border Backbone link as a Backbone. A 6BBR acts as a 6LoWPAN Border
Routers (6LBR) and an Energy Aware Default Router (NEAR). Routers (6LBR) and an Energy Aware Default Router (NEAR).
Extended LLN This is the aggregation of multiple LLNs as defined in Extended LLN This is the aggregation of multiple LLNs as defined in
RFC 4919 [RFC4919], interconnected by a Backbone Link via RFC 4919 [RFC4919], interconnected by a Backbone Link via
Backbone Routers, and forming a single IPv6 MultiLink Subnet. Backbone Routers, and forming a single IPv6 MultiLink Subnet.
Registration The process during which a wireless Node registers its Registration The process during which a wireless Node registers its
address(es) with the Border Router so the 6BBR can proxy ND for address(es) with the Border Router so the 6BBR can proxy ND for
it over the backbone. it over the Backbone.
Binding The state in the 6BBR that associates an IP address with a Binding The state in the 6BBR that associates an IP address with a
MAC address, a port and some other information about the node MAC address, a port and some other information about the node
that owns the IP address. that owns the IP address.
Registered Node The node for which the registration is performed, Registered Node The node for which the registration is performed,
which owns the fields in the EARO option. which owns the fields in the EARO option.
Registering Node The node that performs the registration to the Registering Node The node that performs the registration to the
6BBR, either for one of its own addresses, in which case it is 6BBR, either for one of its own addresses, in which case it is
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Address of the Registered Node as SLLA in the NS(EARO). Address of the Registered Node as SLLA in the NS(EARO).
Otherwise, it is expected that the Registered Device is Otherwise, it is expected that the Registered Device is
reachable over a Route-Over mesh from the Registering Node, in reachable over a Route-Over mesh from the Registering Node, in
which case the SLLA in the NS(ARO) is that of the Registering 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 Node, which causes it to attract the packets from the 6BBR to
the Registered Node and route them over the LLN. the Registered Node and route them over the LLN.
Registered Address The address owned by the Registered Node node Registered Address The address owned by the Registered Node node
that is being registered. that is being registered.
4. Extending RFC 7400 4. Updating RFC 6775
RFC 7400 [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 capability to act as a 6LR, 6LBR and
6BBR.
With RFC 7400 [RFC7400], the 6CIO is typically sent Router
Solicitation (RS) messages. When used to signal the capabilities
above per this specification, the 6CIO is typically present Router
Advertisement (RA) messages but can also be present in RS, Neighbor
Solicitation (NS) and Neighbor Advertisement (NA) messages.
5. Updating RFC 6775
This specification extends the Address Registration Option (ARO) This specification extends the Address Registration Option (ARO)
defined in RFC 6775 [RFC6775]; in particular a "T" flag is added that 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 must be set is NS messages when this specification is used, and
echo'ed in NA messages to confirm that the protocol effectively echo'ed in NA messages to confirm that the protocol effectively
supported. Support for this specification can thus be inferred from supported. Support for this specification can thus be inferred from
the presence of the Extended ARO ("T" flag set) in ND messages. the presence of the Extended ARO ("T" flag set) in ND messages.
In order to support various types of link layers, this specification In order to support various types of link layers, this specification
also adds recommendation to allow multiple registrations, including also adds recommendation to allow multiple registrations, including
for privacy / temporary addresses, and provides new mechanisms to for privacy / temporary addresses, and provides new mechanisms to
help clean up stale registration states as soon as possible. help clean up stale registration states as soon as possible.
A Registering Node that supports this specification will favor A Registering Node that supports this specification will favor
registering to a 6LR that indicates support for this specification registering to a 6LR that indicates support for this specification
over that of RFC 6775 [RFC6775]. over that of RFC 6775 [RFC6775].
5.1. Extended Address Registration Option 4.1. Extended Address Registration Option
This specification extends the ARO option that is used for the This specification extends the ARO option that is used for the
process of address registration. The new ARO is referred to as process of address registration. The new ARO is referred to as
Extended ARO (EARO), and its semantics are modified as follows: Extended ARO (EARO), and its semantics are modified as follows:
The address that is being registered with a Neighbor Solicitation The address that is being registered with a Neighbor Solicitation
(NS) with an EARO is now the Target Address, as opposed to the Source (NS) with an EARO is now the Target Address, as opposed to the Source
Address as specified in RFC 6775 [RFC6775] (see Section 5.4 for Address as specified in RFC 6775 [RFC6775] (see Section 4.4 for
more). This change enables a 6LBR to use an address of his as source more). This change enables a 6LBR to use an address of his as source
to the proxy-registration of an address that belongs to a LLN Node to 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 a 6BBR. This also limits the use of an address as source address
before it is registered and the associated Duplicate Address before it is registered and the associated Duplicate Address
Detection (DAD) is complete. Detection (DAD) is complete.
The Unique ID in the EARO option does no more have to be a MAC The Unique ID in the EARO option does no more have to be a MAC
address (see Section 5.3 for more). This enables in particular the address (see Section 4.3 for more). This enables in particular the
use of a Provable Temporary UID (PT-UID) as opposed to burn-in MAC use of a Provable Temporary UID (PT-UID) as opposed to burn-in MAC
address, the PT-UID providing a trusted anchor by the 6LR and 6LBR to address, the PT-UID providing a trusted anchor by the 6LR and 6LBR to
protect the state associated to the node. protect the state associated to the node.
The specification introduces a Transaction ID (TID) field in the EARO The specification introduces a Transaction ID (TID) field in the EARO
(see Section 5.2 for more on TID). The TID MUST be provided by a (see Section 4.2 for more on TID). The TID MUST be provided by a
node that supports this specification and a new T flag MUST be set to node that supports this specification and a new T flag MUST be set to
indicate so. The T bit can be used to determine whether the peer indicate so. The T bit can be used to determine whether the peer
supports this specification. supports this specification.
Finally, this specification introduces a number of new Status codes Finally, this specification introduces a number of new Status codes
to help diagnose the cause of a registration failure (more in to help diagnose the cause of a registration failure (more in
Table 1). Table 1).
5.2. Transaction ID 4.2. Transaction ID
The specification expects that the Registered Node can provide a The specification expects that the Registered Node can provide a
sequence number called Transaction ID (TID) that is incremented with sequence number called Transaction ID (TID) that is incremented with
each re-registration. The TID essentially obeys the same rules as each re-registration. The TID essentially obeys the same rules as
the Path Sequence field in the Transit Information Option (TIO) found the Path Sequence field in the Transit Information Option (TIO) found
in the RPL Destination Advertisement Object (DAO) [RFC6550]. This in the RPL Destination Advertisement Object (DAO) [RFC6550]. This
way, the LLN node can use the same counter for ND and RPL, and a 6LBR 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 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 a RPL node deep inside the mesh by simply using the RPL TIO Path
Sequence as TID for EARO. Sequence as TID for EARO.
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If the TIDs are different, a conflict resolution inherited from RPL If the TIDs are different, a conflict resolution inherited from RPL
sorts out the most recent registration and other ones are removed. sorts out the most recent registration and other ones are removed.
The operation for computing and comparing the Path Sequence is The operation for computing and comparing the Path Sequence is
detailed in section 7 of RFC 6550 [RFC6550] and applies to the TID in detailed in section 7 of RFC 6550 [RFC6550] and applies to the TID in
the exact same fashion. The resolution is used to determine the the exact same fashion. The resolution is used to determine the
freshest registration for a particular address, and an EARO is freshest registration for a particular address, and an EARO is
processed only if it is the freshest, otherwise a Status code 3 processed only if it is the freshest, otherwise a Status code 3
"Moved" is returned. "Moved" is returned.
5.3. Owner Unique ID 4.3. Owner Unique ID
The Owner Unique ID (OUID) enables to differentiate a real duplicate The Owner Unique ID (OUID) enables to differentiate a real duplicate
address registration from a double registration or a movement. An ND address registration from a double registration or a movement. An ND
message from the 6BBR over the backbone that is proxied on behalf of 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 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 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 represent different nodes and if they relate to a same target then
they reflect an address duplication. The Owner Unique ID can be as 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 simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are
avoided. avoided.
Alternatively, the unique ID can be a cryptographic string that can Alternatively, the unique ID can be a cryptographic string that can
can be used to prove the ownership of the registration as discussed can be used to prove the ownership of the registration as discussed
in "Address Protected Neighbor Discovery for Low-power and Lossy in "Address Protected Neighbor Discovery for Low-power and Lossy
Networks" [I-D.ietf-6lo-ap-nd]. Networks" [I-D.ietf-6lo-ap-nd].
In any fashion, it is recommended that the node stores the unique Id In any fashion, it is recommended that the node stores the unique Id
or the keys used to generate that ID in persistent memory. or the keys used to generate that ID in persistent memory.
Otherwise, it will be prevented to re-register after a reboot that 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 would cause a loss of memory until the Backbone Router times out the
registration. registration.
5.4. Registering the Target Address 4.4. Registering the Target Address
This specification changes the behavior of the 6LN and the 6LR so This specification changes the behavior of the 6LN and the 6LR so
that the Registered Address is found in the Target Address field of that the Registered Address is found in the Target Address field of
the NS and NA messages as opposed to the Source Address. the NS and NA messages as opposed to the Source Address.
The reason for this change is to enable proxy-registrations on behalf 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 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 RPL root registers addresses on behalf LLN nodes that are deeper in a
6TiSCH mesh, as discussed in Appendix B.4. In that case, the 6TiSCH mesh, as discussed in Appendix B.4. In that case, the
Registering Node MUST indicate its own address as source of the ND Registering Node MUST indicate its own address as source of the ND
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of the 6LN that owns the address, whereas the SLLA Option in a NS 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 message indicates that of the Registering Node, which can be the
owner device, or a proxy. owner device, or a proxy.
Since the Registering Node is the one that has reachability with the Since the Registering Node is the one that has reachability with the
6LR, and is the one expecting packets for the 6LN, it makes sense to 6LR, and is the one expecting packets for the 6LN, it makes sense to
maintain compatibility with RFC 6775 [RFC6775], and it is REQUIRED maintain compatibility with RFC 6775 [RFC6775], and it is REQUIRED
that an SLLA Option is always placed in a registration NS(EARO) that an SLLA Option is always placed in a registration NS(EARO)
message. message.
5.5. Link-Local Addresses and Registration 4.5. Link-Local Addresses and Registration
Considering that LLN nodes are often not wired and may move, there is Considering that LLN nodes are often not wired and may move, there is
no guarantee that a Link-Local address stays unique between a no guarantee that a Link-Local address stays unique between a
potentially variable and unbounded set of neighboring nodes. potentially variable and unbounded set of neighboring nodes.
Compared to RFC 6775 [RFC6775], this specification only requires that Compared to RFC 6775 [RFC6775], this specification only requires that
a Link-Local address is unique from the perspective of the peering a Link-Local address is unique from the perspective of the peering
nodes. This simplifies the Duplicate Address Detection (DAD) for nodes. This simplifies the Duplicate Address Detection (DAD) for
Link-Local addresses, and there is no DAR/DAC exchange between the Link-Local addresses, and there is no DAR/DAC exchange between the
6LR and a 6LBR for Link-Local addresses. 6LR and a 6LBR for Link-Local addresses.
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to the Source Address of an NS(EARO) message. For that reason, when to the Source Address of an NS(EARO) message. For that reason, when
possible, it is RECOMMENDED to use an address that is already possible, it is RECOMMENDED to use an address that is already
registered with a 6LR registered with a 6LR
When registering to a 6LR that conforms this specification, a node When registering to a 6LR that conforms this specification, a node
MUST use a Link-Local address as the source address of the MUST use a Link-Local address as the source address of the
registration, whatever the type of IPv6 address that is being registration, whatever the type of IPv6 address that is being
registered. That Link-Local Address MUST be either already registered. That Link-Local Address MUST be either already
registered, or the address that is being registered. registered, or the address that is being registered.
When a Registering Node does not have an already-registered address, When a Registering Node does not have an already-Registered Address,
it MUST register a Link-Local address, using it as both the Source 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 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) 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 globally unique, e.g. derived from a burn-in MAC address. An EARO
option in the response NA indicates that the 6LR supports this option in the response NA indicates that the 6LR supports this
specification. specification.
Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR
may answer immediately to the registration of a Link-Local address, may answer immediately to the registration of a Link-Local address,
based solely on its existing state and the Source Link-Layer Option based solely on its existing state and the Source Link-Layer Option
skipping to change at page 10, line 13 skipping to change at page 9, line 38
[RFC6775]. [RFC6775].
A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA) A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA)
to a 6LR in order to obtain a global reachability for these addresses to a 6LR in order to obtain a global reachability for these addresses
via that 6LR. As opposed to a node that complies to RFC 6775 via that 6LR. As opposed to a node that complies to RFC 6775
[RFC6775], a Registering Node registering a GUA does not use that GUA [RFC6775], a Registering Node registering a GUA does not use that GUA
as Source Address for the registration to a 6LR that conforms this as Source Address for the registration to a 6LR that conforms this
specification. The DAR/DAC exchange MUST take place for non-Link- specification. The DAR/DAC exchange MUST take place for non-Link-
Local addresses as prescribed by RFC 6775 [RFC6775]. Local addresses as prescribed by RFC 6775 [RFC6775].
5.6. Maintaining the Registration States 4.6. Maintaining the Registration States
This section discusses protocol actions that involve the registering This section discusses protocol actions that involve the Registering
node, the 6LR and the 6LBR. It must be noted that the portion that 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 deals with a 6LBR only applies to those addresses that are registered
to it, which, as discussed in Section 5.5, is not the case for Link- to it, which, as discussed in Section 4.5, is not the case for Link-
Local addresses. The registration state includes all data that is Local addresses. The registration state includes all data that is
stored in the router relative to that registration, in particular, stored in the router relative to that registration, in particular,
but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store
additional registration information in more complex data structures additional registration information in more complex data structures
and use protocols that are out of scope of this document to keep them and use protocols that are out of scope of this document to keep them
synchonized when they are distributed. synchonized when they are distributed.
When its Neighbor Cache is full, a 6LR cannot accept a new When its Neighbor Cache is full, a 6LR cannot accept a new
registration. In that situation, the EARO is returned in a NA registration. In that situation, the EARO is returned in a NA
message with a Status of 2, and the registering node may attempt to 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 register to another 6LR. Conversely the registry in the 6LBR may be
saturated, in which case the 6LBR cannot guarantee that a new address saturated, in which case the 6LBR cannot guarantee that a new address
is effectively not a duplicate. In that case, the 6LBR replies to a is effectively not a duplicate. In that case, the 6LBR replies to a
DAR message with a DAC message that carries a Status code 9 DAR message with a DAC message that carries a Status code 9
indicating "6LBR Registry saturated", and the address stays in indicating "6LBR Registry saturated", and the address stays in
TENTATIVE state. TENTATIVE state.
A node renews an existing registration by repeatedly sending NS(EARO) A node renews an existing registration by repeatedly sending NS(EARO)
messages for the registered address. In order to refresh the messages for the Registered Address. In order to refresh the
registration state in the 6LBR, these registrations MUST be reported registration state in the 6LBR, these registrations MUST be reported
to the 6LBR. This is normally done through a DAR/DAC exchange, but to the 6LBR. This is normally done through a DAR/DAC exchange, but
the refresh MAY alternatively be piggy-backed in another protocol the refresh MAY alternatively be piggy-backed in another protocol
such as RPL [RFC6550], as long as the semantics of the EARO are fully such as RPL [RFC6550], as long as the semantics of the EARO are fully
carried in the alternate protocol. In the particular case of RPL, carried in the alternate protocol. In the particular case of RPL,
the TID MUST be used as the Path Sequence in the TIO, and the the TID MUST be used as the Path Sequence in the TIO, and the
Registration Lifetime MUST be used as Path Lifetime. It is also Registration Lifetime MUST be used as Path Lifetime. It is also
REQUIRED that the root of the RPL DODAG passes that information to REQUIRED that the root of the RPL DODAG passes that information to
the 6LBR on behalf of the 6LR, either through a DAR/DAC exchange, or the 6LBR on behalf of the 6LR, either through a DAR/DAC exchange, or
through internal methods if they are collocated. through internal methods if they are collocated.
skipping to change at page 11, line 10 skipping to change at page 10, line 35
A node that ceases to use an address SHOULD attempt to deregister A node that ceases to use an address SHOULD attempt to deregister
that address from all the 6LRs to which it has registered the that address from all the 6LRs to which it has registered the
address, which is achieved using an NS(EARO) message with a address, which is achieved using an NS(EARO) message with a
Registration Lifetime of 0. Registration Lifetime of 0.
A node that moves away from a particular 6LR SHOULD attempt to A node that moves away from a particular 6LR SHOULD attempt to
deregister all of its addresses registered to that 6LR. deregister all of its addresses registered to that 6LR.
Upon receiving a NS(EARO) message with a Registration Lifetime of 0 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 and determining that this EARO is the freshest for a given NCE (see
Section 5.2), a 6LR cleans up its NCE. If the address was registered 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 to the 6LBR, then the 6LR MUST report to the 6LBR, through a DAR/DAC
exchange with the 6LBR, or an alternate protocol, indicating the null exchange with the 6LBR, or an alternate protocol, indicating the null
Registration Lifetime and the latest TID that this 6LR is aware of. Registration Lifetime and the latest TID that this 6LR is aware of.
Upon the DAR message, the 6LBR evaluates if this is the freshest EARO Upon the DAR message, the 6LBR evaluates if this is the freshest EARO
it has received for that particular registry entry. If it is, then it has received for that particular registry entry. If it is, then
the entry is scheduled to be removed, and the DAR is answered with a the entry is scheduled to be removed, and the DAR is answered with a
DAC message bearing a Status of 0 "Success". If it is not the DAC message bearing a Status of 0 "Success". If it is not the
freshest, then a Status 2 "Moved" is returned instead, and the freshest, then a Status 2 "Moved" is returned instead, and the
existing entry is conserved. The 6LBR SHOULD conserve the address in existing entry is conserved. The 6LBR SHOULD conserve the address in
a DELAY state for a configurable period of time, so as to protect a 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 mobile node that deregistered from one 6LR and did not register yet
to a new one. to a new one.
6. Updated ND Options 5. Extending RFC 7400
This specification does not introduce new options, but it modifies
existing ones and updates the associated behaviors as follow:
6.1. New 6LoWPAN capability Bits in the Capability Indication Option
This specification defines a number of capability bits in the CIO
that was introduced by RFC 7400 [RFC7400].
Support for this specification is indicated by setting the "E" flag
in a CIO option. Routers that are capable of acting as 6LR, 6LBR and
6BBR SHOULD set the L, B and P flags, respectively.
Those flags are not mutually exclusive and if a router is capable of
multiple roles, 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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |_______________________________________________________________|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: New capability Bits L, B, P, E in the CIO
Option Fields
Type: 36
L: Node is a 6LR, it can take registrations. RFC 7400 [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 capability to act as a 6LR, 6LBR and
6BBR.
B: Node is a 6LBR. With RFC 7400 [RFC7400], the 6CIO is typically sent Router
Solicitation (RS) messages. When used to signal the capabilities
above per this specification, the 6CIO is typically present Router
Advertisement (RA) messages but can also be present in RS, Neighbor
Solicitation (NS) and Neighbor Advertisement (NA) messages.
P: Node is a 6BBR, proxying for nodes on this link. 6. Updated ND Options
E: This specification is supported and applied. This specification does not introduce new options, but it modifies
existing ones and updates the associated behaviors as follow:
6.2. The Enhanced Address Registration Option (EARO) 6.1. The Enhanced Address Registration Option (EARO)
The Enhanced Address Registration Option (EARO) is intended to be The Enhanced Address Registration Option (EARO) is intended to be
used as a replacement to the ARO option within Neighbor Discovery NS 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 and NA messages between a LLN node and its 6LoWPAN Router (6LR), as
well as in Duplicate Address Request (DAR) and the Duplicate Address well as in Duplicate Address Request (DAR) and the Duplicate Address
Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes
such as 6TiSCH networks. such as 6TiSCH networks.
An NS message with an EARO option is a registration if and only if it 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 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 messages between Backbone Routers over the Backbone link to sort out
the distributed registration state, and in that case, it does not the distributed registration state, and in that case, it does not
carry the SLLAO option and is not confused with a registration. carry the SLLAO option and is not confused with a registration.
The EARO extends the ARO and is recognized by the "T" flag set. The EARO extends the ARO and is recognized by the "T" flag set.
When using the EARO option, the address being registered is found in When using the EARO option, the address being registered is found in
the Target Address field of the NS and NA messages. This differs the Target Address field of the NS and NA messages. This differs
from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address from 6LoWPAN ND RFC 6775 [RFC6775] which specifies that the address
being registered is the source of the NS. being registered is the source of the NS.
skipping to change at page 12, line 50 skipping to change at page 12, line 17
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length = 2 | Status | Reserved | | Type | Length = 2 | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |T| TID | Registration Lifetime | | Reserved |T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Owner Unique ID (EUI-64 or equivalent) + + Owner Unique ID (EUI-64 or equivalent) +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: EARO Figure 1: EARO
Option Fields Option Fields
Type: 33 Type: 33
Length: 8-bit unsigned integer. Length: 8-bit unsigned integer.
Status: 8-bit unsigned integer. Indicates the status of a Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in NS messages. registration in the NA response. MUST be set to 0 in NS messages.
See Table 1 below. See Table 1 below.
skipping to change at page 13, line 38 skipping to change at page 12, line 52
Owner Unique Identifier (OUI): A globally unique identifier for the Owner Unique Identifier (OUI): A globally unique identifier for the
node associated. This can be the EUI-64 derived IID of an node associated. This can be the EUI-64 derived IID of an
interface, or some provable ID obtained cryptographically. interface, or some provable ID obtained cryptographically.
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
| Value | Description | | Value | Description |
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
| 0..2 | See RFC 6775 [RFC6775]. Note that a Status of 1 | | 0..2 | See RFC 6775 [RFC6775]. Note that a Status of 1 |
| | "Duplicate Address" applies to the Registered Address. If | | | "Duplicate Address" applies to the Registered Address. If |
| | the Source Address conflicts with an existing | | | the Source Address conflicts with an existing |
| | registration, "Duplicate Source Address" should be used | | | registration, "Duplicate Source Address" should be used. |
| | instead |
| | | | | |
| 3 | Moved: The registration fails because it is not the | | 3 | Moved: The registration fails because it is not the |
| | freshest. This Status indicates that the registration is | | | freshest. This Status indicates that the registration is |
| | rejected because another more recent registration was | | | rejected because another more recent registration was |
| | done, as indicated by a same OUI and a more recent TID. | | | done, as indicated by a same OUI and a more recent TID. |
| | One possible cause is a stale registration that has | | | One possible cause is a stale registration that has |
| | progressed slowly in the network and was passed by a more | | | progressed slowly in the network and was passed by a more |
| | recent one. It could also indicate a OUI collision. | | | recent one. It could also indicate a OUI collision. |
| | | | | |
| 4 | Removed: The binding state was removed. This may be | | 4 | Removed: The binding state was removed. This may be |
| | placed in an asynchronous NS(ARO) message, or as the | | | placed in an asynchronous NS(ARO) message, or as the |
| | rejection of a proxy registration to a Backbone Router | | | rejection of a proxy registration to a Backbone Router |
| | | | | |
| 5 | Proof requested: The registering node is challenged for | | 5 | Proof requested: The Registering Node is challenged for |
| | owning the registered address or for being an acceptable | | | owning the Registered Address or for being an acceptable |
| | proxy for the registration. This Status is expected in | | | proxy for the registration. This Status is expected in |
| | asynchronous messages from a registrar (6LR, 6LBR, 6BBR) | | | asynchronous messages from a registrar (6LR, 6LBR, 6BBR) |
| | to indicate that the registration state is removed, for | | | to indicate that the registration state is removed, for |
| | instance due to time out of a lifetime, or a movement. It | | | instance due to time out of a lifetime, or a movement. |
| | is used for instance by a 6BBR in a NA(ARO) message to | | | The receiver of the NA is the device that has performed a |
| | indicate that the ownership of the proxy state on the | | | registration that is now stale and it should clean up its |
| | backbone was transferred to another 6BBR, which is | | | state. |
| | indicative of a movement of the device. The receiver of |
| | the NA is the device that has performed a registration |
| | that is now stale and it should clean up its state. |
| | | | | |
| 6 | Duplicate Source Address: The address used as source of | | 6 | Duplicate Source Address: The address used as source of |
| | the NS(ARO) conflicts with an existing registration. | | | the NS(ARO) conflicts with an existing registration. |
| | | | | |
| 7 | Invalid Source Address: The address used as source of the | | 7 | Invalid Source Address: The address used as source of the |
| | NS(ARO) is not a Link-Local address as prescribed by this | | | NS(ARO) is not a Link-Local address as prescribed by this |
| | document. | | | document. |
| | | | | |
| 8 | Registered Address topologically incorrect: The address | | 8 | Registered Address topologically incorrect: The address |
| | being registered is not usable on this link, e.g. it is | | | being registered is not usable on this link, e.g. it is |
| | not topologically correct | | | not topologically correct |
| | | | | |
| 9 | 6LBR Registry saturated: A new registration cannot be | | 9 | 6LBR Registry saturated: A new registration cannot be |
| | accepted because the 6LBR Registry is saturated. This | | | accepted because the 6LBR Registry is saturated. This |
| | code is used by 6LBRs instead of Status 2 when responding | | | code is used by 6LBRs instead of Status 2 when responding |
| | to a DAR/DAC exchange and passed on to the registering | | | to a DAR/DAC exchange and passed on to the Registering |
| | node by the 6LR. There is no point for the node to retry | | | Node by the 6LR. There is no point for the node to retry |
| | this registration immediately via another 6LR, since the | | | this registration immediately via another 6LR, since the |
| | problem is global to the network. The node may either | | | problem is global to the network. The node may either |
| | abandon that address, deregister other addresses first to | | | abandon that address, deregister other addresses first to |
| | make room, or keep the address in TENTATIVE state and | | | make room, or keep the address in TENTATIVE state and |
| | retry later. | | | retry later. |
+-------+-----------------------------------------------------------+ +-------+-----------------------------------------------------------+
Table 1: EARO Status Table 1: EARO Status
6.2. New 6LoWPAN capability Bits in the Capability Indication Option
This specification defines a number of capability bits in the CIO
that was introduced by RFC 7400 [RFC7400].
Support for this specification is indicated by setting the "E" flag
in a CIO option. Routers that are capable of acting as 6LR, 6LBR and
6BBR SHOULD set the L, B and P flags, respectively.
Those flags are not mutually exclusive and if a router is capable of
multiple roles, 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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|_______________________________________________________________|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: New capability Bits L, B, P, E in the CIO
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. Backward Compatibility
7.1. Discovering the capabilities of an ND peer 7.1. Discovering the capabilities of an ND peer
7.1.1. Using the E Flag in the CIO 7.1.1. Using the E Flag in the CIO
If the CIO is used in an ND message, then the "E" Flag MUST be set by If the CIO is used in an ND message, then the "E" Flag MUST be set by
the sending node if supports this specification. the sending node if supports this specification.
It is RECOMMENDED that a router that supports this specification It is RECOMMENDED that a router that supports this specification
indicates so with a CIO option, but this might not be practical if indicates so with a CIO option, but this might not be practical if
the link-layer MTU is too small. the link-layer MTU is too small.
If the registering node receives a CIO in a RA, then the setting of If the Registering Node receives a CIO in a RA, then the setting of
the E" Flag indicates whether or not this specification is supported. the E" Flag indicates whether or not this specification is supported.
7.1.2. Using the T Flag in the EARO 7.1.2. Using the T Flag in the EARO
One alternate way for a 6LN to discover the router's capabilities to 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 first register a Link Local address, placing the same address in the
Source and Target Address fields of the NS message, and setting 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 "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 based on EUI-64. For such address, DAD is not required and using the
SLLAO option in the NS is actually more amenable with existing ND SLLAO option in the NS is actually more amenable with existing ND
skipping to change at page 15, line 39 skipping to change at page 15, line 35
A node that supports this specification MUST always use an EARO as a 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 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 harmless since the "T" flag and TID field are reserved in RFC 6775
[RFC6775] are ignored by a legacy router. A router that supports [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 this specification answers to an ARO with an ARO and to an EARO with
an EARO. an EARO.
This specification changes the behavior of the peers in a This specification changes the behavior of the peers in a
registration flows. To enable backward compatibility, a node that registration flows. To enable backward compatibility, a node that
registers to a router that is not known to support this specification registers to a router that is not known to support this specification
MUST behave as prescribed by RFC 6775 [RFC6775]. Once the router is MUST behave as prescribed by RFC 6775. Once the router is known to
known to support this specification, the node MUST obey this support this specification, the node MUST obey this specification.
specification.
7.2. Legacy 6LoWPAN Node 7.2. Legacy 6LoWPAN Node
A legacy 6LN will use the registered address as source and will not A legacy 6LN will use the Registered Address as source and will not
use an EARO option. In order to be backward compatible, an updated use an EARO option. In order to be backward compatible, an updated
6LR needs to accept that registration if it is valid per the 6LR needs to accept that registration if it is valid per the RFC 6775
"Cryptographically Generated Addresses (CGA)" [RFC3972] [RFC6775] specification, and manage the binding cache accordingly.
specification, and manage the binding cache accordingly.
The main difference with RFC 3972 [RFC3972] is that DAR/DAC exchange The main difference with RFC 6775 is that DAR/DAC exchange for DAD
for DAD may be avoided for Link-Local addresses. Additionally, the may be avoided for Link-Local addresses. Additionally, the 6LR
6LR SHOULD use an EARO in the reply, and may use any of the Status SHOULD use an EARO in the reply, and may use any of the Status codes
codes defined in this specification. defined in this specification.
7.3. Legacy 6LoWPAN Router 7.3. Legacy 6LoWPAN Router
The first registration by a an updated 6LN is for a Link-Local The first registration by a an updated 6LN is for a Link-Local
address, using that Link-Local address as source. A legacy 6LN will address, using that Link-Local address as source. A legacy 6LN will
not makes a difference and accept -or reject- that registration as if not makes a difference and accept -or reject- that registration as if
the 6LN was a legacy node. the 6LN was a legacy node.
An updated 6LN will always use an EARO option in the registration NS An updated 6LN will always use an EARO option in the registration NS
message, whereas a legacy 6LN will always areply with an ARO option message, whereas a legacy 6LN will always areply with an ARO option
in the NA message. So from that first registration, the updated 6LN in the NA message. So from that first registration, the updated 6LN
can figure whether the 6LR supports this specification or not. can figure whether the 6LR supports this specification or not.
When facing a legacy 6LR, an updated 6LN may attempt to find an When facing a legacy 6LR, an updated 6LN may attempt to find an
alternate 6LR that is updated. In order to be backward compatible, alternate 6LR that is updated. In order to be backward compatible,
based on the discovery that a 6LR is legacy, the 6LN needs to based on the discovery that a 6LR is legacy, the 6LN needs to
fallback to legacy behavior and source the packet with the registered fallback to legacy behavior and source the packet with the Registered
address. Address.
The main difference is that the updated 6LN SHOULD use an EARO in the The main difference is that the updated 6LN SHOULD use an EARO in the
request regardless of the type of 6LN, legacy or updated request regardless of the type of 6LN, legacy or updated
7.4. Legacy 6LoWPAN Border Router 7.4. Legacy 6LoWPAN Border Router
With this specification, the DAR/DAC transports an EARO option as With this specification, the DAR/DAC transports an EARO option as
opposed to an ARO option. As described for the NS/NA exchange, opposed to an ARO option. As described for the NS/NA exchange,
devices that support this specification always use an EARO option and devices that support this specification always use an EARO option and
all the associated behavior. all the associated behavior.
skipping to change at page 16, line 50 skipping to change at page 16, line 48
prevent a rogue access, either by means of physical or IP security on prevent a rogue access, either by means of physical or IP security on
the Backbone Link and link layer cryptography on the LLN. This the Backbone Link and link layer cryptography on the LLN. This
specification also expects that the LLN MAC provides secure unicast specification also expects that the LLN MAC provides secure unicast
to/from the Backbone Router and secure Broadcast from the Backbone to/from the Backbone Router and secure Broadcast from the Backbone
Router in a way that prevents tempering with or replaying the RA Router in a way that prevents tempering with or replaying the RA
messages. messages.
This specification does not mandate any particular way for forming This specification does not mandate any particular way for forming
IPv6 addresses, but it recognizes that use of EUI-64 for forming the IPv6 addresses, but it recognizes that use of EUI-64 for forming the
Interface ID in the Link-Local address prevents the usage of "SEcure Interface ID in the Link-Local address prevents the usage of "SEcure
Neighbor Discovery (SEND)" [RFC3971] and CGA [RFC3972], and that of Neighbor Discovery (SEND)" [RFC3971] and "Cryptographically Generated
address privacy techniques. This specification RECOMMENDS the use of Addresses (CGA)" [RFC3972], and that of address privacy techniques,
additional protection against address theft such as provided by such as recommended in "Privacy Considerations for IPv6 Adaptation-
"Address Protected Neighbor Discovery for Low-power and Lossy Layer Mechanisms" [RFC8065]. This specification RECOMMENDS the use
Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the of privacy techniques, and that of additional protection against
OUID. 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.
As indicated in section Section 2, this protocol does not aim at As indicated in section Section 2, this protocol does not aim at
limiting the number of IPv6 addresses that a device can form, either. limiting the number of IPv6 addresses that a device can form, either.
A host should be able to register any address that is topologically A host should be able to register any address that is topologically
correct in the subnet(s) advertised by the 6LR/6LBR. correct in the subnet(s) advertised by the 6LR/6LBR.
On the other hand, the registration mechanism may be used by a rogue On the other hand, the registration mechanism may be used by a rogue
node to attack the 6LR or the 6LBR with a Denial-of-Service attack 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 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 or a 6LBR is saturated and cannot take any more registration, which
effectively denies the requesting a node the capability to use a new effectively denies the requesting a node the capability to use a new
address. In order to alleviate those concerns, Section 5.6 provides address. In order to alleviate those concerns, Section 4.6 provides
a number of recommendations that ensure that a stale registration is a number of recommendations that ensure that a stale registration is
removed as soon as possible from the 6LR and 6LBR. In particular, removed as soon as possible from the 6LR and 6LBR. In particular,
this specification recommends that: this specification recommends that:
o A node that ceases to use an address should attempt to deregister o A node that ceases to use an address should attempt to deregister
that address from all the 6LRs to which it is registered. The that address from all the 6LRs to which it is registered. The
flow is propagated to the 6LBR when needed, and a sequence number 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. is used to make sure that only the freshest command is acted upon.
o The nodes should be configured with a Registration Lifetime that o The nodes should be configured with a Registration Lifetime that
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addresses if such can be recognized, e.g. from the way the IID is 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 formed or because they are used over a much longer time span than
other (privacy, shorter-lived) addresses. other (privacy, shorter-lived) addresses.
o Administrators should take great care to deploy adequate numbers o Administrators should take great care to deploy adequate numbers
of 6LR to cover the needs of the nodes in their range, so as to of 6LR 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 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 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 in a network condition where it may become saturated, a particular
deployment should distribute the 6LBR functionality, for instance deployment should distribute the 6LBR functionality, for instance
by leveraging a high speed backbone and Backbone Routers to by leveraging a high speed Backbone and Backbone Routers to
aggregate multiple LLNs into a larger subnet. aggregate multiple LLNs into a larger subnet.
When the ownership of the OUID cannot be assessed, this specification When the ownership of the OUID cannot be assessed, this specification
limits the cases where the OUID and the TID are multicasted, and limits the cases where the OUID and the TID are multicasted, and
obfuscates them in responses to attempts to take over an address. 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 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 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, acting in these roles, so as to avoid threats such as black-holing,
or bombing attack whereby an impersonated 6LBR would destroy state in or bombing attack whereby an impersonated 6LBR would destroy state in
the network by using the "Removed" Status code. the network by using the "Removed" Status code.
9. IANA Considerations 9. IANA Considerations
IANA is requested to create a new subregistry for "ARO Flags" under IANA is requested to create a new subregistry for "ARO Flags" under
the "Internet Control Message Protocol version 6 (ICMPv6) the "Internet Control Message Protocol version 6 (ICMPv6)
Parameters". This specification defines 8 positions, bit 0 to bit 7, Parameters". This specification defines 8 positions, bit 0 to bit 7,
and assigns bit 7 for the "T" flag in Section 6.2. The policy is and assigns bit 7 for the "T" flag in Section 6.1. The policy is
"IETF Review" or "IESG Approval" [RFC5226]. The initial content of "IETF Review" or "IESG Approval" [RFC5226]. The initial content of
the registry is as shown in Table 2. the registry is as shown in Table 2.
New subregistry for ARO Flags under the "Internet Control Message New subregistry for ARO Flags under the "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" Protocol version 6 (ICMPv6) Parameters"
+------------+--------------+-----------+ +------------+--------------+-----------+
| ARO Status | Description | Document | | ARO Status | Description | Document |
+------------+--------------+-----------+ +------------+--------------+-----------+
| 0..6 | Unassigned | | | 0..6 | Unassigned | |
skipping to change at page 20, line 9 skipping to change at page 20, line 9
10. Acknowledgments 10. Acknowledgments
Kudos to Eric Levy-Abegnoli who designed the First Hop Security Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure at Cisco. infrastructure at Cisco.
11. References 11. References
11.1. Normative References 11.1. Normative References
[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-03 (work in progress), January 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>. 2006, <http://www.rfc-editor.org/info/rfc4291>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
skipping to change at page 21, line 18 skipping to change at page 21, line 18
Chakrabarti, S., Nordmark, E., Thubert, P., and M. Chakrabarti, S., Nordmark, E., Thubert, P., and M.
Wasserman, "IPv6 Neighbor Discovery Optimizations for Wasserman, "IPv6 Neighbor Discovery Optimizations for
Wired and Wireless Networks", draft-chakrabarti-nordmark- Wired and Wireless Networks", draft-chakrabarti-nordmark-
6man-efficient-nd-07 (work in progress), February 2015. 6man-efficient-nd-07 (work in progress), February 2015.
[I-D.delcarpio-6lo-wlanah] [I-D.delcarpio-6lo-wlanah]
Vega, L., Robles, I., and R. Morabito, "IPv6 over Vega, L., Robles, I., and R. Morabito, "IPv6 over
802.11ah", draft-delcarpio-6lo-wlanah-01 (work in 802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
progress), October 2015. 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-08 (work in progress), March 2017.
[I-D.ietf-6lo-ap-nd] [I-D.ietf-6lo-ap-nd]
Sarikaya, B., Thubert, P., and M. Sethi, "Address Sarikaya, B., Thubert, P., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-00 (work in progress), Networks", draft-ietf-6lo-ap-nd-00 (work in progress),
November 2016. November 2016.
[I-D.ietf-6lo-dect-ule] [I-D.ietf-6lo-backbone-router]
Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D. Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
Barthel, "Transmission of IPv6 Packets over DECT Ultra Low backbone-router-03 (work in progress), January 2017.
Energy", draft-ietf-6lo-dect-ule-09 (work in progress),
December 2016.
[I-D.ietf-6lo-nfc] [I-D.ietf-6lo-nfc]
Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi, Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
"Transmission of IPv6 Packets over Near Field "Transmission of IPv6 Packets over Near Field
Communication", draft-ietf-6lo-nfc-06 (work in progress), Communication", draft-ietf-6lo-nfc-06 (work in progress),
March 2017. March 2017.
[I-D.ietf-6tisch-architecture] [I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work
skipping to change at page 23, line 42 skipping to change at page 23, line 37
[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., [RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015, Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<http://www.rfc-editor.org/info/rfc7668>. <http://www.rfc-editor.org/info/rfc7668>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204, "Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016, RFC 7934, DOI 10.17487/RFC7934, July 2016,
<http://www.rfc-editor.org/info/rfc7934>. <http://www.rfc-editor.org/info/rfc7934>.
[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>.
[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>.
[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>.
11.3. External Informative References 11.3. External Informative References
[IEEEstd802154] [IEEEstd802154]
IEEE, "IEEE Standard for Low-Rate Wireless Networks", IEEE, "IEEE Standard for Low-Rate Wireless Networks",
IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875, IEEE Standard 802.15.4, DOI 10.1109/IEEESTD.2016.7460875,
<http://ieeexplore.ieee.org/document/7460875/>. <http://ieeexplore.ieee.org/document/7460875/>.
Appendix A. Applicability and Requirements Served Appendix A. Applicability and Requirements Served
This specification extends 6LoWPAN ND to sequence the registration This specification extends 6LoWPAN ND to sequence the registration
skipping to change at page 24, line 30 skipping to change at page 24, line 37
implement the 6TiSCH architecture and serves the requirements listed implement the 6TiSCH architecture and serves the requirements listed
in Appendix B.2. in Appendix B.2.
The term LLN is used loosely in this specification to cover multiple 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 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 Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so
as to address the requirements discussed in Appendix B.3 as to address the requirements discussed in Appendix B.3
This specification can be used by any wireless node to associate at 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 Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
services including proxy-ND operations over the backbone, effectively services including proxy-ND operations over the Backbone, effectively
providing a solution to the requirements expressed in Appendix B.4. providing a solution to the requirements expressed in Appendix B.4.
"Efficiency aware IPv6 Neighbor Discovery Optimizations" "Efficiency aware IPv6 Neighbor Discovery Optimizations"
[I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND [I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND
[RFC6775] can be extended to other types of links beyond IEEE Std. [RFC6775] can be extended to other types of links beyond IEEE Std.
802.15.4 for which it was defined. The registration technique is 802.15.4 for which it was defined. The registration technique is
beneficial when the Link-Layer technique used to carry IPv6 multicast beneficial when the Link-Layer technique used to carry IPv6 multicast
packets is not sufficiently efficient in terms of delivery ratio or packets is not sufficiently efficient in terms of delivery ratio or
energy consumption in the end devices, in particular to enable energy consumption in the end devices, in particular to enable
energy-constrained sleeping nodes. The value of such extension is energy-constrained sleeping nodes. The value of such extension is
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burden of supporting the Multicast Listener Discovery Version 2 burden of supporting the Multicast Listener Discovery Version 2
[RFC3810] (MLDv2) for IPv6. [RFC3810] (MLDv2) for IPv6.
B.3. Requirements Related to the Variety of Low-Power Link types 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 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 and in particular the capability to derive a unique Identifier from a
globally unique MAC-64 address. At this point, the 6lo Working Group globally unique MAC-64 address. At this point, the 6lo Working Group
is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique
to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token- to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token-
Passing [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field
[I-D.ietf-6lo-dect-ule], Near Field Communication [I-D.ietf-6lo-nfc], Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah
IEEE Std.802.11ah [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 [I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband
Narrowband Powerline Communication Networks Powerline Communication Networks
[I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R) [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R)
Low Energy [RFC7668]. Low Energy [RFC7668].
Related requirements are: Related requirements are:
Req3.1: The support of the registration mechanism SHOULD be extended 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 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 links for which an "IPv6 over foo" specification exists, as well as
Low-Power Wi-Fi. Low-Power Wi-Fi.
skipping to change at page 27, line 12 skipping to change at page 27, line 20
Req3.3: The Address Registration Option used in the ND registration Req3.3: The Address Registration Option used in the ND registration
SHOULD be extended to carry the relevant forms of unique Identifier. SHOULD be extended to carry the relevant forms of unique Identifier.
Req3.4: The Neighbour Discovery should specify the formation of a Req3.4: The Neighbour Discovery should specify the formation of a
site-local address that follows the security recommendations from site-local address that follows the security recommendations from
[RFC7217]. [RFC7217].
B.4. Requirements Related to Proxy Operations B.4. Requirements Related to Proxy Operations
Duty-cycled devices may not be able to answer themselves to a lookup 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 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 proxy. Additionally, the duty-cycled device may need to rely on the
6LBR to perform registration to the 6BBR. 6LBR to perform registration to the 6BBR.
The ND registration method SHOULD defend the addresses of duty-cycled The ND registration method SHOULD defend the addresses of duty-cycled
devices that are sleeping most of the time and not capable to defend devices that are sleeping most of the time and not capable to defend
their own Addresses. their own Addresses.
Related requirements are: Related requirements are:
Req4.1: The registration mechanism SHOULD enable a third party to Req4.1: The registration mechanism SHOULD enable a third party to
proxy register an Address on behalf of a 6LoWPAN node that may be proxy register an Address on behalf of a 6LoWPAN node that may be
sleeping or located deeper in an LLN mesh. sleeping or located deeper in an LLN mesh.
Req4.2: The registration mechanism SHOULD be applicable to a duty- Req4.2: The registration mechanism SHOULD be applicable to a duty-
cycled device regardless of the link type, and enable a 6BBR to cycled device regardless of the link type, and enable a 6BBR to
operate as a proxy to defend the registered Addresses on its behalf. operate as a proxy to defend the Registered Addresses on its behalf.
Req4.3: The registration mechanism SHOULD enable long sleep Req4.3: The registration mechanism SHOULD enable long sleep
durations, in the order of multiple days to a month. durations, in the order of multiple days to a month.
B.5. Requirements Related to Security B.5. Requirements Related to Security
In order to guarantee the operations of the 6LoWPAN ND flows, the 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 spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a
node successfully registers an address, 6LoWPAN ND should provide node successfully registers an address, 6LoWPAN ND should provide
energy-efficient means for the 6LBR to protect that ownership even energy-efficient means for the 6LBR to protect that ownership even
 End of changes. 61 change blocks. 
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