6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     cisco
Updates: 6775 (if approved)                                  E. Nordmark
Intended status: Standards Track                         Arista Networks
Expires: June 26, July 14, 2017                                    S. Chakrabarti
                                                       December 23, 2016
                                                        January 10, 2017

                        An Update to 6LoWPAN ND


   This specification updates 6LoWPAN Neighbor Discovery (RFC6775), to
   clarify the role of the protocol as a registration technique,
   simplify the registration operation in 6LoWPAN routers, and provide
   enhancements to the registration capabilities, in particular for the
   registration to a backbone router for proxy ND operations.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 29, July 14, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Transaction ID  . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Owner Unique ID . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  Extended Address Registration Option  . . . . . . . . . .   4
     3.2.   5
     3.4.  Registering the Target Address  . . . . . . . . . . . . .   5
     3.3.   6
     3.5.  Link-local Addresses and Registration . . . . . . . . . .   5   6
   4.  Applicability and Requirements Served . . . . . . . . . . . .   7   8
   5.  The Enhanced Address Registration Option (EARO) . . . . . . .   7   8
   6.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  11  12
     6.1.  Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . .  11  12
     6.2.  Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . .  11  12
     6.3.  Legacy 6LoWPAN Border Router  . . . . . . . . . . . . . .  12  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12  13
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13  14
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  13  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  14  15
     10.3.  External Informative References  . . . . . . . . . . . .  16  17
   Appendix A.  Requirements . . . . . . . . . . . . . . . . . . . .  17  18
     A.1.  Requirements Related to Mobility  . . . . . . . . . . . .  17  18
     A.2.  Requirements Related to Routing Protocols . . . . . . . .  17  18
     A.3.  Requirements Related to the Variety of Low-Power Link
           types . . . . . . . . . . . . . . . . . . . . . . . . . .  18  19
     A.4.  Requirements Related to Proxy Operations  . . . . . . . .  19  20
     A.5.  Requirements Related to Security  . . . . . . . . . . . .  20
     A.6.  Requirements Related to Scalability . . . . . . . . . . .  21  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21  22

1.  Introduction

   IPv6 Neighbor Discovery (ND) Optimization for IPv6 over Low-Power
   Wireless Personal Area Networks(6LoWPANs) [RFC6775] introduced a
   proactive registration mechanism to IPv6 ND services that is well
   suited to nodes belonging to a LLN.

   The scope of this draft is an IPv6 Low Power Lossy Network (LLN),
   which can be a simple star or a more complex mesh topology.  The LLN
   may be anchored at an IPv6 Backbone Router (6BBR).  The Backbone
   Routers interconnect the LLNs over a Backbone Link and emulate that
   the LLN nodes are present on the Backbone using proxy-ND operations.

   IPv6 Neighbor Discovery (ND) Optimization for IPv6 over Low-Power
   Wireless Personal Area Networks(6LoWPANs) [RFC6775] introduced a
   proactive registration mechanism to IPv6 ND services for nodes
   belonging to a LLN.

   This specification modifies and extends the behaviour and protocol
   elements of [RFC6775] to enable additional capabilities, in
   particular the registration to a 6BBR for proxy ND operations

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   Readers are expected to be familiar with all the terms and concepts
   that are discussed in "Neighbor Discovery for IP version 6"
   [RFC4861], "IPv6 Stateless Address Autoconfiguration" [RFC4862],
   "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
   Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
   Neighbor Discovery Optimization for Low-power and Lossy Networks
   [RFC6775] and "Multi-link Subnet Support in IPv6"

   Additionally, this document uses terminology from "Terms Used in
   Routing for Low-Power and Lossy Networks" [RFC7102] and
   [I-D.ietf-6tisch-terminology], as well as this additional

   Backbone  This is an IPv6 transit link that interconnects 2 or more
         Backbone Routers.  It is expected to be deployed as a high
         speed backbone in order to federate a potentially large set of
         LLNS.  Also referred to as a LLN backbone or Backbone network.

   Backbone Router  An IPv6 router that federates the LLN using a
         Backbone link as a backbone.  A 6BBR acts as a 6LoWPAN Border
         Routers (6LBR) and an Energy Aware Default Router (NEAR).

   Extended LLN  This is the aggregation of multiple LLNs as defined in
         [RFC4919], interconnected by a Backbone Link via Backbone
         Routers, and forming a single IPv6 MultiLink Subnet.

   Registration  The process during which a wireless Node registers its
         address(es) with the Border Router so the 6BBR can proxy ND for
         it over the backbone.

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

   Registered Node  The node for which the registration is performed,
         which owns the fields in the EARO option.

   Registering Node  The node that performs the registration to the
         6BBR, either for one of its own addresses, in which case it is
         Registered Node and indicates its own MAC Address as SLLA in
         the NS(ARO), or on behalf of a Registered Node that is
         reachable over a LLN mesh.  In the latter case, if the
         Registered Node is reachable from the 6BBR over a Mesh-Under
         mesh, the Registering Node indicates the MAC Address of the
         Registered Node as SLLA in the NS(ARO).  Otherwise, it is
         expected that the Registered Device is reachable over a Route-
         Over mesh from the Registering Node, in which case the SLLA in
         the NS(ARO) is that of the Registering Node, which causes it to
         attract the packets from the 6BBR to the Registered Node and
         route them over the LLN.

   Registered Address  The address owned by owned by the Registered Node node
         that is being registered.

3.  Updating RFC 6775

   The support of this specification is signaled in Router Advertisement
   (RA) messages by 6LoWPAN Router (6LR) (how: tbd).  Support for this
   specification can also be inferred from the update of the ARO option
   in the ND exchanges.

   A Registering Node that supports this specification will favor
   registering to a 6LR that indicates support for this specification
   over that of [RFC6775].

3.1.  Transaction ID

   The specification expects that the Registered Node can provide a
   sequence number called Transaction ID (TID) that is incremented with
   each re-registration.  The TID essentially obeys the same rules as
   the Path Sequence field in the Transit Information Option (TIO) found
   in RPL's Destination Advertisement Object (DAO).  This way, the LLN
   node can use the same counter for ND and RPL, and a 6LBR acting as
   RPL root may easily maintain the registration on behalf of a RPL node
   deep inside the mesh by simply using the RPL TIO Path Sequence as TID
   for EARO.

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

   If the TIDs are different, the resolution inherited from RPL sorts
   out the most recent registration and other ones are removed.  The
   operation for computing and comparing the Path Sequence is detailed
   in section 7 of [RFC6550] and applies to the TID in the exact same

3.2.  Owner Unique ID

   The Owner Unique ID (OUID) enables to differentiate a real duplicate
   address registration from a double registration or a movement.  An ND
   message from the 6BBR over the backbone that is proxied on behalf of
   a Registered Node must carry the most recent EARO option seen for
   that node.  A NS/NA with an EARO and a NS/NA without a EARO thus
   represent different nodes and if they relate to a same target then
   they reflect an address duplication.  The Owner Unique ID can be as
   simple as a EUI-64 burn-in address, if duplicate EUI-64 addresses are

   Alternatively, the Registered Node node unique ID can be a cryptographic string that is being registered.

3.  Updating RFC 6775

   The support of this specification is signaled in Router Advertisement
   (RA) messages by 6LoWPAN Router (6LR) (how: tbd).  Support for this
   specification can also
   can be inferred from used to prove the update ownership of the ARO option 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 ND exchanges

   .  A Registering Node node stores the unique Id
   or the keys used to generate that supports this specification ID in persistent memory.
   Otherwise, it will favor
   registering be prevented to re-register after a 6LR that indicates support for this specification
   over reboot that
   would cause a loss of [RFC6775].

3.1. memory until the Backbone Router times out the

3.3.  Extended Address Registration Option

   This specification extends the Address Registration Option (ARO) used
   for the process of address registration.  The new ARO is referred to
   as Extended ARO (EARO), and its semantics are modified as follows:

   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 [RFC6775].  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 a 6BBR.  This also limits the use of an
   address as source address before it is registered and the associated
   Duplicate Address Detection (DAD) is complete.

   The Unique ID in the EARO option does no more have to be a MAC
   address.  A new TLV format is introduced and a IANA registry is
   created for the type (TBD).  This enables in particular the 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 protect
   the state associated to the node.

   The specification introduces a Transaction ID (TID) field in the
   EARO.  The TID MUST be provided by a 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 supports this


3.4.  Registering the Target Address

   One of the requirements that this specification serves is the
   capability by a router such as a RPL root to proxy-register an
   address to a 6BBR on behalf of a 6LN, as discussed in Appendix A.4.
   In order to serve that requirement, this specification changes the
   behaviour 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.

   With this convention, a TLLA option would indicate 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 Registering Node is the one that has reachability with the
   6LR, and is the one expecting packets for the 6LN, it makes sense to
   maintain compatibility with [RFC6775], and it is REQUIRED that an
   SLLA Option is always placed in a registration NS(EARO) message.


3.5.  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 [RFC6775], this specification only requires that a link-
   local address is unique from the perspective of the peering nodes.
   This simplifies the Duplicate Address Detection (DAD) for link-local
   addresses, and there is no DAR/DAC exchange between the 6LR and a
   6LBR for link-local addresses.

   Additionally, [RFC6775] requires that a 6LoWPAN Node (6LN) uses 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 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 a same link-local
   address but different link-layer addresses.  In that case, a 6LN may
   only interact with one of the 6LR so as to avoid confusion in the 6LN
   neighbor cache.

   The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR),
   which is based on a Duplicate Address Request (DAR) / Duplicate
   Address Confirmation (DAC) exchange as described in [RFC6775], 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
   registrered, 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

   Since there is no DAR/DAC 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 [RFC6775].

   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
   via that 6LR.  As opposed to a node that complies to [RFC6775], a
   Registering Node registering a GUA does not use that GUA as Source
   Address for the registration to a 6LR that conforms this
   specification.  The DAR/DAC exchange MUST take place for non-link-
   local addresses as prescribed by [RFC6775].

4.  Applicability and Requirements Served

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

   In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
   [IEEEstd802154], the 6TiSCH architecture
   [I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could
   connect to the Internet via a RPL mesh Network, but this requires
   additions to the 6LOWPAN ND protocol to support mobility and
   reachability in a secured and manageable environment.  This
   specification details the new operations that are required to
   implement the 6TiSCH architecture and serves the requirements listed
   in Appendix A.2.

   The term LLN is used loosely in this specification to cover multiple
   types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low
   Energy, IEEE802.11AH IEEE std 802.11AH and IEEE802.15.4 IEEE std 802.15.4 wireless meshes, so
   as to address the requirements discussed in Appendix A.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 A.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 IEEE802.15.4 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-
   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 A.6.

5.  The Enhanced Address Registration Option (EARO)

   With the ARO option defined in 6LoWPAN ND [RFC6775], the address
   being registered and its owner can be uniquely identified and matched
   with the Binding Table entries of each Backbone Router.

   The Enhanced Address Registration Option (EARO) is intended to be
   used as a replacement to the ARO option within Neighbor Discovery NS
   and NA messages between a LLN node and its 6LoWPAN Router (6LR), as
   well as in Duplicate Address Request (DAR) and the Duplicate Address
   Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes
   such as 6TiSCH networks.

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

   The EARO extends the ARO and is recognized by the setting of the TID
   bit.  A node that supports this specification MUST always use an EARO
   as a replacement to an ARO in its registration to a router.  This is
   harmless since the TID bit and fields are reserved in [RFC6775] are
   ignored by a legacy router.  A router that supports this
   specification answers to an ARO with an ARO and to an EARO with an

   This specification changes the behavior of the peers in a
   registration flows.  To enable backward compatibility, a node that
   registers to a router that is not known to support this specification
   MUST behave as prescribed by [RFC6775].  Once the router is known to
   support this specification, the node MUST obey this specification.

   When using the EARO option, the address being registered is found in
   the Target Address field of the NS and NA messages.  This differs
   from 6LoWPAN ND [RFC6775] which specifies that the address being
   registered is the source of the NS.

   The reason for this change is to enable proxy-registrations on behalf
   of other nodes in Route-Over meshes, for instance to enable that a
   RPL root registers addresses on behalf LLN nodes that are deeper in a
   6TiSCH mesh.  In that case, the Registering Node MUST indicate its
   own address as source of the ND message and its MAC address in the
   Source Link-Layer Address Option (SLLAO), since it still expects to
   get the packets and route them down the mesh.  But the Registered
   Address belongs to another node, the Registered Node, and that
   address is indicated in the Target Address field of the NS message.

   One way of achieving all the above is for a node to first register an
   address that it owns in order to validate that the router supports
   this specification, placing the same address in the Source and Target
   Address fields of the NS message.  The node may for instance register
   an address that is based on EUI-64.  For such address, DAD is not
   required and using the SLLAO option in the NS is actually more
   amenable with older ND specifications such as ODAD [RFC4429].

   Once that first registration is complete, the node knows from the
   setting of the TID in the response whether the router supports this
   specification.  If this is verified, the node may register other
   addresses that it owns, or proxy-register addresses on behalf some
   another node, indicating those addresses being registered in the
   Target Address field of the NS messages, while using one of its own,
   already registered, addresses as source.

   The format of the EARO option is as follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     |     Type      |   Length = 2  |    Status     |   Reserved    |
     |   Reserved  |T|     TID       |     Registration Lifetime     |
     |                                                               |
     +         Owner Unique ID   (EUI-64 or equivalent)              +
     |                                                               |

                              Figure 1: EARO

   Option Fields


   Length:  2


   | Value | Description                                               |
   |  0..2 | See [RFC6775].  Note that a Status of 1 "Duplicate        |
   |       | Address" applies to the Registered Address. If the Source |
   |       | Address conflicts with an existing registration,          |
   |       | "Duplicate Source Address" should be used instead         |
   |       |                                                           |
   |   3   | Moved: The registration fails because it is not the       |
   |       | freshest                                                  |
   |       |                                                           |
   |   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: The registering node is challenged for   |
   |       | owning the registered address or for being an acceptable  |
   |       | proxy for the registration                                |
   |       |                                                           |
   |   6   | Duplicate Source Address: The address used as source of   |
   |       | the NS(ARO) conflicts with an existing registration.      |
   |       |                                                           |
   |   7   | Administrative Rejection: The address being registered is |
   |       | reserved for another use by an administrative decision    |
   |       | (e.g. placed in a DHCPv6 pool); The Registering Node is   |
   |       | requested to form a different address and retry           |
   |       |                                                           |
   |   8   | Invalid Registered Address: The address being registered  |
   |       | is not usable on this link, e.g. it is not topologically  |
   |       | correct                                                   |
   |       |                                                           |
   |   9   | Invalid Source Address: The address used as source of the |
   |       | NS(ARO) is not usable on this  link, e.g. it is not       |
   |       | topologically correct                                     |

                                  Table 1

   Reserved:  This field is unused.  It MUST be initialized to zero by
      the sender and MUST be ignored by the receiver.

   T: One bit flag.  Set if the next octet is a used as a TID.

   TID:  1-byte integer; a transaction id that is maintained by the node
      and incremented with each transaction.  it is recommended that the
      node maintains the TID in a persistent storage.

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

   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.

   New status values are introduced, their values to be confirmed by

   Moved:  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

   Removed:  This status is expected in asynchronous messages from a
      registrar (6LR, 6LBR, 6BBR) to indicate that the registration
      state is removed, for instance due to time out of a lifetime, or a
      movement.  It is used for instance by a 6BBR in a NA(ARO) message
      to indicate that the ownership of the proxy state on the backbone
      was transfered to another 6BBR, which is 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.  Backward Compatibility

6.1.  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 updated
   6LR needs to accept that registration if it is valid per [RFC3972],
   and manage the binding cache accordingly.

   The main difference with [RFC3972] is that DAR/DAC exchange for DAD
   may be avoided for link-local addresses.  Additionally, the 6LR
   SHOULD use an EARO in the reply, and may use all the status codes
   defined in this specification.

6.2.  Legacy 6LoWPAN Router

   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
   not makes 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 6LN will always areply 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 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 that a 6LR is legacy, the 6LN needs to
   fallback to legacy behaviour and source the packet with the
   registrered address.

   The main difference is that the updated 6LN SHOULD use an EARO in the
   request regardless of the type of 6LN, legacy or updated

6.3.  Legacy 6LoWPAN Border Router

   With this specification, the DAR/DAC transports an EARO option as
   opposed to an ARO option.  As described for the NS/NA exchange,
   devices that support this specification always use an EARO option and
   all the associated behaviour.

7.  Security Considerations

   This specification expects that the link layer is sufficiently
   protected, either by means of physical or IP security for the
   Backbone Link or MAC sublayer cryptography.  In particular, it is
   expected that the LLN MAC provides secure unicast to/from the
   Backbone Router and secure Broadcast from the Backbone Router in a
   way that prevents tempering with or replaying the RA messages.

   The use of EUI-64 for forming the Interface ID in the link-local
   address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and
   address privacy techniques.  This specification RECOMMENDS the use of
   additional protection against address theft such as provided by
   [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the OUID.

   When the ownership of the OUID cannot be assessed, this specification
   limits the cases where the OUID and the TID are multicasted, and
   obfuscates them in responses to attempts to take over an address.

   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.

8.  IANA Considerations

   This document requires the following additions:

            Address Registration Option Status Values Registry

                   | Status | Description              |
                   |   3    | Moved                    |
                   |        |                          |
                   |   4    | Removed                  |
                   |        |                          |
                   |   5    | Proof requested          |
                   |        |                          |
                   |   6    | Invalid Source Address   |
                   |        |                          |
                   |   7    | Administrative Rejection |

            IANA is required to change the registry accordingly

                      Table 2: New ARO Status values

9.  Acknowledgments

   Kudos to Eric Levy-Abegnoli who designed the First Hop Security
   infrastructure at Cisco.

10.  References

10.1.  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,

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
              for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,

   [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,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [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,

   [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,

10.2.  Informative References

              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.

              Vega, L., Robles, I., and R. Morabito, "IPv6 over
              802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
              progress), October 2015.

              Lynn, K., Martocci, J., Neilson, C., and S. Donaldson,
              "Transmission of IPv6 over MS/TP Networks", draft-ietf-
              6lo-6lobac-06 (work in progress), June October 2016.

              Sarikaya, B., Thubert, P., and M. Sethi, "Address
              Protected Neighbor Discovery for Low-power and Lossy
              Networks", draft-ietf-6lo-ap-nd-00 (work in progress),
              November 2016.

              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-02 (work in progress), September 2016.

              Mariager, P., Petersen, J., Shelby, Z., Logt, M., and D.
              Barthel, "Transmission of IPv6 Packets over DECT Ultra Low
              Energy", draft-ietf-6lo-dect-ule-07 draft-ietf-6lo-dect-ule-09 (work in progress),
              December 2016.

              Choi, Y., Youn, J., and Y. Hong, "Transmission of IPv6
              Packets over Near Field Communication", draft-ietf-6lo-
              nfc-05 (work in progress), October 2016.

              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 (work
              in progress), June 2016.

              Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
              "Terminology in IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-ietf-6tisch-terminology-07 draft-ietf-6tisch-terminology-08 (work in
              progress), March December 2016.

              Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
              S. Aldrin, "Multicast using Bit Index Explicit
              Replication", draft-ietf-bier-architecture-04 draft-ietf-bier-architecture-05 (work in
              progress), July October 2016.

              Thaler, D. and C. Huitema, "Multi-link Subnet Support in
              IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
              progress), July 2002.

              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.

              Sethi, M., Thubert, P., and B. Sarikaya, "Address
              Protected Neighbor Discovery for Low-power

   [RFC3610]  Whiting, D., Housley, R., and Lossy
              Networks", draft-sarikaya-6lo-ap-nd-04 (work in progress),
              August 2016. N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
              2003, <http://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,

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,

   [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,

   [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,

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <http://www.rfc-editor.org/info/rfc7102>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,

   [RFC7428]  Brandt, A. and J. Buron, "Transmission of IPv6 Packets
              over ITU-T G.9959 Networks", RFC 7428,
              DOI 10.17487/RFC7428, February 2015,

   [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,

10.3.  External Informative References

              IEEE standard for Information Technology, "IEEE Standard
              for Information technology-- Telecommunications and
              information exchange between systems Local and
              metropolitan area networks-- Specific requirements Part
              11: Wireless LAN Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications".

              IEEE standard for Information Technology, "IEEE Standard
              for Information Technology - Telecommunications and
              Information Exchange Between Systems - Local and
              Metropolitan Area Networks - Specific Requirements. - Part
              15.1: Wireless Medium Access Control (MAC) and Physical
              Layer (PHY) Specifications for Wireless Personal Area
              Networks (WPANs)".


              IEEE standard for Information Technology, "IEEE Standard
              for Local and metropolitan area networks-- Part 15.4: Low-
              Rate Wireless Personal Area Networks (LR-WPANs)".

Appendix A.  Requirements

   This section lists requirements that were discussed at 6lo for an
   update to 6LoWPAN ND.  This specification meets most of them, but
   those listed in Appendix A.5 which are deferred to a different
   specification such as [I-D.sarikaya-6lo-ap-nd]. [I-D.ietf-6lo-ap-nd].

A.1.  Requirements Related to Mobility

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

A.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

   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.

A.3.  Requirements Related to the Variety of Low-Power Link types

   6LoWPAN ND [RFC6775] was defined with a focus on IEEE802.15.4 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 [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy
   [I-D.ietf-6lo-dect-ule], 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-
   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

A.4.  Requirements Related to Proxy Operations

   Duty-cycled devices may not be able to answer themselves to a lookup
   from a node that uses classical ND on a backbone and may need a
   proxy.  Additionally, the duty-cycled device may need to rely on the
   6LBR to perform registration to the 6BBR.

   The ND registration method SHOULD defend the addresses of duty-cycled
   devices that are sleeping most of the time and not capable to defend
   their own Addresses.

   Related requirements are:

   Req4.1: The registration mechanism SHOULD enable a third party to
   proxy register an Address on behalf of a 6LoWPAN node that may be
   sleeping or located deeper in an LLN mesh.

   Req4.2: The registration mechanism SHOULD be applicable to a duty-
   cycled device regardless of the link type, and enable a 6BBR to
   operate as a proxy to defend the registered Addresses on its behalf.

   Req4.3: The registration mechanism SHOULD enable long sleep
   durations, in the order of multiple days to a month.

A.5.  Requirements Related to Security

   In order to guarantee the operations of the 6LoWPAN ND flows, the
   spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided.  Once a
   node successfully registers an address, 6LoWPAN ND should provide
   energy-efficient means for the 6LBR to protect that ownership even
   when the node that registered the address is sleeping.

   In particular, the 6LR and the 6LBR then should be able to verify
   whether a subsequent registration for a given Address comes from the
   original node.

   In a LLN it makes sense to base security on layer-2 security.  During
   bootstrap of the LLN, nodes join the network after authorization by a
   Joining Assistant (JA) or a Commissioning Tool (CT).  After joining
   nodes communicate with each other via secured links.  The keys for
   the layer-2 security are distributed by the JA/CT.  The JA/CT can be
   part of the LLN or be outside the LLN.  In both cases it is needed
   that packets are routed between JA/CT and the joining node.

   Related requirements are:

   Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR, 6LBR and 6BBR to authenticate and authorize one another for
   their respective roles, as well as with the 6LoWPAN Node for the role
   of 6LR.

   Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR and the 6LBR to validate new registration of authorized
   nodes.  Joining of unauthorized nodes MUST be impossible.

   Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet
   sizes.  In particular, the NS, NA, DAR and DAC messages for a re-
   registration flow SHOULD NOT exceed 80 octets so as to fit in a
   secured IEEE802.15.4 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

   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

   Req5.8: Routing of packets should continue when links pass from the
   unsecured to the secured state.

   Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR and the 6LBR to validate whether a new registration for a
   given address corresponds to the same 6LoWPAN Node that registered it
   initially, and, if not, determine the rightful owner, and deny or
   clean-up the registration that is duplicate.

A.6.  Requirements Related to Scalability

   Use cases from Automatic Meter Reading (AMR, collection tree
   operations) and Advanced Metering Infrastructure (AMI, bi-directional
   communication to the meters) indicate the needs for a large number of
   LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected
   to the 6LBR over a large number of LLN hops (e.g. 15).

   Related requirements are:

   Req6.1: The registration mechanism SHOULD enable a single 6LBR to
   register multiple thousands of devices.

   Req6.2: The timing of the registration operation should allow for a
   large latency such as found in LLNs with ten and more hops.

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   MOUGINS - Sophia Antipolis  06254

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

   Erik Nordmark
   Arista Networks
   Santa Clara, CA

   Email: nordmark@arista.com

   Samita Chakrabarti
   San Jose, CA

   Email: samita.chakrabarti@ericsson.com samitac.ietf@gmail.com