6Lo                                                      P. Thubert, Ed.
Internet-Draft                                                     cisco
Intended status: Standards Track                         August 22, 2014
Expires: February 21, 2015

                Requirements for an update to 6LoWPAN ND


   Work presented at the ROLL, 6lo, 6TiSCH and 6MAN Working Groups
   suggest that enhancements to the 6LoWPAN ND mechanism are now needed.
   This document elaborates on those requirements and suggests
   approaches to serve them.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  RPL Leaf Support in 6LoWPAN ND . . . . . . . . . . . . . .  5

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     3.2.  registration Failures Due to Movement  . . . . . . . . . .  6
     3.3.  Proxy registration . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Target Registration  . . . . . . . . . . . . . . . . . . .  6
     3.5.  RPL root vs. 6LBR  . . . . . . . . . . . . . . . . . . . .  7
     3.6.  Securing the Registration  . . . . . . . . . . . . . . . .  7
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Requirements Related to Mobility . . . . . . . . . . . . .  8
     4.2.  Requirements Related to Routing Protocols  . . . . . . . .  9
     4.3.  Requirements Related to the Variety of Low-Power Link types 9
     4.4.  Requirements Related to Proxy Operations . . . . . . . . . 10
     4.5.  Requirements Related to Security . . . . . . . . . . . . . 10
     4.6.  Requirements Related to Low-Power devices  . . . . . . . . 11
   5.  Suggested Changes to Protocol Elements . . . . . . . . . . . . 11
     5.1.  ND Neighbor Solicitation (NS)  . . . . . . . . . . . . . . 11
     5.2.  ND Router Advertisement (RA) . . . . . . . . . . . . . . . 12
     5.3.  RPL DODAG Information Object (DIO) . . . . . . . . . . . . 12
     5.4.  ND Enhanced Address Registration Option (EARO) . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.  Introduction

   A number of use cases, including the Industrial Internet, require a
   large scale deployment of sensors that can not be realized with wires
   and is only feasible over wireless Low power and Lossy Network (LLN)
   technologies.  When simpler hub-and-spoke topologies are not
   sufficient for the expected throughput and density, mesh networks
   must be deployed, which implies the concepts of hosts and routers,
   whether operated at Layer-2 or Layer-3.

   The IETF has designed the LLN host-to-router and router-to-router
   protocol that supports address assignment and the router-to-router
   protocol that supports reachability across Route-Over LLNs in
   different Areas.  It was clear for both efforts that the scalability
   requirements could only be met with IPv6 [RFC2460], and there is no
   fundamental contradiction between those protocols to that regard.

   While DHCPv6 is still a viable option in LLNs, the new IETF standard
   that supports address assignment specifically for LLNs is 6LoWPAN ND,
   the Neighbor Discovery Optimization for Low-power and Lossy Networks
   [RFC6775].  6LoWPAN ND was designed as a stand-alone mechanism
   separately from its IETF routing counterpart, the IPv6 Routing
   Protocol for Low power and  Lossy Networks [RFC6550] (RPL), and the
   interaction between the 2 protocols was not defined.

   The 6TiSCH WG is now considering an architecture [I-D.ietf-6tisch-
   architecture] whereby a 6LowPAN ND host could connect to the Internet
   via a RPL Network, but this requires additions to the protocol to
   support mobility and reachability in a secured and manageable

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   At the same time, new work at 6MAN on Efficiency aware IPv6 Neighbor
   Discovery Optimizations [I-D.chakrabarti-nordmark-6man-efficient-nd]
   suggests that 6LoWPAN ND can be extended to other types of networks
   on top of the Low power and Lossy Networks (LLNs) for which it was
   already defined.  The value of such extension is especially apparent
   in the case of mobile wireless devices, to reduce the multicast
   operations that are related to classical ND ([RFC4861], [RFC4862])
   and plague the wireless medium.  In this context also, there is a
   need for additions to the protocol.

   The Optimistic Duplicate Address Detection [RFC4429] (ODAD)
   specification details how an address can be used before a Duplicate
   Address Detection (DAD) is complete, and insists that an address that
   is TENTATIVE should not be associated to a Source Link-Layer Address
   Option in a Neighbor Solicitation message.  As we expect the 6LoWPAN
   ND protocol for a more general use, it can make sense to keep
   respecting that rule, which is another change to the specification.

   This document suggests a limited evolution to [RFC6775] so as to
   allow operation of a 6LoWPAN ND node as a leaf in a RPL network.  It
   also suggests a more generalized use of the information in the ARO
   option outside of the strict LLN domain, for instance over a
   converged backbone.

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 "Transmission of IPv6 Packets over IEEE 802.15.4
   Networks" [RFC4944].

   Additionally, this document uses terminology from 6TiSCH [I-D.ietf-
   6tisch-terminology] and ROLL [RFC7102].

3.  Overview

   The 6TiSCH architecture  [I-D.ietf-6tisch-architecture] expects that
   a 6LoWPAN device can connect as a leaf to a RPL network, where the
   leaf support is the minimal functionality to connect as a host to a
   RPL network without the need to participate to the full routing
   protocol.  The support of leaf can be implemented as a minor

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   increment to 6LoWPAN ND, with the additional capability to carry a
   sequence number that is used to track the movements of the device,
   and optionally some information about the RPL topology that this
   device will join.

   The scope of the 6TiSCH Architecture is a Backbone Link that
   federates multiple LLNs as a single IPv6 Multi-Link Subnet.  Each LLN
   in the subnet is anchored at a Backbone Router (6BBR).  The Backbone
   Routers interconnect the LLNs over the Backbone Link and emulate that
   the LLN nodes are present on the Backbone by proxy-ND operations.  An
   LLN node can move freely from an LLN Route-Over mesh anchored at a
   Backbone Router to another anchored at a same or a different Backbone
   Router inside the Multi-Link Subnet and conserve its addresses.

                  |          Plant Network
               |     | Gateway
               |     |
                  |    Backbone Link (with VLANs)
            |                    |                  |
         +-----+             +-----+             +-----+
         |     | Backbone    |     | Backbone    |     | Backbone
         |     | router      |     | router      |     | router
         +-----+             +-----+             +-----+
           | |                | | |                 |
           0 0                0 0 0         (6LBR == RPL root)
        o o   o  o       o o   o  o  o         o  o  o  o o
       o  o o  o o       o   o  o  o  o     (6LR == RPL router)
       o   o  o  o          o    o  o             z
       o   o o               o  o                  z
              RPL Instances               (6LoWPAN Host == RPL leaf)

   The root of the RPL topology is logically separated from the 6BBR
   that is used to connect the RPL topology to the backbone.  The RPL
   root can use Efficient ND as the interface to register an LLN node in
   its topology to the 6BBR for whatever operation the 6BBR performs,
   such as ND proxy operations, or injection in a routing protocol.  It
   results that, as illustrated in Figure 2, the periodic signaling
   could start at the leaf node with 6LoWPAN ND, then would be carried
   over RPL to the RPL root, and then with Efficient-ND to the 6BBR.

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   Efficient ND being an adaptation of 6LoWPAN ND, it makes sense to
   keep those two homogeneous in the way they use the source and the
   target addresses in the Neighbor Solicitation (NS) messages for
   registration, as well as in the options that they use for that

    6LoWPAN Node        6LR             6LBR            6BBR
     (RPL leaf)       (router)         (root)
         |               |               |               |
         |  6LoWPAN ND   |6LoWPAN ND+RPL | Efficient ND  | IPv6 ND
         |   LLN link    |Route-Over mesh|  IPv6 link    | Backbone
         |               |               |               |
         |  NS(ARO)      |               |               |
         |-------------->|               |               |
         | 6LoWPAN ND    | DAR (then DAO)|               |
         |               |-------------->|               |
         |               |               |  NS(ARO)      |
         |               |               |-------------->|
         |               |               |               | DAD
         |               |               |               |------>
         |               |               |               |
         |               |               |  NA(ARO)      |
         |               |               |<--------------|
         |               | DAC           |               |
         |               |<--------------|               |
         |  NA(ARO)      |               |               |
         |<--------------|               |               |

   As the network builds up, a node should start as a leaf to join the
   RPL network, and may later turn into both a RPL-capable router and a
   6LR, so as to accept leaf nodes to recursively join the network.

3.1.  RPL Leaf Support in 6LoWPAN ND

   RPL needs a set of information in order to advertise a leaf node
   through a DAO message and establish reachability.

   At the bare minimum the leaf device must provide a sequence number
   that matches the RPL specification in section 7.  [I-D.chakrabarti-
   nordmark-6man-efficient-nd] section "4.1.  Address Registration
   Option" (ARO) already incorporates that addition with a new field in
   the option called the Transaction ID.

   If for some reason the node is aware of RPL topologies, then
   providing the RPL InstanceID for the instances to which the node
   wishes to participate would be a welcome addition.  In the absence of
   such information, the RPL router must infer the proper instanceID
   from external rules and policies.

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   On the backbone, the InstanceID is expected to be mapped onto a
   VLANID. Neither WiFi nor Efficient ND do provide a mapping to
   VLANIDs, and it is unclear, when a wireless node attaches to a
   backbone where VLANs are defined, which VLAN the wireless device
   attaches to.  Considering that a VLAN is effectively the IP link on
   the backbone, adding the InstanceID to both specifications could be a
   welcome addition.

3.2.  registration Failures Due to Movement

   Registration to the 6LBR through DAR/DAC messages [RFC6775] may
   percolate slowly through an LLN mesh, and it might happen that in the
   meantime, the 6LoWPAN node moves and registers somewhere else.  Both
   RPL and 6LoWPAN ND lack the capability to indicate that the same node
   is registered elsewhere, so as to invalidate states down the
   deprecated path.

   In its current expression and functionality, 6LoWPAN ND considers
   that the registration is used for the purpose of DAD only as opposed
   to that of achieving reachability, and as long as the same node
   registers the IPv6 address, the protocol is functional.  In order to
   act as a RPL leaf registration protocol and achieve reachability, the
   device must use the same TID for all its concurrent registrations,
   and registrations with a past TID should be declined.  The state for
   an obsolete registration in the 6LR, as well as the RPL routers on
   the way, should be invalidated.  This can only be achieved with the
   addition of a new Status in the DAC message, and a new error/clean-up
   flow in RPL.

3.3.  Proxy registration

   The 6BBR provides the capability to defend an address that is owned
   by a 6LoWPAN Node, and attract packets to that address, whether it is
   done by proxying ND over a MultiLink Subnet, redistributing the
   address in a routing protocol or advertising it through an alternate
   proxy registration such as the Locator/ID Separation Protocol
   [RFC6830] (LISP) or Mobility Support in IPv6 [RFC6275] (MIPv6). In a
   LLN, it makes sense to piggyback the request to proxy/defend an
   address with its registration.

3.4.  Target Registration

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   In their current incarnations, both 6LoWPAN ND and Efficient ND
   expect that the address being registered is the source of the NS(ARO)
   message and thus impose that a Source Link-Layer Address (SLLA)
   option be present in the message.  In a mesh scenario where the 6LBR
   is physically separated from the 6LoWPAN Node, the 6LBR does not own
   the address being registered.  This suggests that [I-D.chakrabarti-
   nordmark-6man-efficient-nd] should evolve to register the Target of
   the NS message as opposed to the Source Address.  From another
   perspective, it may happen, in the use case of a Star topology, that
   the 6LR, 6LBR and 6BBR are effectively collapsed and should support
   6LoWPAN ND clients.  The convergence of efficient ND and 6LoWPAN ND
   into a single protocol is thus highly desirable.

   In any case, as long as the DAD process is not complete for the
   address used as source of the packet, it is against the current
   practice to advertise the SLLA, since this may corrupt the ND cache
   of the destination node, as discussed in the Optimistic DAD
   specification [RFC4429] with regards to the TENTATIVE state.

   This may look like a chicken and an egg problem, but in fact 6LoWPAN
   ND acknowledges that the Link-Local Address that is based on an
   EUI-64 address of a LLN node may be autoconfigured without the need
   for DAD.  It results that a node could use that Address as source,
   with an SSLA option in the message if required, to register any other
   addresses, either Global or Unique-Local Addresses, which would be
   indicated in the Target.

   The suggested change is to register the target of the NS message, and
   use Target Link-Layer Address (TLLA) in the NS as opposed to the SLLA
   in order to install a Neighbor Cache Entry.  This would apply to both
   Efficient ND and 6LoWPAN ND in a very same manner, with the caveat
   that depending on the nature of the link between the 6LBR and the
   6BBR, the 6LBR may resort to classical ND or DHCPv6 to obtain the
   address that it uses to source the NS registration messages, whether
   for itself or on behalf of LLN nodes.

3.5.  RPL root vs.  6LBR

   6LoWPAN ND is unclear on how the 6LBR is discovered, and how the
   liveliness of the 6LBR is asserted over time.  On the other hand, the
   discovery and liveliness of the RPL root are obtained through the RPL

   When 6LoWPAN ND is coupled with RPL, it makes sense to collocate the
   6LBR and the RPL root functionalities.  The DAR/DAC exchange becomes
   a preamble to the DAO messages that are used from then on to
   reconfirm the registration, thus eliminating a duplication of
   functionality between DAO and DAR messages.

3.6.  Securing the Registration

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   A typical attack against IPv6 ND is address spoofing, whereby a rogue
   node claims the IPv6 Address of another node in and hijacks its

   SEcure Neighbor Discovery (SEND) [RFC3971] is designed to protect
   each individual ND lookup/advertisement in a peer to peer model where
   each lookup may be between different parties.  This is not the case
   in a 6LoWPAN ND LLN where, as illustrated in Figure 2, the 6LBR
   terminates all the flows and may store security information for later

   Additionally SEND requires considerably enlarged ND messages to carry
   cryptographic material, and requires that each protected address is
   generated cryptographically, which implies the computation of a
   different key for each Cryptographically Generated Address (CGA).
   SEND as defined in [RFC3971] is thus largely unsuitable for
   application in a LLN.

   Once an Address is registered, the 6LBR maintains a state for that
   Address and is in position to bind securely the first registration
   with the Node that placed it, whether the Address is CGA or not.  It
   should thus be possible to protect the ownership of all the addresses
   of a 6LoWPAN Node with a single key, and there should not be a need
   to carry the cryptographic material more than once to the 6LBR.

   The energy constraint is usually a foremost factor, and attention
   should be paid to minimize the burden on the CPU. Hardware-assisted
   support of variants of the Counter with CBC-MAC [RFC3610] (CCM)
   authenticated encryption block cipher mode such as CCM* are common in
   LowPower ship-set implementations, and 6LoWPAN ND security mechanism
   should be capable to reuse them when applicable.

   Finally, the code footprint in the device being also an issue, the
   capability to reuse not only hardware-assist mechanisms but also
   software across layers has to be considered.  For instance, if code
   has to be present for upper-layer operations, e.g AES-CCM Cipher
   Suites for Transport Layer Security (TLS) [RFC6655], then the
   capability to reuse that code should be considered.

4.  Requirements

4.1.  Requirements Related to Mobility

   Due to the nature of LLN networks, even a fixed 6LoWPAN Node may
   change its point of attachment (a 6LR) and may not be able to notify
   the 6LR that it has disconnected from.  It results that the previous
   6LR may still attract traffic that it cannot deliver any more.  When
   the 6LR changes, there is thus a need to identify stale states and
   restore reachability timely.

   Req1.1: Upon a change of point of attachment, connectivity via a new

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   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
   multiple registrations from a same 6LoWPAN Node from two different
   6LoWPAN Nodes claiming a same address.

   Req1.3: This information MUST be passed from the 6LR to the 6LBR, and
   the 6LBR SHOULD be able to clean up the stale state asynchronously in
   the previous 6LR.

   Req1.4: A 6LoWPAN Node SHOULD also be capable to register a same
   Address to multiple 6LRs, and this, concurrently.

4.2.  Requirements Related to Routing Protocols

   The point of attachment of a 6LoWPAN Node may be a 6LR in an LLN
   mesh.  An LLN route-over mesh is typically based on RPL, which is the
   routing protocol that was defined at the IETF for this particular
   purpose.  It derives that in this scenario, the 6LR would classically
   support RPL.  One goal is that a 6LoWPAN Node attached via ND to a
   RPL-capable 6LR would not need to participate to the RPL protocol to
   obtain reachability via the 6LR. An additional goal would be to
   obtain reachability via other routing protocols through a same ND-
   based abstraction.

   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
   RPL and obtain reachability to that Address over the RPL domain.

   Req2.2: 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 DAOSequence and, as an option,
   a RPLInstanceID.

   Req2.3: Depending on their applicability to LLNs, other standard mesh
   /MANET protocols MAY be considered as well.

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

   6LoWPAN ND [RFC6775] was defined with a focus on IEEE802.15.4 and in
   particular the capability to derive a unique Identifier from a
   globally unique MAC-64 address.  At this point, the 6lo Working Group
   is extending the 6LoWPAN Header Compression (HC)  [RFC6282] technique
   to other link types ITU-T G.9959 [I-D.brandt-6man-lowpanz], Master-

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   Slave/Token-Passing [I-D.ietf-6lo-6lobac], DECT Ultra Low Energy [I-D
   .ietf-6lo-dect-ule], Near Field Communication [I-D.hong-6lo-ipv6
   -over-nfc], as well as IEEE1901.2 Narrowband Powerline Communication
   Networks [I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and
   BLUETOOTH(R) Low Energy [I-D.ietf-6lo-btle].

   Related requirements are:

   Req3.1: The support of the registration mechanism SHOULD be extended
   to more LLN links, matching at least the links that are considered by
   6lo as well as other popular Low-Power links such as Low-Power Wi-Fi.

   Req3.2: As part of this extension, a mechanism to compute a unique
   Identifier should be provided, with the capability to form a Link-
   Local Address that can not be a duplicate.  The Identifier SHOULD be
   unique at least to the domain where an Address formed by this device
   may be advertised through ND mechanisms.

   Req3.3: The Address Registration Option used in the ND registration
   SHOULD be extended to carry the relevant forms of unique Identifier.

4.4.  Requirements Related to Proxy Operations

   Sleeping 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
   operation by a 6BBR. Additionally, the device may need to rely on the
   6LBR to perform that registration to the 6BBR.

   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.

4.5.  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 to protect that ownership even if the node is
   sleeping.  In particular, the 6LR and the 6LBR then should be able to
   verify whether a subsequent registration for a same Address comes
   from a same node or is a duplicate.

   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

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   of 6LR.

   Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
   the 6LR and the 6LBR to validate whether a new registration
   corresponds to a same 6LoWPAN Node, and, if not, determine the
   rightful owner, and deny or clean-up the registration that is deemed
   in excess.

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

   Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be
   computationally intensive on the LoWPAN Node CPU. When a Key hash
   calculation is employed, a mechanism lighter than SHA-1 SHOULD be

   Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate
   SHOULD be minimized.

   Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable CCM* for use
   at both Layer 2 and Layer 3, and SHOULD enable the reuse of security
   code that has to be present on the device for upper layer security
   such as TLS.

   Req5.7: Public key and signature sizes SHOULD be minimized while
   maintaining adequate confidentiality and data origin authentication
   for multiple types of applications with various degrees of

4.6.  Requirements Related to Low-Power devices

   The ND registration method is designed to save energy on Low-Power
   devices, and in particular enable duty-cycled devices that are
   sleeping most of the time and not capable to defend their own
   Addresses against always-on devices.

   Related requirements are:

   Req6.1: The registration mechanism SHOULD be applicable to a Low-
   Power device regardless of the link type, and enable a 6BBR to
   operate as a proxy to defend the registered Addresses on its behalf.

5.  Suggested Changes to Protocol Elements

5.1.  ND Neighbor Solicitation (NS)

   The NS message used for registration should use a source address that
   respects the rules in [RFC6775], [RFC4861], and [RFC4429] for DAD.
   The SLLA Option may be present but only if the address passed DAD,
   and it is used to allow the 6LR to respond as opposed to as a
   registration mechanism.

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   The address that is being registered is the target address in the NS
   message and the TLLA Option must be present.

5.2.  ND Router Advertisement (RA)

   [I-D.chakrabarti-nordmark-6man-efficient-nd] adds an 'E' bit in the
   Router Advertisement flag, as well as a new Registrar Address Option
   (RAO). These fields are probably pertinent to LLNs inclusion into a
   revised 6LoWPAN ND should be studied.  If the new 6LoWPAN flows
   require a change of behaviour (e.g.  registering the Target of the NS
   message) then the RA must indicate that the router supports the new
   capability, and the NS must indicate that the Target is registered as
   opposed to the Source in an unequivocal fashion.

   There is some amount of duplication between the options in the RPL
   DIO [RFC6550] and the options in the ND RA messages.  At the same
   time, there are a number of options, including the 6LoWPAN Context
   Option (6CO) [RFC6775], the MTU and the SLLA Options [RFC4861]  that
   can only be found in the RA messages.  Considering that these options
   are useful for a joining node, the recommendation would be to
   associate the RA messages to the join beacon, and make them rare when
   the network is stable.  On the other hand, the DIO message is to be
   used as the propagated heartbeat of the RPL network and provide the
   sense of time and liveliness.

   RAs should also be issued and the information therein propagated when
   a change occurs in the information therein, such as a router or a
   prefix lifetime.

5.3.  RPL DODAG Information Object (DIO)

   If the RPL root serves as 6LBR, it makes sense to add at least a bit
   of information in the DIO to signal so.  A Registrar Address Option
   (RAO) may also be considered for addition.

5.4.  ND Enhanced Address Registration Option (EARO)

   The ARO option contains a Unique ID that is supposed to identify the
   device across multiple registrations.  It is envisioned that the
   device could form a single CGA-based Unique Interface ID (CUID) to
   securely bind all of its addresses.  The CUID would be used as Unique
   Interface Identifier in the ARO option and to form a Link-Local
   address that would be deemed unique regardless of the Link type.
   Provided that the relevant cryptographic material is passed to the
   6LBR upon the first registration or on-demand at a later time, the
   6LBR can validate that a Node is effectively the owner of a CUID, and
   ensure that the ownership of an Address stays with the CUID that
   registered it first.

   This option is designed to be used with standard NS and NA messages
   between backbone Routers as well as between nodes and 6LRs over the
   LLN and between the 6LBR and the 6BBR over whatever IP link they use
   to communicate.

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      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    |    Status     | RPLInstanceID |
      |Res|P|N| IDS |T|      TID      |     Registration Lifetime     |
      |                                                               |
      ~         Unique Interface Identifier (variable length)         ~
      |                                                               |

   The representation above is based on [I-D.chakrabarti-nordmark-6man-
   efficient-nd].  Only the proposed changes from that specification are
   discussed below but the expectation is that 6LoWPAN ND and Efficient
   ND converge on the ARO format.

   Status: 8-bit integer.  A new value of 3 is suggested to indicate a
      rejection due to an obsolete TID, typically an indication of a

   RPLInstanceID: 8-bit integer.  This field is set to 0 when unused.
      Otherwise it contains the RPLInstanceID for which this address is
      registered, as specified in RPL [RFC6550], and discussed in
      particular in section 3.1.2.

   P: One bit flag.  When the bit is set, the address being registered
      is Target of the NS as opposed to the Source, for instance to
      enable ND proxy operation.

   N: One bit flag.  Set if the device moved.  If not set, the 6BBR will
      refrain from sending gratuitous NA(O) or other form of distributed
      ND cache clean-up over the backbone.  For instance, the flag
      should be reset after the DAD operation upon address formation.

6.  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.
   Still, Section 4.5 has a requirement for a mutual authentication and
   authorization for a role for 6LRs, 6LBRs and 6BBRs.

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   This documents also suggests in Section 5.4 that a 6LoWPAN Node could
   form a single Unique Interface ID (CUID) based on cryptographic
   techniques similar to CGA.  The CUID would be used as Unique
   Interface Identifier in the ARO option and new Secure ND procedures
   would be proposed to use it as opposed to the source IPv6 address to
   secure the binding between an Address and its owning Node, and
   enforce First/Come-First/Serve at the 6LBR.

7.  IANA Considerations

   A new type is requested for an ND option.

8.  Acknowledgments

   The author wishes acknowledge the contributions by Samita
   Chakrabarti, Erik Normark, JP Vasseur, Eric Levy-Abegnoli, Patrick
   Wetterwald, Thomas Watteyne, and Behcet Sarikaya.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S.E. and R.M. Hinden, "Internet Protocol, Version
              6 (IPv6) Specification", RFC 2460, December 1998.

   [RFC3775]  Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

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

   [RFC4443]  Conta, A., Deering, S. and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W. and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

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

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J. and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

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   [RFC6275]  Perkins, C., Johnson, D. and J. Arkko, "Mobility Support
              in IPv6", RFC 6275, July 2011.

   [RFC6282]  Hui, J. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              September 2011.

   [RFC6550]  Winter, T., Thubert, P., 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, March 2012.

   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655, July 2012.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E. and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D. and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830, January

9.2.  Informative References

              Brandt, A. and J. Buron, "Transmission of IPv6 packets
              over ITU-T G.9959 Networks", Internet-Draft draft-brandt-
              6man-lowpanz-02, June 2013.

              Chakrabarti, S., Nordmark, E., Thubert, P. and M.
              Wasserman, "Wired and Wireless IPv6 Neighbor Discovery
              Optimizations", Internet-Draft draft-chakrabarti-nordmark-
              6man-efficient-nd-04, October 2013.

              Hong, Y., Choi, Y., Youn, J., Kim, D. and J. Choi,
              "Transmission of IPv6 Packets over Near Field
              Communication", Internet-Draft draft-hong-6lo-ipv6-over-
              nfc-01, August 2014.

              Lynn, K., Martocci, J., Neilson, C. and S. Donaldson,
              "Transmission of IPv6 over MS/TP Networks", Internet-Draft
              draft-ietf-6lo-6lobac-00, July 2014.

              Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
              Shelby, Z. and C. Gomez, "Transmission of IPv6 Packets
              over BLUETOOTH(R) Low Energy", Internet-Draft draft-ietf-
              6lo-btle-02, June 2014.

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              Mariager, P., Petersen, J., Shelby, Z., Logt, M. and D.
              Barthel, "Transmission of IPv6 Packets over DECT Ultra Low
              Energy", Internet-Draft draft-ietf-6lo-dect-ule-00, June

              Thubert, P., Watteyne, T. and R. Assimiti, "An
              Architecture for IPv6 over the TSCH mode of IEEE
              802.15.4e", Internet-Draft draft-ietf-6tisch-
              architecture-01, February 2014.

              Palattella, M., Thubert, P., Watteyne, T. and Q. Wang,
              "Terminology in IPv6 over the TSCH mode of IEEE
              802.15.4e", Internet-Draft draft-ietf-6tisch-
              terminology-00, November 2013.

              Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets
              over IEEE 1901.2 Narrowband Powerline Communication
              Networks", Internet-Draft draft-popa-6lo-6loplc-ipv6-over-
              ieee19012-networks-00, March 2014.

   [RFC3610]  Whiting, D., Housley, R. and N. Ferguson, "Counter with
              CBC-MAC (CCM)", RFC 3610, September 2003.

   [RFC3963]  Devarapalli, V., Wakikawa, R., Petrescu, A. and P.
              Thubert, "Network Mobility (NEMO) Basic Support Protocol",
              RFC 3963, January 2005.

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

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

   [RFC4389]  Thaler, D., Talwar, M. and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, April 2006.

   [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, August 2007.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, January 2014.

Author's Address

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   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

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