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Versions: 00 01 02 03 04 draft-ietf-6lo-ap-nd

6lo                                                        M. Sethi, Ed.
Internet-Draft                                                  Ericsson
Updates: 6775 (if approved)                                   P. Thubert
Intended status: Standards Track                                   Cisco
Expires: February 23, 2017                              B. Sarikaya, Ed.
                                                              Huawei USA
                                                         August 22, 2016


 Address Protected Neighbor Discovery for Low-power and Lossy Networks
                      draft-sarikaya-6lo-ap-nd-04

Abstract

   This document defines an extension to 6LoWPAN Neighbor Discovery.
   This extension is designed for low-power and lossy network
   environments and it supports multi-hop operation.  Nodes supporting
   this extension compute a Cryptographically Unique Interface ID and
   associate it with one or more of their Registered Addresses.  The
   Cryptographic ID (Crypto-ID) uniquely identifies the owner of the
   Registered Address.  It is used in place of the EUI-64 address that
   is specified in RFC 6775.  Once an address is registered with a
   Cryptographic ID, only the owner of that ID can modify the state
   information of the Registered Address in the 6LR and 6LBR.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 23, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Interactions . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Updating RFC 6775 . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Crypto-ID Calculation . . . . . . . . . . . . . . . .  10
     4.3.  Multihop Operation  . . . . . . . . . . . . . . . . . . .  13
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative references  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Neighbor discovery for IPv6 [RFC4861] and stateless address
   autoconfiguration [RFC4862] are together referred to as neighbor
   discovery protocols (NDP).  They are defined for regular hosts that
   have sufficient memory and computation capabilities.  These protocols
   are however not suitable for resource-constrained devices.
   Therefore, they require adaptation to work on resource-constrained
   hosts operating over a low-power and lossy network (LLN).  Neighbor
   Discovery optimizations for 6LoWPAN networks include simple
   optimizations such as a host address registration feature.  This
   feature uses the address registration option (ARO) which is sent in
   the unicast Neighbor Solicitation (NS) and Neighbor Advertisement
   (NA) messages [RFC6775].

   With 6LoWPAN ND [RFC6775], the ARO option includes a EUI-64 interface
   ID to uniquely identify the interface of the Registered Address on
   the registering device, so as to correlate further registrations for
   the same address and avoid address duplication.  The EUI-64 interface
   ID is not secure and its ownership cannot be verified.  Consequently,



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   any device claiming the same EUI-64 interface ID may take over an
   existing registration and attract the traffic for that address.  The
   address registration mechanism in [RFC6775] is limited as it does not
   require a node to prove its ownership of the EUI-64 Interface ID.
   Therefore, any node connected to the subnet and aware of the
   registered address to EUI-64 interface ID mapping may effectively
   fake the same interface ID and steal an address.

   In this document, we extend 6LoWPAN ND to protect the address
   ownership with cryptographic material, but as opposed to Secure
   Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated
   Addresses (CGAs) [RFC3972], the cryptographic material generated is
   not embedded in the Interface ID (IID) as an IPv6 address.  Instead,
   the generated cryptographic ID is used as a correlator associated
   with the registration of the IP address.  This approach is made
   possible with 6LoWPAN ND [RFC6775], where the 6LR and the 6LBR
   maintain state information for each Registered Address.  If a
   cryptographic ID is associated with the first 6LoWPAN ND
   registration, then it can be used to validate any future updates to
   the registration.

   In order to achieve this ownership verification, in this extension
   specification, the EUI-64 interface ID used in 6LoWPAN ND is replaced
   with cryptographic material whose ownership can be verified.  The
   extension also provides new means for the 6LR to validate ownership
   of the registration, and thus, the ownership of registered address.
   The resulting protocol is called Protected Address Registration
   protocol (ND-PAR).

   In ND-PAR, a node typically generates one 64-bit cryptographic ID
   (Crypto-ID) and uses it as Unique Interface ID in the registration of
   one (or more) of its addresses with the 6LR, which it attaches to and
   uses as default router.  The 6LR validates ownership of the
   cryptographic ID typically upon creation or update of a registration
   state, for instance following an apparent movement from one point of
   attachment to another.  The ARO option is modified to carry the
   Unique Interface ID, and through the DAR/DAC exchange.

   Compared with SeND, this specification saves ~1Kbyte in every NS/NA
   message.  Also SeND requires one cryptographic address per IPv6
   address.  This specification separates the cryptographic identifier
   from the IPv6 address so that a node can have more than one IPv6
   address protected by the same cryptographic identifier.  SeND forces
   the IPv6 address to be cryptographic since it integrates the CGA as
   an IID. 6LoWPAN derives the IPv6 address from other things like a
   short address in 802.15.4 to enable a better compression.





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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Readers are expected to be familiar with all the terms and concepts
   that are discussed in [RFC3971], [RFC3972], [RFC4861], [RFC4919],
   [RFC6775], and [I-D.ietf-6lo-backbone-router] which proposes an
   evolution of [RFC6775] for wider applicability.

   This document defines Crypto-ID as an identifier of variable size
   which in most cases is 64 bits long.  It is generated using
   cryptographic means explained later in this document.

   The document also conforms to the terms and models described in
   [RFC5889] and uses the vocabulary and the concepts defined in
   [RFC4291] for the IPv6 Architecture.

   This document uses [RFC7102] for Terminology in Low power And Lossy
   Networks.

3.  Requirements

   In this section we state requirements of a secure neighbor discovery
   protocol for low-power and lossy networks.

   o  The protocol MUST be based on the Neighbor Discovery Optimization
      for Low-power and Lossy Networks protocol defined in [RFC6775].
      RFC6775 utilizes optimizations such as host-initiated interactions
      for sleeping resource-constrained hosts and elimination of
      multicast address resolution.

   o  New options to be added to Neighbor Solicitation messages MUST
      lead to small packet sizes, especially compared with existing
      protocols such as SEcure Neighbor Discovery (SEND).  Smaller
      packet sizes facilitate low-power transmission by resource-
      constrained nodes on lossy links.

   o  The support for this registration mechanism SHOULD be extensible
      to more LLN links than IEEE 802.15.4 only.  Support for at least
      the LLN links for which a 6lo "IPv6 over foo" specification
      exists, as well as Low-Power Wi-Fi SHOULD be possible.

   o  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.



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   o  The Address Registration Option used in the ND registration SHOULD
      be extended to carry the relevant forms of Unique Interface
      IDentifier.

   o  The Neighbour Discovery should specify the formation of a site-
      local address that follows the security recommendations from
      [RFC7217].

4.  Protocol Interactions

   Protected address and registration neighbor discovery protocol (ND-
   PAR) modifies Neighbor Discovery Optimization for Low-power and Lossy
   Networks [RFC6775] as explained in this section.

4.1.  Overview

   The scope of the present work is a 6LoWPAN Low Power Lossy Network
   (LLN), typically a stub network connected to a larger IP network via
   a Border Router called a 6LBR per [RFC6775].

               ---+-------- ............
                  |      External Network
                  |
               +-----+
               |     | LLN Border
               |     | router
               +-----+
             o    o   o
      o     o   o     o
         o   o LLN   o    o     o
            o   o   o       o
                    o

                       Figure 1: Basic Configuration

   The 6LBR maintains a registration state for all devices in the
   attached LLN, and, in conjunction with the first-hop router (the
   6LR), is in a position to validate uniqueness and grant ownership of
   an IPv6 address before it can be used in the LLN.  This is a
   fundamental difference with a classical network that relies on IPv6
   address auto-configuration [RFC4862], where there is no guarantee of
   ownership from the network, and any IPv6 Neighbor Discovery packet
   must be individually secured [RFC3971].

   In a mesh network, the 6LR is directly connected to the host device.
   This specification expects that the peer-wise layer-2 security is
   deployed so that all the packets from a particular host are securely
   identifiable by the 6LR.  The 6LR may be multiple hops away from the



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   6LBR.  Packets are routed between the 6LR and the 6LBR via other
   6LRs.  This specification expects that a chain of trust is
   established so that a packet that was validated by the first 6LR can
   be safely routed by the next 6LRs to the 6LBR.

   [I-D.ietf-6tisch-architecture] suggests to use of RPL [RFC6550] as
   the routing protocol between the 6LRs and the 6LBR, and leveraging a
   backbone router [I-D.ietf-6lo-backbone-router] to extend the LLN in a
   larger multilink subnet [RFC4903].  In that model, a registration
   flow happens as shown in Figure 2.  Note that network beyond the 6LBR
   is out of scope for this document.

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

          Figure 2: (Re-)Registration Flow over Multi-Link Subnet

   A new device that joins the network auto-configures an address and
   performs an initial registration to an on-link 6LR with an NS message
   that carries a new Address Registration Option (ARO) [RFC6775].  The
   6LR validates the address with the central 6LBR using a DAR/DAC
   exchange, and the 6LR confirms (or denies) the address ownership with
   an NA message that also carries an Address Registration Option.

   The registration mechanism in [RFC6775] was created for the original
   purpose of Duplicate Address Detection (DAD), whereby use of an
   address would be granted as long as the address is not already
   present in the subnet.  But [RFC6775] does not require that the 6LR
   use the registration for source address validation (SAVI) [RFC7039].



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   Protected address registration protocol proposed in this document
   enforces SAVI.  With this we ensure that only the correct owner uses
   the registered address in the source address field.  Therefore a
   destination node can trust that the source is the real owner without
   using SeND.  All packets destined for a node go through the 6LR to
   which it is attached.  The 6LR maintains state information for the
   registered addressed along with the MAC address, and link-layer
   cryptographic key associated with that node.  The 6LR therefore only
   delivers packets to the real owner based on its state information.

   In order to validate address ownership, the registration mechanism
   (that goes all the way to the 6LBR with the DAR/DAC) enables the 6LBR
   to correlate further claims for a registered address from the device
   to which it is granted, based on a Unique Interface IDentifier (UID).
   This UID is derived from the MAC address of the device (EUI-64).

   This document uses a randomly generated value as an alternate UID for
   the registration.  Proof of ownership of the UID is passed with the
   first registration to a given 6LR, and enforced at the 6LR, which
   validates the proof.  With this new operation, the 6LR allows only
   packets from a connected host if the connected host owns the
   registration of the source address of the packet.

   In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
   to 6LBR as described in Section 4.3.  If a chain of trust is present
   between the 6LR and the 6LBR, then there is no need to propagate the
   proof of ownership to the 6LBR.  All the 6LBR needs to know is that
   this particular UID is randomly generated, so as to enforce that any
   update via a different 6LR is also random.

4.2.  Updating RFC 6775

   Protocol interactions are as defined in Figure 2.  The Crypto-ID is
   calculated as described in Section 4.2.1.

   The Target Address field in NS message is set to the prefix
   concatenated with the node's address.  This address does not need
   duplicate address detection as Crypto-ID is globally unique.  So a
   host cannot steal an address that is already registered unless it has
   the key used for generating the Crypto-ID.  The same Crypto-ID can
   thus be used to protect multiple addresses e.g. when the node
   receives a different prefix.

   Local or on-link protocol interactions are shown in Figure 3.
   Crypto-ID and ARO are passed to and stored by the 6LR/6LBR on the
   first NS and not sent again in the next NS.  The operation starts
   with 6LR sending a Router Advertisement (RA) message to 6LN.




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   The 6LR/6LBR ensures first-come/first-serve by storing the ARO and
   the Crypto-ID correlated to the node being registered.  The node is
   free to claim any address it likes as long as it is the first to make
   such a claim.  The node becomes owner of that address and the address
   is bound to the Crypto-ID in the 6LR/6LBR registry.  This procedure
   avoids the constrained device to compute multiple keys for multiple
   addresses.  The registration process allows the node to tie all the
   addresses to the same Crypto-ID and have the 6LR/6LBR enforce first-
   come first-serve after that.

   A condition where a 6LN uses multiple IPv6 addresses may happen when
   the node moves at a different place and receives a different prefix.
   In this scenario, the node uses the same Crypto-ID to protect its new
   IPv6 address.  This prevents other nodes from stealing the address
   and trying to use it as their source address.

   Note that if the device that moves always forms new MAC and IP
   address [RFC6775], then this new address can be used for
   registration.  In case of a collision of the new MAC and therefore IP
   address, the node can easily form a new IPv6 address.  This is one
   case where the use of Crypto-ID would not be needed.  Crypto-ID or
   ND-PAR should be activated when the IP address is claimed at another
   place, or for a different MAC address at the same place, e.g. for MAC
   address privacy [I-D.ietf-6man-ipv6-address-generation-privacy].



























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         6LN                                                6LR
          |                                                  |
          |<------------------- RA --------------------------|
          |                                                  |
          |----------- NS with ARO and Crypto-ID ----------->|
          |                                                  |
          |<---------- NA with ARO (status=req-proof) -------|
          |                                                  |
          |----------- NS with ARO and Crypto-ID ----------->|
          |                                                  |
          |<---------------- NA with ARO --------------------|
          |                                                  |
          ...                                              ...
          |                                                  |
          |------------ NS with ARO and Crypto-ID ---------->|
          |                                                  |
          |                                                  |
          |<---------------- NA with ARO --------------------|
          ...                                              ...
          |                                                  |
          |----------- NS with ARO and Crypto-ID ----------->|
          |                                                  |
          |                                                  |
          |<---------------- NA with ARO --------------------|

                   Figure 3: On-link Protocol Operation

   Elliptic Curve Cryptography (ECC) is used in the calculation of
   cryptographic identifier (Crypto-ID).  The digital signature is
   constructed by using the 6LN's private key over its EUI-64 (MAC)
   address.  The signature value is computed using the ECDSA signature
   algorithm and the hash function used is SHA-256 [RFC6234].  Public
   Key is the most important parameter in CGA Parameters (sent by 6LN in
   an NS message).  ECC Public Key could be in uncompressed form or in
   compressed form where the first octet of the OCTET STRING is 0x04 and
   0x02 or 0x03, respectively.  Point compression can further reduce the
   key size by about 32 octets.

   After calculating its Crypto-ID, a 6LN sends it along with the CGA
   parameters in the first NS message, see Figure 3.  In order to send
   Crypto-ID, a modified address registration option called Enhanced
   Address Registration Option (EARO) is defined in Figure 4.  As
   defined in the figure this ID is variable length, varying between 64
   to 128 bits.  This ID is 128 bits long only if it is used as IPv6
   address.  This may happen when some application uses one IP address
   of the device as device ID.  It would make sense in that case to
   build a real CGA IPv6 address.  The prefix of the address would be
   obtained from prefix information option (PIO in RA) [RFC4861].



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   6LN also sends some other parameters to enable 6LR or 6LBR to verify
   the Crypto-ID.  The option shown in Figure 5 can be used.  In the
   figure, CGA Parameters field contains the public key, prefix and some
   other values.  It is a simplified form of CGA Option defined in
   [RFC3971].

4.2.1.  Crypto-ID Calculation

   First, the modifier is set to a random or pseudo-random 128-bit
   value.  Next, concatenate from left to right the modifier, 9 zero
   octets and the ECC public key.  SHA-256 algorithm is applied on the
   concatenation.  The 112 leftmost bits of the hash value is taken.
   Concatenate from left to right the modifier value, the subnet prefix
   and the encoded public key.  NIST P-256 is executed on the
   concatenation.  The leftmost bits of the result is used as the
   Crypto-ID.  The length is normally 64 bits, however it could be 128
   bits.

   In respecting the cryptographical algorithm agility [RFC7696], Curve
   25519 [RFC7748] can also be used instead of NIST P-256.  This is
   indicated by 6LN by setting the Crypto Type field in CGA Parameters
   Option to a value of 1.  If 6LBR does not support Curve 25519, it
   will set Crypto Type field to zero.  This means that the default
   algorithm (NIST P-256) will be used.


       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     |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Reserved  |C|T|     TID       |     Registration Lifetime     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +          Owner Unique ID (EUI-64 or equivalent)               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 4: Enhanced Address Registration Option

   Type:

      TBA1

   Length:





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      8-bit unsigned integer.  The length of the option (including the
      type and length fields) in units of 8 bytes.  The value 0 is
      invalid.  A value of 3 with the C flag set indicates a Crypto-ID
      of 128 bits.

   Status:

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

   Reserved:

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

   C:

      C bit when set is used to indicate that Owner Unique ID fields
      contains Crypto-ID.

   T and TID:

      Defined in [I-D.ietf-6lo-backbone-router].

   Owner Unique ID:

      In this specification, this field contains Crypto-ID, a variable
      length field to carry the Crypto-ID or random UID.  This field is
      normally 64 bits long.  It could be 128 bits long if IPv6 address
      is used as the Crypto-ID.





















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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     |   Pad Length  |  Crypto Type  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                      Modifier (16 octets)                     +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                    Subnet Prefix (8 octets)                   +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                                                               |
      +                  Public Key (variable length)                 +
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .                           Padding                             .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                      Figure 5: CGA Parameters Option

   Type:

      TBA2

   Length:

      The length of the option in units of 8 octets.

   Pad Length:

      The length of the Padding field.

   Crypto Type:





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      The type of cryptographic algorithm used in calculation Crypto-ID.
      Default value of all zeros indicate NIST P-256.  A value of 1 is
      assigned for Curve 25519.  New values may be defined later.

   Modifier:

      128 bit random value.

   Subnet Prefix:

      64 bit subnet prefix.

   Public Key:

      ECC public key of 6LN.

   Padding:

      A variable-length field making the option length a multiple of 8,
      containing as many octets as specified in the Pad Length field.

4.3.  Multihop Operation

   In multihop 6LoWPAN, 6LBR sends RAs with prefixes downstream and it
   is the 6LR that receives and relays them to the nodes. 6LR and 6LBR
   communicate with the ICMPv6 Duplicate Address Request (DAR) and the
   Duplicate Address Confirmation (DAC) messages.  The DAR and DAC use
   the same message format as NS and NA with different ICMPv6 type
   values.

   In ND-PAR we extend DAR/DAC messages to carry cryptographically
   generated UID.  In a multihop 6LoWPAN, the node exchanges the
   messages shown in Figure 2.  The 6LBR must be aware of who owns an
   address (EUI-64) to defend the first node if there is an attacker on
   another 6LR.  Because of this the content that the source signs and
   the signature needs to be propagated to the 6LBR in DAR message.  For
   this purpose the DAR message sent by 6LR to 6LBR MUST contain CGA
   Parameters and Digital Signature Option carrying the CGA that the
   node calculates and its public key.  DAR message also contains ARO.

   It is possible that occasionally, 6LR may miss the node's UID (that
   it received in ARO). 6LR should be able to ask for it again.  This is
   done by restarting the exchanges shown in Figure 3.  The result
   enables 6LR to refresh the information that was lost. 6LR MUST send
   DAR message with ARO to 6LBR.  6LBR as a reply forms a DAC message
   with the information copied from the DAR and the Status field is set
   to zero.  With this exchange, the 6LBR can (re)validate and store the
   information to make sure that the 6LR is not a fake.



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   In some cases 6LBR may use DAC message to signal to 6LR that it
   expects Crypto-ID from 6LR also asks 6LR to verify the EUI-64 6LR
   received from 6LN.  This may happen when a 6LN node is compromised
   and a fake node is sending the Crypto-ID as if it is the node's EUI-
   64.  Note that the detection in this case can only be done by 6LBR
   not by 6LR.

5.  Security Considerations

   The same considerations regarding the threats to the Local Link
   Network covered in [RFC3971] apply.

   The threats discussed in Section 9.2 of [RFC3971] are countered by
   the protocol described in this document as well.

   Collisions of Crypto-ID is a possibility that needs to be considered.
   The formula for calculating probability of a collision is 1 -
   e^{-k^2/(2n)}. If the Crypto-ID is 64-bit long, then the chance of
   finding a collision is 0.01% when the network contains 66 million
   nodes.  It is important to note that the collision is only relevant
   when this happens within one stub network (6LBR).  A collision of ID
   in ND-PAR is a rare event.  However, when such a collision does
   happen, the protocol operation is not affected, although it opens a
   window for a node to hijack an address from another.  The link-layer
   security ensures that the nodes would normally not be aware of a
   collision on the subnet.  If a malicious node is able to gain
   knowledge of a collision through other means, the only thing that it
   could do is to steal addresses from the other honest node.  This
   would be no different from what is already possible in a 6lo network
   today.

6.  IANA considerations

   IANA is requested to assign two new option type values, TBA1 and TBA2
   under the subregistry "IPv6 Neighbor Discovery Option Formats".

7.  Acknowledgements

   We are grateful to Rene Struik and Robert Moskowitz for their
   comments that lead to many improvements to this document.

8.  References

8.1.  Normative References







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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <http://www.rfc-editor.org/info/rfc3971>.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,
              <http://www.rfc-editor.org/info/rfc3972>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <http://www.rfc-editor.org/info/rfc4291>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <http://www.rfc-editor.org/info/rfc4862>.

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
              DOI 10.17487/RFC4903, June 2007,
              <http://www.rfc-editor.org/info/rfc4903>.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, DOI 10.17487/RFC4919, August 2007,
              <http://www.rfc-editor.org/info/rfc4919>.

   [RFC5889]  Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
              Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
              September 2010, <http://www.rfc-editor.org/info/rfc5889>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <http://www.rfc-editor.org/info/rfc6234>.





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   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <http://www.rfc-editor.org/info/rfc6550>.

   [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
              Bormann, "Neighbor Discovery Optimization for IPv6 over
              Low-Power Wireless Personal Area Networks (6LoWPANs)",
              RFC 6775, DOI 10.17487/RFC6775, November 2012,
              <http://www.rfc-editor.org/info/rfc6775>.

   [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>.

   [RFC7039]  Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
              "Source Address Validation Improvement (SAVI) Framework",
              RFC 7039, DOI 10.17487/RFC7039, October 2013,
              <http://www.rfc-editor.org/info/rfc7039>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <http://www.rfc-editor.org/info/rfc7217>.

   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
              <http://www.rfc-editor.org/info/rfc7696>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <http://www.rfc-editor.org/info/rfc7748>.

8.2.  Informative references

   [I-D.ietf-6lo-backbone-router]
              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-01 (work in progress), March 2016.

   [I-D.ietf-6tisch-architecture]
              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.




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   [I-D.ietf-6man-ipv6-address-generation-privacy]
              Cooper, A., Gont, F., and D. Thaler, "Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              draft-ietf-6man-ipv6-address-generation-privacy-08 (work
              in progress), September 2015.

Authors' Addresses

   Mohit Sethi (editor)
   Ericsson
   Hirsalantie
   Jorvas  02420

   Email: mohit@piuha.net


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

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


   Behcet Sarikaya (editor)
   Huawei USA
   5340 Legacy Dr. Building 3
   Plano, TX  75024

   Email: sarikaya@ieee.org


















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