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

6lo                                                     B. Sarikaya, Ed.
Internet-Draft                                                Huawei USA
Updates: 6775 (if approved)                              P. Thubert, Ed.
Intended status: Standards Track                                   Cisco
Expires: September 11, 2016                               March 10, 2016


 Address Protected Neighbor Discovery for Low-power and Lossy Networks
                      draft-sarikaya-6lo-ap-nd-02

Abstract

   This document defines an extension of 6LoWPAN Neighbor Discovery for
   application in low-power and lossy networks.  The protocol is
   specified to be protected and to support multi-hop operation.  A node
   computes its Cryptographic, Unique Interface ID, and associates one
   or more of its Registered Addresses with that Cryptographic ID in
   place of the EUI-64 that is used in RFC 6775 to uniquely identify the
   interface of the Registered Address.  Once an address is registered
   with a Cryptographic ID, only the owner of that ID can modify the
   state in the 6LR and 6LBR regarding the Registered Address.

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 September 11, 2016.

Copyright Notice

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

   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



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   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  . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   Neighbor discovery for IPv6 [RFC4861] and stateless address
   autoconfiguration [RFC4862], together referred to as neighbor
   discovery protocols (NDP), are defined for regular hosts operating
   with wired/wireless links.  These protocols are not suitable and
   require optimizations for resource constrained, low power hosts
   operating over a low-power and lossy network (LLN) for low-power and
   lossy networks.  Neighbor Discovery optimizations for 6LoWPAN
   networks include simple optimizations such as a host address
   registration feature using the address registration option (ARO)
   which is sent in unicast Neighbor Solicitation (NS) and Neighbor
   Advertisement (NA) messages [RFC6775].  With 6LoWPAN ND [RFC6775],
   the ARO option includes a EUI-64 address 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 address is not secured and its
   ownership cannot be verified.  It results that any device claiming
   the same EUI-64 address may take over a registration and attract the
   traffic for that address.

   The limitation of the mechanism in [RFC6775] is that it does not
   enable to prove the UID itself, so any node connected to the subnet




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   and aware of the address/UID mapping may effectively fake the same
   UID 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], [RFC3972], the cryptographic
   material is not embedded in the Interface ID (IID) in an IPv6 address
   but used as a correlator associated to the registration of the IPv6
   address.  This approach is made possible with 6LoWPAN ND [RFC6775],
   where the 6LR and the 6LBR maintain a state for each Registered
   Address.  If a cryptographic ID is associated with an original
   6LoWPAN ND registration and stored in the registration state, then it
   can be used to validate that any update to the registration state is
   made by the owner of that ID.

   To achieve this, this specification replaces the EUI-64 address, that
   is used in 6LoWPAN ND to avoid address duplication, with
   cryptographic material whose ownership can be verified; it also
   provides new means for the 6LR to validate ownership of the
   registration thus that of the registered address by the registering
   device.  The resulting protocol is called Protected Address
   Registration protocol (ND-PAR).

   A node generates one 64-bit cryptographic 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 a point of attachment to another.  The ARO
   option is modified to carry the Unique Interface ID, and through the
   DAR/DAC exchange, the 6LBR is kept aware that this is the case, i.e.
   unique and whether the 6LR has verified the claim.

   Compared with SeND, this specification saves ~1Kbytes in every NS/NA
   message.  Also SeND requires one cryptographic address per IPv6
   address.  This specification separates the crypto from the IPv6
   address so we can have more than one IPv6 address protected by the
   same crypto.  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.  Looking from securing neighbor discovery protocol point
   of view the cryptographical ID protocol presented in this
   specification secures 6LoWPAN ND for Low-power and Lossy Networks.








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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], "Neighbor Discovery for
   IP version 6" [RFC4861], "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] where the 6LoWPAN Router (6LR) and the
   6LoWPAN Border Router (6LBR) are introduced, and
   [I-D.ietf-6lo-backbone-router], which proposes an evolution of
   [RFC6775] for a larger applicability.

   This document defines Crypto-ID as an identifier of variable size,
   while in most cases being 64 bits generated using cryptographical
   means explained 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.

   The protocol MUST be based on the Neighbor Discovery Optimization for
   Low-power and Lossy Networks protocol defined in [RFC6775] due to the
   host-initiated interactions to allow for sleeping hosts, elimination
   of multicast-based address resolution for hosts, etc.

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

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





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   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.

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

   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 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].





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   In a route-over mesh network, the 6LR is directly connected to the
   host device; this specification expects that peer-wise Layer-2
   security is deployed so that all the packets from a particular host
   are identified as such by the 6LR.  The 6LR may be multiple hops away
   from the 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.

   The [I-D.ietf-6tisch-architecture] suggests to use RPL [RFC6550] as
   the routing protocol between the 6LRs and the 6LBR, and to leverage
   [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 side of 6LBR is out
   of scope in 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 infirms) the address ownership
   with an NA message that also carries an Address Registration Option.



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   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].

   Protected address registration protocol proposed in this document
   enforces SAVI.  With this we ensure that only the owner uses the
   source address.  One consequence is that the onlink destination can
   trust that the source is the owner without doing SeND.  In ND-PAR,
   since the addresses are not on link there is never a (NS Look-Up
   based) DNS resolution, all packets go to the router, 6LR first.  6LR
   has a state for the registered router (?) with the link and the MAC
   address, and usually L2 crypto associated.  The 6LR only delivers
   packets to the real owner based on the state it has. 6LR can check a
   source as being the owner.

   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 with the device
   to which it is granted, based on a Unique Interface IDentifier (UID)
   that 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 for the Crypto-ID.  The same Crypto-ID can thus be used to




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   protect multiple addresses e.g. when the node receives a different
   prefix.

   Local or on-link protocol interactions are given 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.

   The 6LR/6LBR ensures first-come/first-serve by storing the ARO and
   the Crypto-ID correlated to the target being registered.  Then, if
   the node is the first to claim any address it likes, then it 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.

   6LN using multiple IPv6 addresses may happen when the node moves at a
   different place and receives a different prefix.  The node uses the
   same Crypto-ID to protect its new IP address from other nodes
   stealing this 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] 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 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
   cryptographical identifier.  The digital signature is constructed by
   using the 6LN's private key over its EUI-64, i.e. its MAC address.
   The signature value is computed using the ECDSA signature algorithm
   and 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 using secp256r1 reduces the key size
   by 32 octets.

   After the calculation, 6LN sends it along with the CGA parameters in
   the first NS message, see Figure 3.  In order to send Cryptographical
   Identifier 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 that
   figure, CGA Parameters field contains the public key, prefix and some
   other values.  It is 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.  NIST P-256 or SHA-2 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, 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 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:

      8-bit unsigned integer.  The length of the option (including the
      type and length fields) in units of 8 bytes.  The value 0 is



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      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 cryptographical identifier 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 cryptographical algorithm used in calculation Crypto-
      ID.  Default value of all zeros indicate NIST P-256.  A value of 1
      is assigned for Curve 25519.

   Modifier:

      128 bit random value.

   Subnet Prefix:

      64 bit subnet prefix.

   Public Key:

      ECC public key of 6LN.

   Padding:

      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 user 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



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   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.

   In some cases 6LBR may use DAC message to signal to 6LR that it
   expects Crypto-ID from 6LR also askss 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 Not
   Covered (as in [RFC3971]) apply.

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

   As to the attacks to the protocol itself, denial of service attacks
   that involve producing a very high number of packets are deemed
   unlikely because of the assumptions on the node capabilities in low-
   power and lossy networks.

   A collision of ID in ND-PAR is a really rare event that does not
   prevent the protocol operation though it opens a window for a node to
   hijack an address from another.  The nodes would normally not be
   aware that they are in this situation, and the only thing they could
   do if they knew would be to steal addresses from one another, so the
   damage is limited to these 2 nodes.

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 Mohit Sethi and Rene Struik for their comments
   that lead to many improvements in the 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>.

   [RFC3756]  Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
              Neighbor Discovery (ND) Trust Models and Threats",
              RFC 3756, DOI 10.17487/RFC3756, May 2004,
              <http://www.rfc-editor.org/info/rfc3756>.

   [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>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
              <http://www.rfc-editor.org/info/rfc5480>.




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   [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>.

   [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>.






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   [Guide]    "Guidelines for 64-bit global Identifier (EUI-64TM)",
              November 2012,
              <http://standards.ieee.org/develop/regauth/tut/eui64.pdf>.

8.2.  Informative references

   [I-D.rafiee-6man-ssas]
              Rafiee, H. and C. Meinel, "A Simple Secure Addressing
              Scheme for IPv6 AutoConfiguration (SSAS)", draft-rafiee-
              6man-ssas-11 (work in progress), September 2014.

   [I-D.ietf-6lo-backbone-router]
              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-00 (work in progress), January 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-09 (work
              in progress), November 2015.

   [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

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

   Email: sarikaya@ieee.org


   Pascal Thubert (editor)
   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






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