6lo                                                     B. Sarikaya, Ed.
Internet-Draft                                                Huawei USA
Intended status: Standards Track                         P. Thubert, Ed.
Expires: April 21, 2016                                            Cisco
                                                        October 19, 2015

 Address Protected Neighbor Discovery for Low-power and Lossy Networks


   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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on April 21, 2016.

Copyright Notice

   Copyright (c) 2015 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
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   (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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Interactions . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Protocol Operations . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Calculation of Cryptographic Identifier . . . . . . .   8
     4.3.  Multihop Operation  . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative references  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

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 with 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.

   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

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   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
   autoconfiguration and registration protocol (ND-PAAR).

   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.

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 [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.chakrabarti-nordmark-6man-efficient-nd], which proposes an
   evolution of [RFC6775] for a larger applicability.

   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

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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 small packet sizes.  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.

   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 autoconfiguration and registration neighbor
   discovery protocol (ND-PAAR) modifies Neighbor Discovery Optimization
   for Low-power and Lossy Networks [RFC6775] as explained in this

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].

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

   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 and 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.chakrabarti-nordmark-6man-efficient-nd] to extend the LLN in a
   larger multilink subnet [RFC4903].  In that model, a registration
   flow happens as shown in Figure 2:

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    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)      |               |               |
         |<--------------|               |               |

          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.

   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).

   In order to validate address ownership, that mechanism 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).

   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
   and aware of the address/UID mapping may effectively fake the same
   UID and steal an address.

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   This draft 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.

   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 need 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.  Protocol Operations

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

   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 the in the next NS.

   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.

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  6LN                                                       6LR
   |                                                         |
   |                                                         |
   |---------------NS with ARO and Random UID   --------------->|
   |                                                         |
   |<-----------------------NA with ARO (status=req-proof) --|
   |                                                         |
   |---------------NS with ARO and Random UID->|
   |                                                         |
   |<-----------------------NA with ARO----------------------|
   |                                                         |
   |                                                         |
   |---------------NS with ARO and Random UID   --------------->|
   |                                                         |                                                          |
   |<-----------------------NA with ARO----------------------|
   |                                                         |
   |---------------NS with ARO and Random UID   --------------->|
   |                                                         |                                                          |
   |<-----------------------NA with ARO----------------------|

                   Figure 3: On-link Protocol Operation

4.2.1.  Calculation of Cryptographic Identifier

   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.  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 neighbor discovery option 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 if it is used as IPv6 address.

   6LN also sends some other parameters to enable 6LR or 6LBR to verify
   the crypto ID.  One of them is 6LN's MAC address which is sent in
   Address Registration Option (ARO) as defined in [RFC6775].  The next

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   one is shown in Figure 5.  In that figure, CGA Parameters field
   contains the public key, prefix and some other values.  Digital
   signature option contains the signature of the CGA calculated using
   6LN's private key.

       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            |     Registration Lifetime     |
      |                                                               |
      +                           crypto ID                           +
      |                                                               |

                        Figure 4: Crypto ID Option

   Type: TBA

   Length: 8-bit unsigned integer.  The length of the option in units of
   8 bytes.  It is 2 or 3, if crypto ID is 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.

   Registration Lifetime: 16-bit unsigned integer.  The amount of time
   in units of 60 seconds that the router should retain the NCE for the
   sender of the NS that includes this option.

   Crypto ID 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 |  Sig. Length  |
       |                                                               |
       .                                                               .
       .                        CGA Parameters                         .
       .                                                               .
       |                                                               |
       |                                                               |
       .                                                               .
       .                       Digital Signature                       .
       .                                                               .
       |                                                               |
       |                                                               |
       .                                                               .
       .                           Padding                             .
       .                                                               .
       |                                                               |

                      Figure 5: CGA Parameters Option

   Type TBA

   Length The length of the option in units of 8 octets.

   Pad Length The length of the Padding field.

   Sig Length The length of the Digital Signature field.

   CGA Parameters The CGA Parameters field is variable-length containing
   the CGA Parameters data structure.

   Digital Signature The Digital Signature field is a variable length
   field containing a Elliptic Curve Digital Signature Algorithm (ECDSA)
   signature (with SHA-256 and P-256 curve of [FIPS-186-3]).

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

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   the same message format as NS and NA with different ICMPv6 type

   In ND-PAAR 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
   we need 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.

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-PAAR 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.

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6.  IANA considerations


7.  Acknowledgements


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

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

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

   [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,

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

   [RFC4903]  Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
              DOI 10.17487/RFC4903, June 2007,

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   [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,

   [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,

   [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>.

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

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

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

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

   [Guide]    "Guidelines for 64-bit global Identifier (EUI-64TM)",
              November 2012,

8.2.  Informative references

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

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              Chakrabarti, S., Nordmark, E., Thubert, P., and M.
              Wasserman, "IPv6 Neighbor Discovery Optimizations for
              Wired and Wireless Networks", draft-chakrabarti-nordmark-
              6man-efficient-nd-07 (work in progress), February 2015.

              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work
              in progress), May 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

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

Sarikaya & Thubert       Expires April 21, 2016                [Page 14]