Designating 6LBR for IID Assignment
draft-rashid-6lo-iid-assignment-00

Abstract

In IPv6 Stateless Address Autoconfiguration (SLAAC), use of a random interface identifier (IID) is a common practice to promote privacy. If there are a very large number of nodes, as has been discussed in several use cases, the effect will to proportionately increase the number of IIDs. A duplicate address detection (DAD cycle) is needed for each configured IID, introducing more and more overhead into the network. Each failed DAD requires the initiating node to regenerate a new IID and undergo the DAD cycle again. This document proposes an optimized approach that requires 6LBR (6LoWPAN Border Router) to provide a unique IID, avoiding the potential duplication.

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This Internet-Draft will expire on September 17, 2016.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. IID Assignment by 6LBR
• 3.1. Extended Confirmation Message
• 3.2. Extended Address Registration Option
• 4. IANA Considerations
• 4.1. Additions of EDAC Message and EARO Option
• 4.2. Additions to Status Field
• 5. Security Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Authors' Addresses

1. Introduction

IPv6 addresses in SLAAC are formed by concatenating a network prefix, acquired from Router Advertisement (RA) messages, with a locally generated IID [RFC4862], [RFC2464]. Since the best method for generating IIDs depends on the nature of networks, none of the proposed mechanisms is considered a default mechanism [RFC4941], [RFC7217]. Using neighbour discovery (ND), the uniqueness of newly generated IID is verified [RFC6775]. 6LBR ensures the duplication detection, and replies with a status. A failed DAD would require the initiating 6LN (6LoWPAN Node) to regenerate an IID and undergo another DAD cycle, until either 6LN succeeds or reaches its maximum number of retries[RFC6775].

A locally generated IID can be derived from embedded IEEE identifier [RFC4941] or randomly (based on a few variables) [RFC7217]. MAC reuse is far common than assumed [RFC7217], and IIDs derived from MAC address are likely to cause more than the expected number of DAD failures. As soon as the 6LN generates an IID, it sends the NS (Neighbor Solicitation) message to 6LR (LLN Router) and 6LR proceeds with the address duplication request routine with 6LBR by sending an ICMPv6 based DAR (Duplicate Address Request) message. An LN sends out a NS after checking its local cache for duplication; before proceeding with DAR, the 6LR also protects against address duplication within a locally maintained Neighbor Cache Entry (NCE) [RFC7217].

[RFC5548], [RFC5827] discuss use cases including huge numbers of nodes and vast scale networks. The arbitrary use of IIDs resolves the privacy concerns of participating node. A simple NS supposedly targeted to a very small group of nodes MAY ends-up polluting whole wireless bandwidth [I-D.vyncke-6man-mcast-not-efficient]. Multicast NS and NA are much more frequent in large scale radio environment with mobile devices [I-D.thubert-6lo-backbone-router]. Additionally, as the IIDs are periodically changed for privacy, the probability becomes high for a duplicate IIDs that would results in DAD failure and repeated cycles.

This document describes optimization to 6LoWPAN ND by enabling 6LBR to grant a unique IID for failed DAD.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Additionally, this document uses terminology from [RFC6775], [RFC2464], [I-D.ietf-6man-default-iids], and [I-D.ietf-6man-ipv6-address-generation-privacy]. This document also uses the following terms:

RID: Random identifier.

PRF: Pseudo random function.

LSB: Least significant bit.

EDAC: Extended duplicate address confirmation.

EARO: Extended address registration option.

3. IID Assignment by 6LBR

MAC driven IIDs [RFC2464] reduce or eliminate the the need for DAD, but in practice such IID generation is discouraged ([I-D.ietf-6man-default-iids], [I-D.ietf-6man-ipv6-address-generation-privacy]), as common privacy concerns still persist, for instance:

o Network activity correlation,

o Location tracking,

o Address scanning, and

o Device-specific vulnerability exploitation.

Moreover, multiple approaches are proposed to suit different network constraints. Considering the scalability of a network and enabling 6LBR to suggest an IID, this draft proposes another IID generating [RFC7217] approach to support periodically changing IIDs.

   RID (Random Identifier) :=
    |Prefix|Interface Index|N/W ID|DAD Counter|Randomized Secret Key|
          \                                            /
              \                                    /   
                  \                            /
                   +--------+--------+--------+
                   |      Hash Function       |
                   +--------+--------+--------+
                  /                            \
                /                                \ 
                        Extract 64 LSBs

        6LN                           6LR                        6LBR
         |                             |                           |
   1.    | --- NS with Address Reg --> |                           |
         |       [ARO + SLLAO]         |                           |
         |                             |                           |
   2.    |                             | ---------- DAR ---------> |
         |                             |                           |
   3.    |                             | <--------- EDAC --------- |
         |                             |                           |
   4.    | <-- NA with Address Reg --- |                           |
         |      [EARO with Status]     |                           |

     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     |      Code     |            Checksum           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Status      |    Reserved   |       Registration Lifetime   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                            EUI-64                             +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                     6LBR Generated IID                        +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Type     |   Length = 2  |     Status    |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved            |     Registration Lifetime     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                            EUI-64                             +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +                     6LBR Generated IID                        +
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    

 
         +--------+--------------------------------------------+
         | Status | Description                                |
         +--------+--------------------------------------------+
         | 0      | Success                                    |
         | 1      | Duplicate Address                          |
         | 2      | Neighbor Cache Full                        |
         | 3      | 6LBR generated IID                         |
         | 4-255  | Allocated using Standards Action [RFC5226] |
         +--------+--------------------------------------------+
                        Addition to Status bits