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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Updates: RFC4941 (if approved)                                    W. Liu
Intended status: Standards Track                     Huawei Technologies
Expires: November 24, 2016                                  May 23, 2016

        Recommendation on Non-Stable IPv6 Interface Identifiers


   This document clarifies the stability requirements for IP6 addresses,
   and provides recommendations regarding the generation of non-stable
   addresses.  Finally, it formally updates RFC4941 such that nodes are
   allowed to configure only temporary addresses.

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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   This Internet-Draft will expire on November 24, 2016.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Stability Requirements for IPv6 Addresses . . . . . . . . . .   3
   4.  Requirements for Non-Stable IPv6 Addresses  . . . . . . . . .   3
   5.  Generation of Non-Stable IPv6 Addresses . . . . . . . . . . .   4
   6.  Update to existing RFCs . . . . . . . . . . . . . . . . . . .   4
   7.  Future Work . . . . . . . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IPv6 StateLess Address AutoConfiguration (SLAAC) [RFC4862] has
   traditionally resulted in stable addresses, since the Interface
   Identifier (IID) has been generated by embedding a stable layer-2
   numeric identifier (e.g., a MAC address).  [RFC4941] implies,
   throughout the specification, that temporary addresses are generated
   and employed along with temporary addresses.

   While the use of stable addresses (only) or mixed stable and
   temporary addresses can be desirable in a number of scenarios, there
   are other scenarios in which, for security and privacy reasons, a
   node may want to use only non-stable address (e.g., a temporary

   This document clarifies the requirements for stability of IPv6
   addresses, such that nodes are not required to configure stable
   addresses.  It also specifies a set of requirements for the
   generation of non-stable addresses.  Finally, it formally updates
   [RFC4941] such that temporary addresses can be employed without the
   need to configure a stable address along side.

2.  Terminology

   This document employs the terms defined in [RFC7721].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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3.  Stability Requirements for IPv6 Addresses

   Nodes are not required to generate addresses with any specific
   stability properties.  That is, the generation of stable addresses is
   OPTIONAL.  This means that a node may end up configuring only stable
   addresses, only non-stable, or both stable and non-stable addresses.

4.  Requirements for Non-Stable IPv6 Addresses

   The requirements for non-stable IPv6 addresses are as follows:

   1.  The resulting Interface Identifiers MUST be different when
       addresses are configured for different prefixes.  That is, if
       different autoconfiguration prefixes are used to configure
       addresses for the same network interface card, the resulting
       Interface Identifiers must be (statistically) different.  This
       means that, given two addresses, it must be difficult for an
       outside entity to tell whether the addresses have been generated
       by the same host.

   2.  The resulting interface identifiers MUST NOT embed layer-2
       identifiers (e.g.  MAC addresses).

   3.  It must be difficult for an outside entity to predict the
       Interface Identifiers that will be generated by the algorithm,
       even with knowledge of the Interface Identifiers generated for
       configuring other addresses.

   4.  The resulting Interface Identifiers must be semantically opaque
       and must not follow any specific patterns.

   The IIDs of addresses configured for different autoconfiguration
   prefixes must be different, such that traffic for those addresses
   cannot be correlated.

   The reuse of identifiers that have their own semantics or properties
   across different contexts or scopes can be detrimental for security
   and privacy [I-D.gont-predictable-numeric-ids] [RFC6973] [RFC4941].
   For example, if two different layer-3 protocols generate their
   addresses by embedding a layer-2 identifier (e.g., a MAC address),
   then the traffic for such protocols could be correlated (irrespective
   of whether the aforementioned layer-2 identifier has been randomized
   or not).  Besides, a node that generates an IPv6 address by embedding
   a link-layer address in the IPv6 address will, when configuring
   addresses for different prefixes, result in the same IID being used
   for such prefixes, thus allowing the corresponding traffic to be

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   For security and privacy reasons, the IIDs generated for non-stable
   addresses must not be predictable.  Otherwise, the node may be
   subject to many (if not all) of the security and privacy issues that
   are meant to be mitigated (please see [RFC7721].

   Any semantics or patterns in an IID might be leveraged by an attacker
   to e.g. reduce the search space when performing address-scanning
   attacks, infer the identity of the node, etc.

5.  Generation of Non-Stable IPv6 Addresses

   One possible algorithm for generating non-stable IPv6 addresses is
   that specified in [RFC4941].

   Another possible approach would be to select a random IID when
   performing SLAAC.  In this case, a node that disconnects from the
   network and subsequently reconnects would employ a (statistically
   different) IID for the same prefix.  A different (random) IID should
   be employed for each autoconfiguration prefix.  These addresses, as
   opposed to the temporary addresses specified in RFC4941, would be
   stable for as long as the node stays attached (without disconnecting)
   to the network, but would change when a node reconnects.

6.  Update to existing RFCs

   The following subsections clarify how each of the RFCs affected by
   this document are updated.

6.1.  Update to RFC4941

   The temporary addresses specified in [RFC4941] MAY be used in
   replacement of the stable addresses [I-D.ietf-6man-default-iids].
   That is, a node MAY configure temporary addresses only, without
   configuring any stable addresses.

7.  Future Work

   This document clarifies the requirements for stability requirements
   for IPv6 addresses.  A subsequent document will discuss the tradeoffs
   involved when considering different stability properties of IPv6
   addresses, and and the different configuration setups such as: stable
   addresses only, non-stable addresses only, or mixed stable and non-
   stable addresses.

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8.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an

9.  Security Considerations

   This document clarifies the stability requirements for IPv6
   addresses, and specifies requirements for the generation of non-
   stable addresses.  Additionally, it formally updates [RFC4941] such
   that stable addresses are not required to be configured along with
   the temporary addresses.

10.  Acknowledgements

   The authors would like to thank (in alphabetical order) [TBD] for
   providing a detailed review of this document.

11.  References

11.1.  Normative References

              Gont, F., Cooper, A., Thaler, D., and S. LIU,
              "Recommendation on Stable IPv6 Interface Identifiers",
              draft-ietf-6man-default-iids-11 (work in progress), April

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [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>.

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

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   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

11.2.  Informative References

              Gont, F. and I. Arce, "Security and Privacy Implications
              of Numeric Identifiers Employed in Network Protocols",
              draft-gont-predictable-numeric-ids-00 (work in progress),
              February 2016.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC7721]  Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
              Considerations for IPv6 Address Generation Mechanisms",
              RFC 7721, DOI 10.17487/RFC7721, March 2016,

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com

   Will Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com

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