IPv6 maintenance Working Group                                   F. Gont
(6man)                                                           UTN/FRH
Internet-Draft                                               R. Broersma
Updates: 4861 (if approved)                                         DREN
Intended status: Standards Track                          March 12, 2011
Expires: September 13, 2011


      Managing the Use of Privacy Extensions for Stateless Address
                       Autoconfiguration in IPv6
             draft-gont-6man-managing-privacy-extensions-01

Abstract

   This document describes an operational problem that arises due to the
   impossibility of managing the use of "Privacy Extensions" for IPv6
   Stateless Address Autoconfiguration (SLAAC) in network scenarios that
   employ SLAAC.  Additionally, this document specifies new flag in the
   Prefix Information option of Router Advertisement messages, such that
   routers can advertise, for each network prefix to be used for SLAAC,
   whether the aforementioned "Privacy Extensions" should be used.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.

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   This Internet-Draft will expire on September 13, 2011.

Copyright Notice

   Copyright (c) 2011 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



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   (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
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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Updating the Prefix Information option . . . . . . . . . . . .  4
     2.1.  Router specification . . . . . . . . . . . . . . . . . . .  5
     2.2.  Host specification . . . . . . . . . . . . . . . . . . . .  5
   3.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     6.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Possible alternatives . . . . . . . . . . . . . . . . 11
     A.1.  Specifying a 'hardware-addresses' bit  . . . . . . . . . . 11
     A.2.  Specifying a 'privacy-addresses' bit . . . . . . . . . . . 12
   Appendix B.  Changes from previous versions of the draft (to
                be removed by the RFC Editor before publication
                of this document as a RFC . . . . . . . . . . . . . . 14
     B.1.  Changes from
           draft-gont-6man-managing-privacy-extensions-00 . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15





















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1.  Introduction

   [RFC4862] specifies the Stateless Address Autoconfiguration (SLAAC)
   for IPv6, which typically results in hosts configuring one or more
   addresses composed of a network prefix advertised by a local router,
   and an Interface Identifier (IID) derived from a hardware address
   (such as an Ethernet MAC address).

   Since e.g.  Ethernet MAC addresses are typically globally unique,
   IPv6 addresses generated as specified in [RFC4862] could possibly be
   levareged to track and correlate the activity of a node, thus
   negatively affecting the privacy of users.

   The "Privacy Extensions for Stateless Address Autoconfiguration in
   IPv6" [RFC4941] were introduced difficult the task of eavesdroppers
   and other information collectors to correlate the activities of a
   node, and basically result in random Interface Identifiers which may
   be more difficult to leverage than their hardware-derived
   counterpart.  These "Privacy Extensions" have been implemented in a
   variety of systems, some of which (notably that in Microsoft Windows
   Vista and Microsoft Windows 7) enable them by default.

   The imposibility of managing the use of "Privacy Extensions" poses
   poses a problem when a site has a specific policy for the generation
   of IPv6 Interface Identifiers.  For example, if hosts that enable
   "Privacy Extensions" (by default) need to be deployed on sites that
   require the use of hardware-derived Interface Identifiers, an
   administrator may need to manually disable the use of "Privacy
   Extensions" in each of the attached nodes.  This not only may result
   in a lot of work on the side of the administrator, but may also be
   difficult to implement (particularly when considering mobile
   computers such as laptops) [Broersma].  On the other hand, in some
   environments (e.g., a typical home network) the use of "Privacy
   Extensions" might be desirable.  However, the imposibility to
   automatically enable "Privacy Extensions" may preclude their use
   (unless they are manually enabled by the administrator).

   This document specifies a new flag in the Prefix Information option
   of Router Advertisement messages, such that routers can advertise,
   for each network prefix to be used for SLAAC, whether the
   aforementioned "Privacy Extensions" should be used.

   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 RFC 2119 [RFC2119].






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2.  Updating the Prefix Information option

   The syntax of the Prefix Information option is updated as follows:


      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     | Prefix Length |L|A|R|SAG|Rsvd1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Valid Lifetime                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Preferred Lifetime                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved2                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                            Prefix                             +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An additional field, the two-bit "SAG" (Stateless Address Generation)
   field, is ispecified for the Prefix Information option.  The
   semantics of each of the possible values are:

   00:
      No specific advice is provided for the generation of addresses for
      this prefix.

   01:
      When generating addresses for this prefix, the resulting addresses
      SHOULD be based on the underlying hardware address of the
      interface (e.g., the Ethernet MAC address).

   10:
      When generating addresses for this prefix, Privacy Extensions for
      SLAAC SHOULD be employed.

   11:
      Unused (reserved for future use).







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      The "R" bit was specified by [RFC3775].  The Rsvd1 field
      corresponds to the remaining reserved bits, and thus MUST be set
      to zero by the sender of this option, and ignored by the receiver.

   Since the "SAG" bits correspond to a previously "reserved" field,
   implementations that predate this specification should be setting the
   SAG field to "00" when sending the option, and ignoring the SAG bits
   upon receipt.

2.1.  Router specification

   Routers that have no particular preference on the address generation
   policy MUST set the SAG bits to "00".  Otherwise, they SHOULD set the
   SAG bits to "01" or "10" according to the preferred address
   generation policy.  The special value "11" is reserved for future
   extensions, and MUST NOT be set by routers implementing this
   specification.

2.2.  Host specification

   When generating addresses for the prefix contained in the "Prefix
   Information Option", hosts SHOULD apply the policy specified by the
   "SAG" field.  If no specific advice is provided (i.e., the SAG field
   is set to "00"), hosts are free with respect to which policy to
   employ when generating addresses for this prefix.  Hosts that
   implement this specification MUST interpret the special value "11" in
   the same way as "00" (i.e., no specific advice is provided for
   address generation).























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3.  Security Considerations

   An attacker could exploit the mechanism specified in this document to
   cause hosts in a given subnet to disable Privacy Extensions, thus
   causing their Interface Identifiers to be derived from hardware
   addresses, instead.  Thus, the privacy of the victim hosts that would
   have enabled the Privacy Extensions could possibly be reduced.

   However, it should be noted that this attack would require from an
   attacker the same effort as all the other Neighbor Discovery attack
   vectors that are based on crafted Router Advertisement messages, most
   of which are far more interesting for an attacker than this possible
   attack vector.

   Among the possible options for mitigating this and other attack
   vectors based on crafted Router Advertisement messages is the
   deployment of the so-called "Router Advertisement guard" mechanism
   [I-D.ietf-v6ops-ra-guard].

   SEND (SEcure Neighbor Discovery) [RFC3971] could be pontentially
   deployed to mitigate most Neighbor Discovery attacks.  However, a
   number of issues (such as the requirement for Public Key
   Infrastructure) preclude the deployment of SEND in most general
   network scenarions.  [CPNI-IPv6]

   Finally, we note that while the value and effectiveness of privacy
   addreses have been questioned in a number of studies
   [I-D.dupont-ipv6-rfc3041harmful] [Escudero] [CPNI-IPv6], this
   document does not take a stance about their value and effectiveness:
   it limits itself to discussing the operational problem that arises
   due to the impossibility of managing the use of "Privacy Extensions",
   and updating the "Prefix Information" option such that "Privacy
   Extensions" can be more easily managed when IPv6 Stateless Address
   Autoconfiguration (SLAAC) is employed.

















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4.  IANA Considerations

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














































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5.  Acknowledgements

   Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for
   their continued support.















































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6.  References

6.1.  Normative References

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

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

   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
              in IPv6", RFC 3775, June 2004.

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

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

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

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

6.2.  Informative References

   [I-D.ietf-v6ops-ra-guard]
              Levy-Abegnoli, E., Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard",
              draft-ietf-v6ops-ra-guard-08 (work in progress),
              September 2010.

   [I-D.dupont-ipv6-rfc3041harmful]
              Dupont, F. and P. Savola, "RFC 3041 Considered Harmful",
              draft-dupont-ipv6-rfc3041harmful-05 (work in progress),
              June 2004.

   [Broersma]
              Broersma, R., "IPv6 Everywhere: Living with a Fully IPv6-
              enabled environment",  Australian IPv6 Summit 2010,
              Melbourne, VIC Australia, October 2010,
              <http://www.ipv6.org.au/summit/talks/Ron_Broersma.pdf>.

   [Escudero]
              Escudero, A., "PRIVACY EXTENSIONS FOR STATELESS ADDRESS



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              AUTOCONFIGURATION IN IPV6 - "REQUIREMENTS FOR
              UNOBSERVABILITY",  RVK02, Stockholm, 2002,
              <http://web.it.kth.se/~aep/PhD/docs/paper3-rvk2002.pdf>.

   [CPNI-IPv6]
              Gont, F., "Security Assessment of the Internet Protocol
              version 6 (IPv6)",  UK Centre for the Protection of
              National Infrastructure, (to be published).











































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Appendix A.  Possible alternatives

   The following subsections describe possible alternatives (less
   optimal from the point of vew of the authors of this document).  The
   main drawback is that if a single bit is specifed, then it's
   impossible to disambiguate between the case in which this
   specification is not supported (and thus the bit was "Reserved and
   set to "0"), and the case whether this specification is supported and
   the correspoding bit is meant to give specific advice on the desired
   address generation policy.

A.1.  Specifying a 'hardware-addresses' bit

   The syntax of the Prefix Information option is updated as follows:


      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     | Prefix Length |L|A|R|H| Rsvd1 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Valid Lifetime                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Preferred Lifetime                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved2                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                            Prefix                             +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   An additional bit, "H" ("Hardware-derived addresses"), is specified
   for the Prefix Information option.  When set, this bit indicates that
   hardware-derived addresses SHOULD be used when configuring IPv6
   addresses as a result of Stateless Address Autoconfiguration.  When
   not set, this bit indicates that Privacy Extensions SHOULD be enabled
   when configuring IPv6 addresses as a result of Stateless Address
   Autoconfiguration








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      The "R" bit was specified by [RFC3775].  The Rsvd1 field
      corresponds to the remaining reserved bits, and thus MUST be set
      to zero by the sender of this option, and ignored by the receiver.

   Since the "H" bit was a previously reserved field, implementations
   that predate this specification should be setting this bit to zero
   when sending the option, and ignoring this bit upon receipt.

   The following table illustrates the result of SLAAC depending on
   whether this specification is supported by the router and/or the host
   participanting in SLAAC.

   +---------------+--------------------------+------------------------+
   | Router / Host |         Supported        |      Not Supported     |
   +---------------+--------------------------+------------------------+
   |   Supported   |  As indicated by the "H" |      As in current     |
   |               |            bit           |        scenarios       |
   +---------------+--------------------------+------------------------+
   | Not Supported |     Privacy Addresses    |      As in current     |
   |               |                          |        scenarios       |
   +---------------+--------------------------+------------------------+

               Table 1: Possible results of SLAAC scenarios

A.2.  Specifying a 'privacy-addresses' bit

   If rather than specifying an "H" bit, our I-D were to specify a "P"
   ("Privacy addresses") bit, the resulting possible scenarios would
   change as follows:

   The following table illustrates the result of SLAAC depending on
   whether this specification is supported at the router and/or host
   participanting in SLAAC.

   +---------------+---------------------------+-----------------------+
   | Router / Host |         Supported         |     Not Supported     |
   +---------------+---------------------------+-----------------------+
   |   Supported   |  As indicated by the "P"  |     As in current     |
   |               |            bit            |       scenarios       |
   +---------------+---------------------------+-----------------------+
   | Not Supported |      Hardware-derived     |     As in current     |
   |               |         addresses         |       scenarios       |
   +---------------+---------------------------+-----------------------+

             Table 2: Alt. Possible results of SLAAC scenarios

   As you may see, in this case only one scenario changes: when this
   spec is not supported by the router, but *is* supported by the host,



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   hardware addresses are used.  This would mean that if e.g.  MS were
   to implement this spec before e.g.  Cisco, Privacy Addresses would be
   disabled.

   Clearly, there's a tradeoff here.














































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Appendix B.  Changes from previous versions of the draft (to be removed
             by the RFC Editor before publication of this document as a
             RFC

B.1.  Changes from draft-gont-6man-managing-privacy-extensions-00

   o  Rather that specifying a single bit in the Prefix Information
      Options, a two-bit SAG field is specified -- with the previous
      options being moved to an appendix (Appendix A).

   o  Fixes writeos in the tables contained in Appendix A.1 and
      Appendix A.2.







































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Authors' Addresses

   Fernando Gont
   Universidad Tecnologica Nacional / Facultad Regional Haedo
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fernando@gont.com.ar


   Ron Broersma
   Defense Research and Engineering Network

   Email: ron@spawar.navy.mil



































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