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DHC Working Group                                            T. Fujisaki
Internet-Draft                                              A. Matsumoto
Intended status: Standards Track                                     NTT
Expires: April 16, 2010                                        R. Hiromi
                                                           Intec Netcore
                                                        October 13, 2009


           Distributing Address Selection Policy using DHCPv6
               draft-fujisaki-dhc-addr-select-opt-08.txt

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   Copyright (c) 2009 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document describes a new DHCPv6 option for distributing address
   selection policy information defined in RFC3484 to a client.  With
   this option, site administrators can distribute address selection
   policy to control the node's address selection behavior.


1.  Introduction

   RFC3484 [RFC3484] describes algorithms for selecting a default
   address when a node has multiple destination and/or source addresses
   by using an address selection policy.  However, there are some
   problems with the default address selection policy in RFC3484
   [RFC5220], and mechanisms to control a proper source address
   selection will be necessary.  Requiremets for those mechanisms are
   described in [RFC5221], and solutions are discussed in
   [I-D.ietf-6man-addr-select-sol] This document describes an option for
   distributing address selection policy information using DHCPv6, which
   is refered as `most proactive approach' in the solution document.

1.1.  Conventions Used in This Document

   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 [RFC2119].

1.2.  Terminology

   This document uses the terminology defined in [RFC2460] and the DHCP
   specification defined in [RFC3315]


2.  Address Selection Policy Option

   The Address Selection Policy Option provides policy information for
   address selection rules.  Specifically, it transmits a set of IPv6
   source and destination address prefixes and some parameters that are
   used to control address selection as described in RFC 3484.

   Each end node is expected to configure its policy table, as described
   in RFC 3484, using the Address Selection Policy option information as



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   an reference.

   The format of the Address Selection Policy option is given below:




       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          OPTION_DASP          |         option-len            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    label      |  precedence   |z|n|  reserved |   prefix-len  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               zone-index (if present (z = 1))                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   Prefix   (Variable Length)                  |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    label      |  precedence   |z|n| reserved  |   prefix-len  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               zone-index (if present (z = 1))                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   Prefix   (Variable Length)                  |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    label      |  precedence   |z|n| reserved  |   prefix-len  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               zone-index (if present (z = 1))                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   Prefix   (Variable Length)                  |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                                [Fig. 1]




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   Fields:

   option-code:  OPTION_DASP (TBD)

   option-len:  The total length of the label fields, precedence fields,
        zone-index fields, prefix-len fields, and prefix fields in
        octets.

   label:  An 8-bit unsigned integer; this value is used to make a
        combination of source address prefixes and destination address
        prefixes.

   precedence:  An 8-bit unsigned integer; this value is used for
        sorting destination addresses.

   z bit  'zone-index' bit.  If z bit is set to 1, 32 bit zone-index
        value is included right after the "prefix-len" field, and
        "Prefix" value continues after the "zone-index" field.  If z bit
        is 0, "Prefix" value contitunes right after the "prefix-len"
        value.

   n bit  'no privacy iid' bit.  If n bit is set to 1, RFC 4941
        [RFC4941] privacy extensions MUST not be used for this prefix.
        If n bit is 0, interface ID may use RFC4941.

   reserved  6-bit reservied field.  Initialized to zero by sender, and
        ignored by receiver.

   zone-index:  If z-bit is set to 1, this field is inserted between
        "prefix-len" field and "Prefix" field.  Zone-index field is an
        32-bit unsigned integer and used to specify zones for scoped
        addresses.  This bit length is defined in RFC3493 [RFC3493] as
        'scope ID'.

   prefix-len:  An 8-bit unsigned integer; the number of leading bits in
        the prefix that are valid.  The value ranges from 0 to 128.  The
        Prefix field is 0, 4, 8, 12, or 16 octets, depending on the
        length.

   Prefix:  A variable-length field containing an IP address or the
        prefix of an IP address.  IPv4-mapped address [mapped] must be
        used to represent an IPv4 address as a prefix value.



3.  Appearance of this Option

   The Address Selection Policy option MUST NOT appear in any messages



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   other than the following ones : Solicit, Advertise, Request, Renew,
   Rebind, Information-Request, and Reply.


4.  Implementation Considerations

   o  The value 'label' is passed as an unsigned integer, but there is
      no special meaning for the value, that is whether it is a large or
      small number.  It is used to select a preferred source address
      prefix corresponding to a destination address prefix by matching
      the same label value within this DHCP message.  DHCPv6 clients
      need to convert this label to a representation specified by each
      implementation (e.g., string).

   o  Currently, the value label, precedence are defined as 8-bit
      unsigned integers.  In almost all cases, this value will be
      enough.

   o  The 'precedence' is used to sort destination addresses.  There
      might be some cases where precedence values will conflict when a
      client already has a selection policy configured or a client
      receives multiple policies from multiple DHCP servers (e.g., when
      a home gateway in a user network is connected to multiple upstream
      ISPs).  In such cases, manual configuration of the policy will be
      necessary.

   o  The maximum number of address selection rules in one DHCPv6
      message depend on the prefix length of each rules and maximum
      DHCPv6 message size defined in RFC3315.  It is possible to carry
      over 3,000 rules (e.g. default policy table defined in RFC3484
      contains 5 rules) in one DHCPv6 message (maximum UDP message
      size).

   o  Since the number of selection rules would be large, policy
      distributer should be care about the DHCPv6 message size.

   o  If a node has multiple interfaces, the node may have multiple
      address selection policies.  Since RFC3484 policy table is one and
      global for a node, multiple polices should be merged in one.  In a
      case that node's interfaces belong to different management domain
      (e.g. each interfaces are connected different site), it would have
      conflict policies.  Solutions for this policy conflict are
      discussed in [I-D.arifumi-6man-addr-select-conflict].








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5.  Discussion

   o  The 'zone index' value is used to specify a particular zone for
      scoped addresses.  This can be used effectively to control address
      selection in the site scope (e.g., to tell a node to use a
      specified source address corresponding to a site-scoped multicast
      address).  However, in some cases such as a link-local scope
      address, the value specifying one zone is only meaningful locally
      within that node.  There might be some cases where the
      administrator knows which clients are on the network and wants
      specific interfaces to be used though.  However, in general case,
      it is hard to use this value.

   o  Since we got a comment that some implementations use 32-bit
      integers for zone index value, we extended the bit lenght of the
      'zone index' field.  However, as described above, there might be
      few cases to specify 'zone index' in policy distribution, we
      defined this field as optional, controled by a flag.

   o  There may be some demands to control the use of special address
      types such as the temporary addresses described in RFC4941
      [RFC4941], address assigned by DHCPv6 and so on. (e.g., informing
      not to use a temporary address when it communicate within the an
      organization's network).  It is possible to indicate the type of
      addresses using reserved field value.

   o  We also proposed a policy distribution option using a Router
      Advertisement message defined in RFC4861 [RFC4861].  There was a
      discussion that using DHCPv6 was more suitable to distribute a
      selection policy, because such policy should be distributed under
      the site administrator's centralized control.



6.  Security Considerations

   A rogue DHCPv6 server could issue bogus address selection policies to
   a client.  This might lead to incorrect address selection by the
   client, and the affected packets might be blocked at an outgoing ISP
   because of ingress filtering.

   To guard against such attacks, both DCHP clients and servers SHOULD
   use DHCP authentication, as described in section 21 of RFC 3315,
   "Authentication of DHCP messages."







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7.  IANA Considerations

   IANA is requested to assign option codes to OPTION_DASP from the
   option-code space as defined in section "DHCPv6 Options" of RFC 3315.


Appendix A.  RFC3484 implementation status

   Today, many operating systems implement address selection mechanism
   defined in RFC3484.  Many of them, however, implement the
   specification partially.  We summarize current implementation status
   of RFC 3484 at http://www.nttv6.net/dass/.


Appendix B.  Revision History

   08:
      Add reference for policy conflict discussion.
      Update some references.

   07:
      Added the n bit and its description.

   06:
      Added the reason to extend zone index field in discussions
      section.
      References updated.
      Authors' e-mail addresses corrected.
      Some editorial changes.

   05:
      Extended bit length of the zone-index field to 32-bits (thank you
      Jinmei-sanfor your comment), and changed packet format to reflect
      the extension.
      Refrect Yoshifuji-san's comment to use this option information as
      an reference.
      Modified the text controling special address types.

   04:
      Added description about policy merge.
      Modified the text controling special address types.

   03:
      Discussion about DHCPv6 packetsize and number of rules added.







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      Authors' e-mail addresses corrected.
      Some editorial changes.


8.  References

8.1.  Normative References

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

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

8.2.  Informative References

   [I-D.arifumi-6man-addr-select-conflict]
              Matsumoto, A., Fujisaki, T., and R. Hiromi,
              "Considerations of address selection policy conflicts",
              draft-arifumi-6man-addr-select-conflict-00 (work in
              progress), July 2009.

   [I-D.ietf-6man-addr-select-sol]
              Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
              "Solution approaches for address-selection problems",
              draft-ietf-6man-addr-select-sol-02 (work in progress),
              July 2009.

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

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6",
              RFC 3493, February 2003.

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

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

   [RFC5220]  Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,



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              "Problem Statement for Default Address Selection in Multi-
              Prefix Environments: Operational Issues of RFC 3484
              Default Rules", RFC 5220, July 2008.

   [RFC5221]  Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
              "Requirements for Address Selection Mechanisms", RFC 5221,
              July 2008.


Authors' Addresses

   Tomohiro Fujisaki
   NTT PF Lab
   3-9-11 Midori-Cho
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 7351
   Email: fujisaki@nttv6.net


   Arifumi Matsumoto
   NTT PF Lab
   3-9-11 Midori-Cho
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 3334
   Email: arifumi@nttv6.net


   Ruri Hiromi
   Intec Netcore, Inc.
   Shinsuna 1-3-3
   Koto-ku, Tokyo  136-0075
   Japan

   Phone: +81 3 5665 5069
   Email: hiromi@inetcore.com












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