Network Working Group                                             F. Xia
Internet-Draft                                               B. Sarikaya
Expires: April 25, 2010                                         S. Jiang
                                                     Huawei Technologies
                                                        October 22, 2009


        Usage of Host Generating Interface Identifier in DHCPv6
                    draft-xia-dhc-host-gen-id-02.txt

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Abstract

   This document describes a procedure for configuring a host's IPv6
   address which prefix is allocated from a DHCPv6 server while it's
   interface identifier is independently generated by the host.  The
   method is applicable to Cryptographically Generated Addresses (CGA).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Address Auto-configuration in SEND . . . . . . . . . . . . . .  4
   4.  DHCPv6 Operation . . . . . . . . . . . . . . . . . . . . . . .  4
   5.  DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Identity Association for Prefix Assignment Option  . . . .  6
     5.2.  IA_PD Prefix option  . . . . . . . . . . . . . . . . . . .  8
     5.3.  IA Address Option  . . . . . . . . . . . . . . . . . . . .  8
   6.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  IANA consideration . . . . . . . . . . . . . . . . . . . . . .  8
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     10.2. Informative references . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

























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1.  Introduction

   [RFC3315] describes the operation of address assignment by a DHCP
   server.  A client uses a Solicit message to discover DHCP servers
   configured to assign addresses.  A server sends an Advertise message
   in response to announce the availability of the server to the client.
   The client then uses a Request message to request addresses.  The
   server then returns addresses in a Reply message.  The operation
   assumes that the server is responsible for the assignment of an
   integral address which include prefix and interface identifier parts
   as described in [RFC4291].

   [RFC3633] defines Prefix Delegation options providing a mechanism for
   automated delegation of IPv6 prefixes using the DHCPv6.  This
   mechanism is intended for delegating a long-lived prefix from a
   delegating router to a requesting router.  The practice of separating
   prefix assignment from interface identifier assignment is only used
   for routers not hosts.

   [RFC3972] describes a method for binding a public signature key to an
   IPv6 address in the Secure Neighbor Discovery (SEND) protocol
   [RFC3971].  The basic idea is to generate the interface identifier
   (i.e., the rightmost 64 bits) of the IPv6 address by computing a
   cryptographic hash of the public key.  That is, the host decides its
   interface identifier.  As for the prefix part of the CGA, it is
   probably got through Router Advertisement message defined in
   [RFC4861], or through DHCPv6 operations defined in this document.

   [I-D.ietf-csi-dhcpv6-cga-ps]describes potential issues in the
   interaction between DHCPv6 and CGA.  A usage of DHCPv6 for generating
   CGA is proposed in the document to facilitate separation of prefix
   and interface identifier assignment.  A host's IPv6 address prefix is
   allocated from a DHCPv6 server while interface identifier is
   independently generated by the host.


2.  Terminology

   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].

   The terminology in this document is based on the definitions in
   [RFC3315], in addition to the ones specified in this section







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   derivative prefix:  A prefix is derived from another prefix.  For
      example, a /64 prefix is derived from a /48 prefix, that is, the
      /64 prefix has the same leftmost 48 bits with the /48 prefix.

   authorized prefix:  A specific router is given a specific set of
      subnet prefixes to advertise; other routers have an authorization
      to advertise other subnet prefixes.  In [RFC3971],Certification
      Path Advertisement message is used to convey authorized prefixes.


3.  Address Auto-configuration in SEND

   Router Advertisements in [RFC4861] allow routers to inform hosts how
   to perform Address Auto-configuration.  For example, routers can
   specify whether hosts should use DHCPv6 and/or stateless address
   configuration.  In Router Advertisement message, M and O bits are
   used for indication of address auto-configuration mode.

   Whatever address auto-configuration mode a host uses, the following
   two parts are necessary for the host to formulate it's IPv6 address:

   o  A prefix part.  In [RFC3971], Certification Path Solicitation and
      Certification Path Advertisement messages are designed for
      verifying routers being authorized to act as routers.
      Certification Path Advertisement message can also be used to
      verify that routers are authorized to advertise a certain set of
      subnet prefixes.  In stateless auto-configuration mode, the
      prefixes in Router Advertisement message should be a subset of
      authorized prefixes, or derivative prefixes from authorized
      prefixes.  In the stateful auto-configuration mode, Section 4
      illustrates a procedure for prefix allocation from a DHCPv6
      server.
   o  An interface identifier.  The basic idea of [RFC3972] is to
      generate the interface identifier (i.e., the rightmost 64 bits) of
      the IPv6 address by computing a cryptographic hash of a public key
      of a host.  The host is responsible for interface identifier
      generation.


4.  DHCPv6 Operation

   Figure 1 shows the operation of separating prefix assignment and
   interface identifier generation.







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        +------------+          +-----------+
        |Host(Client)|          |DHCP Server|
        +------------+          +-----------+
              |                       |
              |                       |
              |                       |
              |  1 Solicit            |
              |---------------------> |
              |                       |
              |  2 Advertise          |
              |<--------------------- |
              |                       |
              |                       |
    3 Combination of Prefix           |
     and Interface Identifier         |
              |                       |
              |                       |
              |  4 Request            |
              |---------------------> |
              |                       |
              |  5 Reply              |
              |<--------------------- |
              |                       |
              |                       |


                        Figure 1: DHCPv6 Operation

   1.  A host uses a Solicit message to discover DHCP servers configured
       to assign prefixes for the host.  Identity Association for Prefix
       Delegation Option (IA_PD) is defined in [RFC3633] for prefix
       delegation between a requesting router and delegating router.
       Referring to the definition, we design Identity Association for
       Prefix Assignment Option (IA-PA) in Section 5.1 for prefix
       assignment from a DHCPv6 server to a host.  The host uses hints
       for prefix assignment preference.  The hints are authorized
       prefixes advertised by an authorized router through Certification
       Path Advertisement defined in [RFC3971].
   2.  Based on the hints, the DHCP server assigns one or more prefixes
       to the host.  The assigned prefixes SHOULD be a subset of the
       authorized prefixes or derivative prefixes of the authorized
       prefixes.  Identity Association for Prefix Assignment Option in
       Section 5.1 is used for conveying the assigned prefixes.  If
       there is not a proper prefix available, a status-code is returned
       to the host and the procedure is terminated.
   3.  The host generates an interface identifier and formulates a
       combined IPv6 address by concatenating the assigned prefix and
       the self-generated interface identifier.  There are many ways to



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       generate interface identifier.  [RFC3972] defines a method to
       generate the interface identifier by computing a cryptographic
       hash of a public key of the host.
   4.  The host sends a Request message for confirming usage of the
       combined address.  An IA Address option described in Section 5.3
       SHOULD be included to convey the combined address.
   5.  The DHCP server SHOULD verify the uniqueness of the combined IP
       address, and send Reply with IA Address option to grant the usage
       of the combined address.  Otherwise, a status code is included to
       deny the usage of the combined address.


5.  DHCPv6 Options

   In this section, one new option is defined, Identity Association for
   Prefix Assignment Option .  At the same time, we extend the usage of
   existing options, IA_PD Prefix and IA Address option.

5.1.  Identity Association for Prefix Assignment Option

   The IA_PA option is used to carry a prefix assignment identity
   association, the parameters associated with the IA_PA and the
   prefixes associated with it.

   The format of the IA_PA option is:


























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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         OPTION_IA_PA          |         option-length         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         IAID (4 octets)                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              T1                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                              T2                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    .                                                               .
    .                          IA_PA-options                        .
    .                                                               .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   option-code:      OPTION_IA_PA (TDB by IANA)

   option-length:    12 + length of IA_PA-options field.

   IAID:             The unique identifier for this IA_PA; the IAID must
                     be unique among the identifiers for all of this
                     host's IA_PAs.

   T1:               The time at which the host should
                     contact the DHCPv6 server from which the
                     prefixes in the IA_PA were obtained to extend the
                     lifetimes of the prefixes assigned to the IA_PA;
                     T1 is a time duration relative to the current time
                     expressed in units of seconds.

   T2:               The time at which the host should
                     contact any available DHCPv6 server to extend
                     the lifetimes of the prefixes assigned to the
                     IA_PA; T2 is a time duration relative to the
                     current time expressed in units of seconds.

   IA_PA-options:    Options associated with this IA_PA.



   The details of the fields are similar to the IA_PD option description
   in [RFC3633].  The difference is here a DHCP server and a host
   involved, while a delegating router and requesting router involved in
   [RFC3633].







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5.2.  IA_PD Prefix option

   IA_PD Prefix option in [RFC3633] is reused here.  Originally the
   option is used for conveying prefix information between a delegating
   router and a requesting router.  Here the IA_PD Prefix option is used
   to specify IPv6 address prefixes associated with an IA_PA in
   Section 5.1.  The IA_PD Prefix option must be encapsulated in the
   IA_PA-options field of an IA_PA option.

5.3.  IA Address Option

   The IA Address option in [RFC3315] is reused here.  It must be
   encapsulated in the Options field of an IA_NA or IA_TA option.  IA_NA
   and IA_TA are also described in [RFC3315].

   A host sends a DHCPv6 message with an IA Address option to a DHCPv6
   server for validating the usage of an address in the option.


6.  Applicability

   In point-to-point link model, DHCPv6 operation with host generating
   interface identifier described in this document may be used.
   [RFC4968] provides different IPv6 link models that are suitable for
   802.16 based networks and a point-to-point link model is recommended.
   Also, 3GPP and 3GPP2 have earlier adopted the point-to-point link
   model based on the recommendations in [RFC3314].  In this model, one
   prefix can only be assigned to one interface of a host (mobile
   station) and different hosts (mobile stations) can't share a prefix.
   The unique prefix can be used to identify the host.  It is not
   necessary for a DHCP server to generate an interface identifier for
   the host.  The host may generates it's interface identifier as
   described in [RFC4941].  An interface identifier could even be
   generated via random number generation.


7.  IANA consideration

   The option code OPTION_IA_PA SHOULD be assigned by IANA.


8.  Security Considerations

   Security considerations in DHCPv6 are described in [RFC3315].

   To guard against attacks through prefix assignment and address
   confirmation, a host and a DHCPv6 server SHOULD use DHCP
   authentication as described in section "Authentication of DHCP



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   messages" of [RFC3315].


9.  Acknowledgements


10.  References

10.1.  Normative References

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

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

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

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

   [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.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

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

10.2.  Informative references

   [RFC4968]  Madanapalli, S., "Analysis of IPv6 Link Models for 802.16
              Based Networks", RFC 4968, August 2007.

   [RFC3314]  Wasserman, M., "Recommendations for IPv6 in Third
              Generation Partnership Project (3GPP) Standards",
              RFC 3314, September 2002.

   [I-D.ietf-csi-dhcpv6-cga-ps]



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              Jiang, S., Shen, S., and T. Chown, "DHCPv6 and CGA
              Interaction: Problem Statement",
              draft-ietf-csi-dhcpv6-cga-ps-00 (work in progress),
              October 2009.















































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Authors' Addresses

   Frank Xia
   Huawei Technologies
   1700 Alma Dr. Suite 500
   Plano, TX  75075

   Phone: +1 972-509-5599
   Email: xiayangsong@huawei.com


   Behcet Sarikaya
   Huawei Technologies
   1700 Alma Dr. Suite 500
   Plano, TX  75075

   Phone: +1 972-509-5599
   Email: sarikaya@ieee.org


   Sheng Jiang
   Huawei Technologies
   KuiKe Building, No.9 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing  100085
   P.R. China

   Phone: +86 10-82836774
   Email: shengjiang@huawei.com























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