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DHC Working Group                                           Hee Jin Jang
Internet-Draft                                               Alper Yegin
Expires: October 27, 2005                                 JinHyeock Choi
                                                             SAMSUNG AIT
                                                          April 25, 2005


             DHCP Option for Home Agent Discovery in MIPv6
                      draft-jang-dhc-haopt-01.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on October 27, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This draft defines a DHCP-based scheme to enable dynamic discovery of
   Mobile IPv6 home agent address and home subnet. New DHCP options are
   defined to carry the information from a DHCP server to the DHCP
   client running on the mobile node.






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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  DHCP options for HA Dynamic Discovery  . . . . . . . . . . . .  5
     3.1   Home Network Identifier Option . . . . . . . . . . . . . .  5
     3.2   Home Network Information Option  . . . . . . . . . . . . .  6
   4.  Option Usage . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1   DHCP Server - Home Agent Relation  . . . . . . . . . . . .  8
     4.2   Mobile Node Considerations . . . . . . . . . . . . . . . .  8
     4.3   DHCP Server Considerations . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
       Intellectual Property and Copyright Statements . . . . . . . . 13



































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1.  Introduction

   Before a mobile node can engage in Mobile IPv6 signaling with a home
   agent, it should either know the IP address of the home agent via
   preconfiguration, or dynamically discover it.  Mobile IPv6
   specification[2] describes how home agents can be dynamically
   discovered by mobile nodes that know the home subnet prefix.  This
   scheme does not work when prefix information is not already available
   to the mobile node.  This problem can be solved by delivering one or
   more home subnet prefix information to the mobile node by means of
   DHCP.  Subsequently, the mobile node can engage dynamic home agent
   discovery using the prefix information.  In addition to delivering
   the prefix information, DHCP can also be used to directly provide the
   IP addresses or FQDNs of the home agents that are available to the
   mobile node.

   The solution involves defining new DHCP options to carry home subnet
   prefix, home agent IP address and FQDN information.  A similar
   solution has already been defined for Mobile IPv4 home agents[3].

   As part of configuring the initial TCP/IP parameters, a mobile node
   can obtain home network information for the subnet it is directly
   attached to, other subnets in the visited domain, or a subnet from
   its home domain.  Mobile node can convey the target home subnet's
   identity in order to receive corresponding information.  For example
   the mobile node can provide realm portion of its user NAI and expect
   that a home agent information from its home domain is returned.  The
   availability of the requested information depends on the DHCP server
   having prior knowledge or dynamically discovering it.  While the
   specific details are outside the scope of this document, use of
   static tables and AAA-assisted discovery are possible options[8].

   The mobile node may or may not be connected to the "home" subnet when
   it attempts to learn Mobile IPv6 home network information.  This
   allows operators to centrally deploy home agents while being able to
   bootstrap mobile nodes that are already roaming.  This scenario
   occurs when HMIP[7]is used, where the mobile node is required to
   discover the MAP (a special home agent) that is located multiple hops
   away from the mobile node's attachment point.












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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[1].

   Most of terms used in this draft are defined in Mobile IPv6[2] and
   RFC3315[4].











































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3.  DHCP options for HA Dynamic Discovery

   This section introduces two DHCP options used for dynamic home agent
   discovery in Mobile IPv6.

3.1  Home Network Identifier Option

   This option is used to carry the identifier of the target home
   network.  This identification allows mobile node to request
   information for a home subnet within the visited domain, or from a
   specific domain.  It is assumed that the DHCP server has some
   mechanism to know or retrieve the requested Mobile IPv6 information.
   The specifics of these mechanisms are outside the scope of this
   draft.

   The mobile node MUST include this option along with its Option
   Request option in its request.

       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_HNId             |           option-len          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    id-type    |                                               |
      +-+-+-+-+-+-+-+-+                                               +
      |                                                               |
      .                                                               .
      .                    Home Network Identifier                    .
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



             option-code

                OPTION_HNId (TBD)

             option-len

                Total length of the option

             id-type

                The type of Home Network Identifier:

                           0    Local (visited) domain




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                           1    Network realm

   Id-type 0 indicates the mobile node is interested in learning the
   home network information that pertains to the immediately connected
   (visited) network.  In that case, Home Network Identifier field is
   not used.  This type can be used to discover local home agents in a
   visited network.

   Id-type 1 indicates the format of Home Network Identifier field is a
   network realm as defined in [5].  In this case, the mobile node is
   interested in learning home network information that pertains to the
   given realm.  This type can be used to discover home agents that are
   hosted by a user's home domain (as indicated by his/her NAI-based
   username -- user@HomeRealm).

3.2  Home Network Information Option

   This option is used to carry home network information in the form of
   one or more of home subnet prefix(es), home agent address(es), and
   FQDN(s) to a mobile node.

   The server MUST provide all of the matching home subnet prefix(es),
   home agent address(es) and FQDN(s) in a Home Network Information
   option.  If the server has no information to provide, it MUST set the
   option-len field to zero in this option.

       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_HNInf          |           option-len          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  hainfo-type  |  hainfo-len   |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
      |                                                               |
      .                                                               .
      .                   Home Network Information                    .
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+












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             option-code

                OPTION_HNInf (TBD)

             option-len

                Total length of the option

             hainfo-type

                The type of following Home Network Information field.
                Possible values are:

                        0    Home subnet prefix

                        1    Complete IPv6 address of the home agent

                        2    FQDN of the home agent

          hainfo-len

             8-bit unsigned integer. Length of the home agent
             information field plus 1.

          Home Network Information

                A home subnet prefix, home agent IP address or FQDN.

                When hninfo-type is set to 0, the data field MUST
                contain 8-bit prefix length information followed
                by a 128-bit IPv6 address.

                When hninfo-type is set to 1, the data field MUST
                contain a 128-bit IPv6 address.

                When hninfo-type is set to 2, the data field MUST
                contain a FQDN as described in RFC1035[6].

   Single option can carry multiple information preceded by hninfo-type
   and hninfo-len fields.  The length fields help identify the
   information boundaries.










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4.  Option Usage

   The requesting and sending of this option follows the rules for DHCP
   options in [4].

4.1  DHCP Server - Home Agent Relation

   The DHCP server does not have to be co-located with a home agent, or
   even be on the home subnet of the mobile node.  Its location with
   respect to home network does not matter as long as it possesses the
   requested information.

4.2  Mobile Node Considerations

   When a Mobile IPv6 Mobile Node finds itself with neither a home
   subnet prefix nor a home agent address, it may request the needed
   information with Option Request option.  For instance, a mobile node
   connecting to a network for the first time may acquire a DHCP address
   and solicit for home network information at the same time.

   A mobile node MUST identify the desired information with Home Network
   Identifier option.  For example, a DHCP server may have information
   about home agents from several domains (and subnets).  It relies on
   the mobile node to select the domain for determining which ones it
   should provide in response to the client's request.

   When the mobile node gets more than one home agent address, it MUST
   have a selection mechanism to determine which one to use for
   establishing a Mobile IPv6 session.  In case it retrieves only home
   subnet prefix(es), it needs to perform dynamic home agent discovery
   to learn the IP addresses of the home agents.  Similarly, if FQDN of
   a home agent is retrieved, the mobile node can use DNS to resolve it
   to IPv6 address(es).

4.3  DHCP Server Considerations

   It is assumed that the DHCP server has access to home network
   information for its clients for this option to be useful.  The DHCP
   server can rely on pre-configuration, or some dynamic discovery
   mechanisms for obtaining this information.  In case it does not have
   any information, or it cannot locate matching information based on
   Home Network Identifier, it returns a Home Network Information option
   with 0-length data.

   The DHCP server MUST NOT send the Home Network Information option if
   the client sends a Option Request option and the code for the Home
   Network Information option does not appear in the parameter request
   list, even if the Home Network Identifier option appears in the



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   client's list of options.


















































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5.  Security Considerations

   Secure delivery of home agent and home link information from a DHCP
   server to the mobile node (DHCP client) relies on the overall DHCP
   security.  The particular option defined in this draft does not have
   additional impact on the DHCP security.

   Aside from the DHCP client to server interaction, an operator must
   also ensure secure delivery of mobile IP information to the DHCP
   server.  This is outside the scope of DHCP and the newly defined
   option.








































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6.  IANA Consideration

   This document introduces two new DHCPv6 options, Home Agent Request
   option and Home Agent Reply option.  The type numbers for new DHCP
   options are currently TBD.  An appropriate request will be made to
   IANA if this Internet draft gets accepted as an RFC.

7.  Normative References

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

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

   [3]  Levkowetz, H., "DHCP Option for Mobile IP Mobility Agents",
        draft-ietf-dhc-mipadvert-opt-02 (work in progress),
        February 2004.

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

   [5]  Aboba, B. and M. Beadles, "The Network Access Identifier",
        RFC 2486, January 1999.

   [6]  Mockapetris, P., "Domain names - implementation and
        specification", STD 13, RFC 1035, November 1987.

   [7]  Soliman, H., Castelluccia, C., Malki, K., and L. Bellier,
        "Hierarchical Mobile IPv6 mobility management (HMIPv6)",
        draft-ietf-mipshop-hmipv6-04 (work in progress), December 2004.

   [8]  Chowdhury, K. and A. Lior, "RADIUS Attributes for Mobile IPv6
        bootstrapping", draft-chowdhury-mip6-bootstrap-radius-01 (work
        in progress), November 2004.


Authors' Addresses

   Hee Jin Jang
   i-Networking Lab Samsung AIT
   P.O. Box 111 Suwon
   440-600 Korea

   Email: heejin.jang@samsung.com





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   Alper E. Yegin
   i-Networking Lab Samsung AIT
   75 West Plumeria Drive
   San Jose, CA 95134 USA

   Email: alper.yegin@samsung.com


   JinHyeok Choi
   i-Networking Lab Samsung AIT
   P.O. Box 111 Suwon
   440-600 Korea

   Email: athene@sait.samsung.co.kr





































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