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DHC Working Group                                        Narasimha Swamy
INTERNET DRAFT                                            Nokia Networks

Updates: RFC 2131                                              July 2003
                                                    Expires January 2004


                Client Identifier option in server replies
                   <draft-swamy-dhc-client-id-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract


   This document clarifies the use of 'client identifier' option by the
   clients and servers as mentioned in [RFC2131]. The clarification
   addresses the issue arising out of the point specified by [RFC2131]
   that the server 'MUST NOT' return client identifier' option to the
   client.









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1.  Introduction

   In some cases, client may not be having valid hardware address value
   to be filled in 'chaddr' field of the packet (one such example is
   when DHCP is used to assign IP addresses to Mobile phones). In this
   case, client sets 'client identifier' option, and both client and
   server use this field to uniquely identify the client with in
   a subnet. But [RFC2131] specifies that server "MUST NOT" return
   'client identifier' in DHCPOFFER and DHCPACK messages. In this case,
   when a client receives response from server, it can't guarantee that
   response is intended for it. Note that even though 'xid' field is
   present to map responses with requests, this field alone can't guar-
   antee that a particular response is for a particular client, as 'xid'
   values generated by multiple clients within a subnet need not be
   unique. This draft proposes modification to server behavior to addr-
   ess this problem.


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 RFC 2119 [RFC 2119].

   This document uses the following terms:

      o "DHCP client"

        A DHCP client is an Internet host using DHCP to obtain confi-
        guration parameters such as a network address.

      o "DHCP server"

        A DHCP server is an Internet host that returns configuration
        parameters to DHCP clients.


3.  Proposed modification to [RFC2131]

   If the 'client identifier' option is set in the message received from
   client, the server MUST return 'client identifier' value in its
   response message.

   Following table is extracted from section 4.3.1 of [RFC2131] and
   relevant fields are modified accordingly.

Option                    DHCPOFFER    DHCPACK            DHCPNAK
------                    ---------    -------            -------
Client identifier         MAY          MAY                MAY

           Table 1:  Options used by DHCP servers

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4.  Security Considerations

   No known security considerations.


5.  Acknowledgments

   I would like to thank Umesh Kulkarni, Harish Raghuveer and Hari Mallath
   for their support and feedback.


6.  References


   [RFC 951] Croft, B., Gilmore, J., "Bootstrap Protocol (BOOTP)", RFC
      951, September 1985.

   [RFC 1542] Wimer, W., "Clarifications and Extensions for the
      Bootstrap Protocol", RFC 1542, October 1993.

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

   [RFC 2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
      2131, March 1997.

   [RFC 2132] Alexander, S., Droms, R., "DHCP Options and BOOTP Vendor
      Extensions", RFC 2132, March 1997.



7.  Author's information


        Narasimha Swamy
        Nokia India Pvt Ltd
        #50, Vanivilas Rd
        Basavanagudi
        Bangalore - 560 004

        Phone: +91 80 6618100

        Email: narasimha.nelakuditi@nokia.com


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identify any such rights.  Information on the IETF's procedures with

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