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Client Identifier Option in DHCP Server Replies
draft-ietf-dhc-client-id-01

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 6842.
Expired & archived
Authors Gaurav Halwasia , Narasimha Swamy
Last updated 2011-08-16 (Latest revision 2004-02-02)
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IESG IESG state Became RFC 6842 (Proposed Standard)
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draft-ietf-dhc-client-id-01
DHC Working Group                                               N. Swamy
Internet-Draft                                                     Nokia
Updates: 2131 (if approved)                                  G. Halwasia
Intended status: Standards Track                             P. Jhingran
Expires: February 17, 2012                                 Cisco Systems
                                                         August 16, 2011

            Client Identifier Option in DHCP Server Replies
                      draft-ietf-dhc-client-id-01

Abstract

   This document updates RFC2131 [RFC2131].  The changes to [RFC2131]
   defined in this draft clarifies the use of 'client identifier' option
   by the DHCP servers.  The clarification addresses the issues arising
   out of the point specified by [RFC2131] that the server 'MUST NOT'
   return client identifier' option to the client.

Requirements

   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].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 17, 2012.

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

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   Provisions Relating to IETF Documents
   (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
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Proposed Modification To [RFC2131]  . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5

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1.  Introduction

   The Dynamic Host Configuration Protocol (DHCP) defined in [RFC2131]
   provides configuration parameters to hosts on a TCP/IP based network.
   DHCP is built on a client-server model, where designated DHCP server
   allocate network addresses and deliver configuration parameters to
   dynamically configured hosts.

   The changes to [RFC2131] defined in this document clarifies the use
   of 'client identifier' option by the DHCP servers.  The clarification
   addresses the issues arising out of the point specified by [RFC2131]
   that the server 'MUST NOT' return client identifier' option to the
   client and thus facilitates DHCP relay agents and hosts to process
   downstream DHCP messages (DHCPOFFER,DHCPACK and DHCPNAK) when a DHCP
   client sets the 'chaddr' field as zero in DHCP request messages.

2.  Problem Statement

   [RFC2131] specifies that a combination of 'client identifier' or
   'chaddr' and assigned network address constitute a unique identifier
   for the client's lease and are used by both the client and server to
   identify a lease referred in any DHCP messages.  [RFC2131] also
   specifies that the server "MUST NOT" return 'client identifier' in
   DHCPOFFER and DHCPACK messages.  DHCP relay agents and servers,
   following these recommendations MAY drop the DHCP packets in the
   absence of both 'client identifier' and 'chaddr'.

   In some cases, client may not be having valid hardware address value
   to be filled in 'chaddr' field of the packet and hence may set this
   field as zero.  One such example is when DHCP is used to assign IP
   address to a mobile phone or a tablet and where the 'chaddr' field is
   set to zero in DHCP request packets.  In such cases, client usually
   sets the 'client identifier' option field (to a value as permitted in
   [RFC2131]), and both client and server use this field to uniquely
   identify the client with in a subnet.

   Note that due to above mentioned recommendations in [RFC2131], valid
   downstream DHCP packets (DHCPOFFER, DHCPACK and DHCPNAK) from the
   server MAY get dropped at the DHCP relay agent in the absence of
   'client identifier' option when 'chaddr' field is set as zero.

   The problem may get aggravated when a client receives a response from
   the server without 'client identifier' and with 'chaddr' value set to
   zero, as it cannot guarantee that the response is intended for it.
   This is because even though the 'xid' field is present to map
   responses with requests, this field alone cannot guarantee that a
   particular response is for a particular client, as 'xid' values

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   generated by multiple clients within a subnet need not be unique.

   This document attempts to address these problems faced by DHCP relay
   agent and client by proposing modification to DHCP server behavior.
   The proposed solution is in line with DHCPv6 [RFC3315] where the
   server always includes the Client Identifier option in the Reply
   messages.

3.  Proposed Modification To [RFC2131]

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

   Following table is extracted from section 4.3.1 of [RFC2131] and
   relevant fields are modified accordingly to overcome the problems
   mentioned in this document.

   Option                    DHCPOFFER    DHCPACK            DHCPNAK
   ------                    ---------    -------            -------
   Client identifier (if     MUST         MUST               MUST
     sent by client)
   Client identifier (if     MUST NOT     MUST NOT           MUST NOT
     not sent by client)

4.  IANA Considerations

   This memo asks the IANA for no new parameters.

5.  Security Considerations

   No known security considerations.

6.  Acknowledgements

   The authors would like to thank Bernie Volz, Ted Lemon, Barr Hibbs
   for their insightful discussions on the previous version of this
   document.

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7.  Normative References

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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, 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.

Authors' Addresses

   Narasimha Swamy Nelakuditi
   Nokia
   Visiokatu 3
   Tampere,   33720
   Finland

   Phone: +358 50487 2126
   Email: narasimha.nelakuditi@nokia.com

   Gaurav Halwasia
   Cisco Systems
   SEZ Unit, Cessna Business Park
   Sarjapur Marathalli Outer Ring Road
   Bangalore,   560103
   India

   Phone: +91 80 4426 1321
   Email: ghalwasi@cisco.com

   Prashant Jhingran
   Cisco Systems
   SEZ Unit, Cessna Business Park
   Sarjapur Marathalli Outer Ring Road
   Bangalore,   560103
   India

   Phone: +91 80 4426 1800
   Email: pjhingra@cisco.com

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