DHC Working Group                                               N. Swamy
Internet-Draft                                                     Nokia                                             Samsung India
Updates: 2131 (if approved)                                  G. Halwasia
Intended status: Standards Track                             P. Jhingran
Expires: January 12, March 15, 2013                                    Cisco Systems
                                                      September 11, 2012

            Client Identifier Option in DHCP Server Replies


   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.


   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
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   This Internet-Draft will expire on January 12, March 15, 2013.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5

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 (as mentioned in Problem Statement) arising out
   of the point specified by [RFC2131] that the server 'MUST NOT' return
   client identifier' option to the client.

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

   Lack of 'client identifier' option in DHCP reply messages also
   affects the scenario where multiple DHCP clients may be running on
   the same host sharing the same 'chaddr'.

   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

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)

   When a client receives a DHCP message containing a 'client
   identifier' option, the client MUST compare that client identifier to
   the one it is configured to send.  If the two client identifiers do
   not match, the client MUST silently discard the message.

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,
   Richard Johnson for their insightful discussions on the previous
   version of this document.

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
   Visiokatu 3
   Tampere,   33720
   Samsung India
   Block-B, Bagmane Lakeview,
   66/1, Bagmane Tech Park,
   Byrasandra, C.V. Raman Nagar, Bangalore,   560093

   Phone: +358 50487 2126 +91 80 4181 9999
   Email: narasimha.nelakuditi@nokia.com nn.swamy@samsung.com

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

   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

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