Network Working Group                                           R. Droms
INTERNET DRAFT                                       Bucknell University
Obsoletes: draft-ietf-dhc-options-opt127-02.txt                July 1997
                                                    Expires January 1998


                 An Extension to the DHCP Option Codes
                 <draft-ietf-dhc-options-opt127-03.txt>

Status of this memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
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   ftp.isi.edu (US West Coast).

Abstract

   The Dynamic Host Configuration Protocol (DHCP) provides a framework
   for passing configuration information to hosts on a TCP/IP network.
   This document defines a new option to extend the available option
   codes.

. Introduction

   The Dynamic Host Configuration Protocol (DHCP) [1] provides a
   framework for passing configuration information to hosts on a TCP/IP
   network.  Configuration parameters and other control information are
   carried in tagged data items that are stored in the 'options' field
   of the DHCP message.  The data items themselves are also called
   "options."

   Each option is assigned a one-octet option code.  Options 128-254 are
   reserved for local use and at this time over half of the available
   options in the range 0-127 and option 255 have been assigned.  This
   document defines a new option to extend the available option codes
   and new option to request the parameters represented by those new



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DRAFT            An extension to the DHCP Option Codes         July 1997


   option codes.

. Definition of option 127

   Option code 127 indicates that the DHCP option has a two-octet
   extended option code.  The format of these options is:

                Extended
    Code   Len  option code   Data...
   +-----+-----+-----+-----+-----+-----+----
   | 127 | XXX |  oh |  ol |  d1 |  d2 | ...
   +-----+-----+-----+-----+-----+-----+----

   Other than the two-octet extended option code, these options are
   encoded and carried in DHCP messages identically to the options
   defined in RFC 1533 [2].  The high-order and low-order octets of the
   extended option code are stored in 'oh' and 'ol', respectively.  The
   number of octets given in the 'len' field includes the two-octet
   extended option code.

   The two-octet extended option codes will be assigned through the
   mechanisms defined for the assignment of new options [2] after the
   current one-octet option codes have been exhausted.

. Definition of option 126

   This option is used by a DHCP client to request values for specified
   configuration paramaters that are identified by extended option codes
   as defined above.  The list of n requested parameters is specified as
   2n octets, where each pair of octets is a valid extended option code.

   The client MAY list the options in order of preference.  The DHCP
   server is not required to return the options in the requested order,
   but MUST try to insert the requested options in the order requested
   by the client.

   The code for this option is 126.  Its minimum length is 2.

                Extended
    Code   Len  option codes
   +-----+-----+-----+-----+-----+-----+----
   | 126 | XXX | c1h | c1l | c2h | c2l | ...
   +-----+-----+-----+-----+-----+-----+----








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. References

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

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

. Security Considerations

   DHCP currently provides no authentication or security mechanisms.
   Potential exposures to attack are discussed in section 7 of the DHCP
   protocol specification [1].

. Author's Address

   Ralph Droms
   Computer Science Department
   323 Dana Engineering
   Bucknell University
   Lewisburg, PA 17837

   Phone: (717) 524-1145
   EMail: droms@bucknell.edu



























Droms                                                           [Page 3]