Procedures and IANA Guidelines for Definition of New DHCP Options and Message Types
RFC 2939

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Network Working Group                                            R. Droms
Request for Comments: 2939                            Bucknell University
BCP: 43                                                    September 2000
Obsoletes: 2489
Category: Best Current Practice

            Procedures and IANA Guidelines for Definition of
                   New DHCP Options and Message Types

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The Dynamic Host Configuration Protocol (DHCP) provides a framework
   for passing configuration information to hosts on a Transmission
   Control Protocol/Internet Protocol (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".

   DHCP protocol messages are identified by the 'DHCP Message Type'
   option (option code 51).  Each message type is defined by the data
   value carried in the 'DHCP Message Type' option.

   New DHCP options and message types may be defined after the
   publication of the DHCP specification to accommodate requirements for
   conveyance of new configuration parameters or to accommodate new
   protocol semantics.  This document describes the procedure for
   defining new DHCP options and message types.

1. 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" [2].

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RFC 2939            Procedures for New DHCP Options       September 2000

   DHCP protocol messages are identified by the 'DHCP Message Type'
   option (option code 51).  Each message type is defined by the data
   value carried in the 'DHCP Message Type' option.

   This document describes the procedure for defining new DHCP options
   and message types.  The procedure will guarantee that:

   * allocation of new option numbers and message type numbers is
     coordinated from a single authority,
   * new options and message types are reviewed for technical
     correctness and appropriateness, and
   * documentation for new options and message types is complete and
     published.

   As indicated in, "Guidelines for Writing an IANA Considerations
   Section in RFCs", (see references), IANA acts as a central authority
   for assignment of numbers such as DHCP option and message type codes.
   The new procedure outlined in this document will provide guidance to
   IANA in the assignment of new option and message type codes.

   This document updates and replaces RFC 2489.

2. Overview and background

   This document specifies procedures for defining new option codes and
   message types.

2.1 New DHCP option codes

   The procedure described in this document modifies and clarifies the
   procedure for defining new options in RFC 2131 [2].  The primary
   modification is to the time at which a new DHCP option is assigned an
   option number.  In the procedure described in this document, the
   option number is not assigned until specification for the option is
   about to be published as an RFC.

   Since the publication of RFC 2132, the option number space for
   publicly defined DHCP options (1-127) has almost been exhausted.
   Many of the defined option numbers have not been followed up with
   Internet Drafts submitted to the DHC WG.  There has been a lack of
   specific guidance to IANA from the DHC WG as to the assignment of
   DHCP option numbers.

   The procedure as specified in RFC 2132 does not clearly state that
   new options are to be reviewed individually for technical
   correctness, appropriateness and complete documentation.  RFC 2132
   also does not require that new options are to be submitted to the
   IESG for review, and that the author of the option specification is

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RFC 2939            Procedures for New DHCP Options       September 2000

   responsible for bringing new options to the attention of the IESG.
   Finally, RFC 2132 does not make clear that newly defined options are
   not to be incorporated into products, included in other
   specifications or otherwise used until the specification for the
   option is published as an RFC.

   In the future, new DHCP option codes will be assigned by IETF
   consensus.  New DHCP options will be documented in RFCs approved by