Network Working Group R. Droms
Request for Comments: 2489 Bucknell University
BCP: 29 January 1999
Category: Best Current Practice
Procedure for Defining New DHCP Options
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 (C) The Internet Society (1999). All Rights Reserved.
The Dynamic Host Configuration Protocol (DHCP) 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."
New DHCP options may be defined after the publication of the DHCP
specification to accommodate requirements for conveyance of new
configuration parameters. This document describes the procedure for
defining new DHCP options.
The Dynamic Host Configuration Protocol (DHCP)  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
This document describes the procedure for defining new DHCP options.
The procedure will guarantee that:
* allocation of new option numbers is coordinated from a single
* new options are reviewed for technical correctness and
* documentation for new options is complete and published.
Droms Best Current Practice [Page 1]RFC 2489 Defining New DCHP Options January 1999
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 codes. The new
procedure outlined in this document will provide guidance to IANA in
the assignment of new option codes.
2. Overview and background
The procedure described in this document modifies and clarifies the
procedure for defining new options in RFC 2131 . 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
publically 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
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
the IESG, and the codes for those options will be assigned at the
time the relevant RFCs are published. Typically, the IESG will seek
input on prospective assignments from appropriate sources (e.g., a
relevant Working Group if one exists). Groups of related options may
be combined into a single specification and reviewed as a set by the
IESG. Prior to assignment of an option code, it is not appropriate
to incorporate new options into products, include the specification
in other documents or otherwise make use of the new options.
The DHCP option number space (1-254) is split into two parts. The
site-specific options (128-254) are defined as "Private Use" and
require no review by the DHC WG. The public options (1-127) are
Droms Best Current Practice [Page 2]