RFC2489 - Procedure for Defining New DHCP Options

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　　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 Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

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.

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]

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
authority,
* new options are reviewed for technical correctness and
appropriateness, and
* documentation for new options 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 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 RFC2131 [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 RFC2132, 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 RFC2132 does not clearly state that
new options are to be reviewed individually for technical
correctness, appropriateness and complete documentation. RFC2132
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, RFC2132 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

defined as "Specification Required" and new options must be reviewed
prior to assignment of an option number by IANA. The details of the
review process are given in the following section of this document.

3. Procedure

The author of a new DHCP option will follow these steps to obtain
approval for the option and publication of the specification of the
option as an RFC:

1. The author devises the new option.

2. The author documents the new option, leaving the option code as
"To Be Determined" (TBD), as an Internet Draft.

The requirement that the new option be documented as an Internet
Draft is a matter of expediency. In theory, the new option could
be documented on the back of an envelope for submission; as a
practical matter, the specification will eventually become an
Internet Draft as part of the review process.

3. The author submits the Internet Draft for review by the IESG.
Preferably, the author will submit the Internet Draft to the DHC
Working Group, but the author may choose to submit the Internet
Draft directly to the IESG.

Note that simply publishing the new option as an Internet Draft
does not automatically bring the option to the attention of the
IESG. The author of the new option must explicitly forward a
request for action on the new option to the DHC WG or the IESG.

4. The specification of the new option is reviewed by the IESG. The
specification is reviewed by the DHC WG (if it exists) or by the
IETF. If the option is accepted for inclusion in the DHCP
specification, the specification of the option is published as an
RFC. It may be published as either a standards-track or a non-
standards-track RFC.

5. At the time of publication as an RFC, IANA assigns a DHCP option
number to the new option.

4. References

[1] Droms, R., "Dynamic Host Configuration Protocol", RFC2131,
March 1997.

[2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC2132, March 1997.

[3] Droms, R. and K. Fong, "NetWare/IP Domain Name and Information",
RFC2142, November 1997.

[4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC2434, October 1998.

5. Security Considerations

Information that creates or updates an option number assignment needs
to be authenticated.

An analysis of security issues is required for all newly defined DHCP
options. The description of security issues in the specification of
new options must be as accurate as possible. The specification for a
new option may reference the "Security Considerations" section in the
DHCP specification [1]; e.g. (from "NetWare/IP Domain Name and
Information" [3]):

DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the
DHCP protocol specification [RFC2131].

6. IANA Considerations

RFC2132 provided guidance to the IANA on the procedure it should
follow when assigning option numbers for new DHCP options. This
document updates and replaces those instructions. In particular,
IANA is requested to assign DHCP option numbers only for options that
have been approved for publication as RFCs; i.e., documents that have
been approved through "IETF consensus" as defined in RFC2434 [4].

7. Author's Address

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

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

8. Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

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