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Network Working Group                                           R. DromsRequest for Comments: 2489                           Bucknell UniversityBCP: 29                                                     January 1999Category: Best Current PracticeProcedure for Defining New DHCP OptionsStatus 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.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 inRFC 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 ofRFC 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 inRFC 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) areDroms                    Best Current Practice                  [Page 2]

RFC 2489               Defining New DCHP Options            January 1999   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",RFC 2131,       March 1997.   [2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor       Extensions",RFC 2132, March 1997.Droms                    Best Current Practice                  [Page 3]

RFC 2489               Defining New DCHP Options            January 1999   [3] Droms, R. and K. Fong, "NetWare/IP Domain Name and Information",RFC 2142, November 1997.   [4] Narten, T. and  H. Alvestrand, "Guidelines for Writing an IANA       Considerations Section in RFCs",BCP 26,RFC 2434, 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 insection 7 of the      DHCP protocol specification [RFC 2131].6. IANA ConsiderationsRFC 2132 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 inRFC 2434 [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.eduDroms                    Best Current Practice                  [Page 4]

RFC 2489               Defining New DCHP Options            January 19998.  Full Copyright Statement   Copyright (C) The Internet Society (1999).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Droms                    Best Current Practice                  [Page 5]