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Network Working Group                                            B. VolzRequest for Comments: 3942                           Cisco Systems, Inc.Updates:2132                                              November 2004Category: Standards TrackReclassifying Dynamic Host Configuration Protocolversion 4 (DHCPv4) OptionsStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2004).Abstract   This document updatesRFC 2132 to reclassify Dynamic Host   Configuration Protocol version 4 (DHCPv4) option codes 128 to 223   (decimal) as publicly defined options to be managed by IANA in   accordance withRFC 2939.  This document directs IANA to make these   option codes available for assignment as publicly defined DHCP   options for future options.Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .23.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .23.1.  Publicly Defined Options Range . . . . . . . . . . . . .23.2.  Site-Specific Options Range  . . . . . . . . . . . . . .34.  Reclassifying Options  . . . . . . . . . . . . . . . . . . . .35.  Security Considerations  . . . . . . . . . . . . . . . . . . .46.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .57.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .58.  References . . . . . . . . . . . . . . . . . . . . . . . . . .58.1.  Normative References . . . . . . . . . . . . . . . . . .58.2.  Informative References . . . . . . . . . . . . . . . . .6   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .6   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . .7Volz                        Standards Track                     [Page 1]

RFC 3942              Reclassifying DHCPv4 Options         November 20041.  Introduction   The DHCPv4 [RFC2131] publicly defined options range, options 1 - 127,   is nearly used up.  Efforts such as [RFC3679] help extend the life of   this space, but ultimately the space will be exhausted.   This document reclassifies much of the site-specific option range,   which has not been widely used for its original intended purpose, to   extend the publicly defined options space.2.  Requirements Notation   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].3.  Background   The DHCP option space (0 - 255) is divided into two ranges [RFC2132]:   1. 1 - 127 are publicly defined options, now allocated in accordance      with [RFC2939].   2. 128 - 254 are site-specific options.   Options 0 (pad) and 255 (end) are special and defined in [RFC2131].3.1.  Publicly Defined Options Range   The publicly defined options space (1 - 127) is nearly exhausted.   Recent work [RFC3679] will buy more time, as several allocated but   unused option codes have been reclaimed.  A review could be made from   time to time to determine whether there are other option codes that   can be reclaimed.   A longer-term solution to the eventual exhaustion of the publicly   defined options space is desired.  The DHC WG evaluated several   solutions:   1. Using options 126 and 127 to carry 16-bit options as originally      proposed by Ralph Droms in late 1996.  However, this significantly      penalizes the first option assigned to this new space, as it      requires implementing the 16-bit option support.  Because of this,      options 126 and 127 have been reclaimed [RFC3679].   2. Using a new magic cookie and 16-bit option code format.  However,      this proposalVolz                        Standards Track                     [Page 2]

RFC 3942              Reclassifying DHCPv4 Options         November 2004      *  penalizes the first option assigned to this new space, as it         requires significant changes to clients, servers, and relay         agents,      *  could adversely impact existing clients, servers, and relay         agents that fail to properly check the magic cookie value,      *  requires support of both message formats for the foreseeable         future, and      *  requires clients to send multiple DHCPDISCOVER messages -- one         for each magic cookie.   3. Reclassifying a portion of the site-specific option codes as      publicly defined.  The impact is minimal, as only those sites      presently using options in the reclassified range need to renumber      their options.3.2.  Site-Specific Options Range   The site-specific option range is rather large (127 options in all)   and little used.  The original intent of the site-specific option   range was to support local (to a site) configuration options, and it   is difficult to believe a site would need 127 options for this   purpose.  Further, many DHCP client implementations do not provide a   well documented means to request site-specific options from a server   or to allow applications to extract the returned option values.   Some vendors have made use of site-specific option codes that violate   the intent of the site-specific options, as the options are used to   configure features of their products and thus are specific to many   sites.  This usage could potentially cause problems if a site that   has been using the same site-specific option codes for other purposes   deploys products from one of the vendors, or if two vendors pick the   same site-specific options.4.  Reclassifying Options   The site-specific option codes 128 to 223 are hereby reclassified as   publicly defined options.  This leaves 31 site-specific options, 224   to 254.   To allow vendors that have made use of site-specific options within   the reclassified range to publish their option usage and to request   an official assignment of the option number to that usage, the   following procedure will be used to reclassify these options:Volz                        Standards Track                     [Page 3]

RFC 3942              Reclassifying DHCPv4 Options         November 2004   1. The reclassified options (128 to 223) will be placed in the      "Unavailable" state by IANA.  These options are not yet available      for assignment to publicly defined options.   2. Vendors that currently use one or more of the reclassified options      have 6 months following this RFC's publication date to notify the      DHC WG and IANA that they are using particular options numbers and      agree to document that usage in an RFC.  IANA will move these      options from the "Unavailable" to "Tentatively Assigned" state.      Vendors have 18 months from this RFC's publication date to start      the documentation process by submitting an Internet-Draft.      NOTE: If multiple vendors of an option number come forward and can      demonstrate that their usage is in reasonably wide use, none of      the vendors will be allowed to keep the current option number, and      they MUST go through the normal process of getting a publicly      assigned option [RFC2939].   3. Any options still classified as "Unavailable" 6 months after the      RFC publication date will be moved to the "Unassigned" state by      IANA.  These options may then be assigned to any new publicly      defined options in accordance with [RFC2939].   4. For those options in the "Tentatively Assigned" state, vendors      have 18 months following this RFC's publication date to submit an      Internet-Draft documenting the option.  The documented usage MUST      be consistent with the existing usage.  When the option usage is      published as an RFC, IANA will move the option to the "Assigned"      state.      If no Internet-Draft is published within the 18 months or should      one of these Internet-Drafts expire after the 18 months, IANA will      move the option to the "Unassigned" state, and the option may then      be assigned to any new publicly defined options in accordance with      [RFC2939].   Sites presently using site-specific option codes within the   reclassified range SHOULD take steps to renumber these options to   values within the remaining range.  If a site needs more than 31   site-specific options, the site must switch to using suboptions, as   has been done for other options, such as the Relay Agent Information   Option [RFC3046].5.  Security Considerations   This document in and by itself provides no security, nor does it   impact existing DCHP security as described in [RFC2131].Volz                        Standards Track                     [Page 4]

RFC 3942              Reclassifying DHCPv4 Options         November 20046. IANA Considerations   IANA is requested to   1. expand the publicly defined DHCPv4 options space from 1 - 127 to 1      - 223.  The new options (128 - 223) are to be listed as      "Unavailable" and MUST NOT be assigned to any publicly defined      options.   2. receive notices from vendors that have been using one or more of      the options in the 128-223 range that they are using the option      and are willing to document that usage.  IANA will list these      options as "Tentatively Assigned".   3. change the listing of any options listed as "Unavailable" to      "Available" 6 months from this RFC's publication date.  These      options may now be assigned in accordance with [RFC2939].   4. change the listing of any options listed as "Tentatively-Assigned"      to "Unavailable" 18 months from this RFC's publication date and      periodically thereafter as long as there is an option listed as      "Tentatively-Assigned", if no un-expired Internet-Draft exists      documenting the usage.7.  Acknowledgements   Many thanks to Ralph Droms and Ted Lemon for their valuable input and   earlier work on the various alternatives.8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",RFC2131, March 1997.   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor              Extensions",RFC 2132, March 1997.   [RFC2939]  Droms, R., "Procedures and IANA Guidelines for Definition              of New DHCP Options and Message Types",BCP 43,RFC 2939,              September 2000.Volz                        Standards Track                     [Page 5]

RFC 3942              Reclassifying DHCPv4 Options         November 20048.2.  Informative References   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",RFC3046, January 2001.   [RFC3679]  Droms, R., "Unused Dynamic Host Configuration Protocol              (DHCP) Option Codes",RFC 3679, January 2004.Author's Address   Bernard Volz   Cisco Systems, Inc.   1414 Massachusetts Ave.   Boxborough, MA  01719   USA   Phone: +1 978 936 0382   EMail: volz@cisco.comVolz                        Standards Track                     [Page 6]

RFC 3942              Reclassifying DHCPv4 Options         November 2004Full Copyright Statement   Copyright (C) The Internet Society (2004).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the IETF's procedures with respect to rights in IETF Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Volz                        Standards Track                     [Page 7]