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Network Working Group                                           G. StumpRequest for Comments: 3004                                           IBMCategory: Standards Track                                       R. Droms                                                           Cisco Systems                                                                   Y. Gu                                                          R. Vyaghrapuri                                                            A. Demirtjis                                                               Microsoft                                                                B. Beser                                        Pacific Broadband Communications                                                               J. Privat                                                          Northstream AB                                                           November 2000The User Class Option for DHCPStatus 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 (2000).  All Rights Reserved.Abstract   This option is used by a Dynamic Host Configuration Protocol (DHCP)   client to optionally identify the type or category of user or   applications it represents.  The information contained in this option   is an opaque field that represents the user class of which the client   is a member.  Based on this class, a DHCP server selects the   appropriate address pool to assign an address to the client and the   appropriate configuration parameters.  This option should be   configurable by a user.1. Introduction   DHCP administrators may define specific user class identifiers to   convey information about a client's software configuration or about   its user's preferences.  For example, the User Class option can be   used to configure all clients of people in the accounting department   with a different printer than clients of people in the marketing   department.Stump, et al.               Standards Track                     [Page 1]

RFC 3004             The User Class Option for DHCP        November 20002. Requirements Terminology   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 inRFC 2119 [3].3. DHCP Terminology   o "DHCP client"     A DHCP client or "client" is an Internet host using DHCP to obtain     configuration parameters such as a network address.   o "DHCP server"     A DHCP server or "server" is an Internet host that returns     configuration parameters to DHCP clients.   o "binding"     A binding is a collection of configuration parameters, including at     least an IP address, associated with or "bound to" a DHCP client.     Bindings are managed by DHCP servers.4. User Class option   This option is used by a DHCP client to optionally identify the type   or category of user or applications it represents.  A DHCP server   uses the User Class option to choose the address pool it allocates an   address from and/or to select any other configuration option.   This option is a DHCP option [1,2].   This option MAY carry multiple User Classes.  Servers may interpret   the meanings of multiple class specifications in an implementation   dependent or configuration dependent manner, and so the use of   multiple classes by a DHCP client should be based on the specific   server implementation and configuration which will be used to process   that User class option.   The format of this option is as follows:         Code   Len   Value        +-----+-----+---------------------  . . .  --+        | 77  |  N  | User Class Data ('Len' octets) |        +-----+-----+---------------------  . . .  --+   where Value consists of one or more instances of User Class Data.   Each instance of User Class Data is formatted as follows:Stump, et al.               Standards Track                     [Page 2]

RFC 3004             The User Class Option for DHCP        November 2000         UC_Len_i     User_Class_Data_i        +--------+------------------------  . . .  --+        |  L_i   | Opaque-Data ('UC_Len_i' octets)   |        +--------+------------------------  . . .  --+   Each User Class value (User_Class_Data_i) is indicated as an opaque   field.  The value in UC_Len_i does not include the length field   itself and MUST be non-zero.  Let m be the number of User Classes   carried in the option.  The length of the option as specified in Len   must be the sum of the lengths of each of the class names plus m:   Len= UC_Len_1 + UC_Len_2 + ... + UC_Len_m + m.  If any instances of   User Class Data are present, the minimum value of Len is two (Len =   UC_Len_1 + 1 = 1 + 1 = 2).   The Code for this option is 77.   A server that is not equipped to interpret any given user class   specified by a client MUST ignore it (although it may be reported).   If a server recognizes one or more user classes specified by the   client, but does not recognize one or more other user classes   specified by the client, the server MAY use the user classes it   recognizes.   DHCP clients implementing this option SHOULD allow users to enter one   or more user class values.5. IANA Considerations   Option 77, which IANA has already assigned for this purpose, should   be used as the User Class Option for DHCP.6. Security Considerations   DHCP currently provides no authentication or security mechanisms.   Potential exposures to attack are discussed issection 7 of the   protocol specification [1].   This lack of authentication mechanism means that a DHCP server cannot   check if a client or user is authorized to use a given User Class.   This introduces an obvious vulnerability when using the User Class   option.  For example, if the User Class is used to give out a special   parameter (e.g., a particular database server), there is no way to   authenticate a client and it is therefore impossible to check if a   client is authorized to use this parameter.Stump, et al.               Standards Track                     [Page 3]

RFC 3004             The User Class Option for DHCP        November 20007. 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.   [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.8. Acknowledgments   This document is based on earlier drafts by Glenn Stump, Ralph Droms,   Ye Gu, Ramesh Vyaghrapuri and Burcak Beser.  Thanks to Ted Lemon,   Steve Gonczi, Kim Kinnear, Bernie Volz, Richard Jones, Barr Hibbs and   Thomas Narten for their comments and suggestions.9. Authors' Addresses   Glenn Stump   IBM Networking Software   P.O. Box 12195   RTP, NC 27709   Phone: 919 301 4277   EMail: stumpga@us.ibm.com   Ralph Droms   Cisco Systems   300 Apollo Drive   Chelmsford, MA 01824   Phone: 978 244 4733   EMail: rdroms@cisco.com   Ye Gu   Microsoft Corporation   One Microsoft Way   Redmond, WA 98052   Phone: 425 936 8601   EMail: yegu@microsoft.comStump, et al.               Standards Track                     [Page 4]

RFC 3004             The User Class Option for DHCP        November 2000   Ramesh Vyaghrapuri   Microsoft Corporation   One Microsoft Way   Redmond, WA 98052   Phone: 425 703 9581   EMail: rameshv@microsoft.com   Burcak Beser   Pacific Broadband Communications   3103 North 1st Street   San Jose, CA 95134   Phone: 408 468 6265   Email: Burcak@pacband.com   Ann Demirtjis   Microsoft Corporation   One Microsoft Way   Redmond WA 98052   Phone: 425 705 2254   EMail: annd@microsoft.com   Jerome Privat   Northstream AB   Espace Beethoven 1   1200 Route des Lucioles   BP 302   06906 Sophia Antipolis Cedex   France   Phone: +33 4 97 23 40 45   Fax: +33 4 97 23 24 51   Mobile: +33 6 13 81 76 71   Email: jerome.privat@northstream.seStump, et al.               Standards Track                     [Page 5]

RFC 3004             The User Class Option for DHCP        November 2000Full Copyright Statement   Copyright (C) The Internet Society (2000).  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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Stump, et al.               Standards Track                     [Page 6]