Network Working Group                                           G. Stump
Request for Comments: 3004                                           IBM
Category: Standards Track                                       R. Droms
                                                          Cisco Systems
                                                                  Y. Gu
                                                         R. Vyaghrapuri
                                                           A. Demirtjis
                                                              Microsoft
                                                               B. Beser
                                       Pacific Broadband Communications
                                                              J. Privat
                                                         Northstream AB
                                                          November 2000


                    The User Class Option for DHCP

Status 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.



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RFC 3004             The User Class Option for DHCP        November 2000


2. 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 in RFC 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:





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        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 is section 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.







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RFC 3004             The User Class Option for DHCP        November 2000


7. 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: [email protected]


  Ralph Droms
  Cisco Systems
  300 Apollo Drive
  Chelmsford, MA 01824

  Phone: 978 244 4733
  EMail: [email protected]


  Ye Gu
  Microsoft Corporation
  One Microsoft Way
  Redmond, WA 98052

  Phone: 425 936 8601
  EMail: [email protected]






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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: [email protected]


  Burcak Beser
  Pacific Broadband Communications
  3103 North 1st Street
  San Jose, CA 95134

  Phone: 408 468 6265
  Email: [email protected]


  Ann Demirtjis
  Microsoft Corporation
  One Microsoft Way
  Redmond WA 98052

  Phone: 425 705 2254
  EMail: [email protected]


  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: [email protected]












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RFC 3004             The User Class Option for DHCP        November 2000


Full 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.



















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