Internet Engineering Task Force G. Stump Dynamic Host Configuration Working Group IBM Internet Draft R. Droms Expires: January 2001 Bucknell University draft-ietf-dhc-userclass-10.txt Y. Gu R. Vyaghrapuri A. Demirtjis Microsoft B. Beser 3Com J. Privat BT August 2000 The User Class Option for DHCP <draft-ietf-dhc-userclass-10.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This option is used by a 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. The User Class Option for DHCP August 2000 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. 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. 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 User Class Option for DHCP August 2000 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: 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 . The User Class Option for DHCP August 2000 This lack of authentication mechanism means that a DHCP server cannot check if a client or user is authorised 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 authorised to use this parameter. 7. References  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Alexander, S., and Droms R., "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," 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. Author Information Glenn Stump IBM Networking Software P.O. Box 12195 RTP, NC 27709 Phone: (919) 301-4277 Email: firstname.lastname@example.org Ralph Droms Computer Science Department 323 Dana Engineering Bucknell University Lewisburg, PA 17837 Phone: (717) 524-1145 Email: email@example.com Ye Gu Microsoft Corporation The User Class Option for DHCP August 2000 One Microsoft Way Redmond, WA 98052 Phone: 425 936 8601 Email: firstname.lastname@example.org Ramesh Vyaghrapuri Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: 425 703 9581 Email: email@example.com Burcak Beser 3Com Corporation 3800 Golf Road Rolling Meadows, IL Phone: 847 262 2195 Email: Burcak_Beser@3com.com Ann Demirtjis Microsoft Corporation One Microsoft Way Redmond WA 98052 Phone: 425-705-2254 Email: firstname.lastname@example.org Jerome Privat BT Advanced Communications Technology Centre Adastral Park, Martlesham Heath, IP5 3RE UK Phone: +44 1473 606304 Email: email@example.com The User Class Option for DHCP August 2000 Full Copyright Statement "Copyright (C) The Internet Society (2000). 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