Internet Engineering Task Force Glenn Stump, IBM INTERNET DRAFT Ralph Droms, Bucknell University Date:
MayJune 2000 Ye Gu, Ramesh Vyaghrapuri, Expires: OctoberNovember 2000 Ann Demirtjis, Microsoft Burcak Beser, 3Com Jerome Privat, BT The User Class Option for DHCP <draft-ietf-dhc-userclass-07.txt><draft-ietf-dhc-userclass-08.txt> Status of this Memo The document is an Internet-Draft and is in full conformance with all of the provisions of Section 10 of RFC 2026. 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 Intenet-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. 1. Introduction It is often desirable to provide different levels of service to different users of an IP network. In order for an IP network to implement this service differentiation, it needs a way to classify users. A simple solution to this is to use source IP addresses for classification. Under this scheme, network administrators first configure network devices such as routers to recognize traffic from a particular source IP address (or address range) and handle it specially to meet the desired level of service. Next, they assign the IP addresses to the hosts of the intended users so that the user will receive the appropriate level of service. They can configure the hosts manually with these addresses. However, they cannot use DHCP for address assignment, even if they are already running a DHCP server in their network. A current RFC-compliant DHCP server assigns IP addresses based on the location of the DHCP Client in the network topology, not the type of user it supports. This document describes a simple extension of the DHCP protocol that enables a DHCP server to assign IP addresses from different address pools depending on the type of users from which it receives DHCP requests. With this new extension, network administrators will be able to use DHCP to hand out the appropriate addresses to clients. An example intended usage is a corporate network subnet consisting of different departments of users, such as Accounting, Legal, Staff, etc. It may be desirable to allocate logical address pools to each of the departments so that network policies may be implemented easily on IP address ranges; and this would facilitate providing differential services, such as network reachibility. A DHCP server can also use the information contained in the User Class to allocate other configuration parameters than the IP address. For example, a DHCP server receiving a request from a client with the User Class set to "accounting auditors" may return an option with the address of a particular database server. Indeed a DHCP server may have a single pool of addresses and only use the user class to select parameters other than IP addresses. 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 of "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 code forformat of this option is TBD.as follows: Code Len Value +-----+-----+--------------------- . . . --+ | 77 | N | User Class Data ('Len' octets) | +-----+-----+--------------------- . . . --+ where Value consists of zero 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 inas an opaque field. The value in UC_Len_i does not include the length field itself and is preceded by a one-byte field giving its length.MUST be non-zero. Let nm 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 n:m: Len= Len1UC_Len_1 + Len2UC_Len_2 + ...+ Lenn... + n. CodeUC_Len_m + m. If any instances of User Class Data are present, the minimum value of Len Len1 Len2 +-----+-----+-----+----------+-----+--------------+---- | TBD | N | L1 | classis two (Len = UC_Len_1 + 1 | L2 | class 2 |... +-----+-----+-----+----------+-----+--------------+----= 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 . 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. 6.This introduces an obvious vulnerability when using the User Class option. For example, if the User Class is used to give out special IP addresses that have better QoS associated with them (as described in section 1), there is no way to authenticate a client and it is therefore impossible to check if a client is authorised to use such an IP address. 7. References  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  S. Alexander, R. Droms, "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. 7.8. Acknowledgments This document combines ideas from draft-ietf-dhc-userclass-03.txt (byis based on earlier drafts by Glenn Stump andStump, Ralph Droms) and draft-ietf-dhc-useraddr-00.txt (byDroms, Ye Gu, Ramesh Vyaghrapuri and Burcak Beser). It has been published as a revision to draft-ietf-dhc-userclass-05.txt.Beser. Thanks to Ted Lemon, Steve Gonczi, Kim Kinnear, Bernie Volz, Richard Jones, Barr Hibbs and Thomas Narten for their comments and suggestions. 8.9. Author Information Glenn Stump IBM Networking Software P.O. Box 12195 RTP, NC 27709 Phone: (919) 301-4277 Email: email@example.com Ralph Droms Computer Science Department 323 Dana Engineering Bucknell University Lewisburg, PA 17837 Phone: (717) 524-1145 Email: firstname.lastname@example.org Ye Gu Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: 425 936 8601 Email: email@example.com Ramesh Vyaghrapuri Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: 425 703 9581 Email: firstname.lastname@example.org 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: email@example.com Jerome Privat BT Advanced Communications Technology Centre Adastral Park, Martlesham Heath, IP5 3RE UK Phone: +44 1473 648910 Email: firstname.lastname@example.org 9.10. Expiration This document will expire on OctoberNovember 2000. 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