INTERNET-DRAFT D. Jones Dynamic Host Control Working Group YAS Corporation Expires May 2001 R. Woundy Cisco November 2000 Addition of Device Class to Agent Options 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. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Abstract This document proposes a new sub-option to the DHCP Relay Information Agent Option. This new sub-option is for use with DOCSIS cable modems and describes a "device class" to which the cable modem belongs. The cable modem signals its device class information to the Relay Agent using DOCSIS signalling, and the Relay Agent forwards the device class information to the DHCP Server which can then make a policy decision based on it. Doug Jones, Rich Woundy Expires May 2001 [Page 1] Internet Draft Addition of Device Class to Agent Options November 2000 1. Introduction DHCP Agent Options is described in [1] and includes several Relay Agent Information sub-options. This I-D proposes an additional sub- option for use with DOCSIS cable modems. This sub-option MAY be added by DHCP relay agents which terminate cable modems. The sub- option encodes an identifier of the device class to which the cable modem belongs. It is intended for use by DHCP servers to make policy decisions based on the device class of the host. The motivation for using a Relay Agent Information sub-option, rather than a new or existing DHCP option, is the introduction of CPE Con- trolled Cable Modems (CCCMs) [2]. In an implementation of a CCCM, the modem firmware controls DOCSIS signalling, but the attached computer (CPE) manages other protocol activities -- particularly DHCP client message handling. The assumption of this document is that it is better to trust the operation of the CCCM firmware, than to trust the operation of CCCM software running on the attached computer (e.g. a standard PC). 2. Device Class Sub-option The DOCSIS RFI specification [3] specifies the Device Class encoding within the payload of the Device Class Identification Request (DCI- REQ) message. The relay agent passes the Device Class value unchanged to the DHCP server. Possible uses of this field include: o host endpoint information o host hardware capabilities o host software capabilities o host options information The Device Class sub-option is coded as follows: SubOpt Len Device Class +------+------+------+------+------+------+------+------+-- | 4 | n | d1 | d2 | d3 | d4 | d5 | d6 | ... +------+------+------+------+------+------+------+------+-- The DHCP server needs to understand the meaning of this sub-option in order to offer different policy options in its reply to the host. DHCP servers MAY use the Device Class for IP and other parameter assignment policies for cable modems. Doug Jones, Rich Woundy Expires May 2001 [Page 2] Internet Draft Addition of Device Class to Agent Options November 2000 3. Security Considerations Operation of the DHCP Relay Agent Information Option relies on an implied trusted relationship between the DHCP relay agent and the DHCP server. Operation of the Device Class sub-option also relies on an implied trusted relationship between the DHCP client (i.e. the cable modem) and the DHCP relay agent, through DOCSIS signalling. According to DOCSIS specifications, the cable modem firmware always controls DOCSIS signalling, but may not control DHCP client message handling (e.g. CCCMs). This document assumes that the cable modem firmware is trustworthy for DOCSIS signalling information. This document introduces a new identifier, the Device Class sub- option, that is provided by the relay agent device and is assumed to be trusted. Cryptographic or other techniques to authenticate the Device Class are beyond the scope of this document. 4. References [1] M. Patrick, "DHCP Relay Agent Information Option", Internet-Draft , October 2000. [2] "Data-Over-Cable Service Interface Specifications: Cable Modem to Customer Premise Equipment Interface Specification SP-CMCI-I04- 000714", DOCSIS, July 2000, http://www.cablemodem.com. [3] "Data-Over-Cable Service Interface Specifications: Cable Modem Radio Frequency Interface Specification SP-RFIv1_1-I05-000714", DOCSIS, July 2000, http://www.cablemodem.com. 5. Authors' Addresses Doug Jones YAS Corporation 300 Brickstone Square Andover, MA 01810 Phone: (303) 661-3823 EMail: doug@yas.com Rich Woundy Cisco Systems Doug Jones, Rich Woundy Expires May 2001 [Page 3] Internet Draft Addition of Device Class to Agent Options November 2000 250 Apollo Drive Chelmsford, MA 01824 Phone: (978) 244-8000 EMail: rwoundy@cisco.com 6. Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. 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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 MER- CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Doug Jones, Rich Woundy Expires May 2001 [Page 4]