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Versions: 00 01 02 03 RFC 3256

INTERNET-DRAFT                                                  D. Jones
Dynamic Host Control Working Group                       YAS Corporation
Expires April 2002                                             R. Woundy
                                                            October 2001

               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
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   material or to cite them other than as "work in progress."

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Copyright Notice

   Copyright (C) The Internet Society (2001). All Rights Reserved.


   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.

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Internet Draft Addition of Device Class to Agent Options    October 2001

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 is 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 deci-
   sions 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).

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT" and "MAY" in
   this document are to be interpreted as described in RFC 2119 [4].

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 MUST pass 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

   DOCSIS defines the Device Class to be a 32-bit field where individual
   bits represent individual attributes of the CM. Bit #0 is the least
   significant bit of the field. Bits are set to 1 to select the attri-
   butes defined below.

      bit #0 - CPE Controlled Cable Modem (CCCM)

      bits #1-31 - Reserved and set to zero

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   The device class sub-option is coded as follows:

            SubOpt   Len     Device Class
           | TBD  |   4  |  d1  |  d2  |  d3  |  d4  |

   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.

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 cannot 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.  IANA Considerations

   IANA has assigned a value of TBD from the DHCP Relay Agent Sub-
   options space [RFC 3046] for the device class sub-option defined in
   section 2.

5.  References

   [1] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
      January 2001.

   [2] "Data-Over-Cable Service Interface Specifications: Cable Modem to
      Customer Premise Equipment Interface Specification SP-CMCI-I06-

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      010829", DOCSIS, August 2001, http://www.cablemodem.com.

   [3] "Data-Over-Cable Service Interface Specifications: Cable Modem
      Radio Frequency Interface Specification SP-RFIv1.1-I07-010829",
      DOCSIS, August 2001, http://www.cablemodem.com.

   [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.

6.  Authors' Addresses

      Doug Jones
      YAS Corporation
      300 Brickstone Square
      Andover, MA 01810
      Phone: (303) 661-3823
      EMail: doug@yas.com

      Rich Woundy
      Cisco Systems
      250 Apollo Drive
      Chelmsford, MA 01824
      Phone: (978) 244-8000
      EMail: rwoundy@cisco.com

7.  Full Copyright Statement

   Copyright (C) The Internet Society (2001). 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 develop-
   ing 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.

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   This document and the information contained herein is provided on an

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