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+Network Working Group                                           D. Jones
+Request for Comments: 3256                               YAS Corporation
+Category: Standards Track                                      R. Woundy
+                                                          AT&T Broadband
+                                                              April 2002
+
+
+  The DOCSIS (Data-Over-Cable Service Interface Specifications) Device
+      Class DHCP (Dynamic Host Configuration Protocol) Relay Agent
+                         Information Sub-option
+
+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.
+
+Abstract
+
+   This document proposes a new sub-option to the DHCP (Dynamic Host
+   Configuration Protocol) Relay Agent Information Option.  This new
+   sub-option is for use with DOCSIS (Data-Over-Cable Service Interface
+   Specifications) 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 signaling, and the Relay
+   Agent forwards the device class information to the DHCP Server which
+   can then make a policy decision based on it.
+
+1.  Introduction
+
+   The "Relay Agent Information" Option is described in [1] and includes
+   several Relay Agent Information sub-options.  This RFC 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 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
+   Controlled Cable Modems (CCCMs) [2].  In an implementation of a CCCM,
+   the modem firmware controls DOCSIS signaling, but the attached
+   computer (CPE) manages other protocol activities -- particularly DHCP
+   client message handling.  The assumption of this document is that it
+
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+Jones & Woundy              Standards Track                     [Page 1]
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+RFC 3256              The DOCSIS Device Class DHCP            April 2002
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+   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.  DOCSIS 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
+   attributes defined below.
+
+      bit #0 - CPE Controlled Cable Modem (CCCM)
+
+      bits #1-31 - Reserved and set to zero
+
+   The DOCSIS Device Class sub-option is coded as follows:
+
+       SubOpt   Len     Device Class
+      +------+------+------+------+------+------+
+      |  4   |   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.
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+Jones & Woundy              Standards Track                     [Page 2]
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+RFC 3256              The DOCSIS Device Class DHCP            April 2002
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+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.  The discussion of security considerations for the DHCP
+   relay agent information option [1] apply to this sub-option as well.
+
+   Operation of the DOCSIS Device Class sub-option relies on an implied
+   trusted relationship between the DHCP client (i.e., the cable modem)
+   and the DHCP relay agent, through DOCSIS signaling.  According to
+   DOCSIS specifications [2], the cable modem firmware always controls
+   DOCSIS signaling, but cannot control DHCP client message handling
+   (e.g., CCCMs).  This document assumes that the cable modem firmware
+   is trustworthy for DOCSIS signaling information.
+
+   This document introduces a new identifier, the DOCSIS 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 4 from the DHCP Relay Agent Sub-options
+   space [RFC 3046] for the DOCSIS 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-
+         I07-020301", DOCSIS, March 2002, http://www.cablemodem.com.
+
+   [3]  "Data-Over-Cable Service Interface Specifications: Cable Modem
+         Radio Frequency Interface Specification SP-RFIv1.1-I08-020301",
+         DOCSIS, March 2002, http://www.cablemodem.com.
+
+   [4]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
+         Levels", BCP 14, RFC 2119, March 1997.
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+Jones & Woundy              Standards Track                     [Page 3]
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+RFC 3256              The DOCSIS Device Class DHCP            April 2002
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+6.  Authors' Addresses
+
+   Doug Jones
+   YAS Corporation
+   300 Brickstone Square
+   Andover, MA 01810
+
+   Phone: (303) 661-3823
+   EMail: doug@yas.com
+
+
+   Rich Woundy
+   AT&T Broadband
+   27 Industrial Avenue
+   Chelmsford, MA 01824
+
+   Phone: (978) 244-4010
+   EMail: rwoundy@broadband.att.com
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+7.  Full Copyright Statement
+
+   Copyright (C) The Internet Society (2002).  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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+Jones & Woundy              Standards Track                     [Page 5]
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