INTERNET-DRAFT D. Jones
Dynamic Host Control Working Group YAS Corporation
Expires August 2001 R. Woundy
Cisco
February 2001
Addition of Device Class to Agent Options
<draft-ietf-dhc-agentoptions-device-class-01.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2001). 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.
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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
+------+------+------+------+------+------+------+------+--
| TBD | 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.
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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.
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] 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-I05-
001215", DOCSIS, December 2000, http://www.cablemodem.com.
[3] "Data-Over-Cable Service Interface Specifications: Cable Modem
Radio Frequency Interface Specification SP-RFIv1.1-I06-001215",
DOCSIS, December 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
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Internet Draft Addition of Device Class to Agent Options February 2001
250 Apollo Drive
Chelmsford, MA 01824
Phone: (978) 244-8000
EMail: rwoundy@cisco.com
6. Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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