RFC 3256 (rfc3256) - Page 2 of 5

The DOCSIS (Data-Over-Cable Service Interface Specifications) Device Class DHCP (Dynamic Host Configuration Protocol) Relay Agent Information Sub-option

RFC 3256              The DOCSIS Device Class DHCP            April 2002


   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.









Jones & Woundy              Standards Track