2.2.1.3 DHCPv4 Vendor-Identifying Vendor-Specific Information Option Structure

DHCPv4 options are constrained to be of maximum size of 255 bytes due to the length of the 8-bit Option Length field that DHCP defines. The DHCPv4 Vendor-Identifying Vendor-Specific Information Option structure consists of the following fields:

0	1	2	3	4	5	6	7	8	9	1 0	1	2	3	4	5	6	7	8	9	2 0	1	2	3	4	5	6	7	8	9	3 0	1
A								B								Enterprise Number
...																C								D
...

A - Option Code (1 byte): As specified in [RFC3925] section 4, this field is used to indicate the DHCPv4 Vendor-Identifying Vendor-Specific Information Option. The value of this field MUST be 125 (0x7D).

B - Option Length (1 byte): This field is the unsigned length, in bytes, of the option, not including the Option Code and Option Length fields. The value of this field MUST be 135 (0x87).

Enterprise Number (4 bytes): This field MUST be set to 0x0137 (decimal 311), which is the Microsoft Enterprise number [IANA-ENT] assigned by the Internet Assigned Numbers Authority (IANA).

C - Data Length (1 byte): This field is the unsigned length, in bytes, of the Option Data field.

D - Option Data (variable):  As specified in [RFC3925] section 4, this field MUST contain a byte for the Suboption Code, followed by a byte for the Suboption Length, followed by the Suboption Data itself. The necessary contents of these suboption fields are as follows:

Suboption Code (1 byte):  This field MUST be set to 1 (0x01).

Suboption Length (1 byte): This field MUST be set to 128 (0x80).

Suboption Data (variable): This MUST contain the second 128 bytes of the KP ADM element data, continued from Option 43.