2.2.9 DHCPv4 Option Code 250 (0xFA) - Microsoft Encoding Long Options Packet
DHCPv4 standard options are constrained to be of maximum size 255 bytes due to the length of the option 8-bit length field that the protocol defines in [RFC3396] section 1.
In the case where the option data for any of the DHCPv4 option values exceeds 255 bytes in length, implementations of this specification do not follow [RFC3396] section 5. Instead, Option Code 250 is used to encode the excess data over 255 bytes. Option Code 250 repeats immediately after the option being encoded as many times as necessary to encode the remaining data.
For instance, if the option data for a given Option Code X is 600 bytes, the DHCPv4 client or DHCPv4 server sends Option X with 255 bytes of data, immediately followed by Option 250 with another 255 bytes of data, and then again Option 250 with the remaining 90 (600 – 255 – 255) bytes of data.
Option 250 is encoded by DHCPv4 clients and DHCPv4 servers in the same format as the following standard DHCPv4 options.
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Option Code |
Option Length |
Option Data (variable) |
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Option Code (1 byte): This MUST be 250 (0xFA).
Option Length (1 byte): The unsigned length, in bytes, of the option, not including the Option Code and Option Length fields.
Option Data (variable): This field contains the continuation of the data of the previous option, which was too long to be contained in that option.