Maximum Transmission Unit (--mtu <databytes>)
The maximum transmission unit (MTU) option (--mtu) is an extension of nmap's fragmentation options (-f, -ff). The --mtu option allows any valid data size value, not just 8 or 16 bytes. A fragmentation option of –f is the same as specifying an --mtu of 8, and a fragmentation option of -ff is the same as an --mtu of 16.

The --mtu option must be greater than zero and be specified in multiples of 8. If the MTU specification is larger than the IP data size, then the frame will not be fragmented.


Data Length (--data_length <databytes>)
In most cases, nmap only sends frames with the smallest possible size. The IP data length option (--data_length) can expand the frames to any user-defined size.

The data length option appends a defined number of random bytes after the TCP or UDP header of the frame. This <databyte> variable does not include the IP or TCP/UDP header.