Brother MFC 8840D - Manual (Page 121)

11 - 10 TCP/IP CONFIGURATION
Certain BOOTP host software implementations will not respond to
BOOTP requests if you have not included a download filename in the
configuration file; if this is the case, simply create a null file on the
host and specify the name of this file and its path in the configuration
file.
As with rarp, the Print/Fax server will load its IP address from the
BOOTP server when the machine is powered on.