If you set up the printer Brother MFC-J6920DW on the network and with their brsaneconfig4 utility in Linux, the value is hard-coded in a file, so if the router is reset and you lose the IP address associated with the printer, some of the functionalists (mainly scanner) will not work.

To fix this, you should edit the following file:

vi /etc/opt/brother/scanner/brscan4//brsanenetdevice4.cfg

Or if you prefer gedit

gedit /etc/opt/brother/scanner/brscan4//brsanenetdevice4.cfg

Modify the IP address at the end of the file to the new IP address that the printer has. To find the new IP address, check the settings on the printer or your router.

The line should look something like this:

DEVICE=MFC-J6920DW , "MFC-J6920DW" , 0x4f9:0x2f5 , IP-ADDRESS=192.168.1.4

If this file is empty, most likely you haven’t set up the scanner with the Brother’s tool (you can download it freely from their website), and if you like to set it up, run the following:

brsaneconfig4 -a name=MFC-J6920DW model=MFC-J6920DW ip=192.168.1.4

That should be it.