How to Setup Brother MFC-6490CW Network Printer with Ubuntu
Configure your router to reserve a static IP address for your printer. This way your computer will always know which address to contact the printer on.
Here's a rough guide on how to do that: http://lifehacker.com/5822605/how-to-set-up-dhcp-reservations-so-you-never-have-to-check-an-ip-address-again
Make a note of your printer's IP address.