Norton cannot detect external hard drive plugged into the router usb port

Running Norton 360 6.0.  Had same issue with 5.0  Using windows 7 and trying to install a seagate FreeAgent ext drive in the USB port on a Linksys E3200 router and use it as a network back up device.  The Seagate drive works with Norton when plugged into the USB port on my tower,   And my computer recognizes it when it is plugged into the router.  I can use it like a flash drive.  But when I try to create a Norton backup, my Norton software cannot detect the hard drive plugged into the router.  Is it possible that Norton 360 cannot work with a network drive?