Coming from a largely Windows world, the raw print server function was a little weird to me at first. However, after playing with it a bit more, I found out a little more under the hood. I'll just share this with everybody in case anybody is like me and pulling their hairs out. The short story: Thibor 15c uses p910nd as the printer daemon. The printer must be on when the print server option is enabled in the router (and/or whenever the router is rebooted). The reason is that the p910nd daemon will not start without a USB printer already mounted at /dev/usb/lp0. Long story: even after the daemon is up, one cannot turn the printer off and on without breaking the print server function. The reason is, when you manually unplug or turn off the printer, /dev/usb/lp0 is not unmounted (my hypothesis is that p910nd is locking that file). Then, when you turn on the printer again, since lp0 is still busy, the printer will actually be mounted as lp1 instead. However, there is obviously no p910nd daemon serving that particular location; therefore, you can no longer print through the router. So, right now the raw print server functions perfectly when the printer is already on every time you reboot the router. If you then turn the printer off, next time you turn it on, you need to reboot the router again.