I followed the same steps for my Brother DCP 7010L, an older laser printer without network interfaces. Initially, I could not get it to work, although I could see that the p910nd print server was listening and receiving requests on port 9100:
root@turris:~# netstat -an | grep 9100
tcp 6 0 192.168.1.1:9100 0.0.0.0:* LISTEN
tcp 0 0 192.168.1.1:9100 192.168.1.175:59230 SYN_RECV
tcp 1 0 192.168.1.1:9100 192.168.1.248:59676 CLOSE_WAIT
tcp 1 0 192.168.1.1:9100 192.168.1.248:59680 CLOSE_WAIT
In my case, the solution was to uncheck “Bidirectional mode” on the LuCI p901nd configuration page. Since then, all is well. 