When printing across different subnets, or configuring a personal firewall, certain ports need to be opened. For RAW and LPD/LPR printing, use the following:

• TCP 9100
• TCP 515

If printing from Microsoft Windows, the operating system will need SNMP access open as well, otherwise the printer detection procedure won’t work. Open the following port:

• UDP 161

Make sure that the SNMP access is read-only, or that it has a strong password if read-write is really needed.

Tags: firewall, lpd, lpr, printing, raw, snmp, subnet, tcp 515, tcp 9100, udp 161