Printing may not be possible if the firewall is enabled on the print server. Depending on the service you use, open the following ports:
For LPRng: TCP port 515 (LPD)
For CUPS: TCP, UDP port 631 (IPP)
For Samba/CIFS: TCP, UDP ports 137-139 and 445 (NetBIOS and SMB)
 
Firewall settings depend on the distribution. For more information, see your distribution's documentation.