3.5.3. Creating Network Packet Filter Rules
Before assigning any iptables rules for FTP service, review the information in Section 3.4.1, “Assigning Firewall Marks” concerning multi-port services and techniques for checking the existing network packet filtering rules.
Below are rules which assign the same firewall mark, 21, to FTP traffic. For these rules to work properly, you must also use the VIRTUAL SERVER subsection of Piranha Configuration Tool to configure a virtual server for port 21 with a value of 21 in the Firewall Mark field. See Section 4.6.1, “The VIRTUAL SERVER Subsection” for details.