The rules for active connections tell the kernel to accept and forward connections coming to the internal floating IP address on port 20 — the FTP data port.

The following iptables command allows the LVS router to accept outgoing connections from the real servers that IPVS does not know about:

/sbin/iptables -t nat -A POSTROUTING -p tcp -s n.n.n.0/24 --sport 20 -j MASQUERADE

In the iptables command, n.n.n should be replaced with the first three values for the floating IP for the NAT interface's internal network interface defined in the GLOBAL SETTINGS panel of Piranha Configuration Tool.