FTP not working in passive mode – proftpd, iptables and ISPconfig
If you are using proftpd FTP server together with iptables firewall, which is the case if you for example are using ISPconfig, you will probably have problems using FTP against your server in passive mode. The problem is that the iptables firewall will not allow the incoming connections in passive mode.
The solution is to configure proftpd to use a small, defined range of incoming ports and open iptables for this range.