How to setup up firewall rules to allow FTP for Plesk server?

There are two type of FTP connection mode: active and passive mode.

The following describe setup firewall rules for passive mode mode FTP, specifically for Plesk server (Proftpd server).  However, other FTP servers follow the same type of solution described below.

For passive mode FTP, there are two connections that need to be allowed:

1. From FTP client to FTP server over FTP control connection on TCP port 21

2. From FTP client to FTP server over FTP data transfer connection over a range of TCP ports.

The range of TCP ports for FTP data transfer connection is typically specified in a setting on the FTP server configuration.

For Plesk server on Linux, it uses Proftpd FTP server and the configuration files can be:

1. /etc/proftpd.conf

2. Files inside /etc/proftpd.d/