After initial authentication, FTP can work in 2 different modes called passive FTP & active FTP. Generally, passive FTP is the default method to access FTP.
Passive FTP uses some undefined higher random ports to complete FTP related operations. As it is random port by default, firewall can often interfere with this passive FTP connection.
In order to avoid the issue with firewall, we need to define passive FTP ports used by FTP server in its configuration as ports from 55000 to 60000 . Further, we need to open these ports in Plesk firewall.
Steps to edit FTP server configuration is given below
1. Login to server as root via ssh
2. Open the file /etc/proftpd.conf using a CLI editor like vi
3. Add "PassivePorts 55000 60000" in the "Global" section of /etc/proftpd.conf
PassivePorts 55000 60000
4. Now, restart xinetd using the command "/etc/init.d/xinetd restart".
Steps to open ports in firewall is given below.
1. Go to Plesk >> Tools & Settings >> Firewall
2. Click "Edit Firewall Configuration" button
3. Click "Add Custom Rule"
4. Give name of the rule as "Passive FTP Ports"
5. Give "Add port or port range" as 55000-60000
6. Press OK
7. Pres "Apply Configuration"
8. Press "Activate"