Generally, considered to be an advanced firewall, CSF blocks external IPs (Inbound Connections) to avoid Brute force attacks or attacks similar to that (Multiple login failures, hacking attempts, etc.) on a server. The firewall might block the connection while uploading files using Filezilla.
It might be possible that Filezilla is trying to open multiple simultaneous connections to speed up the transfer. The firewall may interpret it as brute force or port scan activity and block the IP address from where the connection is originating.
To avoid this or to reduce the number of simultaneous connections, You need to select passive connection under the transfer settings of FileZilla to remove the IP ban. There is another way to remove the IP ban as below –
- Go to the Site Manager. File -> Site Manager or click the first toolbar button.
- Here you will need to create an entry for that server. Now, enter all details you know. Remember the more precise, the better.
- Open the Transfer Settings tab.
- Tick the option Limit number of simultaneous connections checkbox.
- Enter the desired limit into the Maximum number of connections field.
Now, if you connect using the Site Manager entry, connections will be limited.
If all these tricks fail then please use WS_FTP pro-FTP client with passive mode as this client doesn’t create multiple connections while uploading or downloading files.