There are two main reasons for syncing your files that are stored on two different FTP servers. First reason could be that you are changing the web server hosts. When you change a web server host, you have to copy your files from your old server to the new server. For this reason you may want to sync files between the old and new servers using FTP.
The second reason is for keeping the backups of your files on more than one location. When you keep your important backups on more than one location, it increases the chances of recovery. If something happens to your remote backup 1, then you still have another remote backup.
For these purposes and many others, you can use a freeware called CyberKiko FTPSync. It is a command line utility that can quickly sync files between two specified remote FTP folders. In order to user FTPSync, the first thing that you have to do is prepare an INI file containing the FTP server configurations for both the servers. FTPSync comes with a few sample INI files which can be used as a starting point.
Once you have entered all the details inside these INI files, you can simply give the command FTPSync ftp.ini to start the FTP syncing. In this example, ftp.ini is the file that contains all the entries including FTP server address, username, password, port, working folder, exclusions and more.
As soon as the command line is issued, it displays a GUI. In its widow, you can see the entire progress and a log of all the events is saved in the same folder as the FTPSync program. If all the entries in the INI file are correct then a connection is established between the two FTP servers and the files are synced.
FTPSync supports many different types of FTP servers including Novell, Microsoft, IBM and UNIX type FTP servers. It supports both insecure an secure FTP protocols. It does not remove files and only transfers new or modified files.
You can download FTPSync from https://www.cyberkiko.com/page/ftpsync/.