In the default firewall configuration, there are ports 10000 and ports 20? I am pretty sure that port 20 is pure-ftpd data from what I can tell, but why is port 10000 open?
10000 is the default port of webmin. Even if I recommend to not use it in conjunction with ispconfig, many users have it installed on their servers so we decided to open that port too. If webmin is not installed.