Active FTP connection is not working

Hello

I have problems connecting to my FTP-Site per active connection. The passive connection works.

I run into a timeout after opening the data connection:

PORT 77,56,161,71,201,211
200 PORT command successful.
LIST
150 Opening BINARY mode data connection.
TIMEOUT

I already disabled my firewall for testing purposes, but this was not the reason.

What can I do on the server side to allow active FTP-connections? A client and myself cannot connect per active connection. That means I have to change something on the server.

Thank you!