CrushFTP can operate in a restricted environment where a front end DMZ server processes protocols and connections, and a secured internal server has access to the file system, database, or other protected resources.

To start a DMZ instance waiting for its configuration from the internal server:
java -jar CrushFTP.jar -dmz 9000   #accept a connection from any IP on port 9000 to receive settings and run

java -jar CrushFTP.jar -dmz 9000,,   #accept a connection from these IPs on port 9000 and run
If you specify acceptable IPs, and the IP isn't int he list, the connection is dropped, and a message logged.