Active and Passive modes in FTP / FTPS protocol and in FTPSBlackbox - SecureBlackbox®
FTP protocol is different from other protocols in that it uses two socket connections - command and data channel, and information about data channel parameters is passed over command channel.
Historically the data channel was opened by the server (the socket connection is initiated on the server and the client opens the port and listens to the socket). This is called Active mode. Active mode doesn't work well when the client is behind the firewall.
In Passive mode the client initiates connection for both control and data channels. Passive mode doens't work well in cases when the server is behind the firewall.
FTPSBlackbox supports both Active and Passive mode in both client and server classes. In addition FTPSBlackbox client can detect when the server is behind the firewall and adjust connection settings for Passive mode automatically.
Download SecureBlackbox which includes FTPSBlackbox package.