Clear Command Channel (CCC) - KB Article #1495Related Articles --
If the CCC command is sent by the client and accepted by the server during a secured session, the command channel will no longer be secured and will instead be sent in clear text. The data channel will still be secured according to the protection level set using the PROT command.
The CCC command is useful on client's requiring the usage of active (PORT) mode data transfers when they are behind a router that implements NAT. A clear command channel allows NAT to function on the router so that it can continue to "follow" the FTP transaction and alter the PORT command with an external IP address while preparing for the server's inbound connection on the port specified in that PORT command.