Ftp-proxy is a proxy for the Internet File Transfer Protocol.  FTP
control connections are being redirected into the proxy, after which
the proxy connects to the server on behalf of the client.

The proxy allows data connections to pass, rewriting and redirecting them
so that the right addresses are used.  All connections from the client to
the server have their source address rewritten so they appear to come
from the proxy.  Consequently, all connections from the server to the
proxy have their destination address rewritten, so they are redirected to
the client.