keyword

    The FTP client program starts with the value AUTO. All keyword
    comparisons are done without regard for typographical case (case-
    blind).

    o  ALL

       Does nothing.

    o  AUTO

       The FTP client uses the version of network protocol in use on
       the control connection to determine how the data connection is
       initiated. If the network protocol is IPv4, FTP client behaves
       as though SET PASSIVE OFF had been specified. If the network
       protocol is IPv6, FTP client behaves as though SET PASSIVE ON
       had been specified.

    o  OFF

       The FTP server initiates the data connection.

    o  ON

       The FTP client initiates the data connection. This is often
       useful when a network firewall exists on the path between the
       client and the server and prevents the FTP server from making
       outbound connections.