def makepasv # :nodoc:
      if @sock.peeraddr[0] == "AF_INET"
        host, port = parse227(sendcmd("PASV"))
      else
        host, port = parse229(sendcmd("EPSV"))
        #     host, port = parse228(sendcmd("LPSV"))
      end
      return host, port
    end
sends the appropriate command to enable a passive connection