Aviso FTP (ftp-access.aviso.altimetry.fr) is an authenticated FTP. All users need an account on FTP, whether for NRT   or for DT data, for along-track and gridded products.

Please, subscribe to get access to Ssalto/Duacs products by filling the registration form.

Access restrictions are applied on folders.  Your account gives you an access to a given list of altimetry data. Thus, the folders you're not subscribed to are empty.
Information about products are detailed in the product pages, and a dedicated search products page is available.

Please try to limit simultaneous accesses to one or two, in order to leave bandwidth for others users.