Port 21 is the default port we use for accessing the ALM repository and is turned on in Site Administration.
Here is a link to a list of all the Site Admin parameters:
https://supportweb.orasi.com/downloads/hp_man_ALM12.20_Site_Administration_Parameters_htm.htm

Here is the information concerning port 21:
FTP_PORT
Description The port number of the FTP service that enables you to browse ALM project repositories. For more information, see Browsing the Project Repository. Recommended values are 21 or 2121. Note: Defining the parameter starts the FTP service on the specified port. Reconfiguring the parameter restarts the FTP service. Deleting the parameter stops the FTP service.
Min value 1
Max value 9223372036854775807
Introduced in release ALM 11.00
Introduced in patch 1
System false