I know that explicit "negotiated" FTPS is preferred, because it still uses the standard port 21 with that method but in regards to "implicit" non-negotiated FTPS using a standard port of 990 vs. port 22 (which I have seen some people describe), why is there this difference in a "standard" for the non-negotiated port number?
Note: I also noticed that a FileZilla server won't work properly (when connecting from a FileZilla client) if I configure it to use anything other than the default of port 990.
Best Answer
SFTP (SSH File Transfer Protocol) is not the same as FTPS (FTP-SSL).
SFTP is intimately related to SSH, and has no relation, except in purpose and name, with FTP.
Contrast with FTPS, which is simply the FTP protocol with SSL.
The main difference is that SFTP only uses one stream, whereas FTPS, like FTP, uses at least two: a control stream, where the commands are issued, and another one for each data transfer.