Is FTPS port 21 or 990?

Why is port 20 not used for FTP anymore?

Is there any good reason why port 20 has been reserved for FTP?

I've been working with a web hosting company, who have their own FTP server on there. I tried to connect through FileZilla and connected fine and everything - until they changed the FTP URL in the hosts file! Now I can't connect to it. Could I be missing something? Why doesn't FileZilla use port 20 any more?
Edit: Sorry guys, didn't mean to make an ass of myself! It's a great solution for me and it appears to be working with everyone else in the hostel! The FTP protocol originally used port 20 to indicate the data channel (the information being sent back to the client) but the protocol has now changed and so this is no longer in use. However an FTP client using TCP port 20 should still be able to establish a data connection as the data connection will be taken from this port if one does not already exist.

If the site is a Windows FTP client, it is also possible that the site blocked port 20. However you shouldn't really rely on sites doing this as the site administrators could change this at any time.

Filezilla is probably just trying to connect to a standard FTP protocol on the default ports and so it should pick up the protocol automatically unless this port has been blocked.

Is FTPS port 21 or 990?

(A case for the latter)

I have a program in an FTP site with about 4k active users and it downloads at about 20K of the 30K bytes/sec on a gigabit port on my router, which is fine. My client however is connected to me via ISDN to download to another server and as a part of this I have to transfer a large file using an SFTP transfer. How much do you think my router (Linksys WRT110N) is capable of uploading at?

My ISP's limit is 50kb/sec but since I can't find any sort official documentation on the router I don't really know how these things work. My router's network bandwidth is: 100/100 so 100/200 would be double and if this means anything here are some other details: The client machine downloads all the data from the SFTP with about 70ms pause. So it seems to me that the server has to send something to the client every 70ms so its speed is about 60-80KB/sec (or 20Kbps, since I'm limited by my ISP), meaning that it uploads that much to the server once a second.

So what is my client's limit? My upload speed via ftp is 3-4 times the download speed of the clients so that limit would be 990MB/min, or 0.9 mbps. Does it make any sense?

Well you're lucky the client only downloads, upload limits are per TCP connection, so the upload speed your clients can sustain are the limiting factor. In other words, its limited by both your client and router. The upload speed your client can sustain depend not only on the routers network bandwidth, but also the speed of the client itself.

FTPS (as well as SCP and FTP) is based on TCP, which can theoretically sustain 1 megabits/sec (roughly, though they do use their own network protocol and you'd need to look at specs to figure it out). If it can handle that (and it has a lot of horsepower), then your client can easily upload 2.5 gigaBytes/min without too many issues

However there's no reason you shouldn't limit your downloads and it doesn't harm you too much, because they can always download when and how ever they want.