When I trIed to set the NAT with port 21, the router prompts with this message:
"Since port 21 is used, the DSL router FTP server port will be moved to port 2121."
Anyways, I still did that, and now it works with filezilla server listening on port 21. I do not know why it now works. The truth is that I also updated filezilla client to the last version as I was offered by a pop up message. Therefore, I do not know if the problem had to do with the fact of not having the last filezilla client update or may be other. I hope the problem had to do with the filezilla client update because otherwise I would not know why it is working now.
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