I have installed Vsftpd Server listening on port 21 in ubuntu server. I've forwarded a port in my router to forward external port 8500 to internal port 21 where my vsftpd server is listening on. However, when I try to connect using ftp client, I'm seeing the following message in filezilla,
"Server sent passive reply with unroutable address. Using server address instead"
I've read that this has to do with being behind a router. But I never had any issues with other routers. Any reason why I am able to access ftp from the outside when using one router but not the other?