I have installed a Linux Redhat 8.0 which masquaders my internal IP (eth1)to the internet(by eth0). Every thing is working except FTP. When I upload or download within my internal LAN or try to download from intenet it is working fine. But when I try to upload any file to the any internet IP it says

ftp>put x.txt
200 prt command successfull
425 Can't build data connection : Connection timed out.

What should I so that I can upload files to the internet