A client is using NAS WD ShareSpace with a build in FTP server, running on port 21. Everything works fine, but one of their supplier (just the one!) have problem to connect to the FTP server. Exactly - he's able to log on, but the rest looks like that:
ftp> open ftp.estat.cz
Conencted to ftp.estat.cz
220 vsFTP 2.0.4+ (ext.3) ready...
230 Login succesful.
500 Illegal PORT command.
425 Use PORT or PASV first.
Does anyone have an idea, where the problem could be?