Personally I’m mostly advising against using ROS device for any high-level service (such as DNS server, web proxy server, file server, …) if possible. They are, due to space constraints and MT in-house development, mostly quite limited functionality-wise, so using some general-purpose server machine with those servers installed will almost every time win both functionality and performance wise.
As to your answer above: no, it doesn’t answer my question about how exactly FTP connection fails (when not using FTP proxy). FTP is a pretty convoluted protocol and detailed diagnosis is necessary to properly fix a problem.