Problems streaming from FTP

[Nemok]

Hello,

I am trying to stream from a NAS over FTP using the iPhone app.
Streaming works if I connect on the local network address (192.168.1.x) but fails if I use my public IP (port 21 is forwarded for TCP and UDP).
I can browse, see the files, I can even download any file but when I try to play a video it shows the player UI for a couple seconds and then it says playback failed and shows the file list again.

Any idea what could be wrong? Could I access the logs and send them to you?

Thank you.

[fkuehne]

FTP is an old school network protocol, which is using 2 connections to get 2 things done.

Port 21 is used for the "control" connection, which allows the app to fetch directory contents, etc.

To actually transfer a file aka play a media, a "data" connection is opened. VLC is using Passive FTP for this, so be basically tell the server "hey, we'd like to fetch file blabla, please give me a port where you are sharing it". As response, the server sends back a random port above 4096, usually in the 40 to 50000 range. Most likely, those ports are blocked or not forwarded correctly by your router, so playback fails.

I hope this makes some sense to you