Region : Hongkong

Model : TL-WDR4300

Hardware Version : V1

Firmware Version : 3.14.7 Build 130424 Rel.72646n

ISP :

Hello!:) my TL-WDR4900 router has incurred a failure in accessing the FTP server held by the router via internet access.
I have plugged an external hard drive (WD 1TB) into USB slot1 (volume1-8) and it is functional with LAN access.
I can access it on my computer by accessing 192.168.1.1(my router's default gateway) and add/remove files normally.

Then I try the FTP server function:
- Server Status is Started.
- Internet Access: Enable
- Service Port: 21(unchanged)
- Internet Address: [my ip address]
- I have shared a folder for testing
After that, it cannot be accessed by typing ftp://[myIPadress] in the browser, windows explorer and ftp software(FileZilla).
Here is the message in FileZilla:
----------------------------------------------------------------
Status: Connecting to [myIPadress]:21...
Error: Connection timed out
Error: Could not connect to server
Status: Waiting to retry...
Status: Connecting to [myIPadress]:21...
Error: Connection timed out
Error: Could not connect to server
---------------------------------------------------------------
Then, I try to use a web tool ( http://www.yougetsignal.com/tools/open-ports) to check whether the 21 port is working:
It shows that my IP's Port 21 is open when I enable the Server Status in FTP server setting page, and vice versa.
It can show that the switching is workable.

I really don't know why that happen and looking forward you guys can help me!
Thanks a lot and a million appreciation.