Equipment Support > Hardware By Brand > D-Link > [Help Me] [DIR-300] FTP Port must be 21?!

reply to ThomasLee

Re: [Help Me] [DIR-300] FTP Port must be 21?!

Yes. I have assigned another port to the FTP Server in the Router Configuration. However, It did not work properly.

I've encountered this problem in the DSL-2540B router, and there is no workaround for it. Only a firmware upgrade has a chance of success.

The problem lies in the Netfilter modules used by the Linux kernel (the router uses Linux as its O/S). There is a particular module (ip_conntrack_ftp) which is supposed to be notified if a non-standard ftp port is to be put in use so that it can properly rewrite the ftp packets. Unfortunately, the module has been compiled in such a way that it will not accept an alternative ftp port, and you're stuck with port 21 even if you attempt to use passive mode. I discovered the problem while telneted to the router and using command line "insmod" and "iptables ..." commands.

I happen to use a non-standard ftp port for security reasons from time to time (I don't like every Tom, Dick, and Harry beating on my ftp server), and I use a different router when that's necessary. Otherwise, I use secure FTP (a part of Secure Shell, or ssh), and it doesn't require any special packet rewriting to work. I'd recommend running an ssh server in sftp mode if you can manage it.

Good luck.