Hello there,

I'm sure this has been discussed before, but I have yet been able to find a solution.

I'm running RH 7.1 with Netfilters (iptables). I have a very vanilla setting so far. No firewall policies, only NAT. I also have
/sbin/modprobe ip_conntrack_ftp
/sbin/modprobe iptable_nat
/sbin/modprobe ip_nat_ftp
modules loaded. I can ftp to an external ftp site on any of my machine on the LAN, but I can't issue commands like "ls" to retrieve any type of information from the ftp server. Did I miss something in the setup? Thanks in advance.

what ftp client are you using?
make sure that pasive mode is _ON_

actually, none of the FTP applications I tried was working. In this case, the standard ftp program in MacOS X (FreeBSD).

give ncftp a try if you like using terminal based ftp

for gui try DeadFTP, it rocks

The problem is that the ftp client sends its own ip address. This is the internal ip address, not the external ip address so the ftp server doesnt know where to reply to.

You need to install an ftp proxy server. The one I'm using is jftpgw. It basically rewrites the ip addresses so that the ftp server knows the correct external ip address.

In iptables set it up to redirect all traffic going out on port 21 to the your server on whatever port jftpgw is listening on.

You may have some problems with other sites if they use a port other that 21. Either setup iptables to redirect these ports as well (if its a site you use regularly) or connect to the ftp proxy direct and tell it yourself where to connect to.

The alternative, and slightly easier, method is to use PASV (passive) mode in your ftp client. In this mode, your ftp client doesnt need to tell the ftp server the ip address so the problem doesnt occur.