I have been annoyed for a long time with an error message I get when connecting to my *NIX desktop via FTP. I run vsftpd. My *NIX box is on two networks, a local and an external network. When I connect locally I see the problem, if I go outside to the public network, everything is fine. I thought I didn't have a firewall exception for the ftp-data (tcp/udp port 20). Turns out that wasn't the right solution. It was my vsftpd.conf file. At one point in the past I added commands for the pasv_min_port and pasv_max_port (my firewall has an exception for these ports), as well as specifying the pasv_address. That was my problem—by specifying the IP address, I was allowing PASV mode to work only when it was connecting via that specific address. By commenting out the pasv_address line (and leaving the min/max range alone), I fixed the problem.