Really quick post this time. I was having problems FTPing out to a corporate FTP site. I could log on, but I couldn’t list, put or get anything. I called our FTP host, and they could see no problems on their end until they ran a packet capture, filtered for our IP address.
What was happening was the outbound connection from our office to the FTP server was succeeding in making a connection, but the inbound connection from the FTP site to us was blocked. I tried connecting via FTP from three machines on the same network, and two out of the three could connect. A windows machine and a different Slackware Linux machine.
After a little exploration on the subject, it turned out that the answer was a simple module loading problem. The module ip_conntrack_ftp wasn’t loaded. All it took was editing /etc/rc.d/rc.modules, searching for the line which contained modprobe ip_conntrack_ftp, and taking the hash from the beginning of the line, then manually running the command, to avoid having to reboot.