When I first configured my P3 450MHz LAN server I wanted to add support for active FTP connections from behind NAT. Linux is smart enough to do this with connection tracking (old article describing Linux connection tracking).

It didn’t seem to work… until I came across a web page mentioning the unknown to me kernel module named “ip_nat_ftp”. I manually loaded it up, it loaded its dependencies and everything started to work.

[root@server:~]# lsmod | grep ftp
ip_nat_ftp 4720 0
iptable_nat 22692 2 ip_nat_ftp
ip_conntrack_ftp 71600 1 ip_nat_ftp
ip_conntrack 30348 4 ipt_state,ip_nat_ftp,iptable_nat,ip_conntrack_ftp

Pretty impressive. Simple and elegant solution, exactly how I like it.