Loading modules

Netfilter comes with various kernel modules to enable specific packet filtering functionality, and we're going to take advantage of a few of the more common ones.
The two main categories of netfilter modules are “nat” and “conntrack”, which do advanced NAT & connection tracking features, respectively.
In the script, add the following lines: modprobe iptable_nat modprobe ip_nat_ftp modprobe ip_nat_irc modprobe ip_conntrack modprobe ip_conntrack_ftp modprobe ip_conntrack_irc
The NAT modules will ensure that FTP & IRC connections will work for computers sharing the internet connection behind our gateway.
The connection tracking modules will allow for passive FTP & IRC DCC connections to work, since they don't use preset ports.

Netfilter comes with various kernel modules to enable specific packet filtering functionality, and we're going to take advantage of a few of the more common ones.