A Guide to Securing Your Home Computer System
with a Linux Firewall
The key software for the firewall is the Linux packet filter firewalling and masquerading toolipchains or ipfwadm. Linux kernel version 2.2 introduced ipchains; earlier kernels used ipfwadm. Either ipchains or ipfwadm will filter the traffic between your personal computers and the Internet, which will allow or block connections according to rules that you define.
Both ipfwadm and ipchains carry out network address translation (NAT). This means that connections coming in and going out through your Internet connection—such as a cable or a DSL modem—are translated from your internal private network IP addresses into a single IP address that has been assigned to your Internet connection. When the IP packets are passed back and forth over the Internet, the outside world sees only the IP address of the Linux firewall computer. Your computers behind the Linux firewall remain hidden and are therefore protected from attackers.