Introduction - If you have any usage issues, please Google them yourself
linux iptables.Linux has an extremely powerful firewall built in, commonly referred to as iptables, but more accurately is iptables/netfilter. Iptables is the userspace module, the bit that you, the user, interact with at the commandline to enter firewall rules into predefined tables. Netfilter is a kernel module, built into the kernel, that actually does the filtering.