I felt a personal attachment to writing a recipe on setting up firewall rules on the Linux server, because several years ago I fell victim to an invasion on a Linux server that cost almost $10,000 in bandwidth charges in five days. Basically, I was hacked because I allowed several standard ports to be opened, even though they were not being actively used.
iptables project (
netfilter.org) is a user command-line program that allows a system administrator to configure the Linux IPv4 packet filtering rules to create very simple, to incredibly complex firewalls.
iptables is included with pretty much every modern Linux distribution, there should be no need to install anything. The only caveat would ...