When it comes to managing the firewall service within Linux, there are many options, the most popular being iptables and ufw. For Ubuntu distributions, ufw is the default firewall management tool; however, overall, iptables is by far the most popular across multiple Linux distributions. Both of these, however, in themselves, are simply user interfaces to Netfilter.
Netfilter is a framework within the Linux kernel that allows for packet filtering as well as network and port translation. Tools such as the iptables command are simply interacting with the netfilter framework to apply these rules.
For this book, we will concentrate on utilizing the iptables command and service to manage our firewall rules. Not only is it the most popular firewall tool, it has also been the default firewall service for Red Hat based operating systems for quite a while. Even with the newer firewalld service arriving in Red Hat Enterprise Linux 7, this is simply a service...