[ Thanks to An Anonymous Reader for
this link. ]
“Linux comes with a host based firewall called Netfilter.
According to the official project site:“netfilter is a set of hooks inside the Linux kernel that allows
kernel modules to register callback functions with the network
stack. A registered callback function is then called back for every
packet that traverses the respective hook within the network
stack.“This Linux based firewall is controlled by the program called
iptables to handles filtering for IPv4, and ip6tables handles
filtering for IPv6. I strongly recommend that you first read our
quick tutorial that explains how to configure a host-based firewall
called Netfilter (iptables) under CentOS / RHEL / Fedora / Redhat
Enterprise Linux. This post list most common iptables solutions
required by a new Linux user to secure his or her Linux operating
system from intruders.”