Mastering Linux Security and Hardening - Second Edition

Securing Your Server with a Firewall - Part 1

Security is one of those things that's best done in layers. Security-in-depth, we call it. So, on any given corporate network, you will find a firewall appliance separating the internet from the demilitarized zone (DMZ), where your internet-facing servers are kept. You will also find a firewall appliance between the DMZ and the internal LAN, and firewall software installed on each individual server and client. We want to make it as tough as possible for intruders to reach their final destinations within our networks.

Interestingly, though, of all the major Linux distros, only the SUSE distros and the Red Hat type distros come with firewalld already set up and enabled. When you look at your Ubuntu ...