Book Review: Designing and Implementing Linux Firewalls and QoS using netfilter, iproute2, NAT, and L7-filter
As is reminiscent of many of the books written by authors for Packt Publishing, the first chapter begins with descriptions and re-introductions to many of the basic networking concepts. These include the OSI model, subnetting, supernetting, and a brief overview of the routing protocols. Chapter 2 discusses the need for network security and how it applies to each of the layers of the OSI model.
There are complex and simple firewalls. They can be as simple or as in depth as one is willing to put the time and effort into learning and configuring them. The simple firewalls being to just allow or drop packets based on protocol or source or destination IP. The complex being that which deals with QoS (Quality of Service) or the L7 packet classification filter.