Designing and Implementing Linux Firewalls and QoS using netfilter, iproute2, NAT and l7-filter PDF

The author draws on his experience to offer the reader valuable advice on the best practices. Providing only necessary theoretical background, the book takes a practical approach, presenting case studies and plenty of illustrative examples. This book is aimed at Linux Network administrators with some understanding of Linux security threats and issues, or any one interested in securing their systems behind a firewall. Basic knowledge of Linux is presumed but other than that this book shows you how to do the rest, from configuring your system to dealing with security breaches.