I happen to stumble upon this book today.
Receive your free copy here: http://linuxcareer.tradepub.com/free/w_infk01/
Or view it online: http://www.scribd.com/doc/184626959/w-infk01
Offered by: InformIT
**Insights: **
Installing an open source firewall using Ipchains, Iptables, Turtle firewall, or Smoothwall
Scanning ports and testing for vulnerabilities
Using Nmap, Nlog, Nmap for Windows, Nessus,and NessusWX
Using sniffers and network-intrusion systems, including Tcpdump, Ethereal, Windump, Snort™, and Snort™ for Windows
Tracking and analyzing collected data with Swatch, ACID, and NCC
Encrypting communications with PGP, GnuPG, SSH, and Free S/WAN