Inside Network Perimeter Security: The Definitive Guide to Firewalls, Virtual Private Networks (VPNs), Routers, and Intrusion Detection Systems
by Stephen Northcutt
It has very crisp explanations of various concepts and shall form a good book for newbies to intermediates.....
****** Any man who knows all the answers most likely misunderstood the questions *****
If you're still looking for some FREE firewall books, then perhaps I could help you out. I stumbled upon several great resources while browsing WindowSecurity.com that seem to contain pretty much everything on firewalls. Here are the links:
The largest and most informative resource there would be "Firewalls Complete." It's quite long (several hundred pages), but it should contain everything you need to know about firewalls.
Hope this helps you out!
Happy BHH (Black Hat Hunting) and Happy WHH (White Hat Hacking)
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