Cisco IOS 12.0 Network Security

This is not a book that you will read end-to-end. It's got little overview sections before the configuration chapters that explain Kerberos, AAA .... The true power of the book lies in the handiness of having the information in an easy-to-reference place, rather than the nightmare that is CCO's search engine. I didn't give it 5 stars because it was not a groundbreaker like Doyle's book, but it is worth the money if you are interested in implementing some of the more complex security features in the 12.x IOSs.