The book is a guide that covers the full stack when you're trying to do security assesment in your network. It is mainly offensive, more than defensive, but at the end of each chapter you can find a small guide on hardening that specific layer/app.
The book is quite hands-on, with many commands, and lots of links. So reading it on paper is not the best use of your time and/or money. Also I was expecting something more theoretical, but it's full of details on specific technologies.
All in all, it's a well-written book, but I was not the target.