I'm trying to put together a list of topics in Network Security and prioritize them accordingly. A little background on the book - we are trying to gear the text towards college students, as an introduction to security, and toward IT professionals who have recently been tasked with securing a network.

The idea is to create a book that covers the most vital and important parts of securing a network with no assumptions. So, if you were a novice student interested in network security OR an IT professional who needed a crash course on network security, what topics do you feel would be of the upmost importance in such a text?