Where do I go from here?
Once you’ve mastered the basics of Nmap and Nessus, you should dig into the advanced options for both tools. This chapter only scratched the surface of both of these fine tools. Insecure.org is a great resource for learning more about Nmap. You should dedicate time to exploring and learning all the various switches and options. Likewise, Nessus has a plethora of additional features. Take time to review the various scans and policy options.
After you’re comfortable with the advanced features of these tools, you should look at other scanners as well. There are dozens of good port scanners available. Pick a few; install them and learn their features. There are several commercial products that you should become familiar with; these products ain’t exclusively vulnerability scanners (they’re much more), but Core Compact and Saint both provide excellent vulnerability assessment components, although both of these will cost you actual cash.