First, this chapter covers some topics that are not covered elsewhere in this book, namely some troubleshooting commands on both hosts and routers. Second, this chapter reviews the core concepts of addressing and routing, but with a focus on how to approach new problems to analyze and understand how to troubleshoot any problems. Additionally, this chapter includes a troubleshooting scenario that shows how to use some of the tools and concepts from earlier in this chapter, with an opportunity for you to try and discover the problems before the text explains the answers.