Network administrators can be assured that their routing will break every once in a while. Internet routing is not yet a science—many parts of the Internet have been glued together in a hodge-podge fashion. And sometimes the glue comes loose. Fortunately a number of tools are available to help you debug the situation.
In this chapter, we survey the available tools—what they do, how they work, and their strengths and weaknesses. In addition to being used by network administrators, some of these tools may be used by users of the network to diagnose routing problems before reporting them to their ISPs. For example, the first two tools that we examine,
traceroute, are often performed by network users. ...