The Internet pervades many aspects of our lives and is becoming indispensable to critical functions in areas such as commerce, government, production and general information dissemination. To maintain the stability and efficiency of the Internet, every effort must be made to protect it against various forms of attacks, malicious uses, and errors. One way is to routinely examine Internet routing data, which, however, can be too large and sophisticated to browse directly. We have developed an interactive visualization process which proves to be very effective for the analysis of Internet routing data. In this application paper, we show how each step in the visualization process helps direct the analysis and glean insights from the data, which include discovering patterns, detecting faults and abnormal events, understanding event correlations, making causation hypotheses, and classifying anomalies. We also discuss lessons learned in our visual analysis study, and how some of the visual ...