End-to-End Routing Behavior in the Internet

The large-scale behavior of routing in the Internet has gone virtu-ally without any formal study, the exception being Chinoy's anal-ysis of the dynamics of Internet routing information [Ch93]. We report on an analysis of 40,000 end-to-end route measurements con-ducted using repeated “traceroutes ” between 37 Internet sites. We analyze the routing behavior for pathological conditions, routing stability, and routing symmetry. For pathologies, we characterize the prevalence of routing loops, erroneous routing, infrastructure failures, and temporary outages. We find that the likelihood of en-countering a major routing pathology more than doubled between the end of 1994 and the end of 1995, rising from 1.5 % to 3.4%. For routing stability, we define two separate types of stability, “preva-lence, ” meaning the overall likelihood that a particular route is en-countered, and “persistence, ” the likelihood that a route remains un-changed over a long period of time. We find that Internet paths are heavily dominated by a single prevalent route, but that the time pe-riods over which routes persist show wide variation, ranging from seconds up to days. About 2/3's of the Internet paths had routes persisting for either days or weeks. For routing symmetry, we look at the likelihood that a path through the Internet visits at least one different city in the two directions. At the end of 1995, this was the case half the time, and at least one different autonomous system was visited 30 % of the time.