The large-scale behavior of routing in the Internet has gone virtually without any formal study, the exceptions being Chinoy's analysis of the dynamics of Internet routing information [Ch93], and recent work, similar in spirit, by Labovitz, Malan and Jahanian [LMJ97]. We report on an analysis of 40,000 end-to-end route measurements conducted 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 encountering a major routing pathology more than doubled between the end of 1994 and the end of 1995, rising from 1.5 % to 3.3%. For routing stability, we define two separate types of stability, “prevalence, ” meaning the overall likelihood that a particular route is encountered, and “persistence, ” the likelihood that a route remains unchanged over a long period of time. We find that Internet paths are heavily dominated by a single prevalent route, but that the time periods 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.

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Abstract—This paper examines the network interdomain routing information exchanged between backbone service providers at the major U.S. public Internet exchange points. Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency and time to convergence. At the extreme, high levels of routing instability have led to the loss of internal connectivity in wide-area, national networks. In this paper, we describe several unexpected trends in routing instability, and examine a number of anomalies and pathologies observed in the exchange of inter-domain routing information. The analysis in this paper is based on data collected from BGP routing messages generated by border routers at five of the Internet core’s public exchange points during a nine month period. We show that the volume of these routing updates is several orders of magnitude more than expected and that the majority of this routing information is redundant, or pathological. Furthermore, our analysis reveals several unexpected trends and ill-behaved systematic properties in Internet routing. We finally posit a number of explanations for these anomalies and evaluate their potential impact on the Internet infrastructure. Index Terms—Communication system, communication system routing, computer network, Internet, routing, stability.

The path taken by a packet traveling across the Internet depends on a large number of factors, including routing protocols and pernetwork routing policies. The impact of these factors on the endto -end performance experienced by users is poorly understood. In this paper, we conduct a measurement-based study comparing the performance seen using the "default" path taken in the Internet with the potential performance available using some alternate path. Our study uses five distinct datasets containing measurements of "path quality", such as round-trip time, loss rate, and bandwidth, taken between pairs of geographically diverse Internet hosts. We construct the set of potential alternate paths by composing these measurements to form new synthetic paths. We find that in 30-80% of the cases, there is an alternate path with significantly superior quality. We argue that the overall result is robust and we explore two hypotheses for explaining it.

In this paper, we describe an experimental study of Internet stability and the origins of failure in Internet protocol backbones. The stability of end-to-end Internet paths is dependent both on the underlying telecommunication switching system, as well as the higher level software and hardware components specific to the Internet's packet-switched forwarding and routing architecture. Although a number of earlier studies have examined failures in the public telecommunication system, little attention has been given to the characterization of Internet stability. Our paper analyzes Internet failures from three different perspectives. We first examine several recent major Internet failures and their probable origins. These empirical observations illustrate the complexity of the Internet and show that unlike commercial transaction systems, the interactions of the underlying components of the Internet are poorly understood. Next, our examination focuses on the stability of paths between In...

The Internet routing fabric is partitioned into several domains. Each domain represents a region of the fabric administered by a single commercial entity. Over the past two years, the routing fabric has experienced significant growth. From more than a year's worth of inter-domain routing traces, we analyze the Internet inter-domain topology, its route stability behavior, and the effect of growth on these characteristics. Our analysis reveals several interesting results. Despite growth, the degree distribution and the diameter of the inter-domain topology have remained relatively unchanged. Furthermore, there exists a four-level hierarchy of Internet domains classified by degree. However, connectivity between domains is significantly nonhierarchical. Despite increased connectivity at higher levels in the topology, the distributionof paths to prefixes from the backbone remained relatively unchanged. There is evidence that both route availability and the mean reachability duration have de...

This paper examines the network routing messages exchanged between core Internet backbone routers. Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency and time to convergence. At the extreme, high levels of routing instability have led to the loss of internal connectivity in wide-area, national networks. In an earlier study of inter-domain routing, we described widespread, significant pathological behaviors in the routing information exchanged between backbone service providers at the major U.S. public Internet exchange points. These pathologies included several orders of magnitude more routing updates in the Internet core than anticipated, large numbers of duplicate routing messages, and unexpected frequency components between routing instability events. The work described in this pape...

Abstract—In this paper, we study traffic demands in an IP bacbkone, identify the routes used by these demands, and evaluate traffic granularity levels that are attractive for improving the poor load balancing that our study reveals. The data used in this study was collected at a major POP in a commercial Tier-1 IP backbone. In the first part of this paper we ask two questions. What is the traffic demand between a pair of POPs in the backbone? How stable is this demand? We develop a methodology that combines packet-level traces from access links in the POP and BGP routing information to build components of POP-to-POP traffic matrices. Our analysis shows that the geographic spread of traffic across egress POPs is far from uniform. In addition, we find that the time of day behaviors for different POPs and different access links also exhibit a high degree of heterogeneity. In the second part of this work, we examine commercial routing practices to assess how these demands are routed through the backbone. We find that traffic between a pair of POPs is engineered to be restricted to a few paths and that this contributes to widely varying link utilization levels. The natural question that follows from these findings is whether or not there is a better way to spread the traffic across backbone paths. We identify traffic aggregates based on destination address prefixes and find that this set of criteria isolates a few aggregates that account for an overwhelmingly large portion of inter-POP traffic. We demonstrate that these aggregates exhibit stability throughout the day on perhour time scales, and thus form a natural basis for splitting traffic over multiple paths to improve load balancing.

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In this paper, we describe an experimental study of Internet topological stability and the origins of failure in Internet protocol backbones. The stability of end-toend Internet paths is dependent both on the underlying telecommunication switching system, as well as the higher level software and hardware components speci c to the Internet's packet-switched forwarding and routing architecture. Although a number of earlier studies have examined failures in the public telecommunication system, little attention has been given to the characterization of Internet stability. We provide analysis of the stability of major paths between Internet Service Providers based on the experimental instrumentation of key portions of the Internet infrastructure. We describe unexpectedly high levels of path uctuation and an aggregate low mean time between failures for individual Internet paths. We also provide a case study of the network failures observed in a large regional Internet backbone. We characterize the type, origin, frequency and duration of these failures. 1.