Although recent advances in the IETF's Differentiated Services workinggroup promise to improve the performance of application-level services within some networks, across the wide-area Internet these QoS algorithms are usuallypredicated on the existence of a stable underlying forwarding infrastructure. In recent work, we showed that the Internet lacks effective inter-domain pathfail-over [1]. Specifically, we found that multi-homed Internet sites may experience periods of degraded performance as well as complete loss of connectivitypersisting fifteen minutes or more after a single fault.

The Border Gateway Protocol (BGP) is the routing protocol used to maintain connectivity between autonomous systems in the Internet. Empirical measurements have shown that there can be considerable delay in BGP convergence after routing changes. One contributing factor in this delay is a BGP-specific timer used to limit the rate at which routing messages are transmitted. We use the SSFNet simulator to explore the relationship between convergence time and the configuration of this timer. For each simple network topology simulated, we observe that there is an optimal value for the rate-limiting timer that minimizes convergence time. 1

Abstract — The impact of routing policy on Internet paths is poorly understood. In theory, policy can inflate shortest-router-hop paths. To our knowledge, the extent of this inflation has not been previously examined. Using a simplified model of routing policy in the Internet, we obtain approximate indications of the impact of policy routing on Internet paths. Our findings suggest that routing policy does impact the length of Internet paths significantly. For instance, in our model of routing policy, some 20 % of Internet paths are inflated by more than five router-level hops. Keywords—Routing, Routing Policy, Policy Routing, Internet Paths I.

In any IP network, routing protocols provide the intelligence that takes a collection of physical links and transforms them into a network that enables packets to travel from one host to another. Though routing design is arguably the single most important design task for large IP networks, there has been very little systematic investigation into how routing protocols are actually used in production networks to implement the goals of network architects. We have developed a methodology for reverse engineering a coherent global view of a network’s routing design from the static analysis of dumps of the local configuration state of each router. Starting with a set of 8,035 configuration files, we have applied this method to 31 production networks. In this paper we present a detailed examination of how routing protocols are used in operational networks. In particular, the results show the conventional model of “interior ” and “exterior ” gateway protocols is insufficient to describe the diverse set of mechanisms used by architects. We provide examples of the more unusual designs and examine their trade-offs. We discuss the strengths and weaknesses of our methodology, and argue that it opens paths towards new understandings of network behavior and design.

In this paper we evaluate a method of using interleaved spanning trees to compose a resilient, high performance overlay mesh. Though spanning trees of arbitrary type could be used to construct an overlay mesh, we focus on a distributed algorithm that computes k minimum spanning trees on an arbitrary graph. The principal motivation behind this strategy is to provide applications with a k-redundant, high quality mesh suitable for demanding applications like A/V broadcast, video conferencing, data collection, multi-path routing, and file mirroring/transfer. We elaborate details of k-MST, pointing out advantages and potential problem points of the protocol, and then analyze its performance using a variety of metrics with simulation as well as a functional PlanetLab implementation.

Distance estimation is important to many Internet applications. It can aid a WWW client when selecting among several potential candidate servers, or among candidate peer-to-peer servers. It can also aid in building efficient overlay or peer-to-peer networks that dynamically react to change in the underlying Internet. One of the approaches to distance (i.e., time delay) estimation in the Internet is based on placing Tracer stations in key locations and conducting measurements between them. The Tracers construct an approximated map of the Internet after processing the information obtained from these measurements. This work presents a novel algorithm, based on Algebraic tools, that computes additional distances, which are not explicitly measured. As such, the algorithm extracts more information from the same amount of measurement data. Our algorithm has several practical impacts. First, it can reduce the number of Tracers and measurements without sacrificing information. Second, our algorithm is able to compute distance estimates between locations where Tracers cannot be placed. To evaluate the algorithm’s performance, we tested it both on randomly generated topologies and on real Internet measurements. Our results show that the algorithm computes up to 50-200 % additional distances beyond the basic Tracer-to-Tracer measurements. A. Background I.

Recently there have been several papers examining aspects of the Internet topology. This paper follows in that tradition and addresses two issues related to Internet topology. First, we use three properties -- expansion, resilience, and distortion -- to characterize real and generated networks. For these metrics, we find that existing network topology generators differ qualitatively from most real networks. Second, we ask what impact topology has on four different multicast design questions. We find that, for many of these questions, a single topology metric appears to influence the answer.

Failures at the BGP level can have significant impact on the overall Internet. Understanding the behavior of BGP is thus both an important practical challenge and an interesting research problem. To understand the true dynamics, and help interpret the multiple gigabytes of BGP log data, we have developed the “Link-Rank ” graphical toolset. Link-Rank weights the links between Autonomous Systems by the number of routing prefixes going through each link. Tracing these graphs over time results in a directed graph that shows the weight changes of the logical inter-AS links. From this graph one can easily visualize the complex BGP path changes and also combine views from multiple vantage points, to get a better picture of global routing dynamics. We illustrate the usefulness of Link-Rank by using it to examine BGP routing dynamics in three example cases. These examples show that Link-Rank is able to help BGP analysts estimate the scope of routing changes and to reveal important routing dynamics in the presence of superfluous BGP update messages.

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Abstract—One approach to achieving scalability in reliable multicast is to use a hierarchy. A hierarchy can be established at the application level, or by using router-assist. With router-assist we have more fine-grain control over the placement of error-recovery functionality, therefore, a hierarchy produced by assistance from the routers is expected to have better performance. In this paper, we test this hypothesis by comparing two schemes, one that uses an application-level hierarchy (ALH) and another that uses router-assisted hierarchy (RAH). Contrary to our expectations, we find that the qualitative performance of ALH is comparable to RAH. We do not model the overhead of creating the hierarchy nor the cost of adding router-assist to the network. Therefore, our conclusions inform rather than close the debate of which approach is better. Index Terms—Reliable multicast, router-assist for reliable multicast. I.