4 research outputs found

    Interdomain Ingress Traffic Engineering through Optimized AS-Path Prepending

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    In Interdomain Ingress Traffic Engineering (INITE), a "target" Autonomous System (AS) aims to control the ingress link through which the traffic of one or more upstream source networks flows to the target network or to its customers. Currently, there are few methodologies for systematic INITE. In practice, ISPs often attempt to manipulate, mostly in a trial-and-error manner, the AS-Path length attribute of upstream routes through a simple technique known as prepending (or padding). In this paper, we focus on prepending and propose a polynomial-time algorithm (referred to as OPV) that determines the optimal padding for an upstream route at each ingress link of the target network. Specifically given a set of "elephant" source networks for a particular customer of the target network, and a set of maximum load constraints on the ingress links of the latter, OPV determines the minimum padding at each ingress link so that the load constraints are met, when it is feasible to do so. OPV requires as input an AS-Path length estimate from each source to each ingress link. We describe how to estimate this matrix, leveraging the BGP Looking Glass Servers that are abundant today for monitoring interdomain routing. To deal with unavoidable inaccuracies in the AS-Path length estimates, and also to compensate for the generally unknown BGP tie-breaking process in upstream networks, we develop a robust variation (RPV) of the OPV algorithm. We show that RPV manages to identify a padding vector that meets the given maximum load constraints, when it is feasible to do so, even in the presence of inaccurate AS-Path lengths and unknown BGP tie-breaking behavior

    Joint Optimization of Intra- and Inter-Autonomous System Traffic Engineering

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    Traffic Engineering (TE) is used to optimize IP operational network performance. The existing literature generally considers intra- and inter-AS (Autonomous System) TE independently. However, the overall network performance may not be truly optimized when these aspects are considered separately. This is due to the interaction between intra- and inter-AS TE, where a solution of intra-AS TE may not be a good input to inter-AS TE and vice versa. To remedy this situation, we propose considering intra-AS aspects during inter-AS TE and vice versa. We propose a joint optimization of intra- and inter-AS TE to further improve the overall network performance by simultaneously finding the best egress points for the inter-AS traffic and the best routing scheme for the intra-AS traffic. Three strategies are presented to attack the problem, namely sequential, nested and integrated optimization. Our simulation study shows that, compared to sequential and nested optimization, integrated optimization can significantly improve the overall network performance by accommodating 30%-60% more traffic demands

    Interdomain ingress traffic engineering through optimized as path prepending

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    In INterdomain Ingress Traffic Engineering (INITE), a “target” Autonomous System (AS) aims to control the ingress link at which the traffic of one or more upstream source networks enters that AS. In practice, ISPs often manipulate, mostly in a trial-and-error manner, the length of the AS-Path attribute of upstream routes through a simple technique known as prepending (or padding). In this paper, we focus on prepending and propose a polynomial-time algorithm (referred to as OPV) that determines the optimal padding for an advertised route at each ingress link of the target network. Specifically, given a set of “elephant” source networks and some maximum load constraints on the ingress links of the target AS, OPV determines the minimum padding at each ingress link so that the load constraints are met, when it is feasible to do so. OPV requires as input an AS-Path length estimate from each source network to each ingress link. We describe how to estimate this matrix, leveraging the BGP Looking Glass Servers. To deal with unavoidable inaccuracies in the AS-Path length estimates, and also to compensate for the generally unknown BGP tie-breaking process in upstream networks, we also develop a robust variation (RPV) of the OPV algorithm. Document type: Part of book or chapter of boo

    Proactive techniques for correct and predictable Internet routing

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 185-193).The Internet is composed of thousands of autonomous, competing networks that exchange reachability information using an interdomain routing protocol. Network operators must continually reconfigure the routing protocols to realize various economic and performance goals. Unfortunately, there is no systematic way to predict how the configuration will affect the behavior of the routing protocol or to determine whether the routing protocol will operate correctly at all. This dissertation develops techniques to reason about the dynamic behavior of Internet routing, based on static analysis of the router configurations, before the protocol ever runs on a live network. Interdomain routing offers each independent network tremendous flexibility in configuring the routing protocols to accomplish various economic and performance tasks. Routing configurations are complex, and writing them is similar to writing a distributed program; the (unavoidable) consequence of configuration complexity is the potential for incorrect and unpredictable behavior. These mistakes and unintended interactions lead to routing faults, which disrupt end-to-end connectivity. Network operators writing configurations make mistakes; they may also specify policies that interact in unexpected ways with policies in other networks.(cont.) To avoid disrupting network connectivity and degrading performance, operators would benefit from being able to determine the effects of configuration changes before deploying them on a live network; unfortunately, the status quo provides them no opportunity to do so. This dissertation develops the techniques to achieve this goal of proactively ensuring correct and predictable Internet routing. The first challenge in guaranteeing correct and predictable behavior from a routing protocol is defining a specification for correct behavior. We identify three important aspects of correctness-path visibility, route validity, and safety-and develop proactive techniques for guaranteeing that these properties hold. Path visibility states that the protocol disseminates information about paths in the topology; route validity says that this information actually corresponds to those paths; safety says that the protocol ultimately converges to a stable outcome, implying that routing updates actually correspond to topological changes. Armed with this correctness specification, we tackle the second challenge: analyzing routing protocol configurations that may be distributed across hundreds of routers.(cont.) We develop techniques to check whether a routing protocol satisfies the correctness specification within a single independently operated network. We find that much of the specification can be checked with static configuration analysis alone. We present examples of real-world routing faults and propose a systematic framework to classify, detect, correct, and prevent them. We describe the design and implementation of rcc ("router configuration checker"), a tool that uses static configuration analysis to enable network operators to debug configurations before deploying them in an operational network. We have used rcc to detect faults in 17 different networks, including several nationwide Internet service providers (ISPs). To date, rcc has been downloaded by over seventy network operators. A critical aspect of guaranteeing correct and predictable Internet routing is ensuring that the interactions of the configurations across multiple networks do not violate the correctness specification. Guaranteeing safety is challenging because each network sets its policies independently, and these policies may conflict. Using a formal model of today's Internet routing protocol, we derive conditions to guarantee that unintended policy interactions will never cause the routing protocol to oscillate.(cont.) This dissertation also takes steps to make Internet routing more predictable. We present algorithms that help network operators predict how a set of distributed router configurations within a single network will affect the flow of traffic through that network. We describe a tool based on these algorithms that exploits the unique characteristics of routing data to reduce computational overhead. Using data from a large ISP, we show that this tool correctly computes BGP routing decisions and has a running time that is acceptable for many tasks, such as traffic engineering and capacity planning.by Nicholas Greer Feamster.Ph.D
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