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A route in the Internet may take a longer AS path than the shortest AS path due to routing policies. In this paper, we systematically analyze AS paths and quantify the extent to which routing policies inflate AS paths. The results show that AS path inflation in the Internet is more prevalent than expected. We first present the extent of AS path inflation observed from the Route View routing tables. From an ISP, at least 55% of AS paths are inflated by at least one AS hop and AS paths can be inflated by as long as 6 AS hops. We then employ two typical routing policies to show the extent of AS path inflation for all AS pairs, we find that at least 45% of AS paths are inflated by at least one AS hop and AS paths can be inflated by as long as 9 AS hops. Quantifying AS path inflation in the Internet has important implications on the extent of routing policies and traffic engineering performed on the Internet, and BGP convergence speed.

The Internet has experienced explosive growth since its commercialization. The sizes of the routing tables have increased by an order of magnitude over the past six years. This dramatic growth of the routing table can decrease the packet forwarding speed and demand more router memory space. In this paper, we explore the extent that various factors contribute to the routing table growth and predict the future rate of growth of the routing table. We first perform measurement study to determine the extent that factors such as multi-homing, failure to aggregate, load balancing, and address fragmentation contribute to routing table size, and find that only 20 30% of prefixes are due to multi-homing, 15 20% of prefixes are due to failure to aggregate, 20 25% of prefixes are due to load balancing, and more than 75% of prefixes are due to address fragmentation. This leads us to group all prefixes that are not aggregated due to either failure to aggregate or address fragmentation. We find that the number of prefix clusters is no more than 20% of the number of prefixes. We explore the extent that load balancing contributes to the number of prefix clusters. Furthermore, we predict the growth pattern of prefixes and prefix clusters by observing power-laws on prefixes and prefix clusters. The number of prefixes grows much faster than the number of prefix clusters does. To the best of our knowledge, this is the first study on the explosive growth of routing tables by systematically comparing factors that contribute to the growth and by observing routing table growth patterns.

Abstract: Over the last few years, several nations around the world have set up Grids to share resources such as computers, data, and instruments to enable collaborative science, engineering, and business applications. These Grids follow a restricted organisational model wherein a Virtual Organisation (VO) is created for a specific collaboration and all interactions such as resource sharing are limited to within the VO. Therefore, dispersed Grid initiatives have led to the creation of disparate Grids with little or no interaction between them. In this paper, we propose a model that: (a) promotes interlinking of islands of Grids through peering arrangements to enable inter-Grid resource sharing; (b) provides a scalable structure for Grids that allow them to interconnect with one another and grow in a sustainable way; (c) creates a global Cyberinfrastructure to support e-Science and e-Business applications. This work identifies and proposes architecture, mechanisms and policies that allow the internetworking of Grids and allows Grids to grow in a similar manner as the Internet. We term the structure resulting from such internetworking between Grids as the InterGrid. The proposed InterGrid architecture is composed of InterGrid Gateways responsible for managing peering arrangements between Grids. We discuss the main components of the architecture and present a research agenda to enable the InterGrid vision.

a serious threat to the legitimate use of the Internet. Prevention mechanisms are thwarted by the ability of attackers to forge, or spoof, the source addresses in IP packets. By employing IP spoofing, attackers can evade detection and put a substantial burden on the destination network for policing attack packets. In this paper we propose an inter-domain packet filter (IDPF) architecture that can mitigate the level of IP spoofing on the Internet. IDPFs are constructed from the information implicit in BGP route updates and are deployed in network border routers. A key feature of the scheme is that it does not require global routing information. Based on extensive simulation studies, we show that even with partial deployment on the Internet, IDPFs can proactively limit the spoofing capability of attackers. In addition, they can help localize the origin of an attack packet to a small number of candidate networks. I.

In the valley-free path model, a path in a given directed graph is valid if it consists of a sequence of forward edges followed by a sequence of backward edges. This model is motivated by BGP routing policies of autonomous systems in the Internet. Robustness considerations lead to the problem of computing a maximum number of disjoint paths between two nodes, and the minimum size of a cut that separates them. We study these problems in the valley-free path model. For the problem of computing a maximum number of edge- or vertex-disjoint valid paths between two given vertices s and t, we give a 2-approximation algorithm and show that no better approximation ratio is possible unless P = NP. For the problem of computing a minimum vertex cut that separates s and t with respect to all valid paths, we give a 2-approximation algorithm and prove that the problem is APX-hard. The corresponding problem for edge cuts is shown to be polynomial-time solvable. We present additional results for acyclic graphs.

This paper discusses the structure of the Internet connectivity market by focusing on the business relations of stakeholders involved in network services provision. We believe that the role of information asymmetry is critical when considering interconnection agreements, and should be taken into account in the structure of the contract. Information asymmetry due to incomplete information concerning important operating parameters such as network load, capacity, cost, gives rise to adverse selection during negotiation and contract preparation. The current at structure of interconnection agreements does not address such information asymmetries. In many cases, the di culty of observing the actual e ort allocated by thecontracted network for providing quality of service, and in particular, the absence of appropriate incentives in the contract, allows for the possibility of opportunistic behaviour in the form of moral hazard. We formulate two simple analytical models which demonstrate the e ects of moral hazard in the market for network transport services. The rst deals with the case where the network is contracted for short duration transport where the customer can not use the statistical information obtained during the life time of the service to determine with certainty the actual e ort allocated by the network. The second model deals with transit contracts of longer duration, where the actual cost for provisioning the service at various quality levels is only statistically known at the time the contract is set up. Although these models are too simple for capturing the complexity of interconnection agreements between ISPs, they demonstrate the bad e ects of information asymmetry and motivate the importance of incentive contracts for improving e ciency. 1 1

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Multi-homing is a common practice among many (especially large) customer (or stub) networks. Although the purpose of multi-homing is primarily for enhanced reliability, it has also increasingly been used for load balancing and latency reduction. In this paper, we address the problem of how to perform scalable route selection in a multi-homed stub network to optimize network latency to various destinations as measured by round-trip-time (RTT). A straightforward method is to simply perform RTT measurements (e.g., using ping) to each destination via each provider and select the one with the minimum RTT as the “best ” next-hop to the destination. Is there a more scalable alternative? To answer this question, we carry out a measurementbased study to analyze the differences of RTTs in using two different providers in a multi-homed stub network to reach a large number of randomly selected destinations. Our study reveals that because of the AS hierarchy, for a large fraction of the network prefixes, the two AS paths through two providers merge in the core of the Internet. Furthermore, the router at which the two router level paths merge is actually in the AS at which the AS level paths merge. This phenomenon causes the RTT difference between the two paths through the two providers to be determined by the non-shared portion of the paths. Our study reveals that most of the two router level paths through the two upstream providers merge at the AS at which the two AS level paths merge. Based on this finding, we devise a scalable route (next-hop provider) selection algorithm using BGP information in a multi-homed stub network. We also present a preliminary evaluation.

a serious threat to the legitimate use of the Internet. Prevention mechanisms are thwarted by the ability of attackers to forge, or spoof, the source addresses in IP packets. By employing IP spoofing, attackers can evade detection and put a substantial burden on the destination network for policing attack packets. In this paper, we propose an inter-domain packet filter (IDPF) architecture that can mitigate the level of IP spoofing on the Internet. A key feature of our scheme is that it does not require global routing information. IDPFs are constructed from the information implicit in BGP route updates and are deployed in network border routers. We establish the conditions under which the IDPF framework works correctly in that it does not discard packets with valid source addresses. Based on extensive simulation studies, we show that even with partial deployment on the Internet, IDPFs can proactively limit the spoofing capability of attackers. In addition, they can help localize the origin of an attack packet to a small number of candidate networks.