Abstract not found

Hot-potato routing is a mechanism employed when there are multiple (equally good) interdomain routes available for a given destination. In this scenario, the Border Gateway Protocol (BGP) selects the interdomain route associated with the closest egress point based upon intradomain path costs. Consequently, intradomain routing changes can impact interdomain routing and cause abrupt swings of external routes, which we call hot-potato disruptions. Recent work has shown that hot-potato disruptions can have a substantial impact on large ISP backbones and thereby jeopardize the network robustness. As a result, there is a need for guidelines and tools to assist in the design of networks that minimize hot-potato disruptions. However, developing these tools is challenging due to the complex and subtle nature of the interactions between exterior and interior routing. In this paper, we address these challenges using an analytic model of hot-potato routing that incorporates metrics to evaluate network sensitivity to hot-potato disruptions. We then present a methodology for computing these metrics using measurements of real ISP networks. We demonstrate the utility of our model by analyzing the sensitivity of a large AS in a tier 1 ISP network.

Despite the architectural separation between intradomain and interdomain routing in the Internet, intradomain protocols do influence the path-selection process in the Border Gateway Protocol (BGP). When choosing between multiple equally-good BGP routes, a router selects the one with the closest egress point, based on the intradomain path cost. Under such hot-potato routing, an intradomain event can trigger BGP routing changes. To characterize the influence of hot-potato routing, we conduct controlled experiments with a commercial router. Then, we propose a technique for associating BGP routing changes with events visible in the intradomain protocol, and apply our algorithm to AT&T's backbone network. We show that (i) hot-potato routing can be a significant source of BGP updates, (ii) BGP updates can lag seconds or more behind the intradomain event, (iii) the number of BGP path changes triggered by hot-potato routing has a nearly uniform distribution across destination prefixes, and (iv) the fraction of BGP messages triggered by intradomain changes varies significantly across time and router locations. We show that hot-potato routing changes lead to longer delays in forwarding-plane convergence, shifts in the flow of traffic to neighboring domains, extra externally-visible BGP update messages, and inaccuracies in Internet performance measurements.

this paper, we present Predicate Routing (PR) as a solution to this problem. We briefly describe our centralized implementation and then outline the extension of Internet routing protocols to support Predicate Routing. In current IP networks, the state of the system is primarily represented in an imperative fashion: routing tables and firewall rulesets local to each node strictly specify the action to be performed on each arriving packet. In contrast, Predicate Routing represents the state of the network declaratively as a set of boolean expressions associated with links which assert which kinds of packet can appear where. From these expressions, routing tables and filter rules are derived automatically. Conversely, the consequences of a change in network state can be calculated for any point in the network (link, router, or end system), and predicates derived from known configuration state of routers and links. This subsumes notions of both routing and firewalling

Abstract — In the Internet today, traffic engineering is performed assuming that the offered traffic is inelastic. In reality, end hosts adapt their sending rates to network congestion, and network operators adapt the routing to the measured traffic. This raises the question of whether the joint system of congestion control (transport layer) and routing (network layer) is stable and optimal. Using the established optimization model for TCP and that for traffic engineering as a basis, we find the joint system is stable and typically maximizes aggregate user utility, especially under more homogeneous link capacities. We prove that both stability and optimality of the joint system can be guaranteed for sufficiently elastic traffic simply by tuning the cost function used for traffic engineering. Then, we present a new algorithm that adapts on a faster timescale to changes in traffic distribution and is more robust to large traffic bursts. Uniting the network and transport layers in a multi-layer approach, this algorithm, Distributed Adaptive Traffic Engineering (DATE), jointly optimizes the goals of end users and network operators and reacts quickly to avoid bottlenecks. Simulations demonstrate that DATE converges quickly.

Abstract — A traffic engineering problem consists of setting up paths between the edge nodes of the network to meet traffic demands while optimizing the network performance. It is known that total traffic throughput in a network, hence the resource utilization, can be maximized if the traffic demand is split over multiple paths. However, the problem formulation and practical algorithms, which calculate the paths and the traffic split ratio taking the route constraints or policies into consideration, have not been much touched. This paper proposes practical algorithms that find near optimal paths satisfying the given traffic demand under constraints such as maximum hop count, and preferred or notpreferred node/link list. The mixed integer programming formulation also calculates the traffic split ratio for the multiple paths. The problems are solved with the split ratio of continuous or discrete values. However, the split ratio solved with discrete values (0.1, 0.2 etc.) are more suitable for easy implementation at the network nodes. The proposed algorithms are applied to the multiprotocol label switching (MPLS) that permits explicit path setup. The paths and split ratio are calculated off-line, and passed to MPLS edge routers for explicit label-switched path (LSP) setup. The proposed schemes are tested in a large-scale fictitious backbone network. The experiment results show that the proposed algorithms are fast and superior to the conventional shortest path algorithm in terms of maximum link utilization, total traffic volume, and number of required LSPs.

The performance and reliability of the Internet depend, in large part, on the operation of the underlying routing protocols. Today’s IP routing protocols compute paths based on the network topology and configuration parameters, without regard to the current traffic load on the routers and links. The responsibility for adapting the paths to the prevailing traffic falls to the network operators and management systems. This chapter discusses the modeling and computational challenges of optimizing the tunable parameters, starting with conventional intradomain routing protocols that compute shortest paths as the sum of configurable link weights. Then, we consider the problem of optimizing the interdomain routing policies that control the flow of traffic from one network to another. Optimization based on local search has proven quite effective in grappling with the complexity of the routing protocols and the diversity of the performance objectives, and tools based on local search are in wide use in today’s large IP networks. 1

Tools to measure internet properties usually assume the existence of just one single path from a source to a destination. However, load-balancing capabilities, which create multiple active paths between two end-hosts, are available in most contemporary routers. This paper proposes a methodology to identify load-balancing routers and characterize loadbalanced paths. We enhance our traceroute-like tool, called Paris traceroute, to find all paths between a pair of hosts, and use it from 15 sources to over 68 thousand destinations. Our results show that the traditional concept of a single network path between hosts no longer holds. For instance, 39 % of the source-destination pairs in our traces traverse a load balancer. Furthermore, this fraction increases to 70% if we consider the paths between a source and a destination network.

Coupling Internet protocol (IP) routers with wavelengthselective optical crossconnects makes it possible to extend the existing Internet infrastructure to a wavelength-division --multiplexing optical network. Because optical wavelength routing is transparent to IP, one can achieve very high throughput and low delay when packets are made to bypass the IP forwarding process by being switched directly through the optical crossconnect. We study the performance of a specific instantiation of this approach,which we call packet over wavelengths (POW). We present the POW architecture in detail and discuss its salient features. Realistic simulations of the POW that use actual packet traces in a well-known Internet backbone network reveal the level of performance that can be expected from POW under various options.

Many recent router architectures decouple the routing engine from the forwarding engine, so that packet forwarding can continue even when the routing process is not active. This opens up the possibility of using the forwarding capability of a router even when its routing process is down, thus avoiding the route flaps that normally occur when the routing process goes down. Unfortunately, current routing protocols, such as BGP, OSPF and IS-IS do not support this behavior. In this paper, we describe an enhancement to OSPF, called the IBB (I'll Be Back) capability, that enables other routers to use a router whose OSPF process is inactive for forwarding traffic for a certain period of time. The IBB capability can be used for avoiding route flaps that occur when the OSPF process is brought down in a router to facilitate protocol software upgrade, operating system upgrade, router ID change, AS and interface renumbering, etc.