Papers by Jennifer Rexford
Computer Communication Review, 2008
This whitepaper proposes OpenFlow: a way for researchers to run experimental protocols in the net... more This whitepaper proposes OpenFlow: a way for researchers to run experimental protocols in the networks they use every day. OpenFlow is based on an Ethernet switch, with an internal flow-table, and a standardized interface to add and remove flow entries. Our goal is to encourage networking vendors to add OpenFlow to their switch products for deployment in college campus backbones and wiring closets. We believe that OpenFlow is a pragmatic compromise: on one hand, it allows researchers to run experiments on heterogeneous switches in a uniform way at line-rate and with high port-density; while on the other hand, vendors do not need to expose the internal workings of their switches. In addition to allowing researchers to evaluate their ideas in real-world traffic settings, OpenFlow could serve as a useful campus component in proposed large-scale testbeds like GENI. Two buildings at Stanford University will soon run OpenFlow networks, using commercial Ethernet switches and routers. We will work to encourage deployment at other schools; and We encourage you to consider deploying OpenFlow in your university network too.
This paper describes VINI, a virtual network infrastructure that allows network researchers to ev... more This paper describes VINI, a virtual network infrastructure that allows network researchers to evaluate their protocols and services in a realistic environment that also provides a high degree of control over network conditions. VINI allows researchers to deploy and evaluate their ideas with real routing software, traffic loads, and network events. To provide researchers flexibility in designing their experiments, VINI supports simultaneous experiments with arbitrary network topologies on a shared physical infrastructure. This paper tackles the following important design question: What set of concepts and techniques facilitate flexible, realistic, and controlled experimentation (e.g., multiple topologies and the ability to tweak routing algorithms) on a fixed physical infrastructure? We first present VINI's high-level design and the challenges of virtualizing a single network. We then present PL-VINI, an implementation of VINI on PlanetLab, running the "Internet In a Slice". Our evaluation of PL-VINI shows that it provides a realistic and controlled environment for evaluating new protocols and services.
IEEE/ACM Transactions on Networking, 2001
Quality-of-service (QoS) routing satisfies application performance requirements and optimizes net... more Quality-of-service (QoS) routing satisfies application performance requirements and optimizes network resource usage by selecting paths based on connection traffic parameters and link load information. However, distributing link state imposes significant bandwidth and processing overhead on the network. This paper investigates the performance trade-off between protocol overhead and the quality of the routing decisions in the context of the source-directed, link-state routing protocols proposed for IP and ATM networks. We construct a detailed model of QoS routing that parameterizes the path-selection algorithm, link-cost function, and link-state update policy. Through extensive simulation experiments with several network topologies and traffic patterns, we uncover the effects of stale link-state information and random fluctuations in traffic load on the routing and set-up overheads. We then investigate how inaccuracy of linkstate information interacts with the size and connectivity of the underlying topology. Finally, we show that tuning the coarseness of the link-cost metric to the inaccuracy of underlying link-state information reduces the computational complexity of the path-selection algorithm without significantly degrading performance. This work confirms and extends earlier studies, and offers new insights for designing efficient quality-of-service routing policies in large networks.
Computer Communication Review, 1999
Internet service providers face a daunting challenge in provisioning network resources, due to th... more Internet service providers face a daunting challenge in provisioning network resources, due to the rapid growth of the Internet and wide fluctuations in the underlying traffic patterns. The ability of dynamic routing to circumvent congested links and improve application performance makes it a valuable traffic engineering tool. However, deployment of load-sensitive routing is hampered by the overheads imposed by link-state update propagation, path selection, and signalling. Under reasonable protocol and computational overheads, traditional approaches to load-sensitive routing of IP traffic are ineffective, and can introduce significant route flapping, since paths are selected based on out-of-date link-state information. Although stability is improved by performing load-sensitive routing at the flow level, flapping still occurs, because most IP flows have a short duration relative to the desired frequency of link-state updates. To address the efficiency and stability challenges of load-sensitive routing, we introduce a new hybrid approach that performs dynamic routing of long-lived flows, while forwarding short-lived flows on static preprovisioned paths. By relating the detection of long-lived flows to the timescale of link-state update messages in the routing protocol, route stability is considerably improved. Through simulation experiments using a one-week ISP packet trace, we show that our hybrid approach significantly outperforms traditional static and dynamic routing schemes, by reacting to fluctuations in network load without introducing route flapping.
Sigmetrics Performance Evaluation Review, 2004
Despite the architectural separation between intradomain and interdomain routing in the Internet,... more 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.
The Internet consists of a large number of Autonomous Systems (ASes) that exchange routing inform... more The Internet consists of a large number of Autonomous Systems (ASes) that exchange routing information using the Border Gateway Protocol (BGP). Each AS applies local policies for selecting routes and propagating routes to others, with important implications for the reliability and stability of the global system. In and of itself, BGP does not ensure that every pair of hosts can communicate. In addition, routing policies are not guaranteed be safe, and may cause protocol divergence. Backup routing is often used to increase the reliability of the network under link and router failures, at the possible expense of safety. This paper presents a general model for backup routing that increases network reliability while allowing each AS to apply local routing policies that are consistent with the commercial relationships it has with its neighbors. In addition, our model is inherently safe in the sense that the global system remains safe under any combination of link and router failures. Our model and the proof of inherent safety are cast in terms of the stable paths problem, a static formalism that captures the semantics of interdomain routing policies. Then, we describe how to realize our model in BGP with locally-implementable routing policies. To simplify the specification of local policies, we propose a new BGP attribute that conveys the avoidance level of a route. We also describe how to realize these policies without modification to BGP by using the BGP community attribute.
Computer Communication Review, 2007
Computer Communication Review, 2005
Today's data networks are surprisingly fragile and difficult to manage. We argue that the root of... more Today's data networks are surprisingly fragile and difficult to manage. We argue that the root of these problems lies in the complexity of the control and management planes-the software and protocols coordinating network elements-and particularly the way the decision logic and the distributed-systems issues are inexorably intertwined. We advocate a complete refactoring of the functionality and propose three key principles-network-level objectives, network-wide views, and direct control-that we believe should underlie a new architecture. Following these principles, we identify an extreme design point that we call "4D," after the architecture's four planes: decision, dissemination, discovery, and data. The 4D architecture completely separates an AS's decision logic from protocols that govern the interaction among network elements. The AS-level objectives are specified in the decision plane, and enforced through direct configuration of the state that drives how the data plane forwards packets. In the 4D architecture, the routers and switches simply forward packets at the behest of the decision plane, and collect measurement data to aid the decision plane in controlling the network. Although 4D would involve substantial changes to today's control and management planes, the format of data packets does not need to change; this eases the deployment path for the 4D architecture, while still enabling substantial innovation in network control and management. We hope that exploring an extreme design point will help focus the attention of the research and industrial communities on this crucially important and intellectually challenging area.
Computer Communication Review, 2003
Network operators must have control over the flow of traffic into, out of, and across their netwo... more Network operators must have control over the flow of traffic into, out of, and across their networks. However, the Border Gateway Protocol (BGP) does not facilitate common traffic engineering tasks, such as balancing load across multiple links to a neighboring AS or directing traffic to a different neighbor. Solving these problems is difficult because the number of possible changes to routing policies is too large to exhaustively test all possibilities, some changes in routing policy can have an unpredictable effect on the flow of traffic, and the BGP decision process implemented by router vendors limits an operator's control over path selection.
IEEE/ACM Transactions on Networking, 1998
To efficiently transfer diverse traffic over high-speed links, modern integrated networks require... more To efficiently transfer diverse traffic over high-speed links, modern integrated networks require more efficient packetswitching techniques that can capitalize on recent advances in switch hardware. Several promising approaches attempt to improve performance by creating dedicated "shortcut" connections for long-lived traffic flows, at the expense of the network overhead for establishing and maintaining these shortcuts. The network can balance these cost-performance tradeoffs through three tunable parameters: the granularity of flow end-point addresses, the timeout for grouping related packets into flows, and the trigger for migrating a long-lived flow to a shortcut connection. Drawing on a continuous one-week trace of Internet traffic, we evaluate the processor and switch overheads for transferring HTTP server traffic through a flow-switched network. In contrast to previous work, we focus on the full probability distributions of flow sizes and cost-performance metrics to highlight the subtle influence of the HTTP protocol and user behavior on the performance of flow switching. We find that moderate levels of aggregation and triggering yield significant reductions in overhead with a negligible reduction in performance. The traffic characterization results further suggest schemes for limiting shortcut overhead by temporarily delaying the creation of shortcuts during peak load and by aggregating related packets that share a portion of their routes through the network.
In emerging communication networks, a single link may carry tra c for thousands of connections wi... more In emerging communication networks, a single link may carry tra c for thousands of connections with different tra c parameters and quality-of-service requirements. High-speed links, coupled with small packet/cell sizes, require e cient switch architectures that can handle cell arrivals and departures every few microseconds, or faster. This paper presents a collection of self-clocked fair queueing (SCFQ) architectures amenable to e cient hardware implementation in network switches. Exact and approximate implementations of SCFQ e ciently handle a moderate range of connection bandwidth parameters, while hierarchical arbitration schemes scale to a large range of throughput requirements. Simulation experiments demonstrate that these architectures divide link bandwidth fairly on a small time scale, preserving connection bandwidth and burstiness properties.
IEEE Network, 1999
Managing large IP networks requires an understanding of the current traffic flows, routing polici... more Managing large IP networks requires an understanding of the current traffic flows, routing policies, and network configuration. However, the state of the art for managing IP networks involves manual configuration of each IP router, and traffic engineering based on limited measurements. The networking industry is sorely lacking in software systems that a large Internet service provider can use to support traffic measurement and network modeling, the underpinnings of effective traffic engineering. This article describes the AT&T Labs NetScope, a unified set of software tools for managing the performance of IP backbone networks. The key idea behind NetScope is to generate global views of the network on the basis of configuration and usage data associated with the individual network elements. Having created an appropriate global view, we are able to infer and visualize the networkwide implications of local changes in traffic, configuration, and control. Using NetScope, a network provider can experiment with changes in network configuration in a simulated environment rather than the operational network. In addition, the tool provides a sound framework for additional modules for network optimization and performance debugging. We demonstrate the capabilities of the tool through an example traffic engineering exercise of locating a heavily loaded link, identifying which traffic demands flow on the link, and changing the configuration of intradomain routing to reduce the congestion
IEEE/ACM Transactions on Networking, 2001
Abstract| Engineering a large IP backbone network without an accurate, network-wide view of the t... more Abstract| Engineering a large IP backbone network without an accurate, network-wide view of the tra c demands is challenging. Shifts in user behavior, changes in routing policies, and failures of network elements can result in signi cant (and sudden) uctuations in load. In this paper, we present a model of tra c demands to support tra c engineering and performance debugging of large Internet Service Provider networks. By de ning a tra c demand as a volume of load originating from an ingress link and destined to a set of egress links, we can capture and predict how routing a ects the tra c traveling between domains. To infer the tra c demands, we propose a measurement methodology that combines ow-level measurements collected at all ingress links with reachability information about all egress links. We discuss how to cope with situations where practical considerations limit the amount and quality of the necessary data. Speci cally, we show how to infer interdomain tra c demands using measurements collected at a smaller number of edge links | the peering links connecting to neighboring providers. We report on our experiences in deriving the tra c demands in the AT&T IP Backbone, by collecting, validating, and joining very large and diverse sets of usage, con guration, and routing data over extended periods of time. The paper concludes with a preliminary analysis of the observed dynamics of the tra c demands and a discussion of the practical implications for tra c engineering.
Computer Communication Review, 1998
The rapid growth of the World Wide Web has caused serious performance degradation on the Internet... more The rapid growth of the World Wide Web has caused serious performance degradation on the Internet. This paper o ers an end-to-end framework by collectively examining the Web components { clients, proxies, servers, and the network. Our goal is to reduce user-perceived latency and the number of TCP connections, improve cache coherency and cache replacement, and enable prefetching of resources that are likely to be accessed in the near future. In our scheme, server response messages include piggybacked information customized to the requesting proxy. Our enhancement to the existing requestresponse protocol does not require per-proxy state at server or per-server state at the proxy, and can be implemented without changes to HTTP 1.1. The server groups related resources into volumes (based on access patterns and the le system's directory structure) and applies a proxy-generated lter (indicating the type of information of interest to the proxy) to tailor the piggyback information. We present e cient data structures for constructing server volumes and applying proxy lters, and a transparent way to perform volume maintenance and piggyback generation at a router along the path between the proxy and the server. We demonstrate the e ectiveness of our end-toend approach by evaluating various volume construction and ltering techniques across a collection of large client and server logs.
Abstract| Engineering a large IP backbone network without an accurate, network-wide view of the t... more Abstract| Engineering a large IP backbone network without an accurate, network-wide view of the tra c demands is challenging. Shifts in user behavior, changes in routing policies, and failures of network elements can result in signi cant (and sudden) uctuations in load. In this paper, we present a model of tra c demands to support tra c engineering and performance debugging of large Internet Service Provider networks. By de ning a tra c demand as a volume of load originating from an ingress link and destined to a set of egress links, we can capture and predict how routing a ects the tra c traveling between domains. To infer the tra c demands, we propose a measurement methodology that combines ow-level measurements collected at all ingress links with reachability information about all egress links. We discuss how to cope with situations where practical considerations limit the amount and quality of the necessary data. Speci cally, we show how to infer interdomain tra c demands using measurements collected at a smaller number of edge links | the peering links connecting to neighboring providers. We report on our experiences in deriving the tra c demands in the AT&T IP Backbone, by collecting, validating, and joining very large and diverse sets of usage, con guration, and routing data over extended periods of time. The paper concludes with a preliminary analysis of the observed dynamics of the tra c demands and a discussion of the practical implications for tra c engineering.
IEEE Communications Magazine, 2000
Traffic, usage, and performance measurements are crucial to the design, operation and control of ... more Traffic, usage, and performance measurements are crucial to the design, operation and control of Internet protocol networks. This article describes a prototype infrastructure for the measurement, storage, and correlation of network data of different types and origins from AT&T's commercial IP network. We focus first on some novel aspects of the measurement infrastructure, then describe analyses that illustrate the power of joining different measured data sets for network planning and design
IEEE Communications Magazine, 2002
Traffic engineering involves adapting the routing of traffic to the network conditions, with the ... more Traffic engineering involves adapting the routing of traffic to the network conditions, with the joint goals of good user performance and efficient use of network resources. In this paper, we describe an approach to intradomain traffic engineering that works within the existing deployed base of Interior Gateway Protocols (IGPs), such as Open Shortest Path First (OSPF) and Intermediate System-Intermediate System (IS-IS). We explain how to adapt the configuration of link weights, based on a network-wide view of the traffic and topology within a domain. In addition, we summarize the results of several studies of techniques for optimizing OSPF/IS-IS weights to the prevailing traffic. The paper argues that traditional shortest-path routing protocols are surprisingly effective for engineering the flow of traffic in large IP networks. §
IEEE Network, 2001
The smooth operation of the Internet depends on the careful configuration of routers in thousands... more The smooth operation of the Internet depends on the careful configuration of routers in thousands of autonomous systems throughout the world. Configuring routers is extremely complicated because of the diversity of network equipment, the large number of configuration options, and the interaction of configuration parameters across multiple routers. Network operators have limited tools to aid in configuring large backbone networks. Manual configuration of individual routers can introduce errors and inconsistencies with unforeseen consequences for the operational network. In this paper, we describe how to identify configuration mistakes by parsing and analyzing configuration data extracted from the various routers. We first present an overview of IP networking from the viewpoint of an Internet Service Provider (ISP) and describe the kinds of errors that can appear within and across router configuration files. To narrow the scope of the problem, we then focus our attention on the configuration commands that relate to traffic engineering-tuning the intradomain routing protocol to control the flow of traffic through the ISP network. We present a case study of a prototype tool, developed in collaboration with AT&T IP Services, for checking the configuration of the AT&T IP Backbone and providing input to other systems for network visualization and traffic engineering.
Sigmetrics Performance Evaluation Review, 2000
The Border Gateway Protocol (BGP) allows an autonomous system (AS) to apply diverse local policie... more The Border Gateway Protocol (BGP) allows an autonomous system (AS) to apply diverse local policies for selecting routes and propagating reachability information to other domains. However, BGP permits ASes to have conflicting policies that can lead to routing instability. This paper proposes a set of guidelines for an AS to follow in setting its routing policies, without requiring coordination with other ASes. Our approach exploits the Internet's hierarchical structure and the commercial relationships between ASes to impose a partial order on the set of routes to each destination. The guidelines conform to conventional traffic-engineering practices of ISPs, and provide each AS with significant flexibility in selecting its local policies. Furthermore, the guidelines ensure route convergence even under changes in the topology and routing policies. Drawing on a formal model of BGP, we prove that following our proposed policy guidelines guarantees route convergence. We also describe how our methodology can be applied to new types of relationships between ASes, how to verify the hierarchical AS relationships, and how to realize our policy guidelines. Our approach has significant practical value since it preserves the ability of each AS to apply complex local policies without divulging its BGP configurations to others.
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Papers by Jennifer Rexford