Today's networks are maintained by "masters of complexity": network admins who have accumulated the wisdom to troubleshoot complex problems, despite a limiting toolset. This position paper advocates a more structured troubleshooting approach that leverages architectural layering in SoftwareDefined Networks (SDNs). In all networks, high-level intent (policy) must correctly map to low-level forwarding behavior (hardware configuration). In SDNs, intent is explicitly expressed, forwarding semantics are explicitly defined, and each architectural layer fully specifies the behavior of the network. Building on these observations, we show how recently-developed troubleshooting tools fit into a coherent workflow that detects mistranslations between layers to precisely localize sources of errant control logic. Our goals are to explain the overall picture, show how the pieces fit together to enable a systematic workflow, and highlight the questions that remain. Once this workflow is realized, network admins can formally verify that their network is operating correctly, automatically troubleshoot bugs, and systematically track down their root cause -freeing admins to fix problems, rather than diagnose their symptoms.

Software bugs are inevitable in software-defined networking control software, and troubleshooting is a tedious, time-consuming task. In this thesis we discuss how to improve control software troubleshooting by presenting a technique for automatically identifying a minimal sequence of inputs responsible for triggering a given bug, without making assumptions about the language or instrumentation of the software under test. We apply our technique to five open source SDN control platforms-Floodlight, NOX, POX, Pyretic, ONOS-and illustrate how the minimal causal sequences our system found aided the troubleshooting process. AcknowledgmentsMany thanks to the STS team for making this thesis possible:

Software bugs are inevitable in software-defined networking control software, and troubleshooting is a tedious, time-consuming task. In this thesis we discuss how to improve control software troubleshooting by presenting a technique for automatically identifying a minimal sequence of inputs responsible for triggering a given bug, without making assumptions about the language or instrumentation of the software under test. We apply our technique to five open source SDN control platforms-Floodlight, NOX, POX, Pyretic, ONOS-and illustrate how the minimal causal sequences our system found aided the troubleshooting process. AcknowledgmentsMany thanks to the STS team for making this thesis possible:

Abstract. As mobile Internet becomes more popular, carriers and content providers must engineer their topologies, routing configurations, and server deployments to maintain good performance for users of mobile devices. Understanding the impact of Internet topology and routing on mobile users requires broad, longitudinal network measurements conducted from mobile devices. In this work, we are the first to use such a view to quantify and understand the causes of geographically circuitous routes from mobile clients using 1.5 years of measurements from devices on 4 US carriers. We identify the key elements that can affect the Internet routes taken by traffic from mobile users (client location, server locations, carrier topology, carrier/content-provider peering). We then develop a methodology to diagnose the specific cause for inflated routes. Although we observe that the evolution of some carrier networks improves performance in some regions, we also observe many clients -even in major metropolitan areas -that continue to take geographically circuitous routes to content providers, due to limitations in the current topologies.

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