NSDI '18 Technical Sessions

All sessions will be held in the Grand Ballroom unless otherwise noted.

The full Proceedings published by USENIX for the conference are available for download below. Individual papers can also be downloaded from the presentation page. Copyright to the individual works is retained by the author[s].

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Monday, April 9

7:30 am–8:45 am

Continental Breakfast

Grand Prefunction

8:45 am–9:00 am

Opening Remarks and Best Paper Awards

Program Co-Chairs: Sujata Banerjee, VMware Research, and Srinivasan Seshan, Carnegie Mellon University

9:00 am–10:40 am

New Hardware

Session Chair: Amar Phanishayee, Microsoft Research

Approximating Fair Queueing on Reconfigurable Switches

Naveen Kr. Sharma and Ming Liu, University of Washington; Kishore Atreya, Cavium; Arvind Krishnamurthy, University of Washington

Available Media

Congestion control today is predominantly achieved via end-to-end mechanisms with little support from the network. As a result, end-hosts must cooperate to achieve optimal throughput and fairness, leading to inefficiencies and poor performance isolation. While router mechanisms such as Fair Queuing guarantee fair bandwidth allocation to all participants and have proven to be optimal in some respects, they require complex flow classification, buffer allocation, and scheduling on a per-packet basis. These factors make them expensive to implement in high-speed switches.

In this paper, we use emerging reconfigurable switches to develop an approximate form of Fair Queueing that operates at line-rate. We leverage configurable per-packet processing and the ability to maintain mutable state inside switches to achieve fair bandwidth allocation across all traversing flows. Further, present our design for a new dequeuing scheduler, called Rotating Strict Priority scheduler that lets us transmit packets from multiple queues in approximate sorted order. Our hardware emulation and software simulations on a large leafspine topology show that our scheme closely approximates ideal Fair Queueing, improving the average flow completion times for short flows by 2-4x and 99th tail latency by 4-8x relative to TCP and DCTCP.

PASTE: A Network Programming Interface for Non-Volatile Main Memory

Michio Honda, NEC Laboratories Europe; Giuseppe Lettieri, Università di Pisa; Lars Eggert and Douglas Santry, NetApp

Available Media

Non-Volatile Main Memory (NVMM) devices have been integrated into general-purpose operating systems through familiar file-based interfaces, providing efficient bytegranularity access by bypassing page caches. To leverage the unique advantages of these high-performance media, the storage stack is migrating from the kernel into user-space. However, application performance remains fundamentally limited unless network stacks explicitly integrate these new storage media and follow the migration of storage stacks into user-space. Moreover, we argue that the storage and the network stacks must be considered together when being designed for NVMM. This requires a thoroughly new network stack design, including low-level buffer management and APIs.

We propose PASTE, a new network programming interface for NVMM. It supports familiar abstractions—including busy-polling, blocking, protection, and run-to-completion—with standard network protocols such as TCP and UDP. By operating directly on NVMM, it can be closely integrated with the persistence layer of applications. Once data is DMA’ed from a network interface card to host memory (NVMM), it never needs to be copied again—even for persistence. We demonstrate the general applicability of PASTE by implementing two popular persistent data structures: a write-ahead log and a B+ tree. We further apply PASTE to three applications: Redis, a popular persistent key-value store, pKVS, our HTTP-based key value store and the logging component of a software switch, demonstrating that PASTE not only accelerates networked storage but also enables conventional networking functions to support new features.

NetChain: Scale-Free Sub-RTT Coordination

Xin Jin, Johns Hopkins University; Xiaozhou Li, Barefoot Networks; Haoyu Zhang, Princeton University; Nate Foster, Cornell University; Jeongkeun Lee, Barefoot Networks; Robert Soulé, Università della Svizzera italiana; Changhoon Kim, Barefoot Networks; Ion Stoica, UC Berkeley
Awarded Best Paper!

Available Media

Coordination services are a fundamental building block of modern cloud systems, providing critical functionalities like configuration management and distributed locking. The major challenge is to achieve low latency and high throughput while providing strong consistency and fault-tolerance. Traditional server-based solutions require multiple round-trip times (RTTs) to process a query. This paper presents NetChain, a new approach that provides scale-free sub-RTT coordination in datacenters. NetChain exploits recent advances in programmable switches to store data and process queries entirely in the network data plane. This eliminates the query processing at coordination servers and cuts the end-to-end latency to as little as half of an RTT—clients only experience processing delay from their own software stack plus network delay, which in a datacenter setting is typically much smaller. We design new protocols and algorithms based on chain replication to guarantee strong consistency and to efficiently handle switch failures. We implement a prototype with four Barefoot Tofino switches and four commodity servers. Evaluation results show that compared to traditional server-based solutions like ZooKeeper, our prototype provides orders of magnitude higher throughput and lower latency, and handles failures gracefully.

Azure Accelerated Networking: SmartNICs in the Public Cloud

Daniel Firestone, Andrew Putnam, Sambhrama Mundkur, Derek Chiou, Alireza Dabagh, Mike Andrewartha, Hari Angepat, Vivek Bhanu, Adrian Caulfield, Eric Chung, Harish Kumar Chandrappa, Somesh Chaturmohta, Matt Humphrey, Jack Lavier, Norman Lam, Fengfen Liu, Kalin Ovtcharov, Jitu Padhye, Gautham Popuri, Shachar Raindel, Tejas Sapre, Mark Shaw, Gabriel Silva, Madhan Sivakumar, Nisheeth Srivastava, Anshuman Verma, Qasim Zuhair, Deepak Bansal, Doug Burger, Kushagra Vaid, David A. Maltz, and Albert Greenberg, Microsoft

Available Media

Modern cloud architectures rely on each server running its own networking stack to implement policies such as tunneling for virtual networks, security, and load balancing. However, these networking stacks are becoming increasingly complex as features are added and as network speeds increase. Running these stacks on CPU cores takes away processing power from VMs, increasing the cost of running cloud services, and adding latency and variability to network performance.

We present Azure Accelerated Networking (AccelNet), our solution for offloading host networking to hardware, using custom Azure SmartNICs based on FPGAs. We define the goals of AccelNet, including programmability comparable to software, and performance and efficiency comparable to hardware. We show that FPGAs are the best current platform for offloading our networking stack as ASICs do not provide sufficient programmability, and embedded CPU cores do not provide scalable performance, especially on single network flows.

Azure SmartNICs implementing AccelNet have been deployed on all new Azure servers since late 2015 in a fleet of >1M hosts. The AccelNet service has been available for Azure customers since 2016, providing consistent <15μs VM-VM TCP latencies and 32Gbps throughput, which we believe represents the fastest network available to customers in the public cloud. We present the design of AccelNet, including our hardware/software co-design model, performance results on key workloads, and experiences and lessons learned from developing and deploying AccelNet on FPGA-based Azure SmartNICs.

10:40 am–11:10 am

Break with Refreshments

Grand Prefunction

11:10 am–12:25 pm

Distributed Systems

Session Chair: Raluca Ada Popa, University of California, Berkeley

zkLedger: Privacy-Preserving Auditing for Distributed Ledgers

Neha Narula, MIT Media Lab; Willy Vasquez, University of Texas at Austin; Madars Virza, MIT Media Lab

Available Media

Distributed ledgers (e.g. blockchains) enable financial institutions to efficiently reconcile cross-organization transactions. For example, banks might use a distributed ledger as a settlement log for digital assets. Unfortunately, these ledgers are either entirely public to all participants, revealing sensitive strategy and trading information, or are private but do not support third-party auditing without revealing the contents of transactions to the auditor. Auditing and financial oversight are critical to proving institutions are complying with regulation.

This paper presents zkLedger, the first system to protect ledger participants’ privacy and provide fast, provably correct auditing. Banks create digital asset transactions that are visible only to the organizations party to the transaction, but are publicly verifiable. An auditor sends queries to banks, for example “What is the outstanding amount of a certain digital asset on your balance sheet?” and gets a response and cryptographic assurance that the response is correct. zkLedger has two important benefits over previous work. First, zkLedger provides fast, rich auditing with a new proof scheme using Schnorr-type non-interactive zero-knowledge proofs. Unlike zk-SNARKs, our techniques do not require trusted setup and only rely on widely-used cryptographic assumptions. Second, zkLedger provides completeness; it uses a columnar ledger construction so that banks cannot hide transactions from the auditor, and participants can use rolling caches to produce and verify answers quickly. We implement a distributed version of zkLedger that can produce provably correct answers to auditor queries on a ledger with a hundred thousand transactions in less than 10 milliseconds.

Exploiting a Natural Network Effect for Scalable, Fine-grained Clock Synchronization

Yilong Geng, Shiyu Liu, and Zi Yin, Stanford University; Ashish Naik, Google Inc.; Balaji Prabhakar and Mendel Rosenblum, Stanford University; Amin Vahdat, Google Inc.

Available Media

Nanosecond-level clock synchronization can be an enabler of a new spectrum of timing- and delay-critical applications in data centers. However, the popular clock synchronization algorithm, NTP, can only achieve millisecond-level accuracy. Current solutions for achieving a synchronization accuracy of 10s-100s of nanoseconds require specially designed hardware throughout the network for combatting random network delays and component noise or to exploit clock synchronization inherent in Ethernet standards for the PHY.

In this paper, we present HUYGENS, a software clock synchronization system that uses a synchronization network and leverages three key ideas. First, coded probes identify and reject impure probe data—data captured by probes which suffer queuing delays, random jitter, and NIC timestamp noise. Next, HUYGENS processes the purified data with Support Vector Machines, a widely-used and powerful classifier, to accurately estimate one-way propagation times and achieve clock synchronization to within 100 nanoseconds. Finally, HUYGENS exploits a natural network effect—the idea that a group of pair-wise synchronized clocks must be transitively synchronized— to detect and correct synchronization errors even further.

Through evaluation of two hardware testbeds, we quantify the imprecision of existing clock synchronization across server-pairs, and the effect of temperature on clock speeds. We find the discrepancy between clock frequencies is typically 5-10μs/sec, but it can be as much as 30μs/sec. We show that HUYGENS achieves synchronization to within a few 10s of nanoseconds under varying loads, with a negligible overhead upon link bandwidth due to probes. Because HUYGENS is implemented in software running on standard hardware, it can be readily deployed in current data centers.

SnailTrail: Generalizing Critical Paths for Online Analysis of Distributed Dataflows

Moritz Hoffmann, Andrea Lattuada, John Liagouris, Vasiliki Kalavri, Desislava Dimitrova, Sebastian Wicki, Zaheer Chothia, and Timothy Roscoe, ETH Zurich

Available Media

We rigorously generalize critical path analysis (CPA) to long-running and streaming computations and present SnailTrail, a system built on Timely Dataflow, which applies our analysis to a range of popular distributed dataflow engines. Our technique uses the novel metric of critical participation, computed on time-based snapshots of execution traces, that provides immediate insights into specific parts of the computation. This allows SnailTrail to work online in real-time, rather than requiring complete offline traces as with traditional CPA. It is thus applicable to scenarios like model training in machine learning, and sensor stream processing.

SnailTrail assumes only a highly general model of dataflow computation (which we define) and we show it can be applied to systems as diverse as Spark, Flink, TensorFlow, and Timely Dataflow itself. We further show with examples from all four of these systems that SnailTrail is fast and scalable, and that critical participation can deliver performance analysis and insights not available using prior techniques.

12:25 pm–1:50 pm

Symposium Luncheon and Test of Time Award Presentation

Lake Washington Ballroom

View all Test of Time Award winners.

1:50 pm–3:30 pm

Traffic Management

Session Chair: Keith Winstein, Stanford University

Balancing on the Edge: Transport Affinity without Network State

João Taveira Araújo, Lorenzo Saino, Lennert Buytenhek, and Raul Landa, Fastly

Available Media

Content delivery networks and edge peering facilities have unique operating constraints which require novel approaches to load balancing. Contrary to traditional, centralized datacenter networks, physical space is heavily constrained. This limitation drives both the need for greater efficiency, maximizing the ability to absorb denial of service attacks and flash crowds at the edge, and seamless failover, minimizing the impact of maintenance on service availability.

This paper introduces Faild, a distributed load balancer which runs on commodity hardware and achieves graceful failover without relying on network state, providing a cost-effective and scalable alternative to existing proposals. Faild allows any individual component of the edge network to be removed from service without breaking existing connections, a property which has proved instrumental in sustaining the growth of a large global edge network over the past four years. As a consequence of this operational experience, we further document unexpected protocol interactions stemming from misconfigured devices in the wild which have significant ramifications for transport protocol design.

Stateless Datacenter Load-balancing with Beamer

Vladimir Olteanu, Alexandru Agache, Andrei Voinescu, and Costin Raiciu, University Politehnica of Bucharest
Community Award Winner!

Available Media

Datacenter load balancers (or muxes) steer traffic destined to a given service across a dynamic set of backend machines. To ensure consistent load balancing decisions when backends come or leave, existing solutions make a load balancing decision per connection and then store it as per-connection state to be used for future packets. While simple to implement, per-connection state is brittle: SYNflood attacks easily fill state memory, preventing muxes from keeping state for good connections.

We present Beamer, a datacenter load-balancer that is designed to ensure stateless mux operation. The key idea is to leverage the connection state already stored in backend servers to ensure that connections are never dropped under churn: when a server receives a mid-connection packet for which it doesn’t have state, it forwards it to another server that should have state for the packet.

Stateless load balancing brings many benefits: our software implementation of Beamer is twice faster than Google’s Maglev, the state of the art software load balancer, and can process 40Gbps of HTTP uplink traffic on 7 cores. Beamer is simple to deploy both in software and in hardware as our P4 implementation shows. Finally, Beamer allows arbitrary scale-out and scale-in events without dropping any connections.

Larry: Practical Network Reconfigurability in the Data Center

Andromachi Chatzieleftheriou, Sergey Legtchenko, Hugh Williams, and Antony Rowstron, Microsoft Research

Available Media

Modern data center (DC) applications require high crossrack network bandwidth and ultra-low, predictable end-to-end latency. It is hard to meet these requirements in traditional DC networks where the bandwidth between a Top-of-Rack (ToR) switch and the rest of the DC is typically oversubscribed.

Larry is a network design that allows racks to dynamically adapt their bandwidth to the aggregation switches as a function of the traffic demand. Larry reconfigures the network topology to enable racks with high demand to use underutilized uplinks from their neighbors. Operating at the physical layer, Larry has a predictably low traffic forwarding overhead that is adapted to latency sensitive applications. Larry is effective even when deployed on a small set of racks (e.g., 4) because rack traffic demand is not correlated in many DC workloads. It can be deployed incrementally and transparently co-exist with existing non-reconfigurable racks. Our prototype uses a 40 Gbps electrical circuit switch we have built, with a simply local control plane. Using multiple workloads, we show that Larry improves tail latency by to 2.3x for the same network cost.

Semi-Oblivious Traffic Engineering: The Road Not Taken

Praveen Kumar and Yang Yuan, Cornell; Chris Yu, CMU; Nate Foster and Robert Kleinberg, Cornell; Petr Lapukhov and Chiun Lin Lim, Facebook; Robert Soulé, Università della Svizzera italiana

Available Media

Networks are expected to provide reliable performance under a wide range of operating conditions, but existing traffic engineering (TE) solutions optimize for performance or robustness, but not both. A key factor that impacts the quality of a TE system is the set of paths used to carry traffic. Some systems rely on shortest paths, which leads to excessive congestion in topologies with bottleneck links, while others use paths that minimize congestion, which are brittle and prone to failure. This paper presents a system that uses a set of paths computed using Räcke’s oblivious routing algorithm, as well as a centralized controller to dynamically adapt sending rates. Although oblivious routing and centralized TE have been studied previously in isolation, their combination is novel and powerful. We built a software framework to model TE solutions and conducted extensive experiments across a large number of topologies and scenarios, including the production backbone of a large content provider and an ISP. Our results show that semi-oblivious routing provides near-optimal performance and is far more robust than state-of-the-art systems.

3:30 pm–4:00 pm

Break with Refreshments

Grand Prefunction

4:00 pm–5:15 pm

NFV and Hardware

Session Chair: Laurent Vanbever, ETH Zürich

Metron: NFV Service Chains at the True Speed of the Underlying Hardware

Georgios P. Katsikas, RISE SICS and KTH Royal Institute of Technology; Tom Barbette, University of Liege; Dejan Kostic, KTH Royal Institute of Technology; Rebecca Steinert, RISE SICS; Gerald Q. Maguire Jr., KTH Royal Institute of Technology

Available Media

In this paper we present Metron, a Network Functions Virtualization (NFV) platform that achieves high resource utilization by jointly exploiting the underlying network and commodity servers’ resources. This synergy allows Metron to: (i) offload part of the packet processing logic to the network, (ii) use smart tagging to setup and exploit the affinity of traffic classes, and (iii) use tag-based hardware dispatching to carry out the remaining packet processing at the speed of the servers’ fastest cache(s), with zero intercore communication. Metron also introduces a novel resource allocation scheme that minimizes the resource allocation overhead for large-scale NFV deployments. With commodity hardware assistance, Metron deeply inspects traffic at 40 Gbps and realizes stateful network functions at the speed of a 100 GbE network card on a single server. Metron has 2.75-6.5x better efficiency than OpenBox, a state of the art NFV system, while ensuring key requirements such as elasticity, fine-grained load balancing, and flexible traffic steering.

G-NET: Effective GPU Sharing in NFV Systems

Kai Zhang, Fudan University; Bingsheng He, National University of Singapore; Jiayu Hu, University of Science and Technology of China; Zeke Wang, National University of Singapore; Bei Hua, Jiayi Meng, and Lishan Yang, University of Science and Technology of China

Available Media

Network Function Virtualization (NFV) virtualizes software network functions to offer flexibility in their design, management and deployment. Although GPUs have demonstrated their power in significantly accelerating network functions, they have not been effectively integrated into NFV systems for the following reasons. First, GPUs are severely underutilized in NFV systems with existing GPU virtualization approaches. Second, data isolation in the GPU memory is not guaranteed. Third, building an efficient network function on CPUGPU architectures demands huge development efforts.

In this paper, we propose G-NET, an NFV system with a GPU virtualization scheme that supports spatial GPU sharing, a service chain based GPU scheduler, and a scheme to guarantee data isolation in the GPU. We also develop an abstraction for building efficient network functions on G-NET, which significantly reduces development efforts. With our proposed design, G-NET enhances overall throughput by up to 70.8% and reduces the latency by up to 44.3%, in comparison with existing GPU virtualization solutions.

SafeBricks: Shielding Network Functions in the Cloud

Rishabh Poddar, Chang Lan, Raluca Ada Popa, and Sylvia Ratnasamy, UC Berkeley

Available Media

With the advent of network function virtualization (NFV), outsourcing network processing to the cloud is growing in popularity amongst enterprises and organizations. Such outsourcing, however, poses a threat to the security of the client’s traffic because the cloud is notoriously susceptible to attacks.

We present SafeBricks, a system that shields generic network functions (NFs) from an untrusted cloud. SafeBricks ensures that only encrypted traffic is exposed to the cloud provider, and preserves the integrity of both traffic and the NFs. At the same time, it enables clients to reduce their trust in NF implementations by enforcing least privilege across NFs deployed in a chain. SafeBricks does not require changes to TLS, and safeguards the interests of NF vendors as well by shielding NF code and rulesets from both clients and the cloud. To achieve its aims, SafeBricks leverages a combination of hardware enclaves and language-based enforcement. SafeBricks is practical, and its overheads range between ~0–15% across applications.

5:15 pm

Announcement Regarding NSDI '19

NSDI '19 Program Co-Chairs: Jay Lorch, Microsoft, and Minlan Yu, Harvard University

Tuesday, April 10

8:00 am–9:00 am

Continental Breakfast

Grand Prefunction

9:00 am–10:40 am

Web and Video

Session Chair: Jon Howell, Google

Vesper: Measuring Time-to-Interactivity for Web Pages

Ravi Netravali and Vikram Nathan, MIT CSAIL; James Mickens, Harvard University; Hari Balakrishnan, MIT CSAIL

Available Media

Everyone agrees that web pages should load more quickly. However, a good definition for “page load time” is elusive. We argue that, for pages that care about user interaction, load times should be defined with respect to interactivity: a page is “loaded” when above-the-fold content is visible, and the associated JavaScript event handling state is functional. We define a new load time metric, called Ready Index, which explicitly captures our proposed notion of load time. Defining the metric is straightforward, but actually measuring it is not, since web developers do not explicitly annotate the JavaScript state and the DOM elements which support interactivity. To solve this problem, we introduce Vesper, a tool that rewrites a page’s JavaScript and HTML to automatically discover the page’s interactive state. Armed with Vesper, we compare Ready Index to prior load time metrics like Speed Index; across a variety of network conditions, prior metrics underestimate or overestimate the true load time for a page by 24%–64%. We introduce a tool that optimizes a page for Ready Index, decreasing the median time to page interactivity by 29%–32%.

Towards Battery-Free HD Video Streaming

Saman Naderiparizi, Mehrdad Hessar, Vamsi Talla, Shyamnath Gollakota, and Joshua R Smith, University of Washington

Available Media

Video streaming has traditionally been considered an extremely power-hungry operation. Existing approaches optimize the camera and communication modules individually to minimize their power consumption. However, designing a video streaming device requires power-consuming hardware components and computationally intensive video codec algorithms that interface the camera and the communication modules. For example, monochrome HD video streaming at 60 fps requires an ADC operating at a sampling rate of 55.3 MHz and a video codec that can handle uncompressed data being generated at 442 Mbps.

We present a novel architecture that enables HD video streaming from a low-power, wearable camera to a nearby mobile device. To achieve this, we present an “analog” video backscatter technique that feeds analog pixels from the photo-diodes directly to the backscatter hardware, thereby eliminating power-consuming hardware components, such as ADCs and codecs. To evaluate our design, we simulate an ASIC, which achieves 60 fps 720p and 1080p HD video streaming for 321 μW and 806 μW, respectively. This translates to 1000x to 10,000x lower power than it used for existing digital video streaming approaches. Our empirical results also show that we can harvest sufficient energy to enable battery-free 30 fps 1080p video streaming at up to 8 feet. Finally, we design and implement a proof-of-concept prototype with off-the-shelf hardware components that successfully backscatters 720p HD video at 10 fps up to 16 feet.

Prophecy: Accelerating Mobile Page Loads Using Final-state Write Logs

Ravi Netravali, MIT CSAIL; James Mickens, Harvard University

Available Media

Web browsing on mobile devices is expensive in terms of battery drainage and bandwidth consumption. Mobile pages also frequently suffer from long load times due to high-latency cellular connections. In this paper, we introduce Prophecy, a new acceleration technology for mobile pages. Prophecy simultaneously reduces energy costs, bandwidth consumption, and page load times. In Prophecy, web servers precompute the JavaScript heap and the DOM tree for a page; when a mobile browser requests the page, the server returns a write log that contains a single write per JavaScript variable or DOM node. The mobile browser replays the writes to quickly reconstruct the final page state, eliding unnecessary intermediate computations. Prophecy’s server-side component generates write logs by tracking low-level data flows between the JavaScript heap and the DOM. Using knowledge of these flows, Prophecy enables optimizations that are impossible for prior web accelerators; for example, Prophecy can generate write logs that interleave DOM construction and JavaScript heap construction, allowing interactive page elements to become functional immediately after they become visible to the mobile user. Experiments with real pages and real phones show that Prophecy reduces median page load time by 53%, energy expenditure by 36%, and bandwidth costs by 21%.

Salsify: Low-Latency Network Video through Tighter Integration between a Video Codec and a Transport Protocol

Sadjad Fouladi, John Emmons, and Emre Orbay, Stanford University; Catherine Wu, Saratoga High School; Riad S. Wahby and Keith Winstein, Stanford University

Available Media

Salsify is a new architecture for real-time Internet video that tightly integrates a video codec and a network transport protocol, allowing it to respond quickly to changing network conditions and avoid provoking packet drops and queueing delays. To do this, Salsify optimizes the compressed length and transmission time of each frame, based on a current estimate of the network’s capacity; in contrast, existing systems generally control longer-term metrics like frame rate or bit rate. Salsify’s per-frame optimization strategy relies on a purely functional video codec, which Salsify uses to explore alternative encodings of each frame at different quality levels.

We developed a testbed for evaluating real-time video systems end-to-end with reproducible video content and network conditions. Salsify achieves lower video delay and, over variable network paths, higher visual quality than five existing systems: FaceTime, Hangouts, Skype, and WebRTC’s reference implementation with and without scalable video coding.

10:40 am–11:10 am

Break with Refreshments

Grand Prefunction

11:10 am–12:25 pm

Performance Isolation and Scaling

Session Chair: Costin Raiciu, University ­Politehnica of Bucharest

ResQ: Enabling SLOs in Network Function Virtualization

Amin Tootoonchian, Intel Labs; Aurojit Panda, NYU, ICSI; Chang Lan, UC Berkeley; Melvin Walls, Nefeli; Katerina Argyraki, EPFL; Sylvia Ratnasamy, UC Berkeley; Scott Shenker, UC Berkeley, ICSI

Available Media

Network Function Virtualization is allowing carriers to replace dedicated middleboxes with Network Functions (NFs) consolidated on shared servers, but the question of how (and even whether) one can achieve performance SLOs with software packet processing remains open. A key challenge is the high variability and unpredictability in throughput and latency introduced when NFs are consolidated.We show that, using processor cache isolation and with careful sizing of I/O buffers, we can directly enforce a high degree of performance isolation among consolidated NFs – for a wide range of NFs, our technique caps the maximum throughput degradation to 2.9% (compared to 44.3%), and the 95th percentile latency degradation to 2.5% (compared to 24.5%). Building on this, we present ResQ, a resource manager for NFV that enforces performance SLOs for multi-tenant NFV clusters in a resource efficient manner. ResQ achieves 60%-236% better resource efficiency for enforcing SLOs that contain contention-sensitive NFs compared to previous work.

Elastic Scaling of Stateful Network Functions

Shinae Woo, KAIST, UC Berkeley; Justine Sherry, CMU; Sangjin Han, UC Berkeley; Sue Moon, KAIST; Sylvia Ratnasamy, UC Berkeley; Scott Shenker, UC Berkeley, ICSI

Available Media

Elastic scaling is a central promise of NFV but has been hard to realize in practice. The difficulty arises because most Network Functions (NFs) are stateful and this state need to be shared across NF instances. Implementing state sharing while meeting the throughput and latency requirements placed on NFs is challenging and, to date, no solution exists that meets NFV’s performance goals for the full spectrum of NFs.

S6 is a new framework that supports elastic scaling of NFs without compromising performance. Its design builds on the insight that a distributed shared state abstraction is well-suited to the NFV context. We organize state as a distributed shared object (DSO) space and extend the DSO concept with techniques designed to meet the need for elasticity and high-performance in NFV workloads. S6 simplifies development: NF writers program with no awareness of how state is distributed and shared. Instead, S6 transparently migrates state and handles accesses to shared state. In our evaluation, compared to recent solutions for dynamic scaling of NFs, S6 improves performance by 100x during scaling events [25], and by 2-5x under normal operation


Iron: Isolating Network-based CPU in Container Environments

Junaid Khalid, UW-Madison; Eric Rozner, Wesley Felter, Cong Xu, and Karthick Rajamani, IBM Research; Alexandre Ferreira, Arm Research; Aditya Akella, UW-Madison

Available Media

Containers are quickly increasing in popularity as the mechanism to deploy computation in the cloud. In order to provide consistent and reliable performance, cloud providers must ensure containers cannot adversely interfere with one another. Because containers share the same underlying OS, it is more challenging to provide isolation in a container-based framework than a traditional VMbased framework. And while many schemes can isolate CPU, memory, disk, or network bandwidth in multi-tenant environments, less attention has been paid to how the time spent processing network traffic affects isolation on the host server. This paper shows computational overhead associated with the network stack can break isolation in container-based environments. Specifically, a container with heavy network traffic can decrease the computation available to other containers sharing the same server. We propose a scheme, called Iron, that accounts for the time spent in the networking stack on behalf of a container and ensures this processing cannot adversely impact colocated containers through novel enforcement mechanisms. Our results show Iron effectively provides isolation under realistic and adversarial conditions, limiting interference-based slowdowns as high as 6x to less than 5%.

12:25 pm–2:30 pm

Lunch (on your own)

2:30 pm–3:45 pm

Congestion Control

Session Chair: Kai Chen, HKUST

Copa: Practical Delay-Based Congestion Control for the Internet

Venkat Arun and Hari Balakrishnan, MIT CSAIL

Available Media

This paper introduces Copa, an end-to-end congestion control algorithm that uses three ideas. First, it shows that a target rate equal to 1=(δdq), where dq is the (measured) queueing delay, optimizes a natural function of throughput and delay under a Markovian packet arrival model. Second, it adjusts its congestion window in the direction of this target rate, converging quickly to the correct fair rates even in the face of significant flow churn. These two ideas enable a group of Copa flows to maintain high utilization with low queuing delay. However, when the bottleneck is shared with loss-based congestion-controlled flows that fill up buffers, Copa, like other delay-sensitive schemes, achieves low throughput. To combat this problem, Copa uses a third idea: detect the presence of buffer-fillers by observing the delay evolution, and respond with additive-increase/multiplicative decrease on the δ parameter. Experimental results show that Copa outperforms Cubic (similar throughput, much lower delay, fairer with diverse RTTs), BBR and PCC (significantly fairer, lower delay), and co-exists well with Cubic unlike BBR and PCC. Copa is also robust to non-congestive loss and large bottleneck buffers, and outperforms other schemes on long-RTT paths.

PCC Vivace: Online-Learning Congestion Control

Mo Dong and Tong Meng, UIUC; Doron Zarchy, The Hebrew University of Jerusalem; Engin Arslan, UIUC; Yossi Gilad, MIT; Brighten Godfrey, UIUC; Michael Schapira, The Hebrew University of Jerusalem

Available Media

TCP’s congestion control architecture suffers from notoriously bad performance. Consequently, recent years have witnessed a surge of interest in both academia and industry in novel approaches to congestion control. We show, however, that past approaches fall short of attaining ideal performance. We leverage ideas from the rich literature on online (convex) optimization in machine learning to design Vivace, a novel rate-control protocol, designed within the recently proposed PCC framework. Our theoretical and experimental analyses establish that Vivace significantly outperforms traditional TCP variants, the previous realization of the PCC framework, and BBR in terms of performance (throughput, latency, loss), convergence speed, alleviating bufferbloat, reactivity to changing network conditions, and friendliness towards legacy TCP in a range of scenarios. Vivace requires only sender-side changes and is thus readily deployable.

Multi-Path Transport for RDMA in Datacenters

Yuanwei Lu, Microsoft Research and University of Science and Technology of China; Guo Chen, Hunan University; Bojie Li, Microsoft Research and University of Science and Technology of China; Kun Tan, Huawei Technologies; Yongqiang Xiong, Peng Cheng, and Jiansong Zhang, Microsoft Research; Enhong Chen, University of Science and Technology of China; Thomas Moscibroda, Microsoft Azure

Available Media

RDMA is becoming prevalent because of its low latency, high throughput and low CPU overhead. However, current RDMA remains a single path transport which is prone to failures and falls short to utilize the rich parallel paths in datacenters. Unlike previous multipath approaches, which mainly focus on TCP, this paper presents a multi-path transport for RDMA, i.e. MPRDMA, which efficiently utilizes the rich network paths in datacenters. MP-RDMA employs three novel techniques to address the challenge of limited RDMA NICs on-chip memory size: 1) a multi-path ACK-clocking mechanism to distribute traffic in a congestion-aware manner without incurring per-path states; 2) an out-oforder aware path selection mechanism to control the level of out-of-order delivered packets, thus minimizes the meta data required to them; 3) a synchronise mechanism to ensure in-order memory update whenever needed. With all these techniques, MP-RDMA only adds 66B to each connection state compared to single-path RDMA. Our evaluation with an FPGA-based prototype demonstrates that compared with single-path RDMA, MPRDMA can significantly improve the robustness under failures (2x∼4x higher throughput under 0.5%∼10% link loss ratio) and improve the overall network utilization by up to 47%.

3:45 pm–4:15 pm

Break with Refreshments

Grand Prefunction

4:15 pm–5:30 pm


Session Chair: Sanjay Rao, Purdue University

Andromeda: Performance, Isolation, and Velocity at Scale in Cloud Network Virtualization

Michael Dalton, David Schultz, Jacob Adriaens, Ahsan Arefin, Anshuman Gupta, Brian Fahs, Dima Rubinstein, Enrique Cauich Zermeno, Erik Rubow, James Alexander Docauer, Jesse Alpert, Jing Ai, Jon Olson, Kevin DeCabooter, Marc de Kruijf, Nan Hua, Nathan Lewis, Nikhil Kasinadhuni, Riccardo Crepaldi, Srinivas Krishnan, Subbaiah Venkata, Yossi Richter, Uday Naik, and Amin Vahdat, Google, Inc.

Available Media

This paper presents our design and experience with Andromeda, Google Cloud Platform’s network virtualization stack. Our production deployment poses several challenging requirements, including performance isolation among customer virtual networks, scalability, rapid provisioning of large numbers of virtual hosts, bandwidth and latency largely indistinguishable from the underlying hardware, and high feature velocity combined with high availability.

Andromeda is designed around a flexible hierarchy of flow processing paths. Flows are mapped to a programming path dynamically based on feature and performance requirements. We introduce the Hoverboard programming model, which uses gateways for the long tail of low bandwidth flows, and enables the control plane to program network connectivity for tens of thousands of VMs in seconds. The on-host dataplane is based around a high-performance OS bypass software packet processing path. CPU-intensive per packet operations with higher latency targets are executed on coprocessor threads. This architecture allows Andromeda to decouple feature growth from fast path performance, as many features can be implemented solely on the coprocessor path. We demonstrate that the Andromeda datapath achieves performance that is competitive with hardware while maintaining the flexibility and velocity of a software-based architecture.

LHD: Improving Cache Hit Rate by Maximizing Hit Density

Nathan Beckmann, Carnegie Mellon University; Haoxian Chen, University of Pennsylvania; Asaf Cidon, Stanford University and Barracuda Networks

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Cloud application performance is heavily reliant on the hit rate of datacenter key-value caches. Key-value caches typically use least recently used (LRU) as their eviction policy, but LRU’s hit rate is far from optimal under real workloads. Prior research has proposed many eviction policies that improve on LRU, but these policies make restrictive assumptions that hurt their hit rate, and they can be difficult to implement efficiently.

We introduce least hit density (LHD), a novel eviction policy for key-value caches. LHD predicts each object’s expected hits-per-space-consumed (hit density), filtering objects that contribute little to the cache’s hit rate. Unlike prior eviction policies, LHD does not rely on heuristics, but rather rigorously models objects’ behavior using conditional probability to adapt its behavior in real time.

To make LHD practical, we design and implement RankCache, an efficient key-value cache based on memcached. We evaluate RankCache and LHD on commercial memcached and enterprise storage traces, where LHD consistently achieves better hit rates than prior policies. LHD requires much less space than prior policies to match their hit rate, on average 8x less than LRU and 2–3x less than recently proposed policies. Moreover, RankCache requires no synchronization in the common case, improving request throughput at 16 threads by 8x over LRU and by 2x over CLOCK.

Performance Analysis of Cloud Applications

Dan Ardelean, Amer Diwan, and Chandra Erdman, Google

Available Media

Many popular cloud applications are large-scale distributed systems with each request involving tens to thousands of RPCs and large code bases. Because of their scale, performance optimizations without actionable supporting data are likely to be ineffective: they will add complexity to an already complex system often without chance of a benefit. This paper describes the challenges in collecting actionable data for Gmail, a service with more than 1 billion active accounts.

Using production data from Gmail we show that both the load and the nature of the load changes continuously. This makes Gmail performance difficult to model with a synthetic test and difficult to analyze in production. We describe two techniques for collecting actionable data from a production system. First, coordinated bursty tracing allows us to capture bursts of events across all layers of our stack simultaneously. Second, vertical context injection enables us combine high-level events with low-level events in a holistic trace without requiring us to explicitly propagate this information across our software stack.

6:00 pm–7:30 pm

Poster Session and Reception

Lake Washington Ballroom

Check out the cool new ideas and the latest preliminary research on display at the Poster Session and Reception. Take part in discussions with your colleagues over complimentary food and drinks. View the complete list of accepted posters.

Wednesday, April 11

8:00 am–9:00 am

Continental Breakfast

Grand Prefunction

9:00 am–10:40 am


Session Chair: Rachit Agarwal, Cornell University

007: Democratically Finding the Cause of Packet Drops

Behnaz Arzani, Microsoft Research; Selim Ciraci, Microsoft; Luiz Chamon, University of Pennsylvania; Yibo Zhu and Hongqiang (Harry) Liu, Microsoft Research; Jitu Padhye, Microsoft; Boon Thau Loo, University of Pennsylvania; Geoff Outhred, Microsoft

Available Media

Network failures continue to plague datacenter operators as their symptoms may not have direct correlation with where or why they occur. We introduce 007, a lightweight, always-on diagnosis application that can find problematic links and also pinpoint problems for each TCP connection. 007 is completely contained within the end host. During its two month deployment in a tier-1 datacenter, it detected every problem found by previously deployed monitoring tools while also finding the sources of other problems previously undetected.

Efficient and Correct Test Scheduling for Ensembles of Network Policies

Yifei Yuan, Sanjay Chandrasekaran, Limin Jia, and Vyas Sekar, Carnegie Mellon University

Available Media

Testing whether network policies are correctly implemented is critical to ensure a network’s safety, performance and availability. Network operators need to test ensembles of network policies using a combination of native and third-party tools in practice, as indicated by our survey. Unfortunately, existing approaches for running tests for ensembles of network policies on stateful networks face fundamental challenges with respect to correctness and efficiency. Running all tests sequentially is inefficient, while naïvely running tests in parallel may lead to incorrect testing results. In this paper, we propose Mikado, a principled scheduling framework for scheduling tests generated by various (blackbox) tools for ensembles of policies. We make two key contributions: (1) we develop a formal correctness criteria for running tests for ensembles of policies; and (2) we design a provably correct and efficient test scheduling algorithm, based on detecting read-write test conflicts. Mikado is open source and can support a range of policies and testing tools. We show that Mikado can generate correct schedules in real-world scenarios, achieve orders of magnitude reduction on the test running time, and schedule tests for thousands of network policies in large networks with 1000+ nodes within minutes.

Distributed Network Monitoring and Debugging with SwitchPointer

Praveen Tammana, University of Edinburgh; Rachit Agarwal, Cornell University; Myungjin Lee, University of Edinburgh

Available Media

Monitoring and debugging large-scale networks remains a challenging problem. Existing solutions operate at one of the two extremes—systems running at end-hosts (more resources but less visibility into the network) or at network switches (more visibility, but limited resources).

We present SwitchPointer, a network monitoring and debugging system that integrates the best of the two worlds. SwitchPointer exploits end-host resources and programmability to collect and monitor telemetry data. The key contribution of SwitchPointer is to efficiently provide network visibility by using switch memory as a "directory service"—each switch, rather than storing the data necessary for monitoring functionalities, stores pointers to end-hosts where relevant telemetry data is stored. We demonstrate, via experiments over real-world testbeds, that SwitchPointer can efficiently monitor and debug network problems, many of which were either hard or even infeasible with existing designs.

Stroboscope: Declarative Network Monitoring on a Budget

Olivier Tilmans, Université Catholique de Louvain; Tobias Bühler, ETH Zürich; Ingmar Poese, BENOCS; Stefano Vissicchio, University College London; Laurent Vanbever, ETH Zürich

Available Media

For an Internet Service Provider (ISP), getting an accurate picture of how its network behaves is challenging. Indeed, given the carried traffic volume and the impossibility to control end-hosts, ISPs often have no other choice but to rely on heavily sampled traffic statistics, which provide them with coarse-grained visibility at a less than ideal time resolution (seconds or minutes).

We present Stroboscope, a system that enables finegrained monitoring of any traffic flow by instructing routers to mirror millisecond-long traffic slices in a programmatic way. Stroboscope takes as input high-level monitoring queries together with a budget and automatically determines: (i) which flows to mirror; (ii) where to place mirroring rules, using fast and provably correct algorithms; and (iii) when to schedule these rules to maximize coverage while meeting the input budget.

We implemented Stroboscope, and show that it scales well: it computes schedules for large networks and query sizes in few seconds, and produces a number of mirroring rules well within the limits of current routers. We also show that Stroboscope works on existing routers and is therefore immediately deployable.

10:40 am–11:10 am

Break with Refreshments

Grand Prefunction

11:10 am–12:25 pm


Session Chair: Jay Lorch, Microsoft

PLOVER: Fast, Multi-core Scalable Virtual Machine Fault-tolerance

Cheng Wang, Xusheng Chen, Weiwei Jia, Boxuan Li, Haoran Qiu, Shixiong Zhao, and Heming Cui, The University of Hong Kong

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Cloud computing enables a vast deployment of online services in virtualized infrastructures, making it crucial to provide fast fault-tolerance for virtual machines (VM). Unfortunately, despite much effort, achieving fast and multi-core scalable VM fault-tolerance is still an open problem. A main reason is that the dominant primarybackup approach (e.g., REMUS) transfers an excessive amount of memory pages, all of them, updated by a service replicated on the primary VM and the backup VM. This approach makes the two VMs identical but greatly degrades the performance of services.

State machine replication (SMR) enforces the same total order of inputs for a service replicated across physical hosts. This makes most updated memory pages across hosts the same and they do not need to be transferred. We present Virtualized SMR (VSMR), a new approach to tackle this open problem. VSMR enforces the same order of inputs for a VM replicated across hosts. It uses commodity hardware to efficiently compute updated page hashes and to compare them across replicas. Therefore, VSMR can efficiently enforce identical VMs by transferring only divergent pages. An extensive evaluation on PLOVER, the first VSMR system, shows that PLOVER’s throughput on multi-core is 2.2X to 3.8X higher than three popular primary-backup systems. Meanwhile, PLOVER consumed 9.2X less network bandwidth than both of them. PLOVER’s source code and raw results are released on github.com/ hku-systems/plover.

Odin: Microsoft’s Scalable Fault-Tolerant CDN Measurement System

Matt Calder, Microsoft/USC; Manuel Schröder, Ryan Gao, Ryan Stewart, and Jitendra Padhye, Microsoft; Ratul Mahajan, Intentionet; Ganesh Ananthanarayanan, Microsoft; Ethan Katz-Bassett, Columbia University

Available Media

Content delivery networks (CDNs) are critical for delivering high performance Internet services. Using worldwide deployments of front-ends, CDNs can direct users to the front-end that provides them with the best latency and availability. The key challenges arise from the heterogeneous connectivity of clients and the dynamic nature of the Internet that influences latency and availability. Without continuous insight on performance between users, front-ends, and external networks, CDNs will not be able to attain their full potential performance.

We describe Odin, Microsoft's Internet measurement platform for its first-party and third-party customers. Odin is designed to handle Microsoft's large user base and need for large-scale measurements from users around the world. Odin integrates with Microsoft's varied suite of web-client and thick-client applications, all while being mindful of the regulatory and privacy concerns of enterprise customers. Odin has been operational for 2 years. We present the first detailed study of an Internet measurement platform of this scale and complexity.

Deepview: Virtual Disk Failure Diagnosis and Pattern Detection for Azure

Qiao Zhang, University of Washington; Guo Yu, Cornell University; Chuanxiong Guo, Toutiao (Bytedance); Yingnong Dang, Nick Swanson, Xinsheng Yang, Randolph Yao, and Murali Chintalapati, Microsoft; Arvind Krishnamurthy and Thomas Anderson, University of Washington

Available Media

In Infrastructure as a Service (IaaS), virtual machines (VMs) use virtual hard disks (VHDs) provided by a remote storage service via the network. Due to separation of VMs and their VHDs, a new type of failure, called VHD failure, which may be caused by various components in the IaaS stack, becomes the dominating factor that reduces VM availability. The current state-of-the-art approaches fall short in localizing VHD failures because they only look at individual components.

In this paper, we designed and implemented a system called Deepview for VHD failure localization. Deepview composes a global picture of the system by connecting all the components together, using individual VHD failure events. It then uses a novel algorithm which integrates Lasso regression and hypothesis testing for accurate and timely failure localization.

We have deployed Deepview at Microsoft Azure, one of the largest IaaS providers. Deepview reduced the number of unclassified VHD failure events from tens of thousands to several hundreds. It unveiled new patterns including unplanned top-of-rack switch (ToR) reboots and storage gray failures. Deepview reduced the time-to-detection for incidents to under 10 minutes. Deepview further helped us quantify the implications of some key architectural decisions for the first time, including ToR switches as a single-point-of-failure and the compute-storage separation.

12:25 pm–2:30 pm

Lunch (on your own)

2:30 pm–3:45 pm

Physical Layer

Session Chair: Lin Zhong, Rice University

LiveTag: Sensing Human-Object Interaction through Passive Chipless WiFi Tags

Chuhan Gao and Yilong Li, University of Wisconsin-Madison; Xinyu Zhang, University of California San Diego

Available Media

Many types of human activities involve interaction with passive objects. Thus, by wirelessly sensing human interaction with them, one can infer activities at a fine resolution, enabling a new wave of ubiquitous computing applications. In this paper, we propose LiveTag to achieve this vision. LiveTag is a fully passive, thin metal tag that can be printed on paper-like substrates and attached on objects. It has no batteries, silicon chips or discrete electronic components. But when touched by fingers, it disturbs ambientWiFi channel in a deterministic way. Multiple metallic structures can be printed on the same tag to create unique touch points. Further, LiveTag incorporates customized multi-antenna beamforming algorithms that allow WiFi receivers to sense the tag and discriminate the touch events, amid multipath reflections/interferences. Our prototypes of LiveTag have verified its feasibility and performance. We have further applied LiveTag to real-world usage scenarios to showcase its effectiveness in sensing human-object interaction.

Inaudible Voice Commands: The Long-Range Attack and Defense

Nirupam Roy, Sheng Shen, Haitham Hassanieh, and Romit Roy Choudhury, University of Illinois at Urbana-Champaign

Available Media

Recent work has shown that inaudible signals (at ultrasound frequencies) can be designed in a way that they become audible to microphones. Designed well, this can empower an adversary to stand on the road and silently control Amazon Echo and Google Home-like devices in people’s homes. A voice command like "Alexa, open the garage door" can be a serious threat.

While recent work has demonstrated feasibility, two issues remain open: (1) The attacks can only be launched from within 5 ft of Amazon Echo, and increasing this range makes the attack audible. (2) There is no clear solution against these ultrasound attacks, since they exploit a recently discovered loophole in hardware non-linearity.

This paper is an attempt to close both these gaps. We begin by developing an attack that achieves 25 ft range, limited by the power of our amplifier. We then develop a defense against this class of voice attacks that exploit non-linearity. Our core ideas emerge from a careful forensics on voice, i.e., finding indelible traces of nonlinearity in recorded voice signals. Our system, LipRead, demonstrates the inaudible attack in various conditions, followed by defenses that only require software changes to the microphone.

PowerMan: An Out-of-Band Management Network for Datacenters Using Power Line Communication

Li Chen, Jiacheng Xia, Bairen Yi, and Kai Chen, The Hong Kong University of Science and Technology

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Management tasks in datacenters are usually executed in-band with the data plane applications, making them susceptible to faults and failures in the data plane. In this paper, we introduce power line communication (PLC) to datacenters as an out-of-band management channel. We design PowerMan, a novel datacenter management network that can be readily built into existing datacenter power systems. With commercially available PLC devices, we implement a small 2-layer PowerMan prototype with 12 servers. Using this real testbed, as well as large-scale simulations, we demonstrate the potential of PowerMan as a management network in terms of performance, reliability, and cost.

3:45 pm–4:15 pm

Break with Refreshments

Grand Prefunction

4:15 pm–5:30 pm

Configuration Management

Session Chair: Ganesh Ananthanarayanan, Microsoft

NetComplete: Practical Network-Wide Configuration Synthesis with Autocompletion

Ahmed El-Hassany, Petar Tsankov, Laurent Vanbever, and Martin Vechev, ETH Zürich

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Network operators often need to adapt the configuration of a network in order to comply with changing routing policies. Evolving existing configurations, however, is a complex task as local changes can have unforeseen global effects. Not surprisingly, this often leads to mistakes that result in network downtimes.

We present NetComplete, a system that assists operators in modifying existing network-wide configurations to comply with new routing policies. NetComplete takes as input configurations with "holes" that identify the parameters to be completed and "autocompletes" these with concrete values. The use of a partial configuration addresses two important challenges inherent to existing synthesis solutions: (i) it allows the operators to precisely control how configurations should be changed; and (ii) it allows the synthesizer to leverage the existing configurations to gain performance. To scale, NetComplete relies on powerful techniques such as counter-example guided inductive synthesis (for link-state protocols) and partial evaluation (for path-vector protocols).

We implemented NetComplete and showed that it can autocomplete configurations using static routes, OSPF, and BGP. Our implementation also scales to realistic networks and complex routing policies. Among others, it is able to synthesize configurations for networks with up to 200 routers within few minutes.

Automatically Correcting Networks with NEAt

Wenxuan Zhou, Jason Croft, Bingzhe Liu, Elaine Ang, and Matthew Caesar, University of Illinois at Urbana-Champaign

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Configuring and maintaining an enterprise network is a challenging and error-prone process. Administrators often need to consider security policies from a variety of sources such as regulatory requirements, industry standards, and mitigating attack vectors. Erroneous configuration or network application could violet crucial policies, and result in costly data breaches and intrusions. Relying on humans to discover and troubleshoot violations is slow and prone to error, considering the speed at which new attack vectors propagate and the increasing network dynamics, partly an effect of SDN.

To address this problem, we present NEAt, a system analogous to a smartphone’s autocorrect feature that enables on-the-fly repair to policy-violating updates. It does so by modifying the forwarding behavior of updates to automatically repair violations of policies such as reachability, service chaining, and segmentation. NEAt takes as input a set of administrator-defined high-level policies, and formulates these policies as directed graphs. Sitting between an SDN controller and the forwarding devices, NEAt intercepts updates proposed by SDN applications. If an update violates a policy, NEAt transforms the update into one that complies with the policy. Unlike domain-specific languages or synthesis platforms, NEAt allows enterprise networks to leverage the advanced functionality of SDN applications while simultaneously achieving strong, automated enforcement of general policies. Based on a prototype implementation and experimentation using Mininet and operation trace of a large enterprise network we demonstrate that NEAt achieves promising performance in real-time bug-fixing.

Net2Text: Query-Guided Summarization of Network Forwarding Behaviors

Rüdiger Birkner, Dana Drachsler-Cohen, Laurent Vanbever, and Martin Vechev, ETH Zürich

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Today network operators spend a significant amount of time struggling to understand how their network forwards traffic. Even simple questions such as "How is my network handling Google traffic?" often require operators to manually bridge large semantic gaps between lowlevel forwarding rules distributed across many routers and the corresponding high-level insights.

We introduce Net2Text, a system which assists network operators in reasoning about network-wide forwarding behaviors. Out of the raw forwarding state and a query expressed in natural language, Net2Text automatically produces succinct summaries, also in natural language, which efficiently capture network-wide semantics. Our key insight is to pose the problem of summarizing ("captioning") the network forwarding state as an optimization problem that aims to balance coverage, by describing as many paths as possible, and explainability, by maximizing the information provided. As this problem is NP-hard, we also propose an approximation algorithm which generates summaries based on a sample of the forwarding state, with marginal loss of quality.

We implemented Net2Text and demonstrated its practicality and scalability. We show that Net2Text generates high-quality interpretable summaries of the entire forwarding state of hundreds of routers with full routing tables, in few seconds only.