The Transmission Control Protocol.

A survey

Software defined networking (SDN) decouples the control plane from the data plane of forwarding devices. This separation provides several benefits, including the simplification of network management and control. However, due to a variety of reasons, such as budget constraints and fear of downtime, many organizations are reluctant to fully deploy SDN. Partially deploying SDN through the placement of a limited number of SDN devices among legacy (traditional) network devices, forms a so-called hybrid SDN network. While hybrid SDN networks provide many of the benefits of SDN and have a wide range of applications, they also pose several challenges. These challenges have recently been addressed in a growing body of literature on hybrid SDN network structures and protocols. This paper presents a comprehensive up-to-date survey of the research and development in the field of hybrid SDN networks. We have organized the survey into five main categories, namely hybrid SDN network deployment strategies, controllers for hybrid SDN networks, protocols for hybrid SDN network management, traffic engineering mechanisms for hybrid SDN networks, as well as testing, verification, and security mechanisms for hybrid SDN networks. We thoroughly survey the existing hybrid SDN network studies according to this taxonomy and identify gaps and limitations in the existing body of research. Based on the outcomes of the existing research studies as well as the identified gaps and limitations, we derive guidelines for future research on hybrid SDN networks.

Hybrid SDN Networks: A Survey of Existing Approaches

To guarantee network availability and security, operators must ensure that their reachability policies (e.g., A can or cannot talk to B) are correctly implemented. This is a difficult task due to the complexity of network configuration and the constant churn in a network's environment, e.g., new route announcements arrive and links fail. Current network reachability analysis techniques are limited as they can only reason about the current "incarnation" of the network, cannot analyze all configuration features, or are too slow to enable exploration of many environments. We build ERA, a tool for efficient reasoning about network reachability. Instead of reasoning about individual incarnations of the network, ERA directly reasons about the network "control plane" that generates these incarnations. We address key expressiveness and scalability challenges by building (i) a succinct model for the network control plane (i.e., various routing protocols and their interactions), and (ii) a repertoire of techniques for scalable (taking a few seconds for a network with > 1000 routers) exploration of this model. We have used ERA to successfully find both known and new violations of a range of common intended polices.

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Efficient network reachability analysis using a succinct control plane representation

SDN simplifies network management by relying on declarativity (high-level interface) and expressiveness (network flexibility). We propose a solution to support those features while preserving high robustness and scalability as needed in carrier-grade networks. Our solution is based on (i) a two-layer architecture separating connectivity and optimization tasks; and (ii) a centralized optimizer called framework, which translates high-level goals expressed almost in natural language into compliant network configurations. Our evaluation on real and synthetic topologies shows that framework improves the state of the art by (i) achieving better trade-offs for classic goals covered by previous works, (ii) supporting a larger set of goals (refined traffic engineering and service chaining), and (iii) optimizing large ISP networks in few seconds. We also quantify the gains of our implementation, running Segment Routing on top of IS-IS, over possible alternatives (RSVP-TE and OpenFlow).

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A Declarative and Expressive Approach to Control Forwarding Paths in Carrier-Grade Networks

Centralizing routing decisions offers tremendous flexibility, but sacrifices the robustness of distributed protocols. In this paper, we present Fibbing, an architecture that achieves both flexibility and robustness through central control over distributed routing. Fibbing introduces fake nodes and links into an underlying link-state routing protocol, so that routers compute their own forwarding tables based on the augmented topology. Fibbing is expressive, and readily supports flexible load balancing, traffic engineering, and backup routes. Based on high-level forwarding requirements, the Fibbing controller computes a compact augmented topology and injects the fake components through standard routing-protocol messages. Fibbing works with any unmodified routers speaking OSPF. Our experiments also show that it can scale to large networks with many forwarding requirements, introduces minimal overhead, and quickly reacts to network and controller failures.

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Central Control Over Distributed Routing

One of the main concerns on SDN is relative to its ability to quickly react to network failures, while limiting both the control-plane overhead and the additional forwarding state kept by data-plane devices. Despite its practical importance, this concern is often overlooked in OpenFlow-based proposals. In this paper, we propose a new architecture, called IBSDN, in which a distributed routing protocol flanks OpenFlow to improve network robustness, reaction to failures, and controller scalability. In deeply exploring this idea, we complement our architecture with data-plane triggered mechanisms that improve its efficiency. We prove that the resulting solution ensures robustness for any combination of topological failures, and quickly reduces the path stretch. Finally, experimenting with a prototype implementation, we show that our approach is practical and overcomes the main limitations of previous work.

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IGP-as-a-backup for robust SDN networks

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.

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Stroboscope: Declarative Network Monitoring on a Budget

For Internet Service Provider (ISP) operators, getting an accurate picture of how their network behaves is challenging. Given the traffic volumes that their networks carry and the impossibility to control end-hosts, ISP operators are typically forced to randomly sample traffic, and rely on aggregated statistics. This provides coarse-grained visibility, at a time resolution that is far from ideal (seconds or minutes). In this paper, we present Mille-Feuille, a novel monitoring architecture that provides fine-grained visibility over ISP traffic. Mille-Feuille schedules activation and deactivation of traffic-mirroring rules, that are then provisioned network-wide from a central location, within milliseconds. By doing so, Mille-Feuille combines the scalability of sampling with the visibility and controllability of traffic mirroring. As a result, it supports a set of monitoring primitives, ranging from checking key performance indicators (e.g., one-way delay) for single destinations to estimating traffic matrices in sub-seconds. Our preliminary measurements on existing routers confirm that Mille-Feuille is viable in practice.

Mille-Feuille: Putting ISP traffic under the scalpel

Video streaming, in conjunction with social networks, have given birth to a new traffic pattern over the Internet: transient, localized traffic surges, known as flash crowds. Traditional traffic-engineering methods can hardly cope with these surges, as they are unpredictable by nature. Consequently, networks either have to be over-provisioned, which is expensive and wastes resources, or risk to periodically incur congestion, which infuriates customers. This demonstration shows how Fibbing can improve network performance and preserve users’ quality of experience when accessing video streams, by implementing a fine-grained load-balancing service. This service leverages two unique features of Fibbing: programming per destination load-balancing and implementing uneven splitting ratios.

https://dl.acm.org/doi/pdf/10.1145/2934872.2959084

Olivier Tilmans

Papers

Central Control Over Distributed Routing

IGP-as-a-backup for robust SDN networks

Stroboscope: Declarative Network Monitoring on a Budget

Mille-Feuille: Putting ISP traffic under the scalpel

Fibbing in action: On-demand load-balancing for better video delivery