Self-healing and SDN: bridging the gap

Achieving high programmability has become an essential aim of network research due to the ever-increasing internet traffic. Software-Defined Network (SDN) is an emerging architecture aimed to address this need. However, maintaining accurate knowledge of the network after a failure is one of the largest challenges in the SDN. Motivated by this reality, this paper focuses on the use of self-healing properties to boost the SDN robustness. This approach, unlike traditional schemes, is not based on proactively configuring multiple (and memory-intensive) backup paths in each switch or performing a reactive and time-consuming routing computation at the controller level. Instead, the control paths are quickly recovered by local switch actions and subsequently optimized by global controller knowledge. Obtained results show that the proposed approach recovers the control topology effectively in terms of time and message load over a wide range of generated networks. Consequently, scalability issues of traditional fault recovery strategies are avoided.Postprint (published version

Energy-Efficient Softwarized Networks: A Survey

With the dynamic demands and stringent requirements of various applications, networks need to be high-performance, scalable, and adaptive to changes. Researchers and industries view network softwarization as the best enabler for the evolution of networking to tackle current and prospective challenges. Network softwarization must provide programmability and flexibility to network infrastructures and allow agile management, along with higher control for operators. While satisfying the demands and requirements of network services, energy cannot be overlooked, considering the effects on the sustainability of the environment and business. This paper discusses energy efficiency in modern and future networks with three network softwarization technologies: SDN, NFV, and NS, introduced in an energy-oriented context. With that framework in mind, we review the literature based on network scenarios, control/MANO layers, and energy-efficiency strategies. Following that, we compare the references regarding approach, evaluation method, criterion, and metric attributes to demonstrate the state-of-the-art. Last, we analyze the classified literature, summarize lessons learned, and present ten essential concerns to open discussions about future research opportunities on energy-efficient softwarized networks.Comment: Accepted draft for publication in TNSM with minor updates and editin

Assessment of connectivity-based resilience to attacks against multiple nodes in SDNs

In Software Defined Networks (SDNs), the control plane of a network is decoupled from its data plane. For scalability and robustness, the logically centralized control plane is implemented by physically placing different controllers throughout the network. The determination of the number and placement of controllers is known as the Controller Placement Problem (CPP). In the regular (i.e., failure-free) state, the control plane must guarantee a given maximum delay between every switch and its primary controller and a given maximum delay between every pair of controllers. In general, these delay bounds allow multiple solutions and, so, other goals can be used to determine the best CPP solution. In this paper, we assess the connectivity-based resilience to malicious attacks against multiple network nodes of the CPP solutions obtained with three different aims: the regular state delay optimization without any concern about attacks, the regular state delay optimization taking into consideration the worst-case attacks and the resilience optimization to attacks against multiple nodes. We assess the CPP solutions considering attacks of targeted nature (when the attacker has complete knowledge of the data plane) and attacks of non-targeted nature (i.e., random and epidemic attacks). We present computational results providing an analysis of the CPP solutions to the different types of attacks. The main conclusion is that the connectivity-based resilience between the different CPP solutions strongly depends on the network topology, the regular state delay bounds and the type of attacks. Finally, we provide insights on how SDN operators can consider the conducted assessment when deciding the controller placements in their networks.publishe

Load Balancing Mechanisms in the Software Defined Networks: A Systematic and Comprehensive Review of the Literature

With the expansion of the network and increasing their users, as well as emerging new technologies, such as cloud computing and big data, managing traditional networks is difficult. Therefore, it is necessary to change the traditional network architecture. Lately, to address this issue, a notion named software-defined network (SDN) has been proposed, which makes network management more conformable. Due to limited network resources and to meet the requirements of quality of service, one of the points that must be considered is load balancing issue that serves to distribute data traffic among multiple resources in order to maximize the efficiency and reliability of network resources. Load balancing is established based on the local information of the network in the conventional network. Hence, it is not very precise. However, SDN controllers have a global view of the network and can produce more optimized load balances. Although load balancing mechanisms are important in the SDN, to the best of our knowledge, there exists no precise and systematic review or survey on investigating these issues. Hence, this paper reviews the load balancing mechanisms which have been used in the SDN systematically based on two categories, deterministic and non-deterministic. Also, this paper represents benefits and some weakness regarded of the selected load balancing algorithms and investigates the metrics of their algorithms. In addition, the important challenges of these algorithms have been reviewed, so better load balancing techniques can be applied by the researchers in the future. © 2018 IEEE

Migration of networks

Tese de mestrado em Engenharia Informática, Universidade de Lisboa, Faculdade de Ciências, 2021A forma como os recursos computacionais são geridos, mais propriamente os alojados nos grandes centros de dados, tem vindo, nos últimos anos, a evoluir. As soluções iniciais que passavam por aplicações a correr em grandes servidores físicos, comportavam elevados custos não só de aquisição, mas também, e principalmente, de manutenção. A razão chave por trás deste facto prendia-se em grande parte com uma utilização largamente ineficiente dos recursos computacionais disponíveis. No entanto, o surgimento de tecnologias de virtualização de servidores foi o volte-face necessário para alterar radicalmente o paradigma até aqui existente. Isto não só levou a que os operadores dos grandes centros de dados pudessem passar a alugar os seus recursos computacionais, criando assim uma interessante oportunidade de negócio, mas também permitiu potenciar (e facilitar) negócios dos clientes. Do ponto de vista destes, os benefícios são evidentes: poder alugar recursos, num modelo pay-as-you-go, evita os elevados custos de capital necessários para iniciar um novo serviço. A este novo conceito baseado no aluguer e partilha de recursos computacionais a terceiros dá-se o nome de computação em nuvem (“cloud computing”). Como referimos anteriormente, nada disto teria sido possível sem o aparecimento de tecnologias de virtualização, que permitem o desacoplamento dos serviços dos utilizadores do hardware que os suporta. Esta tecnologia tem-se revelado uma ferramenta fundamental na administração e manutenção dos recursos disponíveis em qualquer centro de dados. Por exemplo, a migração de máquinas virtuais facilita tarefas como a manutenção das infraestruturas, a distribuição de carga, a tolerância a faltas, entre outras primitivas operacionais, graças ao desacoplamento entre as máquinas virtuais e as máquinas físicas, e à consequente grande mobilidade que lhes é assim conferida. Atualmente, muitas aplicações e serviços alojados na nuvem apresentam dimensão e complexidade considerável. O serviço típico é composto por diversos componentes que se complementam de forma a cumprir um determinado propósito. Por exemplo, diversos serviços são baseados numa topologia de vários níveis, composta por múltiplos servidores web, balanceadores de carga e bases de dados distribuídas e replicadas. Daqui resulta uma forte ligação e dependência dos vários elementos deste sistema e das infraestruturas de comunicação e de rede que os suportam. Esta forte dependência da rede vem limitar grandemente a flexibilidade e mobilidade das máquinas virtuais, o que, por sua vez, restringe inevitavelmente o seu reconhecido potencial. Esta dependência é particularmente afetada pela reduzida flexibilidade que a gestão e o controlo das redes apresentam atualmente, levando a que o processo de migração de máquinas virtuais se torne num demorado processo que apresenta restrições que obrigam à reconfiguração da rede, operação esta que, muitas vezes, é assegurada por um operador humano (de que pode resultar, por exemplo, a introdução de falhas). Num cenário ideal, a infraestrutura de redes de que depende a comunicação entre as máquinas virtuais seria também ela virtual, abstraindo os recursos necessários à comunicação, o que conferiria à globalidade do sistema uma maior flexibilidade e mobilidade que, por sua vez, permitiria a realização de uma migração conjunta das referidas máquinas virtuais e da infraestrutura de rede que as suporta. Neste contexto, surgem as redes definidas por software (SDN) [34], uma nova abordagem às redes de computadores que propõe separar a infraestrutura responsável pelo encaminhamento do tráfego (o plano de dados) do plano de controlo, planos que, até aqui, se encontravam acoplados nos elementos de rede (switches e routers). O controlo passa assim para um grupo de servidores, o que permite criar uma centralização lógica do controlo da rede. Uma SDN consegue então oferecer uma visão global da rede e do seu respetivo estado, característica fundamental para permitir o desacoplamento necessário entre a infraestrutura física e virtual. Recentemente, várias soluções de virtualização de rede foram propostas (e.g., VMware NSX [5], Microsoft AccelNet [21] e Google Andromeda [2]), ancoradas na centralização oferecida por uma SDN. No entanto, embora estas plataformas permitam virtualizar a rede, nenhuma delas trata o problema da migração dos seus elementos, limitando a sua flexibilidade. O objetivo desta dissertação passa então por implementar e avaliar soluções de migração de redes recorrendo a SDNs. A ideia é migrar um dispositivo de rede (neste caso, um switch virtual), escolhido pelo utilizador, de modo transparente, quer para os serviços que utilizam a rede, evitando causar disrupção, quer para as aplicações de controlo SDN da rede. O desafio passa por migrar o estado mantido no switch de forma consistente e sem afetar o normal funcionamento da rede. Com esse intuito, implementámos e avaliámos três diferentes abordagens à migração ( freeze and copy, move e clone) e discutimos as vantagens e desvantagens de cada uma. É de realçar que a solução baseada em clonagem se encontra incorporada como um módulo do virtualizador de rede Sirius.The way computational resources are managed, specifically those in big data centers, has been evolving in the last few years. One of the big stepping-stones for this was the emergence of server virtualization technologies that, given their ability to decouple software from the hardware, allowed for big data center operators to rent their resources, which, in its turn, represented an interesting business opportunity for both the operators and their potential customers. This new concept that consists in renting computational resources is called cloud computing. Furthermore, with the possibility that later arose of live migrating virtual machines, be it by customer request (for example, to move their service closer to the target consumer) or by provider decision (for example, to execute scheduled rack maintenances without downtimes), this new paradigm presented really strong arguments in comparison with traditional hosting solutions. Today, most cloud applications have considerable dimension and complexity. This complexity results in a strong dependency between the system elements and the communication infrastructure that lays underneath. This strong network dependency greatly limits the flexibility and mobility of the virtual machines (VMs). This dependency is mainly due to the reduced flexibility of current network management and control, turning the VM migration process into a long and error prone procedure. From a network’s perspective however, software-defined networks (SDNs) [34] manage to provide tools and mechanisms that can go a long way to mitigate this limitation. SDN proposes the separation of the forwarding infrastructure from the control plane as a way to tackle the flexibility problem. Recently, several network virtualization solutions were proposed (e.g., VMware NSX [5], Microsoft AccelNet [21] and Google Andromeda [2]), all supported on the logical centralization offered by an SDN. However, while allowing for network virtualization, none of these platforms addressed the problem of migrating the virtual networks, which limits their functionality. The goal of this dissertation is to implement and evaluate network migration solutions using SDNs. These solutions should allow for the migration of a network element (a virtual switch), chosen by the user, transparently, both for the services that are actively using the network and for the SDN applications that control the network. The challenge is to migrate the virtual element’s state in a consistent manner, whilst not affecting the normal operation of the network. With that in mind, we implemented and evaluated three different migration approaches (freeze and copy, move and clone), and discussed their respective advantages and disadvantages. It is relevant to mention that the cloning approach we implemented and evaluated is incorporated as a module of the network virtualization platform Sirius

Review of SDN-based load-balancing methods, issues, challenges, and roadmap

The development of the Internet and smart end systems, such as smartphones and portable laptops, along with the emergence of cloud computing, social networks, and the Internet of Things, has brought about new network requirements. To meet these requirements, a new architecture called software-defined network (SDN) has been introduced. However, traffic distribution in SDN has raised challenges, especially in terms of uneven load distribution impacting network performance. To address this issue, several SDN load balancing (LB) techniques have been developed to improve efficiency. This article provides an overview of SDN and its effect on load balancing, highlighting key elements and discussing various load-balancing schemes based on existing solutions and research challenges. Additionally, the article outlines performance metrics used to evaluate these algorithms and suggests possible future research directions

In-Production Continuous Testing for Future Telco Cloud

Software Defined Networking (SDN) is an emerging paradigm to design, build and operate networks. The driving motivation of SDN was the need for a major change in network technologies to support a configuration, management, operation, reconfiguration and evolution than in current computer networks. In the SDN world, performance it is not only related to the behaviour of the data plane. As the separation of control plane and data plane makes the latter significantly more agile, it lays off all the complex processing workload to the control plane. This is further exacerbated in distributed network controller, where the control plane is additionally loaded with the state synchronization overhead. Furthermore, the introduction of SDNs technologies has raised advanced challenges in achieving failure resilience, meant as the persistence of service delivery that can justifiably be trusted, when facing changes, and fault tolerance, meant as the ability to avoid service failures in the presence of faults. Therefore, along with the “softwarization” of network services, it is an important goal in the engineering of such services, e.g. SDNs and NFVs, to be able to test and assess the proper functioning not only in emulated conditions before release and deployment, but also “in-production”, when the system is under real operating conditions.   The goal of this thesis is to devise an approach to evaluate not only the performance, but also the effectiveness of the failure detection, and mitigation mechanisms provided by SDN controllers, as well as the capability of the SDNs to ultimately satisfy nonfunctional requirements, especially resiliency, availability, and reliability. The approach consists of exploiting benchmarking techniques, such as the failure injection, to get continuously feedback on the performance as well as capabilities of the SDN services to survive failures, which is of paramount importance to improve the effective- ness of the system internal mechanisms in reacting to anomalous situations potentially occurring in operation, while its services are regularly updated or improved. Within this vision, this dissertation first presents SCP-CLUB (SDN Control Plane CLoUd-based Benchmarking), a benchmarking frame- work designed to automate the characterization of SDN control plane performance, resilience and fault tolerance in telco cloud deployments. The idea is to provide the same level of automation available in deploying NFV function, for the testing of different configuration, using idle cycles of the telco cloud infrastructure. Then, the dissertation proposes an extension of the framework with mechanisms to evaluate the runtime behaviour of a Telco Cloud SDN under (possibly unforeseen) failure conditions, by exploiting the software failure injection