Abstract-The Internet has led to the creation of a digital society, where (almost) everything is connected and is accessible from anywhere. However, despite their widespread adoption, traditional IP networks are complex and very hard to manage. It is both difficult to configure the network according to predefined policies, and to reconfigure it to respond to faults, load and changes. To make matters even more difficult, current networks are also vertically integrated: the control and data planes are bundled together. Software-Defined Networking (SDN) is an emerging paradigm that promises to change this state of affairs, by breaking vertical integration, separating the network's control logic from the underlying routers and switches, promoting (logical) centralization of network control, and introducing the ability to program the network. The separation of concerns introduced between the definition of network policies, their implementation in switching hardware, and the forwarding of traffic, is key to the desired flexibility: by breaking the network control problem into tractable pieces, SDN makes it easier to create and introduce new abstractions in networking, simplifying network management and facilitating network evolution.In this paper we present a comprehensive survey on SDN. We start by introducing the motivation for SDN, explain its main concepts and how it differs from traditional networking, its roots, and the standardization activities regarding this novel paradigm. Next, we present the key building blocks of an SDN infrastructure using a bottom-up, layered approach. We provide an in-depth analysis of the hardware infrastructure, southbound and northbound APIs, network virtualization layers, network operating systems (SDN controllers), network programming languages, and network applications. We also look at cross-layer problems such as debugging and troubleshooting. In an effort to anticipate the future evolution of this new paradigm, we discuss the main ongoing research efforts and challenges of SDN. In particular, we address the design of switches and control platforms -with a focus on aspects such as resiliency, scalability, performance, security and dependability -as well as new opportunities for carrier transport networks and cloud providers. Last but not least, we analyze the position of SDN as a key enabler of a software-defined environment.

No abstract

We present two asynchronous Byzantine fault-tolerant state machine replication (BFT) algorithms, which improve previous algorithms in terms of several metrics. First, they require only 2f + 1 replicas, instead of the usual 3f + 1. Second, the trusted service in which this reduction of replicas is based is quite simple, making a verified implementation straightforward (and even feasible using commercial trusted hardware). Third, in nice executions the two algorithms run in the minimum number of communication steps for non-speculative and speculative algorithms, respectively 4 and 3 steps. Besides the obvious benefits in terms of cost, resilience and management complexity-fewer replicas to tolerate a certain number of faults-our algorithms are simpler than previous ones, being closer to crash fault-tolerant replication algorithms. The performance evaluation shows that, even with the trusted component access overhead, they can have better throughput than Castro and Liskov's PBFT, and better latency in networks with non-negligible communication delays.

This paper proposes a hierarchy of three Byzantine-resistant protocols aimed to be used in practical distributed systems: multi-valued consensus, vector consensus and atomic broadcast. These protocols are designed as successive transformations from one to another. The first protocol, multi-valued consensus, is implemented on top of a randomized binary consensus. The protocols share a set of important structural properties. Firstly, they do not use signatures obtained with public-key cryptography, a well-known performance bottleneck in this kind of protocols. Secondly, they are time-free, i.e., they make no synchrony assumptions, since these assumptions are often vulnerable to subtle but effective attacks. Thirdly, they have no leaders, thus avoiding the cost of detecting corrupt processes. Fourthly, they have optimal resilience, i.e., they tolerate f = n−1 3 out of a total of n processes. The multi-valued consensus protocol terminates in a constant expected number of rounds, while the vector consensus and atomic broadcast protocols have time complexities O(f). * This work was partially supported by the FCT through project POSI/CHS/39815/2001 (COPE) and the Large-Scale Informatic Systems Laboratory (LASIGE). 1 We follow the recent literature that uses interchangeably the terms 'Byzantine faults' and 'intrusions', or 'Byzantine-resistant' and 'intrusion-tolerant'. However, papers like [25, 21] consider accidental Byzantine faults, which are different from malicious Byzantine faults, i.e., intrusions. These latter faults should not be assumed to happen independently.

Venssimo, Paulo, 1956-Distributed systems for system architects / Paulo Venssimo, Luis Rodrigues. p. cm.--(Advances in distributed computing and middleware; distl) Includes bibliographical references and index.

There is a significant body of research on distributed computing architectures, methodologies and algorithms, both in the fields of fault tolerance and security. Whilst they have taken separate paths until recently, the problems to be solved are of similar nature. In classical dependability, fault tolerance has been the workhorse of many solutions. Classical security-related work has on the other hand privileged, with few exceptions, intrusion prevention. Intrusion tolerance (IT) is a new approach that has slowly emerged during the past decade, and gained impressive momentum recently. Instead of trying to prevent every single intrusion, these are allowed, but tolerated: the system triggers mechanisms that prevent the intrusion from generating a system security failure. The paper describes the fundamental concepts behind IT, tracing their connection with classical fault tolerance and security. We discuss the main strategies and mechanisms for architecting IT systems, and report on recent advances on distributed IT system architectures.

No abstract

No abstract