Marinho P. Barcellos

Piecing together the NFV provisioning puzzle: Efficient placement and chaining of virtual network functions

Network Function Virtualization (NFV) is a promising network architecture concept, in which virtualization technologies are employed to manage networking functions via software as opposed to having to rely on hardware to handle these functions. By shifting dedicated, hardware-based network function processing to software running on commoditized hardware, NFV has the potential to make the provisioning of network functions more flexible and cost-effective, to mention just a few anticipated benefits. Despite consistent initial efforts to make NFV a reality, little has been done towards efficiently placing virtual network functions and deploying service function chains (SFC). With respect to this particular research problem, it is important to make sure resource allocation is carefully performed and orchestrated, preventing over- or under-provisioning of resources and keeping end-to-end delays comparable to those observed in traditional middlebox-based networks. In this paper, we formalize the network function placement and chaining problem and propose an Integer Linear Programming (ILP) model to solve it. Additionally, in order to cope with large infrastructures, we propose a heuristic procedure for efficiently guiding the ILP solver towards feasible, near-optimal solutions. Results show that the proposed model leads to a reduction of up to 25% in end-to-end delays (in comparison to chainings observed in traditional infrastructures) and an acceptable resource over-provisioning limited to 4%. Further, we demonstrate that our heuristic approach is able to find solutions that are very close to optimality while delivering results in a timely manner.

Virtual network security: threats, countermeasures, and challenges

Network virtualization has become increasingly prominent in recent years. It enables the creation of network infrastructures that are specifically tailored to the needs of distinct network applications and supports the instantiation of favorable environments for the development and evaluation of new architectures and protocols. Despite the wide applicability of network virtualization, the shared use of routing devices and communication channels leads to a series of security-related concerns. It is necessary to provide protection to virtual network infrastructures in order to enable their use in real, large scale environments. In this paper, we present an overview of the state of the art concerning virtual network security. We discuss the main challenges related to this kind of environment, some of the major threats, as well as solutions proposed in the literature that aim to deal with different security aspects.

Survivor: An enhanced controller placement strategy for improving SDN survivability

In SDN, forwarding devices can only operate correctly while connected to a logically centralized controller. To avoid single-point-of-failure, controller architectures are usually implemented as distributed systems. In this context, recent literature identified fundamental issues, such as device isolation and controller overload, and proposed controller placement strategies to tackle them. However, current proposals have crucial limitations: (i) device-controller connectivity is modeled using single paths, yet in practice multiple concurrent connections may occur; (ii) peaks in the arrival of new flows are only handled on-demand, assuming that the network itself can sustain high request rates; and (iii) failover mechanisms require predefined information, which, in turn, has been overlooked. This paper proposes Survivor, a controller placement strategy that addresses these challenges. The strategy explicitly considers path diversity, capacity, and failover mechanisms at network design. Comparisons to the state-of-the-art on survivable controller placement show that Survivor is superior because (a) path diversity increases the survivability significantly; and (b) capacity-awareness is essential to handle overload during both normal and failover states.

Attacking a Swarm with a Band of Liars: evaluating the impact of attacks on BitTorrent

BitTorrent has become one of the most popular Internet applications, given the number of users and the fraction of the Internet traffic it consumes. Its wide adoption has exposed some potential problems, like selfish peer behavior. Related research efforts so far have focused on modeling the dynamics of swarms, as well as devising incentive mechanisms that improve fairness without sacrificing efficiency. To the best of our knowledge, this is the first paper to evaluate the impact of attacks that exploit BitTorrent vulnerabilities with the sole intention of harming a swarm. The paper sheds light on BitTorrent behavior by presenting state diagrams, describes two attacks, and then evaluates their negative impact in realistic swarm settings. To evaluate the impact of attacks, a discrete-event simulator was developed and validated against an experimental evaluation performed in a controlled environment. Our findings show the seriousness of the problem and should be the basis for the development of new mechanisms to increase BitTorrent security.

An end-to-end reliable multicast protocol using polling for scaleability

Reliable sender-based one-to-many protocols do not scale well due mainly to implosion caused by the excessive rate of feedback packets arriving from receivers. We show that this problem can be circumvented by making the sender poll the receivers at carefully planned timing instants, so that the arrival rate of feedback packets is not large enough to cause implosion. We describe a generic end-to-end protocol which incorporates this polling scheme together with error and flow control mechanisms. We analyse the behaviour of our protocol using simulations which indicate that our scheme can be effective in minimising losses due to implosion, achieving high throughput with low network cost.

Flexible security in peer-to-peer applications: Enabling new opportunities beyond file sharing

The widespread adoption of P2P applications in environments beyond ordinary file sharing demands the fulfillment of several security requirements. Important steps have been taken towards security in P2P systems, with relevant mechanisms being proposed in the past to address specific vulnerabilities. However, existing approaches lack flexibility, since they do not (include enough mechanisms to) tackle a wide range of requirements in an integrated fashion. In addition, they oblige the user/application to manipulate a complex programming interface, as well as going through a cumbersome configuration process. To address these issues, we present P2PSL (P2P Security Layer), a software architecture that allows gradual and flexible integration of security functionality into P2P applications. To show concept and technical feasibility, we have implemented P2PSL, assessed the overhead it induces, and estimated the feasibility of incorporating the layer into two categories of real world P2P applications.

Policy-based access control in peer-to-peer grid systems

Access control to resources is one of the most important requirements to be satisfied in grid systems that span over multiple administrative domains. Such a mechanism allows every institution taking part of a grid community to define and enforce policies for the use of their local resources by remote users. Despite the efforts of the research community to address this topic, existing approaches do not scale (e.g., in terms of communication overhead) for a large number of nodes (peers) providing resources, as these approaches rely on centralized servers to process access requests. Furthermore, they provide limited, large-grain policy specification functionality and are not committed to employing open, standardized formats to express policies. In this paper, we address these limitations by proposing PeGAC (peer-to-peer grid access control), a policy-based, distributed access control mechanism, which can be applied to P2P grid systems. In our proposal, policies are specified using the role-based access control model and coded using the extensible access control markup language. As a proof-of-concept we have integrated PeGAC into OurGrid, a middleware for the implementation of P2P grid systems. Preliminary results of experiments carried out at the resulting infrastructure show that our solution poses small communication and processing overhead, and can handle large policy repositories efficiently.

Towards a flexible security framework for peer-to-peer based grid computing

The dynamic, multi-organization nature of large-scale grid computing introduces security issues that must be addressed before grid systems can become widely popular. This paper proposes P2PSLF (Peer-to-Peer Security Layer Framework), a flexible security framework for peer-to-peer based grid computing. P2PSLF provides a wide range of security mechanisms (e.g., authentication, confidentiality, integrity, authorization, and audit), and allows the creation of new ones. It is independent of the overlying application, which enables new systems to be implemented without having to deal with security issues within the application. In addition, the framework is modular and reconfigurable. The set of security requirements to be satisfied in communications is determined per peer, and can be changed without recompiling the application. The framework is exercised using OurGrid, a P2P-based middleware that enables the creation of a multi-organization grid computing environment for the execution of bag-of-tasks applications.

Flexible and secure service discovery in ubiquitous computing

The realization of ubiquitous computing requires achieving seamless service provisioning for users and devices everywhere. However, potentially uneven conditions imposed (by heterogeneous, overlapping environments) and a high degree of user autonomy pose long-term challenges for mobile application design and implementation. In this context, service discovery protocols can be used as a building block to foster peer collaboration, allowing user-provided services to be found and used. Promoting user collaboration, in turn, raises issues regarding security and privacy. Interacting peers (i.e. users) may belong to multiple domains, and authentication cannot always rely on an infrastructure provided by an administrative domain. Thus, user privacy, security, and collaboration may be regarded as conflicting goals. This paper presents a flexible protocol for service discovery in ubiquitous systems whose peer-to-peer design enables the dynamic choice among the levels of collaboration, security and privacy desired by participants. The proposed approach is based on decentralized mechanisms that harness well-known trust management principles to control the exposure of service information. The resulting protocol is called Flexible and Secure Service Discovery (FSSD). An evaluation with a simple prototype was conducted to support our claims of flexibility (e.g. allowing run-time decisions). Results demonstrate that the proposed approach can reflect well the balance among the conflicting goals of security, privacy and user collaboration.

Protecting BitTorrent: Design and Evaluation of Effective Countermeasures against DoS Attacks

BitTorrent is a P2P file-sharing protocol that can be used to efficiently distribute files such as software updates and digital content to very large numbers of users. In a previous paper, we have shown that vulnerabilities can be exploited to launch Denial-of-Service attacks against BitTorrent swarms, which can substantially increase download times and network traffic. In this paper, we review the three most damaging attacks, and propose two algorithms as countermeasures to effectively tackle them. We implemented the attacks and countermeasures in a packet-level BitTorrent simulator. The results indicate that our proposed approach is effective when there is an ongoing attack while at the same time efficient when the countermeasure is active but there is no attack. To the best of our knowledge, this is the first proposal in the literature to make BitTorrent more robust against Denial-of-Service (DoS) attacks.