CONTRIBUTED PAPER Software-DefinedNetworking: AComprehensiveSurvey This paper offers a comprehensive survey of software-defined networking covering its context, rationale, main concepts, distinctive features, and future challenges. By Diego Kreutz,Member IEEE, Fernando M. V. Ramos,Member IEEE, Paulo Esteves Ver ssimo,Fellow IEEE, Christian Esteve Rothenberg,Member IEEE, Siamak Azodolmolky,Senior Member IEEE, and Steve Uhlig,Member IEEE ABSTRACT|The Internet has led to the creation of a digital society, where (almost) everything is connected and is acces- sible from anywhere. However, despite their widespread adop- tion, 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 network- ing (SDN) is an emerging paradigm that promises to change this state of affairs, by breaking vertical integration, separating the networks 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 regard- ing 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 application prog- ramming interfaces (APIs), network virtualization layers, network operating systems (SDN controllers), network prog- ramming 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 pa- radigm, we discuss the main ongoing research efforts and challenges of SDN. In particular, we address the design of switches and control platformsVwith a focus on aspects such as resiliency, scalability, performance, security, and dependabilityVas well as new opportunities for carrier trans- port networks and cloud providers. Last but not least, we ana- lyze the position of SDN as a key enabler of a software-defined environment. KEYWORDS|Carrier-grade networks; dependability; flow- based networking; network hypervisor; network operating sys- tems (NOSs); network virtualization; OpenFlow; programmable networks; programming languages; scalability; software- defined environments; software-defined networking (SDN) I. INTRODUCTION The distributed control and transport network protocols running inside the routers and switches are the key tech- nologies that allow information, in the form of digital packets, to travel around the world. Despite their wide- spread adoption, traditional IP networks are complex and Manuscript received June 15, 2014; revised October 6, 2014; accepted November 10, 2014. Date of current version December 18, 2014. D. Kreutz and F. M. V. Ramos are with the Department of Informatics of Faculty of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal (e-mail: kreutzieee.org; fvramosfc.ul.pt). P. E. Ver ssimo is with the Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, L-2721 Walferdange, Luxembourg (e-mail: paulo.verissimouni.lu). C. E. Rothenberg is with the School of Electrical and Computer Engineering (FEEC), University of Campinas, Campinas 13083-970, Brazil (e-mail: chestevedca.fee.unicamp.br). S. Azodolmolky is with the Gesellschaft fu r Wissenschaftliche Datenverarbeitung mbH Go ttingen (GWDG), 37077 Go ttigen, Germany (e-mail: siamak.azodolmolkygwdg.de). S. Uhlig is with Queen Mary University of London, London E1 4NS, U.K. (e-mail: steveeecs.qmul.ac.uk). Digital Object Identifier: 10.1109/JPROC.2014.2371999 0018-9219?2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http:/www.ieee.org/publications_standards/publications/rights/index.html for more information. 14Proceedings of the IEEE| Vol. 103, No. 1, January 2015 hard to manage 1. To express the desired high-level net- work policies, network operators need to configure each individual network device separately using low-level and often vendor-specific commands. In addition to the config- uration com