VERSION 2.01 1 Software-Defined Networking: A …

1 VERSION 1. software -Defined networking : a comprehensive survey Diego Kreutz, Member, IEEE, Fernando M. V. Ramos, Member, IEEE, Paulo Verissimo, 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 Index Terms software -defined networking , OpenFlow, net- society, where (almost) everything is connected and is accessible work virtualization, network operating systems, programmable from anywhere. However, despite their widespread adoption, networks, network hypervisor, programming languages, flow- [ ] 8 Oct 2014.

2 Traditional IP networks are complex and very hard to manage. based networking , scalability, dependability, carrier-grade net- It is both difficult to configure the network according to pre- works, software -defined environments. defined 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 I. I NTRODUCTION. planes are bundled together. software -Defined networking (SDN) The distributed control and transport network protocols run- is an emerging paradigm that promises to change this state of affairs, by breaking vertical integration, separating the network's ning inside the routers and switches are the key technologies control logic from the underlying routers and switches, promoting that allow information, in the form of digital packets, to (logical) centralization of network control, and introducing the travel around the world.

3 Despite their widespread adoption, ability to program the network. The separation of concerns traditional IP networks are complex and hard to manage [1]. introduced between the definition of network policies, their To express the desired high-level network policies, network implementation in switching hardware, and the forwarding of traffic, is key to the desired flexibility: by breaking the network operators need to configure each individual network device control problem into tractable pieces, SDN makes it easier to separately using low-level and often vendor-specific com- create and introduce new abstractions in networking , simplifying mands.

4 In addition to the configuration complexity, network network management and facilitating network evolution. environments have to endure the dynamics of faults and In this paper we present a comprehensive survey on SDN. We adapt to load changes. Automatic reconfiguration and response start by introducing the motivation for SDN, explain its main mechanisms are virtually non-existent in current IP networks. concepts and how it differs from traditional networking , its roots, and the standardization activities regarding this novel paradigm. Enforcing the required policies in such a dynamic environment Next, we present the key building blocks of an SDN infrastructure is therefore highly challenging.

5 Using a bottom-up, layered approach. We provide an in-depth To make it even more complicated, current networks are analysis of the hardware infrastructure, southbound and north- also vertically integrated. The control plane (that decides how bound APIs, network virtualization layers, network operating to handle network traffic) and the data plane (that forwards systems (SDN controllers), network programming languages, and network applications. We also look at cross-layer problems such traffic according to the decisions made by the control plane). as debugging and troubleshooting.

6 In an effort to anticipate the are bundled inside the networking devices, reducing flexibility future evolution of this new paradigm, we discuss the main and hindering innovation and evolution of the networking ongoing research efforts and challenges of SDN. In particular, infrastructure. The transition from IPv4 to IPv6, started more we address the design of switches and control platforms with than a decade ago and still largely incomplete, bears witness a focus on aspects such as resiliency, scalability, performance, security and dependability as well as new opportunities for to this challenge, while in fact IPv6 represented merely a carrier transport networks and cloud providers.

7 Last but not protocol update. Due to the inertia of current IP networks, least, we analyze the position of SDN as a key enabler of a a new routing protocol can take 5 to 10 years to be fully software -defined environment. designed, evaluated and deployed. Likewise, a clean-slate approach to change the Internet architecture ( , replacing D. Kreutz and F. Ramos are with the Department of Informatics of IP), is regarded as a daunting task simply not feasible in Faculty of Sciences, University of Lisbon, Lisbon, 1749-016 Portugal e-mail: practice [2], [3]. Ultimately, this situation has inflated the P.

8 Ver ssimo is with the Interdisciplinary Centre for Security, Reliability capital and operational expenses of running an IP network. and Trust (SnT), University of Luxembourg, 4 rue Alphonse Weicker, L-2721 software -Defined networking (SDN) [4], [5] is an emerging Luxembourg. e-mail: C. Esteve Rothenberg is with the School of Electrical and Com- networking paradigm that gives hope to change the lim- puter Engineering (FEEC, University of Campinas, Brazil. e-mail: itations of current network infrastructures. First, it breaks the vertical integration by separating the network's control S.)

9 Azodolmolky is with Gesellschaft f ur Wissenschaftliche Datenverar- beitung mbH G ottingen (GWDG), Am Fa berg 11, 37077 G ottigen, Germany. logic (the control plane) from the underlying routers and e-mail: switches that forward the traffic (the data plane). Second, S. Uhlig is with Queen Mary University of London. is with Queen Mary, with the separation of the control and data planes, network University of London, Mile End Road, London E1 4NS, United Kingdom. e-mail switches become simple forwarding devices and the control Manuscript received May 31, 2014. logic is implemented in a logically centralized controller (or VERSION 2.)

10 Network Applica4on(s) SDN momentum was strong enough to make Google, Face- book, Yahoo, Microsoft, Verizon, and Deutsche Telekom fund Open northbound API Open networking Foundation (ONF) [10] with the main goal Controller Pla+orm of promotion and adoption of SDN through open standards development. As the initial concerns with SDN scalability Open southbound API. were addressed [11] in particular the myth that logical centralization implied a physically centralized controller, an issue we will return to later on SDN ideas have matured and evolved from an academic exercise to a commercial ts success.