Software Defined Networking (SDN) Introduction

Software Defined Networking (SDN)

Though still in an embryonic state, the nascent field of Software Defined Networking (SDN) is showing a promising future. Currently, there is extensive and widespread implementation in cloud computing, multitenant data centers, and other networking environments where scalable and programmable provisioning and administration of network switching and routing is required.

Overview of Software-Defined Networking

What is SDN?

In our present discussion, we will focus upon the approaches to SDN, its’ real-world implementation, and some of the barriers and impediments to its’ development.  Of the former, the OpenFlow communication protocol and the Virtual Network Overlay are implemented in the majority of use cases. Open Flow, gives precedence to access of switch and router forwarding planes, whereas Virtual Network Overlay consists of a virtualized network infrastructure. In both instances this permits the physical network to be abstracted and used with other physical networks.

In a network, there are a plethora of unique events and applications that call for a administrator to configure their devices and topologies to meet ever-changing enterprise requirements. To meet these demands, SDN has been introduced as a means to separate control functions from the co-existing system that forwards data traffic. To accomplish this, SDN architectures will decouple the control functions from the forwarding functions, which permits network control to be programmable and the underlying infrastructure to be abstracted from applications and network services.

At its’ core, this abstraction shields high-level software from the complexity existing in the lower levels. In this context, SDN functionality is defined by a ‘controlling’ software, which results in the hardware equipment functionalities being controlled by that software (Alberti, 2013). Because of this decoupling, network administration becomes more flexible, adaptable, scalable, and easier to manage in the mutable and high-bandwidth networks of todays’ business entities.  

SDN Planes

Control Plane

As its’ name connotes, the control plane is tasked with making decisions as to where traffic is directed.  Figure 1 illustrates a three-layer model of SDN architecture. In it, we see an abstract and centralized view of the overall network. The packets of the control plane either originate with the router, or are directed to the router. Other tasks performed by the control plane are system configuration, management, or an interchange of routing table information. Based upon routing protocols, such as RIP, OSPF, BGP, the route controller will exchange topology information with other routers and construct a routing table.

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Image attribution - "SDN-architecture-overview-transparent" by Open Networking Foundation (ONF) - SDN Architecture Overview (PDF), Version 1.0, December 12, 2013.. Licensed under CC BY-SA 3.0 via Commons -