What is SDN?

Software-Defined Networking (SDN) is a new perspective on the design, implementation and management of networks. SDN is designed to merge the network into the age of the cloud. This most recent evolution of the modern network promises to make the network more elastic, agile, and dynamic, yet to keep pace with today’s rapidly changing business demands.

How does Software-Defined Networking work?

SDN is an approach to network virtualisation that seeks to optimise network resources and quickly adapt networks to changing business needs, applications, and traffic. It works by separating the network's control plane and the data plane, creating a software-programmable infrastructure that is distinct from physical devices.

With SDN, the functions of network orchestration, management, analytics, and automation become the job of SDN controllers. Because these controllers are not networking devices, they can take advantage of the scale, performance, and availability of modern cloud computing and storage resources. Increasingly, SDN controllers are built on open platforms, using open standards and open APIs, enabling them to orchestrate, manage, and control network equipment from different vendors.

Controller / Southbound API within SDN

Within an SDN environment, a controller acts as the "Brains" within the network through which an abstract, centralised view of the network becomes available. From this controller, network administrators can quickly and easily provision new configurations to the network, and errors can be centrally detected. The way underlying systems (routers, switches) of the forwarding plane handle network traffic can be directly influenced through the controller.

Protocols within SDN networks to facilitate communication from the controller (southbound API) to switches include Openflow, MPLS over GRE and VXLAN. These protocols offer the ability to build an 'overlay' network, allowing the underlying infrastructure (routers, switches) in the forwarding plane to be virtualised and the forwarding capacity to be used much more efficiently than in traditional data centre networks.

Open API / Northbound API within SDN

An SDN environment also uses open 'Application Programmatic Interfaces' (APIs) to support services and applications running on the network. These APIs, also known as Northbound APIs, enable innovation and therefore efficient service orchestration and automation. As a result, Software Defined Networks allow network administrators to roll out new services faster without having to change the configuration on each individual router or switch (within the forwarding planes).

Benefits of SDN

SDN delivers a wide array of business benefits. Separation of the control and transport layers increases flexibility and accelerates time-to-market for new applications. The ability to respond more swiftly to issues and outages improves network availability. And programmability makes it easier for IT organisations to automate network functions, reducing operating costs.

SDN allows network administrators to manage network services through the abstraction of lower-level functionality. This is done by splitting the system into two. One part makes decisions about where traffic is sent (the control plane). The other part forwards traffic to the selected destination (the data plane).

SDN dovetails with another technology, Network Functions Virtualisation (NFV). NFV offers the ability to virtualise appliance-based network functions such as firewalls, load balancers, and WAN accelerators. The centralised control that SDN provides can efficiently manage and orchestrate virtual network functions that are enabled by NFV.