What is SDN and where software-defined networking is going

Software-defined networking (SDN) established a foothold in cloud computing, intent-based networking, and network security, with Cisco, VMware, Juniper and others leading the charge.

Hardware reigned supreme in the networking world until the emergence of software-defined networking (SDN), a category of technologies that separate the network control plane from the forwarding plane to enable more automated provisioning and policy-based management of network resources.

SDN's origins can be traced to a research collaboration between Stanford University and the University of California at Berkeley that ultimately yielded the OpenFlow protocol in the 2008 timeframe.

OpenFlow is only one of the first SDN canons, but it's a key component because it started the networking software revolution. OpenFlow defined a programmable network protocol that could help manage and direct traffic among routers and switches no matter which vendor made the underlying router or switch.

In the years since its inception, SDN has evolved into a reputable networking technology offered by key vendors including Cisco, VMware, Juniper, Pluribus and Big Switch. The Open Networking Foundation develops myriad open-source SDN technologies as well.


"Datacenter SDN no longer attracts breathless hype and fevered expectations, but the market is growing healthily, and its prospects remain robust," wrote Brad Casemore, IDC research vice president, data center networks, in a recent report, Worldwide Datacenter Software-Defined Networking Forecast, 2018–2022. "Datacenter modernization, driven by the relentless pursuit of digital transformation and characterized by the adoption of cloudlike infrastructure, will help to maintain growth, as will opportunities to extend datacenter SDN overlays and fabrics to multicloud application environments."

SDN will be increasingly perceived as a form of established, conventional networking, Casemore said.

IDC estimates that the worldwide data center SDN market will be worth more than $12 billion in 2022, recording a CAGR of 18.5% during the 2017–2022 period. The market generated revenue of nearly $5.15 billion in 2017, up more than 32.2% from 2016.

In 2017, the physical network represented the largest segment of the worldwide datacenter SDN market, accounting for revenue of nearly $2.2 billion, or about 42% of the overall total revenue. In 2022, however, the physical network is expected to claim about $3.65 billion in revenue, slightly less than the $3.68 billion attributable to network virtualization overlays/SDN controller software but more than the $3.18 billion for SDN applications.

“We're now at a point where SDN is better understood, where its use cases and value propositions are familiar to most datacenter network buyers and where a growing number of enterprises are finding that SDN offerings offer practical benefits,” Casemore said. “With SDN growth and the shift toward software-based network automation, the network is regaining lost ground and moving into better alignment with a wave of new application workloads that are driving meaningful business outcomes.”

What is SDN? 
The idea of programmability is the basis for the most precise definition of what SDN is: technology that separates the control plane management of network devices from the underlying data plane that forwards network traffic.

IDC broadens that definition of SDN by stating: “Datacenter SDN architectures feature software-defined overlays or controllers that are abstracted from the underlying network hardware, offering intent-or policy-based management of the network as a whole. This results in a datacenter network that is better aligned with the needs of application workloads through automated (thereby faster) provisioning, programmatic network management, pervasive application-oriented visibility, and where needed, direct integration with cloud orchestration platforms.”

The driving ideas behind the development of SDN are myriad. For example, it promises to reduce the complexity of statically defined networks; make automating network functions much easier; and allow for simpler provisioning and management of networked resources, everywhere from the data center to the campus or wide area network.

Separating the control and data planes is the most common way to think of what SDN is, but it is much more than that, said Mike Capuano, chief marketing officer for Pluribus.

“At its heart SDN has a centralized or distributed intelligent entity that has an entire view of the network, that can make routing and switching decisions based on that view,” Capuano said. “Typically, network routers and switches only know about their neighboring network gear. But with a properly configured SDN environment, that central entity can control everything, from easily changing policies to simplifying configuration and automation across the enterprise.”

How does SDN support intent-based networking?
Intent-based networking (IBN) has a variety of components, but basically is about giving network administrators the ability to define what they want the network to do, and having an automated network management platform create the desired state and enforce policies to ensure what the business wants happens.

“If a key tenet of SDN is abstracted control over a fleet of infrastructure, then the provisioning paradigm and dynamic control to regulate infrastructure state is necessarily higher level,” Bushong said. “Policy is closer to declarative intent, moving away from the minutia of individual device details and imperative and reactive commands.”

IDC says that intent-based networking “represents an evolution of SDN to achieve even greater degrees of operational simplicity, automated intelligence, and closed-loop functionality.”

For that reason, IBN represents a notable milestone on the journey toward autonomous infrastructure that includes a self-driving network, which will function much like the self-driving car, producing desired outcomes based on what network operators and their organizations wish to accomplish, Casemore stated.

“While the self-driving car has been designed to deliver passengers safely to their destination with minimal human intervention, the self-driving network, as part of autonomous datacenter infrastructure, eventually will achieve similar outcomes in areas such as network provisioning, management, and troubleshooting — delivering applications and data, dynamically creating and altering network paths, and providing security enforcement with minimal need for operator intervention,” Casemore stated.

While IBN technologies are relatively young, Gartner says by 2020, more than 1,000 large enterprises will use intent-based networking systems in production, up from less than 15 in the second quarter of 2018.