Nutanix Glossary

What is Software-Defined Networking (SDN)?

May 23, 2023 | min

Software-defined networking (SDN) describes an architecture that separates the network control plane and the forwarding plane, aiming to simplify and improve network control. IT teams are better able to rapidly adapt to changing business requirements and application needs. 

SDN is a highly flexible, agile way to adapt to growing networking  requirements and enable automation and agility. By separating the network control and forwarding planes, SDN makes network control a programmable entity and abstracts the infrastructure underneath. 

Network engineers benefit from SDN because they no longer have to wrangle individual network devices to offer network services, connect locations and applications, or govern resource and capacity utilisation. Instead, SDN takes care of this task by directing these individual “switches” to provide services when the business requires them.

Features of software-defined networking 

There are four unique and defining features of SDN:

  1. Agility - As business and application needs change, administrators can adjust network configuration as required.
  2. Centralised management - SDN consolidates network intelligence, which provides a holistic view of the network configuration and activity.
  3. Programmability - The ability to directly program network features and configure network resources quickly and easily through automated SDN services.
  4. Open connectivity - Software-defined networking is based on and implemented via open standards. As a result, SDN streamlines network design and provides consistent networking in a vendor-neutral architecture.

Software-defined Networking Architecture

SDN relies on APIs to create a centralised management plane that lets administrators and managers decide and program network behaviour. SDN creates an abstraction or virtual overlay on top of otherwise complex networking infrastructure. This enables IT teams to manage their network, application, and devices consistently with minimal knowledge of or direct interaction with that underlying technology. 

SDN performs various tasks and encompasses various technologies. But its original defining purpose was to create a programmable abstraction that separates the network data and network control planes.

The control plane is the brain of the operation, managing network services and deciding how and where packets should move throughout the network. The data plane is the transport system that connects endpoints and moves packets according to the control plane’s directions.

What is the difference between SDN and traditional networking?

In a traditional network environment, networks are mostly unaware of the requirements for applications running throughout the system. Operators can observe application characteristics like packet size, volume, latency, and errors. However, the types of applications and information about health or needed performance cannot always be determined.

In an SDN, applications can have information about the network and network configurations can be tailored to the applications to create a two-way flow of information.

Components of an SDN

There are three major components that make up SDN.

SDN applications 

These applications relay actions and request resources through the SDN controller using APIs. SDN applications can assume various forms and serve various functions, such as network management, providing analytics, adding security or common network functions. Examples include IP address management (IPAM), managing quality of service (QoS), load balancing, or detection and mitigation of denial-of-service (DoS) cyberattacks. 

SDN controller 

SDN applications send instructions to the SDN controller, which relays that information to networking components. The SDN controller also collects network information from hardware and delivers this information and relevant statistics back to the applications.

SDN networking devices 

These devices are responsible for forwarding and data processing tasks, which can be performed for the data path as well. The SDN controller integrates all three layers. These API integrations are commonly called northbound or southbound interfaces. The northbound is the integration between the controller and the application while the southbound is the integration between the controller and the physical networking devices.

The benefits of software-defined networking

Businesses that invest in SDN are often lured in by its ability to support data-heavy applications. But beyond that purpose, there are innumerable benefits that make SDN a worthy venture. Below are several of the top advantages.

Context and visibility 

In an SDN, users can view the entire network through a centralised source, which simplifies provisioning and managing processes.

Lifecycle management and automation 

Business demands vary day-to-day, so IT managers need to set up what-if network configurations to accommodate demands from new applications and virtual machines (VMs). In an SDN, these what-if configurations are easy to do and pose no impact on the network.


Improved security makes SDN a no-brainer for many businesses. Security is centralised in an SDN. In this central controller, an IT manager can create and distribute security policies throughout the enterprise with ease. 

TCO and ROI 

Lower operating expenses are another alluring benefit of SDN. Because an SDN improves overall resource and server utilisation, businesses will experience reduced operational costs and administrative expenses.


SDN is an excellent way to help “cloudify” the datacenter, ultimately helping to unify the components of a business’s infrastructure. Specifically, a business can abstract, and therefore unify, cloud resources through SDN. 


The ability to redirect and shape data traffic is a defining feature of SDN. This enables IT teams to improve their service delivery and network responsiveness, which makes the end-user experience more seamless.

Software-defined networking (SDN) security

There are different levels of security protection offered via SDN. Perhaps most notable is the centralised intelligence SDN offers, enabling IT administrators to quickly and easily set and keep security policies. These policies can be universally enforced throughout the network and can be maintained and enforced through central control. 

Furthermore, SDN creates an abstraction layer between the software and the hardware, allowing IT teams to bypass proprietary devices and simply start developing security tools to implement across the network. As a result, there is greater transparency for gathering insights and possible threats if a security breach occurs.

Security is scalable with SDN. Rather than requiring expensive, proprietary hardware and security controls, IT teams can create, control and deploy security policies at scale as software grows, new clouds and applications are provisioned, or as business needs change. If a segment shuts down or has a security gap, the transparency of SDN allows administrators to quickly and easily detect malware.

How is Software-defined Networking (SDN) used?

There are multiple use cases where SDN is beneficial. First, SDN can help support DevOps initiatives. Application updates, deployments and even IT infrastructure components can be automated through SDN while DevOps applications and platforms are created and deployed.

Second, businesses can leverage SDN controllers to improve the functionality of campus networks, which are often complex due to ongoing Wi-Fi and Ethernet needs. The central SDN controller delivers automation and centralised management that improves security and helps businesses deliver more high-quality services across the network.

Third, service provider networks can leverage SDN to automate the process of provisioning networks for improved service management and increased control.

Finally, businesses can enjoy the increased protection and simplified firewall administration that SDN provides. Businesses can create distributed firewall systems through the virtualisation capabilities of SDN, delivering an extra layer of security to prevent a breach from hopping from one VM to another.

Administrators and managers can also centrally track and change network activity to proactively detect vulnerabilities and eliminate possible data breaches.

Related Resources

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Modernising Your Datacentre: A Security-First Approach


Application-Centric Security

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Big Switch + Nutanix: Ideal SDN Fabric for Hyperconverged Infrastructure

Learn more about software-defined networking

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