What is Software Defined Networking?

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Software-defined networking marks the shift from hardware devices to the use of software to maintain and secure today’s increasingly complex networks effectively, efficiently, and flexibly. 

Companies are quickly moving their data to the cloud, and networks are becoming ever more complex with varied and distributed device ecosystems. This not only makes networks more vulnerable but also more difficult to manage. 

Software-defined networking (SDN) helps network administrators more closely monitor company networks. SDN also complements and supports emerging technologies, such as 5G networks and secure access server edge (SASE), to name a few, keeping company computing environments adaptable to new technology.

The SDN market is expected to continue growing rapidly. In fact, it is forecast to grow from its 2020 market size of $13.7 billion to an estimated total value of $32.7 billion by the year 2025.

What is SDN?

Software-defined networking is a network architecture approach that allows network engineers and administrators to centrally control or program the network and its traffic through software applications. SDN helps companies remain adaptable, allowing network engineers to efficiently orchestrate network services to devices as needed.

SDN is similar but distinct from SD-WAN. SD-WAN is born out of SDN and indeed applies the same basic concepts as SDN to direct network traffic quickly and efficiently. However, SDN has a smaller geographic scope than SD-WAN, which can span a greater geography. Another key difference between the two is that users (network administrators) program an SDN, while the vendor provisions and optimizes the services that SD-WAN delivers.

It may sound paradoxical, but SDNs help companies achieve an integrated network ecosystem but, at the same time, divorce the control plane from the data plane in the network. This allows software to run independently and in a device-agnostic and operating system agnostic manner, even at the edges of the network. The software is still accessible to network switches and routers that would otherwise stand behind closed proprietary firmware.

Types of SDNs

There are four different types of SDNs.

API: Controls the flow of data between the control and infrastructure layers through programming interfaces.

Open: Uses open protocols to route communications between virtual and hardware devices.

Overlay: Maps a virtual layer on top of a hardware ecosystem to provide segmented access and bandwidth between devices and data centers.

Hybrid: Bridges traditional and software-defined networking by assigning the best protocol depending on the kind of data traffic.

Who uses SDN?

The utility of SDN varies, depending on business size and type. 

Mainly smaller businesses

Because of the more localized nature of SDNs, primarily small and medium-sized businesses adopt them to simplify network control. Plus, the centralized nature of SDNs keeps operational costs down for SMBs. 

However, behemoths Facebook, Google, and Microsoft as well as universities also use SDN for its open-source elements, which helps keep costs low. SDNs help cloud service providers deliver optimal service to the edge. They also help universities centrally manage automation, service, and security across both wi-fi and ethernet networks on campus.

Fintech companies

Companies operating in the tech and financial services sectors tend to capitalize on the advantages of SDNs. 

SDNs are attractive to tech companies—such as cloud service providers—for a number of reasons, including but not limited to:

  • Streamline network provisioning.
  • Optimize network performance.
  • Automate manual tasks to expedite customer onboarding.
  • Quickly add new services or expand existing ones.

Companies in the financial services industry use SDNs to keep confidential data on the network secure. SDNs provide a virtual layer of firewalls to fortify and protect devices on the network. Moreover, SDNs enable users to quickly respond to rapid changes in financial markets by moving funds, making quick trades and other time-sensitive financial transactions. 

Industrial/manufacturing environments

Manufacturing facilities often run 24/7, necessitating an SDN to maintain network resilience and efficiency. With a distributed SDN, companies with geographically dispersed manufacturing facilities can remotely and efficiently control different parts of the manufacturing process, for instance, lighting in one facility and robotics in another.

Additionally, SDNs can be combined with other technologies that mutually enhance one another. For instance, SDN combined with Network Function Virtualization achieves security, performance, and reliability requirements for some industrial settings.

Parts of the SDN and How They Work Together

SDN is made up of three layers: application, control, and infrastructure. 

Application level

The application level houses the network’s apps. The apps send requests to the network’s control layer. The SDN uses APIs to interact with and manage apps through an application-run controller. 

Control level

The control layer (or control plane) contains the controller and runs every service on all devices within the network from one central location. This layer is therefore often aptly referred to as the brain of the network. 

The control layer acts as the intermediary between apps running on devices and the underlying switch infrastructure. It directs requests to the infrastructure layer, establishes routes, and assigns time and frequency slots

The controller comes in three different types, according to the architecture of the SDN network: centralized, distributed, and hybrid. The right controller for any given computing environment depends on the system size as well as the desired level of security, resilience, and scalability. The distributed controller is a good compromise between security and system complexity.

Infrastructure level

The infrastructure layer – also called the data plane or forward plane – is the bedrock of the network. It contains physical devices, known as data plane devices, namely routers and switches. This layer basically regulates and segments traffic within and across networks.

The switches change the traffic across the network, directing traffic where it’s most needed at any given moment and determining how it gets delivered. They are like the muscles of the body that act based on messages sent from the brain (control). The infrastructure layer needs to be able to support various types of devices and operating systems, so that apps work properly.

Benefits and Disadvantages of SDN

Benefits of SDN


SDNs render networks more flexible and scalable to adapt to the changing needs of today’s organizations by, for example, rerouting traffic to reduce downtime and prevent outages.

Easy provisioning

Since network engineers, rather than SDN vendors, program SDNs, they make on-demand configuration, customization, service expansion, and service additions possible.


SDNs use automation for load balancing, repetitive manual tasks, and to automatically deploy, update, and fix apps. This supports optimal performance and increases end-user satisfaction. 


By consolidating services within one common infrastructure, SDNs streamline management of hardware, software, and devices and give administrators greater network control and visibility.


SDNs lower operational costs by reducing hardware (in hybrid adoptions) or eliminating hardware (in pure play adoption).


Visibility and control from SDNs boost network security by allowing network engineers to monitor the network and intervene in network activity to prevent a cyber attack. Distributed and hybrid SDN controllers, in particular, segment networks and their respective traffic and classify them according to level of confidentiality. This way, a hack stays contained to the network within which it occurred and cannot spread to other network segments. 

Disadvantages of SDN

Vulnerability to a network-wide attack

For starters, while central control is a major advantage, it’s also the Achilles heel of the SDN. Since the controller is the central point through which the network traffic is managed, all it takes is a cyber attack on the controller to bring the entire system down. A distributed or hybrid controller, however, mitigates widespread data loss or data breach, limiting an attack more locally within the network. 

Limited capacity for complexity

Another shortfall related to centralized control is that it opens up the door for network administrator error when operating several workloads simultaneously. However, new solutions address this shortcoming (see Trends section below).

Potential for inefficiency

One final disadvantage of centralized control is that the volume of traffic on large networks can overburden the controller, leading to bottlenecks and overall inefficiency. 

Also read: 6 Enterprise Networking Security Trends

Trends and the Future of SDN

SDN is here to stay, as it has given rise to and supports other technologies that today’s enterprise networks need.

SDN and container management

Container management software such as Kubernetes assist network administrators with managing several loads across the network at the same time. It enables network administrators to build and configure apps, infrastructure, and services each with their own specific requirements that help meet overarching business objectives.

SDN and 5G

SDN, particularly when paired with network functions virtualization (NFV), provides the necessary support to launch, power, and optimize 5G infrastructure.


Secure access service edge (SASE) is a comprehensive collection of security features, including WAN and Zero Trust, that enhances the security of SDN and strengthens a network’s security posture.  

Segment routing

Segment routing technology is one of several that have emerged from SDN. Segment routing adds a layer of security to the network that protects against loop attacks and DoS attacks and, combined with software-defined perimeter, distinguishes between trusted and malicious devices that try to connect to the network.

As a networking approach that programs networks through software rather than hardware, SDN has become a cornerstone of enterprises’ resilient, quickly adaptable network strategy. SDN has evolved to include a range of SDN types, enabling businesses of all sizes to take advantage of SDN’s benefits of agility, simplicity, and its support of newer technologies, such as 5G. 

Read next: Top Enterprise Networking Companies 2022

Lauren Hansen
Lauren Hansen
Lauren Hansen is a writer for TechnologyAdvice, covering IT strategy and trends, enterprise networking, and PM software for CIOInsight.com, enterprisenetworkingplanet.com, project-management.com, and technologyadvice.com. When she's not writing about technology trends, she's working out or spending time with family.

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