What Is Software-Defined Networking (SDN)?

Updated on Jun 1, 2022

Software-defined networking, which is often abbreviated as SDN, or SDN network, is a network architecture approach that enables IT managers to use software to achieve centralized network management, improving flexibility and agility. Organizations have found many advantages of software-defined networking and introduced SDN to their networking for years. This article will take a comprehensive look at software-defined networking and explain the definition, the components, types, benefits and how SDN network impacts data centers.


Components of SDN Network

SDN network can be classified into three layers, each of which consists of various components.

  • Application layer

  • Control layer

  • Infrastructure layer

Software Defined Networking (SDN) Layer

The infrastructure layer consists of various networking equipment, for instance, network switches, servers or gateways, which form the underlying network to forward network traffic to their destinations.

The control layer is the mid layer that connects the infrastructure layer and the application layer. It means the centralized SDN controller software and serves as the land of control plane where intelligent logic is connected to the application plane.

The application layer contains network applications or functions that organizations use. There can be several applications related to network monitoring, network troubleshooting, network policies and security.

To communicate between the three layers of SDN network, northbound and southbound application programming interfaces (APIs) are used. Northbound API enables communications between the application layers and the controller, while southbound API allows the controller communicate with the networking equipment.


Types of SDN Network

Depending on how the controller layer is connected to the SDN devices, SDN network can be divided into four different types which we can classify as follows:

Open SDN

Open SDN has a centralized control plane and uses OpenFlow for the southbound API of the traffic from physical or virtual switches to the SDN controller.


API SDN, different from open SDN, which requires OpenFlow enabled switch, works well with traditional switches. SDN via existing APIs consists of employing functions for networking devices through remote connection such as traditional methods such as SNMP or CLI, or newer method like REST API. Though the SDN via API is non-proprietary and made open, individual APIs used in API SDN are proprietary to specific vendors. And openness can vary from one vendor to another.

Overlay model SDN

Overlay model SDN doesn't address physical netwroks underneath but builds a virtual network on top of the current hardware. It operates on an overlay network and offers tunnels with channels to data centers to solve data center connectivity issues.

Hybird Model SDN

Hybrid model SDN, also called automation-based SDN, blends SDN features and traditional networking equipment. It uses automation tools such as agents, Python, etc. And components supporting different types of OS. Hybrid model SDN is often used as a phrase-in approach to SDN.


Benefits of SDN Network

Different SDN models have their own merits. Here we will only talk about the general benefits that SDN has for the network.

Centralized Management

Centralization is one of the main advantages granted by SDN. SDN network enables centralized management over the network using a central management tool, from which data center managers can benefit. It breaks out the barrier created by traditional systems and provides more agility for both virtual and physical network provisioning, all from a central location.


SDN controller provides a centralized location for network engineers to control the entire security of the network. Despite the fact that the trend of virtualization has made it more difficult to secure networks against external threats, SDN brings massive advantages. Through the SDN controller, security policies and information are ensured to be implemented within the network. And SDN is equipped with a single management system, which helps to enhance security.


SDN network lands users with low operational costs and low capital expenditure costs. For one thing, the traditional way to ensure network availability was by redundancy of additional equipment, which of course adds costs. Compared to the traditional way, a software-defined network is much more efficient without the need to acquire more network switches. For another, SDN works great with virtualization, which also helps to reduce the cost for adding hardware.


Owing to the OpenFlow agent and SDN controller that allow access to the various network components through its centralized management, SDN gives users more scalability. Compared to a traditional network setup, engineers are provided with more choices to change network infrastructure instantly without purchasing and configuring resources manually.


How SDN Network Impacts Data Center?

The trends of virtualization and new demands on IT staff to support the new applications and services such as cloud computing services, BYOD, and big data applications are placing new requirements on data centers for more flexibility, better performance, and greater security.

Data centers have begun to utilize SDN in practice to accommodate the needs. For many hyperscale data centers such as Amazon and Google, it is hard to manage a software-defined strategy. However, with SDN, virtual machine communications are simplified.

Also, it supports connecting multiple data centers. SDN helps to manage data flow for both bandwidth and low cost, as well as allows maximum optimization of network resources.

Meanwhile, SDN supports the multi-tenancy requirements of future data centers. Without changing hardware configurations manually, SDN helps data centers integrate legacy networks and improve network performance.

Finally, with the rise of cloud-based applications and cloud data centers, SDN helps real-time monitoring and dynamic allocation of redundant resources.

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