How does SDN work?

Answered by Phillip Nicastro

Software-Defined Networking (SDN) is a networking approach that separates the control plane from the data plane in a network. This means that the decision-making process of where to send traffic is moved from the hardware switches and routers to a centralized software controller. By doing so, SDN enables network administrators to have more control and flexibility in managing their networks.

In traditional networks, the control plane and data plane are tightly integrated within the network devices. The control plane is responsible for making routing decisions and managing network protocols, while the data plane handles the actual forwarding of packets based on those decisions. However, this tightly coupled architecture can lead to inflexibility and limitations in network management.

In SDN, the control plane is abstracted and placed in a separate software entity called the SDN controller. The SDN controller acts as a central brain that oversees the entire network and makes decisions on how traffic should be handled. Network devices, such as switches and routers, become simpler and are responsible only for forwarding packets based on the instructions received from the SDN controller.

The communication between the SDN controller and the network devices is established through a standardized protocol called OpenFlow. OpenFlow allows the SDN controller to program the flow tables in the network devices, specifying how traffic should be forwarded. This decoupling of the control plane from the data plane enables network administrators to dynamically control and manage network traffic flow.

One of the key advantages of SDN is its ability to provide a more programmable and agile network infrastructure. With the control plane centralized in the SDN controller, network administrators can define and deploy network policies and configurations through software. This means that network changes and updates can be made more efficiently and rapidly, without the need for manual configuration on individual network devices.

Another benefit of SDN is its support for network virtualization. By abstracting the control plane, SDN allows for the creation of virtual networks on top of the physical infrastructure. This enables the isolation and segmentation of network traffic, providing enhanced security and flexibility in network deployments. Virtual networks can be easily created, modified, and scaled as needed, without the constraints of physical network topology.

SDN also facilitates network automation and orchestration. With the control plane centralized and programmable, network operations can be automated through software-defined policies and scripts. This automation streamlines network management tasks, reduces human errors, and improves overall network efficiency. Network orchestration platforms can be utilized to automate the provisioning, configuration, and monitoring of network services and resources.

In my personal experience, implementing SDN has brought significant benefits to network management and operations. By decoupling the control plane from the data plane, we were able to gain more control and visibility over our network infrastructure. We could easily define and enforce network policies, ensuring optimal traffic flow and security. Additionally, the ability to create and manage virtual networks allowed us to support diverse and dynamic applications with different network requirements.

To summarize, SDN works by separating the control plane from the data plane in a network. The control plane is moved to a centralized software controller, while the data plane remains in the hardware devices. This decoupling allows for more flexibility, programmability, and automation in network management. SDN enables network administrators to define and control traffic flow through a centralized controller, and supports network virtualization and automation.