What Is Software-Defined Networking? (2024)

Software-defined networking adopts a software-driven methodology for network architecture and management. Its goal is to create an open and programmable network that can consolidate multiple services into a single infrastructure.

At the heart of SDN is the controller, which acts as the brain of the network. It can facilitate communication between application programming interfaces (APIs) that want to interact with hardware infrastructure and vice versa.

A key advantage of SDN is its programmability. Network administrators can program the network for specific use cases (e.g., database traffic, security policies). In addition, they can define network policies, traffic routing and security measures through software applications that interact with the controller.

SDN is usually composed of three layers—the application layer, the control layer and the infrastructure layer.

Application Layer

The application layer includes network applications that convey information about network behavior and policies. Using northbound APIs, applications and services on this layer can interact with the controller.

Control Layer

The control layer also functions as the network operating system. Thanks to the network controller within this layer, it can manage the flow of data and traffic. More importantly, it allows software applications (in the application layer) and network devices (in the infrastructure layer) to interact. Since SDN controllers can monitor data packets and send instructions about their destination, there are minimal issues when data packets move across the network.

Besides communication between the top and bottom layers, the control layer consists of essential core services for host tracking, inventory service and topology service. Host tracking can help determine the IP addresses and locations of hosts. Meanwhile, the inventory service can track all SDN devices in the network.

Infrastructure Layer

The infrastructure layer is composed of physical or virtual network infrastructure. It includes network devices such as routers, switches and other network elements that forward data.

Using southbound APIs, network devices in this layer can receive instructions from the controller. OpenFlow is the most popular protocol that lets the controller instruct switches and routers. Established by the Open Networking Foundation, it enabled the standardization of the protocol and other SDN technologies.

All these layers combined allow organizations to streamline their network. A centralized entity, the controller, sends instructions to devices on the infrastructure layer to forward network traffic. At the same time, applications send standard HTTP calls conveyed to the controller to collect information on direct traffic within the network.

Let’s take a look at the benefits of software-defined networking.

• Centralized management: The SDN controller facilitates efficient management and control of network resources. Network administrators can configure, monitor and troubleshoot the entire network from a central point, leading to improved efficiency, faster troubleshooting and efficient policy enforcement.
• Flexibility and Agility: Network administrators can easily define and modify network policies, routing rules and security measures through a software-based control layer. As a result, SDN can quickly adapt to changing business needs and application requirements.
• Scalability: Organizations can program the network infrastructure based on their specific needs, making it easier to scale it as needed. Developers can integrate new applications, services and functions within the network ecosystem. It allows for efficient resource utilization and better allocation of network resources based on real-time demands.
• Security: SDN allows for dynamic control over network security policies. IT staff can easily enforce security measures such as access control and firewall rules, and intrusion detection can be easily implemented across the entire network from a centralized point. Furthermore, it’s easy to integrate security applications and services for real-time threat detection, rapid response to security incidents and enhanced overall network security.

Here’s a look at the main types of software-defined networking (SDN):

Open SDN

Open SDN uses open-source technologies to implement the SDN ecosystem. OpenFlow protocol is often used to control the communication between the controller and the physical and virtual devices on the data plane.

This protocol thrives in an environment that fosters community and collaboration. Projects in this space often have active communities of developers, network operators and vendors working together to improve and enhance the technology.

Examples of popular open-source SDN projects include OpenDaylight, ONOS (Open Network Operating System) and Open vSwitch. These projects provide open-source SDN controllers, libraries and tools that facilitate SDN solutions’ development, deployment and customization.

API SDN

While Open SDN leverages open protocols, API SDN uses application programming interfaces (APIs) to control the movement of data on the network. APIs provide the means to program the behavior of the SDN controller and network devices. It includes defining forwarding rules, traffic policies, security measures and Quality of Service (QoS) parameters.

API SDN supports the integration of SDN infrastructure with cloud management frameworks, orchestration platforms or network management systems. Thanks to these integrations, network services and resources are managed and orchestrated.

Hybrid Model SDN

Hybrid Model SDN combines the elements of software-defined networking with traditional networking protocols. For instance, network administrators can program the SDN control plane to handle select traffic flows while standard networking protocols manage other traffic flows on the network. It also leverages networking technologies such as Ethernet, MPLS, VPNs and more to connect multiple locations and workers.

This SDN type is characterized by multiple domains or regions. Each domain may have its controller. These distributed controllers operate autonomously and make decisions based on local network conditions. Despite multiple controllers, there are mechanisms in place to ensure the requirements of each location are met, and policy consistency across domains.

SDN Overlay

SDN overlay refers to a networking approach that creates a virtual overlay on top of an existing physical network infrastructure. By establishing a virtual connection between two endpoints, the SDN can have multiple secure overlays using software on top of existing networking hardware infrastructure. Endpoints can be software addresses in the networking cloud or physical locations such as a network port.

As with most SDN, the overlay network has an SDN controller, which controls the behavior and routing of the virtual network. VN configurations dictate higher-level policies, while the underlying physical networks handle the forwarding of packets.

As its foundation, traditional networking relies on dedicated network devices—such as switches, firewalls and routers. Each device has a specific role that helps fulfill the control and data plane functions. Along with an SDN, a traditional network can forward traffic, implement protocols and enforce security policies. However, each device makes individual decisions based on local configurations.

While traditional networking has been the predominant approach, it has certain limitations. Control mechanisms are often decentralized. Devices operate independently and lack awareness on the network’s status. Traditional networking devices also have limited programmability and require manual updates to accommodate changes in business needs or security requirements.

Unlike a traditional network, SDN enables centralized control and management of the network. Network administrators can dynamically configure and control the behavior of the network through a software-based controller. In addition, open APIs (application programming interfaces) allow administrators and developers to customize and automate network behavior.

Modern-day SDN technologies emerged as a response to the limitations of traditional networking. It introduced centralized control, programmability and dynamic management of network resources, making it the better option for network architecture.