Software Defined Networking (SDN): Definition

The Software-Defined Networking (SDN) approach to network architecture has been steadily gaining ground. More and more companies are designing their network infrastructure with this approach in mind. The increasing popularity of software-defined networking across a variety of industries shows how important this technology has become for global businesses. 

What is Software-Defined Networking (SDN)?

Software-Defined Networking (SDN) is an approach to networking that uses software-based controllers or application programming interfaces (APIs) to communicate with underlying hardware infrastructure and direct traffic on a network.

This model differs from that of traditional networks, which use dedicated hardware devices (i.e., routers and switches) to control network traffic. SDN can create and control a virtual network – or control traditional hardware – via software.

While network virtualization allows organizations to segment different virtual networks within a single physical network, or to connect devices on different physical networks to create a single virtual network, software-defined networking enables a new way of controlling the routing of data packets through a centralized server.

How does it work?

In software-defined networking, a software application controller manages the network and its activities. Instead of using hardware to support network services, SDN allows network administrators to virtualize physical network connectivity.

This network virtualization is made up of three layers—the application layer, the control layer, and the infrastructure layer—connected through northbound and southbound APIs.

The application layer includes a set of applications and network functions that help improve application performance, simplify IT, and increase security. Examples include application firewalls, wide-area network (WAN) optimization controllers (WOCs), load balancing, authentication, and application delivery controllers (ADCs). Traditional networks use a specialized appliance for these functions, while a software-defined network uses the controller to manage data-plane behavior. The application layer contains programs that communicate specific network instructions to the SDN controller.

The control layer manages policies and the flow of traffic throughout the network. It consists of the SDN controller, which connects the application layer to the infrastructure layer. This layer processes the requirements sent by the application layer via the southbound API and then passes them on to the actual network infrastructure via the northbound API. It also communicates information extracted from the infrastructure layer back to the application layer to optimize functionality.

The infrastructure layer contains the network’s physical switches and routers in the data center. These network devices control important forwarding functions and data processing capabilities and are responsible for collecting critical information – such as network usage and topology – to send back to the control layer.

Benefits of Software-Defined Networking (SDN)

Many of today’s services and applications, especially when they involve the cloud, could not function without SDN. SDN allows data to move easily between distributed locations, which is critical for cloud applications.

Additionally, SDN supports moving workloads around a network quickly. For instance, dividing a virtual network into sections, using a technique called network functions virtualization (NFV), allows telecommunications providers to move customer services to less expensive servers or even to the customer’s servers. Service providers can use a virtual network infrastructure to shift workloads from private to public cloud infrastructures as necessary and to make new customer services available instantly. SDN also makes it easier for any network to flex and scale as network administrators add or remove virtual machines, whether those machines are on-premises or in the cloud.

Finally, because of the speed and flexibility offered by SDN, it can support emerging trends and technologies such as edge computing and the Internet of Things, which require transferring data quickly and easily between remote sites.

Why is Software-defined Networking useful?

There are many benefits of software-defined networking (SDN) architecture, several of which stem from the centralization of network control and management as well as the ease of scalability, evolution, and change implementation. Some of the benefits are as follows:

• Ease of network control via direct programming resulting from the separation from forwarding functions.
• Agility and the ability to dynamically use load balancing to manage the traffic flow as need and usage fluctuate. This reduces latency, increasing the efficiency of the network.
• The greater granularity of control over security. SDN lets network administrators set policies from one central location to determine access control and security measures across the network by workload type or by network segments. You can also use micro-segmentation to reduce complexity and establish consistency across any network architecture — whether public cloud, private cloud, hybrid cloud, or multi-cloud.
• Ease of configuration. With SDN, automated programs can be more easily written, enabling the organization to configure, secure, and optimize resources as needed.
• Simplified network design and operation through the use of open controllers rather than vendor-specific devices and protocols.
• SDN technology combined with virtual machines and virtualization of networks provides efficiencies to service providers as well. With these resources, they can provide distinct network separation and control to customers. As a result, SDN is modernizing the telecommunications industry. Service providers can improve their flexibility and provide bandwidth on demand to customers who need greater flexibility and have variable bandwidth usage.
  

The risks of software-defined networking

As we have seen, SDN can be beneficial to an organization in many ways, including increased agility and control, simplifying management and configuration, and providing stronger security. The controller is critical in maintaining a secure network. It is centralized and, therefore, a potential single point of failure. This potential vulnerability can be mitigated by implementing controller redundancy on the network with automatic fail-over. This may be costly but is no different from creating redundancy in other areas of the network to ensure business continuity.

What are the challenges of SDN?

Main adopters of Software-defined Networking include service providers, network operators, telecoms, carriers, and large companies, such as Facebook and Google. However, there are still some challenges behind SDN.

• Security: Security is both a benefit and a concern with SDN technology. The centralized SDN controller presents a single point of failure and, if targeted by an attacker, can prove detrimental to the network.
• Unclear definition: Another challenge with SDN is the industry has no established definition of software-defined networking. Different vendors offer various approaches to SDN, ranging from hardware-centric models and virtualization platforms to hyper-converged networking designs and controllerless methods.
• Market confusion: Some networking initiatives are often mistaken for SDN, including white box networking, network disaggregation, network automation, and programmable networking. While SDN can benefit and work with these technologies and processes, it remains a separate technology.
• Slow adoption and costs: SDN technology emerged with a lot of hype around 2011 when it was introduced alongside the OpenFlow protocol. Since then, adoption has been relatively slow, especially among enterprises that have smaller networks and fewer resources. Many enterprises cite the cost of SDN deployment to be a deterring factor.