What’s Software-Defined Networking (SDN)?

Interested in learning more about Software-defined Networking (SDN)? Check out our SDN Topic page. It's filled with current SDN articles, white papers, videos and other resources curated by experts on SDNCentral.

Interested in learning more about Software-defined Networking (SDN)? Check out our SDN Topic page. It’s filled with current SDN articles, white papers, videos and other resources curated by experts on SDNCentral.

Software-defined networking (SDN) is a new approach to designing, building, and managing networks that separates the network’s control (brains) and forwarding (muscle) planes to better optimize each.

How Does SDN or Software Defined Networking Work?

SDN providers offer a wide selection of competing architectures, but at its most simple, the SDN method centralizes control of the network by separating the control logic to off-device computer resources. All SDN models have some version of an SDN Controller, as well as southbound APIs and northbound APIs:

  • Controllers: The “brains” of the network, SDN Controllers offer a centralized view of the overall network, and enable network administrators to dictate to the underlying systems (like switches and routers) how the forwarding plane should handle network traffic.
  • Southbound APIs: SDN uses southbound APIs to relay information to the switches and routers “below.” OpenFlow, considered the first standard in SDN, was the original southbound API and remains as one of the most common protocols. Despite some considering OpenFlow and SDN to be one in the same, OpenFlow is merely one piece of the bigger SDN landscape.
  • Northbound APIs: SDN uses northbound APIs to communicates with the applications and business logic “above.” These help network administrators to programmatically shape traffic and deploy services.

The SDN Framework

SDN Framework

SDN is Not OpenFlow

Often people point to OpenFlow as being synonymous with SDN, but it is only a single element in the overall SDN architecture. OpenFlow is an open standard for a communications protocol that enables the control plane to interact with the forwarding plane. It must be noted that OpenFlow is not the only protocol available or in development for SDN.

The Benefits of SDN

Offering a centralized, programmable network that can dynamically provision so as to address the changing needs of businesses, SDN also provides the following benefits:

  • Reduce CapEx: SDN potentially limits the need to purchase purpose-built, ASIC-based networking hardware, and instead supports pay-as-you-grow models
  • Reduce OpEX: SDN enables algorithmic control of the network of network elements (such as hardware or software switches / routers that are increasingly programmable, making it easier to design, deploy, manage, and scale networks. The ability to automate provisioning and orchestration optimizes service availability and reliability by reducing overall management time and the chance for human error.
  • Deliver Agility and Flexibility: SDN helps organizations rapidly deploy new applications, services, and infrastructure to quickly meet changing business goals and objectives.
  • Enable Innovation: SDN enables organizations to create new types of applications, services, and business models that can offer new revenue streams and more value from the network.

Why SDN Now?

Social media, mobile devices, and cloud computing are pushing traditional networks to their limits. Compute and storage have benefited from incredible innovations in virtualization and automation, but those benefits are constrained by limitations in the network. Administrators may spin up new compute and storage instances in minutes, only to be held up for weeks by rigid and oftentimes manual network operations.

SDN has the potential to revolutionize legacy data centers by providing a flexible way to control the network so it can function more like the virtualized versions of compute and storage today.

SDN Use Cases

As detailed above, SDN offers several benefits for businesses trying to move into a virtual environment. There are a multitude of use cases that SDN offers for different organizations, including carrier and service providers, cloud and data centers, as well as enterprise campuses.

For carrier and service providers, SDN offers bandwidth on demand, which gives controls on carrier links to request additional bandwidth when necessary, as well as WAN optimization and bandwidth calendaring. For cloud and data centers, network virtualization for multi-tenants is an important use case as it offers better utilization of resources and faster turnaround times for creating a segregated network. Enterprise campuses experience network access control and network monitoring when using SDN policies.

Additional Software Defined-Networking Resources:

2015 SDN & NFV Market Size and Forecast Report

Programmability of SDN Networks

Security Challenges in SDN Environments

SDN, NFV and Network Virtualization Defines the Wave of New IP

Which is Better — SDN or NFV?

What is an OpenFlow Controller?

What is the OpenDaylight Project?