Server virtualization is now a proven practice, creating a cost-effective means of allocating compute resources to changing user and application requirements. But when packets leave the server, they still pass through a traditional switching architecture, which doesn't have that same level of flexibility.
The goal of software-defined networking (SDN) is to bring the benefits of virtualization--shared resources, user customization, and fast adaptation--to the switched network. SDN puts the "intelligence" of the network into a controller or hierarchy of controllers in which switching paths are centrally calculated based on IT-defined parameters, and then downloaded to the distributed switching architecture.
The cost savings are apparent. The expensive part of a high-end switch is the sophisticated control plane and custom silicon. By moving the control plane to a centralized controller, the architecture can use inexpensive commodity switches built with standard silicon. Reducing the cost of each switch by 70% or more, spread across a data center or campus, quickly adds up to real money.
SDN is also about improving performance. A centralized control plane lets companies customize their networks without depending on or coordinating different vendor operating systems. Networking pros can quickly change what data types get forwarding priority, as business requirements change.
The first step toward SDN is to define a messaging protocol between the controller and the individual switches making up the forwarding plane. This is where the emerging OpenFlow networking standard comes in. OpenFlow enables open, virtualized, and programmable networks. Each of these elements is key.
Open: The standardized instruction set means any OpenFlow controller can send a common set of instructions to any OpenFlow-enabled switch, regardless of the vendor.
Virtualized: IT can specify different forwarding rules for different data types, creating multiple logical forwarding paths over the same physical network, depending on the needs of a particular app.
Programmable: The still-evolving OpenFlow instruction set lets IT create rule sets that work in combination with a switch vendor's configuration options, or independent of them. With its roots in academic research networks, OpenFlow lets users try new ideas or create new protocols independent of any vendor. Most important, IT can program a network for specific application requirements.
This report includes additional analysis, an in-depth tutorial on the OpenFlow protocol, and seven diagrams illustrating software-defined networks.