SDN stands for “Software Defined Network”, a simple name with thousands of different meanings. As defined by WikiPedia “SDN separates the control plane from the data plane in network switches and routers. Under SDN, the control plane is implemented in software in servers separate from the network equipment and the data plane is implemented in commodity network equipment.”
The most important aspect of SDN is the separation of the control and data planes. This decoupling allows end users (Service Providers, Enterprises) to use commodity hardware to build and expand their networks.
Some of the major players in the SDN space are Vyatta, Cisco, Big Switch and Nicira. Nicira was recently purchased by VMWare and is being merged into VMWares core product offerings.
Vyatta offers a Quagga based software router with firewall and VPN support. I recently talked with Vyatta and found their vision and commitment to the Open Source community great. Vyatta is currently the top player when it comes to software defined routers.
Cisco offers many of the parts needed to create SDNs but some parts have not been released yet. Cisco has released the Nexus 1000v software switch, the ASA 1000v software firewall and has announced the CSR 1000v IOS XE based software router. Once Cisco gets the full solution out, they have a chance to leapfrog over the competition due to their history and ability to re-use their current software features.
Big Switch offers an SDN Controller. Currently they are offering Floodlight, a Open Source version of their product with promises of a commercial version coming soon.
The last company I will cover is Nicira. Nicira provides what they call NVP, or the Nicira Virtualization Platform. They combine their software with the Open Source OpenVSwitch to provide a fully software controlled and forwarded network.