Submission + - OpenFlow takes networks in a different direction (theregister.co.uk)
Then along came virtualisation and suddenly we’re back out into the weeds. In a fully virtualised datacenter, any workload can be located on any physical server inside any rack. Not only that, but these workloads move.
To see how an OpenFlow switch might work in a real environment, we have to look at how these rules might be applied.
A switch sees a frame from MAC address A destined for MAC address B. The central configuration server is aware of which MAC addresses live on which ports of which switches across the entire fabric. The server is also aware of link states for every connection, as well as throughput statistics per port.
Since the central database is aware of all this, so too are the individual switches. The best route between the source switch and the destination switch is computed and the frame is forwarded.
Should a link anywhere in the switching fabric become saturated or a cable become unplugged, the central database is made aware of it. The information is quickly disseminated throughout the fabric, and new paths for packets can then be computed as required. This provides high availability with fast convergence.