They are using it for network virtualization for private cloud buildouts to extend beyond the limits of virtual LANs, which top out at 4,096. Once those private clouds are implemented, enterprises then look for more business critical applications for OpenFlow and SDNs, like data center interconnect, disaster recovery and granular security.
"There are all these requirements on the application for the private cloud 2.0 and that's where, on the network side, the VLAN architecture really starts to break," Forster says.
Even before enterprises implement private cloud, data center network virtualization is some low hanging fruit for OpenFlow and SDNs, Forster says. Server virtualization across eight to 30 racks, with 200 to 2,000 VMs per rack, usually breaks the VLAN limit and opens up an opportunity for SDNs.
"That's the end of the all VLANs everywhere path," he says.
But OpenFlow and SDNs are not network virtualization, per se; they are network construction tools to facilitate network virtualization, which is really a "solution" built on top of an SDN foundation, says Martin Casado, co-founder and CTO of network virtualization start-up Nicira.
Casado was also one of the chief developers of the OpenFlow protocol and API.
"The enterprise use case motivated the work that I did that became OpenFlow and grew into this SDN mania," Casado says. "Within the business enterprise, there has long been requirements for security, for isolation and for service interposition. How do you build an enterprise network that allows for security and isolation, with simplified operations and service interposition?"
Casado believes network virtualization brings these attributes to enterprise networks. But whether or not those virtualized networks are built using OpenFlow and SDNs is irrelevant to the user, he says.
"Traditionally, OpenFlow does not do network virtualization," Casado says. "All OpenFlow does is allow you to control switches and it may allow you to run different applications on the switch. But it doesn't provide you the ability to create a virtual network that's topology independent that supports L2 and L3. I don't know of any OpenFlow solution that does this.