2013 is the year that software-defined networking gets its early installations, having gone through product trials and technology evolution over the past several years. Now, as vendors roll out their SDN networking offerings and companies start the buying process, the question for many is: “How can I best use this technology in my network?”


Network use cases, in fact, were one of the most asked for items at the Gartner Data Center Summit meeting my colleague Gary Lee went to in December 2012. In order to give a sense of what problems SDN can solve in your network I am starting a series of blog posts on key SDN use cases, starting with network virtualization.


First, let’s discuss server virtualization, which has helped to power cloud services by allowing data centers to scale computing power at a lower cost. Server virtualization dramatically reduces the cost of computing services and allows multiple customers to leverage a single server. Both server virtualization and SDN are tied in terms of being high-profile solutions that can have dramatic impact on a data center.


Network virtualization logically divides a 10GB Ethernet connection into multiple lower speed connections so that each virtual machine in a server can have its own dedicated connection without requiring a separate NIC and cable.


In an IP network, this is done using virtual LANs, but that doesn’t scale well across a heterogeneous network unless each vendor supports the same VLAN protocols. By replacing the per-switch IP decision making with a central SDN controller over the entire network, virtualized network connections can be more easily made from one end of the network to the other.




How does this work? In the diagram, the three virtual networks are shown in their logical grouping, but below that we see how the actual switching infrastructure is organized to make this happen. Top-of-rack switches have connections to virtual machines located in the different servers. The connections through the physical infrastructure are guided by the SDN controller. The controller must map the logical network connections to the physical network across all of the switches. This is a very complex state-management task that SDN is particularly good at.


Going forward, as server connections increase from 10GB Ethernet to 40GB Ethernet, there will be even more headroom for virtualized network connections, making for dramatically complex network designs. But SDN is intended to simplify that complexity, so that all cloud networks can use this technology to maximize their networking investment.