OpenFlow® and SDN, Overlays and Pure OpenFlow, Hardware vs Software Switching
The explosion of interest in the industry on Software-Defined Networking reveals a genuine interest to provide the benefits of SDN to the commercial market, and the vendor responses to the opportunity reflect the variety of approaches we have come to expect. But they also give ONF the opportunity to reinforce the original motivation behind this movement: to bring software programmability to networks worldwide and to change how those networks operate.
As an organization driven by users, ONF strives for standardized approaches that allow users to govern the operation of their networks according to their business objectives. Many in our industry talk about the importance of open standards, but our 80+ member companies are standing behind a non-profit entity designed to further innovation in SDN as a whole. The reality is that in the context of SDN, OpenFlow® is the standard. It is the only standard that abstracts the network's switching infrastructure for software control by users and their agents. While many are doing comparisons of SDN to data network virtualization, it should also be said that SDN is an architecture for delivering networking applications. Data center network virtualization is just one example of one of many things you can do with SDN.
In taking a deeper look at SDN, ONF is the first to say that there is much more to SDN than OpenFlow. However, we are also quick to point out that OpenFlow® is a building block for SDN and much of the value of SDN is lost when it is not built on an OpenFlow® substrate. That value is the ability to create a global viewpoint and a consistent, system-wide programming interface. Most non-OpenFlow-based SDN solutions we see from vendors employ proprietary protocols.
Among the approaches that users have adopted to deploy OpenFlow® and SDN are overlays and pure OpenFlow® networks. With overlays, portions of a legacy network are wrapped with OpenFlow-controlled switches, which tunnel through the legacy portions. This approach can provide a useful and widely accessible first step toward a pure OpenFlow® network, which of course brings the benefits of abstraction and software control to the entire network, not just the wrapper. I have seen users deploy both pure OpenFlow® in green-field buildouts and overlays in legacy portions.
In both overlay and pure incarnations, OpenFlow® is equally beneficial in both hardware and software switches, including virtual switches. With virtual switches (vswitches), traffic between virtual machines in the same server need not travel out actual physical ports. An OpenFlow® controller can itself reside in one of the virtual machines and can talk to a vswitch in the same server, vswitches in other servers, single-thread software switches at the edge, or hardware switches. Thus, an operator's choice of server structure, switching technology, virtualization approach, and pure or overlay deployment does not affect the choice of using OpenFlow, which brings benefits – including multivendor support because it is a standard – to every scenario that no other technology does. ONF's commitment to network users everywhere underscores our passion for ongoing innovation in SDN and standards where they are needed, as they are here.