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What is 'real SDN'?

Networking pros continue to argue about what 'real SDN' is. Here is a breakdown of the major SDN categories that exist in research and real-world environments.

Long ago, there was a TV show called "To Tell the Truth," where three contestants pretended to be a specific individual, and a panel of judges would try to guess which one was the "real" individual. We've been in this situation for a while now with respect to SDN, with individuals, organizations and vendors arguing about what real SDN is.

In my opinion, it's too late for that discussion, because the proverbial cat (or cats, in this case) is (or are) out of the bag. A better approach may be to come up with some solid definitions of the major categories of SDN that exist today in research institutions as well as in real-world environments. These might be those categories:

Open SDN. The classic, traditional, original SDN, which emerged from educational institutions, focused on separation of the control and data planes and using OpenFlow for communication between the controller and simpler, less expensive devices.

This category is most popular with research institutions, the Open Networking Foundation and certain vendors that are interested in major disruption to the networking landscape with products such as white-box switches.

API-based SDN. This is the response by networking vendors. It involves a centralized controller with an open API that allows applications to manage and manipulate the behavior of the network. These APIs can exist in basic form at the controller, or at a higher-level policy abstraction on top of the controller. APIs could even exist on the devices themselves.

This category is most popular with established networking vendors that are interested in either minimizing disruption to the networking landscape; preserving existing customer investments; or protecting their bottom line, depending on your personal bias.

Overlay-based SDN. This is the prevalent solution in data centers, overcoming networking limitations related to multi-tenancy and mac-table exhaustion by using tunneling technologies to run virtual networks across the top of existing physical networks.

Overlay-based SDN is most popular with data center virtualization vendors that are tired of waiting for simple and effective network virtualization solutions to be provided by established networking vendors.

So then, which is the real SDN? That depends on whom you ask -- but based on current usage by the population at large, they all are. Since we purists have lost that battle of the name itself, perhaps it is best to understand and articulate what each different type or category of SDN is talking about, which issues each addresses, and who the main proponents of each type are. Hopefully this discussion provides some assistance towards that end.

This was last published in October 2014

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