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SDN and network virtualization: A reality check

Jim Metzler | Sept. 10, 2014
The Software Defined Networking movement is still evolving, but profiles of SDN users are becoming more clear and we're getting a bead on some of the common evaluation criteria companies are using to gauge how to go forward. We also have a sense of when companies expect to start the process in earnest.

It is likely, however, that these very large enterprise shops will drive the adoption of SDN in the short- to mid-term.  In fact, given the amount of attention some of these financial firms have paid to SDN, it is a safe bet that some will start to deploy SDN in production networks sometime in 2015. 

The remaining class of potential SDN consumers: everybody else companies of all sizes and in virtually all industries.  Market research suggests this class of consumer has deployed very little SDN to date. I was the keynote speaker at the recent Network World Open Network Exchange (ONX) conference in Chicago and tested that belief by asking the 200 attendees how many had at least a modest SDN implementation. Only a handful of hands went up. 

Evaluation criteria

Given  the great interest in SDN but lack of deployment, here are some key criteria you can use to begin the basic job of evaluating SDN options.

The key (and most obvious) criteria is to identify the problem or problems IT is attempting to solve. For example, if IT wants to support the dynamic movement of workloads, than a network virtualization overlay is worth considering for. (See a description of the differences between the approaches.) However, this approach can't help IT respond to some other challenges, such as being able to centralize the provisioning of physical switches and routers. 

Other important criteria to consider is the role of hardware vs. software, and the degree to which control is centralized. VMware has been quite clear that it doesn't see a role for specialized hardware in the data center.  Cisco is on the other side of this discussion due to the fact that, as noted, ACI uses specialized hardware.

Regarding where the network control functions should be located, the majority of SDN solutions are based on centralizing control. An exception to that is Cisco's ACI, which leaves some control functionality in the switches and routers. 

The best way for IT organizations to use these two criteria to evaluate SDN solutions is to ask the vendors for the rationale behind how they designed their solutions. For example, what are the advantages of having specialized hardware other than increased performance?  How do IT organizations balance the fact that centralizing control simplifies the management of the switches and routers, but may result in a performance bottleneck?

A key criterion for evaluating any solution, but particularly a solution based on centralized control, is scalability. It is important to understand how many flow set-ups per second a solution can realistically support and how that changes if, instead of a single controller, there is a cluster of controllers.  It is also important to understand how many switches and routers a solution can realistically support. 


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