What are the key things I should be thinking about when evaluating SDN technology?
The biggest thing to understand is that not all SDN solutions are solving the same problem. In addition, different SDN technologies have different expectations of the end user. While some solutions plan to abstract away network and operational complexity by providing you with a glossy solution, other solutions are more of a toolkit that lets you create your own application. Therefore, understanding the problem you're trying to solve at a deep technical level is quite important. The better you communicate your needs to your vendor, the better it will be able to articulate how its solution meets those needs.
Does SDN introduce new security risks to my environment?
While it's hard to say categorically that SDN introduces "new" risks, the fact is that exposing network devices via programmatic interfaces is risk to be managed. That said, SNMP is roughly analogous to programmatic APIs, but has a well defined risk mitigation strategy. In that sense, SDN presents nothing unusually risky. Yes, SDN presents a risk, but it is a risk that IT as a discipline can mitigate via access controls, trusts, encryption, deep packet inspection, etc.
That said, SDN advocates point out that a security benefit of centralized control is the reduction in human touch required to provision the network. On the assumption that human error is the greatest security risk to an IT infrastructure, SDN may actually prove to be a security asset.
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