Cisco's unveiling of its Application-Centric Infrastructure (ACI) strategy and plans for its Insieme Networks "spin-in" has raised some core questions for all those interested in the software-defined networking (SDN) debate: Can, or even should, the theory of pure SDN be put into practice?

I won't go into the details of what Cisco Systems Inc. is doing -- my colleague Dan O'Shea has done an admirable job on that front already. (See Cisco's ACI Gets Physical With SDN.)

What is more interesting is whether Cisco's hardware-centric approach -- even if it is driven by an inevitable protectionist streak -- is the one that will, ultimately, make most sense for network operators. Because the debate really isn't about whether this is a SDN play or not. And it isn't just about whether Cisco is looking to lock customers into its technology, though of course that is a major issue and talking point.

The key debate is whether network decision-makers will weigh up their options and decide they are more happy with what Cisco has to offer compared with the alternatives. And this isn't a straightforward issue: Such decisions will be based on personal experiences, finances, skill sets, perceptions, prejudices, and all the other criteria that come into play when human beings (flawed, complex and often unpredictable as we all are) are involved. Only the other week I heard a senior executive from a major mobile operator say that he didn't care if the next-generation technology he was sourcing for his advanced 4G network was proprietary or not -- he just wants it to work.

So maybe the big question, then, is: Will the majority of network operators of any type (datacenter, wide area network, or both) bet their future on conformance to the emerging SDN specifications, standards, and models that are based on open source software and generic hardware?

Cisco, it seems, is betting that enough of them won't walk away from the IP giant with the sometimes intimidating reputation.

Of course, the Cisco pitch was always going to attract criticism. And given that Cisco has said its proposition will only work to optimum performance levels if its hardware (rather than any third-party gear) is deployed, it would be shocking if there wasn't some sort of outburst from the SDN community.

One of Cisco's main rivals, HP Inc. (NYSE: HPQ), was pretty quick to issue a statement attacking the router giant's strategy. The "Insieme ACI poorly addresses market needs" because it is "incompatible and complex," claims HP. "ACI is incompatible with existing Nexus products, and ACI doesn't allow for inevitable migration or provide customer investment protection... Cisco is limiting customers' access to the benefits promised by SDN by locking them into a proprietary and Cisco-only architecture." It concludes that Cisco is "trying to defy the SDN movement with hardware-defined proprietary infrastructure."

Naturally, HP goes on to explain how its OpenFlow 1.3-enabled switches provide "the benefits promised by SDN now."

Here's an alternative, and more neutral, perspective from David Krozier, a telecom network infrastructure principal analyst at Ovum Ltd. .

If you hear someone say "Better the devil you know" in networking circles in the coming months, those uttering that phrase might just be talking about Cisco's ACI.

— Ray Le Maistre, Editor-in-Chief, Light Reading