"The end of the Cisco relationship" is the quip Zeus Kerravala, analyst with ZK Research, gave me over Twitter.

That's his response to Monday's announcement, at VMworld, of VMware's NSX — specifically, the opening-up of NSX, giving switch vendors a way to connect their physical network gear with the virtual switches populating the data center. It's being presented at VMworld with an air of unity and of everybody being friends, and as a major step toward VMware's dream of the software-defined data center (SDDC).

But it's also a step toward a software-defined networking (SDN) world that could mean major change for equipment vendors.

All of them, especially Cisco, contend SDN and network virtualization are more opportunity than threat. But this kind of transition also opens the chance for an outsider to stroll into the party and turn heads. That's the role I think VMware is primed for, but I'm holding back the hyperbole after a short conversation with Martin Casado last week.

VMware's language certainly hints at conflict. It's exaggerated press-release language, sure, but still bold: NSX "will help position VMware to do for networking what it did for compute," reads the media briefing sheet.

That can sound intimidating when you think about VMware's influence on the computing side. During his keynote kicking off VMworld Monday, CEO Pat Gelsinger (pictured above) said VMware is nowhere close to saturation — because the goal is literal 100 percent coverage. "We're not done until every application, every mission-critical application, every physical server, is replaced by a virtual server," he said. And now he wants VMware to work on the network.

Casado, VMware's chief network architect and a founder of Nicira, doesn't hold back with his language either. But he's got a way of describing VMware's networking goals that sounds less threatening to the equipment makers.

"VMware made its name as a hypervisor — that's ESX — a thin layer of software" between the network and the server, he told me. "We want to do the same thing for the network. We won't sell network hardware. We want to be a thin software layer."

This time, that layer sits between the network hardware and the applications. "My goal is to change network operations, by providing an abstraction" while still letting operators keep their F5 and Citrix toys, Casado said.

The key word there is "operations," and it's going to be the focus of Casado's VMworld session on Tuesday.

Coincidentally, I just heard Tom Edsall, CTO of Insieme, complaining about the lack of these things — the lack of debugging tools that can keep pace with the SDDC. Casado is going to shine a ray of hope on that concern.

"The level of information you can pull from these systems is more than anything we've ever been able to do," Casado said: knowing when something happened or what virtual networks it affected, for example — and being able to find these things out in real time. "Networks have never had the correct interfaces to pull information in an interesting manner."

So, for the moment, it's more about management than about driving hardware businesses into the ground. That still doesn't mean everything is cool between VMware and Cisco. The "thin layer of software" is something Cisco certainly wants to do itself — hence, the Cisco Open Network Environment (ONE) — and won't want to concede.

I'm willing to play along with the theory that VMware isn't (yet) out to make proprietary switches irrelevent, but I'm still having trouble seeing how VMware and Cisco can remain friends in the long run.