“We have enterprises with thousands of virtual machines, and they don’t have sprawl,” Litkey said. “They’re very disciplined, they do a lot of planning, and they have a lot of processes.”

The biggest hurdle may be politics, which George Pradel called the “eighth layer” of the network stack. Pradel, director of strategic alliances, said enterprises have to set policies that virtual machines will be shut off or decommissioned if they are not in use for a certain amount of time. Without planning, virtual server sprawl will get out of control, he said.

“If you are investing in some type of virtualization and you haven’t [experienced sprawl] yet, you will,” he said.

Interop attendees are embracing virtualization in a big way. An of 120 network engineers and IT managers and executives found that 55% have virtualized mission-critical servers. But virtualization caused more problems than benefits for greater than half of the respondents. The survey was conducted by Network Instruments.

Sprawl is one of the most common problems related to virtualization, said Anne Skamarock, who moderated the sprawl panel and is research director for Focus, an IT consulting firm. Nonfunctioning virtual machines still take up memory and space, and must be controlled, she noted.