The good news for the NAC appliance vendors is that the successful ones will make a lot more sales this year. The bad news is they’re not starting off with much.

“Most vendors will double their revenue 2006 to 2007,” says Jeff Wilson, principal analyst for network security at Infonetics Research, who recently completed his report, "NAC Enforcement Appliances." He puts growth at a conservative 105% from year to year starting with $83 million last year.

He says the vendors he has talked to claim it takes less time to complete sales as customers already know something about NAC before they come into contact with NAC vendors. Earlier, the customers needed more education about the gear, he says.

He says announcements that Cisco and Microsoft NAC gear can interoperate helped, as did Microsoft’s announcement that it's NAC (which Microsoft calls NAP) client-server protocol will be contributed to Trusted Computing Group as a standard. “Enterprises wanted someone to tell them there was a [readily available] NAC client there before they’d buy an appliance,” Wilson says.

The equipment Wilson is talking about are appliances that get installed in existing networks and enforce policy decisions about network access that are based on how healthy a machine looks based on a scan. It does not include network switches, which can be used as enforcement points, or back-end policy servers that might be tapped as part of the decision-making process.

If doubling revenue this year looks good, the next three years look pretty good, too. According to Infonetics’ projections, vendors will sell $629 million in NAC enforcement appliances in 2010. “I think three-quarters of a billion dollars in 2010 is nothing to sneeze at,” Wilson says.

Tim Greene is senior editor at Network World.