NAC pioneer ConSentry Networks is the latest company to bite the dust. 

Employees at the company were told about the closure today and were cleaning out their offices, said Mario Nemirovsky, the founder and chief scientist for the company. "This is a sad day," he says.

Nemiriovsky said he had no information about what would happen to customers with support contracts. "Hopefully they will get support," he says. Nobody else on the company's management team was answering the phone. Several of their voicemail boxes were full, and there was no live receptionist answering the main line.

ConSentry joins a growing list of NAC vendors that have either been bought, folded or changed direction since the concept of the technology came on the scene in 2003. Lockdown Networks and Cayman Systems folded and Mirage Networks was bought earlier this year by security service provider TrustWave. Vernier Networks changed its name to Autonomic Networks. Nortel has a NAC offering that is tied up in the company's bankruptcy proceedings.

ConSentry started out selling NAC gear, but it was embedded in intelligent switches, and over time the company altered its marketing pitch to highlight other functionality. It talked about user and application control, but the company faced an uphill battle against all the major switching vendors.

In order to buy into ConSentry, customers had to be willing to substitute ConSentry switches for legacy switches or install an extra layer of switches to distribute ConSentry's access controls to legacy access switches. 

Initially NAC was sold as an appliance that was added to existing networks to check whether devices signing onto networks passed a health check. Over time, vendors such as Cisco, Juniper and Enterasys incorporated NAC in their network devices, making it tougher for the dedicated NAC providers to make inroads.

NAC also expanded to include monitoring of devices once they were admitted to the network to make sure they weren't exhibiting behavior that violated their access rights.