How NAC Works

By Larry Seltzer  |  Posted 2004-04-21 Print this article Print

There are two main parts to NAC, the first being a piece of software that runs on the client (or, more generally, "endpoint," because it could be a server, too, or something unconventional) called the Cisco Trust Agent or CTA. At the back end is a policy management system called the Cisco Access Control Server (ACS). Cisco gives away the CTA, and the ACS is already widely used for various 802.1x-based authentication functions.

Cisco approached the big client security companies (Symantec Corp., Trend Micro Inc., Network Associates Inc.s McAfee Security) and got their cooperation. These three probably constitute more than 90 percent of the corporate antivirus market.

The protocol between the CTA and client software allows it to check the status not only of the antivirus software and definitions, but also firewalls and the operating system version and patches. Depending on what is found, the administrator can set policies to lock out the user or place them in a restrictive environment.

King says Cisco could open up the APIs for communication between the client software and the CTA, as well as the APIs between the ACS and other vendors policy managers, and that would be great. If they opened up the protocols between the CTA and the ACS, that would be even better, although I can see why Cisco would hesitate to do it, since it would open up the possibility of third-party implementations of NAC.

Consider that if NAC caught on, there would be a lot of pressure for a built-in Linux client; lots of people would want this to be a source code version. Cisco is still deciding on how to proceed; I think it would do well to be aggressive in opening it up. It would accelerate general acceptance of the system, and that would only be good for Cisco, which plans to put NAC in everything from routers and switches to wireless access points.

Eventually Id even like to see ISPs implement something like this. Id pay extra for an ISP that did have such rules, but I wouldnt put any money down that they will. ISPs seem loath to lose even their infected customers.

Its true that new attacks come along, and NAC wouldnt be able to stop most of them, but the vast majority of the problem out there comes from old attacks, or at least from those detected by the current definitions of any major AV product. With NAC or something like it in place, networks will be able to defend themselves against users who dont know enough to protect themselves.

Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983. Check out eWEEK.coms Security Center at for security news, views and analysis. Be sure to add our security news feed to your RSS newsreader or My Yahoo page:   More from Larry Seltzer

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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