Blocking Insecure Network Clients

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

You can have the finest perimeter security around, but if someone connects an insecure client inside your network, you've got a big problem. The Cisco Network Admission Control Program could help, and it's not the only system for qualifying clients before

One of the problems I hear about all the time, from analysts and vendors alike, is that of rogue mobile clients. Youve got perimeter defenses on your corporate network worthy of the Maginot Line, but mobile users can still travel, connect to the Internet on the road, pick up a germ on their notebook and release it when they log back in at the office. There are many products and good practices to prevent this, but one of the trends I see developing is that of qualifying clients to connect to the network. When attempting to connect, the client is first queried for whether it meets any of a number of security parameters: Is it running a recent version of antivirus software? Are the definitions up to date? A firewall? Are critical Windows patches applied?

Ive seen this approach taken by a number of vendors, usually with a proprietary approach. The Symantec Series 300 small business security appliances can be set to enforce use of most Symantec antivirus clients. Another appliance vendor Ive been talking with has similar support for McAfees clients in beta.

But the most interesting and comprehensive approach to this is the Cisco Network Admission Control program (NAC). Its still not exactly clear what NAC will turn out to be, but at a minimum it will be a powerful tool for Cisco customers. Taken all the way, it could turn into a general framework for client security policy enforcement. It all depends on how much Cisco decides to open up.

I talked to David King, a director in Ciscos VPN and security business, about NAC. According to King, Cisco observed about a year and a half ago that conventional network defenses, such as firewalls and antivirus gateways, were not successful enough. (Gee, you must need an expensive consultant to tell you that; never would have occurred to me.) Networks are porous for lots of reasons, not least of which is the traveling employee mentioned above. NAC helps to create what Cisco calls the "self-defending network."

For insights on security coverage around the Web, check out Security Center Editor Larry Seltzers Weblog. Next page: How Ciscos NAC program works.

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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