Moving on Up to Network-Based Protection

By Larry Seltzer  |  Posted 2003-03-17 Print this article Print

A network isn't just a convenience, writes Security Supersite Editor Larry Seltzer; it's an opportunity to protect yourself against attackers.

If you have a small network for your home or business it probably grew up from some small number of disconnected systems. You may have—and should have—security measures implemented at each client system and, I would hope, at any servers.

But once you have a network connected to the Internet, its important to consider network-based protections. This gives you protection in case a weakness emerges on any one of the internal computers. It probably also provides protection from two different vendors, which makes it even more likely to catch rare problems that would slip through one of them. Finally, network protection gives you an element of control over your users in case you dont completely trust them.

There are two important classes of products in this regard: firewalls and antivirus protection. Actual network firewalls and network devices claiming to be firewalls are relatively common, but unfortunately network-based antivirus is still a fairly high-end product.

If you have a broadband router from a company such as D-Link or Linksys, you may have the impression that its also a firewall, but it probably isnt. These devices all provide NAT (Network Address Translation), which means that the router uses your real IP address that you got from your ISP when communicating with the rest of the Internet. Internally your computers all get fake IP addresses (probably in the 192.168.x.x range) that dont actually route out to the Internet. The fact that computers on the outside cant directly address your computers does provide some measure of protection, but its an exaggeration to call this a "firewall."

Hardware appliances that do have true firewall functionality are more expensive and more complicated to administer, but they do present a much more difficult barrier to an attacker. A talented and determined attacker will be able to penetrate the average NAT router. A true firewall performs a task called "stateful inspection," where it actually examines the packets of data moving in and out of the network, looking for evidence of attacks. For instance, if a firewall sees ICMP packets, it can look for the famous "PING Of Death" attack, which involves an oversize buffer.

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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