Peeking Behind NAT

Joseph Laszlo | April 25, 2003, 04:01 PM

The geeky online press this week featured a couple of discussions on a new software-based technique for detecting NAT gateways (see: Slashdot and Broadband Reports coverage).

NAT (network address translation) is fundamental to how some firewalls and most home networking gear work, taking a single IP address and using it to support traffic from multiple devices on the back end, without any upstream point on the network being directly aware of the device or devices that are sharing the connection.

Why does this matter? Well, broadband ISPs have been increasingly interested in home networking. And if the ISP wants you to buy its own networking gear, it may have an incentive to monitor and penalize "unauthorized" networks attached to its lines.

More legitimately, some of the broadband providers I talk to are concerned about supporting wireless networking because of the possibility of consumers running open access points. Time Warner Cable [News.com coverage], among others, has tried to crack down on this, but is forced to resort to monitoring lists of public hotspots and identifying customers. They can't see behind a NAT device to tell that it's going on directly.

But now it seems like they might be able to.

Whether this is a problem or not depends on where the broadband provider draws the line between "use" and "abuse" of the connection. It's hard to disagree with the idea that open access points are abuse--though Speakeasy would beg to differ with me. But if providers start peeking behind NAT intending to charge extra, just because a consumer happens to have bought a home network so mom and the kids can be online simultaneously, I have a hard time justifying that.