Using a Computer as an Internet Barrier
For those who can't afford or don't want an Internet appliance, there are plenty of ways to protect your always on Internet links for little or no cost. Up to three software components are often found on the "home or office" side of an Internet link (actual composition will depend on whether only a single computer uses that link, or a network of computers shares that link). These components include the following:
A firewall: a piece of software that interposes itself between the local PC or network and the Internet. Its job is to look for unwanted traffic, probes, or other signs of malign interest and block them from entering your PC or network. Numerous free and low-cost personal firewalls are available on today's market. ZoneAlarm offers free and commercial personal firewalls, as do many other vendors. Visit the "Home PC Firewall Guide" for the best resource we know of on relevant choices and options.
A DHCP server: the Dynamic Host Configuration Protocol provides IP addresses to computers on a network so they don't have to be configured manually. For very small home networks (three PCs or less), this may be overkill (and newer Windows versions, like XP, have built-in addressing capability you can use instead). Shareware and freeware DHCP servers are available for most desktop computers, though.
Address translation: this software hides internal network details by translating addresses on the private side of the network before passing traffic to the Internet side. This prevents outsiders from easy access to computers there. When used with private IP addresses, this combination can block most attempts to access computers on the inside network completely.
Windows users for Windows 2000 and Windows XP can use Internet Connection Sharing (ICS) services to provide most of these functions, using elements built into Windows itself. But the preceding approach works with most Windows versions, provided the right components are located, installed, and properly configured. Linux and Macintosh users will find plenty of freeware (often Open Source programs), shareware, and low-cost commercial software to perform the same functions. It's not uncommon to set something like this up for under $50 (if not for free).