What is Internet Connection Sharing?

A. In a small office/home office (SOHO) environment with two or more networked computers, Internet Connection Sharing (ICS) is a great addition to Windows XP and Windows 2000. ICS lets all machines on your network use one machine's RAS connection (e.g., modem, ADSL, cable modem, ISDN) for Internet access without additional software. ICS is available on XP and Win2K Professional systems as well as on Win2K Server products.

When you enable ICS, the machine becomes a cut-down DHCP server with the nonroutable IP address 192.168.0.1. The ICS machine gives out addresses in the 192.168.0.x range to the other machines in the network (which you must configure to use DHCP). Because of the IP address change, you shouldn't enable ICS on a domain controller (DC), DNS server, DHCP server, or any other machine that offers a static service. When you enable ICS, you lose any current TCP/IP connections, and you have to reconnect them.

You can't modify the network configuration ICS uses (e.g., changing the range of private IP addresses it hands out, enabling or disabling DNS, configuring a range of public IP addresses, or configuring inbound mappings). In addition, some services can't run on the same box as ICS. ICS uses Network Address Translation (NAT), and only one service per box can run NAT. So if, for example, you also have RRAS's NAT capability enabled, ICS won't start. To resolve this problem, you have to remove NAT from the IP routing section of the RRAS administrative menu. The same is true for such products as Proxy Server or Internet Security and Acceleration (ISA) Server 2000—which are both superior to ICS anyway.

Other computers on the network don't have to run XP or Win2K to access the Internet through ICS. They can run Windows NT, Windows Me, or Windows 9x. Because the ICS machine must use IP address 192.168.0.1, you can't have more than one machine on the network running ICS.