Windows XP ICS Internet Gateway
When using Windows XP Internet Connection Sharing (ICS, an ICS client computer can be used to remotely monitor and control the ICS server computer's Internet connection. This Internet Gateway feature is available on computers running Windows 98, Windows 98 Second Edition, Windows Millennium Edition or Windows XP that have been configured as an ICS client using XP's Network Setup Wizard. It isn't available if you've configured the clients manually.
If you're sharing an always-on DSL or cable modem connection, a client computer can enable or disable it. If you're sharing a dial-up connection, a client computer can connect or disconnect it, causing the ICS server computer to dial in or hang up. This can be a great convenience, since you don't have to go to the server computer to take these actions. But it can cause trouble if someone disables or disconnects the server's connection while other people are using the Internet.
See also "XP ICS - Internet Gateway" on PracticallyNetworked.com.