What Is Internet Connection Sharing (ICS)?

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Internet Connection Sharing (ICS), allows a local area network (LAN) of Windows computers to share a single internet connection. Microsoft developed ICS as part of Windows 98 Second Edition. The feature has been included as part of all subsequent Windows releases. It is not available as a separately installable program.

How ICS Works

ICS follows a client/server model. To set up ICS, one computer must be chosen as the server. The designated computer—which is referred to as the ICS host or gateway—must support two network interfaces, one directly connected to the internet and the other connected to the remainder of the LAN. All the outgoing transmissions from the client computers flow through the server computer and on to the internet. All the incoming transmissions from the internet flow through the server computer and on to the correct connected computer.

In a traditional home network, the server computer is directly connected to the modem. ICS works with most types of internet connections including cable, DSL, dial-up, satellite, and ISDN.

When configured through Windows, the ICS server behaves as a NAT router, directing messages on behalf of multiple computers. ICS incorporates a DHCP server that allows clients to obtain their local addresses automatically rather than needing to be set manually.

How ICS Compares to Hardware Routers

Compared to hardware routers, ICS has the advantage of being included in the operating system so no additional purchase is required. On the other hand, ICS lacks many of the configuration options that hardware routers possess.

ICS Alternatives

WinGate and WinProxy are third-party shareware applications that turn a computer into a gateway. A hardware solution requires a router that connects to the modem or a combination router/modem.