Using Internet Connection Sharing
For most people, most of the time, the easiest and fastest way to set up a network with a shared Internet connection entails nothing more than picking up the phone and calling the local phone company or cable company. They install a router, connect it to the Internet, and you can plug all your PCs into the back of the router - fair enough.
Sometimes, though, you have an Internet connection that's attached to just one PC and you want to share that connection with other PCs on the network. For example, you may have a fast wireless connection through your iPhone or an HSDPA or LTE card on a laptop and you want to share that connection across the network. You can do it with a Windows 7 feature known as Internet Connection Sharing (ICS). For a schematic of ICS, see Figure below.
The PC that runs Internet Connection Sharing must have two adaptors - one that connects to the Internet and one that connects to the network.
In the most common configuration, you plug your Internet connection (typically, a phone line, cable company line, or satellite connection) into a router and then run a cable from each PC to the router. The router turns into an Internet mother hen (that's a technical term). The computers on your network interact with the router, the router interacts with the cable or DSL modem, the modem talks to the Internet, and to the outside world you have only one connected PC. All the PCs on your network think they're connected directly to the Internet, thanks to the hardware mother hen.
But if you have only one computer connected directly to the Internet, ICS makes it easy to share that single computer's Internet connection among all computers on the network. ICS turns that lone PC into an Internet mother hen (there's that technical term again). The anointed ICS PC interacts with the Internet. All other PCs on the network interact with the ICS PC. To the outside world, you have only one connected PC. But all the other PCs in your network think they're on the Internet, too, thanks to the ICS mother hen. Clever - and effective.
Warning:
Things get truly nasty when a network has two or more mother hens and they both believe that they're in control: One fights for all the chicks and the other fights for all the chicks, and then they both start looking at each other as chicks, and - all hell breaks loose. You think a catfight looks bad? You should see what these mother hens do to each other. At least 90 percent of all the confusion I've seen in setting up a network has to do with two or more mother hens fighting for control.
