Setting up a computer to share its internet connection should be easy right? After all, you've successfully networked your computers together and even shared files with all your home computers, so why not the Internet? Well if you have a small home network of computers all connected and have tried to open up a browser, you've probably found out that things aren't quite as straight forward as connecting one machine with an Ethernet cable
The secret is that everything comes down to having a gateway.
A gateway is a computer or device than can route data between different networks. Put it this way, if your computers are on one network and every other computer connected to the Internet is on a different one, to pass information across network boundaries you need a device which is connected to both networks and equipped to decide whether information from one network should go out to the other network, and vice versa.
So, without a gateway there is no way for the other computers in your network to receive or pass information to the other networks, and consequently, they have no Internet access.
The computer in your small network which is directly connected to the cable or DSL modem is provided with a default gateway by the Internet service provider. That allows the computer to connect to the interenet, but unfortunately for us that gateway is not part of your home network - rather it is a separate network formed between the computer connected to the cable/DSL modem and the ISP itself.
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In order to enable Internet access on the rest of your small home network, the computer or device that connects with your ISP must become a gateway for the computers in your local home network. Once this has been configured, it will enable all of the other home network computers to access the Internet by sending and receiving information through that gateway.
The easiest way of acquiring a gateway for your home network is to buy a cable/DSL router. Given how cheap they currently are (about a quarter of the price they commanded when they first appeared in the marketplace), there really isn't much of an excuse not to buy one.
The major advantages of having a hardware router doing your internet sharing include minimal configuration, since they are set up to act as a gateway by default (it's pretty much all they do), increased reliability (they are not a PC… PCs crash.), and security, since most of these devices incorporate a firewall. Highly recommended!