“Now that relatively high-bandwidth Internet connections are
becoming both commonplace and inexpensive, cable modem and DSL
users wanting to put more than one computer on the Internet find
that their Internet service provider will not allow them to do so.
Typically, an ISP will grant a user a single, dynamically-allocated
IP address to be used by only one computer at the user’s home, in
order to conserve their precious pool of IP addresses.“
“However, that one IP address can be put to much use by
employing IP masquerading. In this technique, one’s Linux box acts
as a gateway between an Internet connection and one’s other home
computers (whichever operating system they run). The other
computers are assigned “private” IP addresses which are not
routable on the Internet, and the Linux box takes the address
granted to you by your ISP. Once masquerading is working, all
traffic bound to the Internet from your home network will be sent
to your Linux box, which will translate the private IP addresses of
your local machines into the one real address from your ISP.
Traffic returning from the Internet will pass through your Linux
box, which determines the computer on your home network that will
receive the data. This way, multiple machines on your home network
can be using identical services (such as ftp), and your Linux
gateway will automatically sort which data goes where.”
“Phew! Sounds complicated, but don’t worry: we’ll break it down
into a few simple steps, and go from there.”