"Whether for Internet connectivity or wide area networking to
various physical locations, routing has become an invaluable asset
to networking. Although routers have existed since the original
ARPAnet, they have become increasing more common in corporate
environments as the 1990's trend of local area networking grew into
Wide and Metropolitan area networks."
"The first step in both Windows NT and Linux is to add a
second network interface card. One card must be connected to the
local area network, the second being routed to the network that the
LAN will use. The local NIC must have a local IP address and
be functioning. The external NIC must also function, obviously, but
it must have an IP address in the external range."
"Like almost any essential task in Linux, there are many ways to
set-up routing. Here we will briefly cover just one such way. For
the benefit of readers with older distributions, we will cover
routing procedures that function in both newer and older Linux's.
Again, for more advanced tasks, be sure to read the how-to's."