Configuring a machine to switch packets between two Ethernets is
pretty straightforward. Assume we're back at vlager, which
is equipped with two Ethernet boards, each being connected to one
of the two networks. All you have to do is configure both interfaces
separately, giving them their respective IP-address, and that's it.
It is quite useful to add information on the two interfaces to
the hosts file in the way shown below, so we have handy
names for them, too: