[OT]two networks, one nic

[jekillen]

Hello FreeBSD users,
I have been operating under the assumption that
the same network interface card cannot handle two
different networks. But then I seem to have seen
an example in one of the OReill¥ books on networking
that had one interface with one assigned inet address
and also aliased with another address that could only
be on another network. If I understood that right, it
seems to imply that I can use one Network interface
card for at least two different networks, like so;
192.168.1.<somthing> and
alias 172.0.0.<something>
or;
192.168.1.<something>
alias 192.168.2.<something>
If this is possible is it accomplished via a special routing?
My concern is that I have a laptop with one network
interface, built in,  but would like to access it both at
a public static address and a private network address.
Is this possible?

Thanks in advance for time and attention;
Jeff K