IP Aliasing

[David Allen]

This may be a dumb question, but I'm puzzled by the following (taken
from the Virtual Hosts section in the Handbook):

	For example, consider the case where the fxp0 interface is connected
	to two networks, the 10.1.1.0 network with a netmask of
	255.255.255.0 and the 202.0.75.16 network with a netmask of
	255.255.255.240.

IP aliasing I get, but two different networks on the same interface?
What would this be plugged into to make that work?