Force my cluster to respond by the virtual interface

Hi,

I define several services that use virtual interfaces.

My problem is the following :
If a request come into my virtual adress eth0:0 (x.x.x.120) (or :1...
or else) my computer answer by eth0 (x.x.x.119)

I found a way to "force" the answer by eth0:0 if the request come from
a specific network by a "route add -net y.y.y.y netmask blablabla gw
xxxxx dev eth0:0".

But I wonder if it is not possible to simply say to my computer "if
you are adressed by eth:0 then answer by eth0:0 (and respectivly from
eth0:1)"

Excuse me if my question seems to be stupid but I am not an expert in
linux networking.

Thanks for reading my post.

Regards.

Just a precision, my OS is RedHat AS 3.0. maybe it's usefull

^_^