MAC aliasing

[Mauro Calderara <mcalderara_(_at_)_phys_(_dot_)_ethz_(_dot_)_ch>]

Hi everyone

I've a simple problem and not yet a proper solution, maybe someone can 
give some pointers.

My cable-provider gives me 4 IPs via DHCP, but only one per MAC. The 
question is whether it is possible to "fake" MACs on a NIC. Since by 
concept this is something simple there might be a solution but it is 
highly possible that I didn't find the right words to feed the search 
engines.

Is the idea broken by concept? I know that a MAC is supposed to be 
unique worldwide, but still it was cool if I could get all IPs. I 
thought of a workaround but maybe you guys will just shake your heads 
when reading it, if so, please tell me (and why):

given that I have 5 NICs in the router, I thought that I could set up a 
vlan-interface on those not directly connected to the cable-modem (they 
were supposed to inherit their's parent's MAC, right?) and bridge these 
vlans to the one NIC attached to the modem. Then I'd just let the dhcp 
client try to configure them and hope the best. From a firewalling point 
of view this would probably be not so nice, but I guess that could be 
worked around with some added complexity to pf.conf to prevent spoofing 
on those interfaces but that shouldn't be much of a problem as far as I 
can see. Still it seems a bit hackish and since I don't have PCI-Slots 
ad infinitum it wouldn't "scale" well when adding another cable-modem :)

Any pointers, hints & flames appreciated

Mauro