I am switching to a business Internet service with Mediacom. 
Unfortunately, they want to bond each public IP with a mac address. This 
is less than desirable, but I don't have anyone in the area that can 
provide a better solution with the bandwidth I need.

I spoke with a few people about setting up a firewall with three 
external interfaces-one per IP. It seems that might work, but I am 
partial to my IPcop firewall.

The addresses will all be assigned via DHCP. I'm wondering if I could 
just create aliases on the red interface of IPCOP, and set different 
hardware addresses per sub interface. I haven't got it to work yet, and 
assume I have something wrong in my syntax. Is there a way to create the 
three interfaces this way? Maybe there is a better way to do this???