Snapgear 580

I have a snapgear 580. I have a public IP addres coming into the
snapgear, and I have the snapgear handing out private ip addresses.
The LAN side of the snapgear is hooked up to a switch.

I have a particular machine on that switch that I want to have a
public IP address on. So essentially, I am looking for a way to let a
second IP address through the snapgear.

I am just trying to find the term for this so that I can research it.
.