CURL module IP

I have a shopping cart which connects my secure server to a merchant gateway through php’s CURL module. The DreamHost web server binds an IP address (which is not my server’s secure IP) to the CURL module. For security’s sake, I’d like to restrict the IP addresses from which my merchant gateway will accept XML-based connections.

My question is: Does this DH’s CURL module IP address change periodically, or can I depend on a fixed IP, or even a range of IP’s. I know what that IP is currently, I just can’t afford to have it change down the road and lock out legitimite purchases.