IP addresses on a VPS

[Bellthorpe]

I've recently taken out a VPS plan, with InterWorx. I have three IP addresses.

My thinking was not to use addresses 2 & 3 for DNS servers, rather to use those provided by the registrar. In fact, the registrar is eNom through my re-seller account, and so it's a Landis Holdings (JPC) address in any case.

Then, I figured I would be able to add domains, with shared use of those IP addresses. Much as I do on my re-seller account, where they all go on the one server (manticore) IP.

But InterWorx won't let me do that. I've added two domain names, and it won't let me add more. Does InterWork know something I don't? Is it a configuration issue? Do I have to buy more IP addresses, one for each domain I plan to host?

Edit: I found the answer, it's configurable on InterWorx's "IP Management" page.