DNN does not limit you in any way in terms of implementing this.  It's simply a matter of configuring your websites in IIS (and your router).  If you do three completely separate instances of DNN, that would be pretty straightforward.  If you're wanting to use one instance of DNN and it's mutliportal capabilities, it simply means associating all the IP's with the same site (host headers are optional, depending upon desired behavior) and allowing DNN to sort out the requests based on the PortalAlias.

You can test this without involving DNN at all, if that makes it easier.  Simply setup sites with just an index.aspx page and ensure that you can reach them according to your rules... then add DNN to the mix after.

Scott Willhite, Co-Founder DNN