I hope I'm understanding the question correctly though I'm definitely not versed in this area but based on what I do know is that the applications need to be able to find each other using some method. Most applications use a central server with an IP address(es) that does not change (static). This allows all copies of the application to find the server as well as potentially connect to each other.
I asked almost this same question a while back on a different site that's way more anal about how things are to be posted and aren't nice about when you don't phrase it perfectly the first time.
