Setting Up Named SQL Server Instance Network Connection
As Ronaldo mentioned - SQL Server Browser is needed when using dynamic port.  There are numerous reasons that it may not work correctly, though, too - for example if UDP port 1434 is blocked. (More about Browser here).  Because you said that the IP address was &quot;originally something outside of our firewall&quot; - presumably not the home IP 127.0.0.1 - I'm guessing that you've checked to ensure that TCP is enabled via Configuration Manager-&gt;Network Configuration-&gt;Protocols for instance. If not, check that:

SQL Server will report the IP and port it's using in its log as well.  Here's an example from my test VM:

Then should be able to connect using either servername,port or IP,port.  You might want to test both methods, both on the local VM and remote boxes to isolate issue.  For example:
.
If connecting locally always works, but remotely doesn't, check firewall.
If connecting with IP always works, but instance name never does, check Browser.
If connecting with IP always works, but servername doesn't remotely, check DNS.
Of course there are numerous other possibilities, but this is where I'd start.