It All Comes Down To Infrastructure Redux

I was pulled into an IRT over the weekend.  A development team was moving their application from DEV to QA and experiencing an unexpected error.  They could not connect to the database from their web application.  Turns out they had two databases on the same server and they could connect to one using a connection string like this:

connectionString="Data Source=DIXON08;Initial Catalog=VideoGames;Integrated Security=True"

but not the other one.  After going through the typical algorithm  of ports open, impersonation set correctly, etc…, it was found that the connection string needed to fully qualify the server name and the port like this (I didn’t come up with the right answer, Rob Seder did):

connectionString="Data Source=Com.Tff.DIXON08:8001;Initial Catalog=VideoGames;Integrated Security=True"

Why it worked on one database without fully qualifying versus another that did need it, I don’t know.