Here I show you how to trouble a DB connection issue to eliminate the firewall as a suspect.
Using telnet you can tell pretty clearly whether or not the access is being blocked by the firewall or not.
One thing I didn’t mention in the video is that this works for all DBs and not just SQL Server.
And again, you have to verify that the server is actively accepting connections. But this is a really good way
to determine whether the firewall is blocking access or not.