I don’t know much about database or web apps, but I’ll throw in my 2c in case it helps…
IP 192.168.1.3 is not external, but I assume you only used that as an example. Do you get any error message when you try to communicate with the webserver, and with the database? Anything in the webserver logs?
If the the same web app is going to be used internally & by external users, why don’t you create a certificate linked to a URL, like myapp.mycompany.com instead of to an IP address (make sure the name record is publicly available)?
Is the database in the same machine as the webserver? Hope not, because it’d be pretty risky (IIS notorious for break-ins, leaving your database wide open). If the database is in your LAN (or DMZ) and the IIS in a (different) DMZ, you may have some routing issues.
Best of luck,