Normally on development environment the 1434 port would be open and SQL Server Browser running in SQL Server machine. If developers code based on that assumption, it may fail in higher environments. Most of the developers know what might have happened. But some may not and ends up in complete darkness. The symptom of this issue will be connection failure from application to SQL Server database.
This post is mainly to demonstrate how to check network failures on SQL Server Browser operations. The prerequisite is the availability of Wireshark in the machine where application runs and basic knowledge how to run the same. The above link has some screenshots which would help to run Wireshark for UDP connections.
This is usually the first service I disable post-installation.