Performance issue when using Windows server 2012 and SQL 2012 express and you want to connect to a database from a workstation
In this occasion
D:\Program Files\Microsoft SQL Server\MSSQL11.SNELSTART\MSSQL\Binn\sqlservr.exe Allow the program for Domain, Private and Public.
If this is not enough you have to add more ports to the firewall. You can follow the following URL: