add SPN entry for Kerberos SQL server authentication

SETSPN -A MSSQLSvc/.:1433

this is in case the instance is using the default port 1433.

to check what authentication a SQL connection is using, log on to your WFE and satrt the SQL Server Managemnet Studio (client tools), connect to the BE and place a new query:

select auth_scheme from sys.dm_exec_connections Where session_id=@@spid