Manual intervention might be required to register or unregister the SPN if the service account lacks the permissions that are required for these actions.To register the SPN manually, the administrator must use the tool that is provided with the Microsoft Windows Server 2003 Support Tools.
For more information, see Microsoft Kerberos Configuration Manager for SQL Server.
You can verify that a connection is using Kerberos by querying the sys.dm_exec_connections dynamic management view.
Run the following query and check the value of the auth_scheme column, which will be "KERBEROS" if Kerberos is enabled.
In an Active Directory environment, Kerberos authentication is always attempted first.
Kerberos authentication is not available for SQL Server 2005 clients using named pipes.