When you are facing slow logons into domain and you also get events 1030 and 1006 you need to look into your network. By default Kerberos uses UDP packets to communicate. You need to force Kerberos to use TCP instead of UDP by changing registry key:
If it doesn’t exists just create it
Create DWORD key called MaxPacketSize and set it to value 1.
For more infor there is official KB http://support.microsoft.com/kb/244474/en-us