DAC [Dedicated Administrator Connection ] is feature added from SQL Server 2005 version . Database administrator use this fetaure to connect to a SQL Server instance When the database engine not responding to the regular connection so the database administrator use this fetaure to connect to the instance to solve the problem Instead of rebooting the SQL Server.
By Defult this feature is disable in All SQL Server version From 2005 to the New version 2012.
Note : your SQL Server browser must be Runing
enable the DAC using below T-SQL command
sp_configure ‘show advanced options’ , 1
sp_configure ‘remote admin connections’, 1
G O RECONFIGURE
enable the DAC using SSMS
1- write click on your SQL Server Probirties >> Factes >> Service Area Configuration >> RemoteDacEnabled
Change it from False To True
Now try to connect by write ADMN: before your instance name like this
then your User name and your password or connect windows Authentication but if you try to connect by the default way SQL Server will give you this Error
Dedicated administrator connections are not supported. (ObjectExplorer)
So if you want to connect with this Feature you must make this steps
Go to File >>> New >>> Database Engine Query >>>> Admin:InstanceName
Note : You can not open 2 Session