DAC comes as a very handy feature to help you connect and run basic troubleshooting queries in cases of serious performance problems.
And for using this it must be enable already beacause we only use DAC when we are not able to connect sql server and if its not then forget using it till next time, To enable (Click Here). sql server
There are 2 ways to connect
1. Connecting DAC using SQL Server Management Studio
Open SSMS à File à New àDatabase Engine Query
You need to specify "ADMIN:" before the SQL Server Instance name when trying to connect to an SQL Server Instance using DAC.
2. Connecting DAC with SQLCMD
To do this You should be member of the sysadmin server role in order to use this feature. The "-A" switch is used to specify that the user is trying to connect to SQL Server using the Dedicated Administrator Connection.
Syntax : SQLCMD -S [SQL Server Name] -U [User Name] -P [Password] -A
Example : SQLCMD -S saurabhTEST2 -Usaurabh -P'saurabh' -A