Enabling the Dedicated Admin Connection (DAC)

The Dedicated Admin Connection (DAC) or Remote Admin Connection allows one administrator connection to a server. A good thing to have enabled for an emergency.

To enable the DAC ;

1. Open port 1434 on Windows firewall / ISA / Any hardware firewalls present.
   
2. sp_configure 'remote admin connections', 1;
   GO
   
3. RECONFIGURE;
   GO

Links :

Enabling DAC via TSQL 
The Dedicated Admin Connection: Why You Want It, When You Need It, and How To Tell Who’s Using It
MSDN : remote admin connections Server Configuration Option