What is the Dedicated Admin Connection (DAC) connection in SQL Server?
It’s a diagnostic connection for a database administrator to access SQL Server.
The DAC can make remote troubleshooting easier when SQL Server is unresponsive.
When SQL Server is experiencing issues, the DAC can be used to log in to fix problems and avoid downtime.
How to identify the issue?
DAC is only allowed from a client running on the server by default.
It’s a best practice to enable network connections to use it from a remote machine.
You can check if the feature is enabled by following the steps below:
- Using SQL Server Management Studio (SSMS), connect to the SQL Server instance and then right-click the Server and select Facets as shown below.
- In the View Facets window, you need to choose the Facet as Surface Area Configuration and then check for RemoteDacEnabled.
How do I enable DAC? How to fix it?
You can enable it using the interface above, just changing the property to ENABLED.
Another way is to implement the change by running the following script:
sp_configure ‘show advanced options’
,1 GO
RECONFIGURE
WITH override GO sp_configure ‘remote admin connections’
,1 GO
RECONFIGURE
WITH overrideNotes:
- Only members of the SQL Server sysadmin role can connect using the DAC, and only one connection can be made at a time.
- Make sure to get firewall ports opened, this will probably be port 1434, but that will vary depending on your installation.
