EXEC sp_configure 'remote admin connections', 1;
From Kendra’s blog:
There’s always a catch. You many need to get firewall ports opened as well, depending on your environment and where you intend to connect from. This will probably be port 1434, but that will vary depending on your configuration. (Books Online has got your back: read more in the “DAC Port” section here.)
How to tell who is using the DAC if you cannot log in with it:
WHEN dmes.session_id = @@SPID THEN 'It''s me! '
+ COALESCE(dmes.login_name, '???') AS WhosGotTheDAC,
FROM sys.endpoints AS ep
JOIN sys.dm_exec_sessions dmes ON ep.endpoint_id = dmes.endpoint_id
WHERE ep.name = 'Dedicated Admin Connection'
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