Using DNS name connects via NTLM, not Kerberos

  • Hello,

    We are seeing a strange issue when we connect to our SQL server using the DNS name vs the hostname or fqdn. When connected via the DNS name and running the statement, select auth_scheme from sys.dm_exec_connections where session_id=@@spid the auth_schema returns as NTLM. However that same select statement returns kerberos when we use the name of the server. Any ideas? The SPN is registered and delegation has been setup but maybe something else has to be changed when using DNS names?

    Thanks for any advice.

  • Had similar issue, with bit of messing got it resolved

    1. Found that I had to register SPN for both - servername and it's dns alias. Ensure you have FQDN registered as well.

    #setspn -l sqlserviceaccount

    MSSQLSvc/server123:1433

    MSSQLSvc/server123.renre.com:1433

    MSSQLSvc/alias123:1433

    MSSQLSvc/alias123.renre.com:1433

    2. Another SPN that you might need is the HOST for the alias (this solved my issue with bulk inserts from network using alias, i.e. \\alias123\share\somefile.csv):

    #setspn -l server123

    these 2 should be there by default when server is added to AD:

    HOST/server123

    HOST/server123.yourdomain.com

    these 2 might need to be added:

    HOST/alias123

    HOST/alias123.yourdomain.com

    To add alias host spn:

    setspn -A host/alias123 server123

    setspn -A host/alias123.yourdomain.com server123

    3. Last option that I'd check is if your service account used in kerberos is trusted for Delegation (in AD users & computers, find the account and look at Delegation tab).

  • Thank you!

    I will give that a shot, or my SysAdmin will.

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