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How does an SMB client identify which authentication style to use?

Last Updated:

Applies to

  • ONTAP 9
  • SMB / CIFS Authentication


An SMB client chooses between Kerberos and NTLM authentication based on client and server capabilities, domain membership, Service Principal Name (SPN) registration, network configuration, and explicit settings.

Modern systems prefer Kerberos, a more secure protocol. Kerberos is used when:

  • Both client and server support it.
  • They are members of the same or trusted Active Directory (AD) domains.
  • A valid SPN is registered for the target server.

In summary, an SMB client prefers Kerberos when supported and properly configured; otherwise, it uses NTLM authentication.

Additional Information


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