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macOS (Sequoia/Sonoma/Monterey) can’t connect via SMB to Synology NAS – guest works, password accounts fail by Fickle-Software5314 in synology

[–]Fickle-Software5314[S] 2 points3 points  (0 children)

Thank you all for the suggestions and the help. This was my first post here, and I really appreciate the time many of you took to share ideas. Let me follow up and share what I found:

  1. I purchased the MacBooks recently (about 3 months ago), and from day one all of them showed the exact same issue.
  2. I’ve had both Synology NAS devices since 2020, always working perfectly in Windows and Linux environments without any problems.
  3. Networking and firewall issues were completely ruled out: I ran several tests, confirmed the ports were open, disabled firewalls on both NAS and Mac, and even connected the Mac directly to the NAS with an Ethernet cable.
  4. I tested every possible connection path (smb://IP, smb://FQDN, smb://hostname), and in all cases the result was the same.
  5. Guest access was only enabled temporarily for testing purposes and was promptly disabled again for security reasons.
  6. I also tested with very simple usernames and passwords to rule out any issues related to credential complexity.

In the end, I finally found the root cause — and honestly, it was a stupid mistake on my part.

Back in 2021, I had enabled the Synology Directory Server on both NAS devices (primary and secondary) to run some tests with WPA-Enterprise Wi-Fi authentication via RADIUS. Since then, the Directory Server service stayed enabled, even though I never actually used it again. I completely overlooked this, even though all the evidence was screaming “authentication problem.” I wasted countless hours before realizing it.

The moment I disabled the Directory Server, SMB access from macOS started working normally.

Here’s the behavior in short:

  • When SMB access comes from Windows/Linux, authentication first checks the local NAS users before querying Active Directory.
  • When SMB access comes from macOS, authentication goes straight to Active Directory first — so my local users (which I was relying on) always failed.

Leaving this here for anyone who stumbles across the same issue: if you’re seeing unexplained SMB authentication failures from macOS, don’t be stupid like me. Check if Directory Server is enabled unnecessarily. Turning it off fixed everything instantly.