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Ice Drake
Asked: 2024-12-12 10:09:03 +0800 CST

How to enable NetBIOS over TCP/IP on an ethernet of a Domain Controller?

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I recently did some cable management (including ethernet). After I was done, I found that none of my Synology NAS units weren't able to reconnect to the Active Directory on my domain server. To be exact, they did intermittently reconnect, but disconnect roughly every other time I checked it. Fiddling with the domain setting on the NAS made no difference.

Tracing back, the only thing that was different is that I installed the recent server updates before shutting it down for cable management:

  1. 2024-11 Cumulative Update for Windows Server 2016 for x64-based Systems (KB5046612)
  2. Security Update for SQL Server 2017 RTM GDR (KB5046857)
  3. 2024-09 Servicing Stack Update for Windows Server 2016 for x64-based Systems (KB5043124)

I tried reverting back by uninstalling the updates, but it makes no difference. After troubleshooting for the past few days, I noticed something I haven't before. The ethernet port on the Domain Controller has NetBIOS over TCP/IP disabled. Research says that NetBIOS is required for SMB to work, which makes sense why the Synology NAS units can't properly reconnect if they can't get SMB to work reliably. (Note that I have disabled SMB 1.0 long ago for security and performance reason, and it did work with no issue when SMB 1.0 was disabled.)

However, I can't seem to figure how to get NetBIOS over TCP/IP enabled. Is it not possible for ethernet port, vEthernet (Virtual Switch)?

What I have tried:

  1. Changing the setting in the WINS tab of IPv4 setting from Default to Enable NetBIOS over TCP/IP with IPv6 disabled.
  2. Edit the registry in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetBT\Parameters for all the interfaces I saw for the key value NetbiosOptions from 0 to 1.

Thinking that it might be a Windows bug, I installed the latest update, but it is still disabled: 2024-12 Cumulative Update for Windows Server 2016 for x64-based Systems (KB5048671)

windows-server-2016

1 Answers

  1. Best Answer

    I finally located the source of the problem. It was the

    binding issue where the process or 'port' can't bind to the actual NIC itself

    as stated by Gostega here.

    Even though the domain controller was showing via netstat -an command that it is listening at port 445, it is not working as expected. I believe that this problem has occurred for quite some times, but I didn't have any issue with it since I didn't use SMB on the server much and it was able to fallback to NetBIOS over TCP/IP till it was disabled recently.

    I recalled fixing Synology Active Directory issue in the past now by removing and adding back the virtual ethernet adapter. Since I don't remember how I did that last time, I uninstalled and reinstalled Hyper-V server instead; thereby, it got rid of the problematic virtual ethernet adapter and recreated a working one. While this is not the best solution, it is a solution that I used.

    Afterward, I did further testing if I can disable NetBIOS over TCP/IP since it is security risk. And it continues to work with no issue.

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