How to fix Error 8575 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 8575 – Invalid NetBIOS Hostname from FQDN

Why This Error Happens

Error 8575 occurs when SQL Server 2025 attempts to derive a NetBIOS-compatible hostname from the server’s Fully Qualified Domain Name (FQDN), but the resulting string violates NetBIOS naming constraints (typically because the hostname portion exceeds 15 characters, contains invalid characters, or the FQDN itself is malformed). This commonly happens after a server rename, a domain migration, or when Windows Server 2025 registers a DNS suffix that doesn’t align with the legacy NetBIOS naming scheme. Since SQL Server still relies on NetBIOS name resolution for certain legacy components (such as Failover Clustering and SQL Browser), a mismatch between the FQDN and NetBIOS name breaks service registration and startup.

Step-by-Step Resolution Guide

Step 1: Verify the Current Hostname and FQDN Configuration

  • Open PowerShell as Administrator and run [System.Net.Dns]::GetHostByName($env:computername) to inspect the resolved FQDN.
  • Check the NetBIOS name length using hostname — ensure it does not exceed 15 characters.
  • Confirm there are no invalid characters (underscores, special symbols) in the hostname via Get-WmiObject Win32_ComputerSystem | Select-Object Name.

Step 2: Correct the Hostname via System Properties

  • Navigate to Control Panel > System > Advanced System Settings > Computer Name > Change.
  • Rename the machine to a name that is 15 characters or fewer and contains only alphanumeric characters and hyphens.
  • Avoid using domain-style names (e.g., “server.contoso.com”) directly as the NetBIOS/computer name field.
  • Restart the server to apply the new name and refresh AD/DNS registration.

Step 3: Update SQL Server Configuration Manager Settings

  • Open SQL Server Configuration Manager and navigate to SQL Server Network Configuration > Protocols.
  • Verify the TCP/IP properties under the “IP Addresses” tab do not reference the old, invalid FQDN-derived name.
  • Restart the SQL Server service (net stop MSSQLSERVER then net start MSSQLSERVER) to force re-registration of the Service Principal Name (SPN).

Step 4: Flush DNS and Re-register the Computer Name

  • Run ipconfig /flushdns followed by ipconfig /registerdns to force Windows Server 2025 to re-sync NetBIOS and DNS records.
  • If using Active Directory, run klist purge to clear stale Kerberos tickets tied to the old name.
  • Reboot the server once more to ensure the Netlogon service re-establishes the correct SPN/NetBIOS mapping.

Step 5: Validate Cluster and Browser Service Dependencies (If Applicable)

  • If running SQL Server in a Failover Cluster Instance (FCI), open Failover Cluster Manager and confirm the Network Name resource matches the corrected NetBIOS name.
  • Restart the SQL Server Browser service to ensure it picks up the corrected name resolution path.

Alternative or Verification Steps

  • To verify the fix, restart the SQL Server service and check the SQL Server Error Log (via ERRORLOG in the MSSQL\Log directory) to confirm Error 8575 no longer appears during startup.
  • If renaming the host is not feasible, use the nodename registry override under HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters to manually force a valid, truncated NetBIOS alias without changing the full FQDN.