Connectivity Issue

Question

Hi Team,

Our VM, running Windows Server 2012 R2 with SQL Server, was accessible via an internal load balancer on port 1433. The VM was part of the backend pool, and SQL connectivity through the load balancer worked as expected.

Recently, we upgraded the server from Windows Server 2012 R2 to Windows Server 2016. SQL services are running fine, and we can connect directly to SQL without any issues. However, SQL connectivity via the load balancer is no longer working. No changes were made to the load balancer—only the OS was upgraded.

Here are some details:

• Netstat Output (Port 1433)

    
    TCP    0.0.0.0:1433           0.0.0.0:0              LISTENING       5600  
  

TCP 10.192.86.53:1433 10.69.5.167:64117 ESTABLISHED 5600
TCP 10.192.86.53:1433 168.63.129.16:61855 ESTABLISHED 5600
TCP [::]:1433 [::]:0 LISTENING 5600

  
  **Connection Tests:**
  
     `Test-NetConnection -ComputerName localhost -Port 1433` → **Successful**
     
        `Test-NetConnection -ComputerName <Load Balancer> -Port 1433` → **Failed**
        
Since the only change was the OS upgrade, this may be related to firewall settings, network configurations, or load balancer health probes. Please advise on further troubleshooting steps.