Unable to add remote Microsoft SQL Server to Plesk for Windows: A network-related or instance-specific error has occurred

Symptoms

• Unable to connect remote Microsoft SQL Server to Plesk in Tools & Settings > Database Servers > Add database server:

  Error: The test connection to the database server has failed because of network problems:

  mssqlmng failed: Named Pipes Provider: Could not open a connection to SQL Server [53]. A network-related or instance-specific error has occurred while establishing a connection to SQL Server. Server is not found or not accessible. Check if instance name is correct and if SQL Server is configured to allow remote connections. For more information see SQL Server Books Online. Login timeout expired
  at (VADOConnection::open line 48)
  at Unable to ADO conect with connection string: Provider=SQLNCLI11;Initial Catalog=master;Data Source=203.0.113.2(VADODatabaseProvider::connect line 182)
  at execute console command --check(vconsoleapp::start line 93)
  at execute "C:Program Files (x86)Pleskadminbinmssqlmng" --check "--server=203.0.113.2" "--login=sa" "--password=*"(vconsoleapp::run line 110)
  (Error code 1)

• Connection to the remote MS SQL Server over telnet or any other TCP client also fails:

  C:> telnet 203.0.113.2 1433
  Connecting To 203.0.113.2...
  Could not open connection to the host, on port 1433: Connect failed

  PS (New-Object Net.Sockets.TcpClient).Connect('203.0.113.2', 1433)

  Exception calling "Connect" with "2" argument(s): "A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 203.0.113.2:1433"

Cause

The firewall on the remote MS SQL Server or before it prevents the connection, or the remote server is not configured properly and does not accept connections. 

Resolution

• Make sure that the remote SQL Server accepts connections from non-local clients: How to enable remote connections to MS SQL server?

• Disable Windows Firewall on the remote server, or configure it to accept connections to the SQL Server, for example:

  PS New-NetFirewallRule -DisplayName "SQL Server Remote Access" -Direction Inbound -Protocol TCP -LocalPort 1433-1434 -Action Allow

• If the issue persists, contact remote SQL Server administrator to clarify access restrictions and proper configuration.