Symptoms
- Websites using MSSQL databases are unavailable with the following error in the browser:
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
- Many of the following errors are observed in Event Viewer > Windows Logs > Application :
Length specified in network packet payload did not match number of bytes read; the connection has been closed. Please contact the vendor of the client library. [CLIENT: 203.0.113.2]
Cause
MSSQL server is under DDoS attack.
Resolution
Configure firewall rules for MSSQL port, so that it will be accessible only from the local network and for the remote administrator.
In order to configure server firewall through Plesk Firewall, refer to the documentation: The Plesk Firewall (Windows)
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