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This article helps you troubleshoot network-related or instance-specific errors that occur when

you connect to a SQL Server instance. These errors typically appear when the SQL Server

instance isn’t running, the server or instance name is incorrect, network protocols aren’t

configured correctly, or firewalls block required ports. This guide explains how to gather

diagnostic information and outlines a structured troubleshooting approach, starting with basic

checks and moving on to more advanced techniques.

The complete error messages vary depending on the client library that the application uses and

the server environment. Expand each message to check if you’re encountering one of the

following error messages:

provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server

(Microsoft SQL Server, Error: 53)

A network-related or instance-specific error occurred while establishing a connection to SQL

Server. The server was not found or was not accessible. Verify that the instance name is correct

and that SQL Server is configured to allow remote connections.

provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server

(Microsoft SQL Server, Error: 53)

provider: TCP Provider, error: 0 - No such host is known. (Microsoft SQL Server, Error: 11001)

provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified

A network-related or instance-specific error occurred while establishing a connection to SQL

Server. The server was not found or was not accessible. Verify that the instance name is correct