Why is my JDBC connection to SQL Server failing with a \'TCP/IP connection to host failed\' error?

Troubleshooting TCP/IP Connection Failure in JDBC

Problem Summary

When attempting to establish a JDBC connection to SQL Server 2012 using SQL Server authentication, the following error is encountered:

Error: The TCP/IP connection to the host 127.0.0.1, port 1433 has failed.
Verify the connection properties. Make sure that an instance of SQL Server is running on the host and accepting TCP/IP connections at the port. Make sure that TCP connections to the port are not blocked by a firewall.

Analysis

The error suggests that the JDBC client is unable to establish a TCP/IP connection to the specified host and port. This may be due to various reasons, including:

• SQL Server is not running or is not configured to accept TCP/IP connections.
• The firewall is blocking traffic on port 1433.
• The provided host or port is incorrect.

Resolution

To resolve this error, follow the following steps:

1. Check SQL Server Configuration:

   • Open SQL Server Configuration Manager.
   • Expand SQL Server 2012 Network Configuration.
   • Click Protocols for the relevant instance.
   • Verify that TCP/IP is enabled.
   • Note the value of the Listen All item and the TCP Port.

2. Configure Firewall:

   • Ensure that TCP port 1433 is allowed through any firewall or network security appliances.

3. Verify Connection Parameters:

   • Check that the provided host (127.0.0.1) is correct.
   • Confirm that the TCP Port is 1433.

4. Update Connection String:

   • Modify the JDBC connection string to match the verified host, port, database name, username, and password.

5. Retest Database Connection:

   • Re-run the Java program to establish the JDBC connection.

By following these steps, it is possible to successfully establish a TCP/IP connection to SQL Server and resolve the "TCP/IP connection to host failed" error.

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