SQL server error 18 triggers when users connect to the SQL server due to issues with encryption or TLS version.

As a part of our Server Management Services, we help our Customers to fix SQL related errors regularly.

Let us today discuss the possible causes and fixes for this error.

What causes SQL server error 18?

At times, users on the attempt to connect to SQL server receives the following error:

The major reasons for this error message include:

1. Clients that have the Force Protocol Encryption option set ON on the client may fail to connect to SQL Server if clients specify an IP address for the server name.
2. The SQL Server version may not be supported.
3. SQL cmd is not configured.
4. An error with sqlcmd.
5. TLS 1.0 is disabled.
6. The administrator is using the older ‘SQL Server’ ODBC driver

How to fix the SQL server error 18?

The error 18 occurs generally when the clients try to connect to the server by specifying an IP address. Using a server name to connect to SQL server can help to fix the error message.

We can use the SQL Server Client Network Utility to set up an alias for the server that is running SQL Server or implement name resolution by using WINS, DNS, or LMHOST file so that you can connect by server name.

We can set the Force Protocol Encryption option to ON on the server by using the SQL Server Server Network Utility. If we turn on encryption on the server, all the clients must connect by using encryption, and a certificate is required on the server.

Another common reason for this error is an issue with the sqlcmd. We can verify if sqlcmd works, with the steps below:

• Launch the command prompt on the server.
• Run sqlcmd to check if SQL cmd is configured.
• If the command returns an error, rectify the issue and retry the backup operation.

The SQL error 18 can also occur when the older TLS versions are disabled. It generally happens when the SQL version is not up to date. Thus it would be a good idea to update the upgrade to the supported SQL version.

Alternatively, as this happens due to disabling the old TLS versions, enabling them will help to resolve the error message. However, the use of the older TLS versions like TLS 1.0 and 1.1 are not supported by the browsers anymore. Thus it is not recommended to enable them.

To enable the TLS version 1.0, change the value from 0 to 1 in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.0\Client\

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Conclusion

In short, SQL server error 18 triggers when users connect to the SQL server due to issues with encryption or TLS version. Today, we saw how our Support Engineers fix this error.